Spatial and temporal trends in nutrient concentrations in the Belgian Continental area of the North Sea during the period 1993-2000

Statistical analysis of nutrient data obtained during 8 years of monitoring indicated strong seasonal and spatial variability, with highest concentrations in winter and significantly higher concentrations (on average >2 times higher) in the salinity zone S < 33 than in the salinity zone S = 33. In the North Sea ammonium concentrations significantly decreased from 1995 on (47% in zone S < 33 and 64% in zone S = 33), while for nitrate no significant decrease was observed in the zone S = 33. Despite a drastic reduction (50%) in the riverine inputs of phosphorus to the North Sea during the last decade, phosphate concentrations decreased only slightly in the zone S < 33 (