Stonnwaier and Sediment 



temporary sink for these materials, which may be rcmobilized during storm events or 

 dredging operations, posing further environmental hazards (Galvin and Moore, 1982). 



Nutrients 



Excess nutrient levels in runoff can lead to eutrophication of receiving waters (see also 

 Chapter 2.2 on Agricultural Non-point Sources). Nitrogen is the limiting nutrient in most 

 coastal waters, while phosphorus is controlling in freshwater systems, and in some fresher 

 portions of estuaries (Nowicki and Nixon, 1981). NURP research has indicated that 

 typical nutrient concentrations in urban runoff are sufficient in themselves to stimulate 

 eutrophication, absent the input from point sources. In runoff, nutrients may be present in 

 soluble forms which are readily taken up by algae and other primary producers. 

 Eutrophication processes are affected by numerous factors, including retention times and 

 flushing rates, seasonal and climatic factors, inputs of other sources, etc. Generally, 

 nutrient export is largest from development sites having greatest impervious area, or from 

 golf courses, cemeteries, and other intensively landscaped areas. 



Light penetration and availability is also an important factor in algae response. 

 Maintenance of conditions suited to sustained growth of native macrophyte communities 

 may be very important in preventing noxious algal blooms. Similarly, protection of 

 indigenous riparian plant and tree buffers may prevent excessive algae growth in tributary 

 streams (Moreland, 1985). 



Pathogens 



Almost without exception, runoff from urban and suburban areas contains bacteria at 

 levels exceeding public health standards for water contact recreation (Koppelman et al., 

 1982). Pathogens (including Enterobacter aerognenes and Streptococcus faecalis), in 

 addition to fecal baaeria and viruses, have been documented to occur in runoff (EPA, 

 1983). Bacterial levels may exhibit a twenty-fold increase between winter and summer, 

 due to increased reproduction rates, multiplying potential hazards for recreational use and 

 consumption of seafood. Combined sewer overflows from intensively developed urban 

 areas and overland flow of domestic waste from failed septic systems produce the most 

 significant levels of coliform bacteria, as these sources export bacteria derived directly from 

 human wastes. 



Oxygen Demand 



In lakes, estuaries, and slow-moving sections of receiving waters, decomposition of 

 organic matter by microorganisms depletes dissolved oxygen levels. Depletion of oxygen 

 due to urban mnoff is difficult to measure. First, the BOD test (which expresses the 

 amount of easily oxidized organic matter present in water) relies on bacterial growth, which 

 is inhibited by trace metals. Secondly, the COD test (or chemical oxygen demand test) 

 measures all oxidizable material, including that which does not contribute to oxygen 

 demand, and is therefore poorly correlated with oxygen depletion. 



Nevertheless, urban mnoff has been shown to severely depress DO levels in adjacent 

 waters after large storms, yielding BOD levels exceeding 10 to 20 mg./l. Pulses of such 

 mnoff input have led to periods of anoxia (zero oxygen conditions) in shallow, slow- 

 moving, or poorly-flushed receiving waters (EPA, 1983). Again, the most significant 



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