Spatial and temporal variation in river corridor exchange across a 5th order mountain stream network

Abstract

Abstract. Although most field and modeling studies of river corridor exchange have been conducted a scales ranging from 10’s to 100’s of meters; results of these studies are used to predict their ecological and hydrological influences at the scale of river networks. Further complicating prediction, exchange are expected to vary with hydrologic forcing and the local geomorphic setting. While we desire predictive power, we lack a complete spatiotemporal relationship relating discharge to the variation in geologic setting and hydrologic forcing that are expected across a river basin. Indeed, Wondzell’s [2011] conceptual model predicts systematic variation in river corridor exchange as a function of (1) variation in discharge over time at a fixed location, (2) variation in discharge with location in the river network, and (3) local geomorphic setting. To test this conceptual model we conducted more than 60 solute tracer studies collected in a synoptic campaign in the 5th order river network of the H. J. Andrews Experimental Forest (Oregon, USA). We interpret the data using a series of metrics describing river corridor exchange and solute transport, testing for consistent direction and magnitude of relationships relating these metrics to discharge and local geomorphic setting. We confirmed systematic decrease in river corridor exchange space through the river networks, from headwaters to the larger mainstem. However, we did not find systematic variation with changes in discharge through time, nor with local geomorphic setting. While interpretation of our results are complicated by problems with the analytical methods, they are sufficiently robust for us to conclude that space-for-time and time-for-space substitutions are not appropriate in our study system. Finally, we suggest two strategies that will improve the interpretability of tracer test results and help the hyporheic community develop robust data sets that will enable comparisons across multiple sites and/or discharge conditions.

Microbial community assembly in a multi-layer dendritic metacommunity

“…This scale dependence may arise from variable dispersal kernels (e.g., along preferential 351 flow paths) or from vertical hydrological exchange at the stream reach scale, which could 352 generate idiosyncratic spatial variation in community structure. In our study system, it has been 353 shown that vertical hydrological exchange plays a more important role in headwaters than in 354 downstream reaches (Ward et al 2019), suggesting that vertical fluxes may be responsible for 355 disrupting the species sorting process predominantly in the headwater reaches. If so, stochastic 356 dispersal may increase in importance downstream as channels widen and the relative importance 357 of vertical exchange diminishes.…”

Solute Transport and Transformation in an Intermittent, Headwater Mountain Stream with Diurnal Discharge Fluctuations

“…We used the StorAge Selection (SAS) approach to interpret conservative solute transport through the study reach [94][95][96]. Briefly, the SAS approach considers outflow as a combination of waters sampled from different ages within the total storage volume between the injection and observation locations.…”

“…Moreover, common model formulations are not appropriate for interpreting experimental data in intermittent streams, as they require the presence of a continuously flowing stream [91][92][93], though exceptions do exist [23]. To overcome these limitations, new approaches, such as the StorAge Selection (SAS) model, take transport as a continuum and can simulate continuously variable discharge [94][95][96].…”

Superlinear scaling of riverine biogeochemical function with watershed size

“…Further, data needed to validate scaling estimates are not available because monitoring networks are typically not designed for nested, network scale analyses within individual watersheds that can be used to further constrain scaling dynamics. River networks therefore remain an important "missing scale" in our observational toolkit of in situ measurements 45 . Superlinear scaling of cumulative biogeochemical processing results from efficient resource use due to disproportionate material inputs from the landscape in headwaters, upstream-downstream connectivity, and high uptake potential downstream, underscoring the role of river networks to functioning of the earth system.…”