Florida Wetland Condition Index for depressional forested wetlands

Abstract

Increasingly in the last decade biological monitoring and assessment have been used by federal and state agencies to assess water quality standards as required under the Clean Water Act. These efforts have led to the development of indices of biological integrity (often referred to as IBIs). Many states have created multi-metric indices, incorporating individual metrics into a quantitative value of community condition or biological integrity. The primary objective of this study was to develop the Florida Wetland Condition Index (FWCI) as a tool to evaluate the biological integrity of Florida depressional freshwater forested wetlands. Vegetative community composition and chemical and physical water and soil parameters were measured at 118 wetlands throughout Florida. An independent measure of the human disturbance gradient, the Landscape Development Intensity (LDI) index, which is based on the use of nonrenewable energy within a 100 m buffer around a wetland, was calculated. Six macrophyte community composition metrics were selected for inclusion in the FWCI based on the strength of correlation with LDI (P < 0.01) and differentiation between low (LDI < 2.0) and high (LDI ≥ 2.0) LDI groups (P < 0.01). The metrics included tolerant indicator species, sensitive indicator species, exotic species, floristic quality assessment index, native perennial species, and wetland status species. Metrics were scaled between 0 and 10, with 10 representing the reference wetland condition (correlating to wetlands in undeveloped landscapes). Scaled metrics were then added together to create the FWCI, with values ranging from 0 to 60. The FWCI was significantly correlated with LDI (P < 0.001), and significantly differentiated among sample wetlands categorized by low and high LDI groups (P < 0.001). In addition, significant correlations were found among the six metrics, FWCI, and LDI with measured chemical and physical water and soil parameters, including water column pH, turbidity, ammonia-nitrogen concentration, and total phosphorus concentration, and soil moisture, organic matter, total Kjeldahl nitrogen, and total phosphorus concentration. The primary efficacy of the FWCI was the calculation of a quantitative value of biological integrity for wetlands across a gradient of anthropogenic land use activities, which can be used objectively to assess water quality standards of Florida wetlands.