Towards experimentally-based environmental flows for infrastructure management in high-altitude tropical streams

Thresholds from flow–benthic fauna relationships in the light of data-scarce hydrosystems constitute an advance in implementing sustainable principles for water infrastructure management. To quantify thresholds the limits to the amount of water that can be withdrawn from Andean river networks before their natural functioning, biodiversity and ecosystem services become degraded, we conducted a whole-ecosystem experimental flow alteration. We reduced flow in the reach of a stream above a water intake from the supply system for the city of Quito, Ecuador. During the low-flow season, we diverted water using a system of weirs to accommodate streamflow in complementary percent (i.e., 90% flow deviation and 10% flow left in the stream). We performed seven reductions and kept them for seven days, during that time we sampled benthic algae chlorophyll-a concentration, flow, temperature, conductivity, light, and measured stream morphology. Our preliminary results indicate a high variability of ecological and physical responses to hydrological alterations in high-altitude tropical streams. A reduction to minimum flow similar to conditions observed for low-flows caused significant changes in stream morphology, and reductions above this threshold evidenced changes in the relative presence of major benthic algae groups.