The effects of mountain pine beetle killed trees on water quality in north-central Colorado

The beetle epidemic in Colorado continues to decrease the forest canopy, resulting in decreased precipitation interception and decreased summer evapotranspiration. A progression of beetle-killed watershed areas in Northern Colorado was used to assess if water yield increases are measurable using nearby relatively undisturbed watershed as a paired watershed study. Hypothesized changes in hydrologic process rates suggested increased soil moisture and thus increased annual water yield (streamflow). Surprisingly, water yield increases were not always detected, nor were other flow metrics - low or peak flows. The literature suggested that the disruption of nutrient cycles will result in increased nitrate-nitrogen concentrations, but such increases were not measured. Nitrate/nitrite concentrations remain very low and did not exceed 5μg/L. Measured concentrations of total trihalomethanes (TTHMs), drinking water disinfection byproducts, exceeded the 80 μg/L national drinking water quality standard approximately 95% of the time. TTHM formation potential was positively correlated with increased total organic carbon and turbidity in surface waters. Water quality samples from undisturbed forested watersheds also frequently exceeded the standard, thus the beetle activity does not necessarily portend a loss in water quality from forested watersheds.