Reservoir Trophic State Evaluation Using Landsat TM Images and Geostatistical Simulation

摘要

Reservoir water quality is traditionally monitored and evaluated based on field data collected at limited locations. Whether the limited field data represent the overall trophic state of a vast water body is often disputed. In this study we utilize Landsat TM data to evaluate the overall trophic state of Te-Chi Reservoir in Central Taiwan. Three water quality parameters: concentrations of chlorophyll-a, total phosphorous measurement, and secchi disk depth, are found to have high correlations with transformed spectral features derived from bands 1, 2, 3 and 4 of TM data. Therefore, TM data are used to yield a trophic-state-index (TSI) map of the reservoir. We then apply the geostatistical simulation technique to generate a large number of TSI realizations. Using these realizations probability distribution of the overall reservoir trophic state can be estimated. TSI cutoff values of 60.6 and 73.5 are used to signify the reservoir trophic state of eutrophication and hypereutrophication. The reservoir trophic state is considered eutrophic or hypereutrophic if the probability that the overall TSI exceeds the cutoff value (60.6 or 73.5) is greater than 0.9. Based on this criterion, the trophic state of Te-Chi reservoir is found to be eutrophic, and occasionally hypereutrophic.