The influence of atmospheric deposition of pollutants on cross–domain causal relationships for three tropical freshwater lakes in India

Abstract

AbstractThis long‐term study on three freshwater lakes in India was designed to investigate the following: (i) atmospheric deposition of major nutrient elements; (ii) microbial biomass (Cmic) and activity at the land–water interface and their relation to lake ecosystem functioning, as influenced by catchment inputs; and (iii) the modifying influence of atmospheric deposition on trans‐surface causal relationships. These study results illustrated significant differences (P < 0.001) in the atmospheric deposition of nitrate (), ammonia (), phosphate (), sulfate (), calcium (Ca2+), and magnesium (Mg2+), with consistently rising inputs over time. The interface of Lake Baghdara, characterized by woodland catchment, was found to be rich in phenolics and supported low Cmic and activity. Alkaline phosphatase in humus declined by 13.60–25.30% over time, although the Cmic, SIR, and FDAase at the land–water interface increased significantly in response to atmospheric nutrient deposition. Although it increased primary productivity, nutrient deposition exhibited a significant (P < 0.001) modifying influence on the Cmic and lake productivity relationships, with a time lag of 3 years. A substantial increase in dissolved organic carbon (DOC), especially in Lake Baghdara, indicated that the modifying influence of atmospheric deposition on microbial biomass and activity at the land–water interface could significantly alter the carbon capture and storage in surface waters and consequently future carbon balance and climate change processes. This study demonstrated that, if present trends of atmospheric deposition of pollutant elements continue, they can modify the microbial processes at the land–water interface and productivity of lakes and will alter the cross–domain causal relationships of freshwater tropical lakes over the long term.