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of the high nutrient concentrations in groundwater compared to those in
receiving coastal water. Although highly variable, the nutrient content of
groundwater discharging onto coastal water may be up to five orders of
magnitude larger than concentrations in receiving seawater.
2. Consequences of Groundwater Nutrient Transport
There is enormous freshwater literature that deals with the consequences
of eutrophication. The response of primary producers to nutrient loading
within an estuary must be dependent on the balance between increased
growth due to elevated inputs of the limiting nutrient and losses related to
the flushing rate. This is the point of the well-documented relation between
phosphorous loading and phytoplankton chlorophyll. Additional evidence,
based on correlations and inference from N:P values, on enrichments within
small containers, and on whole-system enrichments in freshwaters, is con-
sistent with the phosphorus loading results, and shows that in freshwater
phosphorus limits potential primary production.
In coastal systems, the evidence of the role of nitrogen in limiting phyto-
plankton growth is based on inferences from loading calculations, on ambi-
ent nutrient concentrations, and more importantly, on nutrient enrichment
experiments.
Groundwater entering the coastal areas flows from watersheds where
urbanization has taken place. Human activities such as disposal of waste-
water via septic tanks, and use of fertilizers increase nutrient concentra-
tions in groundwater. We presently lack of data groundwater along coastal
areas, but can make preliminary comparisons using data from nearby loca-
tions, where watersheds include some urbanized areas. This paper focuses
on application of numerical model to predict subsurface water and pollution
discharge to coast.
3. Subsurface Hydrology of a Coastal Watershed
The two main sources of pollutants are point sources (Table 1) and non-
point sources (Table 2). Pollutants from the two sources may be released
continuously or at discrete intervals (Fig. 1). Point sources of pollution can
be geometrically defined and the dimensions are amenable to mathemati-
cal analysis in assessing pollution loads and rates of discharge determined.
Distributed sources of pollutants are much more widespread and can rarely
be geometrically defined as precisely as a point source. Hence, it is more
