1. Gulls Are Big Polluters at Topanga Lagoon and State Beach in California
Gulls are one of the main causes of fecal pollution at Topanga Lagoon and State Beach in California, according to a microbial source tracking (MST) study conducted by the University of California Los Angeles in collaboration with the Resource Conservation District of the Santa Monica Mountains and the Southern California Coastal Water Research Project Authority.
Topanga State Beach, located between Santa Monica and Malibu in California, was ranked one of the dirtiest beaches in the state of California based on fecal indicating bacteria (FIB) levels in the 2005-2006, 2010-2011, and 2011-2012 seasons. Researchers wanted to know the origin of the bacteria impairing water quality at the beach.
The study involved long-term molecular marker monitoring at 10 sampling locations in the Topanga Creek watershed. Monitoring was done over a 21-month period between October 2011 and June 1, 2013. Samples were collected twice monthly at five creek sites, three lagoon sites, and two marine sites. Monitoring was done over a 21-month period between October 2011 and June 1, 2013. Samples were collected twice monthly at five creek sites, three lagoon sites, and two marine sites.
Four host-associated markers were deployed to identify sources of fecal pollution present within the watershed ? the human-associated Bacteroidales HF183 TaqMan assay, the BacHum TaqMan assay, the Catellicoccus gull-associated Gull2 TaqMan assay, and the dog-associated Bacteroidales DogBact TaqMan markers. The markers were analyzed using quantitative polymerase chain reaction (qPCR).
Both Gull and Dog-associated markers were present at high frequency and were identified as important sources to Topanga Lagoon and State Beach. Seasonal variability was seen for both markers, with highest levels occurring in winter. Some gulls exhibit migrating behaviors, and it has been documented that larger shorebird populations are present in Southern California beaches in winter months. There are also many dogs belonging to owners who live along the beach and lifeguard presence on the beach decrease in winter months.
Human markers were also found frequently in the upper watershed and their levels appear to consistently decrease downstream. Researchers point to transient populations and faulty septic systems possible culprits.