Heleen de Wit

• Pirk, Norbert; Aalstad, Kristoffer; Holmlund, Erik Schytt; Clayer, Francois; de Wit, Heleen & Christiansen, Casper Tai [Vis alle 9 forfattere av denne artikkelen] (2024). Disaggregating the Carbon Exchange of Degrading Permafrost Peatlands Using Bayesian Deep Learning. Geophysical Research Letters. ISSN 0094-8276. 51(10). doi: 10.1029/2024GL109283.
• Aas, Elin Cecilie Ristorp; de Wit, Heleen & Berntsen, Terje Koren (2024). Modeling boreal forest soil dynamics with the microbially explicit soil model MIMICS+ (v1.0). Geoscientific Model Development. ISSN 1991-959X. 17(7), s. 2929–2959. doi: 10.5194/gmd-17-2929-2024.
• Vogt, Rolf David; Garmo, Øyvind Aaberg; Austnes, Kari; Kaste, Øyvind; Haaland, Ståle Leif & Sample, James Edward [Vis alle 10 forfattere av denne artikkelen] (2024). Factors Governing Site and Charge Density of Dissolved Natural Organic Matter. Preprints. ISSN 2310-287X. doi: 10.20944/preprints202404.0533.v1.
• Bergström, Ann-Kristin; Creed, Irena F.; Paltsev, Aleksey; de Wit, Heleen; Lau, Danny C. P. & Drakare, Stina [Vis alle 15 forfattere av denne artikkelen] (2024). Declining calcium concentration drives shifts toward smaller and less nutritious zooplankton in northern lakes. Global Change Biology. ISSN 1354-1013. 30(3). doi: 10.1111/gcb.17220.
• Pilla, Rachel M.; Williamson, Craig E.; Overholt, Erin P.; Rose, Kevin C.; Berger, Stella Angela & Couture, Raoul-Marie [Vis alle 16 forfattere av denne artikkelen] (2023). Deepwater dissolved oxygen shows little ecological memory between lake phenological seasons. INLAND WATERS. ISSN 2044-2041. doi: 10.1080/20442041.2023.2265802.
• Corman, Jessica R.; Zwart, Jacob A.; Klug, Jennifer; Bruesewitz, Denise A.; de Eyto, Elvira & Klaus, Marcus [Vis alle 17 forfattere av denne artikkelen] (2023). Response of lake metabolism to catchment inputs inferred using high-frequency lake and stream data from across the northern hemisphere. Limnology and Oceanography. ISSN 0024-3590. 68(12), s. 2617–2631. doi: 10.1002/lno.12449. Fulltekst i vitenarkiv Vis sammendrag

  In lakes, the rates of gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP) are often controlled by resource availability. Herein, we explore how catchment vs. within lake predictors of metabolism compare using data from 16 lakes spanning 39°N to 64°N, a range of inflowing streams, and trophic status. For each lake, we combined stream loads of dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorus (TP) with lake DOC, TN, and TP concentrations and high frequency in situ monitoring of dissolved oxygen. We found that stream load stoichiometry indicated lake stoichiometry for C : N and C : P (r2 = 0.74 and r2 = 0.84, respectively), but not for N : P (r2 = 0.04). As we found a strong positive correlation between TN and TP, we only used TP in our statistical models. For the catchment model, GPP and R were best predicted by DOC load, TP load, and load N : P (R2 = 0.85 and R2 = 0.82, respectively). For the lake model, GPP and R were best predicted by TP concentrations (R2 = 0.86 and R2 = 0.67, respectively). The inclusion of N : P in the catchment model, but not the lake model, suggests that both N and P regulate metabolism and that organisms may be responding more strongly to catchment inputs than lake resources. Our models predicted NEP poorly, though it is unclear why. Overall, our work stresses the importance of characterizing lake catchment loads to predict metabolic rates, a result that may be particularly important in catchments experiencing changing hydrologic regimes related to global environmental change.

• Monteith, Donald T.; Henrys, Peter A.; Hruška, Jakub; de Wit, Heleen; Krám, Pavel & Moldan, Filip [Vis alle 12 forfattere av denne artikkelen] (2023). Long-term rise in riverine dissolved organic carbon concentration is predicted by electrolyte solubility theory. Science Advances. ISSN 2375-2548. 9(3). doi: 10.1126/sciadv.ade3491. Fulltekst i vitenarkiv Vis sammendrag

  The riverine dissolved organic carbon (DOC) flux is of similar magnitude to the terrestrial sink for atmospheric CO2, but the factors controlling it remain poorly determined and are largely absent from Earth system models (ESMs). Here, we show, for a range of European headwater catchments, that electrolyte solubility theory explains how declining precipitation ionic strength (IS) has increased the dissolution of thermally moderated pools of soluble soil organic matter (OM), while hydrological conditions govern the proportion of this OM entering the aquatic system. Solubility will continue to rise exponentially with declining IS until pollutant ion deposition fully flattens out under clean air policies. Future DOC export will increasingly depend on rates of warming and any directional changes to the intensity and seasonality of precipitation and marine ion deposition. Our findings provide a firm foundation for incorporating the processes dominating change in this component of the global carbon cycle in ESMs.

• de Wit, Heleen; Garmo, Øyvind Aaberg; Jackson-Blake, Leah Amber; Clayer, Francois; Vogt, Rolf David & Austnes, Kari [Vis alle 10 forfattere av denne artikkelen] (2023). Changing water chemistry in one thousand Norwegian lakes during three decades of cleaner air and climate change. Global Biogeochemical Cycles. ISSN 0886-6236. 37(2). doi: 10.1029/2022GB007509. Fulltekst i vitenarkiv
• Valiente Parra, Nicolas; Eiler, Alexander; Allesson, Lina; Andersen, Tom; Clayer, Francois & Crapart, Camille Marie [Vis alle 13 forfattere av denne artikkelen] (2022). Catchment properties as predictors of greenhouse gas concentrations across a gradient of boreal lakes. Frontiers in Environmental Science. ISSN 2296-665X. 10. doi: 10.3389/fenvs.2022.880619. Fulltekst i vitenarkiv
• Clayer, Francois; Thrane, Jan-Erik; Brandt, Uta; Dörsch, Peter & de Wit, Heleen (2021). Boreal Headwater Catchment as Hot Spot of Carbon Processing From Headwater to Fjord. Journal of Geophysical Research (JGR): Biogeosciences. ISSN 2169-8953. 126(12). doi: 10.1029/2021JG006359. Fulltekst i vitenarkiv Vis sammendrag

  Boreal headwaters and aquatic sediments are significant transporters, stores and processors of terrestrial carbon (C) as well as emitters of greenhouse gases (GHGs), mainly CO2 and CH4. While terrestrial ecosystems are net sinks of atmospheric C, lateral fluxes of total organic and dissolved inorganic C (TOC, DIC) as well as GHG release can significantly reduce the land C sink. However, the fate of the laterally exported C remains often unresolved. Here, we combine datasets from high-frequency sensors, monitoring and modeling to produce a C budget for a typical boreal lake and its catchment and examine it in a regional context. We show that lake TOC removal is dominated by microbial metabolism which shows strong seasonal fluctuations following stratification and ice-cover dynamics. We estimate that 11.5 g C m−2 catchment yr−1 are exported from the catchment soils and wetlands, including 9.5 g of TOC. Only 5.4 g C m−2 catchment yr−1 reach the coast while over 50% is reemitted to the atmosphere (5.7 g C m−2 catchment yr−1). Part of the reemitted C originates from rapid turnover cycles and would not affect atmospheric CO2 and the land C sink. However, we show that the land C sink at Langtjern is reduced by >14% over the whole aquatic continuum, and by >10% within the headwater catchment. Our regional analysis suggests that headwater lake TOC mineralization is the main TOC loss along the aquatic continuum with burial being relatively small, and highlights the significance of small headwaters as intensive and fast-responding TOC processors.

• de Wit, Heleen; Stoddard, John L.; Monteith, Donald T.; Sample, James E.; Austnes, Kari & Couture, Suzanne [Vis alle 17 forfattere av denne artikkelen] (2021). Cleaner air reveals growing influence of climate on dissolved organic carbon trends in northern headwaters. Environmental Research Letters. ISSN 1748-9326. 16(10). doi: 10.1088/1748-9326/ac2526. Fulltekst i vitenarkiv Vis sammendrag

  Surface water browning, the result of increasing concentrations of dissolved organic matter (DOM), has been widespread in northern ecosystems in recent decades. Here, we assess a database of 426 undisturbed headwater lakes and streams in Europe and North America for evidence of trends in DOM between 1990 and 2016. We describe contrasting changes in DOM trends in Europe (decelerating) and North America (accelerating), which are consistent with organic matter solubility responses to declines in sulfate deposition. While earlier trends (1990–2004) were almost entirely related to changes in atmospheric chemistry, climatic and chemical drivers were equally important in explaining recent DOM trends (2002–2016). We estimate that riverine DOM export from northern ecosystems increased by 27% during the study period. Increased summer precipitation strengthened upward dissolved organic carbon trends while warming apparently damped browning. Our results suggest strong but changing influences of air quality and climate on the terrestrial carbon cycle, and on the magnitude of carbon export from land to water.

• Forsius, Martin; Posch, Maximilian; Holmberg, Maria; Vuorenmaa, Jussi; Kleemola, Sirpa & Augustaitis, Algirdas [Vis alle 25 forfattere av denne artikkelen] (2021). Assessing critical load exceedances and ecosystem impacts of anthropogenic nitrogen and sulphur deposition at unmanaged forested catchments in Europe. Science of the Total Environment. ISSN 0048-9697. 753. doi: 10.1016/j.scitotenv.2020.141791. Fulltekst i vitenarkiv Vis sammendrag

  Anthropogenic emissions of nitrogen (N) and sulphur (S) compounds and their long-range transport have caused widespread negative impacts on different ecosystems. Critical loads (CLs) are deposition thresholds used to describe the sensitivity of ecosystems to atmospheric deposition. The CL methodology has been a key science-based tool for assessing the environmental consequences of air pollution. We computed CLs for eutrophication and acidification using a European long-term dataset of intensively studied forested ecosystem sites (n = 17) in northern and central Europe. The sites belong to the ICP IM and eLTER networks. The link between the site-specific calculations and time-series of CL exceedances and measured site data was evaluated using long-term measurements (1990–2017) for bulk deposition, throughfall and runoff water chemistry. Novel techniques for presenting exceedances of CLs and their temporal development were also developed. Concentrations and fluxes of sulphate, total inorganic nitrogen (TIN) and acidity in deposition substantially decreased at the sites. Decreases in S deposition resulted in statistically significant decreased concentrations and fluxes of sulphate in runoff and decreasing trends of TIN in runoff were more common than increasing trends. The temporal developments of the exceedance of the CLs indicated the more effective reductions of S deposition compared to N at the sites. There was a relation between calculated exceedance of the CLs and measured runoff water concentrations and fluxes, and most sites with higher CL exceedances showed larger decreases in both TIN and H+ concentrations and fluxes. Sites with higher cumulative exceedance of eutrophication CLs (averaged over 3 and 30 years) generally showed higher TIN concentrations in runoff. The results provided evidence on the link between CL exceedances and empirical impacts, increasing confidence in the methodology used for the European-scale CL calculations. The results also confirm that emission abatement actions are having their intended effects on CL exceedances and ecosystem impacts.

• Strand, Line Tau; Fjellstad, Wendy ; Jackson-Blake, Leah Amber & de Wit, Heleen A (2020). Afforestation of a pasture in Norway did not result in higher soil carbon, 50 years after planting. Landscape and Urban Planning. ISSN 0169-2046. 207. doi: 10.1016/j.landurbplan.2020.104007. Fulltekst i vitenarkiv Vis sammendrag

  Afforestation of marginal cultivated land is an internationally approved climate mitigation strategy, however, with uncertain implications for soil organic carbon (SOC) storage. We examined the effect of forest planting by measuring SOC at two adjacent sites: one with a Norway spruce forest planted in 1968 and one actively grazed pasture. Both sites had similar land-use history before forest planting, and they were as similar as possible in all other edaphic factors. There were no significant differences in SOC stocks down to 30 cm mineral soil, 7.15 and 8.51 kg C m−2 in the forest plantation and pasture respectively. Only a minimal build-up of an O horizon, less than 2 cm, was observed in the plantation. The SOC stocks of the plantation and pasture were not significantly different from that of a nearby old forest, 7.17 kg C m−2. When comparing these three land-uses we found that there were significant differences in the upper 10 cm of the soil with regard to other soil properties. Nitrogen (N) stock and pH were significantly lower in the old forest compared to the plantation, which again was significantly lower than that of the pasture. The opposite was the case for the C/N ratio. We conclude that there were no significant differences in SOC stocks in the upper 30 cm 50 years after afforestation with Norway spruce, but that there is still a legacy from the former cultivation that may influence both productivity and organic matter dynamics.

• de Wit, Heleen A; Lepistö, Ahti; Marttila, Hannu; Wenng, Hannah; Bechmann, Marianne & Blicher-Mathiesen, Gitte [Vis alle 12 forfattere av denne artikkelen] (2020). Land-use dominates climate controls on nitrogen and phosphorus export from managed and natural Nordic headwater catchments. Hydrological Processes. ISSN 0885-6087. 34(25), s. 4831–4850. doi: 10.1002/hyp.13939. Fulltekst i vitenarkiv Vis sammendrag

  Agricultural, forestry‐impacted and natural catchments are all vectors of nutrient loading in the Nordic countries. Here, we present concentrations and fluxes of total nitrogen (totN) and phosphorus (totP) from 69 Nordic headwater catchments (Denmark: 12, Finland:18, Norway:17, Sweden:22) between 2000 and 2018. Catchments span the range of Nordic climatic and environmental conditions and include natural sites and sites impacted by agricultural and forest management. Concentrations and fluxes of totN and totP were highest in agricultural catchments, intermediate in forestry‐impacted and lowest in natural catchments, and were positively related %agricultural land cover and summer temperature. Summer temperature may be a proxy for terrestrial productivity, while %agricultural land cover might be a proxy for catchment nutrient inputs. A regional trend analysis showed significant declines in N concentrations and export across agricultural (−15 μg totN L−1 year−1) and natural (−0.4 μg NO3‐N L−1 year−1) catchments, but individual sites displayed few long‐term trends in concentrations (totN: 22%, totP: 25%) or export (totN: 6%, totP: 9%). Forestry‐impacted sites had a significant decline in totP (−0.1 μg P L−1 year−1). A small but significant increase in totP fluxes (+0.4 kg P km−2 year−1) from agricultural catchments was found, and countries showed contrasting patterns. Trends in annual concentrations and fluxes of totP and totN could not be explained in a straightforward way by changes in runoff or climate. Explanations for the totN decline include national mitigation measures in agriculture international policy to reduced air pollution and, possibly, large‐scale increases in forest growth. Mitigation to reduce phosphorus appears to be more challenging than for nitrogen. If the green shift entails intensification of agricultural and forest production, new challenges for protection of water quality will emerge possible exacerbated by climate change. Further analysis of headwater totN and totP export should include seasonal trends, aquatic nutrient species and a focus on catchment nutrient inputs.

• Marttila, Hannu; Lepistö, Ahti; Tolvanen, Anne; Bechmann, Marianne; Kyllmar, Katarina & Juutinen, Artti [Vis alle 19 forfattere av denne artikkelen] (2020). Potential impacts of a future Nordic bioeconomy on surface water quality. Ambio. ISSN 0044-7447. 49, s. 1722–1735. doi: 10.1007/s13280-020-01355-3. Fulltekst i vitenarkiv Vis sammendrag

  Nordic water bodies face multiple stressors due to human activities, generating diffuse loading and climate change. The ‘green shift’ towards a bio-based economy poses new demands and increased pressure on the environment. Bioeconomy-related pressures consist primarily of more intensive land management to maximise production of biomass. These activities can add considerable nutrient and sediment loads to receiving waters, posing a threat to ecosystem services and good ecological status of surface waters. The potential threats of climate change and the ‘green shift’ highlight the need for improved understanding of catchment-scale water and element fluxes. Here, we assess possible bioeconomy-induced pressures on Nordic catchments and associated impacts on water quality. We suggest measures to protect water quality under the ‘green shift’ and propose ‘road maps’ towards sustainable catchment management. We also identify knowledge gaps and highlight the importance of long-term monitoring data and good models to evaluate changes in water quality, improve understanding of bioeconomy-related impacts, support mitigation measures and maintain ecosystem services.

• Bishop, Kevin; Shanley, James B.; Riscassi, Ami; de Wit, Heleen; Eklöf, Karin & Meng, Bo [Vis alle 11 forfattere av denne artikkelen] (2020). Recent advances in understanding and measurement of mercury in the environment: Terrestrial Hg cycling. Science of the Total Environment. ISSN 0048-9697. 721. doi: 10.1016/j.scitotenv.2020.137647. Fulltekst i vitenarkiv Vis sammendrag

  This review documents recent advances in terrestrial mercury cycling. Terrestrial mercury (Hg) research has matured in some areas, and is developing rapidly in others. We summarize the state of the science circa 2010 as a starting point, and then present the advances during the last decade in three areas: land use, sulfate deposition, and climate change. The advances are presented in the framework of three Hg “gateways” to the terrestrial environment: inputs from the atmosphere, uptake in food, and runoff with surface water. Among the most notable advances:• The Arctic has emerged as a hotbed of Hg cycling, with high stream fluxes and large stores of Hg poised for release from permafrost with rapid high-latitude warming. • The bi-directional exchange of Hg between the atmosphere and terrestrial surfaces is better understood, thanks largely to interpretation from Hg isotopes; the latest estimates place land surface Hg re-emission lower than previously thought. • Artisanal gold mining is now thought responsible for over half the global stream flux of Hg. • There is evidence that decreasing inputs of Hg to ecosystems may bring recovery sooner than expected, despite large ecosystem stores of legacy Hg. • Freshly deposited Hg is more likely than stored Hg to methylate and be incorporated in rice. • Topography and hydrological connectivity have emerged as master variables for explaining the disparate response of THg and MeHg to forest harvest and other land disturbance. These and other advances reported here are of value in evaluating the effectiveness of the Minamata Convention on reducing environmental Hg exposure to humans and wildlife.

• Kaste, Øyvind; Austnes, Kari & de Wit, Heleen (2020). Streamwater responses to reduced nitrogen deposition at four small upland catchments in Norway. Ambio. ISSN 0044-7447. 49, s. 1759–1770. doi: 10.1007/s13280-020-01347-3. Fulltekst i vitenarkiv Vis sammendrag

  Reduced emissions of nitrogen (N) in Europe have resulted in decreasing atmospheric deposition since 1990. Long-term data (1988–2017) from four small Norwegian catchments located along gradients in N deposition, rainfall, and organic carbon (C) show different responses to 25–30% reductions in N deposition during the same period. At three sites the decreased N deposition caused reduced leaching of nitrate to surface water, whereas the westernmost site showed no decrease, probably due to thin soils with low C:N ratio, poor vegetation cover and high precipitation. The loss of total N to streamwater constituted 30–50% of the N deposition. Losses via denitrification are unknown but assumed to be low, as a major fraction of the catchments are well-drained. Hence, the study sites seem to continue to accumulate N, presumably mostly in soil organic matter. Although atmospheric N deposition has declined, ambient loads might still exceed long-term sustainable levels in these vulnerable ecosystems.

• Braaten, Hans Fredrik Veiteberg; Lindholm, Markus & de Wit, Heleen A (2020). Five decades of declining methylmercury concentrations in boreal foodwebs suggest pivotal role for sulphate deposition. Science of the Total Environment. ISSN 0048-9697. 714. doi: 10.1016/j.scitotenv.2020.136774. Fulltekst i vitenarkiv Vis sammendrag

  Widespread declines in mercury (Hg) in fish in pristine lakes in Fennoscandia since the 1970s are unexplained. Interactions between climate, atmospheric deposition, and elemental cycling of carbon (C), sulphur (S) and Hg are complex and affect Hg bioaccumulation. A parallel significant decline in methyl-Hg (MeHg) concentrations in aquatic macroinvertebrates (Chironomidae) was found between 1976–78 and 2004–15 in an intensely studied, pristine boreal lake (Langtjern, boreal Fennoscandia). Monitoring at Langtjern demonstrated a four-fold decrease in aqueous sulphate concentrations (SO4, 50-year record), significant lake browning (30-year records), increasing sediment Hg concentrations (50-year record), warming (45-year record) and increased runoff (40-year record). Contrasting Hg trends in biota (downward) and sediment (upward) indicated a disconnect between lake Hg loading and foodweb Hg bioaccumulation. We suggest that reduced SO4-deposition has 1) constrained substrate availability for SO4-reducing methylating bacteria (causing reduced foodweb MeHg exposure despite increased Hg loading to the lake), and 2), increased the binding affinity between aqueous organic matter and Hg species (leading to reduced MeHg bioavailability). The downward MeHg trend at the base of the foodweb at Langtjern is mirrored at higher trophic levels by strong declines in perch (Perca fluviatilis) and pike (Esox lucius) Hg concentrations in boreal Fennoscandia. A plausible explanation is that declining SO4-deposition, rather than climate change or reduced atmospheric Hg, is currently driving reduced MeHg contamination in northern freshwater foodwebs.

• Weyhenmeyer, Gesa A; Hartmann, Jens; Hessen, Dag O; Kopáček, Jiří; Hejzlar, Josef & Jacquet, Stéphan [Vis alle 29 forfattere av denne artikkelen] (2019). Widespread diminishing anthropogenic effects on calcium in freshwaters. Scientific Reports. ISSN 2045-2322. 9. doi: 10.1038/s41598-019-46838-w. Fulltekst i vitenarkiv Vis sammendrag

  Calcium (Ca) is an essential element for almost all living organisms. Here, we examined global variation and controls of freshwater Ca concentrations, using 440 599 water samples from 43 184 inland water sites in 57 countries. We found that the global median Ca concentration was 4.0 mg L−1 with 20.7% of the water samples showing Ca concentrations ≤ 1.5 mg L−1, a threshold considered critical for the survival of many Ca-demanding organisms. Spatially, freshwater Ca concentrations were strongly and proportionally linked to carbonate alkalinity, with the highest Ca and carbonate alkalinity in waters with a pH around 8.0 and decreasing in concentrations towards lower pH. However, on a temporal scale, by analyzing decadal trends in >200 water bodies since the 1980s, we observed a frequent decoupling between carbonate alkalinity and Ca concentrations, which we attributed mainly to the influence of anthropogenic acid deposition. As acid deposition has been ameliorated, in many freshwaters carbonate alkalinity concentrations have increased or remained constant, while Ca concentrations have rapidly declined towards or even below pre-industrial conditions as a consequence of recovery from anthropogenic acidification. Thus, a paradoxical outcome of the successful remediation of acid deposition is a globally widespread freshwater Ca concentration decline towards critically low levels for many aquatic organisms.

• Hagman, Camilla Hedlund Corneliussen; Skjelbred, Birger; Thrane, Jan-Erik; Andersen, Tom & de Wit, Heleen A (2019). Growth responses of the nuisance algae Gonyostomum semen (Raphidophyceae) to DOC and associated alterations of light quality and quantity. Aquatic Microbial Ecology. ISSN 0948-3055. 82(3), s. 241–251. doi: 10.3354/ame01894. Fulltekst i vitenarkiv Vis sammendrag

  In recent decades, the freshwater alga Gonyostomum semen (Ehrenberg) Diesing has increased in abundance and distribution, which has created problems regarding the use of lakes for drinking water and recreation. Increases in lake dissolved organic carbon (DOC; browning) and climate warming are among current hypotheses that explain the phenomenon of increased abundance of G. semen. A replicated, multifactorial laboratory experiment was performed in order to test the effects of DOC and light quality and irradiance on growth of G. semen in 96-well plates. Each well had a separate light source, creating a gradient of irradiance (10-140 µmol photons m-2 s-1) and wavelength (white, red, green and blue), combined with a DOC gradient (0-50 mg C l-1), all within representative ranges for the summer epilimnion in boreal waters. The experiment showed that growth of G. semen was significantly enhanced by the addition of DOC. No growth response relating to wavelengths was found, but where irradiance was inhibitory, a shading effect from DOC was evident. A composed response to increases in DOC suggests a versatility of G. semen that gives it a competitive advantage over other phytoplankton in humic lake ecosystems. Hence, further increases in abundance and bloom frequency of G. semen as browning continues in boreal lakes are to be expected.

• Krzeminski, Pawel; Vogelsang, Christian; Meyn, Thomas; Köhler, Stephan; Poutanen, Heikki & de Wit, Heleen [Vis alle 7 forfattere av denne artikkelen] (2019). Natural organic matter fractions and their removal in full-scale drinking water treatment under cold climate conditions in Nordic capitals. Journal of Environmental Management. ISSN 0301-4797. 241, s. 427–438. doi: 10.1016/j.jenvman.2019.02.024. Fulltekst i vitenarkiv Vis sammendrag

  Drinking water treatment plants (DWTPs) designed to remove natural organic matter (NOM) are challenged as concentrations of NOM in raw waters are increasing. Here, we assess seasonal differences in NOM quality and quantity, from raw waters to the distribution network, at three large DWTPs in Oslo, Stockholm and Helsinki. Samples, collected during stable stratification in both winter and summer and during the autumnal turnover, were analysed for NOM concentrations and composition. The NOM was characterized by common routine parameters, size and content (TFF, LC-OCD, fluorescence) and biodegradability. The NOM concentration decreased to 2.5 mg/L (55%), 4.0 mg/L (48%) and 5.7 mg/L (76%) at the respective DWTPs in Oslo, Stockholm and Helsinki. The NOM in raw waters were predominantly in the largest size fraction (>50 kDa), in particular from Oslo. High MW fractions >50 kDa and humics remained the largest fractions with minimum 30% and maximum 80% of the total NOM. The BDOC in treated water <0.3 mg/L and the conditions in the distribution network imply low probability for bacteria regrowth. The multi-step treatment consisting of coagulation/flocculation, sedimentation, rapid sand filtration, ozonation and biological activated carbon filtration (BAC) was most effective in removing NOM. Coagulation/flocculation followed by sedimentation and sand filtration were critical, especially for the removal of biopolymers and humics, and somewhat for building blocks. The sand filtration provided up to 25% additional removal of biopolymers and below 7% removal of other fractions. The ozonation and BAC was more effective and removed 11% of biopolymers, and about 35% of building blocks and LMW neutrals.

• Braaten, Hans Fredrik Veiteberg; Åkerblom, Staffan; Kahilainen, Kimmo Kalevi; Rask, Martti; Vuorenmaa, Jussi & Mannio, Jaakko [Vis alle 15 forfattere av denne artikkelen] (2019). Improved Environmental Status: 50 Years of Declining Fish Mercury Levels in Boreal and Subarctic Fennoscandia. Environmental Science and Technology. ISSN 0013-936X. 53(4), s. 1834–1843. doi: 10.1021/acs.est.8b06399. Fulltekst i vitenarkiv Vis sammendrag

  Temporally (1965–2015) and spatially (55°–70°N) extensive records of total mercury (Hg) in freshwater fish showed consistent declines in boreal and subarctic Fennoscandia. The database contains 54 560 fish entries (n: pike > perch ≫ brown trout > roach ≈ Arctic charr) from 3132 lakes across Sweden, Finland, Norway, and Russian Murmansk area. 74% of the lakes did not meet the 0.5 ppm limit to protect human health. However, after 2000 only 25% of the lakes exceeded this level, indicating improved environmental status. In lakes where local pollution sources were identified, pike and perch Hg concentrations were significantly higher between 1965 and 1990 compared to values after 1995, likely an effect of implemented reduction measures. In lakes where Hg originated from long-range transboundary air pollution (LRTAP), consistent Hg declines (3–7‰ per year) were found for perch and pike in both boreal and subarctic Fennoscandia, suggesting common environmental controls. Hg in perch and pike in LRTAP lakes showed minimal declines with latitude, suggesting that drivers affected by temperature, such as growth dilution, counteracted Hg loading and food web exposure. We recommend that future fish Hg monitoring sampling design should include repeated sampling and collection of pollution history, water chemistry, fish age, and stable isotopes to enable evaluation of emission reduction policies.

• Lund, Espen; Garmo, Øyvind A; de Wit, Heleen A; Kristensen, Torstein; Hawley, Kate L & Wright, Richard F (2018). Reduced Acid Deposition Leads to a New Start for Brown Trout (Salmo trutta) in an Acidified Lake in Southern Norway. Water, Air and Soil Pollution. ISSN 0049-6979. 229. doi: 10.1007/s11270-018-4013-9. Fulltekst i vitenarkiv
• de Wit, Heleen A; Couture, Raoul-Marie; Jackson-Blake, Leah; Futter, Martyn N.; Valinia, Salar & Austnes, Kari [Vis alle 8 forfattere av denne artikkelen] (2018). Pipes or chimneys? For carbon cycling in small boreal lakes, precipitation matters most. Limnology and Oceanography Letters. ISSN 2378-2242. 3(3), s. 275–284. doi: 10.1002/lol2.10077. Fulltekst i vitenarkiv
• Braaten, Hans Fredrik Veiteberg; de Wit, Heleen; Larssen, Thorjørn & Poste, Amanda (2018). Mercury in fish from Norwegian lakes: The complex influence of aqueous organic carbon. Science of the Total Environment. ISSN 0048-9697. 627, s. 341–348. doi: 10.1016/j.scitotenv.2018.01.252. Fulltekst i vitenarkiv Vis sammendrag

  Mercury (Hg) concentrations in water and biota are often positively correlated to organic matter (OM), typically measured as total or dissolved organic carbon (TOC/DOC). However, recent evidence suggests that higher OM concentrations inhibit bioaccumulation of Hg. Here, we test how TOC impacts the Hg accumulation in fish in a synoptic study of Methyl-Hg (MeHg) in water and total Hg (THg) in perch (Perca fluviatilis) in 34 boreal lakes in southern Norway. We found that aqueous MeHg (r2 = 0.49, p < 0.0001) and THg (r2 = 0.69, p < 0.0001), and fish THg (r2 = 0.26, p < 0.01) were all positively related with TOC. However, we found declining MeHg bioaccumulation factors (BAFMeHg) for fish with increasing TOC concentrations. The significant correlation between fish THg concentrations and aqueous TOC suggests that elevated fish Hg levels in boreal regions are associated with humic lakes. The declining BAFMeHg with increasing TOC suggest that increased OM promotes increased aqueous Hg concentrations, but lowers relative MeHg bioaccumulation. A mechanistic understanding of the response from OM on BAFMeHg might be found in the metal-complexation properties of OM, where OM complexation of metals reduces their bioavailability. Hence, suggesting that MeHg bioaccumulation becomes less effective at higher TOC, which is particularly relevant when assessing potential responses of fish Hg to predicted future changes in OM inputs to boreal ecosystems. Increased browning of waters may affect fish Hg in opposite directions: an increase of food web exposure to aqueous Hg, and reduced bioavailability of Hg species. However, the negative relationship between BAFMeHg and TOC is challenging to interpret, and carries a great deal of uncertainty, since this relationship may be driven by the underlying correlation between TOC and MeHg (i.e. spurious correlations). Our results suggest that the trade-off between Hg exposure and accumulation will have important implications for the effects of lake browning on Hg transport, bioavailability, and trophodynamics.

• Vuorenmaa, Jussi; Augustaitis, Algirdas; Beudert, Burkhard; Bochenek, Witold; Clarke, Nicholas & de Wit, Heleen A [Vis alle 25 forfattere av denne artikkelen] (2018). Long-term changes (1990–2015) in the atmospheric deposition and runoff water chemistry of sulphate, inorganic nitrogen and acidity for forested catchments in Europe in relation to changes in emissions and hydrometeorological conditions. Science of the Total Environment. ISSN 0048-9697. 625, s. 1129–1145. doi: 10.1016/j.scitotenv.2017.12.245. Fulltekst i vitenarkiv Vis sammendrag

  The international Long-Term Ecological Research Network (ILTER) encompasses hundreds of long-term research/monitoring sites located in a wide array of ecosystems that can help us understand environmental change across the globe. We evaluated long-term trends (1990–2015) for bulk deposition, throughfall and runoff water chemistry and fluxes, and climatic variables in 25 forested catchments in Europe belonging to the UNECE International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems (ICP IM). Many of the IM sites form part of the monitoring infrastructures of this larger ILTER network. Trends were evaluated for monthly concentrations of non-marine (anthropogenic fraction, denoted as x) sulphate (xSO4) and base cations x(Ca + Mg), hydrogen ion (H+), inorganic N (NO3 and NH4) and ANC (Acid Neutralising Capacity) and their respective fluxes into and out of the catchments and for monthly precipitation, runoff and air temperature. A significant decrease of xSO4 deposition resulted in decreases in concentrations and fluxes of xSO4 in runoff, being significant at 90% and 60% of the sites, respectively. Bulk deposition of NO3 and NH4 decreased significantly at 60–80% (concentrations) and 40–60% (fluxes) of the sites. Concentrations and fluxes of NO3 in runoff decreased at 73% and 63% of the sites, respectively, and NO3 concentrations decreased significantly at 50% of the sites. Thus, the LTER/ICP IM network confirms the positive effects of the emission reductions in Europe. Air temperature increased significantly at 61% of the sites, while trends for precipitation and runoff were rarely significant. The site-specific variation of xSO4 concentrations in runoff was most strongly explained by deposition. Climatic variables and deposition explained the variation of inorganic N concentrations in runoff at single sites poorly, and as yet there are no clear signs of a consistent deposition-driven or climate-driven increase in inorganic N exports in the catchments.

• Vuorenmaa, Jussi; Augustaitis, Algirdas; Beudert, Burkhard; Clarke, Nicholas; de Wit, Heleen & Dirnböck, Thomas [Vis alle 17 forfattere av denne artikkelen] (2017). Long-term sulphate and inorganic nitrogen mass balance budgets in European ICP Integrated Monitoring catchments (1990–2012). Ecological Indicators. ISSN 1470-160X. 76, s. 15–29. doi: 10.1016/j.ecolind.2016.12.040. Vis sammendrag

  Empirical evidence based on integrated environmental monitoring including physical, chemical and biological variables is essential for evaluating the ecosystem benefits of costly emission reduction policies. The international multidisciplinary ICP IM (International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems) programme studies the integrated effects of air pollution and climate change on ecosystems in unmanaged and calibrated forested catchments. We calculated site-specific annual input-output budgets for sulphate (SO4) and total inorganic nitrogen (TIN NO3- N + NH4-N) for 17 European ICP IM sites in 1990–2012. Temporal trends for input (deposition) and output (runoff water) fluxes and the net retention/net release of SO4 and TIN were also analysed. Large differences in the input and output fluxes of SO4 and TIN reflect important gradients of air pollution effects in Europe, with the highest deposition and runoff water fluxes at IM sites located in southern Scandinavia and in parts of Central and Eastern Europe and the lowest fluxes at more remote sites in northern European regions. A significant decrease in the total (wet + dry) deposition of non-marine SO4 and bulk deposition of TIN was found at 90% and 65% of the sites, respectively. Output fluxes of non-marine SO4 in runoff decreased significantly at 65% of the sites, indicating positive effects of the international emission abatement actions in Europe during the last 20 years. Catchments retained SO4 in the early and mid1990s, but this shifted towards a net release in the late 1990s, which may be due to the mobilization of legacy S pools accumulated during times of high atmospheric SO4 deposition. Despite decreased deposition, TIN output fluxes and retention rates showed a mixed response with both decreasing (9 sites) and increasing (8 sites) trend slopes, and trends were rarely significant. In general, TIN was strongly retained in the catchments not affected by natural disturbances. The long-term annual variation in net releases for SO4 was explained by variations in runoff and SO4 concentrations in deposition, while a variation in TIN concentrations in runoff was mostly associated with a variation of the TIN retention rate in catchments. The net release of SO4 from forest soils may delay the recovery from acidification for surface waters and the continued enrichment of nitrogen in catchment soils poses a threat to terrestrial biodiversity and may ultimately lead to a higher TIN runoff through N-saturation. Continued monitoring and further evaluations of mass balance budgets are thus needed.

• de Wit, Heleen A; Ledesma, Jose L J & Futter, Martyn N. (2016). Aquatic DOC export from subarctic Atlantic blanket bog in Norway is controlled by seasalt deposition, temperature and precipitation. Biogeochemistry. ISSN 0168-2563. 127(2), s. 305–321. doi: 10.1007/s10533-016-0182-z. Fulltekst i vitenarkiv
• Strand, Line Tau; Callesen, Ingeborg; Dalsgaard, Lise & de Wit, Heleen A (2016). Carbon and nitrogen stocks in Norwegian forest soils — the importance of soil formation, climate, and vegetation type for organic matter accumulation. Canadian Journal of Forest Research. ISSN 0045-5067. 46(12), s. 1459–1473. doi: 10.1139/cjfr-2015-0467.
• de Wit, Heleen A.; Valinia, Salar; Weyhenmeyer, Gesa A; Futter, Martyn N.; Kortelainen, Pirkko & Austnes, Kari [Vis alle 10 forfattere av denne artikkelen] (2016). Current Browning of Surface Waters Will Be Further Promoted by Wetter Climate. Environmental Science and Technology Letters (ES&T Letters). ISSN 2328-8930. 3(12), s. 430–435. doi: 10.1021/acs.estlett.6b00396. Fulltekst i vitenarkiv
• Braaten, Hans Fredrik Veiteberg & de Wit, Heleen A. (2016). Effects of disturbance and vegetation type on total and methylmercury in boreal peatland and forest soils. Environmental Pollution (1987). ISSN 0269-7491. 218, s. 140–149. doi: 10.1016/j.envpol.2016.08.029. Fulltekst i vitenarkiv
• Finstad, Anders Gravbrøt; Andersen, Tom; Larsen, Søren; Tominaga, Koji; Blumentrath, Stefan & de Wit, Heleen A. [Vis alle 8 forfattere av denne artikkelen] (2016). From greening to browning: Catchment vegetation development and reduced S-deposition promote organic carbon load on decadal time scales in Nordic lakes. Scientific Reports. ISSN 2045-2322. 6. doi: 10.1038/srep31944. Fulltekst i vitenarkiv Vis sammendrag

  Increased concentrations of dissolved organic carbon (DOC), often labelled “browning”, is a current trend in northern, particularly boreal, freshwaters. The browning has been attributed to the recent reduction in sulphate (S) deposition during the last 2 to 3 decades. Over the last century, climate and land use change have also caused an increasing trend in vegetation cover (“greening”), and this terrestrially fixed carbon represents another potential source for export of organic carbon to lakes and rivers. The impact of this greening on the observed browning of lakes and rivers on decadal time scales remains poorly investigated, however. Here, we explore time-series both on water chemistry and catchment vegetation cover (using NDVI as proxy) from 70 Norwegian lakes and catchments over a 30-year period. We show that the increase in terrestrial vegetation as well as temperature and runoff significantly adds to the reduced SO4-deposition as a driver of freshwater DOC concentration. Over extended periods (centuries), climate mediated changes in vegetation cover may cause major browning of northern surface waters, with severe impact on ecosystem productivity and functioning.

• Vries, Wim de; Posch, Maximilian; Sverdrup, Harald U.; Larssen, Thorjørn; Wit, Heleen de & Bobbink, Roland [Vis alle 7 forfattere av denne artikkelen] (2015). Geochemical Indicators for Use in the Computation of Critical Loads and Dynamic Risk Assessments. Environmental Pollution. ISSN 1566-0745. 25, s. 15–58. doi: 10.1007/978-94-017-9508-1_2.
• Couture, Raoul-Marie; de Wit, Heleen; Tominaga, Koji; Kiuru, Petri & Markelov, Igor (2015). Oxygen dynamics in a boreal lake responds to long-term changes in climate, ice phenology, and DOC inputs. Journal of Geophysical Research (JGR): Biogeosciences. ISSN 2169-8953. 120(11), s. 2441–2456. doi: 10.1002/2015JG003065. Fulltekst i vitenarkiv
• Moiseenko, Tatiana Ivanovna; Dinu, Marina Ivanovna; Bazova, Maria Mihailovna & de Wit, Heleen (2015). Long-term changes in the water chemistry of arctic lakes as a response to reduction of air pollution: Case study in the Kola, Russia. Water, Air and Soil Pollution. ISSN 0049-6979. 226(98). doi: 10.1007/s11270-015-2310-0.

Se alle arbeider i Cristin

• Vogt, Rolf David; Austnes, Kari; de Wit, Heleen & Gundersen, Cathrine Brecke (2024). Unexpected increases in Calcium - are we moving into a post-acid-rain era? .
• Vogt, Rolf David; Austnes, Kari; de Wit, Heleen & Gundersen, Cathrine Brecke (2023). Diverging trends in Ca and Mg under chemical recovery.
• de Wit, Heleen (2022). Presentation of ICP Waters.
• de Wit, Heleen (2022). Riverine transport and processing of organic carbon from headwaters to coast in subarctic Norway under global change.
• de Wit, Heleen; Clayer, Francois; Jackson-Blake, Leah Amber; Vogt, Rolf David & Garmo, Øyvind Aaberg (2022). Repeated sampling of thousand Norwegian lakes reveals widespread changes in silica, calcium, aluminium and DOC. .
• de Wit, Heleen (2022). Riverine transport and processing of organic carbon from headwaters to coast in subarctic Norway under global change.
• Skarbøvik, Eva; de Wit, Heleen & Kaste, Øyvind (2022). Forestry, water quality and ecology.
• Knutson, Jacqueline; Clayer, Francois; Dörsch, Peter; Westermann, Sebastian & de Wit, Heleen (2022). Investigating hydrology and carbon cycling connections in peatland permafrost, northern Norway.
• Vogt, Rolf David; de Wit, Heleen & Koponen, Kati (2022). Impacts of large-scale forest related NETPs on climate and ecosystem services in Nordic region .
• Vogt, Rolf David; de Wit, Heleen & Koponen, Kati (2022). Impacts of large-scale forest related NETPs ​on climate and ecosystem services in Nordic region.
• Knutson, Jacqueline; Clayer, Francois; Brandt, Uta & de Wit, Heleen (2021). Investigating hydrology and carbon cycling in a permafrost palsa: preliminary data from Iskoras.
• Knutson, Jacqueline; Clayer, Francois; Norling, Magnus Dahler; Lepistö, Ahti; Marttila, Hannu & Futter, Martyn N. [Vis alle 8 forfattere av denne artikkelen] (2021). Hydrological controls of DOC export from Nordic headwater catchments.
• Hessen, Dag Olav; de Wit, Heleen & Vogt, Rolf David (2021). Mindre forsuring, mer skog og brunere kystvann – er det noen sammenheng? Naturen. ISSN 0028-0887. 145(5), s. 236–249.
• Krzeminski, Pawel Konrad; de Wit, Heleen & Uhl, Wolfgang (2019). Natural organic matter variability and removal in main drinking water treatment plants of Northern European capital cities.
• McGovern, Maeve; Evenset, Anita; Borgå, Katrine; Wit, Heleen de; Braaten, Hans Fredrik Veiteberg & Hessen, Dag Olav [Vis alle 9 forfattere av denne artikkelen] (2019). Implications of Coastal Darkening for Contaminant Transport, Bioavailability, and Trophic Transfer in Northern Coastal Waters. Environmental Science and Technology. ISSN 0013-936X. 53(13), s. 7180–7182. doi: 10.1021/acs.est.9b03093. Fulltekst i vitenarkiv Vis sammendrag

  The increased transport of terrestrially derived organic material (tOM) from catchments to rivers and lakes is leading to browning of northern freshwaters.(1) Although the same environmental drivers can be expected to lead to widespread increases in tOM and subsequent darkening in adjacent coastal systems,(2) this has received considerably less attention, and long-term monitoring data for detecting these changes are scarce. This is despite expectations that darkening is likely to have a range of implications for coastal biogeochemistry and food-web ecology. tOM is accompanied by other catchment-derived materials including contaminants, inorganic particles, and nutrients. Together, these terrestrial inputs can affect cycling and food-web accumulation of contaminants, in particular, methyl mercury (MeHg) and persistent organic pollutants (POPs). Because of the human and ecosystem health risks associated with these contaminants, and to ensure informed policy decisions, there is a need for a better understanding of the drivers of darkening and their direct and indirect impacts on the transport, bioavailability, and trophic transfer of contaminants in northern coastal waters.

• Gundersen, Cathrine Brecke; Krzeminski, Pawel; Martinez-Frances, Elena; Ong, Stevenson Harvey Lee; Færgestad, Eline Mosleth & Braaten, Hans Fredrik Veiteberg [Vis alle 8 forfattere av denne artikkelen] (2019). In-Lake Processing Influences DOM Biodegradability and Hg-cycling.
• de Wit, Heleen (2019). Klimaendring og vannkvalitet. Kjemisk vannkvalitet – hva kan vi vente oss? .
• de Wit, Heleen (2019). Progress report ICP Waters. Vis sammendrag

  Faglig rapportering om aktiviteter under ICP Waters. Bl.a. rapportering om kvikksølv i miljøet.

• de Wit, Heleen; Braaten, Hans Fredrik Veiteberg; Gundersen, Cathrine Brecke; Krzeminski, Pawel & Vogt, Rolf David (2019). Long-term Mercury records in a boreal lake: lake Processing and the role of organic matter.
• Krzeminski, Pawel; de Wit, Heleen & Uhl, Wolfgang (2018). Natural organic matter variability and removal in main drinking water treatment plants of Northern European capital cities.
• Krzeminski, Pawel; Vogelsang, Christian; Meyn, Thomas; Köhler, Stephan; Poutanen, Heikki & de Wit, Heleen [Vis alle 7 forfattere av denne artikkelen] (2018). Seasonal changes and removal of NOM fractions in main waterworks of Nordic capital cities.
• de Wit, Heleen (2018). Will an effective policy to reduce Hg emissions lead to cleaner rivers and lakes?
• de Wit, Heleen; Braaten, Hans Fredrik Veiteberg & Lund, Espen (2018). The role of dissolved organic matter in boreal lake mercury cycling.
• Braaten, Hans Fredrik Veiteberg; Åkerblom, Staffan; de Wit, Heleen; Poste, Amanda; Rask, Martti & Vuorenmaa, Jussi [Vis alle 8 forfattere av denne artikkelen] (2018). Mercury in freshwater fish from Fennoscandia (1965-2015) - temporal trends and potential environmental drivers.
• de Wit, Heleen; Couture, Raoul-Marie; Futter, Martin N; Vogt, Rolf David; Krzeminski, Pawel Konrad & Francés, Elena Martínez [Vis alle 8 forfattere av denne artikkelen] (2018). Climate-driven changes in removal of DOC in a small boreal lake: a 30-year time series.
• de Wit, Heleen; Braaten, Hans Fredrik Veiteberg; Krzeminski, Pawel Konrad; Lund, Espen; Martinez-Frances, Elena & Ong, Stevenson Harvey Lee [Vis alle 7 forfattere av denne artikkelen] (2017). The Role of DOM in Catchment and Lake Mercury Cycling in a Boreal lake catchment.
• Avset, Liv Mildrid Melkild; Braaten, Hans Fredrik Veiteberg; de Wit, Heleen & Åkerblom, Staffan (2017). Mindre kvikksølv i ferskvannsfisk. [Internett]. forskning.no.
• Braaten, Hans Fredrik Veiteberg; Åkerblom, Staffan; Christensen, Guttorm N; Poste, Amanda; de Wit, Heleen & Jackson-Blake, Leah Amber (2017). Impacts of climate and lake browning on mercury concentrations in fish – an analysis of resampled perch populations in Scandinavia.
• Braaten, Hans Fredrik Veiteberg; Lindholm, Markus; Halvorsen, Godtfred A. & de Wit, Heleen (2017). Re-writing history: Five decades of methylmercury concentrations in aquatic zoobenthos from lakes in the Norwegian boreal Ecozone.
• Åkerblom, Staffan; Braaten, Hans Fredrik Veiteberg; de Wit, Heleen & Christensen, Guttorm (2017). A Fennoscandian platform of freshwater fish mercury data for the evaluation of effects of transboundary air pollution.
• de Wit, Heleen; Braaten, Hans Fredrik Veiteberg & Vogt, Rolf David (2017). The role of DOM in catchment and lake mercury cycling in a boreal lake catchment.
• Borchgrevink, Harald Bonaventura & de Wit, Heleen (2016). Vannet blir brunere i en våtere fremtid. [Internett]. forskning.no.
• Couture, Raoul-Marie; de Wit, Heleen; Tominaga, Koji; Kiuru, Petri & Markelov, Igor (2015). Modelling the impact of increasing dissolved organic carbon load on seasonal anoxia in a boreal humic lake. Vis sammendrag

  Boreal lakes are impacted by climate change, reduced acid deposition and changing loads of dissolved organic carbon (DOC) from the catchment. We set to explore how these changes, in particular the increasing DOC load, modulate ice phenology and dissolved oxygen (DO) of a boreal humic lake located in southeastern Norway. Observed trends in daily air temperature (+0.045 oC yr-1) and weekly DOC concentration (0.1 mg C yr-1, +1% annually) measured over the past 40 years at the study site were used as forcings for the lake model MyLake. The model was parametrized against year-round time-series of water temperature and DO from a high-frequency lake buoy. A backcast of ice freezing and break-up dates to 1974 reveals that ice break-up occurs on average 8 days earlier in 2014 than in 1974. An earlier ice break-up enhances water column ventilation, resulting in higher DO in the spring. Later in the season, warmer water in late summer lead to longer anoxic periods, as microbial DOC turnover increases. Long-term increase in DOC concentrations causes decline in lake DO, leading to 15% more hypoxic days (< 3 mg L-1) and 10% more anoxic days (< 15 ug L-1) in 2014 than in 1974. We conclude that climate warming and increasing DOC loads are antagonistic with respect to their effect on DO availability. The model suggests that DOC is a stronger driver of DO consumption than temperature. DOC increase thus has the potential to reduce the oxythermal habitat of fish and aquatic biota in boreal lakes.

• Granhus, Aksel; Antón-Fernández, Clara; de Wit, Heleen; Hanssen, Kjersti Holt; Schei, Fride Høistad & Jacobsen, Rannveig Margrete [Vis alle 15 forfattere av denne artikkelen] (2024). Effekter på karbondynamikk, miljø og næring ved økt bruk av lukkede hogstformer. NIBIO. ISSN 978-82-17-03499-5. 10(48). Fulltekst i vitenarkiv Vis sammendrag

  Miljødirektoratet har gitt NIBIO, NINA og NIVA i oppdrag å vurdere hvilken effekt økt bruk av lukkede hogstformer kan ha for karbonlagring i skog, biodiversitet, økologisk tilstand, vannkvalitet og skognæring. Oppdraget er utført ved hjelp av gjennomgang av relevant litteratur, data fra Landsskogtakseringen, modellbaserte simuleringer og ekspertvurderinger.

• Skarbøvik, Eva; Jackson-Blake, Leah Amber; Sample, James Edward; de Wit, Heleen & Clarke, Nicholas (2024). Beregning av næringsstoffavrenning fra skogarealer og skogsdrift til Oslofjorden. Med vurdering av kunnskaps- og databehov. NIBIO. ISSN 978-82-17-03498-8. 10(47). Fulltekst i vitenarkiv Vis sammendrag

  Effekten av skogbruk på eutrofibelastningen i Oslofjorden er anslått basert på tilførsler av løst uorganisk nitrogen (DIN). Dette anslaget er beheftet med en rekke usikkerheter som kan forbedres ved å bl.a. samle inn flere data om effekten av skogsdrift på vann, samt forbedre anslag over årlig hogstareal. Våre anslag antyder at tap av nitrogen fra skogsdrift til Oslofjorden ligger på nivå med tapet fra spredt avløp og bebyggelse. På side 6 finnes et utvidet sammendrag. The effect of forestry on the eutrophic pressure of the Oslo Fjord has been estimated based on fluxes of DIN (dissolved inorganic nitrogen). This estimate is subject to many uncertainties that can be improved by, among other things, collecting more data on the effect of forestry on water, as well as improving estimates of annual logging area. Our estimate suggests that losses of nitrogen to the Oslo Fjord from forestry are in the same range as losses from households not connected to sewage treatment plants and from settlements.

• Vogt, Rolf David; Arle, Jens; Austnes, Kari; Van Dam, Herman; Futter, Martyn & Fölster, Jens [Vis alle 20 forfattere av denne artikkelen] (2024). Trends and patterns in surface water chemistry in Europe and North America between 1990 and 2020, with a focus on calcium. Norsk Institutt for Vannforskning. ISSN 978-82-577-7667-1. Fulltekst i vitenarkiv
• Moldan, Filip; Jutterström, Sara; Stadmark, Johanna; Akujärvi, Anu; Forsius, Martin & Holmberg, Maria [Vis alle 9 forfattere av denne artikkelen] (2023). NKL-1915 National Nitrogen Budgets in Scandinavia: consequences for climate change and for eutrophication – synthesis report. Report number C 814. IVL Swedish Environmental Research Institute. ISSN 978-91-7883-567-6.
• Kaste, Øyvind; Schartau, Ann Kristin; de Wit, Heleen & Vogt, Rolf David (2023). Evaluation of the IKEU programme. An evaluation of the programme’s organization, its organs, financing and contributions. Norsk institutt for vannforskning. ISSN 978-82-577-7631-2. Fulltekst i vitenarkiv Vis sammendrag

  IKEU (Integrated Studies of the Effects of Liming Acidified Waters) is the national monitoring programme for long-term effects of liming in Sweden. The main focus of IKEU is to study the long-term effects of liming on lakes and streams in order to improve the knowledge base for the liming activity. The main aim of this report is to evaluate the current programme structure and IKEU’s fulfilment of the four main objectives since the last evaluation in 2009. The evaluation includes an assessment of scientific quality, the usefulness of the long-term monitoring series produced by the programme, whether the programme produces relevant knowledge for decision making, and to what extent decisionmakers implement the knowledge produced by the programme.

• Velle, Gaute; Bodin, Christian Lucien; Arle, Jens; Austnes, Kari; Boggero, Angela & Bojkova, Jindriska [Vis alle 19 forfattere av denne artikkelen] (2023). Responses of benthic invertebrates to chemical recovery from acidification. Norsk institutt for vannforskning. ISSN 978-82-577-7617-6. Fulltekst i vitenarkiv Vis sammendrag

  The report provides an assessment of biological recovery from acidification in freshwater environments in Europe. The report consists of two parts, a regional data analysis based on an international dataset of biological and water chemical records, and a collection of national contributions on monitoring and assessment of biological recovery in different countries. The regional analysis showed that 47% of all included rivers (21 sites, for the period 1994-2018) and 35% percent of all lakes (34 sites, for the period 2000 to 2018) showed significant increases in species richness. Correlations between species diversity and water chemical components (ANC, pH, SO4) were found, supporting that the biological responses were related to chemical recovery. Additionally, the composition of functional traits in rivers underwent significant changes over time. Both parts of the report demonstrate ongoing biological recovery from acidification in European acid-sensitive freshwater environments.

• Bobbink, Roland; Loran, Christin; Tomassen, Hilde; Aazem, Khalid; Aherne, Julian & Alonso, Rocío [Vis alle 44 forfattere av denne artikkelen] (2022). Review and revision of empirical critical loads of nitrogen for Europe. German Environment Agency. ISSN 1862-4804. Vis sammendrag

  This report describes the scientific background and results from the review and revision of empirical critical loads of nitrogen that had been established for Europe in 2011 under the auspices of the UNECE Convention on Long-range Transboundary Air Pollution (LRTAP Convention). In 2020, the Coordination Centre for Effects started a project under the LRTAP Convention to bring empirical critical loads up to date. New relevant information from studies (2010 - summer 2021) on the impacts of nitrogen on natural and semi-natural ecosystems was incorporated in the existing European database on empirical critical loads of N (CLempN). The current review and revision used for the first time gradient studies to evaluate and determine the ClempN. The CLempN were structured according to the updated classification used within the European Nature Information System (EUNIS). Consensus on the results was reached in a UNECE expert workshop on empirical critical loads of nitrogen (26-28 October 2021, Berne, Switzerland), organised by the Swiss Federal Office for the Environment (BAFU), the Coordination Centre for Effects, and the B-WARE Research Centre. The results, as presented in Table 1 of the Executive Summary, show that in many cases the outer ranges of the empirical critical loads have decreased. The resulting 2021 European database includes both revised and newly established value ranges of CLempN for each EUNIS class. The outcomes of this report are of major importance for the protection of N-sensitive natural and semi-natural ecosystems across Europe. This knowledge is used to support European policies to reduce air pollution.

• Vogt, Rolf David; de Wit, Heleen & Koponen, Kati (2022). Case study on impacts of large-scale re-/afforestation on ecosystem services in Nordic regions . NEGEM project. Fulltekst i vitenarkiv
• Austnes, Kari; Hjermann, Dag Øystein; Sample, James Edward; Wright, Richard Frederic; Kaste, Øyvind & de Wit, Heleen (2022). Nitrogen in surface waters: time trends and geographical patterns explained by deposition levels and catchment characteristics. Norsk institutt for vannforskning. ISSN 978-82-577-7464-6. Fulltekst i vitenarkiv Vis sammendrag

  The report presents a statistical analysis of controls (deposition, land cover, climate) on spatial variability and long-term trends (1992-2016) in surface water concentrations of nitrate (NO3) and carbon to nitrogen (C/N) ratios of dissolved organic matter (DOM) at the ICP Water sites in Europe and North America. Nitrogen (N) deposition has declined over large parts of Europe and North America. Surface water NO3 has decreased significantly at 46% of sites, increased at a few sites (4%) and has had no significant trend at the remaining sites. The C/N ratio of DOM has increased at 52% of the sites, decreased at 5% and has no trend at 43% of the sites. The greatest decline in surface water NO3 occurred at sites with high N deposition and high NO3 concentrations. The increase in C/N ratios of DOM is mainly related to increasing trends in total organic carbon (TOC) and seems largely unaffected by N deposition levels or trends. Data from most of the ICP Waters sites do not suggest that N saturation is occurring presently, but there is still a risk that climate change and ecosystem disturbances might cause higher N leaching in the future.

• Magnussen, Kristin; Aarrestad, Per Arild; Austnes, Kari; Bakkestuen, Vegar; de Wit, Heleen & Fleisje, Erlend M. [Vis alle 8 forfattere av denne artikkelen] (2021). Verdsetting av luftforurensningens kostnader for miljø – en litteraturstudie. Menon Economics.
• Kaste, Øyvind; Skarbøvik, Eva; Clarke, Nicholas & de Wit, Heleen (2021). Gjødsling av skog - vurdering av eksisterende hensynssone og tak for nitrogengjødsling på bakgrunn av ny kunnskap. Norsk institutt for vannforskning. ISSN 978-82-577-7399-1. Fulltekst i vitenarkiv Vis sammendrag

  I 2014 ble det utgitt en rapport om skoggjødsling som klimatiltak, hvor det ut fra hensyn til vannmiljø ble stipulert en hensynssone for nitrogengjødsling av skog og et arealmessig tak for gjødsling innenfor denne sonen. Hensynssonen omfattet deler av Rogaland, Sørlandet og deler av Østlandet rundt Oslofjorden, hvor det ble definert et maksimalt tak på 25 000 daa som kunne gjødsles over en tidsperiode på 5 år. Denne rapporten har vurdert konklusjonene i 2014-rapporten på nytt, og etter en gjennomgang av relevante overvåkingsdata fram til i dag, samt nyere litteratur, finner vi ikke grunnlag for verken å lempe på eller å skjerpe begrensningene innenfor hensynssonen som ble definert da tilskuddsordningen ble lansert i 2016. For å bedre kunnskapsgrunnlaget er det behov for mer systematisk og langsiktig overvåking av effekter av skoggjødsling, ulike hogstmetoder og tiltak for å redusere belastningen på vannforekomster.

• Thrane, Jan-Erik; de Wit, Heleen & Austnes, Kari (2021). Effects of nitrogen on nutrient-limitation in oligotrophic northern surface waters. Norsk institutt for vannforskning. ISSN 978-82-577-7416-5. Fulltekst i vitenarkiv Vis sammendrag

  Nitrogen deposition has a potentially eutrophying impact on oligotrophic freshwaters. Here we present a data analysis and a literature review with a joint focus on nitrogen (N) limitation in oligotrophic lakes and rivers. The data analysis consists of a Nordic lake dataset where relations between algal biomass (chlorophyll a), water chemistry and N deposition are investigated, and an analysis of element stoichiometry (nitrogen : phosphorus ratios) in Norwegian natural rivers. The literature review includes international publications on N limitation from a wide variation of monitoring and experimental studies. The data analysis and literature both support that N limitation exists in surface waters that receive low N deposition and that elevated N deposition can shift an ecosystem from N to P limitation. The results are used to review and revise ranges of critical loads of nitrogen for surface waters, as a contribution to the ongoing review and revision of empirical critical loads under the Convention on Long-range Transboundary Air Pollution.

• Poste, Amanda; Kaste, Øyvind; Frigstad, Helene; de Wit, Heleen; Harvey, E. Therese & Valestrand, Louise [Vis alle 10 forfattere av denne artikkelen] (2021). The impact of the spring 2020 snowmelt floods on physicochemical conditions in three Norwegian river-fjord-coastal systems. Norsk institutt for vannforskning. ISSN 978-82-577-7387-8. Fulltekst i vitenarkiv Vis sammendrag

  Due to very high snow accumulation in the winter of 2019/2020, the Norwegian Water Resources and Energy Directorate (NVE) in late May 2020 issued flood forecasts predicting extremely high flood risk for parts of northern Norway and high flood risk for rivers in south-eastern Norway with mountainous catchments. To capture impacts of these potentially extreme snowmelt floods on water chemistry in rivers and coastal waters, extra sampling campaigns were carried out in three selected river-fjord systems: Glomma river-Ytre Oslofjord-Skagerrak in southern Norway, and the Målselv river-Målselvfjord-Straumsfjorden and Tana river-Tanafjord systems in northern Norway. The overarching goal was to study the impact of the 2020 spring freshet (i.e. snowmelt flood) on river water chemistry, land-ocean fluxes, and physicochemical conditions in coastal waters. In this report we describe between-site differences and seasonal patterns in river and coastal water chemistry based on existing data from national river (2016–2020) and coastal (2017–2020) monitoring in the three study regions, and then use these to provide context for the data from the spring 2020-sampling campaign, with a focus on suspended particulate matter (SPM), dissolved organic carbon (DOC), and nutrients. This report also highlights the complexity of identifying climate change impacts along the terrestrial-freshwater-marine continuum and the need for tighter cross-disciplinary and cross-ecosystem integration between monitoring programmes.

• Sandin, Leonard; Thrane, Jan-Erik; Persson, Jonas; Kile, Maia Røst; Bækkelie, Knut Andreas Eikland & Myrvold, Knut Marius [Vis alle 11 forfattere av denne artikkelen] (2021). Overvåking av referanseelver - Utprøving av klassifiseringssystemet for basisovervåking i referansevassdrag. Norsk institutt for vannforskning. ISSN 978-82-577-7376-2. Vis sammendrag

  Overvåkingsprogrammet for referanseelver har pågått siden 2017, og 2020 var andre år med undersøkelser i de 33 vannforekomstene som første gang ble undersøkt i 2018. Vannforekomstene dekker mange ulike elvetyper i flere økoregioner. I tillegg til økologisk og kjemisk tilstandsklassifisering av lite påvirkede vannforekomster, har programmet som mål styrke datagrunnlaget for fastsettelse av referanseverdier; fange opp langsiktige endringer i vanntilstand; og teste ut metodikk for tilstandsklassifisering. Basert på en samlet vurdering av alle biologiske og fysisk-kjemiske kvalitetselementer oppnådde 13 av 34 stasjoner god økologisk tilstand, og ingen svært god tilstand. Om vi ser bort fra fiskeindeksen (som i dag ikke er godt egnet til klassifisering i alle typer vannforekomster) oppnår 12 vannforekomster god tilstand og 6 svært god tilstand. Moderat eller dårligere tilstand for bunndyrindeksen for organisk belastning (ASPT), forsuringsindeksen for påvekstalger (AIP), samt forhøyede nivåer av PCB7 i fisk, er hovedårsakene til at ikke flere vannforekomster oppnår miljømålet samlet sett. Det er knyttet relativt stor usikkerhet til flere av indeksene og den samlede klassifiseringen, og det er usikkert i hvilken grad mange av vannforekomstene faktisk avviker fra referanse-tilstand. Det ble observert lave konsentrasjoner av de fleste miljøgiftene, med unntak av kvikksølv og polybromerte difenyletere (PBDE), som lå over grenseverdiene for alle 11 vannforekomster der disse var målt. For PCB7 lå 4 av 11 vannforekomster over grenseverdiene og PFOS oversteg grenseverdiene i to vannforekomster.

• Thrane, Jan-Erik; de Wit, Heleen; Blakseth, Tomas Adler; Skancke, Liv Bente & Garmo, Øyvind Aaberg (2020). Korrigering av skjevhet i konsentrasjoner av total nitrogen målt med en modifisert standard (NS4743) metode. Norsk institutt for vannforskning. ISSN 978-82-577-7273-4. Fulltekst i vitenarkiv Vis sammendrag

  En evaluering av langtidstrender i karbon til nitrogen-ratioen (C:N ratioen) fra overvåkingsdata viste at C:N-ratioen hadde økt betydelig i 2019, og ekspertvurderinger indikerte at verdiene var utenfor den naturlige variasjonsbredden for C:N. Økningen i C:N-ratio sammenfalt med en endring av metode for analyse av total nitrogen (TotN) til en modifisert versjon av NS 4743 («metode A»), som ble gjort i september 2018. Det ble derfor reist mistanke om påliteligheten til de analytiske resultatene, spesielt siden C:N-ratioene var mest avvikende ved høy konsentrasjon av totalt organisk karbon (TOC), som vanligvis er assosiert med høy konsentrasjon av organisk N. Det ble framsatt en hypotese om at innholdet av organisk N var underestimert, og en det ble igangsatt en kvalitetssjekk av metoden. Undersøkelsen viste at utilstrekkelig oppslutning av prøvene, trolig på grunn bruk av andre kjemikalier og forhold under selve oppslutningen, så ut til å være årsaken til underestimerte konsentrasjoner av TotN, spesielt for prøver med høy andel organisk bundet N. Oksidasjonskraften til den oksiderende agensen ble funnet å være for lav, og oppslutningstiden var også litt for kort med hensyn til NS 4743- standarden. Metoden for analyse av TotN ble derfor tilpasset til NS 4743 standarden («metode B»), og alle prøvene fra et stort nasjonalt innsjøovervåkingsprogram («1000 sjøer»-prosjektet) ble re-analysert ved bruk av metode B. På grunn av de metodiske utfordringene har det blitt rapportert antatt underestimerte konsentrasjoner av TotN for flere overvåkingsprogrammer mellom september 2018 og 2019. De fleste av disse prøvene er ikke lengre tilgjengelig for re-analyse, og for å unngå enten underestimerte eller tapte verdier for TotN fra de berørte stasjonene og periodene, var det behov for en funksjon for å korrigere de underestimerte verdiene. Siden prøvene fra «1000 sjøer»-undersøkelsen ble analysert med begge metoder for TotN, benyttet vi dette datasettet til å tilpasse en regresjonsmodell for å korrigere de gamle (antatt underestimerte) konsentrasjonene som ble målt med metode A. Den beste regresjonsmodellen inkluderte de gamle TotN-konsentrasjonene og TOC som prediktorer, samt en interaksjon mellom de to variablene. Dette indikerer at forskjellen mellom de gamle (metode A) og nye (metode B) TotN-konsentrasjonene avhenger av TOC. Modellen hadde en R2 på 0.956 og et gjennomsnittlig avvik (root mean squared error; RMSE) på 31,87 μg N/l. Vi validerte modellen på uavhengige datasett med data fra innsjøer, elver/bekker høyt oppe i vassdragene og større elver, og fant at modellen predikerte de nye TotNkonsentrasjonene med adekvat nøyaktighet for innsjøer og bekker/elver høyt oppe i vassdragene (1-3 ordens bekker/elver). TotN-konsentrasjoner fra større elver (>6-orden), ser derimot ikke ut til å trenge korreksjon, ettersom forskjellen mellom TotN fra de to metodene ikke var signifikant for denne typen elver. Vi spekulerer i om dette kan ha en sammenheng med forskjeller i kvaliteten på det organiske materialet (graden av labilitet eller opphav) mellom og bekker/elver høyt oppe og lengre ned i vassdragene. Siden bruk av den modifiserte standardmetoden (metode A) trolig medførte underestimert TotN anbefaler vi at overvåkingsprogrammer for ferskvann bruker NS 4743-standarden (metode B) og ikke metode A for analyse av TotN. Gjenfinning (recovery) av ikke-tilsatt nitrogen i vannprøver med høy konsentrasjon av refraktorisk organisk materiale må dokumenteres før nye eller justerte metoder tas i bruk.

• Thrane, Jan-Erik; Persson, Jonas; Kile, Maia Røst; Bækkelie, Knut Andreas Eikland; Myrvold, Knut Marius & Garmo, Øyvind Aaberg [Vis alle 10 forfattere av denne artikkelen] (2020). Overvåking av referanseelver 2019. Basisovervåking i henhold til vannforskriften. Norsk institutt for vannforskning. ISSN 978-82-577-7220-8. Vis sammendrag

  Rapporten presenterer resultatene fra 2019, som var andre år med overvåking i 40 vannforekomster. Vannforekomstene dekket alle økoregioner og mange ulike elvetyper, men det er knyttet relativt stor usikkerhet til en del av resultatene. Basert på en samlet vurdering av alle biologiske og fysisk-kjemiske kvalitetselementer oppnådde kun fem av 40 vannforekomster miljømålet om god eller svært god økologisk tilstand. Det var fiskeindeksen og forsuringsindeksen for påvekstalger som var bestemmende for at miljømålet ikke ble nådd for hoveddelen av vannforekomstene. Med hensyn til eutrofieringspåvirkning nådde alle vannforekomstene (bortsett fra ett leirvassdrag) miljømålet. Med unntak av fire vannforekomster ble miljømålet nådd med hensyn til organisk belastning (ASPT-indeksen for bunndyr). For forsuringsparameterne oppnådde kun 10 av 26 forsuringsfølsomme vannforekomster miljømålet. De fleste av de 16 som viste tegn til forsuring (og dermed ikke oppnådde miljømålet) lå på Sørlandet og i Midt-Norge. Det er behov for mer data og en sammenstilling av referanseverdier for de ulike forsuringsindeksene/parameterne før vi konkluderer med at såpass mange vannforekomster faktisk er forsuret. For fiskeindeksen er det tydelig at det er behov for mer data og en revidering av indeksen, da kun to vannforekomster havnet i svært god tilstand, og hele 22 vannforekomster ikke nådde miljømålet. Det ble observert lave konsentrasjoner av de fleste miljøgiftene i biota (fisk), med unntak av kvikksølv, polybromerte difenyletere og PCB7, som alle lå over grenseverdiene i alle vannforekomster der disse ble målt. I vann ble det i hovedsak målt lave konsentrasjoner av metaller, med unntak av de tre leirvassdragene, hvor enkelte prøver overskred grenseverdiene.

• Garmo, Øyvind Aaberg; Kaste, Øyvind; Arle, Jens; Austnes, Kari; de Wit, Heleen & Fölster, Jens [Vis alle 18 forfattere av denne artikkelen] (2020). Trends and patterns in surface water chemistry in Europe and North America between 1990 and 2016, with particular focus on changes in land use as a confounding factor for recovery. Norsk institutt for vannforskning. ISSN 978-82-577-7214-7. Fulltekst i vitenarkiv Vis sammendrag

  The report presents trends in sulphate, nitrate, chloride, base cations, ANC (acid neutralising capacity), pH and DOC at circa 500 ICP Waters sites in Europe and North America for the period 1990-2016. Time series were analysed for trends in annual median values, annual extreme values and change points, that indicate years with sudden changes in trend or level. Also provided is a brief overview of possible implications of land use change for recovery of acidified surface waters.

• Moe, Therese Fosholt; Persson, Jonas; Bækkelie, Knut Andreas Eikland; Myrvold, Knut Marius; Garmo, Øyvind Aaberg & Grung, Merete [Vis alle 9 forfattere av denne artikkelen] (2019). Overvåking av referanseelver 2018. Basisovervåking i henhold til vannforskriften. Norsk Insitutt for Vannforskning. ISSN 978-82-577-7113-3. Fulltekst i vitenarkiv Vis sammendrag

  Overvåking av referanseelver har vært gjennomført over to år, og i andre år (2018) ble 34 antatte referansevannforekomster undersøkt. Vannforekomstene dekket mange ulike elvetyper i økoregionene Finnmark, Vestlandet og Østlandet (resten av landet ble dekket med 47 vannforekomster i 2017). Det er knyttet usikkerhet til en del av resultatene, men med tanke på påvirkniger som fører til eutrofiering nådde alle vannforekomstene miljømålet, med unntak av to leirvassdrag. Det kan også se ut til å være noe organisk belastning i enkelte vannforekomster. For forsuringsparameterne var det 8 vannforekomster som ikke nådde miljømålet. Det er behov for mer data og en sammenstilling av de ulike forsuringsparameterne før vi kan konkludere med årsakene. For fiskeindeksen var resultatene for 2018 noe bedre enn i 2017, og 19 vannforekomster nådde miljømålet. Det er fortsatt behov for mer data og en revidering av denne indeksen. Det ble observert lave konsentrasjoner av de fleste miljøgiftene, med unntak av kvikksølv, polybromerte difenyletere og PCB7, som lå over grenseverdiene for alle 11 vannforekomster der disse var målt (i 10 av 11 for PCB7). Også nikkel og PFOS oversteg grenseverdiene for henholdsvis 1 og 2 vannforekomster.

• Braaten, Hans Fredrik Veiteberg; Gundersen, Cathrine Brecke; Sample, James Edward; Selvik, John Rune & de Wit, Heleen (2018). Atmospheric deposition and lateral transport of mercury in Norwegian drainage basins: A mercury budget for Norway. Norsk institutt for vannforskning. ISSN 978-82-577-7045-7. Fulltekst i vitenarkiv Vis sammendrag

  Reduced atmospheric loading of mercury (Hg) can improve the environmental status of freshwaters and coastal ecosystems. Sparse data limit impact assessments of changes in atmospheric Hg on aquatic ecosystems. Here, a Hg budget is calculated for Norway by estimating fluxes of Hg in the environment. Atmospheric inputs (ca. 3.3 tonnes annually) are a factor 10 higher than riverine export to coastal areas, indicating considerable retention in soils and lakes. Environmental loading of Hg to surface waters was separated into headwater (=catchment) export of Hg and atmospheric Hg loadings, which were of similar size (0.2 to 0.3 tonnes), where atmospheric loadings were considered of higher certainty than headwater fluxes. Robust methods for estimations of headwater Hg export at the regional scale are lacking. Hg budgets for small headwater catchments are more reliable and valuable to assess the fate of atmospheric Hg, and the role of aquatic Hg retention. Continued monitoring of Hg in deposition, catchments, and rivers are needed to reduce uncertainties in environmental assessments, in addition to international collaboration.

• Austnes, Kari; Aherne, Julian; Arle, Jens; Čičendajeva, Marina; Couture, Suzanne & Fölster, Jens [Vis alle 21 forfattere av denne artikkelen] (2018). Regional assessment of the current extent of acidification of surface waters in Europe and North America. Norsk institutt for vannforskning. ISSN 1894-7948. Fulltekst i vitenarkiv Vis sammendrag

  The current status of surface water acidification related to air pollution in Europe and North America has been assessed using country reports, monitoring data, critical loads and exceedance data, acid sensitivity and deposition maps, and data reported under the European Commission’s Water Framework Directive (WFD). Acidification is still observed in many countries, but the extent and severity vary. Maps of acid sensitivity and deposition suggest that surface water acidification is present in regions and countries for which no data or reports were delivered for the current assessment. Existing national monitoring varies in the ability to assess the spatial extent of acidification and the recovery responses of acidified sites. The monitoring requirements under the European Union’s National Emission Ceilings Directive are expected to reverse the recent decline in the number of monitoring sites observed in some countries. The information reported under the WFD is currently of limited value in assessing the extent of acidification of surface waters in Europe. Chemical recovery in response to reductions in acid deposition can be slow, and biological recovery can lag severely behind. Despite large and effective efforts across Europe and North America to reduce surface water acidification, air pollution still constitutes a threat to freshwater ecosystems.

• Garmo, Øyvind Aaberg; Ulańczyk, Rafał & de Wit, Heleen (2018). Proceedings of the 34th Task Force meeting of the ICP Waters Programme in Warsaw, May 7-9, 2018. Norsk institutt for vannforskning. ISSN 978-82-577-7033-4. Fulltekst i vitenarkiv Vis sammendrag

  Proceedings of the 34th Task Force meeting of the ICP Waters Programme in Warsaw, May 7-9, 2018. National contributions from Russia and Armenia.

• Moe, Therese Fosholt; Thrane, Jan-Erik; Persson, Jonas; Bækkelie, Knut Andreas Eikland; Myrvold, Knut Marius & Olstad, Kjetil [Vis alle 9 forfattere av denne artikkelen] (2018). Overvåking av referanseelver 2017. Basisovervåking i henhold til vannforskriften. Norsk institutt for vannforskning. ISSN 978-82-577-6994-9. Fulltekst i vitenarkiv Vis sammendrag

  Overvåking av referanseelver startet opp i 2017, og 47 antatte referansevannforekomster ble undersøkt. Vannforekomstene dekket alle økoregioner og mange ulike elvetyper, men det er knyttet relativt stor usikkerhet til en del av resultatene. Med tanke på påvirkniger som fører til eutrofiering nådde alle vannforekomstene miljømålet, mens det kan se ut til å være noe organisk belastning i enkelte vannforekomster. For forsuringsparameterne var det 18 vannforekomster som ikke nådde miljømålet, med noe dårligere tilstand på Sørlandet enn i resten av landet. Det er behov for mer data og en sammenstilling av referanseverdier for de ulike forsuringsparameterne før vi konkluderer med at såpass mange vannforekomster faktisk er forsuret. For fiskeindeksen ble det tydelig at det er stort behov for mer data og en revidering av indeksen, da kun 3 vannforekomster havnet i svært god tilstand, og hele 35 vannforekomster ikke nådde miljømålet. Det ble observert lave konsentrasjoner av de fleste miljøgiftene, med unntak av kvikksølv og polybromerte difenyletere, som begge lå over grenseverdiene for alle vannforekomster der disse var målt. Også noen av de vannregionspesifikke stoffene oversteg grenseverdien for noen vannforekomster.

• Martínez, Elena; Vogt, Rolf David & de Wit, Heleen (2017). Biodegradability and Spectroscopic Properties of Dissolved Natural Organic Matter Fractions Linked to Hg and MeHg Transport and Uptake. Universitetet i Oslo.
• Garmo, Øyvind Aaberg; de Wit, Heleen & Fölster, Jens (2017). Proceedings of the 33rd Task Force meeting of the ICP Waters Programme in Uppsala, May 9-11, 2017. Norsk institutt for vannforskning. ISSN 978-82-577-6913-0. Fulltekst i vitenarkiv Vis sammendrag

  Proceedings of the 33rd Task Force meeting of the ICP Waters Programme in Uppsala, May 9-11, 2017. National contributions from Russia, Switzerland, and Moldova.

• Braaten, Hans Fredrik Veiteberg; Åkerblom, Staffan; de Wit, Heleen; Skotte, Gunnar; Rask, Martti & Vuorenmaa, Jussi [Vis alle 18 forfattere av denne artikkelen] (2017). Spatial and temporal trends of mercury in freshwater fish in Fennoscandia (1965-2015). Norsk institutt for vannforskning. ISSN 978-82-577-6914-7. Fulltekst i vitenarkiv Vis sammendrag

  Mercury (Hg) emissions to the atmosphere cause elevated Hg levels in fish, even in many remote regions of the world. Here we present an extensive database of more than 50 000 measurements of Hg in fish, including 2 775 individual water bodies in Fennoscandia (Norway, Sweden, Finland, Russian part of Kola Peninsula) sampled between 1965 and 2015. The data have been analysed for spatial patterns and temporal trends, on raw and weight-adjusted data. The database presents a useful reference for assessment of impacts of environmental policy on Hg in freshwater fish (i.e. Convention on Long-Range Transboundary Air Pollution and The Minamata Convention on Mercury).

• Valinia, Salar & de Wit, Heleen (2016). Proceedings of the 32nd Task Force meeting of the ICP Waters Programme in Asker, Oslo, May 24-26, 2016. Norsk institutt for vannforskning. ISSN 978-82-577-6825-6. Fulltekst i vitenarkiv Vis sammendrag

  Proceedings of the 32nd Task Force meeting of the ICP Waters Programme in Asker, Norway, May 24-26, 2016. National contributions from Russia and Norway.

• Velle, Gaute; Mahlum, Shad Kenneth; Monteith, Don T.; de Wit, Heleen; Arle, Jens & Fjellheim, Arne [Vis alle 24 forfattere av denne artikkelen] (2016). Biodiversity of macro-invertebrates in acid-sensitive waters: trends and relations to water chemistry and climate. Norsk institutt for vannforskning. ISSN 978-82-577-6812-6. Fulltekst i vitenarkiv Vis sammendrag

  This is a study of the international impact of acid emission reductions on vulnerable freshwater biodiversity of benthic macroinvertebrates. In order to properly attribute impacts it is necessary to also incorporate the potential effects of changes in temperature and precipitation. Most sites show an increasing number of species towards the present. This can be attributed to a decrease in acidification, while temperature has a secondary influence on diversity. We expect that the biodiversity will continue to increase in the future as acid deposition decreases. The widespread response of aquatic diversity resulting from emission reductions of acidifying components to the atmosphere demonstrates the potential of international policy for achieving positive effects on the state of the environment.

• de Wit, Heleen; Valinia, Salar & Steingruber, Sandra (2016). Proceedings of the 31st Task Force meeting of the ICP Waters Programme in Monte Verità, Switzerland, October 6-8, 2015. ICP Waters report 126/2016. Norsk institutt for vannforskning. ISSN 978-82-577-6738-9. Vis sammendrag

  Proceedings of the 31st Task Force meeting of the ICP Waters Programme in Monte Verità, Norway, October 6 – 8, 2015. National contributions from Russia, Italy, Switzerland, Finland, Canada, Sweden, and Norway.

• Hansen, Georg Heinrich; Rasse, Daniel; de Wit, Heleen; Tømmervik, Hans; Bjerke, Jarle W. & Lund, Magnus [Vis alle 7 forfattere av denne artikkelen] (2015). Effects of climate variability on vegetation and carbon uptake in a North-Norwegian coastal wetland. NILU. ISSN 978-82-425-2818-6. Fulltekst i vitenarkiv Vis sammendrag

  Greenhouse gas exchange between terrestrial ecosystems and the atmosphere are an important element of the climate system. Especially boreal and polar wetlands and peatlands may play a crucial role for the future development of atmospheric carbon dioxide and methane concentrations, because they contain stores of these gases in the same order of magnitude as the current atmospheric load. The aim of this project was to estimate the fluxes of CO2 and CH4 from an oceanic wetland in North‐Norway. Seven years of observations reveal that carbon exchange from this ecosystem is comparable to that of moderate zone coastal wetlands, but distinctly different from alpine and continental wetlands at the same latitude in Sweden and Finland. The seven‐year record of meteorological data reveals that the observed period was significantly warmer (especially during winter) and drier (especially in summer) than the climate reference period 1961‐1990. Carbon fluxes during the growing season are sensitive to both draught, cold spells and soil climate conditions before the onset of the growing season, but the annual Net Ecosystem Exchange is much less variable.

• de Wit, Heleen; Hettelingh, Jean-Paul & Harmens, Harry (2015). Trends in ecosystem and health responses to long-range transported atmospheric pollutants - ICP Waters report 125/2015. Norsk institutt for vannforskning. ISSN 978-82-577-6681-8. Fulltekst i vitenarkiv Vis sammendrag

  The aim of this trend report is to assess the effectiveness of air pollution policies under the Convention on Long-range Transboundary Air Pollution (LRTAP), and to document progress and identify remaining challenges. Trends in environmental and health responses to long-range transported air pollution are presented, primarily focusing on 1990 to 2012 and on Europe, with additional data from North America and the Arctic region. Air pollutants included in the report are sulphur and nitrogen as acidifying agents, nutrient-nitrogen, ground-level ozone, particulate matter (PM), heavy metals and persistent organic pollutants (POPs). The results are from work done under the bodies of the Working Group on Effects of the LRTAP Convention, i.e. ICP Integrated Monitoring, ICP Forests, ICP Materials, ICP Modelling and Mapping, ICP Vegetation, ICP Waters, JEG Dynamic Modelling and the Task Force on Health. The European Monitoring and Evaluation Programme (EMEP) and the Arctic Monitoring and Assessment Programme (AMAP) also contributed.

• Fjellheim, Arne; Johannessen, Arne; Landås, Torunn Svanevik & de Wit, Heleen (2015). Biological intercalibration. Invertebrates 1915 - ICP Waters report 124/2015. Norsk institutt for vannforskning. ISSN 978-82-577-6675-7. Fulltekst i vitenarkiv Vis sammendrag

  Six European laboratories participated in the 19th ICP Waters biological intercalibration, which took place in 2015. The laboratories identified a very high portion of the individuals in the test samples, > 95% of the total number of species. On the genus level, few faults were recorded. The mean Quality assurance index was excellent, ranging between 95.4 and 98.5, well above the value 80 - indicating acceptable taxonomic work.

• Garmo, Øyvind Aaberg; de Wit, Heleen & Fjellheim, Arne (2015). Chemical and biological recovery in acid-sensitive waters: trends and prognosis (ICP Waters report 119/2015). Norsk institutt for vannforskning. ISSN 978-82-577-6582-8. Fulltekst i vitenarkiv Vis sammendrag

  We present a trend analysis of surface water chemistry in in acid-sensitive lakes and rivers in Europe and North America, for the period 2000 to 2011, combined with a prognosis for water chemistry in Europe in 2020. Also, trends in freshwater biology in acidified surface waters in Europe are presented. Declining emissions and deposition of sulphur between 2000 and 2011 have lowered sulphate concentrations in surface waters. The clearest indication that water chemistry is getting less hostile to acid sensitive organisms is increased pH. Several examples of partial biological recovery are presented, but also examples where communities of aquatic invertebrates show few signs of recovery. We expect that climate variability will confound effects of reduced sulphur emissions on chemical and biological recovery in the next decades.

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