T. Al Austin

Quantifying the effects of stream discharge on summer river temperature

Abstract Control of summer river temperature is needed for maintaining water temperature standards to protect aquatic biota and wildlife habitats. Given the fact that instream discharge, among meteorological and hydrological factors, may be the only one that can be practically managed, is it feasible to moderate summer river temperature through reservoir and streamflow regulations? An analysis is conducted to quantify the effects of the magnitude of instream flow on summer river temperature with weather as a reference. Relationships between water temperature and river discharge or flow depth are developed using a simplified model and adopting the concept of equilibrium temperature and bulk surface heat exchange coefficient. The relationships are validated against continuous 5-year field measurements at the central Platte River, Nebraska, USA. It was found that the variation of daily maximum water temperature with flow was stronger than that of daily mean. A critical discharge was obtained, which divides d...

Movement of herbicides under two irrigation regimes applied to turfgrass

Abstract Our objective was to investigate the movement of the dimethylamine salt of (2,4-dichlorophenoxy) acetic acid (2,4-D), dicamba, and 2-(2-methyl-4-chlorophenoxy) propionic acid (MCPP), when applied to Kentucky bluegrass turf under both infrequent and frequent irrigation regimes. The turfgrass was established on 50-cm length and 20-cm diameter undisturbed soil columns of Nicollet (fine-loamy, mixed, mesic-Aquic Hapludolls) with intact macropores. The infrequent irrigation regime consisted of four 2.54-cm applications, and the frequent regime consisted of 16 0.64-cm applications. On average, the amounts of 2,4-D, dicamba, and MCPP recovered from the soil columns, and in the leachate, under the infrequent irrigation regime were 3.0, 22.4, and 1.1%, respectively. The average amounts of 2,4-D, dicamba, and MCPP recovered from soil columns, and in the leachate, under the frequent irrigation regime were 3.2, 6.3, and 2.3%, respectively. Average values of 1.9, 21.8, and 0.7% of the applied 2,4-D, dicamba, and MCPP, respectively, were measured in the leachate from the soil columns under infrequent irrigation, in contrast to 0.1, 3.4, and 0.2%, respectively, from the soil columns under frequent irrigation. We concluded that the frequency of irrigation can have an impact on the movement of these herbicides through soil profiles.

COMPARING DISPERSIVITIES AND SOIL CHLORIDE CONCENTRATIONS OF TURFGRASS-COVERED UNDISTURBED AND DISTURBED SOIL COLUMNS

Research relating to soil leaching properties under turfgrass conditions has often been conducted on disturbed soils where macropore structure has been destroyed. The objective of this study was to compare the solute movement characteristics of undisturbed and disturbed soil columns covered with turfgrass. Dispersivities and chloride (Cl) breakthrough curves of undisturbed and disturbed soils were investigated. Soil columns were excavated into three sections after testing, for which the mean bulk density was 1.33 Mg M−3 for the undisturbed columns and 1.16 Mg m−3 for the disturbed columns. The dispersivity for the undisturbed columns was over three times greater than for the disturbed columns. Chloride concentration found in Layer 1 (0–6.7 cm), Layer 2 (6.7–13.4 cm), and Layer 3 (13.4–20.0 cm) were 2.8, 5.3, and 4.8 times higher, respectively, for the disturbed soils than for the undisturbed. Applying conclusions from solute movement studies using repacked columns covered with turfgrass to actual undisturbed field conditions could lead to errors in interpretation because of the effect of macropores.

Midwest (U.S.A.) reservoir water quality modification I. Particulate parameters

Both qualitative and quantitative approaches were used to evaluate the impact of a flood control, low flow augmentation reservoir on seven water quality parameters: Suspended solids and total phosphate (particulate parameters); BOD, COD, and ammonia (O2-demanding parameters); and orthophosphate and nitrite plus nitrate N (soluble nutrients). Fourteen years of weekly sampling data above, in, and downstream of the reservoir both before and after the reservoir became operational were analyzed. This paper considers the effects of the reservoir on the particulate parameters. There was a dramatic decrease in both suspended solids and total phosphate concentrations in the reservoir discharges, particularly during periods of high river flows and high reservoir inflow parameter concentrations. At all sampling stations, the annual parameter loading rates (kg ha−1 yr−1) correlated linearly with annual runoff (cm yr−1). The suspended solids removal efficiency of the reservoir was dependent on annual runoff and averaged about 90%. Non-point source contributions of suspended solids were well over 99% when annual runoff exceeded 6.57 cm y−1 and over 95% even when annual runoff was as low as 1.63 cm yr−1

Midwest (U.S.A.) reservoir water quality modification

The impact of a flood control, low flow argumentation reservoir in the Midwestern part of the United States on BOD, COD, and ammonia was evaluated in this paper. Fifteen years of weekly water quality data (9 yr before impoundment and 6 yr after impoundment) from four sampling stations upstream and downstream of the reservoir were available for analysis. The annual loading rates of these parameters (kg ha−1 vr−1) were found to correlate well with annual runoff (cm yr−1). Besides, the reservoir was found to have had a significant and beneficial impact on the downstream loading rates of BOD and COD, which were reduced by 55 and 75%, respectively. As for ammonia, the results of this study indicate that its annual loadings at downstream locations were not significantly affected by the reservoir. Average non-point source contributions of BOD and ammonia loadings into the system were found to be about 80 and 55%, respectively.