Water Temperature Patterns Below Large Groundwater Springs: Management Implications for Coho Salmon in the Shasta River, California

Abstract

Elevated stream temperature is a primary factor limiting the coho salmon (Oncorhynchus kisutch) population in California's Shasta River Basin. Understanding the mechanisms driving spatial and temporal trends in water temperature throughout the Shasta River is critical to prioritising river restoration efforts aimed at protecting this threatened species. During the summer, the majority of streamflow in the Shasta River comes from large-volume, cold-water springs at the head of the tributary Big Springs Creek. In this study, we evaluated the initial character of this spring water, as well as the downstream fate and transport of these groundwater inflows during July and August 2008. Our results indicated that Big Springs Creek paradoxically provided both cool and warm waters to the Shasta River. During this period, cool groundwater inflows heated rapidly in the downstream direction in response to thermal loads from incoming solar radiation. During the night time, groundwater inflows did not appreciably heat in transit through Big Springs Creek. These diurnally varying water temperature conditions were inherited by the Shasta River, producing longitudinal temperature patterns that were out of phase with ambient meteorological conditions up to 23 km downstream. Findings from this study suggest that large, constant temperature spring sources and spring-fed rivers impart unique stream temperature patterns on downstream river reaches that can determine reach-scale habitat suitability for cold-water fishes such as coho salmon. Recognising and quantifying the spatiotemporal patterns of water temperature downstream from large spring inflows can help identify and prioritize river restoration actions in locations where temperature patterns will allow rearing of cold-water fishes. Figure 1. Stream temperature monitoring sites located in the Shasta River Basin, California. Shasta River (SR) and Big Springs Creek (BSC) river kilometer locations (e.g. SR 44.03) and the downstream distance from groundwater spring sources located at the head of Big Springs Creek [e.g. (13.16)] are presented for each temperature logger WATER TEMPERATURE PATTERNS BELOW SPRINGS 443

Groundwater Is Key to Salmonid Persistence and Recruitment in Intermittent Mediterranean‐Climate Streams

“…Groundwater may modulate temperatures; for example, warm groundwater inflows have been found to enhance the growth of postemergent Chinook salmon (Mejia et al, ). Near the southern extent of the range for salmon, cooler groundwater inflows may enhance habitat suitability (Madej et al, ; Nichols et al, ). Though our sites are geographically near this boundary, persistent cool temperatures (<16.3 °C) within the stream suggested that temperature was not likely a critical factor for salmonid persistence here (Woelfle‐Erskine et al, ).…”

Seasonal macrophyte growth constrains extent, but improves quality, of cold‐water habitat in a spring‐fed river

“…Instead, the primary antinode developed at the mouth of Big Springs Creek less than 6 hr of travel time downstream. The consistent geospatial location of this antinode can be attributed to an abrupt change in channel geometry from the wide and shallow Big Springs Creek to the narrower and deeper Shasta River (Nichols et al, ). Under the largely steady flow conditions in Big Springs Creek and the Shasta River, this abrupt increase in mean water depth effectively truncates the magnitude and range of observed downstream water temperatures.…”

“…Historically, surface runoff from direct precipitation and snowmelt in the Klamath Mountain's headwaters mixed with voluminous groundwater spring sources, creating a complex hydrologic regime characterized by stable baseflows augmented by seasonal runoff. However, due to upstream water storage and flow regulation (see Null, Deas, & Lund, for a description of surface water infrastructure in the Shasta River basin), streamflow in the Shasta River below Dwinnell Dam and Lake Shastina is derived predominantly from discrete springs discharging cool (11–13°C) and nutrient‐rich groundwater (Dahlgren et al, ; Lusardi et al, ; Nichols et al, ; NRC, ). The limited annual precipitation (24–46 cm year −1 ; NCRWQCB, ) in the Shasta River basin infiltrates Quaternary basalts and basaltic andesites of the High Cascades bounding the Shasta River to the north and east (Blodgett, Poeschel, & Thornton, ; Nathenson, Thompson, & White, ), ultimately discharging downslope at numerous springs along the eastern edge of the Shasta Valley.…”

“…Without the shading effects of riparian vegetation, stable and nutrient‐rich streamflow in the low‐gradient (mean slope = 0.003), wide, and shallow (mean bankfull width to depth ratio = 84; Nichols et al, ) Big Springs Creek promotes extraordinary primary productivity, principally characterized by seasonal growth of native emergent and submerged rooted aquatic macrophytes (Willis et al, ). The macrophyte species assemblage in Big Springs Creek is dominated by emergent smartweed ( Polygonum hydropiperoides ) and watercress ( Nasturtium officinale ), as well as submerged northern watermilfoil ( Myriophyllum sibiricum ).…”

“…The macrophyte species assemblage in Big Springs Creek is dominated by emergent smartweed ( Polygonum hydropiperoides ) and watercress ( Nasturtium officinale ), as well as submerged northern watermilfoil ( Myriophyllum sibiricum ). The narrower and deeper downstream reaches of the Shasta River (Nichols et al, ) also exhibit a complex macrophyte species assemblage dominated by submerged species including pondweed (Potamogeton pectinatus ) and white water buttercup (Ranunculus aquatilus ; NCRWQCB, ). Macrophyte communities in Big Springs Creek and the Shasta River exhibit pronounced growth and senescence cycles generally characterized by minimum macrophyte biomass in winter and early spring and maximum biomass in late summer and early fall (Willis et al, ).…”