Wildfire impacts on water quality, macroinvertebrate, and trout populations in the Upper Rio Grande

Abstract Forest fires affect water quality in disrupted watersheds, which can impact aquatic ecosystems including sensitive macroinvertebrates and fish. The West Fork Complex (WFC) fire consumed 44,360 ha of forest in the state of Colorado during the summer of 2013. Damage to the soils was of moderate to high severity in the majority (60%) of the area. The fire surrounded the headwaters of the Rio Grande, affecting water quality and habitat critical to aquatic insects and fish. The current research investigates whether there was a measurable effect on the water quality, insect diversity and fish populations within and downstream of the burn area. Parameters important to the survival of aquatic life, such as discharge, temperature, dissolved oxygen, pH, conductivity, total dissolved solids, total suspended solids, and concentrations of metals and nutrients were measured regularly in the Rio Grande and some of its tributaries for three years after the fire. Macroinvertebrate and fish populations were sampled annually. Precipitation, flow and turbidity data revealed monsoon rain events delivered sediments into the Rio Grande and its tributaries from steep, severely burned hillslopes. The monsoon events caused acute and dramatic fish kills, where hundreds of trout were reported killed in one tributary in a single day event. Turbidity was observed as high as 505 NTU in the impacted stream during the fish kill event and turbidity regularly reached 3000 NTU during subsequent precipitation events. Despite elevated turbidity levels that persisted for three years downstream of severely burned areas, the aquatic ecosystem appears to have recovered. Insect diversity and fish populations recovered to pre-fire levels and were similar to control sites within three years. Results indicate aquatic ecosystems can be resilient to largescale disturbances, such as wildfire.