Following the January 9th, 2018 Montecito debris flow and the Santa Barbara County disposal of muds to Goleta Beach, the Holden Laboratory @ UCSB performed a wintertime study of the mud deposits and water quality at Goleta Beach, using funds provided by the UCSB Associated Students (AS) Coastal Fund. The goals of the study were to assess the evidence for human fecal contamination in and from the muds, and to assess related environmental quality over a time period following mud disposal cessation. The study involved sampling water at three surf zone locations, plus sampling the mud at the deposit location, for 21 days across the period of January 18th through February 28th. Samples were analyzed for culturable fecal indicator bacteria (FIB), DNA-based Enterococcus spp. (Entero1A) by quantitative polymerase chain reaction (qPCR), DNA-based human fecal marker(s) by qPCR, human-specific adenovirus by droplet digital PCR (ddPCR), and Salmonella spp. by qPCR (water samples only). Field water characteristics (dissolved oxygen, conductivity and temperature) were recorded at the time of sampling; water was also analyzed for turbidity, and samples were archived for potential future analyses of nutrients and a chemical marker of sewage. Mud was analyzed for particle sizes (% sand, silt, and clay), moisture content, and total organic matter (loss on ignition). Surf zone FIB results were compared to Santa Barbara County’s FIB results from the same period. Results were also compared to those from the Holden Lab from studies of Goleta Beach during the AB411 (summertime) period in 2016. Highlights of the UCSB AS Coastal Fund report are:
- During the 2018 wintertime study, surf zone fecal indicator bacterial (FIB) concentrations were elevated, mostly exceeding the CA State single sample criterion, and concentrations measured in the Holden Lab were in agreement with Santa Barbara County results.
- For surf zone waters and mud, FIB and Entero1A concentrations were elevated in comparison to summertime 2016 (surf zone water and beach sand) results.
- Surf zone water FIB concentrations and turbidity were correlated, suggesting that mud particles introduced into the surf zone also delivered FIB, or stimulated FIB persistence.
- The mud FIB, % clay and silt, and organic matter, were positively intercorrelated, suggesting that FIB were characteristic, like organic matter and particle sizes, to the deposited mud.
- Similarly to 2016 AB411 (summertime) sampling results, there was low to no evidence of human fecal material across the surf zone and mud samples.
The report states: “There are multiple possible explanations of elevated FIB in Goleta Beach surf zone waters during and after the sediment deposition, including that FIB were directly introduced into the surf zone via deposited sediments, with sediment-associated FIB directly causing elevated water FIB concentrations. Alternatively, or in addition, FIB in the deposited sediments along with high organic matter in the sediments, under indigenous water conditions, fostered the growth of FIB in the surf zone of introduced, plus other indigenous, FIB. Differentiating between these scenarios was beyond the scope of this work, and yet the possibilities suggest avenues for future research. To further complicate, the sediment deposition area at Goleta Beach appears to continuously attract shorebirds which are known to excrete fecal material high in Enterococcus. Thus, ongoing beach water quality problems at Goleta Beach could be arising from secondary or higher order processes introducted via, or compounded by, the sediment deposition.”
The report also states: “Host-specific fecal markers—if introduced during the debris flow or in any period during mud processing or storage—would have decayed rapidly, relative to FIB. However, modeling or otherwise simulating possible introduction and decay scenarios for fecal markers relative to FIB would be challenging unless sediment storage and handling, time periods and procedures, became known. Other analyses of the mud could prove useful to determining original fecal sources. Regardless, owing to the mud characteristics (fines content, and organic matter content), high FIB appeared to be endemic to, and thus an additional characteristic of, the deposited sediment. In future studies, we [Holden Lab @UCSB] seek to understand the origin of the FIB inoculum (i.e. original fecal source) that apparently fluorished in the sediments over the period of sediment excavation, handling, storage, and ultimate disposal to Goleta Beach.”