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Hydrogeochemical controls on brook trout spawning habitats in a coastal stream
Citation:
Briggs, M., J. Harvey, S. Hurley, D. Rosenberry, T. McCobb, D Werkema, AND J. Lane. Hydrogeochemical controls on brook trout spawning habitats in a coastal stream. HYDROLOGY AND EARTH SYSTEM SCIENCES. EGS, 22(12):6383-6398, (2018). https://doi.org/10.5194/hess-22-6383-2018
Impact/Purpose:
The heat tracing of waters can be used to map a distribution of discrete groundwater discharge zones throughout surface water systems at times of contrast between surface and groundwater temperature. The measurement of water temperature from the reach to watershed scale is now possible using thermal infrared (TIR) and fiber-optic distributed temperature sensing (FO-DTS) methodology (Hare et al., 2015). Remote TIR data collection throughout the river corridor has been enabled by handheld cameras, piloted aircraft, and the rapidly evolving capabilities of Unmanned Aircraft Systems. Researchers are capitalizing on the ongoing refinement of these technologies to identify zones of focused groundwater seepage to streams to map potential discrete preferential cold-water fish habitat such as summer thermal refugias (Dugdale et al., 2015). However, surface thermal surveys alone do not directly indicate the 71 suitability (e.g. dissolved gas and solute concentration) of discrete discharge aquatic habitat.
Description:
Brook trout (Salvelinus fontinalis) spawn in fall and overwintering egg development can benefit from stable, relatively warm temperatures in groundwater-seepage zones. However, eggs are also sensitive to dissolved oxygen concentration, which may be reduced in discharging groundwater (i.e., seepage). We investigated a 2 km reach of the coastal Quashnet River in Cape Cod, Massachusetts, USA, to relate preferred fish spawning habitats to geology, geomorphology, and discharging groundwater geochemistry. Thermal reconnaissance methods were used to locate zones of rapid groundwater discharge, which were predominantly found along the central channel of a wider stream valley section. Pore-water chemistry and temporal vertical groundwater flux were measured at a subset of these zones during field campaigns over several seasons. Seepage zones in open-valley sub-reaches generally showed suboxic conditions and higher dissolved solutes compared to the underlying glacial outwash aquifer. These discharge zones were cross-referenced with preferred brook trout redds and evaluated during 10 years of observation, all of which were associated with discrete alcove features in steep cutbanks, where stream meander bends intersect the glacial valley walls. Seepage in these repeat spawning zones was generally stronger and more variable than in open-valley sites, with higher dissolved oxygen and reduced solute concentrations. The combined evidence indicates that regional groundwater discharge along the broader valley bottom is predominantly suboxic due to the influence of near-stream organic deposits; trout show no obvious preference for these zones when spawning. However, the meander bends that cut into sandy deposits near the valley walls generate strong oxic seepage zones that are utilized routinely for redd construction and the overwintering of trout eggs. Stable water isotopic data support the conclusion that repeat spawning zones are located directly on preferential discharges of more localized groundwater. In similar coastal systems with extensive valley peat deposits, the specific use of groundwater-discharge points by brook trout may be limited to morphologies such as cutbanks, where groundwater flow paths do not encounter substantial buried organic material and remain oxygen-rich.
