WSP10284 - Laserfiche WebLink

Home Browse Search

Table 27. Summary of detected pesticides for selected water-quality sites in the Arkansas River, April 199o-March 1993 [1J.g/L, microgram per liter] Maximum COmpound Number of Number 01 concentration Reporting limit Typa 01 name samples detections detected ("giLl Pesllclde analyzed <"giLl Portland 2,4-D 5 2 0.05 0.01 Herbicide Avondale Bromacil 4 I .7 .2 Herbicide Diazinon 5 5 .16 .01 Insecticide Malathion 5 I .04 .01 Insecticide Prometan 5 2 .2 ,2 Herbicide 2.4-D 5 5 .33 .01 Herbicide 2,4-DP 5 2 .01 ,01 Herbicide Catlin Com Diazinon 4 3 .01 ,01 Insecticide Prometon 5 I ,1 .1 Herbicide 2,4-D 4 2 .04 .01 Herbicide Las Animas Bromacil 4 I .7 .2 Herbicide Cyanazine 5 I ,I ,I Herbicide Diazinon 4 I .02 .01 Insecticide Malathion 5 I .01 .01 Insecticide Prometon 5 2 ,2 .2 Herbicide 2,4-D 5 4 .3 .01 Herbicide Below John Martin Reservoir Prometon I ,I .1 Herbicide 2,4-D I .04 .01 Herbicide stream from Wellsville probably is attributable to changing geology and local land use. Excessive erosion on rangeland in the Badger Creek (pI. I) watershed has been identified as a substantial source of suspended sediment to the upper Arkansas River downstream from Wellsville (Valentine and Carochi, 1993). Tributaries that drain sedimentary rocks and overgrazed lands also are likely sources of sediment to the Arkansas River, particularly during periods of high runoff. Suspended-sediment concentrations generally were much larger during snowmelt-runoff regimes, probably in response to tributary inflow and suspen- sion of fluvial sediment. Suspended-sediment concen- trations also can increase substantially during periods of elevated runoff from stonn events; the largest measured concentration in the upper basin (1,650 mg/L) occurred in a storm-runoff sample collected at Parkdale during August 1992. Suspended-sediment concentrations in the lower Arkansas River Basin generally were much larger than those in the upper basin (fig. 30). Initially, median suspended-sediment concentrations decreased down- stream from Pueblo Reservoir (19 mg/L at Pueblo), presumably because of sediment deposition in the reservoir, but increased significantly (a=0.05) down- stream to Avondale (257 mg/L) and to Catlin Dam (724 mg/L). The downstream increases are probably attributable to tributary inflow and suspension of fluvial sediment; Fountain Creek had a median suspended-sediment concentration of 436 mg/L. Median suspended-sediment concentrations decreased significantly (u=0.05) between Las Animas and the site immediately downstream of John Martin Reservoir, presumably due to deposition in the reser- voir. Concentrations at most sites in the lower basin were largest during the post-snowmelt runoff regime. 62 Watar-Quallty Assessment 01 the Arkansos Rlvl!l' Basin, Southaastern Colorado. 1991l-93