Developing an Index of Biotic Integrity for Streams and Wadeable Rivers in Mississippi

The total maximum daily load (TMDL) process requires that water resource systems (such as, streams, rivers, lakes, reservoirs, and wetlands) be evaluated for overall ecological condition, and if assessed as impaired, improved to meet their designated use(s). As of 1999, approximately 700 waterbodies in Mississippi had been listed as impaired (i.e., 303(d) listed), however, little or no quantitative data were used in establishing approximately 550 of these listings. Therefore, the Mississippi Department of Environmental Quality (MDEQ) initiated a project to re-evaluate the state's 303(d) listed streams using biological data. These data are to be calibrated according to reference conditions and summarized in a multimetric Index of Biotic Integrity (IBI) that can be used for assessing the overall ecological condition of sites, as well as evaluating the effects of nutrient enrichment, sedimentation, habitat impairment, and land use conversions. Additionally, an IBI can aid in establishing restoration and remediation goals, tracking the effectiveness of restoration and remediation activities, and developing watershed management strategies. Approximately 130 sites were selected as candidate reference sites based on their location in natural settings according to multiple resolution land cover (MRLC) data or based on personal knowledge of the stream. Over 450 stream locations (303(d) listed and reference streams) were sampled over a 6–7 week period during a winter index period spanning January – March, 2000. Data collected at all sites included field chemistry (pH, water temperature, specific conductance, TDS, turbidity, and dissolved oxygen), water grab samples for laboratory analytical chemistry (COD, TOC, TP, TKN, NH4, nitrate/nitrite, total alkalinity, and total chlorides), physical habitat (visual-based habitat quality assessment and modified 100-particle Wolman pebble count), and benthic macroinvertebrates (multiple-habitat approach). Development of an IBI involves selection of reference and stressor sites according to physical, chemical, and land use data, and subsequent determination of the biological measures (metrics) that most consistently respond to stressor conditions as indicated by abiotic data. Once metric testing and selection has been completed, the IBI is constructed, and narrative ratings that describe stream impairment status are developed. These ratings will be used for assessing the status of 303(d)-listed streams (i.e., whether listing or de-listing should occur).