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61.
Robert Kent Kenneth Belitz Carmen A. Burton 《Journal of the American Water Resources Association》2005,41(5):1109-1128
This study examined algal productivity and nitrate assimilation in a 2.85 km reach of Cucamonga Creek, California, a concrete lined channel receiving treated municipal wastewater. Stream nitrate concentrations observed at two stations indicated nearly continuous loss throughout the diel study. Nitrate loss in the reach was approximately 11 mg/L/d or 1.0 g/m2/d as N, most of which occurred during daylight. The peak rate of nitrate loss (1.13 mg/l/hr) occurred just prior to an afternoon total CO2 depletion. Gross primary productivity, as estimated by a model using the observed differences in dissolved oxygen between the two stations, was 228 mg/L/d, or 21 g/m2/d as O2. The observed diel variations in productivity, nitrate loss, pH, dissolved oxygen, and CO2 indicate that nitrate loss was primarily due to algal assimilation. The observed levels of productivity and nitrate assimilation were exceptionally high on a mass per volume basis compared to studies on other streams; these rates occurred because of the shallow stream depth. This study suggests that concrete‐lined channels can provide an important environmental service: lowering of nitrate concentrations similar to rates observed in biological treatment systems. 相似文献
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63.
Kovacs K Václavík T Haight RG Pang A Cunniffe NJ Gilligan CA Meentemeyer RK 《Journal of environmental management》2011,92(4):1292-1302
Phytophthora ramorum, cause of sudden oak death, is a quarantined, non-native, invasive forest pathogen resulting in substantial mortality in coastal live oak (Quercus agrifolia) and several other related tree species on the Pacific Coast of the United States. We estimate the discounted cost of oak treatment, removal, and replacement on developed land in California communities using simulations of P. ramorum spread and infection risk over the next decade (2010-2020). An estimated 734 thousand oak trees occur on developed land in communities in the analysis area. The simulations predict an expanding sudden oak death (SOD) infestation that will likely encompass most of northwestern California and warrant treatment, removal, and replacement of more than 10 thousand oak trees with discounted cost of $7.5 million. In addition, we estimate the discounted property losses to single family homes of $135 million. Expanding the land base to include developed land outside as well as inside communities doubles the estimates of the number of oak trees killed and the associated costs and losses. The predicted costs and property value losses are substantial, but many of the damages in urban areas (e.g. potential losses from increased fire and safety risks of the dead trees and the loss of ecosystem service values) are not included. 相似文献
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65.
Comparative study of the effects of MCPA, butylate, atrazine, and cyanazine on Selenastrum capricornutum 总被引:2,自引:0,他引:2
The herbicides MCPA, butylate, atrazine and cyanazine are extensively used in Canadian agriculture and information regarding their effects on indigenous biota is scarce. Phytotoxicity assessments were conducted in the laboratory on the common green alga Selenastrum capricornutum using both the active ingredient of the herbicides and their formulated products (for MCPA and butylate). Endpoints determined after the 96 h exposure included algal population growth inhibition (IC50-cell counts), percent lethality (LC50-flow cytometry derived) and photosynthetic electron transport inhibition (EC50-fluorescence induction). Pesticide formulations had greater toxic effects than the active ingredient alone. The 96 h IC50 (50% Inhibition Concentration) and LOEC (Lowest Observable Effects Concentration) using cell counts of S. capricornutum were 18.4 and 8.9 mg l(-1) respectively for MCPA-active ingredient and for MCPA-formulated, these were 0.62 and 0.0062 mg l(-1) respectively. Those for butylateactive ingredient were 61.0 and 8.3 mg l(-1) and for butylate-formulated 1.46 and 0.17 mg l(-1), respectively. The triazines active ingredient, which are photosynthetic inhibitors, had greater effects than either the MCPA or butylate. The IC50 for cyanazine and atrazine were 0.059 and 0.026 mg l(-1), respectively. By comparing the IC50 and LC50 values for the tested active ingredients, it was found that the effects of atrazine were algicidal, whereas those of cyanazine, butylate and MCPA were algistatic. 相似文献
66.
Junjie Guan Kent M. Eskridge Milford A. Hanna 《Journal of Polymers and the Environment》2004,12(3):113-121
Acetylated starches, with degrees of substitution (DS) of 2, 2.5 and 3, were blended with 3%, 7.5% and 12% -cellulose and 14%, 17% or 20% (d.b.) ethanol and twin-screw extruded at 165°C barrel temperature and 225 rpm screw speed. A response surface methodology experimental design was applied to the sub-plot and a completely randomized design to the whole plot design to test the differences among the acetylated starches and the effects of cellulose and ethanol. DS, cellulose and ethanol contents significantly affected the functional properties and specific mechanical energy requirement. DS had positive effects on radial expansion ratio (RER), compressibility and specific mechanical energy requirement and a negative effect on bulk density. Highest (RER) was obtained from 20% ethanol content. Extrudates containing 12% cellulose had the highest bulk density and the highest compressibility. Higher cellulose contents required more specific mechanical energy. 相似文献
67.
Costas J. Saitanis Shafiqul M. Bari Kent O. Burkey Dimitris Stamatelopoulos Evgenios Agathokleous 《Environmental science and pollution research international》2014,21(23):13560-13571
The sensitivity to ozone of ten Bangladeshi wheat cultivars was tested by exposing plants to eight ozone exposure regimes (50, 60, 80, 100, 120, 135, 150, and 200 ppb for 14, 11, 8, 6, 5, 4, 3, and 1 days, respectively, for 8 h/day) in controlled environment chambers. Visible leaf injury, dry weight, chlorophyll, carotenoid content, leaf greenness (SPAD value), quantum yield of photosynthesis, and stomatal resistance were measured to evaluate response. Shoot biomass, total chlorophyll, leaf greenness, and carotenoid content were reduced in ozone-exposed plants. Based on the results of principal component analysis (PCA)-biplot analysis, the order of sensitivity to ozone was: Akbar?>>?Sufi?≥?Bijoy?≥?Shatabdi?>?Bari-26?≥?Gourab?>?Bari-25?≥?Prodip?≥?Sourav?>>?Kanchan. The most important parameters to discriminate cultivars with respect to ozone sensitivity were visible injury and chlorophyll b/a ratio, whereas quantum yield of photosynthesis was less important. Differences in stomatal resistance were not a significant factor in ozone response. Regression of cultivars’ PCA scores against year of release revealed no trend, suggesting that ozone tolerance was not incorporated during cultivar breeding. 相似文献
68.
S. Kent Hoekman Amber Broch Curtis Robbins Richard Purcell 《International Journal of Greenhouse Gas Control》2010,4(1):44-50
A laboratory-scale reactor system was built and operated to demonstrate the feasibility of catalytically reacting carbon dioxide (CO2) with renewably-generated hydrogen (H2) to produce methane (CH4) according to the Sabatier reaction: CO2 + 4H2 → CH4 + 2H2O. A cylindrical reaction vessel packed with a commercial methanation catalyst (Haldor Topsøe PK-7R) was used. Renewable H2 produced by electrolysis of water (from solar- and wind-generated electricity) was fed into the reactor along with a custom blend of 2% CO2 in N2, meant to represent a synthetic exhaust mixture. Reaction conditions of temperature, flow rates, and gas mixing ratios were varied to determine optimum performance. The extent of reaction was monitored by real-time measurement of CO2 and CH4. Maximum conversion of CO2 occurred at 300–350 °C. Approximately 60% conversion of CO2 was realized at a space velocity of about 10,000 h?1 with a molar ratio of H2/CO2 of 4/1. Somewhat higher total CO2 conversion was possible by increasing the H2/CO2 ratio, but the most efficient use of available H2 occurs at a lower H2/CO2 ratio. 相似文献
69.
70.
There Is More to Biodiversity than the Tropical Rain Forests 总被引:1,自引:0,他引:1