Lacustrine Records of Anthropogenic Change and Precipitation in the Monsoonal Core Zone of Central India since the Last Century

Abstract

A sediment core from the Navegaon Bandh Lake (NBL) was studied for diatoms and sediment geochemistry to investigate the anthropogenic impact and climatic variability over the past century. The declined geochemical concentrations show three major impacts on the NBL coinciding with the drought events in the foremost parts of India around 1918, 1975, 1965 and 1991. The rise in the geochemical content of the NBL core was evident in the post dam construction period (i.e., ~1917–1919) with the two major peaks around 1975 and 1998. These major peaks are indicators of the higher rate of soil erosion and improved precipitation in the catchment of the NBL. Anthropogenic activities have caused five major changes in diatom assemblages and ecology in the NBL around 1946, 1956, 1972, 1978 and 2006. The increased agricultural activities in the catchment of the NBL are evident since ~1906–1966 as the fertilizers (K, P) are mainly derived other than soil particles of the catchment. Similarly, deforestation in the region was evident during ~1967–1975 coinciding with the period of the highest soil erosion. Another major phase of soil erosion caused by anthropogenic activities was noticed during ~1992–1998. The hypolimnetic oxygen of the NBL has declined for the past ~80 years indicating increased eutrophication in the lake till the present. The nutrient input in response to climatic conditions and anthropogenic activities has played a vital role in the diatom shift of the NBL. Aulacoseira granulata was predominant during ~1906–1914, ~1920–1922, ~1941–1943, ~1948–1956, ~1972–1976 and ~1973–1982 in the NBL signifying the increased soil erosion and flux, persistent wet period and increased nutrient levels. While the major period of the profusion of Rhopaloidea musculus in the NBL core was during ~1919–1921, ~1933–1940, ~1956–1972 and ~1978–2004, respectively, indicating a mesotrophic, Meso euhyaline and alkalibiontic condition of the lake linked with the long dry period/less rainfall prevailed in the NBL watershed. The planktonic form Discostella stelligera was common during ~2007–2012 and indicates the existence of alkaline lake waters with moderate nutrients coinciding with the comparatively dry period/less rainfall and changing water level and deforestation in the catchment of the NBL. Overall, the investigation of the past evidence shows the importance of the study of fossil diatoms and geochemistry to understand the anthropogenic and precipitation changes along with the trophic status of the lake, which may be used for the management of the tropical wetlands in India.