Quantcast Best Management Practices (Cont.)

 
  
 
sedimentation control practices for disturbed areas in North Carolina. Approximate effectiveness for
construction site erosion and sediment control BMPs are given by Brach (1989).
Compared to other BMPs, little is known on the effect of construction practices on nutrient
runoff. Where excavation is extensive, nutrient exports from construction sites may be less of a problem
than the nutrient export from other areas due to the limited nutrient content of many subsoils.
Vegetative cover is very effective in keeping soil in place. Sediment fences, inlet protection devices,
traps, and basins can retain up to 95% of large sediment particles.
Urban. Nutrient loading from urban areas is a growing concern. Best management practices to
reduce nutrients in urban runoff include source, vegetative, and structural controls such as infiltration and
detention devices. To maximize impacts, a combination of BMPs may be needed to achieve
management goals.
Source Controls. Reducing the amount of nutrients applied to lawns, limiting the accumulation
of leaf litter, proper nutrient storage, and diverting or excluding discharges from storm drains can
control source nutrients. Other BMPs include land use restrictions (e.g. limiting impervious area,
restricting development in riparian areas, and using grassed swales for drainage instead of curbs and
gutters and piped drains. Source control effectiveness increases as the extent of treatment approaches
the need.
Proper timing and rate of fertilizer application to lawns maximizes plant uptake and minimizes
losses. Morton et al. (1988) found mean annual flow-weighted inorganic nitrogen concentrations in
percolate were 0.36 mg/l for an unfertilized, over-watered control and 4.0 mg/l for the high nitrogen
(244 kg N/ha-yr) application treatment. Annual losses were 2 kg/ha for the control and 32 kg/ha for the
over-fertilized lawn. A study in Minnesota on the effect of keeping leaf litter and grass clippings free
from street side curbs has shown phosphorus levels were reduced by 30 to 40% (Shapiro and
Pfannkuch 1973). However, Athayde et al. (1983) found that street sweeping alone was not effective
in reducing total phosphorus or total nitrogen concentrations in urban runoff.
Public education to increase the understanding the of problem and voluntary participation are
generally required to implement urban source controls. Technical assistance may be needed for
stabilizing sites with vegetation or for recommending fertilizer application rates. There are few studies
that have monitored the effect of urban source area controls.
Vegetative Controls. Grassed swales, buffer strips and wetlands increase the time of contact
of runoff and encourage infiltration, deposition, and biological uptake of nutrients. In general, vegetative
controls can achieve moderate removal rates of sediment but they may not be very effective for treating
nutrients (EPA 1989).
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