Wave energy level and geographic setting correlate with Florida beach water quality

Abstract

Many recreational beaches suffer from elevated levels of microorganisms, resulting in beach advisories and closures due to lack of compliance with Environmental Protection Agency guidelines. We conducted the first statewide beach water quality assessment by analyzing decadal records of fecal indicator bacteria (enterococci and fecal coliform) levels at 262 Florida beaches. The objectives were to depict synoptic patterns of beach water quality exceedance along the entire Florida shoreline and to evaluate their relationships with wave condition and geographic location. Percent exceedances based on enterococci and fecal coliform were negatively correlated with both long-term mean wave energy and beach slope. Also, Gulf of Mexico beaches exceeded the thresholds significantly more than Atlantic Ocean ones, perhaps partially due to the lower wave energy. A possible linkage between wave energy level and water quality is beach sand, a pervasive nonpoint source that tends to harbor more bacteria in the low-wave-energy environment.

Significance of beach geomorphology on fecal indicator bacteria levels

“…Results from the present study show that beach type is highly associated with exceedance levels, which is consistent with the prior study that found associations between wave energy and FIB exceedance levels (Feng et al 2016). In this study, we categorized the beaches based on geomorphology and found that open coast beaches had the lowest average exceedance, whereas bay beaches had, on average, 4 times the exceedance relative to category 1 beaches.…”

“…They also receive a considerable amount of river and canal input as water is brought to the ocean. Marsh beaches, although not behind barrier islands, are characterized by extremely shallow bottom slopes (Feng et al 2016) and the presence of surrounding wetland areas. It is possible that marsh areas are characterized by different water chemistry and more highly organic coastal sediments that may play a role in the elevation of enterococci.…”

“…They have focused on evaluating measureable water quality and parameters such as temperature (Leight et al 2016), rainfall (Farnham and Lall 2015), nutrient availability (Shelton et al 2014), hydrodynamics (Feng et al, 2013, He et al, 2007, Ge et al 2012, Rodrigues et al 2016), and sediment (Solo-Gabriele et al 2000, Desmarais et al 2002, Frey et al 2015). Some have been more comprehensive in evaluating beach water quality for the states of California (Dorsey 2010, Yamahara et al 2007) and Florida (Feng et al 2016). The prior study by Feng et al (2016) evaluated historical measurements of FIB levels at 262 Florida beaches and demonstrated the associations of water quality exceedances with both wave energy level and geographic distribution in terms of the Atlantic versus the Gulf of Mexico coasts.…”

“…Some have been more comprehensive in evaluating beach water quality for the states of California (Dorsey 2010, Yamahara et al 2007) and Florida (Feng et al 2016). The prior study by Feng et al (2016) evaluated historical measurements of FIB levels at 262 Florida beaches and demonstrated the associations of water quality exceedances with both wave energy level and geographic distribution in terms of the Atlantic versus the Gulf of Mexico coasts.…”

“…Although Feng et al (2016) provided the first baseline water quality assessment in the state of Florida, the geomorphological and man-made features were not taken into account in that study. The objective of the present study was to evaluate whether geomorphological and man-made features observable through satellite imagery were correlated with enterococci bacterial exceedance levels amongst a large data set.…”