Temporal and spatial assessment of water quality, physical habitat, and benthic communities in an impaired agricultural stream in California's San Joaquin Valley.
The goal of this study was to characterize and discuss the relationships among water quality, physical habitat, and benthic community data collected annually over a three-year period (2000--2002) in an impaired agricultural stream (Orestimba Creek) in California's San Joaquin River watershed. Conductivity, pH, and turbidity were the most important water quality conditions influencing the various benthic metrics. Significantly higher flow conditions and lower dissolved oxygen values were reported in Orestimba Creek in 2001; increased turbidity conditions were reported in 2002. Channel alteration, riparian buffer, sediment deposition, and channel flow were the most important physical habitat metrics influencing the various benthic metrics. Higher total physical habitat scores were reported in 2001 when compared with 2002. The most dominant benthic taxa collected during all three years of sampling were oligochaetes and chironomids. Oligochaetes are found in stressful environments while chironomids can be either sensitive or tolerant to environmental stressors depending on the species. Populations of both daphnids and the exotic clam Corbicula were reported to increase over time. Both of these taxa are generally tolerant to most types of environmental degradation. The exception is that daphnids are highly sensitive to organophosphate insecticides. The % filterers increased over time, which suggests an increase in environmental disturbance. The % collectors decreased from 2000 to 2002, which suggests an improvement in environmental conditions. The presence of approximately 100 taxa in Orestimba Creek during each of the three years of sampling implies that benthic communities in this stream are fairly diverse, considering their ephemeral environment, but without a clear definition of benthic community expectations based on established referenc conditions it is unknown if this water body is actually impaired.
Hall
Lenwood W
LW
University of Maryland, Agricultural Experiment Station, Wye Research and Education Center, Queenstown, Maryland 21658, USA. lh43@umail.umd.edu
Killen
William D
WD
D016573:Agrochemicals / Q000633:toxicity*; D000818:Animals; D002140:California; D002683:Chironomidae / Q000187:drug effects; D004784:Environmental Monitoring; D005618:Fresh Water / Q000032:analysis*; D007448:Invertebrates / Q000187:drug effects*; D009835:Oligochaeta / Q000187:drug effects; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000633:toxicity*
D016573:Agrochemicals; D014874:Water Pollutants, Chemical