Changes to the global nitrogen cycle affect human health well beyond the associated benefits of increased food production. Many intensively fertilized crops become animal feed, helping to create disparities in world food distribution and leading to unbalanced diets, even in wealthy nations. Excessive air‐ and water‐borne nitrogen are linked to respiratory ailments, cardiac disease, and several cancers. Ecological feedbacks to excess nitrogen can inhibit crop growth, increase allergenic pollen production, and potentially affect the dynamics of several vector‐borne diseases, including West Nile virus, malaria, and cholera. These and other examples suggest that our increasing production and use of fixed nitrogen poses a growing public health risk.

Human development along the land-seawater interface is considered to have significant environmental consequences. Development can also pose an increased human health risk. In a rapidly developing coastal region we investigated this phenomenon throughout a series of five estuarine watersheds, each of which differed in both the amount and type of anthropogenic development. Over a four-year period we analyzed the abundance and distribution of the enteric pathogen indicator microbes, fecal coliform bacteria and Escherichia coli. We also examined how these indicator microbes were related to physical and chemical water quality parameters and to demographic and land use factors throughout this system of coastal creeks. Within all creeks, there was a spatial pattern of decreasing enteric bacteria away from upstream areas, and both fecal coliform and E. coli abundance were inversely correlated with salinity. Turbidity was positively correlated with enteric bacterial abundance. Enteric bacterial abundance was strongly correlated with nitrate and weakly correlated with orthophosphate concentrations. Neither fecal coliforms nor E. coli displayed consistent temporal abundance patterns. Regardless of salinity, average estuarine fecal coliform abundance differed greatly among the five systems. An analysis of demographic and land use factors demonstrated that fecal coliform abundance was significantly correlated with watershed population, and even more strongly correlated with the percentage of developed land within the watershed. However, the most important anthropogenic factor associated with fecal coliform abundance was percentage watershed-impervious surface coverage, which consists of roofs, roads, driveways, sidewalks, and parking lots. These surfaces serve to concentrate and convey storm-water-borne pollutants to downstream receiving waters. Linear regression analysis indicated that percentage watershed-impervious surface area alone could explain 95% of the variability in average estuarine fecal coliform abundance. Thus, in urbanizing coastal areas waterborne health risks can likely be reduced by environmentally sound land use planning and development that minimizes the use of impervious surface area, while maximizing the passive water treatment function of natural and constructed wetlands, grassy swales, and other ''green'' areas. The watershed approach used in our study demonstrates that the land-water interface is not restricted to obvious shoreline areas, but is influenced by and connected with landscape factors throughout the watershed.

Water quality data at 12 sites within an urban, a suburban, and a rural stream were collected contemporaneously during four wet and eight dry periods. The urban stream yielded the highest biochemical oxygen demand (BOD), orthophosphate, total suspended sediment (TSS), and surfactant concentrations, while the most rural stream yielded the highest total organic carbon concentrations. Percent watershed development and percent impervious surface coverage were strongly correlated with BOD (biochemical oxygen demand), orthophosphate, and surfactant concentrations but negatively with total organic carbon. Excessive fecal coliform abundance most frequently occurred in the most urbanized catchments. Fecal coliform bacteria, TSS, turbidity, orthophosphate, total phosphorus, and BOD were significantly higher during rain events compared to nonrain periods. Total rainfall preceding sampling was positively correlated with turbidity, TSS, BOD, total phosphorus, and fecal coliform bacteria concentrations. Turbidity and TSS were positively correlated with phosphorus, fecal coliform bacteria, BOD, and chlorophyll a, which argues for better sedimentation controls under all landscape types.

ABSTRACT. Enhanced phytoplankton production and algal blooms, symptoms of eutrophication, are frequently caused by elevated nutrient loading, usually a s nitrogen, to coastal waters. This nitrogen is derived primarily from anthropogenic sources (urban, industrial, and agricultural) but is delivered to coastal waters through meteorological and hydrological means. We utilized a 4 yr monthly data set to investigate the effect of these upstream physical forces upon primary productivity of the Neuse River Estuary (North Carolina. USA), a large temperate coastal plain estuary Our results indicate that the magnitude of estuarine primary production and the periodicity of algal blooms can be directly related to variations in upper watershed rainfall and its subsequent regulation of downstream nver flow Future changes in preclpitatlon patterns for coastal regions may thus lead to substantlal alterations in coastal primary productiv~ty rates and patterns.

Nutrient limitation of phytoplankton production was assessed monthly from 1987 through 1990 in the lower Neuse River Estuary, North Carolina, USA, a well-mixed, mesotrophic system. Nutrient addition bioassays indicated that the lower estuary experienced a general state of nitrogen limitation, with especially pronounced limitation during summer months, a period of high phytoplankton productivity. Bioassays conducted during spring months showed significantly greater stimulation of algal productivity with the addition of nitrogen and phosphorus than that found with nitrogen addition alone. This CO-stimulation occurred during periods when surface-water dissolved inorganic nitrogen : dissolved inorganic phosphorus ratios were elevated above typical values of < 5. Seasonal patterns in ambient nutrient concentrations revealed nitrogen maxima associated with spring, fall, and winter runoff events, with summer minima Hydrologically driven nitrogen loading exerted a strong, yearround influence on primary production and nutrient limitation characteristics. High-flow events acted to oversaturate the upper estuarine nutrient filtering capacity, resulting in increased delivery of nitrogen to the lower estuarine environment. The phytoplankton community responded to increased flow and concomitant nutrient loadings by increasing production and b~omass levels, often very rapidly. In this regard, hydrologic factors influencing nitrogen loading (terrigenous runoff, point source inputs, and wet and dry atmospheric deposition) are key determinants of the trophic state of this estuary.