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201.
Improvements in Fluvial Stability Associated with Two‐Stage Ditch Construction in Mower County,Minnesota 下载免费PDF全文
Lori Krider Joseph Magner Brad Hansen Bruce Wilson Geoffrie Kramer Joel Peterson John Nieber 《Journal of the American Water Resources Association》2017,53(4):886-902
Water quality and stream habitat in agricultural watersheds are under greater scrutiny as hydrologic pathways are altered to increase crop production. Agricultural drainage ditches function to remove water quickly from farmed landscapes. Conventional ditch designs lack the form and function of natural stream systems and tend to be unstable and provide inadequate habitat. In October of 2009, 1.89 km of a conventional drainage ditch in Mower County, Minnesota, was converted to an alternative system with a two‐stage channel to investigate the improvements in water quality, stability, and habitat. Longitudinal surveys show a 12‐fold increase in the pool‐riffle formation. Cross‐sectional surveys show an average increase in bankfull width of approximately 10% and may be associated to an increased frequency in large storm events. The average increase in bankfull depth was estimated as 18% but is largely influenced by pool formation. Rosgen Stability Analyses show the channel to be highly stable and the banks at a low risk of erosion. The average bankfull recurrence interval was estimated to be approximately 0.30 years. Overall, the two‐stage ditch design demonstrates an increase in fluvial stability, creating a more consistent sediment budget, and increasing the frequency of important instream habitat features, making this best management practice a viable option for addressing issues of erosion, sediment imbalance, and poor habitat in agricultural drainage systems. 相似文献
202.
The purpose of this study was to determine the hexavalent chromium (CrVI) biosorption capacities of several agricultural wastes from aqueous solutions. Samples were tested unaltered and after hydrochloric acid (HCl) treatment. Additional parameters tested include sample dose, contact time, particle size, mixing temperature, and the concentrations and pH of the CrVI solutions. Desorption studies were performed to determine if the removed CrVI could be recovered. In addition, tests were conducted to determine if the agricultural waste samples (AWS) could be reused for additional CrVI biosorption cycles. The results of this study demonstrate a wide range of CrVI biosorption proficiencies ranging from 13 to 98 percent removal. The parameters that resulted in higher CrVI removal include HCl treatment, higher sample dose, lower CrVI solution concentration, and lower mixing temperature. Desorption results showed an 8 to 25 percent CrVI recovery rate. Reused AWS were effective at removing CrVI during subsequent trials. Therefore, all AWS can be reused for additional CrVI biosorption cycles. Hence, these could reduce hazardous waste disposal inefficiencies and costs by avoiding disposing of spent AWS following each CrVI biosorption cycle. 相似文献
203.
Historical nitrogen content of bryophyte tissue as an indicator of increased nitrogen deposition in the Cape Metropolitan Area, South Africa 总被引:1,自引:0,他引:1
Information on changes in precipitation chemistry in the rapidly expanding Cape Metropolitan Area (CMA) of South Africa is scarce. To obtain a long-term record of N deposition we investigated changes in moss foliar N, C:N ratios and nitrogen isotope values that might reflect precipitation chemistry. Tissue from 9 species was obtained from herbarium specimens collected between 1875 and 2000 while field samples were collected in 2001/2002. There is a strong trend of increasing foliar N content in all mosses collected over the past century (1.32-1.69 %N). Differences exist between ectohydric mosses which have higher foliar N than the mixohydric group. C:N ratios declined while foliar δ15N values showed no distinct pattern. From relationships between moss tissue N and N deposition rates we estimated an increase of 6-13 kg N ha−1 a−1 since 1950. Enhanced N deposition rates of this magnitude could lead to biodiversity losses in native ecosystems. 相似文献
204.
The potential to capture carbon from industrial sources and dispose of it for the long-term, known as carbon capture and sequestration (CCS), is widely recognized as an important option to reduce atmospheric carbon dioxide emissions. Specifically, CCS has the potential to provide emissions cuts sufficient to stabilize greenhouse gas levels, while still allowing for the continued use of fossil fuels. In addition, CCS is both technologically-feasible and commercially viable compared with alternatives with the same emissions profile. Although the concept appears to be solid from a technical perspective, initial public perceptions of the technology are uncertain. Moreover, little attention has been paid to developing an understanding of the social and political institutional infrastructure necessary to implement CCS projects. In this paper we explore a particularly dicey issue--how to ensure adequate long-term monitoring and maintenance of the carbon sequestration sites. Bonding mechanisms have been suggested as a potential mechanism to reduce these problems (where bonding refers to financial instruments used to ensure regulatory or contractual commitments). Such mechanisms have been successfully applied in a number of settings (e.g., to ensure court appearances, completion of construction projects, and payment of taxes). The paper examines the use of bonding to address environmental problems and looks at its possible application to nascent CCS projects. We also present evidence on the use of bonding for other projects involving deep underground injection of materials for the purpose of long-term storage or disposal. 相似文献
205.
S. B. Weisberg H. T. Wilson D. G. Heimbuch H. L. Windom J. K. Summers 《Environmental monitoring and assessment》2000,61(3):373-385
Aluminum is often used as a conservative tracer toseparate natural from anthropogenic components ofmetal contamination in marine sediments, butidentifying uncontaminated sites to develop baselinemetal:aluminum relationships can be problematic inpopulated areas. Here we present a new method foridentifying baseline relationships in high populationdensity areas. The method involves comparing theresidual from the metal:aluminum regression with anindependent estimate of laboratory measurement error,based on the premise that mean square error from theregression must equal laboratory measurement error forany data set that is free of anthropogenicallyenriched sites. The method is applied to data setsfrom the mid-Atlantic and Gulf coasts of the UnitedStates to test consistency in baseline relationshipsbetween these two coasts of geologically differentorigin. Differences in metal:aluminum relationshipsbetween coasts were found to be small and limited tothe least abundant trace metals. 相似文献
206.
Ronald A. Burt Gregory L. Christians Samuel P. Williams David J. Wilson 《Environmental monitoring and assessment》2001,72(3):297-326
Two dense nonaqueous phase liquid (DNAPL) tracer tests werecarried out in a shallow aquifer north of Fort Worth, TX. i-Propanolwas used as the nonpartitioning tracer; n-hexanol and n-octanol werethe partitioning tracers. Field data, mathematical modeling, theresults of column tests, and field tracer tests with NaCl were usedin designing the DNAPL tracer tests. The results indicated the presenceof DNAPL at both sites tested; semi-quantitative estimates of theamounts of DNAPL present were obtained by mathematical modeling.Interpretation was complicated by heterogeneity of the aquifer andmass transport effects. 相似文献
207.
Puckett LJ Zamora C Essaid H Wilson JT Johnson HM Brayton MJ Vogel JR 《Journal of environmental quality》2008,37(3):1034-1050
Although numerous studies of hyporheic exchange and denitrification have been conducted in pristine, high-gradient streams, few studies of this type have been conducted in nutrient-rich, low-gradient streams. This is a particularly important subject given the interest in nitrogen (N) inputs to the Gulf of Mexico and other eutrophic aquatic systems. A combination of hydrologic, mineralogical, chemical, dissolved gas, and isotopic data were used to determine the processes controlling transport and fate of NO(3)(-) in streambeds at five sites across the USA. Water samples were collected from streambeds at depths ranging from 0.3 to 3 m at three to five points across the stream and in two to five separate transects. Residence times of water ranging from 0.28 to 34.7 d m(-1) in the streambeds of N-rich watersheds played an important role in allowing denitrification to decrease NO(3)(-) concentrations. Where potential electron donors were limited and residence times were short, denitrification was limited. Consequently, in spite of reducing conditions at some sites, NO(3)(-) was transported into the stream. At two of the five study sites, NO(3)(-) in surface water infiltrated the streambeds and concentrations decreased, supporting current models that NO(3)(-) would be retained in N-rich streams. At the other three study sites, hydrogeologic controls limited or prevented infiltration of surface water into the streambed, and ground-water discharge contributed to NO(3)(-) loads. Our results also show that in these low hydrologic-gradient systems, storm and other high-flow events can be important factors for increasing surface-water movement into streambeds. 相似文献
208.
Ornamental Plants as Invasive Aliens: Problems and Solutions in Kruger National Park,South Africa 总被引:1,自引:0,他引:1
The most widespread invasive alien plant species in South Africa’s Kruger National Park (KNP) were either introduced unintentionally
along rivers and roads, or intentionally for use as ornamentals. We examine the spatial distribution of ornamental alien plants
in KNP, look at the link between human population size, history, and species richness, and show how the distribution of particular
species reflects the likely history of ornamental plantings. Results are used to assess whether past management actions have
been appropriately directed.
Two hundred and fifty-eight alien species have been recorded in the 36 tourist camps and staff villages. The number of staff
housed in villages explains much of the diversity of cultivated alien plant species. Older camps also tend to have more ornamental
alien plant species. However, the lack of a strong link between camp age and number of cultivated species suggests that ornamental
plants have been widely spread around the KNP by humans. We also show that increased camp activity (either size or age) has
led to more ornamental species, while, with the notable exception of Skukuza, camp activity has had a much smaller effect
on the number of noncultivated species. Noncultivated species tend to be naturally dispersed, as opposed to directly spread
by humans between camps.
Past management prioritized certain species on the basis of their potential to invade KNP and on the prevailing national legislation.
These species were removed manually and follow-up control was carried out. Once the priority species were deemed to be under
control, less invasive species were targeted. All alien species were removed from vacated houses, regardless of the potential
invasiveness of the species.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
209.
Seth Payton Greg Lindsey Jeff Wilson John R. Ottensmann Joyce Man 《Journal of Environmental Planning and Management》2008,51(6):717-736
This paper measures the benefits of the urban forest by examining its effect on housing prices. A Geographic Information System is used to develop a measure of the urban forest, the Normalised Difference Vegetation Index, from satellite imagery and to construct other variables from a variety of sources. Spatial hedonic housing price models for the Indianapolis/Marion County area are estimated. The models indicate that greener vegetation around a property has a positive, significant effect on housing price, holding everything else constant. This effect is dominated by measures at the neighborhood level. These findings indicate that property owners value the urban forest, at least in part, by the premium they pay to live in neighborhoods with greener, denser vegetation. These findings also indicate that public action to maintain and enhance the urban forest may be warranted. Planners and urban foresters can use these findings to inform public and policy debates over urban forestry programs and proposals. 相似文献
210.
A comparison of catches of fishes and invertebrates by two light trap designs, in tropical NW Australia 总被引:1,自引:0,他引:1
Light traps were deployed in two sampling programs. In the first, small and large traps were released to drift with the current at stations along a cross-shelf transect on the NW Shelf off the coast of Western Australia. In the second program, pairs of small and large traps were deployed on moorings 150 m off the coastline. The composition and size-frequency distributions of catches of fishes in small and large traps were similar for both modes of deployment. In drifting traps, nearly 78% of this catch was composed of reef fishes, and these were collected in significantly greater numbers by the small design than by large traps (9.51 vs. 5.84 individuals h-1, respectively). Nine taxa (amphipods, mysids, crab megalopae, copepods, cumaceans, isopods, caridean shrimps, polychaetes and the euphausiid, Pseudeuphausia latifrons) accounted for 99% of the total catch of invertebrates by drifting traps. Of these, catches of amphipods, copepods, cumaceans and P. latifrons were greater in large traps than in small traps (3,134 vs. 1,687 h-1, 1,018 vs. 214 h-1, 551 vs. 165 h-1 and 74 vs. 9 individuals h-1, respectively). In contrast, crab megalopae were more abundant in catches by small traps than by large traps (3,134 vs. 1,687 individuals h-1, respectively). The catch rate of fishes in moored traps was higher than in drifting traps (105 vs. 20 fishes h-1) and was dominated by baitfishes (86% of total catch). Reef fishes were also captured in greater numbers by small traps than by the large design (10.17 vs. 4.4 individuals h-1) in this mode of deployment. Despite these differences in catch rates, multivariate analysis showed that cross-shelf patterns in catches of fishes and invertebrates were mapped equally well by both trap designs. Variation in the efficiency of trap designs thus appears to be small when compared to changes in the composition and abundance of zooplankton assemblages that occur at scales of tens of kilometers. 相似文献