Blar i NIVA Open Access Archive på forfatter "de Wit, Heleen"

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    • A carbon balance of Norway: terrestrial and aquatic carbon fluxes 

      de Wit, Heleen; Austnes, Kari; Hylen, Gro; Dalsgaard, Lise (Journal article; Peer reviewed, 2015)
      Northern landscapes accumulate carbon in vegetation and soils while rivers transport significant amounts of land-derived carbon to coastal areas. Here, we quantify carbon sources and sinks in main ecosystems (forests, ...

    • Afforestation of a pasture in Norway did not result in higher soil carbon, 50 years after planting 

      Strand, Line Tau; Fjellstad, Wendy Jane; Jackson-Blake, Leah Amber; de Wit, Heleen (Peer reviewed; Journal article, 2020)
      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 ...

    • Assessing critical load exceedances and ecosystem impacts of anthropogenic nitrogen and sulphur deposition at unmanaged forested catchments in Europe 

      Forsius, Martin; Posch, Maximilian; Holmberg, Maria; Vuorenmaa, Jussi; Kleemola, Sirpa; Augustaitis, Algirdas; Beudert, Burkhard; Bochenek, Witold; Clarke, Nicholas; de Wit, Heleen; Dirnböck, Thomas; Frey, Jane; Grandin, Ulf; Hakola, Hannele; Kobler, Johannes; Krám, Pavel; Lindroos, Antti-Jussi; Löfgren, Stefan; Pecka, Tomasz; Rönnback, Pernilla; Skotak, Krzysztof; Szpikowski, Józef; Ukonmaanaho, Liisa; Valinia, Salar; Váňa, Milan (Peer reviewed; Journal article, 2021)
      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 ...

    • Atmospheric deposition and lateral transport of mercury in Norwegian drainage basins: A mercury budget for Norway 

      Braaten, Hans Fredrik Veiteberg; Gundersen, Cathrine Brecke; Sample, James Edward; Selvik, John Rune; de Wit, Heleen (NIVA-rapport;7310, Research report, 2018)
      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 ...

    • Biodiversity in freshwaters: temporal trends and response to water chemistry (ICP Waters report 114/2013) 

      Velle, Gaute; Telford, Richard J.; Curtis, Chris; Eriksson, Lars; Fjellheim, Arne; Frolova, Marina; Fölster, Jens; Grudule, Natalja; Halvorsen, Godtfred A.; Hildrew, Alan; Hoffmann, Andreas; Indriksone, Iveta; Kamasová, Lenka; Kopáèek, Jiøí; Orton, Stuart; Krám, Pavel; Monteith, Don T.; Senoo, Takaaki; Shilland, Ewan M.; Stuchlík, Evžen; Wiklund, Magda-Lena; de Wit, Heleen; Skjelkvaale, Brit Lisa (NIVA-rapport;6580, Research report, 2013-10)
      This report describes trends in biological diversity of benthic invertebrates from acid-sensitive lakes and rivers sampled between 1982 and 2011 in the Czech Republic, Germany, Latvia, Norway, Sweden and the UK. The results ...

    • Biodiversity of macro-invertebrates in acid-sensitive waters: trends and relations to water chemistry and climate. ICP Waters report 127/2016 

      Velle, Gaute; Mahlum, Shad; Monteith, Don T.; de Wit, Heleen; Arle, Jens; Eriksson, Lars; Fjellheim, Arne; Frolova, Marina; Fölster, Jens; Grudule, Natalja; Halvorsen, Godtfred A.; Hildrew, Alan; Hruška, Jakub; Indriksone, Iveta; Kamasová, Lenka; Kopáček, Jiří; Krám, Pavel; Orton, Stuart; Senoo, Takaaki; Shilland, Ewan M.; Stuchlík, Evžen; Telford, Richard J.; Ungermanová, Lenka; Wiklund, Magda-Lena; Wright, Richard F. (NIVA-rapport;7077, Research report, 2016-09)
      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 ...

    • Biological intercalibration: Invertebrates 1713 (ICP Waters report 118/2014) 

      Fjellheim, Arne; Johannessen, Arne; Landås, Torunn Svanevik; de Wit, Heleen (NIVA-rapport;6662, Research report, 2014-04)
      The 17th intercalibration of invertebrates in the ICP Waters programme had contribution from four laboratories. The laboratories identified a very high portion of the individuals in the test samples, usually > 95% of the ...

    • Biological intercalibration: Invertebrates 1814 

      Fjellheim, Arne; Johannessen, Arne; Landås, Torunn Svanevik (NIVA-rapport;6761, Research report, 2014)
      The 18th intercalibration of invertebrates in the ICP Waters programme had contribution from three laboratories. The laboratories identified a very high portion of the individuals in the test samples, > 95% of the total ...

    • Boreal Headwater Catchment as Hot Spot of Carbon Processing From Headwater to Fjord 

      Clayer, Francois; Thrane, Jan-Erik; Brandt, Uta; Dörsch, Peter; de Wit, Heleen (Peer reviewed; Journal article, 2021)
      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 ...

    • Chemical and biological recovery in acid-sensitive waters: trends and prognosis (ICP Waters report 119/2015) 

      Garmo, Øyvind Aaberg; de Wit, Heleen; Fjellheim, A (NIVA-rapport;6847, Research report, 2015)
      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, ...

    • Cleaner air reveals growing influence of climate on dissolved organic carbon trends in northern headwaters 

      de Wit, Heleen; Stoddard, John L.; Monteith, Donald T.; Sample, James E.; Austnes, Kari; Couture, Suzanne; Fölster, Jens; Higgins, Scott N.; Houle, Daniel; Hruška, Jakub; Krám, Pavel; Kopáček, Jiří; Paterson, Andrew M.; Valinia, Salar; Van Dam, Herman; Vuorenmaa, Jussi; Evans, Chris D. (Peer reviewed; Journal article, 2021)
      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 ...

    • Climate warming feedback from mountain birch forest expansion: Reduced albedo dominates carbon uptake 

      de Wit, Heleen; Bryn, Anders; Hofgaard, Annika; Karstensen, Jonas; Kvalevåg, Maria Malene; Peters, Glen Philip (Journal article; Peer reviewed, 2013)
      Expanding high elevation and high latitude forest has contrasting climate feedbacks through carbon sequestration (cooling) and reduced surface reflectance (warming), which are yet poorly quantified. Here, we present an ...

    • Correcting for bias in freshwater total nitrogen concentrations obtained with a modified standard (NS4743) method 

      Thrane, Jan-Erik; de Wit, Heleen; Blakseth, Tomas Adler; Skancke, Liv Bente; Garmo, Øyvind Aaberg (NIVA-rapport;7538, Research report, 2020)
      Concentrations of total nitrogen (TotN) in freshwater monitoring programs were unreliable for a limited period, probably because of inadequate sample digestion when using a modified version of method NS 4743 (“method A”) ...

    • Effects of nitrogen on nutrient-limitation in oligotrophic northern surface waters 

      Thrane, Jan-Erik; de Wit, Heleen; Austnes, Kari (NIVA-rapport;7680, Research report, 2021)
      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. ...

    • Effects of sample preservation and storage on mercury speciation in natural stream water 

      Braaten, Hans Fredrik Veiteberg; de Wit, Heleen; Harman, Christopher Peter; Hageström, Ulla; Larssen, Thorjørn (Journal article; Peer reviewed, 2014)
      Despite an increasing focus on low level methods for determination of mercury species in water over the last decades, few studies have paid attention to direct effects of different sample preparation methods (i.e. preservation ...

    • Environmental factors influencing mercury speciation in Subarctic and Boreal lakes 

      Braaten, Hans Fredrik Veiteberg; de Wit, Heleen; Fjeld, Eirik; Rognerud, Sigurd; Lydersen, Espen; Larssen, Thorjørn (Journal article; Peer reviewed, 2014)
      Environmental drivers of total mercury (TotHg) concentrations, methylmercury (MeHg) concentrations, and MeHg fractions (a proxy for methylation potential, expressed as %MeHg) were assessed in a synoptic study of 51 lakes ...

    • Evaluation of the IKEU programme. An evaluation of the programme’s organization, its organs, financing and contributions 

      Kaste, Øyvind; Schartau, Ann Kristin; de Wit, Heleen; Vogt, Rolf David (NIVA-rapport;7895-2023, Research report, 2023)
      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 ...

    • Five decades of declining methylmercury concentrations in boreal foodwebs suggest pivotal role for sulphate deposition 

      Braaten, Hans Fredrik Veiteberg; Lindholm, Markus; de Wit, Heleen (Peer reviewed; Journal article, 2020)
      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 ...

    • Forest harvest effects on mercury in streams and biota in Norwegian boreal catchments 

      de Wit, Heleen; Granhus, Aksel; Lindholm, Markus; Kainz, Martin J.; Lin, Yan; Braaten, Hans Fredrik Veiteberg; Blaszczak, Joanna (Journal article; Peer reviewed, 2014)
      Forest harvesting practices can potentially increase mercury run-off from catchments. A paired catchment experiment was conducted in a boreal forest in southern Norway, to test effects of forest harvest operations on (i) ...

    • From greening to browning: Catchment vegetation development and reduced S-deposition promote organic carbon load on decadal time scales in Nordic lakes 

      Finstad, Anders Gravbrøt; Andersen, Tom; Larsen, Søren; Tominaga, Koji; Blumentrath, Stefan; de Wit, Heleen; Tømmervik, Hans; Hessen, Dag Olav (Journal article; Peer reviewed, 2016)
      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 ...