Densities of Fecal Indicator Bacteria in Tidal Waters of the Ballona Wetlands, Los Angeles County, California

—Densities of fecal indicator bacteria (FIB) represented by total coliforms, E. coli and enterococci were measured within tidal channels of the Ballona Wetlands (Los Angeles County) to see if the wetlands act as a sink or source for these bacteria and to measure increases in FIB densities during wet weather. Samples were collected on 10 days over a 1-yr period beginning February 2003 at four sites within the wetlands and one site in Ballona Creek opposite the west tide gate. Incoming flood and outgoing ebb tides were sampled during each sampling event at each station. Water from Ballona Creek may be a significant source of indicator bacteria in the wetlands. Within the tidal channels, densities for total coliforms typically ranged from 103–104 MPN/100 ml, but ranged up to 106 during runoff events. Densities of E. coli and enterococci were orders of magnitude less than those measured for total coliforms, generally ranging from 101–104 for E. coli, and 101–105 for enterococci; greater densities were associated with runoff events. Densities of FIB tended to be up to three times greater during flood than ebb tide conditions depending on the tidal range. This result suggests that more FIB may be entering the wetlands on flood tides than leaving during ebbs, so that these bacteria either are being destroyed, sinking into the tidal channel sediments and plant surfaces, or both. This hypothesis needs to be tested by further identifying other possible FIB sources within the wetlands, and increasing the study design’s statistical power to better characterize the flux of these bacteria entering and leaving the wetlands. Wetlands, both freshwater and salt marsh, are noted for their water purification abilities. For example, suspended sediments will settle into the marsh systems including any associated metal and organic pollutant loads while nutrients will be utilized by plants (Keddy 2000; Mitsch and Gosselink 2000) and feces-derived bacteria are eliminated from the water through destruction by sunlight and other mechanisms (Mayo 1995; Sinton et al. 2002). Given these qualities, wetland systems are being used to purify sewage effluents and runoff (Kadlec and Knight 1996; Schueler and Holland 2000). Conversely, wetlands such as coastal salt marshes can be sources of fecal bacteria depending on degrees of biological activity and input of contaminated runoff from surrounding urban areas. Water contaminated with feces-derived coliform and enterococci bacteria outwelling from coastal marshes has been shown to cause water quality problems at adjacent ocean beaches where swimmers and surfers recreate (Grant et al. 2001). If bacterial bathing water standards are not met, then beaches can be posted with advisories or closed resulting in millions of dollars of lost revenues to local businesses. Understanding the sources of fecal bacteria, 1 Dorsey: Densities of Fecal Indicator Bacteria in Tidal Waters of the Ballona Wetlands Published by OxyScholar, 2006 60 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES and their circulation dynamics within coastal marshes, and outwelling to adjacent beaches will help refine regulatory strategies to protect the public. The goal of this study was to characterize levels of fecal indicator bacteria during different tidal flows within the Ballona Wetlands, a salt marsh located in Los Angeles County along the southern border of Marina Del Rey boat harbor. The central question for this study was: Are concentrations of fecal indicator bacteria greater entering the wetlands from Ballona Creek than leaving the wetland system? To begin addressing this question, densities of fecal indicator bacteria (FIB: total coliforms, E. coli, enterococci) were measured in the creek and throughout the wetland during different tidal flows (flood and ebb conditions), and amplitudes (neap vs. spring). To date, FIB measurements have been made in Ballona Creek and Estuary by various storm water monitoring agencies (e.g. LADPW Watershed Management Division: http://ladwp.org/wmd) or runoff research studies (e.g. Dorsey and Lindaman 2004, Stein and Tiefenthaler 2004). Contrastingly, only a single water sample characterizing coliform densities has been collected in the Ballona Wetlands. This work was done in 1998 by a consulting group performing an environmental survey for the Playa Vista development project (Camp Dresser & McKee 1998 as reported in U.S. Army Corps of Engineers 1999). Results reported herein are the first major effort to characterize FIB densities in this wetland system. Ballona Wetland Study Area The Ballona Wetlands consist of approximately 180 acres of tidal salt marsh receiving muted tidal flows. It is the last remaining major coastal wetland in Los Angeles County (West 2001). As such, it is surrounded by extensively developed urban areas and impacted by many other human activities. Historically, rail and roadways have fragmented the wetlands since the 1800’s. In 1937 The Army Corps of Engineers (COE) and the Los Angeles County Flood Control District constructed the Ballona Creek flood control channel that diverted water from the creek straight to the Santa Monica Bay, thus severely limiting tidal flow to the salt marsh. Presently, water entering the wetlands mainly is from Ballona Creek via a single tidal gate (described below). Other sources of freshwater would include intermittent flows of runoff from residential areas on the southern bluffs, and storm runoff from Culver Blvd. running through the wetland area. In 2004, several major events occurred that began reversing the history of negative impacts to this wetland. The State of California purchased the remaining 180 acres of wetlands from a developer for eventual restoration, and the COE constructed a new set of tide gates. Tidal flows within the wetlands are muted. Prior to April 2003 water entered the system through two tidal gates positioned along the southern bank of the Ballona Creek estuary. Both gates were poorly maintained, allowing only a limited amount of tidal flow in and out of the wetlands. The eastern gate was the main gate for the wetlands, allowing in flood and ebb flows. The western gate was a one-way flap-gate allowing only ebb flows to leave the wetlands. Due to corroded hinges, the western gate was frozen in an open position, allowing some flood flows into the wetlands. In April 2003 the COE replaced the old eastern tide gate with a pair of selfregulating gates allowing a maximum tidal level of 1.1 m to occur (U.S. Army 2 Bulletin of the Southern California Academy of Sciences, Vol. 105 [2006], Iss. 2, Art. 2 http://scholar.oxy.edu/scas/vol105/iss2/2 61 FECAL INDICATOR BACTERIA IN THE BALLONA WETLANDS Corps of Engineers 1999). In November 2003, the COE removed marine growth and corrosion from the hinges of the west tide gate so that it now functions to only allow ebb flows to leave the wetlands. The wetlands now receive flood flows only through the east tide. When the tide turns, ebb flows drain the tidal channels via both the east and west gates. Wetland and tidal channel monitoring associated with the new tide gate system is being conducted by the City of Los Angeles (Bureau of Sanitation, Environmental Monitoring Division) to document any changes in the biological community associated with this project. If populations of native species are stable, then tidal levels may be increased by 0.1 m. This decision will be made by the California Department of Fish and Game, who, in conjunction with the California Coastal Conservancy, are now developing a restoration plan and implementation strategy to restore the Ballona Wetlands to a more naturally functioning wetland.