Print PageResearch over the past two decades has shown that streams and rivers close to urbanized areas are degraded both chemically and ecologically. The pattern of degradation observed repeatedly in urban-impacted streams has been termed the “Urban Stream Syndrome”. Mechanisms driving the syndrome are complex and interactive; however, many impacts can be attributed to storm water runoff and wastewater treatment plant effluent. Because benthic macroinvertebrate assemblages show consistent shifts in community structure, they are useful for studying the response of stream biota to urban land use. However, research regarding the secondary production of benthic macroinvertebrates and life histories of aquatic insects in response to urban land use has witnessed far less attention. In addition, organisms living in wastewater effluent are often exposed to contaminants such as the antimicrobial Triclosan, and have been shown to concentrate in the tissue of benthic macroinvertebrates. For organisms with high production values, this may serve as an important link between aquatic and terrestrial ecosystems.
Results/Conclusions
Populations of Cheumatopsyche lasia, a net spinning caddisfly, were examined upstream and downstream of a municipal wastewater treatment facility August 2009 through November 2011. Patterns of life history, secondary production, and aspects of ecology were compared between sites. Distinguishing morphological characteristics were determined for each developmental stage. Counts of each instar were used to compare population structure and development between upstream and downstream sites. Standing stock of C. lasia was estimated as the number of individuals per 500 cm2 of habitat. Pupal abundance was used to determine emergence over the sampling period. As with other southwestern semi-arid streams, stream flow was dramatically augmented by the wastewater treatment facility. Extreme differences in hydrology were observed between sites because a steady discharge was maintained below the wastewater outfall. In addition, differences in water temperature were observed between sites, in particular over the winter months temperatures were often 10 - 15°C higher below the wastewater outfall. Abundance of larvae was significantly different between sites (Independent T Test, p < 0.01), with larval counts approximately 10 times greater below the wastewater outfall. C. lasia was determined to be multivoltine; however, life history structure differed significantly between upstream and downstream populations.
