[Nutrients|Nutrient] export fluxes in coastal systems, primarily as [nitrogen] (N), [phosphorus] (P) and silicon (Si), have a significant impact on water quality and control the nature and magnitude of coastal productivity. In coastal areas, nutrients are delivered by rivers, groundwater discharge and atmospheric deposition. The growing impact of anthropogenic activities has profoundly affected the quality of marine waters over the last 50 years. Such alterations are well documented and have been linked to perturbations in nutrient export fluxes from the continent . In areas of restricted water exchange, the export of excess N and P to coastal waters may cause coastal [eutrophication], a blooming of suspended and bed-anchored algae (including toxic species), alteration of community structures, degradation in the ecosystem function and modifications of marine [food web]s . The continuing changes in land use and global urbanisation of coastal margins thus pose a continual threat to coastal waters.
CONTINENTAL NUTRIENT SOURCES
On a global scale, riverine inputs of N and P to coastal seas have possibly increased by factors of 2 to 3  , ,. Agriculture, in the form of fertilizers, leachates and animal wastes, is the largest contributor of N and P in aquatic systems  . Other major inputs include point-source discharges of wastewater from urban sewer networks , and industrial wastes. The direct discharge of P exchanged with soils and sediments also contributes significantly to the budget of this element.Riverine Si fluxes, originating
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