Satellite-Based Study of Seasonal Variability in Water Quality Parameters in a Tropical Estuary along the Southwest Coast of India

To sustain a healthy ecosystem, continuous monitoring of the water quality is vital. Ocean colour remote sensing is an important tool to carry out such studies. Thus, chlorophyll-a (Chl-a), chromophoric dissolved organic matter (a440), turbidity (T) and sea surface temperature (SST), among others, have been considered in the present study to evaluate the water quality of the Cochin Backwaters, a tropical estuary along the southwest coast of India. Landsat 8/OLI data have been used to derive the water quality parameters (WQP), and seasonal averages have been estimated to study the variations occurring in the area during 2014–2018. These were then plotted against the river runoff occurring in the area to find out its impact upon the said parameters. The results showed that the a440 and Chl-a concentrations were related to the runoff of the area as both the parameters were at their peaks during the southwest monsoon season with values approximately more than 1.6 m and 5.6 mg/m, respectively. However, in the other seasons, a440 was not seen to directly correspond with the runoff in the area. Turbidity was observed to be the highest during the spring inter-monsoon season (SIM) with values reaching more than 60 FNU. As far as the surface temperature of the estuary is concerned, it was found to be around ~ 25 °C for most parts of the year, except for the southwest monsoon season when the temperature dropped below 25 °C. Interannual variability of the WQP showed that they were at their highest in 2014 followed by 2016, 2017 and 2018, while the year 2015 had the lowest concentration. The study also brings out the utility of ocean colour remote sensing products as an alternative to study the Indian coastal and estuarine waters.