Undeveloped Watersheds Research Articles

Water quality impacts of stormwater discharges to Santa Monica Bay

Urban stormwater runoff is a major source of contaminants to southern California's coastal waters, yet little is known about the fate and effects of these discharges. A 3-year multidisciplinary project was conducted to investigate the dispersion of stormwater plumes in Santa Monica Bay and the resultant impacts on the water column and benthos. This paper describes the toxicity component of the study. Sea urchin fertilization toxicity tests were conducted on stormwater from the two largest discharges into the bay: Ballona Creek, which drains a highly urbanized watershed, and Malibu Creek, which receives runoff from a largely undeveloped watershed. Every sample of Ballona Creek stormwater tested was toxic (usually >5 toxic units), while Malibu Creek stormwater had a lower frequency and magnitude of toxicity (usually <4 toxic units). Surface water samples collected within the Ballona Creek stormwater discharge plume were always toxic whenever the concentration of stormwater in the plume exceeded 10%. The toxic portion of the Ballona Creek stormwater plume extended more than 4 km offshore on one occasion. Toxicity identification studies indicated that zinc was the primary cause of toxicity in both Ballona Creek stormwater and the discharge plume. No acute sediment toxicity (10-day amphipod survival) was present in the study area, although interstitial water toxicity was present at some stations located near the mouth of Ballona Creek. Differences in watershed characteristics likely were responsible for the greater toxicity of the Ballona Creek stormwater discharge plume. The Ballona Creek watershed contained a greater degree of urbanization (83% versus 12% for Malibu Creek) and the presence of a network of concrete flood control channels resulted in a stormwater plume containing elevated concentrations of toxins that received less initial dilution (compared to Malibu Creek) in the nearshore environment.

DUAL URBAN AND RURAL HYDROGRAPH SIGNALS IN THREE SMALL WATERSHEDS1

ABSTRACT: Many studies can be found in the literature pertaining to the effects of urbanization on surface runoff in small watersheds and the hydrologic response of undeveloped watersheds. However, an extensive literature review yielded few published studies that illustrate differing hydrologic responses from multiple source areas within a watershed. The concepts discussed here are not new, but the methods used provide a unique, basic procedure for investigating stormwater hydrology in topographically diverse basins. Six storm hydrographs from three small central Pennsylvania watersheds were analyzed for this paper; five are presented. Two important conclusions are deduced from this investigation. First, in all cases we found two distinct peaks in stream discharge, each representing different contributing areas to direct discharge with greatly differing curve numbers and lags representative of urban and rural source regions. Second, the direct discharge represents only a small fraction of the total drainage area with the urban peak becoming increasingly important with respect to the rural peak with the amount of urbanization and as the magnitude of the rain event decreases.

FOREST COVER, IMPERVIOUS‐SURFACE AREA, AND THE MITIGATION OF STORMWATER IMPACTS1

ABSTRACT: For 20 years, King County, Washington, has implemented progressively more demanding structural and nonstructural strategies in an attempt to protect aquatic resources and declining salmon populations from the cumulative effects of urbanization. This history holds lessons for planners, engineers, and resource managers throughout other urbanizing regions. Detention ponds, even with increasingly restrictive designs, have still proven inadequate to prevent channel erosion. Costly structural retrofits of urbanized watersheds can mitigate certain problems, such as flooding or erosion, but cannot restore the predevelopment flow regime or habitat conditions. Widespread conversion of forest to pasture or grass in rural areas, generally unregulated by most jurisdictions, degrades aquatic systems even when watershed imperviousness remains low. Preservation of aquatic resources in developing areas will require integrated mitigation, which must including impervious‐surface limits, forest‐retention policies, stormwater detention, riparian‐buffer maintenance, and protection of wetlands and unstable slopes. New management goals are needed for those watersheds whose existing development precludes significant ecosystem recovery; the same goals cannot be achieved in both developed and undeveloped watersheds.

Comparative zinc dynamics in Atlanta metropolitan region stream and street runoff

Zinc, major ion, and other trace metal (V, Cr, Co, Ni, Cu, Cd, and Pb) concentrations were measured within 172 street and stream runoff samples in the Atlanta metropolitan region and in relatively undeveloped watersheds within the Georgia Piedmont and Blue Ridge Provinces. Peachtree Creek, draining a densely populated area of Atlanta, was the primary sampling location and samples were acquired under a wide range of hydrological conditions. Zinc concentrations within street runoff [median (Zn)urban street runoff=905 µg/l] were significantly greater than zinc concentrations within storm runoff [median (Zn)Peachtree Creek=60 µg/l], which were, in turn, greater than zinc concentrations within non-storm runoff [median (Zn)Peachtree Creek=14 µg/l]. Zinc concentrations were not significantly greater within urban base flow than within non-urban base flow, indicating that the primary source of pollution is "event water" or street runoff. Zinc was the only heavy metal present in greater than "background" concentrations (i.e., >10 µg/l), which is likely the result of automotive pollution that is omnipresent within the study area. Analysis of storm alkalinity dilution trends indicate that simple mixing between polluted street runoff and groundwater cannot account for the zinc concentrations observed within storm and recession flows. A two end member mass balance model suggests that a large proportion of the zinc present in the street runoff is adsorbed and transported on surfaces of the suspended sediment. Adsorption is readily possible at the near neutral pH (~6.5) of turbid storm discharge.

Characterization of urban stormwater runoff

The purpose of this study is to investigate the characteristics of pollutants overflow on storm events, relationships between pollutant load and runoff, and the first flush effect in urban areas. Nine watersheds in the cities of Taejon and Chongju, Korea were selected for sampling and study with different characteristics during the period from June 1995 to November 1997. Runoff and quality parameters such as BOD 5, COD, SS, TKN, NO 3-N, PO 4-P, TP, Pb, Fe, and n-Hexane extracts were analyzed for the development of relationships between runoff and water quality. From the hydrograph and pollutograph analysis, the peak of pollutant concentration preceded that of the flowrate in an area smaller than 100 ha in which impervious area occupied more than 80%. The peak of pollutant concentration, however, was followed by that of flowrate in the watershed in an area larger than 100 ha in which the impervious area was less than 50%. This phenomenon appeared to occur more frequently in the watershed which has the combined sewer systems. In the storm event, the relative magnitude of the pollutants unit loading rate was in the following order; high density residential>low density residential>industrial>undeveloped watershed.

Regional Regression Models of Annual Streamflow for the United States

Estimates of annual streamflow volumes are needed in many different types of hydrologic studies. Usually a streamgauge is unavailable at the location of interest, hence regional methods that relate streamflow to readily measured geomorphic and climate characteristics provide a practical solution. Hydrologic, geomorphic, and climatic characteristics of 1,553 undeveloped watersheds across the United States are used to develop regional regression equations that relate the first two moments of annual streamflow to readily measured basin and climate characteristics. These relations are summarized for each of 18 major U.S. water resource regions. The relationships are remarkably precise, with adjusted R2 values ranging from 90.2–99.8% and an average value of 96.2% across the continent. The usefulness of these relationships is evaluated by deriving their information content in terms of equivalent record length. These results indicate that regional models of annual streamflow, including runoff maps, are less accurate than suggested by traditional goodness-of-fit statistics. We also provide estimates of precipitation and temperature elasticity of streamflow, by region.

Nitrogen Mineralization and Nitrification in Suburban and Undeveloped Atlantic White Cedar Wetlands

AbstractThe presence of urban and suburban lands adjacent to wetlands may cause changes in nutrient‐cycling processes, due to changes in the quality of the ground‐ and surface waters that drain from the developed uplands into the wetland. We studied N‐cycling processes in Atlantic white cedar [Chamaecyparis thyoides (L.)] swamps in the New Jersey Pinelands to determine their sensitivity to the development of adjoining uplands. We conducted a 19‐wk aerobic incubation to measure N mineralization and nitrification potentials in wetland soils from both developed and undeveloped watersheds. The cumulative inorganic N mineralized during the incubation was two to three times higher in soils from developed sites than from the undeveloped sites. There was virtually no nitrification in undeveloped wetlands, while in developed wetlands, most N mineralized was further nitrified. In developed sites, there was also more nitrification in hollow soils than in hummock soils. Both nitrification and the fraction of soil organic matter mineralized were highly correlated with pH and with soil ash content. These results suggest that increases in ash content of peats attributable to sediment transported and deposited in urban runoff, causes increases in pH, which in turn allows large populations of nitrifiers to develop. Excess mineral N generated within the wetlands through changes in microbial function thus may be as important as N inputs in drainage water in affecting plant community composition, and may cause wetlands to become sources of N to downstream ecosystems rather than serving as regional sinks.

Effect of Watershed Disturbance on Pinelands Stream Vegetation

ZAMPELLA, R. A. AND K. J. LAIDIG (Pinelands Commission, New Lisbon, NJ 08064). Effect of watershed disturbance on Pinelands stream vegetation. J. Torrey Bot. Soc. 124: 52-66. 1997.-We related stream channel and stream bank plant species composition to eighteen site specific and regional environmental variables in the New Jersey Pinelands (Pine Barrens). Canonical correspondence analysis (CCA) and detrended correspondence analysis (DCA) related major patterns in species composition to complex watershed disturbance gradients. There were significant correlations between the first axes of both the CCA and DCA stream site ordinations and agricultural and developed land cover in a drainage area, pH, specific conductance, and channel sediment. There was a clear contrast between stream stations found within relatively undeveloped watersheds and those in highly developed or farmed drainage areas. Surface waters of the undisturbed sites displayed lower pH and specific conductance values compared with waters in the more disturbed watersheds. The most heavily impacted sites supported a unique group of peripheral or exotic plant species that replaced characteristic Pine Barrens species. Overall species richness did not change in response to watershed disturbance. The presence of disturbance indicator species, or species found only at disturbed sites, provided a good measure of watershed disturbance. High between-site variability in the species present at relatively undisturbed stations and the persistence of some species at more recently disturbed sites complicated the identification of sensitive species, or species found only at undisturbed sites. A comparison of the number of species historically found within and outside the Pine Barrens, rather than the presence or absence of particular sensitive species, provided an additional measure of ecological integrity.

Correlations between stream sulphate and regional SO2 emissions

The relationship between atmospheric SO2 emissions and stream and lake acidification has been difficult to quantify, largely because of the limitations of sulphur deposition measurements. Precipitation sulphate (SO4) records are mostly <5 yr in length1 and do not account for dry sulphur deposition2. Moreover, a variable fraction of wet- and dry-deposited sulphur is retained in soils and vegetation and does not contribute to the acidity of aquatic systems3,4. We have compared annual SO2 emissions for the eastern United States from 1967 to 1980 with stream SO4 measurements from fifteen predominantly undeveloped watersheds (Figs 1,2). We find that the two forms of sulphur are strongly correlated on a regional basis and that streams in the southeastern United States (SE) receive a smaller fraction (on average, 16%, compared with 24% of regional sulphur emissions than do streams in the northeastern United States (NE). In addition to providing direct empirical evidence of a relationship between sulphur emissions and aquatic chemistry, these results suggest that there are significant regional differences in the fraction of deposited sulphur retained in basin soils and vegetation.