Multiple Indicators of Wastewater Contamination to Shellfish Farms Near a Tidal River

Ashley Frith,Kevin R Calci,Julian Henseler,Ruth H Carmichael,Shahrzad Badri,Alexandra Stenson

doi:10.1007/s12237-021-01033-x

Abstract

Wastewater contamination threatens the shellfish aquaculture industry by posing risks to public health. Multiple indicators of wastewater contamination, including fecal coliforms (fc), male-specific coliphage (MSC), dissolved nutrients, stable isotope ratios, and artificial sweeteners were analyzed to determine possible sources of wastewater to local shellfish farms. Samples were collected at a wastewater treatment plant outfall (WTPO), nonpoint residential, and agricultural areas of a tidal river, and tidal creek inflows adjacent to farms. To capture seasonal variation, we sampled under warm and cold, and wet and dry conditions. Fc ranged < 5–5250 CFU 100 mL−1, NH4+ concentrations ranged up to 9.58 μM, and δ15N ranged 1.4–7.8‰ across all sites and time periods. Fc and NH4+ were higher, and δ15N was lower in the cold wet period and near residential and agricultural areas. Acesulfame and sucralose concentrations ranged 0.004–0.05 μg L−1 and up to > 0.8 μg L−1, respectively, and did not correlate with other indicators but tended to be higher in residential areas and at the WTPO, supporting their value in differentiating human sewage from other sources. Shoreline disturbance during septic system upgrades may have inadvertently contributed bacterial indicators to shellfish farms. Overall, indicator source dominance depended on environmental conditions, with WTPO and residential sources conveying human-specific indicators to farms year-round, while agricultural and industrial sites contributed additional fc during cold wet periods. The use of multiple indicators will aid managers to detect and define wastewater sources, identify targets for monitoring or remediation, and manage shellfish areas in estuaries with a mosaic of land-derived wastewater sources.

Highlights

Shellfish aquaculture is vulnerable to wastewater inputs that convey human pathogens to receiving waters because shellfish can accumulate pathogens in tissues as they filter feed (Rippey 1994; Burkhardt and Calci 2000)
When data were combined for all sites to test correlations between indicators and temperature, salinity, dissolved oxygen (DO), pH, and particulate carbon (Table 2), we found fc and particulate carbon were positively correlated, and ACE and SUC were each positively correlated with pH, salinity, and with each other during the cold wet period
We found fc concentrations were elevated (WTPO, northern residential sites) or high at all major sources and elevated at the shellfish farms in the cold wet period (Fig. 5a)

Summary

Introduction

Shellfish aquaculture is vulnerable to wastewater inputs that convey human pathogens to receiving waters because shellfish can accumulate pathogens in tissues as they filter feed (Rippey 1994; Burkhardt and Calci 2000). Aquaculture is the fastest-growing food production sector, worth an estimated US $232 billion in 2016 and employing more than 19 million people worldwide (FAO 2018). Of this total value, mollusks, including bivalve shellfish, represented US $29.2 billion (FAO 2018). Wastewater contamination can pose significant health risks and cause economic losses in coastal communities (Evans et al 2016). Successful management of wastewater contamination relies on understanding the sources of wastewater to the

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Conclusion