Further modification of the nutrient dynamics was required to accommodate the aggregation of surface and shallow subsurface flows in the hydrologic sector. In the PLM a proportion of nitrogen and phosphorus stored in the upper soil layer is made available for fast horizontal fluxing along with nutrients on the land surface. We have assumed this layer to be 10 cm thick. Dissolved inorganic nutrients are removed from the system through the growth of biomass and released through mineralization of soil or suspended organics. Nutrient uptake and release are modeled as proportional to total biomass growth and decay at rates estimated from elemental carbon ratios measured in similar ecosystems.
Nutrients is the other model component that is significantly altered by spatial dynamics.
Phosphorus did not seem to be readily available for horizontal transport in terrestrial ecosystems, whereas nitrogen in its dissolved forms is closely related to hydrologic fluxes. Therefore we isolated a submodel that in addition to hydrology represented the nitrogen dynamics, referred to here as the Water Quality submodel. Calibration tests were carried out, similar to the ones performed for the hydrologic model alone. Unfortunately the data available for dissolved nitrogen is mostly limited to observations of NO3 content in the estuarine part of the Patuxent river. The northern-most point in that data set is provided by the USGS National Stream WQN at Bowie.