The Role of Hyporheic Connectivity in Determining Nitrogen Availability: Insights From an Intermittent Antarctic Stream

Abstract

The biogeochemical processing of nitrogen (N) in streams has drawn wide interest related to various water quality problems (Davidson et al., 2011) and the mobilization of N from local human activities adjacent to freshwater systems to downstream locations (Fowler et al., 2013). To date, most research has focused on how human manipulation of N sources-through fertilizer applications or emissions-increase the amount of reactive N that is transported from terrestrial to aquatic systems (

Impact of meltwater flow intensity on the spatiotemporal heterogeneity of microbial mats in the McMurdo Dry Valleys, Antarctica

“…Our functional analysis did not detect any genes related to nitrification in any of the four mats types. Potential for nitrification and the accumulation of N has primarily been found to occur in the stream sediment and hyporheic zone [ 57 , 58 ].…”

Dissolved Organic Carbon Chemostasis in Antarctic Polar Desert Streams

“…The long‐term data sets used in these analyses do not distinguish between in‐channel and hyporheic DOC sources. However, a hyporheic DOC source is plausible based on other research: we know that the hyporheic zone contains POM that is sloughed from microbial mats (Cullis et al., 2014; Heindel et al., 2021; Singley et al., 2021), and that this organic matter contributes dissolved nitrogen and likely other solutes to the stream channel (Singley et al., 2021). We also know that the hyporheic zone of MDV streams is an active site of DOC uptake and generation that occurs on sub‐diel timescales (Koch et al., 2010).…”

“…In glaciated systems, DOC fluxes can be a major source of organic carbon (OC) to the ocean or terminal lakes (Hood et al., 2020; McKnight et al., 1999). Understanding how instream DOC concentration (C) changes with discharge ( q ) can elucidate where and how DOC is generated in the watershed, the relative controls of surface and subsurface (hyporheic) processes (Castro & Hornberger, 1991; Singley et al., 2021), how DOC source dynamics respond to changing watershed conditions (i.e., snowmelt, flooding, irrigation, etc. ; Evans & Davies, 1998; Godsey et al., 2009; Thompson et al., 2011), and whether OC is limited by supply or hydrologic transport (Creed et al., 2015; Thompson et al., 2011; Zarnetske et al., 2018).…”

“…Hyporheic biofilm is another potential DOC source (Maurice et al., 2002); this biofilm has not been quantified in the MDV, but it is known to play a central role in the transformation and processing of instream C and N (Heindel et al., 2021; Koch et al., 2010; Singley et al., 2021). The instream DOC concentrations in MDV streams are generally low compared to temperate streams, and in line with other glacial meltwater streams, with a median value below 1 mg C l −1 (Aiken et al., 1996).…”

“…For weathering solutes, the chemostatic behavior reflects their low equilibrium concentrations ( C eq ) and the rapid weathering rates that are characteristic of MDV streams (Gooseff et al., 2002; W. B. Lyons et al., 1997; Wlostowski et al., 2018). For DIN, chemostasis reflects both the low ambient dissolved N concentrations and the increasing release of hyporheic N stores with increasing discharge (Kohler et al., 2018; Singley et al., 2021).…”