Impact of Rainfall during El Nino Years on the Presence of Bacteria in Urban Stormwater on the Coastal Waters of San Diego
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Description
Storm drain systems in urban areas serve to minimize flooding during periods of annual rainfall and divert the urban runoff to receiving bodies of water, which becomes a potential source of coastal bacteria that impacts human and marine health. Water samples from storm drain outfalls and receiving water were collected monthly during the wet weather season (November-April) and weekly during the dry weather season (May-October) at seven sampling sites that are located on the coast from La Jolla down to Pacific Beach. Analysis on water samples provided total bacteria counts (fecal coliforms, Enterococcus, and total coliforms) that were detected in coastal receiving water from November to April in both El Nino and non-El Nino years. Averages in bacteria counts from the wet weather season in 2015-16 range from 0-3951 colony forming units (CFU) while in 2017-18 ranged from 0-5435 CFU. These bacteria counts seem to indicate that El Nino years do not necessarily increase the presence of bacteria in coastal receiving waters even though the rainfall amounts were higher. Additionally, the bacteria counts were higher at two sites (EH290 and EH300) than those at other sampling sites. Further investigation on the relationship between urban stormwater flushing and presence of bacteria would be beneficial in determining the discrepancies in bacteria counts. With other sources of pollution being difficult to track, monitoring pollution from storm drain outfalls is important in assessing human impacts on coastal environments.
Impact of Rainfall during El Nino Years on the Presence of Bacteria in Urban Stormwater on the Coastal Waters of San Diego
Storm drain systems in urban areas serve to minimize flooding during periods of annual rainfall and divert the urban runoff to receiving bodies of water, which becomes a potential source of coastal bacteria that impacts human and marine health. Water samples from storm drain outfalls and receiving water were collected monthly during the wet weather season (November-April) and weekly during the dry weather season (May-October) at seven sampling sites that are located on the coast from La Jolla down to Pacific Beach. Analysis on water samples provided total bacteria counts (fecal coliforms, Enterococcus, and total coliforms) that were detected in coastal receiving water from November to April in both El Nino and non-El Nino years. Averages in bacteria counts from the wet weather season in 2015-16 range from 0-3951 colony forming units (CFU) while in 2017-18 ranged from 0-5435 CFU. These bacteria counts seem to indicate that El Nino years do not necessarily increase the presence of bacteria in coastal receiving waters even though the rainfall amounts were higher. Additionally, the bacteria counts were higher at two sites (EH290 and EH300) than those at other sampling sites. Further investigation on the relationship between urban stormwater flushing and presence of bacteria would be beneficial in determining the discrepancies in bacteria counts. With other sources of pollution being difficult to track, monitoring pollution from storm drain outfalls is important in assessing human impacts on coastal environments.