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Samuel J. Smidt Joseph A. Cullin Adam S. Ward Jesse Robinson Margaret A. Zimmer Laura K. Lautz Theodore A. Endreny 《Ground water》2015,53(6):859-871
While restoring hyporheic flowpaths has been cited as a benefit to stream restoration structures, little documentation exists confirming that constructed restoration structures induce comparable hyporheic exchange to natural stream features. This study compares a stream restoration structure (cross‐vane) to a natural feature (riffle) concurrently in the same stream reach using time‐lapsed electrical resistivity (ER) tomography. Using this hydrogeophysical approach, we were able to quantify hyporheic extent and transport beneath the cross‐vane structure and the riffle. We interpret from the geophysical data that the cross‐vane and the natural riffle induced spatially and temporally unique hyporheic extent and transport, and the cross‐vane created both spatially larger and temporally longer hyporheic flowpaths than the natural riffle. Tracer from the 4.67‐h injection was detected along flowpaths for 4.6 h at the cross‐vane and 4.2 h at the riffle. The spatial extent of the hyporheic zone at the cross‐vane was 12% larger than that at the riffle. We compare ER results of this study to vertical fluxes calculated from temperature profiles and conclude significant differences in the interpretation of hyporheic transport from these different field techniques. Results of this study demonstrate a high degree of heterogeneity in transport metrics at both the cross‐vane and the riffle and differences between the hyporheic flowpath networks at the two different features. Our results suggest that restoration structures may be capable of creating sufficient exchange flux and timescales of transport to achieve the same ecological functions as natural features, but engineering of the physical and biogeochemical environment may be necessary to realize these benefits. 相似文献
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The qanat water supply technology, which gravity drains mountain aquifers into valleys, is considered as a culturally appropriate
and ecological sustainable design to meet northern Cyprus’ drinking water development needs. This research estimates the boundary
and water budget for the proposed qanat recharge area of 370 km2, which is in the upper elevations of the limestone dominated Five Finger Mountain Range. The mountain drainage was analyzed
using global elevation data from the Shuttle Ranging Topography Mission (SRTM). Efforts to use Tropical Rainfall Measuring
Mission (TRMM) annual precipitation for water budget inputs failed due to extreme error when tested against 10–30 years of
meteorological station data; TRMM under-estimated depths on the narrow mountain peaks. Gage records, while few in number,
were area averaged to set average annual precipitation inputs at 530 mm year−1. Evaporation was estimated using a complementary relationship areal evapotranspiration (CRAE) model, setting average atmospheric
outputs at 221 mm year−1. Recharge to the qanat aquifer was set by subtracting evaporation from precipitation, and then allocating 50% of the remaining
water to environmental services. At 25% development, the qanat system supplies 14 mm3 year−1 of water, meeting the drinking water deficit of 13 mm3. 相似文献
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Mark W. Fabian Theodore A. Endreny Andrea Bottacin‐Busolin Laura K. Lautz 《水文研究》2011,25(10):1630-1646
A characterization of hyporheic exchange for dry and wet season baseflow, as well as partially dewatered discharge, was done in Prieta Creek, a first‐order cascade in northern Honduras. The cascade had discharges from 1 to 15 l s?1, had average slopes of 12%, pool spacing of 3 m, and shallow substrate of sand and gravel. Tracer tests were conducted in a 15‐m sub‐reach, a length considered to be adequate for the experiment based on the DaI test, a ratio of exchange and transport processes. In the three tests, between 9 and 18% of tracer was not recovered, possibly due to entrainment in flowpaths passing beneath the downstream monitoring location. Tracer data were analysed by the one‐dimensional transport with inflow and storage (OTIS) transient storage model (TSM) to derive standard exchange parameters, and by the solute transport in rivers (STIR) model to examine hyporheic residence time distributions (RTDs). The best fit of the observed tracer breakthrough curves was obtained by using the STIR model with a combination of two exponential RTDs to represent hyporheic retention. With increasing discharge, the OTIS model predicted increasing storage exchange fluxes and exchange coefficients and decreasing storage zone areas and transient storage times, which are trends supported by riparian and streambed piezometric head data. Riparian water levels rose during the transition from the dry to wet season, which could constrict the hyporheic storage zone. Thirteen of the 19 streambed piezometers recorded seasonal changes in hydraulic gradients and flux direction, with fewer yet stronger upwelling zones during higher discharges. The MODFLOW model missed the observed seasonal changes, possibly due to subtle changes in the seasonal change in water surface profiles. We conclude that partially dewatered dry season exchange, compared to wet season exchange, was initiated and terminated with smaller pressure gradients and, in different streambed locations, was smaller in volume, had longer residence times, and may connect with deeper and longer flow paths. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Polly G. Hill Isabelle Mary Duncan A. Purdie Mikhail V. Zubkov 《Progress in Oceanography》2011,91(4):437-446
The Earth’s most extensive biomes – the oceanic subtropical gyres – are considered to be expanding with current surface ocean warming. Although it is well established that microbial communities control gyre biogeochemistry, comparisons of their metabolic activities between gyres are limited. In order to estimate metabolic activities including production of microbial communities, the uptake rates of amino acids leucine, methionine and tyrosine at ambient concentrations were estimated in surface waters of the Atlantic Ocean using radioisotopically labelled tracers. Data were acquired during six research cruises covering main oceanic provinces herein termed: North and South Atlantic Gyres, Bermuda Atlantic Time-series Study site (BATS), Equatorial region, and Mauritanian Upwelling (off Cape Blanc). Data were divided between provinces, the extents of which were identified by ocean colour data, in order to achieve provincial mean uptake rates. Leucine and methionine uptake rates did not differ between sampling periods, and were comparable between the North and South subtropical gyres. Furthermore, variation in uptake rates measured throughout the two oligotrophic gyres, where sampling covered ∼4 × 106 km2, was considerably lower than that measured within the Mauritanian Upwelling and Equatorial regions, and even at the BATS site. Tyrosine was generally the slowest of the amino acids to be taken up, however, it was assimilated faster than methionine within the Mauritanian Upwelling region. Thus, we propose that one value for leucine (12.6 ± 3.2 pmol L−1 h−1) and methionine (10.0 ± 3.3 pmol L−1 h−1) uptake could be applied to the oligotrophic subtropical gyres of the Atlantic Ocean. However, with the significantly lower uptake rates observed at the BATS site, we would not advise extrapolation to the Sargasso Sea. 相似文献
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TOPMODEL rainfall‐runoff hydrologic concepts are based on soil saturation processes, where soil controls on hydrograph recession have been represented by linear, exponential, and power function decay with soil depth. Although these decay formulations have been incorporated into baseflow decay and topographic index computations, only the linear and exponential forms have been incorporated into infiltration subroutines. This study develops a power function formulation of the Green and Ampt infiltration equation for the case where the power n = 1 and 2. This new function was created to represent field measurements in the New York City, USA, Ward Pound Ridge drinking water supply area, and provide support for similar sites reported by other researchers. Derivation of the power‐function‐based Green and Ampt model begins with the Green and Ampt formulation used by Beven in deriving an exponential decay model. Differences between the linear, exponential, and power function infiltration scenarios are sensitive to the relative difference between rainfall rates and hydraulic conductivity. Using a low‐frequency 30 min design storm with 4·8 cm h?1 rain, the n = 2 power function formulation allows for a faster decay of infiltration and more rapid generation of runoff. Infiltration excess runoff is rare in most forested watersheds, and advantages of the power function infiltration routine may primarily include replication of field‐observed processes in urbanized areas and numerical consistency with power function decay of baseflow and topographic index distributions. Equation development is presented within a TOPMODEL‐based Ward Pound Ridge rainfall‐runoff simulation. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Andrew J. Dugmore Polly I. J. Thompson Richard T. Streeter Nick A. Cutler Anthony J. Newton Martin P. Kirkbride 《第四纪科学杂志》2020,35(1-2):23-38
We explore developments in tephra science that consider more than chronology, using case studies of morphological transformations of tephra deposits. Volcanic processes and prevailing weather conditions determine the distribution of tephra deposits immediately after an eruption, but as these freshly fallen tephra become part of the stratigraphic record, the thickness, morphology and definition of the layers they form changes, reflecting the interplay of the tephra, climate, Earth surface processes, topography and vegetation structure, plus direct or indirect modification caused by people and animals. Once part of the stratigraphic record, there can be further diagnostic changes to the morphology of tephra layers, such as the creation of over folds by cryoturbation. Thus, tephra layers may contain proxy evidence of both past surface environments and subsurface processes. Transformations of tephra deposits can complicate the reconstruction of past volcanic processes and make the application of classical tephrochronology as pioneered by Thorarinsson (Sigurður Þórarinsson in Icelandic) challenging. However, as Thorarinsson also noted, novel sources of environmental data can exist within transformed tephra sequences that include the spread or removal of tephra, variations in layer thickness and internal structures, the nature of contact surfaces and the orientation of layers. 相似文献
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Oregon's Developmental Fisheries Program is designed to encourage the commercial exploration and development of State managed underutilized fishery resources. A key program strategy is allocating relatively secure harvest rights to pioneering entrepreneurs when a fishery successfully transitions from “developing” to “developed” status. Since the program's inception in 1993, two fisheries, sardine and bay clam, have moved from undeveloped to developed status. Case studies of these fisheries show that many challenges impact the success of the Developmental Fisheries Program including difficulties in designing and allocating asset rights, establishing operational program guidelines, selecting measurable targets that meet legislative standards for a developed fishery, and financing developmental fisheries management practices. Developmental fisheries strategies used in other regions and countries are summarized. Recommendations are made for improving Oregon's Developmental Fishery Program including establishing clear objectives and timelines for the Program and identifying appropriate renewal requirements for permits and other developmental incentives on a fishery-by-fishery basis. 相似文献
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