Response of long- to short-term tidal inlet morphodynamics on the ecological ramification of Chilika lake, the tropical Ramsar wetland in India

Abstract

The long- to short-term morphodynamic response in low-lying coastal wetlands raises serious concerns worldwide about the loss of their biodiversity and ecological ramifications due to change in tidal amplitude and cyclonic events. One such place worth studying is Chilika lake, India, a prominent Ramsar site, the largest brackish water lagoon in Asia, and the second-largest coastal lagoon in the world. It experiences frequent cyclone landfalls and strong littoral drift that tends to open/close the tidal inlet. The goal of this study was to analyze the response of slow onset events such as long- (1952-2020) to short-term (~annual scale from 1989 to 2020) tidal inlet movement, shoreline change (1990-2020 with almost every five-year interval), spit morphodynamics (~annual scale from 1989 to 2020) on ecological ramification in Chilika lake as well as the implications of sudden onset event such as cyclonic landfall. In this study, we used the Digital Shoreline Change Analysis System (DSAS) to compute the statistics of shoreline change rate by calculating end point rate (EPR) values for short-term shoreline change (1990, 1995, 2000, 2005, 2011, 2016, and 2020) and weighted linear regression (WLR) for long-term shoreline change (1990-2020). The results show that Chilika lake experienced both erosion and accretion processes with a remarkably high erosion rate of 19.87 m year^-1 and accretion of 16.91 m year^-1 during a long-term scale (1990-2020). The average erosion and accretion rates were 2.25 m year^-1 and 4.67 m year^-1, respectively, during the past three decades (1990-2020). The short-term analysis suggests that the highest mean erosion of 4.37 m year^-1 occurred during 2005-2011, mainly due to cyclonic storms, reduction in sediment discharge, and lunar eclipse, which induced tide with very high amplitude in August 2008. Overall, the annual scale analysis of tidal inlet shows a shifting trend towards the northward side even after the artificial opening of an inlet in 2000. It can be ascribed mainly to the prevalent direction of longshore drift along this coast. This study observed that the landfall of cyclones significantly affects the spit morphodynamics and opening of the tidal inlet, which defines the inflow of the seawater into the lagoon and further substantial impacts on the ecological ramification. The current study's methodology can be extended to comprehend the response of long- to short-term changes of the tidal inlet, shoreline, and spit morphodynamics on the ecological ramification of coastal lagoons worldwide along with impacts of sudden-onset events caused by cyclonic landfall.

Keywords: Accretion; Digital shoreline analysis system; Ecological ramification; Environmental degradation; Erosion.