Actively heated high‐resolution fiber‐optic‐distributed temperature sensing to quantify streambed flow dynamics in zones of strong groundwater upwelling

Abstract

Zones of strong groundwater upwelling to streams enhance thermal stability and moderate thermal extremes, which is particularly important to aquatic ecosystems in a warming climate. Passive thermal tracer methods used to quantify vertical upwelling rates rely on downward conduction of surface temperature signals. However, moderate to high groundwater flux rates (>−1.5 m d−1) restrict downward propagation of diurnal temperature signals, and therefore the applicability of several passive thermal methods. Active streambed heating from within high‐resolution fiber‐optic temperature sensors (A‐HRTS) has the potential to define multidimensional fluid‐flux patterns below the extinction depth of surface thermal signals, allowing better quantification and separation of local and regional groundwater discharge. To demonstrate this concept, nine A‐HRTS were emplaced vertically into the streambed in a grid with ∼0.40 m lateral spacing at a stream with strong upward vertical flux in Mashpee, Massachusetts, USA. Long‐term (8–9 h) heating events were performed to confirm the dominance of vertical flow to the 0.6 m depth, well below the extinction of ambient diurnal signals. To quantify vertical flux, short‐term heating events (28 min) were performed at each A‐HRTS, and heat‐pulse decay over vertical profiles was numerically modeled in radial two dimension (2‐D) using SUTRA. Modeled flux values are similar to those obtained with seepage meters, Darcy methods, and analytical modeling of shallow diurnal signals. We also observed repeatable differential heating patterns along the length of vertically oriented sensors that may indicate sediment layering and hyporheic exchange superimposed on regional groundwater discharge.

Effect of Hyporheic Exchange on Macroinvertebrate Community in the Weihe River Basin, China

“…Thus, downwelling may allow Chironomidae to become the dominant family. Both patterns of hyporheic exchange participate in the regulation of temperature [21], and maintain a suitable thermal niche (temperature range) for macroinvertebrate survival [85]. Actually, whichever environment and pattern of hyporheic flux provide temperatures closer to the macroinvertebrate requirements would likely be preferred.…”

Monitoring and Modelling Interactions between the Montagna dei Fiori Aquifer and the Castellano Stream (Central Apennines, Italy)

“…Nevertheless, often only small-scale and site-specific information can be gained on the relationship between streams and aquifers without employing complex three-dimensional numerical models [7]. Although numerous models have been successfully developed for use in porous aquifers [8,9], their application in fractured aquifers is more problematic. Fractured media are generally highly heterogeneous since they are dominated by secondary porosity (along fractures apertures) and often are characterized by hierarchical permeability structures [10].…”

Scale Effects of Water Saving on Irrigation Efficiency: Case Study of a Rice-Based Groundwater Irrigation System on the Sanjiang Plain, Northeast China

“…Because of the percolation and surface seepage flows from continuously ponded fields into groundwater and drains, seepage and percolation flows account for a large proportion of the water inputs [43][44][45]. The contributions of these flows are particularly high in a rice-based groundwater irrigation system, where a large proportion of groundwater may come from percolation flow.…”