3 results
13 - Nitrogen flows from European regional watersheds to coastal marine waters
- from Part III - Nitrogen flows and fate at multiple spatial scales
-
- By Gilles Billen, University Pierre & Marie Curie, Marie Silvestre, CNRS – FR3020 FIRE, Bruna Grizzetti, European Commission Joint Research Centre, Adrian Leip, European Commission Joint Research Centre, Josette Garnier, UMR Sisyphe UPMC & CNRS, Maren Voss, Leibniz-Institute of Baltic Sea Research Warnemuende, Robert Howarth, Cornell University, Fayçal Bouraoui, European Commission Joint Research Centre, Ahti Lepistö, Finnish Environment Institute, Pirkko Kortelainen, Finnish Environment Institute, Penny Johnes, University of Reading, Chris Curtis, University College London Environmental Change Research Centre, Christoph Humborg, Stockholm University, Erik Smedberg, Stockholm University, Øyvind Kaste, Norwegian Institute for Water Research, Raja Ganeshram, University of Edinburgh, Arthur Beusen, Netherlands Environmental Assessment Agency, Christiane Lancelot, Université Libre de Bruxelles
- Edited by Mark A. Sutton, NERC Centre for Ecology and Hydrology, UK, Clare M. Howard, NERC Centre for Ecology and Hydrology, UK, Jan Willem Erisman, Gilles Billen, Albert Bleeker, Peringe Grennfelt, Hans van Grinsven, Bruna Grizzetti
-
- Book:
- The European Nitrogen Assessment
- Published online:
- 16 May 2011
- Print publication:
- 14 April 2011, pp 271-297
-
- Chapter
- Export citation
-
Summary
Executive summary
Nature of the problem
Most regional watersheds in Europe constitute managed human territories importing large amounts of new reactive nitrogen.
As a consequence, groundwater, surface freshwater and coastal seawater are undergoing severe nitrogen contamination and/or eutrophication problems.
Approaches
A comprehensive evaluation of net anthropogenic inputs of reactive nitrogen (NANI) through atmospheric deposition, crop N fixation, fertiliser use and import of food and feed has been carried out for all European watersheds. A database on N, P and Si fluxes delivered at the basin outlets has been assembled.
A number of modelling approaches based on either statistical regression analysis or mechanistic description of the processes involved in nitrogen transfer and transformations have been developed for relating N inputs to watersheds to outputs into coastal marine ecosystems.
Key findings/state of knowledge
Throughout Europe, NANI represents 3700 kgN/km²/yr (range, 0–8400 depending on the watershed), i.e. five times the background rate of natural N2 fixation.
A mean of approximately 78% of NANI does not reach the basin outlet, but instead is stored (in soils, sediments or ground water) or eliminated to the atmosphere as reactive N forms or as N2.
N delivery to the European marine coastal zone totals 810 kgN/km²/yr (range, 200–4000 depending on the watershed), about four times the natural background. In areas of limited availability of silica, these inputs cause harmful algal blooms.
8 - Nitrogen processes in coastal and marine ecosystems
- from Part II - Nitrogen processing in the biosphere
-
- By Maren Voss, Leibniz-Institute of Baltic Sea Research Warnemuende, Alex Baker, University of East Anglia, Hermann W. Bange, Leibniz-Institut für Meereswissenschaften, Daniel Conley, Lund University, Sarah Cornell, University of Bristol, Barbara Deutsch, Stockholm University, Anja Engel, Alfred Wegener Institute for Polar and Marine Research, Raja Ganeshram, University of Edinburgh, Josette Garnier, UMR Sisyphe UPMC & CNRS, Ana-Stiina Heiskanen, Finnish Environment Institute, Tim Jickells, University of East Anglia, Christiane Lancelot, Université Libre de Bruxelles, Abigail McQuatters-Gollop, Sir Alister Hardy Foundation for Ocean Science, Jack Middelburg, Utrecht University, Doris Schiedek, National Environmental Research Institute, Caroline P. Slomp, Utrecht University, Daniel P. Conley, Lund University
- Edited by Mark A. Sutton, NERC Centre for Ecology and Hydrology, UK, Clare M. Howard, NERC Centre for Ecology and Hydrology, UK, Jan Willem Erisman, Gilles Billen, Albert Bleeker, Peringe Grennfelt, Hans van Grinsven, Bruna Grizzetti
-
- Book:
- The European Nitrogen Assessment
- Published online:
- 16 May 2011
- Print publication:
- 14 April 2011, pp 147-176
-
- Chapter
- Export citation
-
Summary
Executive summary
Nature of the problem
Nitrogen (N) inputs from human activities have led to ecological deteriorations in large parts of the coastal oceans along European coastlines, including harmful algae blooms and anoxia.
Riverine N-loads are the most pronounced nitrogen sources to coasts and estuaries. Other significant sources are nitrogen in atmospheric deposition and fixation.
Approaches
This chapter describes all major N-turnover processes which are important for the understanding of the complexity of marine nitrogen cycling, including information on biodiversity.
Linkages to other major elemental cycles like carbon, oxygen, phosphorus and silica are briefly described in this chapter.
A tentative budget of all major sources and sinks of nitrogen integrated for global coasts is presented, indicating uncertainties where present, especially the N-loss capacity of ocean shelf sediments.
Finally, specific nitrogen problems in the European Regional Seas, including the Baltic Sea, Black Sea, North Sea, and Mediterranean Sea are described.
Key findings/state of knowledge
Today, human activity delivers several times more nitrogen to the coasts compared to the natural background of nitrogen delivery. The source of this is the land drained by the rivers. Therefore, the major European estuaries (e.g. Rhine, Scheldt, Danube and the coastlines receiving the outflow), North Sea, Baltic Sea, and Black Sea as well as some parts of the Mediterranean coastlines are affected by excess nutrient inputs.
Biodiversity is reduced under high nutrient loadings and oxygen deficiency. This process has led to changes in the nutrient recycling in sediments, because mature communities of benthic animals are lacking in disturbed coastal sediments. The recovery of communities may not be possible if high productivity and anoxia persist for longer time periods.
Bottom-up versus top-down control in phytoplankton of the Southern Ocean
- WALKER O. SMITH, CHRISTIANE LANCELOT
-
- Journal:
- Antarctic Science / Volume 16 / Issue 4 / December 2004
- Published online by Cambridge University Press:
- 30 November 2004, pp. 531-539
-
- Article
- Export citation
-
Oceanic phytoplankton communities are a mixture of various algal functional groups, all of which are of different sizes, have variable physiologies, and interact differently with disparate herbivores. We suggest that polar plankton communities, and specifically the larger phytoplankton of Southern Ocean HNLC (high nutrient, low chlorophyll) systems, are controlled primarily by bottom-up processes, but that smaller (pico- and nanoplankton) reach an equilibrium that is set simultaneously by light, iron and grazing by microzooplankton. Thus Southern Ocean phytoplankton conforms to the “ecumenical iron hypothesis”, albeit with the further addition of light as an environmental control. Examples of bottom-up controls include iron availability, irradiance regulation (either by the incident surface irradiance as controlled by season and sea ice cover, or by the effects of vertical turbulence and mixed layer depths), and macronutrient availability (silicic acid and nitrate). While the contribution of various phytoplankton taxa varies spatially and temporally within the Antarctic, we suggest that this is largely due to the specific responses of the important functional groups to the patterns of physical forcing and micronutrient inputs, rather than to changes in controls by small and large grazers. Examples of abiotic and biotic controls are examined from representative regions of the Antarctic, including continental shelf regions and open ocean HNLC systems. Results from models further support our contention that bottom-up control of large forms is paramount in the Southern Ocean, but top-down controls play an important part in regulating the equilibrium standing stocks of smaller taxa. If bottom-up control is indeed universal in the Antarctic, then it has profound implications for the understanding of interannual variability, food web structure, and population dynamics of higher trophic levels in both the present and past Southern Ocean.