<?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%">Tyler J. Kohler</style></author><author><style face="normal" font="default" size="100%">Singley, Joel G.</style></author><author><style face="normal" font="default" size="100%">Wlostowski, Adam</style></author><author><style face="normal" font="default" size="100%">Diane M. McKnight</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Nitrogen fixation facilitates stream microbial mat biomass across the McMurdo Dry Valleys, Antarctica</style></title><secondary-title><style face="normal" font="default" size="100%">Biogeochemistry</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">biofilm</style></keyword><keyword><style  face="normal" font="default" size="100%">C</style></keyword><keyword><style  face="normal" font="default" size="100%">cyanobacteria</style></keyword><keyword><style  face="normal" font="default" size="100%">hyporheic zone</style></keyword><keyword><style  face="normal" font="default" size="100%">MCM LTER</style></keyword><keyword><style  face="normal" font="default" size="100%">mineralization</style></keyword><keyword><style  face="normal" font="default" size="100%">N</style></keyword><keyword><style  face="normal" font="default" size="100%">P biogeochemistry</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2023</style></year><pub-dates><date><style  face="normal" font="default" size="100%">07/2023</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">https://link.springer.com/article/10.1007/s10533-023-01069-0</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;Nitrogen (N) fixation is a fundamental mechanism by which N enters streams. Yet, because of modern N saturation, it is difficult to study the importance of N-fixation to stream nutrient budgets. Here, we utilized relatively simple and pristine McMurdo Dry Valley streams to investigate the role of N-fixing &lt;i&gt;Nostoc&lt;/i&gt; abundance, streamwater dissolved inorganic N (DIN) concentration, and distance from the source glacier in regulating the elemental and isotopic composition of three microbial mat types (black, orange, and green) at the landscape scale. We found &lt;i&gt;Nostoc&lt;/i&gt;-based black mats were the most enriched in δ15N, and δ15N signatures of mats increased where &lt;i&gt;Nostoc&lt;/i&gt; was abundant, but did not surpass the atmospheric standard (δ15N &amp;asymp; 0&amp;permil;). Furthermore, green and orange mat δ15N signatures became more depleted with increasing DIN, indicating that mats utilize glacial meltwater-sourced N when available. The distance from the source glacier explained limited variability in mat δ15N across sites, indicating the influence of individual stream characteristics on N spiraling. To further explore longitudinal N spiraling processes generating observed δ15Ν patterns, we developed a simple steady-state mathematical model. Analysis of plausible scenarios with this model confirmed that streams both have the capacity to remove allochthonous DIN over the plausible range of inputs, and that internal N sources are required to account for δ15N signatures and observed DIN concentrations at stream outlets. Collectively, these data and modeling results demonstrate that N-fixation exerts substantial influence within and across these streams, and is presumably dependent upon interconnected organic matter reserves, mineralization rates, and geomorphology.&lt;/p&gt;</style></abstract></record><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%">Khan, Alia L.</style></author><author><style face="normal" font="default" size="100%">McMeeking, Gavin</style></author><author><style face="normal" font="default" size="100%">Schwarz, Joshua P.</style></author><author><style face="normal" font="default" size="100%">Xian, Peng</style></author><author><style face="normal" font="default" size="100%">Kathleen A. Welch</style></author><author><style face="normal" font="default" size="100%">W. Berry Lyons</style></author><author><style face="normal" font="default" size="100%">Diane M. McKnight</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Near-surface refractory black carbon observations in the atmosphere and snow in the McMurdo Dry Valleys, Antarctica and potential impacts of foehn winds</style></title><secondary-title><style face="normal" font="default" size="100%">Journal of Geophysical Research: Atmospheres</style></secondary-title><short-title><style face="normal" font="default" size="100%">J. Geophys. Res. Atmos.</style></short-title></titles><dates><year><style  face="normal" font="default" size="100%">2018</style></year><pub-dates><date><style  face="normal" font="default" size="100%">01/2018</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">http://doi.wiley.com/10.1002/2017JD027696</style></url></web-urls></urls><volume><style face="normal" font="default" size="100%">123</style></volume><pages><style face="normal" font="default" size="100%">2877 - 2887</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">&lt;p&gt;&lt;span style=&quot;font-family: TimesNewRomanPSMT; font-size: 12pt;&quot;&gt;Measurements of light absorbing particles in the boundary layer of the high southern latitudes are scarce, particularly in the McMurdo Dry Valleys (MDV),&amp;nbsp;&lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;Antarctica. During the 2013 - 2014 austral summer near-surface boundary layer refractory black carbon (rBC) aerosols were measured in air by a single particle soot photometer (SP2) at multiple locations in the MDV. Near-continuous rBC atmospheric measurements were collected at Lake Hoare Camp (LH) over two months and for several hours at more remote locations away from established field camps. We investigated periods dominated by both up and down-valley winds to explore the causes of differences in rBC concentrations and size distributions. Snow samples were also collected in a 1m pit on a glacier near the camp. The range of concentrations rBC in snow were 0.3 &lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;&amp;ndash; &lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;1.2 &amp;plusmn; 0.3 μg-rBC/L-H&lt;/span&gt;&lt;span style=&quot;font-size: 8pt; font-family: TimesNewRomanPSMT; vertical-align: -1pt;&quot;&gt;2&lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;O, and total organic carbon were 0.3 &lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;&amp;ndash; &lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;1.4 &amp;plusmn; 0.3 mg/L. The rBC concentrations measured in this snow pit are not sufficient to reduce surface albedo, however, there is potential for accumulation of rBC on snow and ice surfaces at low elevation throughout the MDV which were not measured as part of this study. At LH, the average background rBC mass aerosol concentrations was 1.3 ng/m&lt;/span&gt;&lt;span style=&quot;font-size: 8pt; font-family: TimesNewRomanPSMT; vertical-align: 5pt;&quot;&gt;3&lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;. rBC aerosol mass concentrations were slightly lower, 0.09 &lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;&amp;ndash; &lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;1.3 ng/m&lt;/span&gt;&lt;span style=&quot;font-size: 8pt; font-family: TimesNewRomanPSMT; vertical-align: 5pt;&quot;&gt;3&lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;, at the most remote sites in the MDV. Concentration spikes as high as 200 ng/m&lt;/span&gt;&lt;span style=&quot;font-size: 8pt; font-family: TimesNewRomanPSMT; vertical-align: 5pt;&quot;&gt;3 &lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;were observed at LH, associated with local activities. During a foehn wind event, the average rBC mass concentration increased to 30-50 ng m&lt;/span&gt;&lt;span style=&quot;font-size: 8pt; font-family: TimesNewRomanPSMT; vertical-align: 5pt;&quot;&gt;-3&lt;/span&gt;&lt;span style=&quot;font-size: 12pt; font-family: TimesNewRomanPSMT;&quot;&gt;. Here we show the rBC increase could be due to resuspension of locally produced BC from generators, rocket toilets, and helicopters, which may remain on the soil surface until redistributed during high wind events. Quantification of local production and long-range atmospheric transport of rBC to the MDV is necessary for understanding the impacts of this species on regional climate.&amp;nbsp;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&amp;nbsp;&lt;/p&gt;</style></abstract><issue><style face="normal" font="default" size="100%">5</style></issue></record><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%">Tyler J. Kohler</style></author><author><style face="normal" font="default" size="100%">David J. Van Horn</style></author><author><style face="normal" font="default" size="100%">Darling, Joshua P.</style></author><author><style face="normal" font="default" size="100%">Cristina D. Takacs-Vesbach</style></author><author><style face="normal" font="default" size="100%">Diane M. McKnight</style></author></authors><secondary-authors><author><style face="normal" font="default" size="100%">Wagner, Dirk</style></author></secondary-authors></contributors><titles><title><style face="normal" font="default" size="100%">Nutrient treatments alter microbial mat colonization in two glacial meltwater streams from the McMurdo Dry Valleys, Antarctica</style></title><secondary-title><style face="normal" font="default" size="100%">FEMS Microbiology Ecology</style></secondary-title><short-title><style face="normal" font="default" size="100%">FEMS Microbiology Ecology</style></short-title></titles><dates><year><style  face="normal" font="default" size="100%">2016</style></year><pub-dates><date><style  face="normal" font="default" size="100%">03/2016</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">http://femsec.oxfordjournals.org/lookup/doi/10.1093/femsec/fiw049</style></url></web-urls></urls><volume><style face="normal" font="default" size="100%">92</style></volume><pages><style face="normal" font="default" size="100%">fiw049</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">&lt;p&gt;&lt;span style=&quot;color: rgb(3, 3, 3); font-family: Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; background-color: rgb(255, 255, 254);&quot;&gt;Microbial mats are abundant in many alpine and polar aquatic ecosystems. With warmer temperatures, new hydrologic pathways are developing in these regions and increasing dissolved nutrient fluxes. In the McMurdo Dry Valleys, thermokarsting may release both nutrients and sediment, and has the potential to influence mats in glacial meltwater streams. To test the role of nutrient inputs on community structure, we created nutrient diffusing substrata (NDS) with agar enriched in N, P and N + P, with controls, and deployed them into two Dry Valley streams. We found N amendments (N and N + P) to have greater chlorophyll-a concentrations, total algal biovolume, more fine filamentous cyanobacteria and a higher proportion of live diatoms than other treatments. Furthermore, N treatments were substantially elevated in Bacteroidetes and the small diatom,&amp;nbsp;&lt;/span&gt;&lt;em style=&quot;outline: 0px; font-variant-numeric: inherit; font-stretch: inherit; font-size: 14px; line-height: 21px; font-family: Helvetica, Arial, sans-serif; color: rgb(3, 3, 3); background-color: rgb(255, 255, 254);&quot;&gt;Fistulifera pelliculosa&lt;/em&gt;&lt;span style=&quot;color: rgb(3, 3, 3); font-family: Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; background-color: rgb(255, 255, 254);&quot;&gt;. On the other hand, species richness was almost double in P and N + P treatments over others, and coccoid green algae and Proteobacteria were more abundant in both streams. Collectively, these data suggest that nutrients have the potential to stimulate growth and alter community structure in glacial meltwater stream microbial mats, and the recent erosion of permafrost and accelerated glacial melt will likely impact resident biota in polar lotic systems here and elsewhere.&lt;/span&gt;&lt;/p&gt;</style></abstract><issue><style face="normal" font="default" size="100%">4</style></issue></record></records></xml>