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  • 1
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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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  • 2
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    Small ponds in headwater catchments are a dominant influence on regional nutrient and sediment budgets (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Small ponds—farm ponds, detention ponds, or impoundments below 0.01 km2—serve important human needs throughout most large river basins. Yet the role of small ponds in regional nutrient and sediment budgets is essentially unknown, currently making it impossible to evaluate their management potential to achieve water quality objectives. Here we used new hydrography datasets and found that small ponds, depending on their spatial position within both their local catchments and the larger river network, can dominate the retention of nitrogen, phosphorus, and sediment compared to rivers, lakes, and reservoirs. Over 300,000 small ponds are collectively responsible for 34%, 69%, and 12% of the mean annual retention of nitrogen, phosphorus, and sediment in the Northeastern United States, respectively, with a dominant influence in headwater catchments (54%, 85%, and 50%, respectively). Small ponds play a critical role among the many aquatic features in long‐term nutrient and sediment loading to downstream waters.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Spatial considerations of stream hydraulics in reach-scale temperature modeling (2015)
    Wiley
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    Publication Date: 2015-06-18
    Description: While a myriad of processes control water temperature, the most significant in streams without notable shading or groundwater inputs are surface heat fluxes at the air-water interface. These fluxes are particularly sensitive to parameters representing the water surface area to volume ratio. Channel geometry dictates this ratio; however, it is currently unclear how spatial variability in stream hydraulics influences temperature predictions or how the contribution of the boundary condition influences interpretation of processes most sensitive to this variability. To investigate these influences over long reach scales, we used high-resolution spatial observations collected over a 25-km reach within a Laplace-domain solution to a two-zone temperature transient storage model. We found that for the study reach and flow condition, changes in the surface area to volume ratio did not generally coincide with changes in stream temperature. Though, notable changes in cumulative mean residence time corresponded with changes in the temperature extremes throughout the study reach. The surface heat fluxes were clearly the most sensitive to spatially variable hydraulics that translated into high residence times once the contribution of the boundary condition decayed. Consistent with solute transport, reach segment lengths that reflect the spatial correlation in observations were necessary to capture the spatial influences of hydraulics on temperature predictions. This approach provides a fundamental step for determining whether spatial detail related to stream hydraulics is important to support accurate temperature predictions and how best to represent that detail. 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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  • 4
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    Community-Derived Standards for LA-ICP-MS U-Th-Pb Geochronology – Uncertainty Propagation, Age Interpretation and Data Reporting (2016)
    Wiley
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    Publication Date: 2016-02-02
    Description: The LA-ICP-MS U-(Th-)Pb geochronology international community has defined new standards for the determination of U-(Th-)Pb ages. A new workflow defines the appropriate propagation of uncertainties for these data, identifying random and systematic components. Only data with uncertainties relating to random error should be used in weighted mean calculations of population ages; uncertainty components for systematic errors are propagated after this stage, preventing their erroneous reduction. Following this improved uncertainty propagation protocol, data can be compared at different uncertainty levels to better resolve age differences. New reference values for commonly used zircon, monazite and titanite reference materials are defined (based on ID-TIMS) after removing corrections for common lead and the effects of excess 230 Th. These values more accurately reflect the material sampled during the determination of calibration factors by LA-ICP-MS analysis. Recommendations are made to graphically represent data only with uncertainty ellipses at 2 s and to submit or cite validation data with sample data when submitting data for publication. New data reporting standards are defined to help improve the peer review process. With these improvements, LA-ICP-MS U-(Th-)Pb data can be considered more robust, accurate, better documented and quantified, directly contributing to their improved scientific interpretation. This article is protected by copyright. All rights reserved.
    Print ISSN: 1639-4488
    Electronic ISSN: 1751-908X
    Topics: Geosciences
    Published by Wiley
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  • 5
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    The influence of spatially variable stream hydraulics on reach scale solute transport modeling (2014)
    Wiley
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    Publication Date: 2014-10-31
    Description: Within the context of reach scale transient storage modeling, there is limited understanding of how best to establish reach segment lengths that represent the effects of spatially variable hydraulic and geomorphic channel properties. In this paper, we progress this understanding through the use of channel property distributions derived from high-resolution imagery that are fundamental for hydraulic routing. We vary the resolution of reach segments used in the model representation and investigate the minimum number necessary to capture spatially variable influences on downstream predictions of solute residence time probability density functions while sufficiently representing the observed channel property distributions. We also test if the corresponding statistical moments of the predictions provide comparable results and, therefore, a method for establishing appropriate reach segment lengths. We find that the predictions and the moment estimates begin to represent the majority of the variability at reach segment lengths coinciding with distances where observed channel properties are spatially correlated. With this approach, reach scales where the channel properties no longer significantly change predictions can be established, which provides a foundation for more focused transient storage modeling efforts.
    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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  • 6
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    Spatiotemporal variability in seawater carbon chemistry for a coral reef flat in Kāne‘ohe Bay, Hawai‘i (2018)
    Wiley
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    Publication Date: 2018
    Description: Abstract Coral reef community composition and ecosystem function may change in response to anthropogenic ocean acidification. However, the magnitude of acidification on reefs will be modified by natural spatial and temporal variability in seawater CO2 chemistry. Consequently, it is necessary to quantify the ecological, biogeochemical, and physical drivers of this natural variability before making robust predictions of future acidification on reefs. In this study, we measured temporal and spatial physiochemical variability on a reef flat in Kāne‘ohe Bay, O‘ahu, Hawai‘i, using autonomous sensors at sites with contrasting benthic communities and by sampling surface seawater CO2 chemistry across the reef flat at different times of the day during June and November. Mean and diurnal temporal variability of seawater CO2 chemistry was more strongly influenced by depth gradients (~ 0.5–10 m) on the reef rather than benthic community composition. Spatial CO2 chemistry gradients across the reef flat reflected the cumulative influence from benthic metabolism, bathymetry, and hydrodynamics. Based on graphical assessment of total alkalinity–dissolved inorganic carbon data, reef metabolism in November was dominated by organic carbon cycling over inorganic carbon cycling, while these processes were closely balanced in June. Overall, this study highlights the strong influence of depth on reef seawater CO2 chemistry variability through its effects on benthic biomass to seawater volume ratio, seawater flow rates, and residence time. Thus, the natural complexity of ecosystems where a combination of ecological and physical factors influence reef chemistry must be considered when predicting ecosystem biogeochemical responses to future anthropogenic changes in seawater CO2 chemistry.
    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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  • 7
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    Hyporheic exchange controlled by dynamic hydrologic boundary conditions (2016)
    Wiley
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    Publication Date: 2016-04-28
    Description: The relative roles of dynamic hydrologic forcing and geomorphology as controls on the timescales and magnitudes of stream-aquifer exchange and hyporheic flowpaths are unknown, but required for management of stream corridors. We developed a comprehensive framework relating diel hydrologic fluctuations to hyporheic exchange in absence of geomorphic complexity. We simulated groundwater flow through an aquifer bounded by a straight stream and hillslope and under time-varying boundary conditions. We found that diel fluctuations can produce hyporheic flowpath lengths and residence times that span orders of magnitude. With these results, hyporheic flowpath residence times and lengths can be predicted from the timing and magnitude of diel fluctuations and valley slope. Finally, we demonstrated that dynamic hydrologic boundary conditions can produce spatial and temporal scales of hyporheic flowpaths equivalent to those driven by many well-studied geomorphic features, indicating that these controls must be considered together in future efforts of upscaling to stream networks.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Hydrogeomorphic controls on hyporheic and riparian transport in two headwater mountain streams during base flow recession (2016)
    Wiley
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    Publication Date: 2016-02-13
    Description: Solute transport along riparian and hyporheic flowpaths is broadly expected to respond to dynamic hydrologic forcing by streams, aquifers, and hillslopes. However, direct observation of these dynamic responses is lacking, as is the relative control of geologic setting as a control on responses to dynamic hydrologic forcing. We conducted a series of four stream solute tracer injections through baseflow recession in each of two watersheds with contrasting valley morphology in the H.J. Andrews Experimental Forest, monitoring tracer concentrations in the stream and in a network of shallow riparian wells in each watershed. We found hyporheic mean arrival time, temporal variance, and fraction of stream water in the bedrock-constrained valley bottom and near large roughness elements in the wider valley bottom were not variable with discharge, suggesting minimal control by hydrologic forcing. Conversely, we observed increases in mean arrival time and temporal variance and decreasing fraction stream water with decreasing discharge near the hillslopes in the wider valley bottom. This may indicate changes in stream discharge and valley bottom hydrology control transport in less constrained locations. We detail five hydrogeomorphic responses to baseflow recession to explain observed spatial and temporal patterns in the interactions between streams and their valley bottoms. Models able to account for the transition from geologically dominated processes in the near-stream subsurface to hydrologically dominated processes near the hillslope will be required to predict solute transport and fate in valley bottoms of headwater mountain streams. 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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  • 9
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    Deducing the spatial variability of exchange within a longitudinal channel water balance (2013)
    Wiley
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    Publication Date: 2013-04-29
    Description: Developing an appropriate data collection scheme to infer stream-subsurface interactions is not trivial due to the spatial and temporal variability of exchange flowpaths. Within the context of a case study, this paper presents the results from a number of common data collection techniques ranging from point to reach scales used in combination to better understand the spatial complexity of subsurface exchanges, infer the hydrologic conditions where individual influences of hyporheic and groundwater exchange components on stream water can be characterized, and determine where gaps in information arise. We start with a tracer-based, longitudinal channel water balance to quantify hydrologic gains and losses at a sub-reach scale nested within two consecutive reaches. Next, we look at groundwater and stream water surface levels, shallow streambed vertical head gradients, streambed and aquifer hydraulic conductivities, water chemistry, and vertical flux rates estimated from streambed temperatures to provide more spatially explicit information. As a result, a clearer spatial understanding of gains and losses was provided, but some limitations in interpreting results were identified even when combining information collected over various scales. Due to spatial variability of exchanges and areas of mixing, each technique frequently captured a combination of groundwater and hyporheic exchange components. Ultimately, this study provides information regarding technique selection, emphasizes that care must be taken when interpreting results, and identifies the need to apply or develop more advanced methods for understanding subsurface exchanges. This article is protected by copyright. All rights reserved.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 10
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    Dynamic hyporheic and riparian flow path geometry through base flow recession in two headwater mountain stream corridors (2017)
    Wiley
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    Publication Date: 2017-04-27
    Description: The hydrologic connectivity between streams and their valley bottoms (stream corridor) is a critical determinant of their ecological function. Ecological functions are known to be spatially and temporally variable, but spatial dimensions of the problem are not easily quantified and thus they are usually overlooked. To estimate the spatial patterns of connectivity, and how connectivity varies with changes in discharge, we developed the Hyporheic Potential Model. We used the model to interpret a series of solute tracer injections in two headwater mountain streams with contrasting valley bottom morphologies to estimate connectivity in the stream corridor. The distributions of flowpath origination locations and the lengths of hyporheic flow paths appear to vary with baseflow recession, even in cases where transport timescales are apparently unchanged. The modeled distribution of origination locations further allowed us to define a spatial analogue to the temporal window of detection associated with solute tracer studies, and enables assessment of connectivity dynamics between streams and their corridors. Altogether, the reduced complexity Hyporheic Potential Model provides an easy way anticipate the spatial distribution and origination locations of hyporheic flow paths from a basic understanding of the valley bottom characteristics and solute transport timescales.
    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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