Abstract:

Monitoring quality of water of the lakes is a critical task towards better environmental management. The trophic state index (TSI) is one of important water quality parameters which represents the trophic state of a waterbody. This work proposes a method for monitoring the TSI based on the remote sensing retrieval of chlorophyll-a concentration (Chla) in the lake water. For that, in-situ reflectance data measured in Linh Dam Lake (in Hanoi) was resampled to match ratio of Landsat 8 band 3 versus band 2 and linear regression analyzed with concurrent measured Chla. The ratio of Landsat 8 band 3 versus band 2 provided the best fit model with TSI retrived from measured Chla (R2 value of 0.78). The model was higly matched up with validation Chla data measured on April 1st and 2nd 2017. Resultant time-series map of TSI for Linh Dam Lake show an increasing trend of TSI over time from 2013 to 2016. Accordingly, trophic state of Lake Linh Dam changed from eutrophic level in 2013 to hypertrophic level in 2017. In space, TSI is high along the lake shore where located local sullage pits and decreaded gradually towards lake’s center. Methods used in this work can be extent to monitor TSI for numerous urban lakes in Hanoi.