Responses of soil and water chemistry to mountain pine beetle induced tree mortality in Grand County, Colorado, USA

Pine forest in northern Colorado and southern Wyoming, USA, are experiencing the most severe mountain pine beetle epidemic in recorded history, and possible degradation of drinking-water quality is a major concern. The objective of this study was to investigate possible changes in soil and water chemistry in Grand County, Colorado in response to the epidemic, and to identify major controlling influences on stream-water nutrients and C in areas affected by the mountain pine beetle. Soil moisture and soil N increased in soils beneath trees killed by the mountain pine beetle, reflecting reduced evapotranspiration and litter accumulation and decay. No significant changes in stream-water NO3- or dissolved organic C were observed; however, total N and total P increased, possibly due to litter breakdown or increased productivity related to warming air temperatures. Multiple-regression analyses indicated that % of basin affected by mountain pine beetles had minimal influence on stream-water NO3- and dissolved organic C; instead, other basin characteristics, such as percent of the basin classified as forest, were much more important.

► Soil and water chemistry responses to a mountain pine beetle epidemic were studied.
► Soil moisture and soil N increased, reflecting reduced uptake of water and N.
► Total N and total P in stream water increased, but there was no change in nitrate.
► Stream water NO3 and DOC were strongly influenced by % forest in the study basins.