Thermal Characteristics of Wisconsin Headwater Streams Occupied by Beaver: Implications for Brook Trout Habitat

Abstract

Expansion of populations of beaver Castor canadensis in northern Wisconsin has raised concerns over warming of coldwater fish habitats as a result of impoundments created by the mammals. We examined temperature with a network of electronic thermographs that recorded hourly water, air, and soil temperatures on four headwater streams occupied by beaver during summer 1990 and 1991. Stream temperatures followed air temperatures, even near groundwater sources. There was no consistent relationship between size or number of beaver impoundments and the degree of downstream warming. Large impoundments, although often warming downstream temperatures slightly, dampened temperature fluctuations immediately downstream. Local groundwater inflow and vegetative and topographic shading also dampened warming by impoundments. Several beaver impoundments were removed to evaluate ensuing temperature changes. Removal of beaver dams did not generally reduce the difference between upstream and downstream temperatures; in some cases dam removal increased the warming rate. Direct thermal benefits of dam removal in headwater streams may be outweighed by the potentially disruptive effects on the composition of fish and invertebrate communities downstream. It is suggested that management focus on relating topographical and geographical attributes to the potential for substantial groundwater discharge and to suitable summer temperatures for coldwater species such as brook trout Salvelinus fontinalis.

Managed Flood Effects on Beaver Pond Habitat in a Desert Riverine Ecosystem, Bill Williams River, Arizona USA

“…This variability has also been noted in mesic regions. McRae and Edwards (1994) experimentally removed dams and found little effect on the difference between upstream and downstream temperatures, attributing the inconsistent insolation effect to local ground water inflow (SE, n). Each mean is calculated from n transect means, with the latter derived from values at three locations on each transect (see Methods); n=1 for Upper Pond and Lotic reaches at PR.…”

“…We expected to find that beaver dam effects on hydrology, water quality, and geomorphology in a desert environment would mirror effects found in mesic environments, i.e., that ponds would warm the surface water (McRae and Edwards 1994;Margolis et al 2001), locally reduce dissolved oxygen concentration (Naiman et al 1986;Snodgrass and Meffe 1998;Smith et al 1991), and trap fluvial sediment (Meentemeyer and Butler 1999). We predicted that net bed aggradation would occur in beaver ponds behind dams that remained intact through a flood event and that pond bottom sediment would become coarser and less well sorted.…”

Beaver Colony Density Trends on the Chequamegon-Nicolet National Forest, 1987 – 2013

“…Stream gradient averages 8.9 m/km on the Chequamegon side and 4.1 m/km on the Nicolet side; because of these low gradients, streams are easily dammed [9]. Water temperatures are regulated by groundwater inflow and degree of vegetative shading [10]. The Forest’s vegetation is composed of mesic mixed northern hardwoods [black ash ( Fraxinus nigra ), American elm ( Ulmus americana ), red maple ( Acer rubrum ), sugar maple ( Acer saccharum ), basswood ( Tilia americana ), oak ( Quercus spp.…”

Water Quality in the Agronomic Context: Flood Irrigation Impacts on Summer In-Stream Temperature Extremes in the Interior Pacific Northwest (USA)

“…Because air temperatures vary across years, and because of the strong influence of air temperature on water temperature (Stefan andPreud'homme 1993, McRae andEdwards 1994), inter-annual variation in air temperature can obscure treatment effects on water temperature. Thus, we compared upper and lower reaches within year.…”

“…shade); under such conditions, fluctuations in water temperature are strongly influenced by parallel fluctuations in air temperature (Stefan andPreud'homme 1993, McRae andEdwards 1994). Flood irrigation can potentially increase in-stream temperature through two mechanisms: 1) decreases in in-stream discharge, and 2) overland flow of warmer flood waters re-entering the stream.…”