Table 1.
Study area precipitation.
Fig 1.
Location of the John Day (a) and Bridge Creek (b) watersheds in OR, USA. Enlarged view (c) depicting the spatial distribution of long-term (black dots, labels are river kilometer) and opportunistic (white dots) monitoring sites on Bridge Creek (black line). Red lines show portions of Bridge Creek treated with beaver dam analog (BDA) structures. Channel scale temperature monitoring locations for the BDA/beaver impounded (white star) and unimpounded (gray star) reaches are also shown.
Fig 2.
Climate, discharge, and stream temperature for the study period.
Seven-day minimum and maximum air temperature range at the study area (a). Seven-day mean discharge measured near the mouth of Bridge Creek (b). Minimum, mean, and maximum daily stream temperatures for monitoring sites located in the cooler upstream (c, river km 32.39) and warmer downstream (d, river km 3.00) reaches of the study area. Gaps in temperature data indicate when a site was not operational, when a logger may have been lost during high flow, or was suspected to have been out of the wetted channel. Right panels show a more detailed view of a single year (2013) of air temperature, discharge, and stream temperatures, with vertical black lines representing astronomical seasons.
Table 2.
Stream temperature monitoring site locations.
Fig 3.
Total number of intact natural dams and BDA structures actively maintained by beaver in the 34-km study area (a), and number of intact natural dams and BDA structures within 500 m upstream of stream temperature monitoring sites that spanned the entirety of the study period (b). Vertical hashed line shows date of BDA structure installation.
Table 3.
Change in wetted channel area.
Fig 4.
Before—After beaver colonization.
Repeat aerial photography from 2005 (upper panel) and 2013 (lower panel) showing location of stream temperature monitoring site at river km 28.45 and increase in upstream pond area due to BDA implementation and proliferation of beaver activity during the study period.
Table 4.
BACI analysis of reach scale stream temperature.
Fig 5.
Distribution of daily stream temperature differences before and after beaver dam increase.
Gaussian distribution of the seasonal difference in daily stream temperatures between the control site with no beaver dams (Rkm 32.39), and sites where dam abundance increased dramatically during the study period. Difference are expressed for each season before (grey curve) and after (black line curve) increased dam abundance for minimum, mean, and max daily stream temperature.
Table 5.
Regression analysis of longitudinal temperature change.
Fig 6.
Longitudinal profile of summer maximum temperatures.
Longitudinal temperature regime on Bridge Creek as the mean of maximum daily temperature observed during August 2014 among 21 monitoring locations. Points at the downstream end of each segment are sized to indicate the number of intact dams and/or beaver maintained BDA structures between monitoring locations. Black dots denote monitoring locations immediately downstream of BDA restoration reaches.
Fig 7.
Regression analysis of longitudinal temperature change.
Linear regressions showing the seasonal relationship between the mean daily longitudinal change in minimum, mean, and maximum temperature and the density of intact beaver dams (dams/km) between each temperature monitoring site. Grey hashed line at 0 provided as a reference for no longitudinal temperature change. Positive regression lines indicate increasing and negative lines indicate decreasing temperatures from up to downstream.
Table 6.
Channel scale temperature variation.
Fig 8.
Channel scale stream temperature heterogeneity.
High-density temperature monitoring locations (upper panels) and hourly stream temperature (lower panels) within the beaver dam/BDA impounded reach (left panels– 22 locations) and the unimpounded reach (right panels– 10 locations). Inset box shows narrow range of stream temperatures observed within the unimpounded reach due to lack of surface water—groundwater exchange.
Fig 9.
Beaver dam induced daily temperature buffering.
Daily temperature regime measured within a beaver influenced site (red line) and the non-beaver influenced control site (black line) over a 10-day period in mid-summer (August 8 –August 17) for a year prior to (2008, left panels) and following (2013, right panels) BDA implementation and natural dam proliferation. Demonstrating buffering of diel temperature cycle (i.e., reduced daily range) in beaver affected sites relative to the control.
Fig 10.
Moderation of maximum summer temperature by beaver dams.
Linear relationship between August maximum daily temperatures measured below the control site with no upstream beaver activity (x-axis, rkm 32.39) and at a site (y-axis, rkm 6.16) prior to (open circles, 2008 and 2010) and following (black circles, 2013 and 2014) development of beaver dam complexes. This regression serves to demonstrate how buffering of daily temperature maxima by beavers minimizes the number of days that temperatures are above or approaching critical thresholds for juvenile steelhead (O.mykiss) during periods of extreme summer temperatures.