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G.F. McIsaac

Publications and source records attributed to G.F. McIsaac.

3 recordsLinked to original sources
USGS2007

Nitrate concentrations in Illinois rivers 1967 to 1974: Comparison among reporting agencies

Long term data on surface water quality can sometimes be assembled by combining data collected by different agencies at different times and assuming that between agency differences in data quality are insignificant. The objective of this paper was to assess the quality of riverine nitrate (NO3) concentrations in Illinois measured and reported by four agencies from 1967 to 1974 by comparing median values for similar sampling locations and periods. A total of 17 river reaches were identified for which two agencies reported NO3 concentrations during similar periods. Nonparametric comparison of median values and analysis of covariance with discharge as a covariant produced similar results. Nitrate concentrations reported by the U.S. Geological Survey (USGS) from 1967 to 1971 were not statistically (P > 0.05) different from values reported by the Illinois State Water Survey (ISWS) for two of three river reaches. Additionally, NO3 concentrations reported by USGS from 1972 to 1974 were not statistically different than concentrations reported by the Illinois Environmental Protection Agency (IEPA) for four of five river reaches. From 1969 to 1971, NO3 concentrations reported by the Illinois Department of Public Heath and the Illinois Environmental Protection Agency (IDPH/IEPA) were less than one-fourth the magnitude of values reported by ISWS. The median NO3 concentrations measured by the Central Illinois Public Service (CIPS) were significantly greater than those measured by USGS and IDPH/IEPA in the three comparable sampling locations. The use of NO 3 concentrations measured by CIPS and IDPH/IEPA prior to 1972 is not recommended.

Illinois↗
USGS2003

Surface water qualit: Revisiting nitrate concentrations in the Des Moines River: 1945 and 1976-2001

Recent compilations of historical and contemporary riverine nitrate (NO 3 ) concentrations indicate that concentrations in many rivers in the north-central USA increased during the second half of the 20th century. The Des Moines River near Des Moines, Iowa, however, was reported to have had similar NO 3 concentrations in 1945 and the 1980s, in spite of substantially greater N input to the watershed during the latter period. The objective of this study was to reconsider the comparison of historical and contemporary NO 3 concentrations in the Des Moines River near Des Moines in light of the following: (i) possible errors in the historical data used, (ii) variations in methods of sample collection, (iii) variations in location of sampling, and (iv) additional data collected since 1990. We discovered that an earlier study had compared the flow-weighted average concentration in 1945 to arithmetic annual average concentrations in the 1980s. The intertemporal comparison also appeared to be influenced by differences in sample collection methods and locations used at different times. Depending on the model used and the estimated effects of composite sample collection, the 1945 arithmetic average NO 3 concentration was between 44 and 57% of the expected mean value at a similar water yield during 1976–2001. The flow-weighted average NO 3 concentration for 1945 was between 54 and 73% of the expected mean value at a similar water yield during 1976–2001. The difference between NO 3 concentrations in 1945 and the contemporary period are larger than previously reported for the Des Moines River.

Iowa↗