Impacts of Beach Wrack Removal via Grooming on Surf Zone Water Quality

Fecal indicator bacteria (FIB) are used to assess the microbial water quality of recreational waters. Increasingly, nonfecal sources of FIB have been implicated as causes of poor microbial water quality in the coastal environment. These sources are challenging to quantify and difficult to remediate. The present study investigates one nonfecal FIB source, beach wrack (decaying aquatic plants), and its impacts on water quality along the Central California coast. The prevalence of FIB on wrack was studied using a multibeach survey, collecting wrack throughout Central California. The impacts of beach grooming, to remove wrack, were investigated at Cowell Beach in Santa Cruz, California using a long-term survey (two summers, one with and one without grooming) and a 48 h survey during the first ever intensive grooming event. FIB were prevalent on wrack but highly variable spatially and temporally along the nine beaches sampled in Central California. Beach grooming was generally associated with either no change or a slight increase in coastal FIB concentrations and increases in surf zone turbidity and silicate, phosphate, and dissolved inorganic nitrogen concentrations. The findings suggest that beach grooming for wrack removal is not justified as a microbial pollution remediation strategy

A Coupled Modeling and Molecular Biology Approach to Microbial Source Tracking at Cowell Beach, Santa Cruz, CA, United States

Consistently high levels of bacterial indicators of fecal pollution rank Cowell Beach as the most polluted beach in California. High levels of fecal indicator bacteria (FIB), <i>E. coli</i> and enterococci, are measured throughout the summer, resulting in beach advisories with social and economic consequences. The source of FIB, however, is unknown. Speculations have been made that the wrack accumulating on the beach is a major source of FIB to the surf zone. The present study uses spatial and temporal sampling coupled with process-modeling to investigate potential FIB sources and the relative contributions of those sources. Temporal sampling showed consistently high FIB concentrations in the surf zone, sand, and wrack at Cowell Beach, and ruled out the storm drain, the river, the harbor, and the adjacent wharf as the sources of the high concentrations observed in the surf zone. Spatial sampling confirmed that the source of FIB to the beach is terrestrial rather than marine. Modeling results showed two dominant FIB sources to the surf zone: sand for enterococci and groundwater for <i>E. coli</i>. FIB from wrack represented a minor contribution to bacterial levels in the water. Molecular source tracking methods indicate the FIB at the beach is of human and bird origin. The microbial source tracking (MST) approach presented here provides a framework for future efforts