Skagit headwater streams show a range of sensitivities to thermal inputs from surface processes (e.g. sunlight, air temperature). Some sites located close to channel heads had a stable temperature regime moderated by cool groundwater inputs. However, most sites were responsive to day-night and week-to-week changes in heat inputs, and thus appear to be surface-flux driven.
• Maximum temperatures at Skagit headwater sites were generally similar to those previously recorded in headwater streams monitored elsewhere in western Washington, especially during 2001 and 2002 when summer weather was fairly typical. Skagit tributaries were warmer than other sites during the unusually warm and dry summer of 2003.
• Although the majority of monitoring sites did not exceed regulatory temperature standards, a sizable number did. Of the 97 sites over three years, 24% exceeded the AA standards currently used and 12% exceeded the proposed water temperature system using Core Rearing standards. The less frequent exceedence of the Core Rearing standard suggests that the newer standard is more lenient. This study did not assess which temperature standard is more suitable for supporting downstream fish populations or watershed health.
• Skagit headwater streams, especially those that are surface-flux driven, appear to be sensitive to riparian forest conditions. Clearcut and debris-flow-scoured streams had significantly higher maxima and wider daily ranges during warm periods than did forested or buffered sites.
• Although temperature maxima generally increased in a downstream direction during the typical summers of 2001 and 2002, downstream warming and cooling were both observed during the unusually warm and dry summer of 2003. This appears to contradict the accepted pattern (Beschta et al. 1987, Moore et al. 2005) that streams experience the greatest warming during the lowest flows. We speculate that temperatures during very low flows are increasingly influenced by groundwater inputs and inter-bed exchange, which have a greater relative influence when surface flows are smallest.
• Buffers comprised of 10-30 m of unthinned forest along each side of headwater streams are largely effective at mitigating increases in temperature maxima. Buffered streams have a greater daily range than fully forested streams, a pattern which resembles clearcut streams. Sparse or blown-down buffers appeared to provide little temperature mitigation.
• Regression analysis suggests that lower gradient streams require more shade and thus wider buffers for equivalent temperature mitigation, relative to steeper streams.
• Further research is needed to determine the effects of temperature changes in headwaters affects biological productivity and the extent that warmed water propagates downstream to potentially affect salmonids. This will strengthen the applicability of these results to riparian management strategies.
Veldhuisen, C. and Couvelier, D., 2006. Summer Temperatures of Skagit Basin Headwater Streams – Results of 2001 – 2003 Monitoring. Skagit River System Cooperative, La Conner, WA. pp. 24.
|
0
File Type:
pdf
File Size:
1 MB
Categories:
Contributions