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Riverine nitrogen export in Swedish catchments dominated by atmospheric inputs
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Cornell University, US.
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The net anthropogenic nitrogen input (NANI) approach addressing N loading from agricultural sources and the atmosphere were applied to 36 major Swedish catchments. We tested three alternatives of the empirical relationship between NANI and riverine N export using different ways of estimating atmospheric N deposition as the major N input (31-94 %) in these catchments. The relationship between riverine N export and NANI was strongest for the NANI calculation using NOy (r2 linear =0.704, r2 exponential =0.723) compared to NOy + net NHx (r2 linear =0.623, r2 exponential =0.670) and total NOy + NHx deposition (r2 linear =0.615, r2 exponential =0.658). The y-intercept (NANI= 0) of the linear and exponential regression models were between 40-160 kg N km-2 year-1 indicating a natural background flux from the catchment without anthropogenic inputs of some 100 kg N km-2 year-1. This agrees with similar results from North American boreal catchments. The slope of the three linear regressions varies from 0.24 (NOy + Net NHx) to 0.25 (NOy and NOy+ NHx), suggesting that in average 25% of the human inputs of nitrogen are exported by the rivers to the Baltic Sea. Agricultural catchments, in the middle and southern Sweden, have increased their riverine N export up to an order of magnitude compared to the inferred natural background flux as an effect of anthropogenic loading. Although, the relatively unperturbed northernmost catchments receive significant N loads from atmospheric deposition these catchments do not show any significant elevated riverine N export. The fact that nitrogen export in Swedish catchments appears to be higher in proportion to NANI at higher loads suggests that N retention could be saturating as loading rates increase. Such nonlinear or threshold responses have significant implications for nutrient management.

National Category
Natural Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-31484OAI: oai:DiVA.org:su-31484DiVA: diva2:280731
Available from: 2009-12-11 Created: 2009-11-17 Last updated: 2011-03-14Bibliographically approved
In thesis
1. Nitrogen land-sea fluxes in the Baltic Sea catchment: Empirical relationships and budgets
Open this publication in new window or tab >>Nitrogen land-sea fluxes in the Baltic Sea catchment: Empirical relationships and budgets
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis empirical relationships and modeling tools are used to describe the relationship between human activities and meso- and large scale riverine N fluxes from land to sea.

On a large scale Paper I showed that by only having knowledge about human population size and runoff one can estimate the riverine export of DIN (r2= 0.76). In Paper II we included two other important anthropogenic N inputs, i.e. atmospheric deposition and primary emission (PE) from animals. In most of the catchments the PE from animals were larger than the PE from humans. Hence, development of livestock is important and increased animal protein consumption by humans might increase the riverine N export. Scenario analysis (Paper II) show that climate change is expected to both decrease and increase the riverine N export depending on which part of the catchment is modeled.

In the southern and eastern parts of the Baltic Sea catchment there is large potential for N reductions from point sources (Papers III & V). The diffuse sources are more difficult to decrease and a reduction of mineral fertilizer does not always lead to reduced N loadings because the agricultural systems can buffer even a slight surplus (Paper III). There is inertia in the catchments which can be seen in for example in the northern part of the catchment. Here atmospheric N deposition is almost as high as in the southern part but the nitrogen flux from these rivers is not elevated. These northern river catchments have N exports of the same magnitude as the natural background (Paper IV), indicating that the atmospheric N deposition is retained in the system and probably taken up by N limited boreal forests. However, important reductions can be achieved in the agricultural sector by detailed management of the planted land and animal manure. The highest sensitivity is in catchments with high animal density and high specific discharge, primarily draining to Kattegat and Danish Straits (Paper II & IV).

Place, publisher, year, edition, pages
Stockholm: Department of Applied Environmental Science (ITM), 2010. 40 p.
Keyword
Nitrogen fluxes, Baltic Sea, primary emissions, riverine export, Scenario analysis, climate change, animal protein consumption, fertilizer use
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-32493 (URN)978-91-7155-988-3 (ISBN)
Public defence
2010-01-29, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of doctoral dissertation the following publications were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: ManuscriptAvailable from: 2010-01-07 Created: 2009-12-11 Last updated: 2010-01-27Bibliographically approved

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Eriksson Hägg, HannaHumborg, ChristophMörth, Carl-Magnus
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