Environmental Engineering Reference
In-Depth Information
Soil erosion,
runoff of soil and
contaminants to streams
Solid and liquid wastes
Soil amendments,
fertilizers (nitrates, phosphates, etc.)
fungicides, pesticides,
insecticides, herbicides
Seepage to
groundwater
Discharge of groundwater to
streams
Aquifer
FIGURE 6.3
Schematic of contaminant transfer from agricultural activities to surface and groundwater: geoenvironmental
perspective.
According to the U.S. Geological Survey report of 1999 (USGS, 1999), nitrate concentra-
tions exceeded the USEPA drinking water standard in 15% of samples collected in shallow
groundwater near urban and agricultural lands. Amounts were measured in agricultural
streams and found to be less than 20% of the phosphorus and less than 50% of the nitrogen
applied annually to the land. This is due to the greater tendency of phosphorus to attach
to soil particles and move with runoff to surface water compared with nitrogen. Extensive
herbicide use is in agricultural areas. Approximately 70% of the total national use of pes-
ticides is in agricultural areas, and thus, there in widespread occurrence in agricultural
streams and shallow groundwater. The highest rates of detection were found for herbi-
cides, atrazine, metolachlor, alachlor, and cyanazine. Insecticides were more frequently
found in some streams draining watersheds with high insecticide use than in shallow
groundwater as they also tend to sorb onto soil or degrade quickly after application. As
there are no USEPA aquatic-life criteria for the major herbicides, Canadian guidelines
were employed and concentrations were found to elevated, particularly for atrazine or
cyanazine in 17 of the 40 agricultural streams studied. Also, in the case of currently used
insecticides, the major organochlorine insecticides (e.g., DDT, dieldrin, and chlordane),
exceeded guidelines for aquatic life in at least one water sample from 18 of the 40 agricul-
tural streams and recommended sediment-quality guidelines for protection of aquatic life
at about 15% of agricultural sites.
Soybeans, alfalfa, and other legumes ix more than 40 Tg/year of nitrogen fertilizer
(Galloway et al., 1994). Depletion in nitrogen levels can impact soil fertility. Nitrate runoff
from agricultural ields can decrease water quality. The nitrogen cycle can subsequently
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