Benthic macroinvertebrate flow sensitivity as a tool to assess effects of hydropower related ramping activities in streams in Ontario (Canada)

Within Canada, hydro-electric power is the leading source of energy for households and industry. It is thus critical to understand and minimize its ecological impacts, by developing management guidelines for hydropower operations. Flow peaking is a common practice at hydroelectric facilities as hydropower generation often tracks the demand in electricity, and understanding its ecological impacts is key to developing sustainable river management guidelines. Based on standard macroinvertebrate biomonitoring data, the Canadian Ecological Flow Index (CEFI) is a tool to assess flow sensitivity based on Canadian rivers. Having already demonstrated its utility to detect changes in flow conditions, CEFI was applied in this study to investigate the ecological effects of altering a peaking hydropower scheme, specifically by changing the ramping rate, or the rate of change of flow from minimum to maximum and back in a peaking cycle. Data were collected in two proximate rivers in Ontario: one experiencing hydropower ramping and the other with a natural flow regime, allowing the detection of the effects unlimited ramping using a BACI (Before-After/Control-Impact) design. In the regulated river, the first two years of the study were subjected to restricted ramping rate practices while unlimited ramping was permitted thereafter. Hydrological data were collected at each station and used to compute a series of 33 Indicators of Hydrologic Alteration (IHA) metrics to characterize the ecohydrological condition of the river systems. The benthic community responded to changes in ramping rate and CEFI was able to discriminate the alteration signal and to diagnose the impact. Hydrological descriptors of the effects of the ramping activities were clear drivers of the CEFI variation in the hydropower-ramping site. This study is the first to apply the CEFI approach to a BACI in situ experiment. The CEFI tool again proved to be a useful indicator of flow alteration, with great promise for its use in the development of hydroecological management guidelines.