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Abstract Seven streams draining agricultural watersheds and representing the agriculturally important physiographic regions of Kentucky were resampled during the months of December 1989 through June 1990. These streams had previously been sampled in 1971–1972. During the intervening 18 yr, the use of fertilizer N in Kentucky has nearly doubled and fertilizer phosphate use has increased slightly. Nevertheless, phosphate contents of these streams averaged somewhat lower than they did 18 yr ago and NO 3 ‐N was almost exactly the same. Only one watershed had changed appreciably in land use; a subdivision had been built and equipped with a sewage plant that drains into one of the creeks. Samples taken above and below the sewage effluent demonstrated the strong effect of the subdivision on both NO 3 and PO 4 in the water. As indicated 18 yr ago, parent rock of the soils continues to have a greater effect on NO 3 ‐N and PO 4 content of streams than does agricultural use.
Thomas et al. (Wed,) studied this question.