Hydrological and landscape dynamics of floodplain wetlands of the Diara region, Eastern India

Abstract

Wetland dynamics research primarily concentrates on individual wetland’s loss or gain of area where landscape specific approach is majorly ignored. While the fate of floodplain wetlands depends largely on the actions of the parent rivers such as increased flow, channel migration path, flooding events, channel cut-offs and others that are rather episodic in nature, so the overall situation may not be defined by the loss or gain of any specific wetland. Therefore, instead of using individual wetland-specific strategies if landscape-specific approaches are adopted, it might be possible to better interpret the wetland scenario. From this perspective, the floodplain wetland dynamics of the Diara region which is an active floodplain region of River Ganga has been assessed in three key dimensions like spatial, hydrological, and landscape ecological. Centroid method, hydro-period analysis, water presence, threshold dependent NDWI-NDVI are the key methods used for spatial and hydrological dynamics. A new method of Mean NDWI-NDVI Depth (MNND) has been introduced to measure the hydrological change in the wetlands. Few major landscape ecological metrics have been calculated using FRAGSTATS and lastly, the forest fragmentation rules are adopted to divide the wetland landscape into patch, edge, perforated and core areas. The result shows that wetland dynamics are very much unpredictable and strongly influenced by the behaviour of River Ganga. The wetland area has significantly gone up to 12095.37 ha in 2011 from 6795.9 ha in 1991 due to massive flood of 2010 and again it has gone down to 5725.35 ha in 2019. In 2019 the wetland centroid location has moved 2.14 km away from 1991′s centroid location in the opposite direction where River Ganga exists. Most of the wetlands are here heavily fragmented into smaller patches that results into the presence of only 10% core wetlands. Thus the vast portion of the floodplain wetlands can be degraded at any time due to hydrological instability, severe fragmentation and over-dependence on episodic events like floods.