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321.
322.
Salt marshes are an important transition zone between terrestrial and marine ecosystems, and in their natural state, they
often function to cycle or trap terrestrially derived nutrients and organic matter. Many US salt marshes were ditched during
the twentieth century, potentially altering their functionality. The goal of this 4-year study was to assess the impact of
water from ditches within seven salt marshes on estuarine water quality and plankton communities within four estuaries on
Long Island, NY, USA. We found that concentrations of inorganic nutrients (ammonium, phosphate), dissolved and particulate
organic nitrogen and carbon (POC, PON, DOC, DON), and total coliform bacteria were significantly enriched in salt marsh ditches
compared to the estuaries they discharged into. In addition, concentrations of ammonium and DON became more enriched in ditches
as tidal levels decreased, suggesting these constituents were generated in situ. Quantification of nitrogen sources in Flanders
Bay, NY, suggested salt marsh ditches could represent a substantial source of N to this estuary during summer months. Experimental
incubations demonstrated that water from salt marsh ditches was capable of significantly enhancing the growth of multiple
classes of phytoplankton, with large diatoms and dinoflagellates displaying the most dramatic increases in growth. Experiments
further demonstrated that salt marsh ditchwater was capable of significantly enhancing pelagic respiration rates, suggesting
discharge from ditches could influence estuarine oxygen consumption. In summary, this study demonstrates that tidal draining
of salt marsh ditches is capable of degrading multiple aspects of estuarine water quality. 相似文献
323.
Corey A Cohn Christopher E Pedigo Shavonne N Hylton Sanford R Simon Martin AA Schoonen 《Geochemical transactions》2009,10(1):8-9
Background
Given the importance of highly reactive oxygen species (hROS) as reactants in a wide range of biological, photochemical, and environmental systems there is an interest in detection and quantification of these species. The extreme reactivity of the hROS, which includes hydroxyl radicals, presents an analytical challenge. 3'-(p-Aminophenyl) fluorescein (APF) is a relatively new probe used for measuring hROS. Here, we further evaluate the use of APF as a method for the detection of hydroxyl radicals in particle suspensions. 相似文献324.
We use an analytical model for the post-injection spreading of a plume of CO2 in a saline aquifer under the action of buoyancy and capillary trapping to show that the spreading behavior is at all times
strongly influenced by the shape of the plume at the end of the injection period. We solve the spreading equation numerically
and confirm that, at late times, the volume of mobile CO2 is given by existing asymptotic analytical solutions. The key parameters governing plume spreading are the mobility ratio,
M, and the capillary trapping number, Γ—the former sets the shape of the plume at the end of the injection period, and the latter sets the amount of trapping. As
a quantitative measure of the dependence of the spreading behavior on the initial shape, we use a volume ratio. That is, we
evolve the plume from a true end-of-injection initial shape and also from an idealized “step” initial shape, and we take the
ratio of these mobile plume volumes in the asymptotic regime. We find that this volume ratio is a power-law in M, where the exponent is governed exclusively by Γ. For conditions that are representative of geologic CO2 sequestration, the ratio of mobile volumes between “true” and “step” initial plume shapes can be 50% or higher. 相似文献
325.
Felicia C. Coleman Kathryn M. Scanlon Christopher C. Koenig 《The Professional geographer》2013,65(4):456-474
The northeastern Gulf of Mexico contains some of the most diverse and productive marine habitat in the United States. Much of this habitat, located on the shelf edge in depths of 50 to 120 m, supports spawning for many economically important species, including groupers. Here, we couple acoustic surveys with georeferenced videography to describe the primary spatial and geologic features of spawning aggregation sites for four economically important species: gag (Mycteroperca microlepis), scamp (M. phenax), red grouper (Epinephelus morio), and red snapper (Lutjanus campechanus), with notes on fish distribution and abundance and spawning activities. We provide information on movement patterns of reef fish determined using acoustic telemetry. Finally, we discuss the possible coupling of geomorphology with hydrographic features to influence the overall productivity of the region and the importance of spatial fishery management in sustaining that productivity. 相似文献
326.
J. Christopher Brown Lisa Rausch Verônica Gronau Luz 《The Professional geographer》2013,65(2):249-259
Brazilian agricultural census data at the municipal level are used to develop and map a simple index of staple food versus nonstaple food agriculture for Brazil over time (1996–2006). The results show spatial variation in the direction and degree of the shift toward or away from staple food cropping across Brazil. The index is presented as an important methodological step toward a systematic geographic understanding of crop share changes surrounding food versus fuel and other nonfood crop production. 相似文献
327.
Christopher J. Brookes 《International journal of geographical information science》2013,27(6):539-559
Optimal patch design is a generic problem in which the objective is to find the best configuration of patches subject to multiple criteria. It is a hard problem in spatial geometry relevant to numerous applications in spatial planning and analysis. GIS packages do not have optimal patch design functions and there has been very little research in this area. This paper describes a computer system for solving optimal patch design problems in raster GIS. The method uses a genetic algorithm search heuristic combined with a region-growing programme that generates alternative patch configurations. The version described here solves multiple patch problems and was developed from an earlier version for designing single patches. In tests on a hypothetical planning problem the multi-patch version was found to be more efficient, but less effective, than the single patch version. The last part of the paper discusses outstanding issues regarding the applicability usability and external validity of the system and suggests ideas for further research. 相似文献
328.
Mir Abolfazl Mostafavi Christopher Gold 《International journal of geographical information science》2013,27(3):211-227
This paper proposes a new Free-Lagrange method based on the kinetic Voronoi diagram for fluid simulation. The objective here is to combine the advantages of an adoptive mesh structure with the advantages of kinetic mesh maintenance, and demonstrate their value for dynamic simulation. Despite the theoretical advantages of the Free-Lagrange method, its use has been handicapped with the reconstruction of topology after each time step that considerably reduces the efficiency of the method. In addition, the use of fixed time steps causes problems such as overshoots and undetected collisions. In order to demonstrate the ability of the proposed model to solve these problems, the method is applied to a dam-breaking problem and global tides. With the results obtained from these numerical experiments, the validity of the global kinetic data structure is approved. In particular, the method is found to be more efficient than existing methods. In addition, qualitative comparison of physical results with analytical solutions demonstrates the similarity of the results and confirms the physical validity of the proposed method. Further investigations with real-world data and the complete equation of motion are suggested to compare it with other numerical methods. 相似文献
329.
330.
Maria Alp Barbara L. Peckarsky Stefano M. Bernasconi Christopher T. Robinson 《Aquatic Sciences - Research Across Boundaries》2013,75(4):595-606
Stable isotopes (13C and 15N) are widely applied in studies of trophic links. We used this method to investigate the contribution of aquatic and terrestrial prey to the diet of riparian predatory arthropods in two mountain headwater streams in Colorado, USA. Aquatic and terrestrial prey and riparian predators were collected during summer 2009. To evaluate the reliability of conclusions based on stable isotope ratios, we compared the isotopic signatures of aquatic larval and terrestrial adult stages of three abundant stream insect species and assessed variation in mixing model estimates for spider diet composition under varying assumptions for trophic fractionation. Adult isotopic signatures of some aquatic prey species were indistinguishable from those of prey species with exclusively terrestrial life histories (stoneflies: 13C and 15N, chironomids: 13C). Other prey had distinctly aquatic isotopic signatures as both larvae and adults (a mayfly and a caddisfly). There was no evidence that prey with aquatic isotopic signatures contributed to the diet of the spiders near one stream. For the other stream, mixing model analysis suggested that chironomids were included in the diets of lycosid, linyphiid and liocranid spiders. Reliable estimates of the contributions of prey sources were compromised by the sensitivity of mixing models to assumptions on trophic fractionation and the presence of “isotopically cryptic” prey. This study emphasizes the importance of supporting isotope-based studies on cross-boundary trophic links with data on isotopic shifts in prey with complex life cycles and assessment of fractionation rates specific to the study system. 相似文献