Climate relationships to fecal bacterial densities in Maryland shellfish harvest waters. (1st February 2016) - Leight, A.K.
Abstract: Coastal states of the United States (US) routinely monitor shellfish harvest waters for types of bacteria that indicate the potential presence of fecal pollution. The densities of these indicator bacteria in natural waters may be related to climate in several ways, including through runoff from precipitation and survival related to water temperatures. The relationship between interannual precipitation and air temperature patterns and the densities of fecal indicator bacteria in shellfish harvest waters in Maryland's portion of the Chesapeake Bay was quantified using 34 years of data (1979–2013). Annual and seasonal precipitation totals had a strong positive relationship with average fecal coliform levels (R 2 = 0.69) and the proportion of samples with bacterial densities above the FDA regulatory criteria (R 2 = 0.77). Fecal coliform levels were also significantly and negatively related to average annual air temperature (R 2 = −0.43) and the average air temperature of the warmest month (R 2 = −0.57), while average seasonal air temperature was only significantly related to fecal coliform levels in the summer. River and regional fecal coliform levels displayed a wide range of relationships with precipitation and air temperature patterns, with stronger relationships in rural areas and mainstem Bay stations. Fecal coliform levels tended to be higher in years when the bulk of precipitation occurred throughout the summer and/or fall (August to September). Fecal coliform levels often peaked in late fall and winter, with precipitation peaking in summer and early fall. Continental-scale sea level pressure (SLP) analysis revealed an association between atmospheric patterns that influence both extratropical and tropical storm tracks and very high fecal coliform years, while regional precipitation was found to be significantly correlated with the Atlantic Multidecadal Oscillation and the Pacific North American Pattern. These findings indicate that management of shellfish harvest waters should account for changes in climate conditions and that SLP patterns may be particularly important for predicting years with extremely high levels of fecal coliforms. Graphical abstract: Highlights: Fecal coliform levels in MD waters correlate to precipitation and air temperature. The strength of these relationships differs between rivers and seasons. A delay in timing often exists between peaks in precipitation and fecal coliforms. Existing climate indices are not well correlated to fecal coliform levels. Sea-level pressure patterns correspond to years of very high fecal coliform levels.