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  • 11
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    Potential Nitrogen Losses in Relation to Spatially Distinct Soil Management History and Biochar Addition (2018)
    Wiley
    Details
    Publication Date: 2018-01-01
    Print ISSN: 0047-2425
    Electronic ISSN: 1537-2537
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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  • 12
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    Nitrate uptake across biomes and the influence of elemental stoichiometry: A new look at LINX II (2016)
    Wiley
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    Publication Date: 2016-07-26
    Description: Considering recent increases in anthropogenic N loading it is essential to identify the controls on N removal and retention in aquatic ecosystems because the fate of N has consequences for water quality in streams and downstream ecosystems. Biological uptake of nitrate (NO 3 - ) is a major pathway by which N is removed from these ecosystems. Here we used data from the second Lotic Intersite Nitrogen eXperiment (LINX II) in a multivariate analysis to identify the primary drivers of variation in NO 3 - uptake velocity among biomes. Across 69 study watersheds in North America, DOC:NO 3 - ratios and photosynthetically active radiation were identified as the two most important predictor variables in explaining NO 3 - uptake velocity. However, within a specific biome the predictor variables of NO 3 - uptake velocity varied, and included various physical, chemical and biological attributes. . Our analysis demonstrates the broad control of elemental stoichiometry on NO 3 - uptake velocity as well as the importance of biome-specific predictors. Understanding this spatial variation has important implications for biome-specific watershed management and the downstream export of NO 3 - , as well as for development of spatially explicit global models that describe N dynamics in streams and rivers.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 13
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    DOC:NO3- ratios control NO3- uptake in forested headwater streams (2015)
    Wiley
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    Publication Date: 2015-12-27
    Description: The underlying mechanisms driving the coupled interactions between inorganic nitrogen uptake and dissolved organic matter are not well understood, particularly in surface waters. To determine the relationship between dissolved organic carbon (DOC) quantity and nitrate (NO 3 - ) uptake kinetics in streams, we performed a series of NO 3 - Tracer Additions for Spiraling Curve Characterization (TASCC) experiments in four streams within the Lamprey River Watershed, New Hampshire, across a range in background DOC concentrations (1 – 8 mg C/L). Experiments were performed throughout the 2013 and 2014 growing seasons. Across streams and experimental dates, ambient uptake velocity (V f ) correlated positively with increasing DOC concentrations and DOC:NO 3 - ratios but was only weakly negatively associated with NO 3 - concentrations. Ambient NO 3 - V f was unrelated to pH, light, temperature, dissolved oxygen and SUVA 254 . Although there were general tendencies across the entire Lamprey River Watershed, individual sites behaved differently in their uptake kinetics. NO 3 - uptake dynamics in the Lamprey River Watershed are most strongly influenced by DOC concentrations rather than NO 3 - concentrations or physico-chemical parameters, which have been identified as regional- to continental-scale drivers in previous research. Understanding the fundamental relationships between dissolved organic matter and inorganic nutrients will be important as global and climatic changes influence the delivery and production of DOC and NO 3 - in aquatic ecosystems.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 14
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    Stream solute tracer time scales changing with discharge and reach length confound process interpretation (2016)
    Wiley
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    Publication Date: 2016-04-05
    Description: Improved understanding of stream solute transport requires meaningful comparison of processes across a wide range of discharge conditions and spatial scales. At reach scales where solute tracer tests are commonly used to assess transport behavior, such comparison is still confounded due to the challenge of separating dispersive and transient storage processes from the influence of the advective timescale that varies with discharge and reach length. To better resolve interpretation of these processes from field-based tracer observations, we conducted recurrent conservative solute tracer tests along a 1-km study reach during a storm discharge period and further discretized the study reach into six segments of similar length but different channel morphologies. The resulting suite of data, spanning an order of magnitude in advective timescales, enabled us to (1) characterize relationships between tracer response and discharge in individual segments and (2) determine how combining the segments into longer reaches influences interpretation of dispersion and transient storage from tracer tests. We found that the advective timescale was the primary control on the shape of the observed tracer response. Most segments responded similarly to discharge, implying that the influence of morphologic heterogeneity was muted relative to advection. Comparison of tracer data across combined segments demonstrated that increased advective timescales could be misinterpreted as a change in dispersion or transient storage. Taken together, our results stress the importance of characterizing the influence of changing advective timescales on solute tracer responses before such reach scale observations can be used to infer solute transport at larger network scales. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 15
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    Water motion and vegetation control the pH dynamics in seagrass‐dominated bays (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Global oceanic pH is lowering, which is causing great concern for the natural functioning of marine ecosystems. Current pH predictions are based on open ocean models; however, coastal zones are dynamic systems with seawater pH fluctuating temporally and spatially. To understand how coastal ecosystems will respond in the future, we first need to quantify the extent that local processes influence the pH of coastal zones. With this study, we show that over a single diurnal cycle, the total pH can fluctuate up to 0.2 units in a shallow seagrass‐dominated bay, driven by the photosynthesis and respiration of the vegetation. However, these biologically controlled pH fluctuations vary significantly over small distances. Monitoring conducted at neighboring sites with contrasting hydrodynamic regimes highlights how water motion controls the extent that the local pH is altered by the metabolism of vegetation. The interactive effects of hydrodynamics and vegetation were further investigated with an in situ experiment, where the hydrodynamics were constrained and thus the local water residence time was increased, displaying the counteractive effect of hydrodynamics on the pH change caused by vegetation. With this research, we provide detailed in situ evidence of the spatial variation of pH within marine ecosystems, highlighting the need to include hydrodynamic conditions when assessing the pH‐effects of vegetation, and identifying potential high‐pH refuges in a future low pH ocean.
    Print ISSN: 0024-3590
    Electronic ISSN: 1939-5590
    Topics: Biology , Geosciences , Physics
    Published by Wiley on behalf of The Association for the Sciences of Limnology and Oceanography (ASLO).
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  • 16
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    Tropical Pioneer Seeds Have Different Dormancy‐Defense Syndromes That Help Them to Survive in the Soil Seed Bank (2018)
    Wiley
    Details
    Publication Date: 2018
    Description: The Bulletin of the Ecological Society of America, Volume 99, Issue 4, October 2018.
    Print ISSN: 0012-9623
    Electronic ISSN: 2327-6096
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 17
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    Response of the hyporheic zone to transient groundwater fluctuations on the annual and storm event time scales (2016)
    Wiley
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    Publication Date: 2016-06-14
    Description: The volume of the water stored in and exchanged with the hyporheic zone is an important factor in stream metabolism and biogeochemical cycling. Previous studies have identified groundwater direction and magnitude as one key control on the volume of the hyporheic zone, suggesting that fluctuation in the riparian water table could induce large changes under certain seasonal conditions. In this study, we analyze the transient drivers that control the volume of the hyporheic zone by coupling the Brinkman-Darcy equation to the Navier-Stokes equations to simulate annual and storm induced groundwater fluctuations. The expansion and contraction of the hyporheic zone was quantified based on temporally dynamic scenarios simulating annual groundwater fluctuations in a humid temperate climate. The amplitude of the groundwater signal was varied between scenarios to represent a range of annual hydrologic forcing. Storm scenarios were then superimposed on the annual scenario to simulate the response to short term storm signals. Simulations used two different groundwater storm responses; one in-phase with the surface water response and one 14 hours out-of-phase with the surface water response to represent our observed site conditions. Results show that annual groundwater fluctuation is a dominant control on the volume of the hyporheic zone, where increasing groundwater fluctuation increases the amount of annual variation. Storm responses depended on the antecedent conditions determined by annual scenarios, where the time of year dictated the duration and magnitude of the storm induced response of the hyporheic zone. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 18
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    Leonardo Da Vinci and the nature of “creative genius” (2015)
    Wiley
    In: BioEssays
    Details
    Publication Date: 2015-04-22
    Print ISSN: 0265-9247
    Electronic ISSN: 1521-1878
    Topics: Biology , Medicine
    Published by Wiley
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  • 19
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    Hydrologic and geomorphic controls on hyporheic exchange during base flow recession in a headwater mountain stream (2012)
    Wiley
    Details
    Publication Date: 2012-04-13
    Description: Hyporheic hydrodynamics are a control on stream ecosystems, yet we lack a thorough understanding of catchment controls on these flow paths, including valley constraint and hydraulic gradients in the valley bottom. We performed four whole-stream solute tracer injections under steady state flow conditions at the H. J. Andrews Experimental Forest (Oregon, United States) and collected electrical resistivity (ER) imaging to directly quantify the 2-D spatial extent of hyporheic exchange through seasonal base flow recession. ER images provide spatially distributed information that is unavailable for stream solute transport modeling studies from monitoring wells alone. The lateral and vertical extent of the hyporheic zone was quantified using both ER images and spatial moment analysis. Results oppose the common conceptual model of hyporheic “compression” by increased lateral hydraulic gradients toward the stream. We found that the extent of the hyporheic zone increased with decreasing vertical gradients away from the stream, in contrast to expectations from conceptual models. Increasing hyporheic extent was observed with both increasing and decreasing down-valley (i.e., parallel to the valley gradient) and cross-valley (i.e., from the hillslope to the stream, perpendicular to the valley gradient) hydraulic gradients. We conclude that neither cross-valley nor down-valley hydraulic gradients are sufficient predictors of hyporheic exchange flux nor flow path network extent. Increased knowledge of the controls on hyporheic exchange, the temporal dynamics of exchange flow paths, and their the spatial distribution is the first step toward predicting hyporheic exchange at the scale of individual flow paths. Future studies need to more carefully consider interactions between spatiotemporally dynamic hydraulic gradients and subsurface architecture as controls on hyporheic exchange.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 20
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    Variations in surface water – ground water interactions along a headwater mountain stream: Comparisons between transient storage and water balance analyses (2013)
    Wiley
    Details
    Publication Date: 2013-02-16
    Description: The accumulation of discharge along a stream valley is frequently assumed to be the primary control on solute transport processes. Relationships of both increasing and decreasing transient storage, and decreased gross losses of stream water have been reported with increasing discharge; however, we have yet to validate these relationships with extensive field study. We conducted transient storage and mass recovery analysis of artificial tracer studies completed for 28 contiguous 100-m reaches along a stream valley, repeated under four baseflow conditions. We calculated net and gross gains and losses, temporal moments of tracer breakthrough curves, and best-fit transient storage model parameters (with uncertainty estimates) for 106 individual tracer injections. Results supported predictions that gross loss of channel water would decrease with increased discharge through time. However, results showed no clear relationship between discharge and transient storage, and our further analysis of solute tracer methods demonstrated that the lack of this relation may be explained by uncertainty and equifinality in the transient storage model framework. Furthermore, comparison of water balance and transient storage approaches reveals complications in clear interpretation of either method due to changes in advective transport time, which sets a the temporal boundary separating transient storage and channel water balance. We have little ability to parse this limitation of solute tracer methods from the physical processes we seek to study. We suggest the combined analysis of both transient storage and channel water balance more completely characterizes transport of solutes in stream networks than can be inferred from either method alone.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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