Agriculture 



availability, temperature, and viscosity), but materials usually associated with the soil itself 

 are of key importance. Nutrients, metals, organic matter, pathogens and other organisms, 

 and pesticides may have imponani effects even at very low levels. Although the chemistry 

 of suspended soil material, deposited sediment, and their constituents arc poorly 

 understood, sufficient scientific evidence is available to justify the consideration of 

 sediment per se as a pollutant. Many state water quality standards have incorporated this 

 principle. 



Much of the nutrient loading to receiving waters results fix)m excessive application of 

 fertilizers and improper incorporation of manure into cropland soil. Of the principal 

 nutrient constituents (nitrogen, phosphorus, and potassium), nitrogen and phosphorus are 

 the major contributors to accelerated eutrophication of water bodies. In Rhode Island, most 

 cash crops grown receive heavy apphcations of chemical fertilizers. According to DEM 

 statistics, roughly 70 percent of the fertilizer used in the state is applied to agricultiuul land, 

 and animal wastes are applied in addition where available. 



Early work by Rediield (1934) and subsequent research on a broad variety of estuarine 

 systems has established that nitrogen is generally the nutrient limiting primary production in 

 coastal waters. In Rhode Island's salt ponds, for example, annual dissolved inorganic 

 nitrogen to phosphorus ratios average 7:1 to 10:1 in the larger, more saline ponds (Nixon 

 and Lee, 1981; in Lee and Olson, 1985). Nowicki and Nixon (1985) suggest Uiat 

 phosphorus may also be limiting in the fresher portions of the ponds. Where background 

 nutrient levels are low, such as in these systems, a minor degree of enrichment can rapidly 

 induce eutrophication. 



Nutrient loadings are also attributable to runoff from animal holding areas, feedlots, and 

 other areas of livestock concentration. These areas contribute nutrients, organic maner, 

 ammonia, fecal bacteria, and other microorganisms. The National Pollutant Discharge 

 Elimination System (NPDES) applies only to large commercial feedlots, and regulates only 

 the feedlot and not the disposal or land application of animal waste. Small operations, and 

 waste handling and application practice, are of concern for non-point source management. 



The magnitude of pesticide loading to receiving waters depends upon crop adsorption 

 rates, soil type, precipitation, slope, chemical characteristics of the pesticide in question 

 (solubility, molecular charge, complexing factors, etc.) and proximity of the application 

 area to a waterway. In the long term, pesticide delivery averages only about 5 percent of 

 total pesticide applied, but loadings may increase substantially where application is 

 followed by storm events (potentially resulting in fish kills) (U.S.EPA, 1984). 



A number of factors have altered patterns of pesticide use in recent years. Use of certain 

 persistent chemicals has been banned, and application requirements have been mandated by 

 regulatory actions. Newer pesticides are less persistent in the environment and pose 

 reduced long-term risk potential, but are frequently more water soluble than older 

 preparations. Pesticides in runoff water are of considerable concern, as toxic water-soluble 

 chemicals may be more biologically available when fireely waterbome than when bound to 

 sediment. The newer pesticides thus pose greater potential to induce acute short-term 

 impacts in surface waters and to affect groundwaters through percolation. 



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