Nutrient Dynamics in an Alpine Headwater Stream: Use of Continuous Water Quality Sensors to Examine Responses to Wildfire and Precipitation Events

Stream water quality can change substantively during diurnal cycles, discrete flow events, and seasonal time scales. In this study, we assessed event responses in surface water nutrient concentrations and biogeochemical parameters through the deployment of continuous water quality sensors from March to October 2011 in the East Fork Jemez River, located in northern New Mexico, USA. Events included two pre-fire non-monsoonal precipitation events in April, four post-fire precipitation events in August and September (associated with monsoonal thunderstorms), and two post-fire non-monsoonal precipitation events in October. The six post-fire events occurred after the Las Conchas wildfire burned a significant portion of the contributing watershed (36%) beginning in June 2011. Surface water nitrate (NO3[BOND]N) concentrations increased by an average of 50% after pre-fire and post-fire non-monsoonal precipitation events and were associated with small increases in turbidity (up to 15 NTU). Beginning 1 month after the start of the large regional wildfire, monsoonal precipitation events resulted in large multi-day increases in dissolved NO3[BOND]N (6 × background levels), dissolved phosphate (100 × background levels), specific conductance (5 × background levels), and turbidity (>100 × background levels). These periods also corresponded with substantial sags in dissolved oxygen (<4 mg l−1) and pH (<6.5). The short duration and rapid rates of change during many of these flow events, particularly following wildfire, highlight the importance of continuous water quality monitoring to quantify the timing and magnitude of event responses in streams and to examine large water quality excursions linked to catchment disturbance. Copyright © 2015 John Wiley & Sons, Ltd.