Stream solute tracer timescales changing with discharge and reach length confound process interpretation

Abstract

Superconducting power cables represent a recent innovative development for highcapacity underground transmission. Their promise lies principally in their high efficiency associated with a small size and with potential advantages in terms of environmental impact. Within the BEST PATHS European project, the DEMO 5 demonstrator aims to illustrate the technological maturity of superconducting HVDC links for operation in the grid. At the same time, this demonstrator is also a first attempt to employ MgB 2 as a superconductor for HVDC cables. More concretely, DEMO 5 aims to develop a monopole superconducting cable designed to operate in helium gas at 10 kA and 320 kV, corresponding to a transferred power of up to 3.2 GW. The project is coordinated by leading cable manufacturer Nexans and encompasses expertise from transmission system operators, industry, and research organizations. Thus, in addition to the design, development, optimization, manufacturing and testing activities, special attention will be devoted to studying the integration of a superconducting link into the future transmission grid and to assessing the availability and economic viability of the system. An overview of the project will be presented at the meeting, including the main tasks and challenges ahead as well as preliminary results after one year of activity.

Streambed restoration to remove fine sediment alters reach‐scale transient storage in a low‐gradient fifth‐order river, Indiana, USA

“…This is likely appropriate for rapid exchange with gravel beds and macrophyte beds but would likely not be sufficient to measure flow through, for example, installation of meander bends with fine‐grained sediment that may have transit times of many hours or even days (Boano et al, ). Furthermore, the study duration itself has been shown to directly scale the window of detection (Schmadel et al, ). Importantly, our scaling of study reach length across discharges to provide comparable data is an important strategy to control.…”

“…Additionally, we used the estimate of advective velocity to establish a downstream sensor location targeting a 20‐min advective time in the study reach. The establishment of constant timescale reaches is based on the known interaction of experimental timescale with experimental results that biases stream solute tracer interpretations (Harvey, Wagner, & Bencala, ; Schmadel et al, ; Ward, Gooseff, et al, ; Ward, Payn, et al, ). This strategy necessarily results in minor changes in the system studied (i.e., shorter and longer reaches under different discharges) but has the advantage of consistency in transit timescales that isolate hydraulic changes from those associated with methodological limitations.…”

“…The normalized CV and γ are preferable to μ 2 and μ 3 because they reflect normalization by advective time and variance, respectively, further minimizing differences that would arise because of experimental limitations (e.g., transit timescales) from those associated with changes in dispersive and short‐term storage processes. Schmadel et al () describe these quantities as “advection independent.” Additionally, we calculated holdback ( H ) for the observed BTCs: …”

“…Interpretation of stream solute data has not yet yielded a consistent understanding of how geologic setting and hydrologic forcing interact to result in reach‐scale transient storage. Studies that directly interpret field data have found that interaction between experimental design and discharge complicate interpretation of results across different discharge conditions due to non‐standard advective timescales in individual study reaches (Ward, Gooseff, et al, ; Ward, Payn, et al, ; Schmadel et al, ). Consistent patterns have not emerged among studies—the relative size of the storage zone has been found to expand with increasing discharge (Fabian, Endreny, Bottacin‐Busolin, & Lautz, ; Morrice, Valett, Dahm, & Campana, ; Wondzell, ), shrink with increasing discharge (Butturini & Sabater, ; Fabian et al, ; Karwan & Saiers, ; Morrice et al, ; Schmid, Innocenti, & Sanfilippo, ; Zarnetske et al, ), or have no clear relationship with discharge (Hart et al, ; Schmid et al, ).…”

Woody debris is related to reach‐scale hotspots of lowland stream ecosystem respiration under baseflow conditions

“…Estimates of Raz and Rru mass recovery were adjusted for potential changes in discharge through the study reach by correcting for conservative tracer (i.e., Uranine) mass recovery. Thus, Raz–Rru transformation rate coefficients were estimated for each subreach as: where (1/s) is the Raz–Rru transformation rate coefficient in the subreach, and (mg s/L) are the zeroth temporal moments (the integral of concentration with respect to time) for Raz and Rru, respectively, at the upstream end of each subreach, is the zeroth order temporal moment for Rru at the downstream end of each subreach, and τ (s) is the median travel time in the subreach as calculated from the first temporal moment of each BTC following Schmadel et al (). Normalizing Raz–Rru transformation values by advective time produces rate estimates that are independent of subreach length and flow velocity.…”