Abstract
Fecal indicator bacteria (FIB) are used in U.S. water quality regulations as sentinels of water quality in safeguarding public health from potential waterborne diseases caused by fecal pathogens transported through aquatic environments. Regulatory indicators Escherichia coli (E. coli) and enterococci are routinely monitored but abundance of FIB as measured at any one location and time is difficult to link to sources in human activities, land uses, unintended releases from sewage infrastructure, or non-human warm-blooded animals due the effect on measured abundance at any time or place by the dynamic nature of the natural systems. This research examines the impact of one type of confounding factor, - tidal mixing in the water column and re-suspension of sediments, both of which may contain reservoirs of FIB from previous discharges and may intermix non-human originating FIB with anthropogenic sources in the watershed. The research uses samples taken at time that control for tide stage and level to quantify measured abundance and variability in the abundance of FIB in one target waterbody: along a 10.5 km tidal reach of the Imperial River in Bonita Springs, Florida. Samples were collected at four locations over the course of 6 sampling events, all conducted under conditions of ‘robust outbound tide’, i.e., moderate to high velocity ebb tide during one wet-weather season, July through September 2021. Results show a mean of 240.3 ± S.D. 131.6 MPN/100 mL for E. coli and a mean of 246.3 ± S.D. 133.7 MPN/100mL for enterococci, which is substantially less variability than observed in previously published research and agency studies in the same and nearby similar waterbodies. Results are used to characterize sources of FIB within the watershed, which leads to the conclusion that FIB inputs from those activities vary substantially less than the observed variability within the waterbody when not controlled for tidal processes. Conclusions also document that FIB abundance in the Imperial River exceeds the regulatory standards during these tide-controlled conditions, suggesting that bringing the waterbody into compliance will require efforts to reduce sources in the watershed. The method is identified as an effective means for agencies responsible for similar waterbodies to determine whether FIB impairments originate inland in developed watershed or are caused by variability in abiotic factors.
