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Modelling the long-term effects of reducing nutrient inputs to the North Sea
Mathisen, L.R. (2007). Modelling the long-term effects of reducing nutrient inputs to the North Sea. Universitas Bergensis: Bergen. 71 pp.

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Document type: Dissertation

Keywords
    Long-term changes; Nutrient depletion; ANE, North Sea [Marine Regions]; Marine

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  • Mathisen, L.R.

Abstract
    The North Sea region is surrounded by highly industrialised and densely populated areas and is thus faced with a number of environmental threats, eutrophication being one of them. This is in particular a problem in the coastal and estuarine areas, which receives large amounts of riverine nutrients. Studies have shown that changing the ratio of nitrogen and phosphorous could potentially lead to a shift in the phytoplankton communities, towards more frequent nuisance algal blooms. The OSPAR Commission, which followed the Paris and Oslo Commissions, drew a set of Ecological Quality Objectives (EcoQO’s) in order to assess the effectiveness of reducing the river nutrient loads by 50%. All member countries must assess their coastal areas in accordance with the OSPAR Common Procedure and the EcoQO’s. The 3-dimensional, coupled physical-chemical-biological model NORWECOM was used in order to assess the long-term effects of reducing riverine DIN and DIP by 50% and 90% on three environmental parameters (N:P, chl amax and Omin). The model results showed that there was a decreasing response gradient from near-shore to offshore, where the largest effect for all parameters was identified along the Dutch coast. The EcoQO’s of N:P ratio and the chl amax concentrations were achieved for most areas, whereas the Omin concentrations had no or very low response to the modelled nutrient reductions. The correlation between large scale meteorology (NAO) and the model parameters seemed to be highest in the German coast and offshore and Dutch offshore, whereas local winds had the highest correlation with the Dutch coast.

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