LET IT FLOW: DEFINING ENVIRONMENTAL STANDARDS FOR WATER ABSTRACTION IN TROPICAL ANDEAN STREAMS

Abstract

The role that environmental flows (e-flows) have in aquatic ecosystems can be explained by the type and extent of processes that are promoted. The establishment of e-flow recommendations is necessary for the restoration and conservation of rivers and streams but requires interdisciplinary research with a strong ecohydrological perspective. At the currently rapid pace of water infrastructure development in Andean ecosystems, this goal will not be feasible without adaptive frameworks, cutting edge tools, and experiments to address ecological responses to flow alterations. Environmental standards for water abstraction in most ecosystems require water managers involvement to ultimately implement guidelines and provide feedback for applied research. Thus, I initially assessed aquatic invertebrate and impacts associated with water abstraction controlled by a water supply company operating in tropical Andean streams of Ecuador. With their cooperation, I explored the opportunity to propose a framework for decision scaling based on research into “flow” thresholds for restoring and maintaining natural ecohydrological processes. Flow thresholds are critical breakpoints in flow-ecology relationships where fundamental ecosystem functions abruptly shift from natural conditions. Often biotic responses to flow changes incorporate large amounts of noise that make it difficult to discern thresholds or ecological limits of change. I used an in situ experimental approach to identify e-flows thresholds for water abstractions. Thresholds for bioindicators of water quality are of utmost interest to water supply systems. So, in addition to using aquatic invertebrates, I evaluated the feasibility and reliability of an in situ fluorometer for assessing benthic algae and cyanobacteria. Results based on the flourometer were comparable to more complicated and time-consuming standard laboratory-based methods. I designed, tested, and used a novel ecohydraulic stream-diversion structure to address the response of cyanobacteria to in situ flow alterations in an experimental stream reach. Through a series of systematic flow reductions and subsequent flow recoveries, I identified e-flow thresholds at a 60% reduction of natural flows at which point there were clear increases in cyanobacteria biomass. Interestingly, there was consummate reduction in cyanobacteria biomass when flow was restored to 60% of the natural flow. These results generally agree with a meta-analysis of global literature on flow-benthic biomass relationships. Thus, my research concludes that there are e-flow thresholds associated with benthic biomass and that these likely vary over a narrow range in alpine environments around the world. Such shifts in rivers are crucial for defining e-flows as standards for water abstractions, specifically in tropical Andean streams.