Contaminant Loading in Drainage and Fresh Water Used for Wetland Management at Stillwater National Wildlife Refuge

Throughout the western United States, studies have identified various detrimental effects of contaminants to aquatic biota from the use of agricultural drainage water for management of arid wetlands. However, little is known about the relative contributions of contaminant loading from pollutants dissolved in water compared with those carried by drifting material (e.g., detritus) associated with drainage water. Consequently, we determined loading rates for contaminants dissolved in water and those incorporated by drifting material for drainage (Diagonal Drain) as well as fresh (S-Line Canal) water used for wetland management at Stillwater National Wildlife Refuge (SNWR), Nevada during the early, middle, and late periods of the irrigation season (June through mid-November) in 1993. We found loading rates for trace elements throughout the irrigation season were almost entirely (> 98%) associated with contaminants dissolved in the water rather than incorporated by drift. Although drift contributed little to the total loading for trace elements to SNWR wetlands, contaminant concentrations were much greater in drift compared with those dissolved in water. Loading rates for dissolved As, B, Hg, and total dissolved solids (TDS) differed among periods for the Diagonal Drain. Along the Diagonal Drain, loading rates for dissolved As, B, Hg, Mo, unionized ammonia (NH3-N), TDS, and Zn differed among its three sampling sites. B was the only trace element with differences in loading rates for drift among periods from the Diagonal Drain. In contrast, loading rates for As, B, Cr, Cu, Hg, Se, and Zn in drift differed among periods for the S-Line Canal. Along Diagonal Drain, loading rates in drift for B (middle and late periods), Cr, Cu, and Zn differed among sites. Hg (x- >/= 12.0 ng/L) and NH3-N (x- >/= 0.985 mg/L) dissolved in water as well as B (x- >/= 97.4 µg/g DW) and Hg (x- >/= 0.461 µg/g DW) in drift from the Diagonal Drain and S-Line Canal exceeded screening levels (SLs) for protection of aquatic biota throughout the irrigation season. Dissolved As (x- >/= 0.0426 mg/L) in water from the Diagonal Drain during all periods exceeded the SL for protection of aquatic biota. Dissolved B (x- = 1.03 mg/L) in water from the Diagonal Drain during the early period exceeded the SL for protection of aquatic biota.