Non-traditional abiotic drivers explain variability of chlorophyll-a in a shallow estuarine embayment.

Understanding the factors influencing eutrophication, as represented by concentrations of chlorophyll-a (Chl-a), is needed to inform effective management and conservation strategies promoting ecological resilience. The objective of this study was to evaluate a unique combination of abiotic explanatory factors to describe Chl-a concentrations within the study estuary (North Biscayne Bay, Florida, USA). Multiple linear regression determined the strength and direction of influence of factors using data from 10 water quality monitoring stations. The analysis also considered time scales for evaluating cumulative effects of freshwater inflow and wind. Results show that dominant drivers of Chl-a were temperature, freshwater volume (whose cumulative effects were evaluated up to a 60-day time scale), and turbidity, which were statistically significant at 60, 60, and 70 % of the investigated stations, respectively. All drivers collectively accounted for 22 to 63 % of the variability of Chl-a measurements. Of the nine variables evaluated, nutrient concentrations (orthophosphate and ammonia) were not among the top three overall drivers. Despite nutrients historically being cited in the literature as the most significant factor, this study asserts that non-nutrient factors often govern Chl-a levels, necessitating a paradigm shift in management strategies to bolster estuarine resilience against climate change.

Fecal indicator bacteria levels at a marine beach before, during, and after the COVID-19 shutdown period and associations with decomposing seaweed and human presence.

Studies are limited that evaluate seaweed as a source of bacteria to beach waters. The objective of the current study was to evaluate whether seaweed, along with humans and other animals, could be the cause of beach advisories due to elevated levels of enterococci. The monitoring period occurred a year prior to and through the COVID-19 beach shutdown period, which provided a unique opportunity to evaluate bacteria levels during prolonged periods without recreational activity. Samples of water, sediment, and seaweed were measured for enterococci by culture and qPCR, in addition to microbial source tracking by qPCR of fecal bacteria markers from humans, dogs, and birds. During periods of elevated enterococci levels in water, these analyses were supplemented by chemical source tracking of human-associated excretion markers (caffeine, sucralose, acetaminophen, ibuprofen, and naproxen). Results show that enterococci with elevated levels of human fecal markers persist in the seaweed and sediment and are the likely contributor to elevated levels of bacteria to the nearshore waters. During the shutdown period the elevated levels of enterococci in the sediment were isolated to the seaweed stranding areas. During periods when the beaches were open, enterococci were distributed more uniformly in sediment across the supratidal and intertidal zones. It is hypothesized from this study that human foot traffic may be responsible for the spread of enterococci throughout these areas. Overall, this study found high levels of enterococci in decomposing seaweed supporting the hypothesis that decomposing seaweed provides an additional substrate for enterococci to grow.

Sampling method comparison of enterococci aerosolization during continuous bubble bursting generation.

This study examined the water-to-air transfer and viability of the fecal indicator bacteria, enterococci, and compared capture performance of an impactor and aerosol filter. Results show that concentration of viable enterococci collected by the impactor (70.1 colony-forming units [CFU]/L) was lower than that using the filter (171.2 CFU/L) at 95% significance. Between the impactor and filter, coefficients of variation equaled 13% and 14%, respectively. Hence, for the collection of aerosolized enterococci in a controlled environment, use of the aerosol filter yielded significantly higher recovery relative to impaction, though equally variable data were collected by both methods. This work confirms that viable enterococci transfer across a simulated air-sea interface and that aerosol filters perform well in capturing viable bacteria. Results from this study are relevant to studies that measure environmentally generated aerosols such as those that occur via wave breaking from sewage-contaminated waters.