<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Singley, Joel G.</style></author><author><style face="normal" font="default" size="100%">Gooseff, Michael N.</style></author><author><style face="normal" font="default" size="100%">Diane M. McKnight</style></author><author><style face="normal" font="default" size="100%">Eve-Lyn S. Hinckley</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">The role of hyporheic connectivity in determining nitrogen availability: Insights from an intermittent Antarctic stream</style></title><secondary-title><style face="normal" font="default" size="100%">Journal of Geophysical Research: Biogeosciences</style></secondary-title><short-title><style face="normal" font="default" size="100%">J Geophys Res Biogeosci</style></short-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Antarctica</style></keyword><keyword><style  face="normal" font="default" size="100%">autochthonous nitrogen</style></keyword><keyword><style  face="normal" font="default" size="100%">hyporheic zone</style></keyword><keyword><style  face="normal" font="default" size="100%">nitrogen cycling</style></keyword><keyword><style  face="normal" font="default" size="100%">streamflow</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2021</style></year><pub-dates><date><style  face="normal" font="default" size="100%">04/2022</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JG006309</style></url></web-urls></urls><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">&lt;p&gt;Due to widespread manipulation of nitrogen (N), much research has focused on processes controlling the fate of anthropogenic N in streams. Yet, in a variety of oligotrophic systems, N fixed by periphyton is a significant driver of ecosystem metabolism. Due to difficulties partitioning allochthonous and autochthonous sources, there is limited information regarding how the latter is processed. Autochthonous N may be particularly important in alpine, arid, or polar environments. We test the hypothesis that the availability of remineralized autochthonous N is controlled by connectivity between the hyporheic zone and main channel due to the contrasting biogeochemical functions of benthic autotrophs (including N‐fixing &lt;em&gt;Nostoc&lt;/em&gt;) and hyporheic heterotrophs in an intermittent Antarctic stream. There, we collected surface water and hyporheic water concurrently at 4‐6 hour intervals over a 32.5‐hr period during one flow season and opportunistically throughout a second. Hyporheic water had 7 to 30 times greater nitrate‐N concentrations relative to surface water across all flow conditions. In contrast, ammonium concentrations were generally lower, although similar among locations. Additionally, nitrate in hyporheic water was positively correlated with silica, an indicator of hyporheic residence time. A laboratory assay confirmed prior inferences that hyporheic microbial communities possess the functional potential to perform nitrification. Together, these findings suggest that remineralized autochthonous N accumulates in the hyporheic zone even as streamflow varies and likely subsidizes stream N availability&amp;mdash;which supports prior inferences from N stable isotope data at this site. These results highlight the importance of hyporheic connectivity in controlling autochthonous N cycling and availability in streams.&lt;/p&gt;</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>32</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Singley, Joel G.</style></author></authors><secondary-authors><author><style face="normal" font="default" size="100%">Eve-Lyn S. Hinckley</style></author><author><style face="normal" font="default" size="100%">Michael N. Gooseff</style></author></secondary-authors></contributors><titles><title><style face="normal" font="default" size="100%">Stream corridor connectivity controls on nitrogen cycling</style></title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Antarctica</style></keyword><keyword><style  face="normal" font="default" size="100%">hyporheic zone</style></keyword><keyword><style  face="normal" font="default" size="100%">nitrogen cycling</style></keyword><keyword><style  face="normal" font="default" size="100%">streams</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2021</style></year><pub-dates><date><style  face="normal" font="default" size="100%">05/2021</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">https://www.proquest.com/docview/2572593127</style></url></web-urls></urls><publisher><style face="normal" font="default" size="100%">University of Colorado Boulder</style></publisher><pub-location><style face="normal" font="default" size="100%">Boulder, CO, USA</style></pub-location><volume><style face="normal" font="default" size="100%">PhD</style></volume><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">&lt;p&gt;As water flows downstream, it is transported to and from environments that surround the visible stream. Along with surface water, these laterally and vertically connected environments comprise the stream corridor. Stream corridor connectivity influences many ecosystem services, including retention of excess nutrients. The subsurface area where stream water and groundwater mixes&amp;mdash;the hyporheic zone&amp;mdash;represents one of the most biogeochemically active parts of stream corridors.&lt;/p&gt;&lt;p&gt;The goal of my research is to advance understanding of how connectivity between different parts of a stream corridor controls the availability and retention of nitrogen (N), a nutrient that can limit primary productivity (low-N) and negatively impact water quality (excess N). First, I developed and applied a new machine learning method to objectively characterize the extent and variability of hyporheic exchange in terms of statistically unique functional zones using geophysical data. In applying this method to a benchmark dataset, I found that hyporheic extent does not scale uniformly with streamflow and that changes in the heterogeneity of connectivity differ over small (&amp;lt;10 m) distances. Next, I leveraged the relative simplicity of ephemeral streams of the McMurdo Dry Valleys (MDVs), Antarctica, to isolate stream corridor processes that influence the fate of N. Through intensive field sampling campaigns, I found that the hyporheic zone can be a persistent source of N even in this low nutrient environment. Next, I combined historic sample data and remote sensing analysis to estimate how much N is stored in an MDV stream corridor. My results indicate that up to 103 times more N is stored in this system than is exported each year, with most of this storage in the shallow (&amp;lt; 10 cm) hyporheic zone. Lastly, I examined 25 years of data for 10 streams to assess how stream corridor processes control concentration-discharge relationships. I found that in the absence of hillslope connectivity, stream corridor processes alone can maintain chemostasis &amp;ndash; relatively small concentration changes with large fluctuations in streamflow &amp;ndash; of both geogenic solutes and primary nutrients. My analysis also revealed that solutes subject to greater control by biological processes exhibit more variability within chemostatic relationships than weathering solutes that are only minimally influenced by biota.&lt;/p&gt;&lt;p&gt;Altogether, this research advances understanding of processes that are difficult to measure or are often overlooked in typical studies of temperate stream corridors. My findings provide insight into the surprising ways in which N is mobilized, transformed, and retained due to stream corridor connectivity in intermittent stream systems with few N inputs.&lt;/p&gt;</style></abstract><work-type><style face="normal" font="default" size="100%">Doctoral</style></work-type></record></records></xml>