A mixing model analysis of stream solute dynamics and the contribution of a hyporheic zone to ecosystem function*

Abstract

SUMMARY 1. We monitored streamwater and streambed sediment porewaters from White Clay Creek (WCC), SE Pennsylvania, for dissolved organic carbon (DOC), dissolved oxygen (DO) and conductivity to investigate organic matter processing within the hyporheic zone. Dissolved organic carbon and DO concentrations were higher in the streamwater than in the porewaters and, in many cases, concentrations continued to diminish with increasing depth into the streambed. 2. Hydrological exchange data demonstrated that the permeability of the stream bed declines with depth and constrains downwelling, effectively isolating porewaters >30 cm from streamwater. 3. End‐member mixing analysis (EMMA) based on conductivity documented a DOC source and DO sink in the hyporheic zone. We calculated hyporheic streambed DOC fluxes and respiration from the EMMA results and estimates of water flux. Based upon our calculations of biodegradable DOC entering the hyporheic zone, we estimate that DOC supports 39% of the hyporheic zone respiration, with the remaining 61% presumably being supported by entrained particulate organic carbon. Hyporheic respiration averaged 0.38 g C m−2 d−1, accounted for 41% of whole ecosystem respiration, and increased baseflow ecosystem efficiency from 46 to 59%. 4. Advective transport of labile organic molecules into the streambed concentrates microbial activity in near‐surface regions of the hyporheic zone. Steep gradients in biogeochemical activity could explain how a shallow and hydrologically constrained hyporheic zone can dramatically influence organic matter processing at the ecosystem scale.

Evaluation of Restoration and Flow Interactions on River Structure and Function: Channel Widening of the Thur River, Switzerland

“…Exchange between the water column and channel bed and river banks (vertical and lateral linkages) can affect water quality because these are biogeochemically active areas where organic matter decomposition and nitrogen removal occurs [50,51]. Our results showed that water chemistry was not influenced by the restoration, and is in agreement with previous studies [52,53].…”

Recurring Seasonal Dynamics of Microbial Communities in Stream Habitats

“…The correlation between DOC concentration and the community structure of the epilithic, but not the sediment, community suggests that sources of organic carbon supporting secondary productivity partition differently between these two streambed habitats (42,54,56). While the epilithic populations are generally limited to dissolved carbon in the bulk flow and endogenous carbon (DOC and POC derived from the biofilm), the sediment populations likely obtain additional resources from entrained POC and DOC upwelling from the hyporheic zone (5,10,30,54). The appearance of both prokaryotic and eukaryotic primary producers in the epilithon during the summer months suggests a seasonal shift towards autocthonous carbon sources within this biofilm, as is also supported by prior estimates of autochthonous primary productivity in White Clay Creek (31).…”

“…Habitat differences in organic resources and sheer stress exist as well. For example, high depositional loads of POC and upwelling hyporheic zone DOC tend to be associated with sediment habitats (5,54), whereas algal biomass and associated exudates are more consistently present within rock-associated epilithic biofilms (30,31). Varying flows alter the sediment system through erosion and transport, redistributing the attached bacteria and likely exposing them to different environmental conditions.…”

A fluid-mechanics based classification scheme for surface transient storage in riverine environments: quantitatively separating surface from hyporheic transient storage

“…The purpose of field-based tracer studies is to gain a better understanding of stream solute transport behavior by accounting for transient storage zones. Previous transient storage studies have focused on relating transient storage to the following hydromorphic parameters: channel order and confinement (D'Angelo et al, 1993;Gabriel and Boufadel, 2002); streambed and aquifer lithology (substrate) (Valett et al, 1996Morrice et al, 1997;Argerich et al, 2011); discharge (Hall et al, 2002;Harvey et al, 2003); transient storage area (Mulholland et al, 1997;Laenen and Bencala, 2001;Gücker and Boëchat, 2004;Ensign and Doyle, 2005); channel bed form (Harvey and Bencala, 1993;Gooseff et al, 2003;Anderson et al, 2005;Wörman et al, 2007;Cardenas et al, 2008); wood debris, leaf packs, and vegetation (Gabriel and Boufadel, 2002;Wondzell et al, 2009b); streambed friction factor Salehin et al, 2003;Zarnetske et al, 2007); stream power per unit width (Zarnetske et al, 2007); channel tortuosity (Kasahara and Wondzell, 2003;Baker et al, 2012); and hyporheic exchange (as determined by hydraulic gradients and streambed-aquifer hydraulic conductivity) (Harvey et al, 1996;Battin et al, 2003;Wondzell et al, 2009a,b).…”