Stormwater and Sediment 



• alterations in pond hydrology; and 



• changes in flushing patterns and salinity regimes. 



Export of Contaminants via Sedimentation 



Unless sufficient erosion controls are installed and maintained at construction sites, very 

 significant loadings of sediment are delivered to receiving waters, carrying attached soil 

 nutrients, organic matter, and complex contaminants. WMle sediment loads from 

 agricultural land use on steep slopes in Rhode Island may range up to 25 tons/acre/year 

 (USDA SCS (1986)), uncontrolled construction site sedunent loads on the order of 35 to 

 50 tons per acre have been reported (Novomy and Chesters, 1981). 



Effects on ecosystems are complex, involving physical and chemical components. In 

 streams, the physical shift from natural flow and channel conditions reduces habitat value, 

 affecting diversity and abundance of aquatic life. Several studies have demonstrated 

 reduced diversity, and have shown a shift to more tolerant species (Ragan and Dietmann 

 (1976) in Schaefer, 1987). In estuaries, changes in flow regimes can have broad impacts 

 on flushing and salinity regimes, significantiy altering habitat character. 



Degradation of Ecosystems 



Urban Runoff 



Following site stabilization, pollutants accumulate rapidly on impervious surfaces and 

 are readily washed off with precipitation. Urban runoff contains a myriad of complex 

 contaminants, including trace metals, hydrocarbons, crankcase oil, pet droppings, 

 suspended solids, vegetative matter, litter, debris, pesticides and fertilizers from home 

 lawns and golf courses, and other constituents. 



Each class of contaminant generally comes from numerous different origins. For 

 example, inputs of three classes of polycyclic aromatic hydrocarbons (PAHs) may be 

 primtuily attributed to atmospheric deposition, sewage effluent, and crankcase oil 

 (Hoffman, 1984). Similarly, trace metals originate from numerous sources (including 

 leaded fuel, building materials, paints, wood preservatives, catalytic converters, brake 

 linings, and tires). In ttim, source inputs depend upon local conditions. Leaching and 

 corrosion of metal surfaces, for example, is exacerbated by acidity of precipitation. 



The nature of the impacts associated with specific runoff contaminants is reviewed in the 

 subsequent sections, along with the development situations which create greatest resource 

 vulnerability. 



Sediment 



Concentrations of suspended sediments in receiving waters cause a range of adverse 

 impacts, including increased turbidity and viscosity, raluced light penetration, reduced 

 prey capture, clogging of gills/filters of fish and invertebrates, reduced spawning and 

 juvenile fish survival, and reduced recreational use (see also Chapter 2.2 on Agricultural 

 Non-point Sources). Deposited sediment may smother or impair the function of benthic 

 communities, alter the composition of substrates, and fill impoundments and embayments. 

 As an efficient carrier of toxicants, nutrients, and trace metals, sediment serves as a 



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