Assessing Water Quality Dynamics in Tidally Influenced Blackwater Rivers along a Rural–Urban Gradient

Abstract

The aim of this research was to identify the impacts of land use and subsequent pulse-driven events on water quality across a gradient of urbanization spanning three blackwater rivers in northeast Florida that contribute to a common estuary ecosystem. Three blackwater rivers in St. Augustine, FL, were classified as rural, suburban, and urban, based on percentages of residential, industrial, and commercial parcel type. Turbidity, dissolved oxygen, fluorescent dissolved organic matter, chlorophyll a, salinity, and pH were measured at 15 min intervals from May to December 2020. Monthly phosphate, nitrate, ammonium, total coliforms, and E. coli concentrations were also examined. Principal component analyses identified the distance to the freshwater source, distance to the inlet, salinity, dissolved oxygen, and pH as major sources of variance between the sites. Significant physicochemical differences between sites are more likely due to a site’s proximity to an inlet or freshwater source, rather than the percent of urban parcels, and site distance to freshwater and saltwater influences should be considered due to its influence on water quality in estuarine systems. This study provides insight into potential water quality responses to urbanization, or lack thereof, and addresses challenges in selecting the optimal site locations for long-term in situ water quality monitoring studies of urbanization in blackwater rivers.