Land-Cover and Climatic Controls on Water Temperature, Flow Permanence, and Fragmentation of Great Basin Stream Networks

Abstract

<jats:p>The seasonal and inter-annual variability of flow presence and water temperature within headwater streams of the Great Basin of the western United States limit the occurrence and distribution of coldwater fish and other aquatic species. To evaluate changes in flow presence and water temperature during seasonal dry periods, we developed spatial stream network (SSN) models from remotely sensed land-cover and climatic data that account for autocovariance within stream networks to predict the May to August flow presence and water temperature between 2015 and 2017 in two arid watersheds within the Great Basin: Willow and Whitehorse Creeks in southeastern Oregon and Willow and Rock Creeks in northern Nevada. The inclusion of spatial autocovariance structures improved the predictive performance of the May water temperature model when the stream networks were most connected, but only marginally improved the August water temperature model when the stream networks were most fragmented. As stream network fragmentation increased from the spring to the summer, the SSN models revealed a shift in the scale of processes affecting flow presence and water temperature from watershed-scale processes like snowmelt during high-runoff seasons to local processes like groundwater discharge during sustained seasonal dry periods.</jats:p>

A riverscape approach reveals downstream propagation of stream thermal responses to riparian thinning at multiple scales

“…In contrast, semivariograms for the Lost Man watershed exhibited a pure nugget effect (i.e., no increase in semivariance with separation distance) during both pre-and posttreatment years. Other studies have shown semivariograms with shapes similar to the ones we observed (i.e., pure nugget effect, spherical, and nested) for fish counts (Torgersen et al 2004, Ganio et al 2005, water chemistry (McGuire et al 2014), and stream temperature (Gendaszek et al 2020). However, few studies have applied semivariograms for change-detection purposes (but see Grimm 1999, Johnson et al 2010).…”

“…Local responses depend on sufficient increases in radiative energy to increase stream temperatures; therefore, minor local reductions in shade may result in no effect. More intensive changes in radiative energy may result in a localized pulse but not extend downstream if advective processes are truncated, for example, during periods of low flow (Gendaszek et al 2020). However, if advective processes are present, local responses may propagate downstream following different trajectories.…”

“…Process-based heat budget models elucidate the energetic drivers of thermal regimes (Johnson 2004, Dugdale et al 2017 but are data-intensive and, therefore, difficult to employ over broad spatial scales (Wondzell et al 2019). Spatial stream network models account for network structure and spatial autocorrelation over broad scales and have greatly improved understanding of thermal regimes in riverscapes (Isaak et al 2014, Fullerton et al 2018, Gendaszek et al 2020. However, the cumulative watershed effects of land use on stream thermal conditions remain difficult to quantify and predict (Steel et al 2017, Ouellet et al 2020, Erdozain et al 2021.…”

Population genomic monitoring provides insight into conservation status but no correlation with demographic estimates of extinction risk in a threatened trout

“…Whitehorse Creeks) ranked at the lower end for several genetic metrics (one notably had an estimated N e of 21 but the highest harmonic mean abundance estimate of all populations at 9143). Though relatively large for LCT in terms of stream miles, these streams have recently been found to be comprised of more marginal/intermittent habitat than previously appreciated (Gendaszek et al, 2020;Schultz et al, 2017) (Peacock et al, 2004), and/or genomic filtering (these data) are influencing these discrepancies to some degree, although different filtering protocols explored here produced highly correlated results (data not shown).…”

Dammed water quality—Longitudinal stream responses below beaver ponds in the Umpqua River Basin, Oregon

“…It is also possible that the minimal discharges observed in August led to a proportionally larger influence of local heat exchanges downstream when streams become hydrologically disconnected during low flow periods (Gendaszek et al, 2020). During these periods, temperature shifts can occur over short distances (Johnson, 2004) when summer stream velocity and thermal mass are limited (Moore, Spittlehouse, & Story, 2005).…”