Rain induced bursts of denitrification activity account for differences in dissolved nitrogen export from forested catchments

This study sought to explain differences in dissolved nitrogen (N) export between catchments in the Turkey Lakes Watershed. Neighbouring catchments c35 and c38 have similar N inputs, but a discrepancy in dissolved N export. It was hypothesized that gaseous N export from wet soils accounted for this discrepancy as c35 contains few isolated wet soils, whereas c38 contains many connected wet soils. To test this hypothesis, N2O efflux from soils was measured during the growing season in 2006 and 2007. Minimal N2O efflux (\u3c 1 g N ha1 day1) was observed on days without rain. However, on days with rain, N2O efflux was observed, with a linear increase in the rate of N2O efflux from wet soils of 0.016 g N ha1 day1 (r2=0.60, p\u3c0.001) per millimetre of rain. Intensive monitoring of the wetland soil profile suggested that rain delivers water to the surface layers of the wetland creating an oxygen poor environment where accumulated NO3 is transformed to N2O then N2. The discrepancy in dissolved N export between c35 and c38 was explained when N2O and associated N2 efflux (based on a ratio of 10N2:1N20) from the wet soils in c38 were considered. This study suggests that rain can produce substantial bursts of N2O and N2 from forest soils and that failure to account for gaseous N export may lead to an underestimation of N export from forested catchments

Collaborative research skills should be meaningfully incorporated into undergraduate programmes

Scientific research has changed, now being largely conducted in collaborative teams. However, undergraduate student training has not necessarily kept pace with these changes. In order to work effectively in collaborative settings, students need to develop not only the technical skills related to their discipline, but also communication and interpersonal skills needed to work in teams. Nora J. Casson reports on research which proposes a model for explicitly teaching collaborative skills, while engaging students in meaningful scientific research. Skills such as managing data from multiple collaborators or giving and receiving feedback via file-sharing platforms should be taught as explicitly as traditional skills such as how to use a pipette or how to formulate a hypothesis

Future of Winter in Northeastern North America: Climate Indicators Portray Warming and Snow Loss that will Impact Ecosystems and Communities

Winters in northeastern North America have warmed faster than summers, with impacts on ecosystems and society. Global climate models (GCMs) indicate that winters will continue to warm and lose snow in the future, but uncertainty remains regarding the magnitude of warming. Here, we project future trends in winter indicators under lower and higher climate-warming scenarios based on emission levels across northeastern North America at a fine spatial scale (1/16°) relevant to climate-related decision making. Under both climate scenarios, winters continue to warm with coincident increases in days above freezing, decreases in days with snow cover, and fewer nights below freezing. Deep snowpacks become increasingly short-lived, decreasing from a historical baseline of 2 months of subnivium habitat to warmer, higher-emissions climate scenario. Warmer winter temperatures allow invasive pests such as Adelges tsugae (Hemlock Woolly Adelgid) and Dendroctonus frontalis (Southern Pine Beetle) to expand their range northward due to reduced overwinter mortality. The higher elevations remain more resilient to winter warming compared to more southerly and coastal regions. Decreases in natural snowpack and warmer temperatures point toward a need for adaptation and mitigation in the multi-million-dollar winter-recreation and forest-management economies

Hydrological and seasonal controls of phosphorus in Northern Great Plains agricultural streams

PostprintControls on nutrient transport in cold, low relief agricultural regions vary dramatically among seasons. The spring snowmelt is often the dominant runoff and nutrient loading event of the year. However, climate change may increase the proportion of runoff occurring with rainfall and there is an urgent need to understand seasonal controls on nutrient transport in order to understand how patterns may change in the future. In this study, we assess patterns and drivers of total phosphorus (TP) dynamics in eight streams draining agriculturally-dominated watersheds, located in southern Manitoba, Canada. Data from three years of monitoring revealed highly coherent patterns of TP concentrations in streams, with pronounced peaks in the spring and mid- summer across the region. This coherent pattern was in spite of considerable interannual variability in the magnitude and timing of discharge; in particular, a major storm event occurred in summer 2014, which resulted in more discharge than the preceding spring melt. Concentration-discharge model fits were generally poor or not significant, suggesting that runoff generation is not the primary driver of TP dynamics in the majority of streams. Seasonal patterns of conductivity and stream temperature suggest mechanisms controlling TP vary by season; a spring TP concentration maximum may be related to surface runoff over frozen soils while the summer TP maximum may be related to temperature-driven biogeochemical processes, which are not well-represented in current conceptual or predictive models. These findings suggest that controls on stream TP concentrations are dynamic through the year, and responses to increases in dormant and non-dormant season temperatures may depend on seasonally-variable processes

Untersuchungen von Beugesehnennähten mittels Bildsequenzanalyse im Experiment

Im Rahmen dieser Arbeit werden die Ergebnisse aus Zugversuchen an Schweinesehnen, die mit verschiedenen Nahtmaterialien und den gängigen Nahttechniken für Beugesehnen der Hand genäht wurden, vorgestellt. Schwerpunkt der Untersuchungen ist die Ermittlung und Dokumentation der Reißfestigkeit der Naht und die Spaltbildung an der Kontaktstelle der genähten Sehnenstümpfe mittels biomechanischer Versuche. Das Eintreten der Spaltbildung und des Nahtrisses wird durch videotechnische Aufzeichnungen, die den eigentlichen Messvorgang an der Universalprüfmaschine begleiten, exakt dokumentiert (Bildsequenzanalyse). Die Bildsequenzanalyse stellt gegenüber den in der Literatur dokumentierten Methoden eine wesentliche Fort- bzw. Neuentwicklung zur Ermittlung der Spaltstabilität und der Reißfestigkeit von genähten Sehnen dar. Die Auswertung der Versuche mittels Bildsequenzanalyse wurde für 12 verschiedene Nahttechnik/Nahtmaterial-Kombinationen durchgeführt. Nach Entwicklung und Anfertigung einer neuen Einspannvorrichtung für die Sehnen, die eine optimale Festhaltung der Sehnenstümpfe gewährleistete, erfolgte die systematische Durchführung von Bildsequenzanalysen für gängige Sehnennaht-Techniken mit verschiedenen Fäden. Auf Grundlage der biomechanischen Versuche und der Weiterentwicklung bisheriger Kenntnisse zur Beugesehnennaht konnte im Rahmen dieser Arbeit eine optimierte bzw. eine neue Nahttechnik entwickelt werden (Marburger Sehnennaht I und II), die eine frühe postoperative Mobilisierung durch entsprechende Nahtfestigkeiten ermöglicht, eine gute Gleitfunktion aufweist sowie durch Erhaltung der Gefäßversorgung der Sehne einen sicheren Heilungsprozess gewährleistet. Die Ergebnisse der biomechanischen Versuche mit der Marburger Sehnennaht I und II sind in dieser Arbeit detailliert dokumentiert. Der Vergleich mit den gängigen Sehnennaht-Techniken zeigt, dass die Marburger Sehnennaht eine hohe Reißfestigkeit und die beste Spaltstabilität besitzt

The ecology of methane in streams and rivers: patterns, controls, and global significance

Streams and rivers can substantially modify organic carbon (OC) inputs from terrestrial landscapes, and much of this processing is the result of microbial respiration. While carbon dioxide (CO₂) is the major end‐product of ecosystem respiration, methane (CH₄) is also present in many fluvial environments even though methanogenesis typically requires anoxic conditions that may be scarce in these systems. Given recent recognition of the pervasiveness of this greenhouse gas in streams and rivers, we synthesized existing research and data to identify patterns and drivers of CH₄, knowledge gaps, and research opportunities. This included examining the history of lotic CH4 research, creating a database of concentrations and fluxes (MethDB) to generate a global‐scale estimate of fluvial CH₄ efflux, and developing a conceptual framework and using this framework to consider how human activities may modify fluvial CH₄ dynamics. Current understanding of CH₄ in streams and rivers has been strongly influenced by goals of understanding OC processing and quantifying the contribution of CH₄ to ecosystem C fluxes. Less effort has been directed towards investigating processes that dictate in situ CH₄ production and loss. CH₄ makes a meager contribution to watershed or landscape C budgets, but streams and rivers are often significant CH₄ sources to the atmosphere across these same spatial extents. Most fluvial systems are supersaturated with CH₄ and we estimate an annual global emission of 26.8 Tg CH₄, equivalent to ~15‐40% of wetland and lake effluxes, respectively. Less clear is the role of CH₄ oxidation, methanogenesis, and total anaerobic respiration to whole ecosystem production and respiration. Controls on CH₄ generation and persistence can be viewed in terms of proximate controls that influence methanogenesis (organic matter, temperature, alternative electron acceptors, nutrients) and distal geomorphic and hydrologic drivers. Multiple controls combined with its extreme redox status and low solubility result in high spatial and temporal variance of CH₄ in fluvial environments, which presents a substantial challenge for understanding its larger‐scale dynamics. Further understanding of CH₄ production and consumption, anaerobic metabolism, and ecosystem energetics in streams and rivers can be achieved through more directed studies and comparison with knowledge from terrestrial, wetland, and aquatic disciplines."Support for this paper was provided by funding from the North Temperate Lakes LTER program, NSF DEB‐0822700."https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/15-102

Freezing plants : exploring the effects of freeze thaw cycles on macrophyte phosphorus release

Every year following the cold winter freeze comes the spring thaw, and with it comes an influx of nutrients that can cause eutrophication problems; even in high nutrient systems. We identified a potential source of nutrients released during the winter freeze; aquatic macrophytes and aimed to determine the quantity of total phosphorus (TP) they release. Specifically, cattails and reeds (Typha and Juncus, respectively). Stalks were harvested from 3 different sites; a pond with an agriculturally dominated watershed, the beginning of a wetland used to treat effluent waste water, and a site further along in the wetland treatment process. Samples from each site were split into four different sample types: wet freeze, dry freeze, wet control, and dry control. Control and freeze samples were placed in at 1.6[degree]C and -1[degree]C respectively, and left for equal amounts of time averaging 31.375 hours (SD 10.25). After treatment, residual water samples were analyzed for total phosphorus concentrations. Results showed that freeze thaw cycles (FTCs) did not induce TP release from macrophytes tested in the lab. These results suggest that the use of macrophytes as a sink for nutrients is a beneficial practice that managers should continue to employ.Matthew Sauer, Osama Ahmed, Jeremy Leathers, Katy Nugent, Tyler Prentice, Helen Baulch, Nora Casson, Jason Venkiteswarab, Colin Whitfield and Rebecca North (University of Missouri, University of Saskatchewan, Wilfred Laurier University, University of Winnipeg

The role of wetland coverage within the near-stream zone in predicting of seasonal stream export chemistry from forested headwater catchments

Postprint version. "This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record."Stream chemistry is often used to infer catchment‐scale biogeochemical processes. However, biogeochemical cycling in the near‐stream zone or hydrologically‐connected areas may exert a stronger influence on stream chemistry compared with cycling processes occurring in more distal parts of the catchment, particularly in dry seasons and in dry years. In this study, we tested the hypotheses that near‐stream wetland proportion is a better predictor of seasonal (winter, spring, summer and fall) stream chemistry compared with whole‐catchment averages and that these relationships are stronger in dryer periods with lower hydrologic connectivity. We evaluated relationships between catchment wetland proportion and 16‐year average seasonal flow‐weighted concentrations of both biogeochemically‐active nutrients, dissolved organic carbon (DOC), nitrate (NO3‐N), total phosphorus (TP), as well as weathering products, calcium (Ca), magnesium (Mg), at ten headwater (< 200 ha) forested catchments in south‐central Ontario, Canada. Wetland proportion across the entire catchment was the best predictor of DOC and TP in all seasons and years, whereas predictions of NO3‐N concentrations improved when only the proportion of wetland within the near‐stream zone was considered. This was particularly the case during dry years and dry seasons such as summer. In contrast, Ca and Mg showed no relationship with catchment wetland proportion at any scale or in any season. In forested headwater catchments, variable hydrologic connectivity of source areas to streams alters the role of the near‐stream zone environment, particularly during dry periods. The results also suggest that extent of riparian zone control may vary under changing patterns of hydrological connectivity. Predictions of biogeochemically‐active nutrients, particularly NO3‐N, can be improved by including near‐stream zone catchment morphology in landscape models.Funding for this project was provided by a Natural Sciences and Engineering Research Council of Canada Discovery Grant to MCE.https://onlinelibrary.wiley.com/doi/abs/10.1002/hyp.1341

Burping wetlands : quantifying greenhouse gas ebullition rates across a range of sediment types and characteristics, water quality variables, and land use

Aquatic ecosystems are a source of greenhouse gases (GHG) to the atmosphere. One pathway of this GHG release is ebullition, or bubbling, from aquatic sediments. The contribution of ebullition is often underestimated in global GHG budgets, as it is rarely included in GHG emission measurements. The ebullition pathway can account for up to 67 percent of methane emissions from water bodies. We aim to determine the factors that influence ebullition of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O), including sediment characteristics, water quality characteristics, and land use. Our study ponds are in urban, agricultural, and woodland areas. We found that N2O flux rates are significantly lower than CH4 and CO2 flux rates across all study ponds. We also found that urban areas have higher GHG flux rates, which is correlated with low organic matter content. Understanding the factors influencing GHG ebullition from aquatic ecosystems will give us a broader understanding of the significance of their contribution to global GHG budgets in a changing climate.Jannice Newson, Jaylen Bragg, Hamza Amjad, Lauren Dyck, Selena Komarevich, Colin Whitfield, Helen Baulch, Jason Venkiteswaran, Nora Casson, Richard Helmle, and Rebecca L. North (University of Missouri, University of Winnipeg, University of Saskatchewan, Wilfred Laurier University

Differences in atmospheric phosphorus deposition amongst rural and urban land use locations in Missouri

Atmospheric phosphorus (AP) produced by both anthropogenic and natural processes influences phytoplankton productivity and alters carbon processing in water bodies, resulting in potential impairment and toxic phytoplankton blooms. The production of AP, which is oftentimes transported vast distances by wind dispersal in the form of enriched mineral dust, can be re-deposited by wet (precipitation based) or dry (continual) deposition. Both rural and urban locations in Missouri experience varying anthropogenic activities; therefore, distinguishing between varying land use locations at these sites provides insight as to why AP may differ. The objective of this study is to determine if AP deposition differs among rural and urban land use locations in Missouri. When soil has been recently agitated and readily exposed, we hypothesize this additional P in the atmosphere will result in higher bulk deposition flux totals (BD) in rural locations. AP was collected from three rural locations and three urban locations, using a standard sized utility bucket, altered to reduce debris. After each two-week sampling period, a total sample water volume for each site is collected, total P is analyzed (TP), which determines the BD flux of each site by factoring the time it took to collect each sample (4 samples over approximately 70 days). Rural locations had the highest BD. Rural locations were not significantly different than urban locations (F5,18 = 1.667, p = 0.194). Further analysis of AP and the implication on water bodies is needed, as AP analysis is exceedingly rare. A multitude of differing land use practices results in variables that contribute significantly to the production of AP.Crystal Rein, Sarahi Viscarra Arellano, Karl Friesen-Hughes, Ashley King, Alexia Marten, Corey Sanderson, Jason J Venkiteswaran, Helen Baulch, Nora Jessie Casson, Colin J Whitfield, and Rebecca North (University of Missouri, University of Saskatchewan, Wilfrid Laurier University, University of Winnipeg