Watersheds runoff

Whereas higher nitrate concentrations in surface (compared to bottom) waters reflect NO3 sources in watershed runoff, higher concentrations of NH4 in bottom waters derive from recychng processes occurring in the aphotic sediments (Fig. 18.6 Kemp and Boynton, 1992). Seasonal variations in bottom water NH4... 

Page, H. M., Petty, R. L., and Meade, D. E. (1995). Influences of watershed runoff on nutrient dynamics in a southern Cahfornia salt marsh. Estuar. Coast. Shelf Sci. 41, 163—180. 

In 1968, reports from Sweden, subsequently confirmed in other industrial countries, noted that shallow lakes with low concentrations of divalent cations were becoming more acidic with consequent decreases in aquatic plants and animals. In severely affected lakes and ponds, only acidophilic algae survived. Increased acidity and the runoff of solubilized aluminum and other metal ions from surrounding watersheds are now known to be primarily responsible for formation of these almost sterile bodies of water. 

Because it depends on a number of conditions that are themselves inherently variable, runoff tends to vary even more than precipitation, particularly over time. Seasonal runoff patterns depend largely on latitude and altitude of the watershed, due to the importance of snowmelt in runoff peaks. In high-latitude basins or those with significant high-altitude contribut-... 

Dunne, T. and Black, R. D. (1970) Partial area contributions to storm runoff in a small New England watershed. Water Resour. Res. 6,1296-1311. 

Willis GH, McDowell LL, SouthwickLM, et al. 1987. Methoxychlor and endosulfan concentrations in unit-source runoff and in channel flow of a complex watershed. Transactions of the American Society of Agricultural Engineers 30 394-399. 

This gives an example of fate modeling in which the risks of an insect growth inhibitor, CGA-72662, in aquatic environments were assessed using a combination of the SWRRB and EXAMS mathematical models.. Runoff of CGA-72662 from agricultural watersheds was estimated using the SWRRB model. The runoff data were then used to estimate the loading of CGA-72662 into the EXAMS model for aquatic environments. EXAMS was used to estimate the maximum concentrations of CGA-72662 that would occur in various compartments of the defined ponds and lakes. The maximum expected environmental concentrations of CGA-72662 in water were then compared with acute and chronic toxicity data for CGA-72662 in fish and aquatic invertebrates in order to establish a safety factor for CGA-72662 in aquatic environments. 

SWRRB - The Simulator for Water Resources on Rural Basins (SWRRB) was developed at EPA by R. Carsel and is a modification of the USDA model CREAMS (. It was orginally developed to predict daily runoff volume for small watersheds throughout the U.S. The basic runoff model is based on the water balance equation ... 

The SWRRB runoff model was used to determine the amount of CGA-72662 that would runoff of a hypothetical 3.2 acre watershed with a predominant muck soil type. The following were the SWRRB input data. 

Glenn, S. and J.S. Angle. 1987. Atrazine and simazine in runoff from conventional and no-till com watersheds. Agric. Ecosys. Environ. 18 273-280. 

McDowell, L.L., G.H. Willis, C.E. Murphree, L.M. Southwick, and S. Smith. 1981. Toxaphene and sediment yields in runoff from a Mississippi Delta watershed. Jour. Environ. Qual. 10 168-173. 

The other output from watershed and slope landscapes positions is related to the surface and subsurface runoff of trace metals. The ecosystems of waterlogged glacial valleys, geochemically subordinate to the above mentioned landscape, can receive with surface runoff an additional amount of various chemical species. This results in 3 1-fold increase of plant productivity in comparison with elevated landscapes and in corresponding increase of all biogeochemical fluxes of elements, which are shown in Table 6. For instance, the accumulation of trace metals in dead peat organic matter of waterlogged valley was assessed as the follows Fe, n x 101 kg/ha, Mn, 1-2 kg/ha, Zn, 0.1-0.3 kg/ha, Cu, Pb, Ni, n x 10-2 kg/ha. 

In watersheds where surface runoff is limited by infiltration rate rather than soil-water storage capacity, areas of the watershed can alternate between sources and sinks of surface flow. This again will be a function of soil properties, rainfall intensity and duration, and antecedent moisture condition. As surface runoff is the main mechanism by which phosphorus is exported from most watersheds, it is clear that, if surface runoff does not occur, phosphorus export can be small. Thus, consideration of hydro-logic pathways and variable source areas is critical to a more detailed understanding of phosphorus export from agricultural watersheds. 

Very little recent information on concentrations of endrin in water could be found in the available literature. Unlike DDT, chlordane, aldrin/dieldrin, and a variety of other chlorinated pesticides, endrin was never used extensively in urban areas. This is reflected in the results from EPA s Nationwide Urban Runoff Program, which showed no detections in 86 high-flow water samples from 51 urbanized watersheds from 19 cities (Cole et al. 1984). Analysis of EPA STORET monitoring information from ambient surface water showed a significant percentage of detections for endrin (32% of 8,789 samples), but most were near the detection limits, with a national median concentration of 0.001 ppb (Staples et al. 1985). A similar analysis of STORET data for endrin aldehyde showed that this compound was not found in 770 samples of ambient surface water. More recently, endrin was not detected (detection limit 49 ng/L [0.045 ppb]) in surface water from the Yakima River Basin, Washington (Foster et al. 1993). However, in... 

Recently, levels of disulfoton in an agricultural watershed were monitored during a spring runoff event in Shell Creek, an eastern tributary of the Platte River in Nebraska. The concentrations of disulfoton in this agricultural watershed ranged from trace to 0.4 pg/L (Spalding and Snow 1989). 

Riparian wetlands are those lands that are periodically inundated with water from adjacent rivers, streams, lakes or other freshwater bodies, and by runoff from upland areas. Large fluxes of energy and nutrients pass through riparian wetlands and they are important sinks and transformers of nutrients. In watersheds with extensive riparian wetlands, the composition of the river water may... 

Caro, J.H., Freeman, H.P., and Turner, B.C. Persistence in soil and losses in runoff in soil-incorporated carbaryl in a small watershed, J. Agrlc. Food Chem., 22(5) 860-863, 1974. 

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