IMPACT OF LARGE RESERVOIR ON AQUATIC BIODIVERSITY; FROM MICROBES TO MEGAFAUNA

Abstract

The worldwide surge in constructing massive dams for irrigation and hydropower has essentially rewritten the rules for freshwater life. We are seeing a fundamental shift where naturally flowing (lotic) rivers are being turned into still, lake-like (lentic) reservoirs. This review dives into the ripple effects of this change, showing how it affects everything from the smallest microbes to the largest river animals. When these dams block a river, they don't just stop water; they disrupt sediment flow and cause the deep water to lose oxygen a process called benthic hypoxia. These shifts start at the very bottom of the food chain. The balance of plankton is thrown off, which frequently triggers harmful algal blooms and break the natural microbial loop. Once you combine this "bottom-up" damage with the fact that habitats are being fragmented, the results are pretty grim: many small water creatures vanish, and specialized fish species start going extinct. For the "big" wildlife, like river dolphins and migratory fish, these reservoirs are basically brick walls. They get cut off from their families, leading to genetic issues and a much higher chance of disappearing forever. On top of that, climate change makes everything worse. Since these rivers are now "managed" by humans, they aren't nearly as resilient as they used to be when it comes to handling heatwaves or unusual rainfall patterns. To stop this downward spiral, the review argues that we need to get smarter with adaptive management using tool like environmental flow rules and nature-based solutions. If we actually want to save what’s left of our freshwater heritage, we have to start filling the gaps in our research with better genetic tracking and basin-scale mapping.