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Monday, June 4, 2007 - 4:15 PM
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Spatial and temporal patterns and causal analyses of benthic algal growth in the San Gabriel River watershed, Southern California
Lei Zheng, Jerry Diamond, Jonathan Bearr, Carolina Gallardo, and Chad Barbour. Center for Ecological Sciences, Tetra Tech, Inc., Owings Mills, MD 21117
The channelized streams of the lower San Gabriel River watershed in Southern California are commonly covered by a heavy layer of benthic algae (e.g. Cladophora) during peak growing season. Excessive algae could impair beneficial uses and raise public concerns. A two-year study to characterize patterns in algal abundance and identify factors responsible for algal growth was carried out during 2005 to 2006 in the lower San Gabriel River watershed. Rapid benthic algae surveys, along with physical, chemical, and macroinvertebrate sampling were conducted in six separate visits between April and October. Our results indicated that algal abundance varied spatially and temporally in different stream channels and in different seasons. Generally, concrete-lined channels had significantly higher algal biomass than natural substrate channels possibly due to higher water temperature, high light availability, and higher nutrient concentrations in these channels. Algal species composition also varied among different stream channels. Algal biomass was positively correlated with dissolved nutrient concentrations and the diatom pollution tolerance index was related to water column total nitrogen concentration. A wedge-shape relationship was observed between the Southern California benthic IBI and percent macroalgal cover indicating that increasing algal cover, along with other factors, may impact aquatic life uses in these streams.