Suburban Watersheds Research Articles

Nitrogen Loading from Coastal Watersheds to Receiving Estuaries: New Method and Application

In this paper we develop a model to estimate nitrogen loading to watersheds and receiving waters, and then apply the model to gain insight about sources, losses, and transport of nitrogen in groundwater moving through a coastal watershed. The model is developed from data of the Waquoit Bay Land Margin Ecosystems Research project (WBLMER), and from syntheses of published information. The WBLMER nitrogen loading model first estimates inputs by atmospheric deposition, fertilizer use, and wastewater to surfaces of the major types of land use (natural vegetation, turf, agricultural land, residential areas, and impervious surfaces) within the landscape. Then, the model estimates losses of nitrogen in the various compartments of the watershed ecosystem. For atmospheric and fertilizer nitrogen, the model allows losses in vegetation and soils, in the vadose zone, and in the aquifer. For wastewater nitrogen, the model allows losses in septic systems and effluent plumes, and it adds further losses that occur during diffuse transport within aquifers. The calculation of losses is done separately for each major type of land cover, because the processes and loss rates involved differ for different tesserae of the land cover mosaic. If groundwater flows into a freshwater body, the model adds a loss of nitrogen for traversing the freshwater body and then subjects the surviving nitrogen to losses in the aquifer. The WBLMER model is developed for Waquoit Bay, but with inputs for local conditions it is applicable to other rural to suburban watersheds underlain by unconsolidated sandy sediments. Model calculations suggest that the atmosphere contributes 56%, fertilizer 14%, and wastewater 27% of the nitrogen delivered to the surface of the watershed of Waquoit Bay. Losses within the watershed amount to 89% of atmospheric nitrogen, 79% of fertilizer nitrogen, and 65% of wastewater nitrogen. The net result of inputs to the watershed surface and losses within the watershed is that wastewater becomes the largest source (48%) of nitrogen loads to receiving estuaries, followed by atmospheric deposition (30%) and fertilizer use (15%). The nitrogen load to estuaries of Waquoit Bay is transported primarily through land parcels covered by residential areas (39%, mainly via wastewater), natural vegetation (21%, by atmospheric deposition), and turf (16%, by atmospheric deposition and fertilizers). Other land covers were involved in lesser throughputs of nitrogen. The model results have implications for management of coastal landscapes and water quality. Most attention should be given to wastewater disposal within the watershed, particularly within 200 m of the shore. Rules regarding setbacks of septic system location relative to shore and nitrogen retention ability of septic systems, will be useful in control of wastewater nitrogen loading. Installation of multiple conventional leaching fields or septic systems in high-flow parcels could be one way to increase nitrogen retention. Control of fertilizer use can help to a modest degree, particularly for optional uses such as lawns situated near shore. Conservation of parcels of accreting natural vegetation should be given high priority, because these environments effectively intercept atmospheric deposition. Areas upgradient from freshwater bodies should be given low priority in plans to control nitrogen loading, because ponds intercept much of the nitrogen transported from upgradient.

NITROGEN LOADING FROM COASTAL WATERSHEDS TO RECEIVING ESTUARIES: NEW METHOD AND APPLICATION

In this paper we develop a model to estimate nitrogen loading to watersheds and receiving waters, and then apply the model to gain insight about sources, losses, and transport of nitrogen in groundwater moving through a coastal watershed. The model is developed from data of the Waquoit Bay Land Margin Ecosystems Research project (WBLMER), and from syntheses of published information. The WBLMER nitrogen loading model first estimates inputs by atmospheric deposition, fertilizer use, and wastewater to surfaces of the major types of land use (natural vegetation, turf, agricultural land, residential areas, and impervious surfaces) within the landscape. Then, the model estimates losses of nitrogen in the various compartments of the watershed ecosystem. For atmospheric and fertilizer nitrogen, the model allows losses in vegetation and soils, in the vadose zone, and in the aquifer. For wastewater nitrogen, the model allows losses in septic systems and effluent plumes, and it adds further losses that occur during diffuse transport within aquifers. The calculation of losses is done separately for each major type of land cover, because the processes and loss rates involved differ for different tesserae of the land cover mosaic. If groundwater flows into a freshwater body, the model adds a loss of nitrogen for traversing the freshwater body and then subjects the surviving nitrogen to losses in the aquifer. The WBLMER model is developed for Waquoit Bay, but with inputs for local conditions it is applicable to other rural to suburban watersheds underlain by unconsolidated sandy sediments. Model calculations suggest that the atmosphere contributes 56%, fertilizer 14%, and wastewater 27% of the nitrogen delivered to the surface of the watershed of Waquoit Bay. Losses within the watershed amount to 89% of atmospheric nitrogen, 79% of fertilizer nitrogen, and 65% of wastewater nitrogen. The net result of inputs to the watershed surface and losses within the watershed is that wastewater becomes the largest source (48%) of nitrogen loads to receiving estuaries, followed by atmospheric deposition (30%) and fer- tilizer use (15%). The nitrogen load to estuaries of Waquoit Bay is transported primarily through land parcels covered by residential areas (39%, mainly via wastewater), natural vegetation (21%, by atmospheric deposition), and turf (16%, by atmospheric deposition and fertilizers). Other land covers were involved in lesser throughputs of nitrogen. The model results have implications for management of coastal landscapes and water quality. Most attention should be given to wastewater disposal within the watershed, par- ticularly within 200 m of the shore. Rules regarding setbacks of septic system location relative to shore and nitrogen retention ability of septic systems, will be useful in control of wastewater nitrogen loading. Installation of multiple conventional leaching fields or septic systems in high-flow parcels could be one way to increase nitrogen retention. Control of fertilizer use can help to a modest degree, particularly for optional uses such as lawns situated near shore. Conservation of parcels of accreting natural vegetation should be given high priority, because these environments effectively intercept atmospheric deposition. Areas upgradient from freshwater bodies should be given low priority in plans to control nitrogen loading, because ponds intercept much of the nitrogen transported from upgradient.

The potential of off-stream livestock watering to reduce water quality impacts

Small commercial and non-commercial animal enterprises (SCAEs) are often located in suburban watersheds. Such operations raise a small number of animals on a few acres and have potential water quality impacts from their manure management. A typical pollution abatement practice includes fencing livestock from streams and providing an off-stream watering area. However, if there is a large stream to land area ratio, this practice becomes very costly for implementation and maintenance. An alternative is to provide off-stream watering areas without fencing to lure animals from the stream. This project demonstrated that off-stream watering areas are an effective alternative to stream fencing. They reduce the time animals spend at the stream under small acreage grazing conditions. In addition, an animal-operated pasture pump was demonstrated to be a viable off-stream watering device. The animal-operated tested pump pulled water from the creek and held the water in a small basin accessible to the animals. It is a usable alternative where conventional watering systems are inconvenient or expensive.

Responses of forested wetland vegetation to perturbations of water chemistry and hydrology

Nineteen mature Atlantic white-cedar swamps, located in four categories of undeveloped and suburban watersheds of the New Jersey Pinelands, were studied to determine the relationship between perturbations of water quality and hydrology and changes in species composition and community structure. Rank-orders of the 19 sites were compared for key variables (ground-water and surface-water NH4 and PO4, mean water-table level and water-table range). Rank orders for the sites were different for the various parameters, suggesting little congruence among water quality and hydrologic changes at wetlands within urban basins. Changes in species composition, measured as the number of invading species, were correlated with the number of perturbed chemical and hydrologic parameters and were not related to the absolute magnitude of any one parameter. Sites in developed watersheds supported a larger fraction of facultative upland and upland species than did sites in undisturbed watersheds; this change could affect wetland delineation of urban wetlands. Urbanization thus increases variability in environmental quality among sites of a given type of wetland and fosters an increase in proportion of non-hydrophytic vegetation within such wetlands.

EFFECTS OF URBAN LAKES ON QUANTITY AND QUALITY OF BASEFLOW1

ABSTRACT: Man‐made lakes have significant impacts on the hydrologic conditions in the watershed in which they are built. This paper examines the nature of the impact upon baseflow by comparing baseflow conditions at the outlet of the lakes with those elsewhere in the watershed. Situated in the upper reaches of a small watershed, the lakes studied have only a minor effect upon the magnitude of baseflow discharge, increasing it slightly from October to January, and decreasing it from May to September. Baseflow quality is substantially affected. Natural dissolved ions, as represented by magnesium, are generally decreased in concentration and total load by the lakes. Road salt related inons are substantially increased in both concentration and total load in the baseflow. Surface runoff stored in the lakes is extremely enriched in salt in the winter, and the storage capacity of the lakes is sufficient to maintain winter salt concentrations in the baseflow near the lakes until summer. The storage effect also tends to damp out seasonal fluctuations in baseflow chloride content which are extreme in suburban watersheds. The difference in quality between the lake and non‐lake baseflows and the linear distance needed for complete mixing are used as measures of the magnitude and distal extent of the lake effect on baseflow quality.

NONPARAMETRIC STATISTICAL ANALYSIS OF ANNUAL PEAK FLOW DATA FROM A RECENTLY URBANIZED WATERSHED1

ABSTRACT. In order to demonstrate the feasibility of a nonparametric statistical application in investigating the hydrologic impact of the rapid land use change accompanying intense urbanization, annual maximum peak flow data from an actual example (the Northeast Branch Basin, a recently urbanized Washington, D.C., suburban watershed) were analyzed. Annual peak flow data from the Patuxent Basin above Unity, Maryland, a rural watershed in close proximity to the study area, were compared to data from the Northeast Branch for the Same period utilizing the Wilcoxon matched‐pairs signed‐ranks test. A change in central tendency of each series was noted at the 0.01 significance level; however, the change was negative in the rural basin and positive in the urbanized Northeast Branch Basin. This central tendency change was considered indicative of an average decrease in the size of rainstorms producing annual maximum peak discharges. Rainstorm data from the Northeast Branch Basin were divided into two equal periods (before urbanization and after) and the Wilcoxon test was applied. It was found that rainstorms producing maximum annual peak discharges in the urbanized period were indeed smaller than those in the prior period (0.01 level of significance); however, larger annual peaks were produced. It was concluded that nonparametric statistical methods can be used readily with conventional methods to isolate and clearly analyze the various problems in an actual urban hydrologic study.

PCB's [polychlorinated biphenyls] in suburban watershed, Reston, Va

PCB's [polychlorinated biphenyls] in suburban watershed, Reston, Va