Linking Watershed, Soil and Landuse Characteristics to the Spatial Variability of In-stream Water Quality in Selected Florida Watersheds

Frederick B. Bradley

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, Department of Environmental Science Policy and Geography, College of Arts and Sciences, University of South Florida St. Petersburg

Abstract

This thesis characterized terrestrial source and aquatic sink relationships of water mediated transport of terrestrial materials from the adjacent terrestrial source (watersheds) to the aquatic sinks (streams and coastal waters). Previous researchers noted that coastal waters of the West Florida Shelf showed variation in concentrations of Colored Dissolved Organic Matter (CDOM) along the north-south gradient. It was hypothesized that since the dominant constituents of CDOM are derived from terrestrial sources, characterization of the adjacent watersheds in terms of their source and water mediated transport potential of terrestrial materials to the aquatic sinks would help explain the variability reported along the north-south gradient. Watershed characteristics analyzed for this study included: soils properties; slope; landuse properties; rainfall and in-stream discharge; as well as Apparent Color (AP) and Total Suspended Solids (TSS). These soil, slope, and landuse based analysis were integrated in a Geographic Information System (GIS) and were further divided into: soil-, model-, flowpath- and landuse-based analysis to quantify source and transport potentials for the watersheds. Due to lack of long-term riverine CDOM data, this research used AP and TSS as a surrogate for water mediated terrestrial sources of materials. The watersheds were grouped into northern watersheds (Group A: Alafia and Hillsborough) and southern watersheds (Group B: Manatee and Peace) based on CDOM concentration and constituent differences noted by other researchers. Results showed that compared to the Group A, the Group B watersheds had a xviii higher potential for source materials as well as watershed characteristics that facilitated water mediated transport of terrestrial materials to the aquatic sinks. The Group B watersheds showed: higher OM; increased highly erodible soils; higher erosion potential; presence of high and very high slope-lengths; increased southeast facing slope (hence increased biomass); increased slope characteristics associated with acceleration and divergent flow (facilitating soil erosion and sediment transport); and dominant agricultural landuse . Since Group B watersheds showed increased source and transport potential as well as increased AP & TSS values under similar rainfall conditions, this research results may be able to help explain some of the variability noted by other researches in terms of CDOM concentration along the north-south gradient. Many terrestrially-derived materials interact and influence water quality parameters and consequently the health of aquatic systems. This thesis aimed to enhance understanding the role of watershed’s characteristics in this vital land (source) -water (sink) relationship and associated water mediated materials transfer.