Riverine Ecosystems

Applications of River Health Assessments, riverine habitat integrity, and reservoir management for conservation across Indian river systems.


River systems are complex ecohydrological systems with a historical significance for human civilization. While there is a growing understanding of the ecosystem services they provide, the impacts of human influence on these dynamic systems are poorly understood. There is a need for a comprehensive measure of assessing the health of rivers and the effects of anthropogenic influence on rivers. River Health Assessments or RHAs are a potential tool to monitor and guide protection, restoration and management of river systems. As a tool, RHA is still in its developmental stages in the country. Most RHA studies in India have been based on a few water quality parameters. At the Freshwater Ecology and Ecosystem Services (FEES) working group in ATREE, as a part of a project in collaboration with WWF, India, we have been developing a field based, multi-dimensional and comprehensive measure of river health, and conducting the field work in the rivers Moyar, Bhavani and Noyyal in Tamil Nadu. Our RHA includes multiple parameters and indicators of river health, including water quality measures, hydrological parameters, ecological and biodiversity indicators like freshwater fish, macroinvertebrate and diatoms compositions, and catchment and bank characteristics. In my talk, I will present some insights from this ongoing study from two seasons of data.

Much of the globally significant habitats of freshwater species such as gharial and Indian Skimmer are now downstream of dams and barrages, and subject to heavily depleted dry-season flow conditions and unseasonal flooding. We examined the impacts of flow modifications on breeding outcomes for the critically endangered gharial Gavialis gangeticus and the endangered Indian skimmer Rynchops albicollis in a regulated river system in central India.
We use primary and secondary data within an integrated life history-hydrological framework to estimate dry-season ecological flow requirements in the Son Gharial Sanctuary by assessing (a) post dam flow conditions, (b) dam operations and breeding disruptions, and (c) feasibility of dam re operation, sediment management and modified rule curves to minimize ecological risks. We also quantify trade-offs in irrigation and hydropower potential in such a scenario.

The Nilgiri shola-grasslands have seen significant reduction in the area during the last two centuries due to the spread of introduced exotic vegetation. Initially introduced to make the grasslands more productive and meet the demands of firewood, many of these exotics have turned invasive and taken over large areas of the landscape causing significant impacts to the local ecology, particularly having hydrological ramifications. We at the ‘Freshwater Ecology and Ecosystem Services’ lab have been studying the hydrologic impact of three specific invasive exotic vegetation- Black wattle (Acacia mearnsii), scotch broom (Cytisus scoparius) and gorse (Ulex europeaus) in the Upper Bhavani region of the landscape. This multi-scale study uses a combination of tools like soil moisture sensors and sapflux sensors were used to understand hydrological impacts of invasion. Soil moisture sensors let us compare the soil moisture across landcovers which could be due to the abstraction of water by these species along with evaporation. Sapflow sensors tell us the amount of water being taken up by individual black wattle trees which could be scaled up to a larger area. I plan to present dry season hydrological impacts measurements made using the data from these methods. Our data throws light on the extent of water abstraction by the invasives and furthers the case for restoration of the landscape.