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991.
Hongfang Lu Yu Bai Hai Ren Daniel E. Campbell 《Journal of environmental management》2010,91(12):2727-2735
China is the largest rice producing and consuming country in the world, but rice production has given way to the production of vegetables during the past twenty years. The government has been trying to stop this land-use conversion and increase the area in rice-vegetable rotation. Important questions that must be answered to determine what strategy is best for society are, “What is the reason behind this conversion?”; “Which system is more productive and which is more sustainable?”; and “How can economic policy be used to adjust the pattern of farmland use to attain sustainable development?” To answer these questions, a combined evaluation of these agricultural production systems was done using emergy, energy and economic methods. An economic analysis clearly showed that the reason for this conversion was simply that the economic output/input ratio and the benefit density of the vegetable production system were greater than that of rice. However, both energy and emergy evaluations showed that long-term rice was the best choice for sustainable development, followed by rotation systems. The current price of rice is lower than the em-value of rice produced from the long-term rice system, but higher than that of rice produced from the rotation system. Scenario analysis showed that if the government increases the price of rice to the em-value of rice produced from the long-term rice system, US$0.4/kg, and takes the value of soil organic matter into account, the economic output/input ratios of both the rice and rotation systems will be higher than that of the vegetable system. The three methods, energy, emergy and economics, are different but complementary, each revealing a different aspect of the same system. Their combined use shows not only the reasons behind a system’s current state or condition, but also the way to adjust these systems to move toward more sustainable states. 相似文献
992.
An assessment of the benthic macroinvertebrate community was conducted to characterize the ecological recovery of a channelized
main stem and two small tributaries at the Watershed Research and Education Center (WREC, Arkansas, USA). Three other headwater
streams in the same basin were also sampled as controls and for biological reference information. A principal components analysis
produced stream groupings along an overall gradient of physical habitat integrity, with degraded reaches showing lower RBP
habitat scores, reduced flow velocities, smaller substrate sizes, greater conductivity, and higher percentages of sand and
silt substrate. The benthic macroinvertebrate assemblage at WREC was dominated by fast-reproducing dipteran larvae (midge
and mosquito larvae) and physid snails, which comprised 71.3% of the total macroinvertebrate abundance over three sampling
periods. Several macroinvertebrate assemblage metrics should provide effective targets for monitoring overall improvements
in the invertebrate assemblage including recovery towards a more complex food web (e.g., total number of taxa, number of EPT
taxa, percent 2 dominant taxa). However, current habitat conditions and the extent of existing degradation, system isolation
and surrounding urban or agricultural land-uses might affect the level of positive change to the system. We therefore suggest
a preliminary restoration strategy involving the addition of pool habitats in the system. At one pool we collected a total
of 29 taxa (dominated by water beetle predators), which was 59% of total number of taxa collected at WREC. Maintaining water-retentive
pools to collect flows and maintain water permanence focuses on enhancing known biology and habitat, thus reducing the effects
of abiotic filters on macroinvertebrate assemblage recovery. Furthermore, biological assessment prior to restoration supports
a strategy primarily focused on improving the existing macroinvertebrate community in the current context of the system, thereby
reducing costs associated with active channel restoration. Monitoring future biological recovery and determining the contribution
of changing assemblages to specific ecological processes would provide a critical underpinning for adaptive management and
ecologically-effective restoration. 相似文献
993.
Unrine JM Tsyusko OV Hunyadi SE Judy JD Bertsch PM 《Journal of environmental quality》2010,39(6):1942-1953
To investigate the role of particle size on the oxidation, bioavailability, and adverse effects of manufactured Cu nanoparticles (NPs) in soils, we exposed the earthworm Eisenia ferida to a series of concentrations of commercially produced NPs labeled as 20- to 40-nm or < 100-nm Cu in artificial soil media. Effects on growth, mortality, reproduction, and expression of a variety of genes associated with metal homeostasis, general stress, and oxidative stress were measured. We also used X-ray absorption spectroscopy and scanning X-ray fluorescence microscopy to characterize changes in chemical speciation and spatial distribution of the NPs in soil media and earthworm tissues. Exposure concentrations of Cu NPs up to 65 mg kg(-1) caused no adverse effects on ecologically relevant endpoints. Increases in metallothionein expression occurred at concentrations exceeding 20 mg kg(-1) of Cu NPs and concentrations exceeding 10 mg kg(-1) of CuSO4. Based on the relationship of Cu tissue concentration to metallothionein expression level and the spatial distribution and chemical speciation of Cu in the tissues, we conclude that Cu ions and oxidized Cu NPs were taken up by the earthworms. This study suggests that oxidized Cu NPs may enter food chains from soil but that adverse effects in earthworms are likely to occur only at relatively high concentrations (> 65 mg Cu kg(-1) soil). 相似文献
994.
The toxicity and bioaccumulation of two heavy metals—lead (Pb) and cadmium (Cd)—in a semi-aquatic plant, Colocasia esculenta (L. Schott), from a synthetic heavy metal solution were studied. Young plants of equal size were grown hydroponically in shallow raceways containing Hoagland medium amended with 20, 40, and 60 mg l?1 of Pb and 2, 4, and 6 mg l?1 of Cd. The medium containing heavy metals was allowed to flow through the raceways with a change in influent heavy metal solution on every 5th day. The experiment was continued for 20 days. A set of control raceways—one comprised of nutrient medium with heavy metal supplements, devoid of plants, and another with the plants and nutrient medium having no metal supplement—was also simultaneously run. Chlorosis in the leaves was the prominent toxicity symptom observed due to Pb and Cd on the test plants. A significant decrease in the relative growth, biomass productivity, and total chlorophyll content were noticed in the plants with an increase in concentration of metal supplement in the solution and exposure time. Both metals accumulated to higher concentrations in the roots than in shoots, suggesting that the metals were bound to the root cells and their translocation to the leaves was limited. The results of the 20-day-long experiments indicate that from a phytoremediation perspective, C. esculenta is a promising plant species for remediation of wastewater polluted with lower concentrations of Pb and Cd. 相似文献
995.
S. O. Asagba G. E. Eriyamremu J. O. T. Emudainohwo I. Okoro 《The Environmentalist》2010,30(3):260-266
The activities of some oxidative enzymes (aldehyde oxidase, AO, EC 1.2.3.1; xanthine oxidase, XO, EC 1.17.3.2; sulphite oxidase,
SO, EC 1.8.3.1; and monoamine oxidase, MO, EC 1.4.3.4) were investigated in the liver, gill, kidney, brain and muscle of a
variety of African catfish (Clarias gariepinus) after 7 and 21 days of exposure to 0.1, 0.2 and 0.4 ppm cadmium (Cd) in ambient water. MO, SO and AO activities were significantly
(p < 0.05) decreased in a dose-dependent manner in the liver, kidney and gill in the 7-day Cd-exposed fish when compared to
control. Conversely, brain MO, AO and SO activities were significantly (p < 0.05) elevated in a dose-dependent manner in the same fishes relative to control. As in the 7-day Cd-exposed fish, the
activities of MO, AO and SO were significantly (p < 0.05) decreased in a dose-dependent manner in the gill, kidney and liver of catfish exposed for 21 days. Same is true for
XO in these organs after both duration of exposure, except in the liver where no significant change was observed relative
to control. The inhibition of these oxidative enzymes in the liver, gill and kidney of catfish may interfere with their biotransformation
function, and ultimately the survival of the fish may be compromised. 相似文献
996.
Nutrient loading to surface water systems has traditionally been associated with agricultural sources. Sources such as on-site wastewater systems (OWS) may be of concern especially in rural, nonagricultural watersheds. The impact of various point and nonpoint sources including OWS in Turkey Creek Watershed was evaluated using the Watershed Analysis Risk Management Framework, which was calibrated using 10 yr of observed stream flow and total P concentrations. Doubling the population in the watershed or OWS septic tank effluent P concentration increased mean stream total P concentration by a factor of 1.05. Converting all the OWS to a conventional sewer system with a removal efficiency of 93% at the wastewater treatment plant increased the mean total P concentration at the watershed outlet by a factor of 1.26. Reducing the soil adsorption capacity by 50% increased the mean stream total P concentration by a factor of 3.2. Doubling the initial P concentration increased the mean stream total P concentration by a factor of 1.96. Stream flow and sediment transport also substantially affected stream P concentration. The results suggest that OWS contribution to stream P in this watershed is minimal compared with other factors within the simulated time frame of 10 yr. 相似文献
997.
Michael J. White Daniel E. Storm Philip Busteed Scott Stoodley Shannon J. Phillips 《Environmental management》2010,45(5):1164-1174
In the United States, many state and federally funded conservation programs are required to quantify the water quality benefits
resulting from their efforts. The objective of this research was to evaluate the impact of conservation practices subsidized
by the Oklahoma Conservation Commission on phosphorus and sediment loads to Lake Wister. Conservation practices designed to
increase vegetative cover in grazed pastures were evaluated using Landsat imagery and the Soil and Water Assessment Tool (SWAT).
Several vegetative indices were derived from Landsat imagery captured before and after the implementation of conservation
practices. Collectively, these indicators provided an estimate of the change in vegetative soil cover attributable to conservation
practices in treated fields. Field characteristics, management, and changes in vegetative cover were used in the SWAT model
to simulate sediment and phosphorus losses before and after practice implementation. Overall, these conservation practices
yielded a 1.9% improvement in vegetative cover and a predicted sediment load reduction of 3.5%. Changes in phosphorus load
ranged from a 1.0% improvement to a 3.5% increase, depending upon initial vegetative conditions. The use of fertilizers containing
phosphorus as a conservation practice in low-productivity pastures was predicted by SWAT to increase net phosphorus losses
despite any improvement in vegetative cover. This combination of vegetative cover analysis and hydrologic simulation was a
useful tool for evaluating the effects of conservation practices at the basin scale and may provide guidance for the selection
of conservation measures subsidized in future conservation programs. 相似文献
998.
Southern Chile encompasses one of the most extensive fjord regions of the world, the Patagonia, currently exposed to natural
and anthropogenic perturbations. These fjord ecosystems provide important services to humans, which have not been adequately
measured and valued. As a consequence, ecosystem services are commonly ignored in public policy design and in the evaluation
of development projects. Here we tackle questions that are highly relevant for the nation’s development, namely (1) understanding
fjord functioning, and (2) developing management strategies based on ecosystem services, in order to secure simultaneous and
adequate use of these ecosystems which area influenced by ecological (e.g., biogeochemical) and productive (e.g., aquaculture,
fisheries) processes. We also seek to strengthen the analysis of fjord ecosystem value from the economical (including coastal
zoning), socio-cultural, institutional, and governmental points of view. In addition, the investigation of current and future
effects of climate change on this large region offers a unique opportunity to understand the social and economic consequences
of a global phenomenon at local to regional scales. Biogeochemical and socio-economic models will be used to simulate future
scenarios under a gamut of management options. 相似文献
999.
Erica Donner Kris Broos Diane Heemsbergen Mike J. McLaughlin Mark E. Hodson 《Environmental pollution (Barking, Essex : 1987)》2010,158(1):339-345
As zinc (Zn) is both an essential trace element and potential toxicant, the effects of Zn fixation in soil are of practical significance. Soil samples from four field sites amended with ZnSO4 were used to investigate ageing of soluble Zn under field conditions over a 2-year period. Lability of Zn measured using 65Zn radioisotope dilution showed a significant decrease over time and hence evidence of Zn fixation in three of the four soils. However, 0.01 M CaCl2 extractions and toxicity measurements using a genetically modified lux-marked bacterial biosensor did not indicate a decrease in soluble/bioavailable Zn over time. This was attributed to the strong regulatory effect of abiotic properties such as pH on these latter measurements. These results also showed that Zn ageing occurred immediately after Zn spiking, emphasising the need to incubate freshly spiked soils before ecotoxicity assessments. 相似文献
1000.
Kathryn E. Lenz George E. Host Anu Sôber 《Environmental pollution (Barking, Essex : 1987)》2010,158(4):1015-1022
The balance of mechanistic detail with mathematical simplicity contributes to the broad use of the Farquhar, von Caemmerer and Berry (FvCB) photosynthetic rate model. Here the FvCB model was coupled with a stomatal conductance model to form an [A,gs] model, and parameterized for mature Populus tremuloides leaves under varying CO2 and temperature levels. Data were selected to be within typical forest light, CO2 and temperature ranges, reducing artifacts associated with data collected at extreme values. The error between model-predicted photosynthetic rate (A) and A data was measured in three ways and found to be up to three times greater for each of two independent data sets than for a base-line evaluation using parameterization data. The evaluation methods used here apply to comparisons of model validation results among data sets varying in number and distribution of data, as well as to performance comparisons of [A,gs] models differing in internal-process components. 相似文献