EFFECT OF SUCCESSIVE RUNOFF EVENTS ON TURBIDITY IN POST-FIRE WATERSHEDS WITHIN VALLES CALDERA NATIONAL PRESERVE

Changes in soil stability and chemistry resulting from wildland fire can have both immediate and long-lasting effects on downstream water quality. Runoff from burned areas can cause dramatic spikes and dips in measured parameters such as turbidity, dissolved oxygen (DO), pH, and specific conductivity (SpC), which have potential to greatly impact the overall health of the stream and its aquatic communities.

This study was conducted to better understand the behavior and rate by which these parameters’ responses change in magnitude as a result of successive runoff-producing rainfall events on recently burned areas. The effects on water quality were investigated in two streams within Valles Caldera National Preserve, New Mexico whose watersheds were impacted by the 2011 Las Conchas fire. Turbidity, DO, pH, SpC, and discharge were measured during spring-to-fall months at 15-minute intervals between 2006 and 2022, capturing the full record of the fire’s impacts as well as its preceding conditions. The turbidity data were analyzed alongside discharge data to identify, then quantify, the number and magnitude of runoff-related high turbidity events which occurred throughout the watershed recovery process. We also investigated the rate by which DO, pH, and SpC rebounded to baseflow values following each turbidity event.

It was observed that with successive runoff events 7 years post-fire, turbidity spikes reduced in magnitude to values more typical of pre-fire conditions. Other parameters affected by high turbidity events exhibited less dramatic spikes and were able to return to baseflow levels more quickly with subsequent events. While it is widely understood that wildland burn-scars do stabilize to some degree over time, the ability to quantify recovery from an upper watershed perspective is invaluable for post-fire land management practices. Further studies may be able to utilize turbidity-spike trends to model erosion-related watershed recovery timelines.