OOS 12-3
Using benthic marcroinvertebrate community composition to assess stream health in the Los Angeles River watershed
The Los Angeles River Watershed is composed of 1,400 miles of streams which run from the San Gabriel Mountains to the Pacific Ocean, and supports a population of more than 4.5 million people. In 2007, a group of local, state and federal stakeholders formed the Los Angeles River Watershed Monitoring Program (LARWMP) to provide managers and the public with a more complete picture of conditions in the Los Angeles River watershed. From 2008 through 2013, LARWMP sampled nearly 60 randomly selected sites in three watershed sub-regions including the “natural” portions of the upper watershed, the “effluent” dominated reaches of the mainstem channel, and the urban tributaries of the lower watershed. Stream condition was assessed using the Southern California Index of Biological Integrity (IBI) for benthic macroinvertebrates, along with multiple stressor indicators including water chemistry, physical habitat and toxicity.
Results/Conclusions
Expectedly, there was a strong positive relationship between the condition of the biological community and physical habitat conditions in the watershed. During the 5-year monitoring period, benthic macroinvertebrate communities in the more natural streams of the upper watershed had the highest Southern CA IBI scores. BMI community composition followed a predictable stressor gradient that was most clearly defined by physical habitat disruption associated urban development and actively managed flood control, which has severely disrupted the hydrology of the watershed.