Relationship Between Land-Use in the Agro-Forestry System of Les Landes, Nitrogen Loading to and Risk of Macro-Algal Blooming in the Bassin d' Arcachon Coastal Lagoon (SW France)

• Published in: Estuarine, coastal and shelf science Vol. 62; no. 3; p. 453
• Main Authors: De Wit, R, Leibreich, J, Vernier, F, Delmas, F, Beuffe, H, Maison, Ph, Chossat, J-C
• Format: Journal Article
• Language: English
• Published: 01.02.2005
• ISSN: 0272-7714

Land use effects on nitrogen (N) loading to the Bassin d'Arcachon coastal lagoon, France, were studied. Some 79% of the catchment is forested and 9% is intensively farmed. N outputs of two hydrological subunits, one dominated by pine forest and one by both forest and farmland, were monitored for 7 yr (1996-2002). Forestry contributes an average of 1.6 kg total N/ha/yr, mainly as organic N. Intensive agriculture contributes 26 times more than forestry does, mainly as nitrate. When these data were scaled up to the catchment level and other known N sources and interannual variability were taken into consideration, N loading to the lagoon averaged 90 kg/ha/yr. The sandy soils in the catchment have potential for denitrification but anoxic conditions and organic matter inputs are needed for this process, and agricultural practices and spatial planning do not facilitate this potential. Seasonal variation in N loading, uptake by macroalgae, and algal blooms in the lagoon also are discussed.