HR: 1330h
AN: B33E-29    [Abstracts]
TI: Scale-Dependent Thermal Patterns in a Groundwater-Influenced Stream
AU: * Anderson, A D
EM: Ara.Anderson@ndsu.edu
AF: Department of Biological Sciences North Dakota State University, Stevens Hall NDSU, Fargo, ND 58105-5517 United States
AU: Butler, M G
EM: Malcolm.Butler@ndsu.edu
AF: Department of Biological Sciences North Dakota State University, Stevens Hall NDSU, Fargo, ND 58105-5517 United States
AB: Thermal patterns vary on different time scales, with differing consequences for temperature-sensitive organisms. We monitored water temperature at 1/2hr intervals from mid-June through October 2003 along a 30km reach of the Straight River, a spring-fed stream in west-central Minnesota that begins with discharge from a warm-water lake. We analyzed temperature data at 20 sites to describe temperature patterns on scales ranging from hours to days to weeks. Patterns were similar among sites, despite differences in canopy cover or proximity to known springs. Daily thermal flux was typically 4-5° C, but maximum diel oscillations of 7-12° C were seen at most sites. Maximum daily temperatures resulted from net daily changes, and varied over periods of days in response to weather patterns. These diel and longer-term oscillations were superimposed on a broad seasonal pattern of summer warmth and autumnal cooling. Although the incipient lethal temperature for the resident population of Salmo trutta (24.7° C) was exceeded at all but one of 20 sites, only at the lake outlet did these thermal spikes exceed 5hr. Thus brown trout survival in this stream is facilitated both by a general lowering of temperature due to groundwater input, and by natural thermal oscillation on a diel time scale.
DE: 1845 Limnology
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
DE: 9810 New fields (not classifiable under other headings)
DE: 9902 NABS Student Award Applied Research
SC: Biogeosciences [B]
MN: 2005 Joint Assembly