Norwegian Institute for Air Research
Netherlands Institute for Ecology
Tyndall Centre for Climate Change Research
Institute for Environmental Studies, Free University Amsterdam
University of Plymouth
Centre for Social and Economic Research on the Global Environment
Land-Ocean Interactions in the Coastal Zone
 


Nutrient Dynamics in European Water Systems
Synthesis Results

2. Characterisation of nutrient sources (4 of 4)

 
2.2 Riverine and groundwater nutrient Inputs
 

The river model for the different stream order of several sub-basins represents full ecological dynamics, including transformation of nutrients in the ecosystem (biogeochemical RIVE model from EROS-21 project) (Garnier et al., 2002). A reasonable agreement was found between the simulations of the model and the observations (Figure 2.2(c)). The sharp drop in nitrogen and phosphorus delivery to the Black Sea, observed since 1991, was simulated with a scenario constructed to reproduce new constraints based on documented modifications of human activity in the watershed.

Present models require conceptual refinements such as; dynamic coupling with biological processes, incorporation of major macronutrient (nitrogen, phosphorus and silica) and organic matter, merging of deterministic and statistical approaches and incorporation of a groundwater module.

Figure 2.2(c). Upper course of the Danube River, simulation by the RIVERSTRAHLER model of the seasonal nitrate variations for the period 1988-1990 (Garnier et al., 2002). Experimental data from the same year are given as comparison.
Figure 2.2(c). Upper course of the Danube River, simulation by the RIVERSTRAHLER model of the seasonal nitrate variations for the period 1988-1990 (ammonium in dotted line). Experimental data from the same year are given as comparison (Garnier et al., 2002).

In the RANR project, the groundwater residence times were calculated for some east German watersheds by using WEKU, a supra-regional GIS-supported stochastic model (Kunkel & Wendland, 1997). It was shown that the groundwater residence times in the upper aquifer vary regionally, differentiated between less than 1 year and more than 2000 years.

Grimvall et al. (2000) presented a purely theoretical analysis of pools and fluxes explaining why the response to increased input of fertilizers in the 1950s and 1960s appears to have been more rapid than response to decreased input in the 1990s. This conceptual model has two reservoirs; one fast responding and one with a long response time. It shows a dual response to changes in nutrient loading; (1) reacts rapidly to increased input from point and diffuse sources and (2) has a very long lag time after a reduction of the input.

The importance of groundwater discharge for nutrient fluxes to the sea is currently investigated in the NAME project (Gregersen, 2002). NAME follows the route of nitrate all the way through the groundwater aquifer, passing the shoreface and into the marine environment at the Danish Ho Bay site (Figure 2.2(d)). The groundwater at the NAME study site is draining agricultural fields and has nitrate concentrations normally ranging from 50-75 mg/l.

 
Figure 2.2(d). Nitrate-bearing groundwater infiltrates from areas with intense agriculture and discharges through the shoreface and seabed at the Ho bay site (NAME project) (Gregsen, 2003).
Figure 2.2(d). Nitrate-bearing groundwater infiltrates from areas with intense agriculture and discharges through the shoreface and seabed at the Ho bay site (NAME project) (Gregsen, 2003).
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