Coastal wetlands, like the Ballona Wetland salt marsh, provide a valuable array of ecosystem functions involving many physical-biological interactions that, for example, support biodiversity, abate flooding, sequester carbon, and purify water (Zedler and Kercher 2005). In purifying water, these systems remove chemical, physical and biological pollutants through filtering and settling processes, destruction by ultraviolet light, and in the case of bacteria from fecal sources, predation by microorganisms and bacteriophage viruses (Mitsch & Gosselink 2007).
The Ballona Wetlands Ecological Reserve (BWER), degraded from decades of human activities and development, still provides valuable water purification services. This salt marsh is located in Los Angeles County between Marina Del Rey and the bluffs of Playa Del Rey, a suburb of the City of Los Angeles. The BWER, covering about 527 acres, is divided into three sections: A, B and C (Figure 1), and receives tidal waters from Santa Monica Bay via the adjacent Ballona Estuary twice daily. Of the total acreage, only approximately 15 ac (2.9%) receive tidal water. This occurs primarily in Area B through a set of tidal gates that allow tidal heights to reach 1.1 m before closing. The main portion of Area B receiving these flows is at the western end where water spills from the tidal channels onto the marsh flat, and the salt panne (Figure 2). The only other part of the BWER receiving tidal flows is the deep Fiji Ditch located in the north side of Area C (Figure 3).
The wetlands generally act as a sink for FIB, but under certain tidal periods, a source. Water flowing into the BWER often is contaminated with fecal indicator bacteria (FIB) from Ballona Creek runoff flowing and mixing with waters in the Ballona Estuary (Stein and Tiefenthaler 2004, Dorsey 2006). Studies within the tidal channels of Area B have shown that as contaminated water flows into the wetlands during flood tides occurring during daylight hours, the densities of these bacteria are significantly reduced by up to two orders of magnitude (Dorsey et al. 2010), especially in the topmost layers of the water (Johnston et al. 2015). Under these conditions, the wetland acts as a sink for these bacteria. Conversely, the wetlands can be a source of FIB under certain low tide flows. Twice each month during the full- and new-moon phases, spring tides occur when tidal ranges are at their maximum. During spring low tides, the wetland tidal channels nearly completely drain, and sediment along with associated FIB are suspended into water flowing into the estuary. However, this contribution of FIB into the estuary was not deemed significant relative to much greater densities in the estuary’s water flowing into Santa Monica Bay during spring low tides (Johnston et al. 2015). Figure 4 (after Dorsey 2006) illustrates the extreme tidal conditions under which the wetlands act as a sink by removing significant loads of FIB, or a source where some FIB are discharged back into the adjacent Ballona Estuary.
Deactivation of FIB through exposure to UV radiation from sunlight is probably a significant factor in the wetlands to reduce bacterial loads. Many studies in experimental mesocosms, constructed, and natural wetlands have demonstrated this point. For example, studies in nearby Del Rey Lagoon (Dorsey et al. 2013) linked reduced concentrations of coliform bacteria with FIB deactivation rates measured by Noble et al. (2004) in mesocosms using local seawater and runoff.
Less is known about predation of FIB in wetlands by other microorganisms, particularly bacteriophages, viruses that predate bacteria. Only in the past few decades has the importance of viruses as members of marine and freshwater communities been realized. Viruses are probably the most abundant biological entity in marine systems with abundances of ten billion in a liter of coastal water, 5-25 times greater than bacteria (Fuhrman 1999). As predators, they can significantly control bacterial densities, and probably are responsible for reducing FIB In the Ballona Wetlands. Initial studies of bacteriophage in the wetlands indicated that during flood-tide flows, viruses were about twice as abundant as bacteria, but increased to 21 times more abundant in water flowing back into the estuary (Figure 5), suggesting that there densities increased by feeding on, thus killing, bacteria (G. Kuleck, Loyola Marymount University, unpublished data).
Extensive restoration planning for the Ballona Wetlands is underway under a partnership between:
Presently, four restoration alternatives are being developed for the environmental documentation, and summarized at the project’s website (http://ballonarestoration.org/vision/). Alternatives 1-3 all increase tidal flow into the BWER; the fourth is the no-project alternative where flows remain the same as present. Because water is the life-blood of a wetland, allowing more into the BWER will boost water purification services as described above, providing an extensive ecosystem service to the region. Compared to a conventional wastewater treatment facility, using a wetland system was found to achieved a capitalized cost savings of $785-$1,209/ac in 1995 dollars (Breaux et al. 1995), so increasing the amount of runoff-contaminated water flowing from Ballona Creek into the wetlands via the estuary will represent a major cost saving to the area compared to treating this water via a wastewater treatment facility. Of equal importance, more water flowing into the wetlands will result in a greater biodiversity of the biota associated with marsh and adjacent habitats as a host of ecosystem services are boosted.
To conclude, the Ballona Wetlands are cleansing water flowing into them from the contaminated Ballona Creek despite their degraded condition from decades of human activities and neglect. If given a chance, i.e. enable greater water flows into the wetlands, then they can provide significant ecosystem services that will provide for enhanced biodiversity, cleaner water, and wonderful recreational, educational and spiritual opportunities for the citizens of the region and its visitors.
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About the Author: John H. Dorsey, Ph.D., is the Director of Urban Ecology Research at CURes. He received his B.S. in Marine Biology (1972) and M.S. in Biology (1975) from California State University, Long Beach, then traveled to Australia where he received his doctorate from the University of Melbourne in Zoology (1982). Presently he is a Professor at Loyola Marymount University, Los Angeles, in the Department of Civil Engineering & Environmental Science where he teaches courses in environmental, atmospheric and marine sciences. Also at LMU, he is the Director of Urban Ecology Science with the Center for Urban Resilience (CURes). Prior to LMU, he worked as a marine biologist for the City of Los Angeles (1983-2002), focusing on marine monitoring in Santa Monica Bay and storm water management. John sits on numerous local and state technical committees dealing with water quality issues and policy, and is past-president of the Southern California Academy of Science where he remains an active member of their Board of Directors and Research Training Program for high school students. His research interests focus on the dynamics of fecal indicator bacteria in coastal waters and wetlands. John’s passion for good water quality is natural — he is an avid surfer, so most days he can be found at dawn surfing at El Porto near his home and LMU’s campus.