Landform features and seasonal precipitation predict shallow groundwater influence on temperature in headwater streams

Abstract

Headwater stream responses to climate change will depend in part on groundwater‐surface water exchanges. We used linear modeling techniques to partition likely effects of shallow groundwater seepage and air temperature on stream temperatures for 79 sites in nine focal watersheds using hourly air and water temperature measurements collected during summer months from 2012 to 2015 in Shenandoah National Park, Virginia, USA. Shallow groundwater effects exhibited more variation within watersheds than between them, indicating the importance of reach‐scale assessments and the limited capacity to extrapolate upstream groundwater influences from downstream measurements. Boosted regression tree (BRT) models revealed intricate interactions among geomorphological landform features (stream slope, elevation, network length, contributing area, and channel confinement) and seasonal precipitation patterns (winter, spring, and summer months) that together were robust predictors of spatial and temporal variation in groundwater influence on stream temperatures. The final BRT model performed well for training data and cross‐validated samples (correlation = 0.984 and 0.760, respectively). Geomorphological and precipitation predictors of groundwater influence varied in their importance between watersheds, suggesting differences in spatial and temporal controls of recharge dynamics and the depth of the groundwater source. We demonstrate an application of the final BRT model to predict groundwater effects from landform and precipitation covariates at 1075 new sites distributed at 100 m increments within focal watersheds. Our study provides a framework to estimate effects of groundwater seepage on stream temperature in unsampled locations. We discuss applications for climate change research to account for groundwater‐surface water interactions when projecting future thermal thresholds for stream biota.

Groundwater Pumping Impacts on Real Stream Networks: Testing the Performance of Simple Management Tools

“…Groundwater is a critical contributor to streamflow and supports both aquatic ecosystems and human needs (Acreman et al, ; Booth et al, ; Gleeson & Richter, ; Zektser et al, ). For instance, groundwater discharge into streams provides a stable supply of water during dry periods and is a key regulator of water temperature, an important water quality parameter for aquatic ecosystems (Johnson et al, ; Kurylyk et al, ; Strauch et al, ; Zorn et al, ). It has long been recognized that groundwater pumping can reduce streamflow via the “capture” of groundwater that would have otherwise discharged into a stream (Barlow et al, ; Bredehoeft, ; Theis, ).…”

Comparison of Underwater Video with Electrofishing and Dive Counts for Stream Fish Abundance Estimation

“…Spatially intensive sampling may be particularly important in stream ecosystems that exhibit sharp gradients or discontinuities in local habitat characteristics influencing population structure and viability (Fausch et al 2002). For instance, patchy groundwater–surface water interactions may affect stream thermal habitat (Snyder et al 2015) based on spatially complex landform features regulating groundwater depth and flow paths (Johnson et al 2017, 2020). Moreover, drought conditions can create fragmented stream networks that require intensive spatial sampling to understand fish population responses (Kovach et al 2019).…”

Hillslope groundwater discharges provide localized stream ecosystem buffers from regional per‐ and polyfluoroalkyl substances contamination

“…The spatial patterns of contaminant loading along stream corridors, and subsequent impact on aquatic ecosystems, are strongly influenced by groundwater/surface‐water connectivity (Harvey & Gooseff, 2015). Groundwater discharge to streams is often highly variable spatially and controlled by the combination of heterogeneous sediment permeability, depth to bedrock, and a nested system of regional and local hydraulic gradients (Johnson, Snyder, & Hitt, 2017; Winter, Harvey, Franke, & Alley, 1998). Temporal patterns in groundwater discharge are tied to short‐ and long‐term variability of precipitation (recharge), pumping for water supply, and wastewater discharge (Barlow & Hess, 1993) and to future sea‐level rise dynamics in permeable coastal watersheds (Walter, McCobb, Masterson, & Fienen, 2016).…”