Ecosystem Responses to Pollution in the Ganga River: Key Issues to Address River Management

From over five decades, there has been a rapid increase in pollutant concentration in the Ganga River. Much of the debates about the rising pollution in the rivers have been focused on urban sewage input and its associated increase in biological oxygen demand (BOD). Here, we present an overview of explicit multifactor causation, ecosystem-level shifts, multiform determinants (nutrient stoichiometry, transparent exopolymeric particles (TEP), diatom dominance-diversity linkages, microbial extracellular enzymes (EE), ecological response index (ERI), and ecosystem feedbacks), and alternative response indicators to address shifts in ecosystem functions coupling human perturbations. Based on a critical analysis of available studies/data and emerging trends, we argue that anthropogenic influences on the Ganga River are far more severe than what is being predicted from short-term small-scale studies. At many locations, especially those located downstream of point sources, the river is overstepping its resilience as demonstrated by dissolved oxygen deficit at sediment-water interface and associated feedbacks (denitrification, sediment-P and sediment-metal release). Because in human-impacted rivers eutrophication and metal pollution generally occur simultaneously, the EE, ERI, and TEP-diatom linkages provide novel tools to assess how the human activities might impact ecological functioning and assimilation capacity of the Ganga River. These issues set the stage for understanding and assessing current and possible future changes on which the Ganga River management strategies can be keyed.