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 eutrophication conditions in lake environments. A trophic state index (TSI) consisting of six physical, chemical and biological indicators including total phosphorus (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 environment. A 0–100 eutrophication scale was also developed to indicate seven different trophic levels within the lake environment: oligotrophic, lower-mesotrophic, mesotrophic, upper-mesotrophic, eutrophic, hypereutrophic and extremely hypereutrophic. A representation of the spatial distribution of TSITP, TSITN, TSICOD, TSISD, TSIChl-a and TSICA was developed using the inverse distance weighted (IDW) interpolation method. By categorizing the interpolated values, a clear illustration of the different trophic levels was developed on six thematic maps. A GIS overlay technique was applied to synthesize the information from the six thematic maps into a final map illustrating the spatial distribution of eutrophication conditions within the study area. The different periods or levels associated with lake eutrophication assessment using GIS were then discussed.