Spatiotemporal Variability in Transport and Reactive Processes Across a First‐ to Fifth‐Order Fluvial Network

Abstract

Fluvial networks integrate, transform, and transport constituents from terrestrial and aquatic ecosystems. To date, most research on water quality dynamics has focused on process understanding at individual streams, and, as a result, there is a lack of studies analyzing how physical and biogeochemical drivers scale across fluvial networks. We performed tracer tests in five stream orders of the Jemez River continuum in New Mexico, USA, to quantify reach-scale hyporheic exchange during two different seasonal periods to address the following: How do hyporheic zone contributions to overall riverine processing change with space and time? And does the spatiotemporal variability of hyporheic exchange scale across fluvial networks? Combining conservative (i.e., bromide) and reactive (i.e., resazurin) tracer analyses with solute transport modeling, we found a dominance of reaction-limited transport conditions and a decrease of the contributions of hyporheic processing across stream orders and flow regimes. Our field-based findings suggest that achieving knowledge transferability of hyporheic processing within fluvial networks may be possible, especially when process variability is sampled across multiple stream orders and flow regimes. Therefore, we propose a shift in our traditional approach to investigating scaling patterns in transport processes, which currently relies on the interpretation of studies conducted in multiple sites (mainly in headwater streams) that are located in different fluvial networks, to a more cohesive, network-centered investigation of processes using the same or readily comparable methods. Key Points: • Reactive tracer tests revealed reaction-limited conditions along a firstto fifth-order fluvial network during contrasting flow regimes • Processing rate coefficients and Damköhler numbers decreased along the continuum • Results support modeling expectations of decreasing hyporheic contributions along fluvial networksSupporting Information:• Supporting Information S1 regional water quality and ecological functioning (Alexander et al., 2007;Freeman et al., 2007;Gomez-Velez & Harvey, 2014).In addition to making up a larger proportion of catchment reach lengths, low-order streams are thought to have greater influence over hyporheic zone processing than their high-order counterparts throughout various fluvial networks. For example, Gomez-Velez et al. (2015) found that vertical hyporheic excursions into the streambed generally decreased with increasing stream order in the Mississippi River network, meaning that watershed hyporheic contributions to overall riverine processing decreased with increasing stream order over large spatial scales. Additionally, shallower stream depths, typically found in low-order streams, maintain closer contact between surface water and reactive bed sediments and may encourage higher streambed reaction rates (Harvey & Gooseff, 2015). The expectation of decreasing hyporheic zone processing relative to total riverine processing with increasing stream order is in line with hydr...

Physical and stoichiometric controls on stream respiration in a headwater stream

“…;Hall et al 2002;Gomez et al 2012;Zarnetske et al 2012;Kiel and Bayani Cardenas 2014;Gootman et al 2020). The mean values of 𝜆 𝑅𝑎𝑧 were directly and weakly correlated with discharge (𝑄) (also depths ℎ and velocities 𝑢) and dispersion (𝐷), and directly and moderately correlated with 𝜏 𝑡𝑠 .…”

“…electron acceptor into energy and biomass). The exchange of water between the main channel and transient storage zones, where most microbes exist, is the primary mechanism supplying carbon, nutrients, and oxygen to metabolically active zones (Gooseff et al 2004;Covino et al 2010bCovino et al , 2011Knapp et al 2017;Gootman et al 2020). The extent of water exchange controls the residence time of solutes (Drummond et al, 2012;Gomez et al, 2012;Patil et al, 2013), their chemical signatures (Covino and McGlynn 2007), as well as the microbial composition and their metabolic functioning (Blume et al 2002;Navel et al 2011;Li et al 2020).…”

“…Conversely, where or when Da >>1, i.e., the transport timescale is much greater than the uptake timescale, resources become scarce or transport-limited, and biologically inactive subregions start to develop Harvey et al 2013;Gootman et al 2020). While Da captures essential components of the potential interactions between the supply and demand of ecologically relevant resources, it does not explicitly capture the role Based on the relevance and co-dependences between hydrologic exchange, stoichiometry, and biological uptake, and the limited amount of field studies available to determine their net effects on the retention and export of resources, we sought to quantify how metabolic activity is controlled by the interactions and supply of essential nutrients (C, N, P).…”

Organizational Principles of Hyporheic Exchange Flow and Biogeochemical Cycling in River Networks Across Scales

“…The majority of experimental or modeling studies to date have focused on individual stream reaches and then scaled up observations, with only a few experimental studies attempting to quantify hyporheic exchange along a river continuum using a river network approach (Gootman et al., 2020; Lee‐Cullin et al., 2018; Ward, Kurz, et al., 2019; Wondzell, 2011). Here, we build on previous conceptual models of landscape organizational principles (Boulton et al., 1998; Boulton & Hancock, 2006; Buffington & Tonina, 2009; Frissell et al., 1986; Helton et al., 2011; Malard et al., 2002) to synthesize and conceptualize the spatial and temporal organization of different drivers and controls of hyporheic exchange and hyporheic biogeochemical cycling along a river network continuum from first order headwaters to lowland streams (Figure 6a).…”

Seasonal and Morphological Controls on Nitrate Retention in Arctic Deltas

“…First, Arctic deltas distribute riverine loads across complicated networks of anabranching and anastomosing channels (Piliouras & Rowland, 2020) where mass balance accounting of solutes using conventional gauging is nonviable. Second, processes occurring in rivers (including their beds and banks), such as denitrification, plant uptake and sedimentation, alter nutrient loads of water flowing downstream (Bernhardt et al., 2005; Gootman et al., 2020; Newbold et al., 1981). The hundreds of kilometers of river channels that make up Arctic deltas likely alter nutrient load before discharge to the ocean.…”