Soil Conservation An Assessment of the National Resources Inventory, Volume 2 (1986) / Chapter Skim
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8. Applications of the NRI Data to Inventory, Monitor, and Appraise Offsite Erosion Damage
8. Applications of the NRI Data to Inventory, Monitor, and Appraise Offsite Erosion Damage
Pages 237-252
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From page 237... ...
Negative offsite impacts have broadened public concern about soil erosion to include more than soil productivity issues. Soil leaving a field due to water erosion represents costs not only to the farmer and consumer in terms of lost profits and high food prices, but also to those downstream, for associated cleanup costs.
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From page 238... ...
The offsite effects of agricultural nonpoint source pollution are diverse and complex. Each type of pollutant has unique characteristics, both with respect to the mode of transport through the water course, and the fate of the pollutant as it moves from field to stream to lake to river or reservoir.
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From page 239... ...
Its area of primary application is the onsite, or farm, level. The NRI data base can be used to address some of the water quality issues influenced by activities based on agricultural land, primarily sediment loadings.
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From page 240... ...
By comparing 1977 and 1982 NRI data for a particular area, it may be feasible to determine some trends in sediment loading rates, particularly in areas where there have been significant changes in land use or cropping or tillage practices. However, although the NRI can be used to estimate partial sediment loads, it provides no information on particle size distribution, which is very important for assessing such offsite impacts as fish reproduction.
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From page 241... ...
There are several ways to predict or simulate agricultural pollutant loads. These range from simple sediment loading functions to physical processes requiring simulation of chemical reaction, transformation, and dynamic transport.
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From page 242... ...
Although loading functions have been used extensively for this purpose, their ability to provide reasonable estimates of agricultural nonpoint source pollution in large watersheds has not been established. The problem often overlooked in the use of simple loading models is that different categories of potential pollutants are transported in different fashions.
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From page 243... ...
Water quality data from the National Stream Quality Accounting Network (NASQUAN) was used to estimate the ambient water quality levels, total suspended solids, total phosphorus, and total nitrate for each of the 99 watershed units defined by the Water Resource Council as aggregated subareas (ASA)
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From page 244... ...
Some use NRI data, but since most models have gone beyond the gross loading stage, they use the NRI data as one input among several, not as the primary data set. A number of these models may be able to take the erosion estimates as input, but others need only the USLE coefficients in the NRI.
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From page 245... ...
A comprehensive basin-scale simulation model developed to predict water quality arising from both point source and agricultural nonpoint source pollution is the Hydrological Simulation Program in For tran (HSPF) (Donigian et al., 1983, 1984)
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From page 246... ...
For particular areas, changes in land use and conservation and tillage practices can be used to estimate changes in gross pollution loads from agriculture, provided sediment delivery ratios and pollution loading coefficients are available. Using the same system, projected changes such as significant shifts to conservation tillage can be analyzed for impact on pollution loads, provided the distinctions are maintained.
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From page 247... ...
Time-series data on meterological and hydrologic data are needed for water quality simulation models such as the nonpoint source model (Donigian and Crawford, 1976b, 1977) , the agricultural runoff model (Donigian and Crawford, 1976a)
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From page 248... ...
Other erosion not measured in the NRI includes streambank erosion, erosion trom federal lands, and erosion from construction sites. Lastly, assessment of the offsite water quality impacts of soil erosion needs to involve major federal and state agencies with capabilities and responsibilities
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From page 249... ...
SUMMARY There are limits on the usefulness of NRI data for assessing the offsite effects of soil erosion. Selected data can be used to estimate pollutant loads, primarily sediment, and thus help identify and inventory potential sources of offsite damages.
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From page 250... ...
1983. Potency factors and loading functions for predicting agricultural nonpoint source pollution.
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From page 251... ...
1984. National Resources Inventory -- A Guide for Users of 1982 NRI Data Files.
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From page 252... ...
More coordination is needed between these programs. Ultimately, groundwater, like nonpoint source pollution of surface water, must be dealt with on an areawide basis in terms of aquifer recharge areas, at least for those pollutants that tend to be dispersed across the landscape.
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