Estimation of pollution load to Anzali Wetland using remote sensing technique

Abstract

To control pollution sources and prioritize the reduction strategies of pollution, estimating the pollution load and contributing to prevent entering the different pollution sources to the water resources is very important. To estimate the pollution load, detailed quantitative and qualitative information of pollutant is needed. However, ground-based measurement is very costly and time consuming. Instead, approaches based on remotely sensing techniques exhibits very high potential in determining the water quality parameters over an extensive area in a short time period. The aim of this study was to evaluate the possibility of applying remotely sensing data and hydrometric station data to estimate the pollution load entering Anzali Wetland. So that, the quality parameters including nitrate concentration, total dissolved solids, total suspended solids and orthophosphate in the entrance point of three important rivers leading to Anzali Wetland (Bahmbar, Siahdarvishan, and Pirbazar Rivers) was measured at the time of satellites overpassing over the period of November 2011 through August 2012. Pre-processing practices including radiometric and geometric corrections were performed on the Landsat images. Then multi-variable equations were derived for estimating the water quality parameters based on ground truth data and spectral reflections in the range of visible to middle infrared. After validating the accuracy of water quality parameters derived from Landsat satellite images (by statistical indices), the contamination loads of nitrate, total dissolved solids, total suspended solids and orthophosphate entering the wetland were estimated. To assay the contamination load of each parameter, the river discharges were multiplied by the concentrations of these parameters which derived from satellite images in the period of April 2012 through July 2013. The highest pollution load occurred during this period at the entrance of Siahdarvishan River into Anzali Wetland. Comparison of pollution load of nitrate, orthophosphate, total suspended solids and total dissolved solids derived from satellite images during the study period revealed that the Pirbazar and Bahmbar rivers discharged the most loads of pollution to Anzali Wetland respectively.