A GIS-based method of lake eutrophication assessment

A geographical information system (GIS)-based method of lake eutrophication assessment was undertaken to study the spatial distribution of eutrophicat ion conditions in lake environments. A trophic state index (TSI) consisting of six physical, chemical and biological indicators including total phosph orus (TP), total nitrogen (TN),. chemical oxygen demand (COD), Secchi disk depth (SD), chlorophyll-a concentration (Chl-a) and phytoplankton biomass ( CA) was constructed to describe the eutrophication state of the lake enviro nment. A 0-100 eutrophication. scale was also developed to indicate seven d ifferent trophic levels within the lake environment: oligotrophic, lower-me sotrophic, mesotrophic, upper-mesotrophic, eutrophic, hypereutrophic and ex tremely hypereutrophic. A representation of the spatial distribution of TSI TP, TSITN, TSICOD, TSISD, TSIChl-a and TSICA was developed using the invers e distance weighted (IDW) interpolation method. By categorizing the interpo lated values, a clear illustration of the different trophic levels was deve loped on six thematic maps. A GIS overlay technique was applied to synthesi ze the information from the six thematic maps into a final map illustrating the spatial distribution of eutrophication conditions within the study are a. The different periods or levels associated with lake eutrophication asse ssment using GIS were then discussed. (C) 2001 Elsevier Science B.V. All ri ghts reserved.