Water quality, substratum and biotic responses of five central Idaho (USA) streams during the first year following the Mortar Creek fire

Abstract

The Mortar Creek Fire burned 26 000 ha of mixed-conifer Rocky Mountain forest in July-August 1979. Changes in burn stream conditions were examined relative to reference streams for various ecological factors on two to six occasions, from October 1979 to August 1980. Factors included major ions and nutrients, suspended and benthic particulate matter, periphyton (algae), and macroinvertebrates. Elevated levels of most dissolved chemicals in the burn streams were evident soon after the fire and again during spring runoff. However, there were no major disruptions in the relative composition of cations (and presumably of anions also) in the burn streams during the study. Concentration (mg/L) and load (g/s) of some constituents were higher (e.g. NO 3 -N) and of others (e.g. Ca) were lower in the burn than in the reference streams during spring runoff, depending on whether they were normally under biological or geological control, respectively. Suspended sediment and particulate organic matter generally were higher in burn streams, especially during snow-melt runoff or following heavy rain storms. Benthic organic matter was higher in burn streams and was mainly charcoal, compared to the usual leaf litter found in the reference streams. Fine sediments increased and periphyton decreased in the burn streams. The fire increased the sensitivity of the burn streams to more routine smaller-scale disturbances, such as rainstorms, which had major impacts on the burn streams but not on the reference streams. The macroinvertebrate assemblage showed little direct effect from the fire but was severely altered in composition and abundance by the subsequent runoff, scouring, and channel alteration initiated by spring runoff. The burn streams showed considerable individuality in their response to fire depending on the particular set of conditions to which they were exposed. s o f I d a h o s t r e a ms t h e f i r s t y e a r a f t e r w i l d f i r e WF 0 1 0 1 7 G . W a y n e M i n s h a l lA , J a m e s T . B r o c k , D o u g l a s A . A n d r e w s , a n d C h r i s t o p h e r T . R o b i n s o n

Short-term changes in-stream macroinvertebrate communities following a severe fire in the Lake Tahoe basin, California

“…More specialized feeders, such as shredders and scrapers, decreased in abundance. These observations are consistent with previous studies where fire effects were shown to alter functional feeding group abundances and favor community dominance by trophic generalists (Mihuc & Minshall, 1995;Minshall et al, 2001a;Vieira et al, 2004). These results also support general predictions about functional feeding groups, which suggest that shredders will respond to the loss of riparian canopy.…”

Effects of prescribed fire on a Sierra Nevada (California, USA) stream and its riparian zone

“…Although the post-fire increase in NO 3 À , TKN, and total P was not seen in the unburned streams, the measured post-fire concentration was within the pre-fire range of concentrations (Table 7; Bêche, 2005). In general, the direct effects of most fires (prescribed or wildfire) on streams (ash deposition and fire-induced temperature increases) are usually negligible (e.g., Minshall et al, 2001a;Minshall, 2003). However, in the case of some severe wildfires, ash deposition and diffusion of smoke into the water can dramatically increase phosphorous and nitrogen (e.g., Spencer and Hauer, 1991;Minshall et al, 1997).…”

“…Current management practices avoid the use of prescribed burning near aquatic ecosystems (e.g., Erman, 1996) with few exceptions (e.g., Chan, 1998;Huntzinger, 2003). These practices are designed to prevent the potentially negative impacts (e.g., increased erosion or altered hydrographs) that have been found to occur after wildfires (e.g., Roby and Azuma, 1995;Rinne, 1996;Minshall et al, 1995Minshall et al, , 1997Minshall et al, , 2001a.…”

Nutrient concentration dynamics in an inland Pacific Northwest watershed before and after timber harvest

“…Seasonal variability can be due to geochemical weathering, as observed in western Montana (Nagorski et al, 2003), or snowmelt runoff (Sickman et al, 2003;Stottlemyer and Troendle, 1992). Primary producers remove N and P (Minshall et al, 2001;Mulholland et al, 2000), and there can be a high demand for N species, especially during the summer (Peterson et al, 2001). However, compared with other land uses, forestland streams generally have relatively low N and P concentrations (Omernik, 1977;Clark et al, 2001;Ice and Binkley, 2003).…”