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151.
To understand the short-term effects of forest gap by human harvesting on soil available nutrient in Pinus massoniana plantations, the variations of soil ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3-N) concentrations in the gap center and gap edge during growing season were observed in seven gaps of different size (Gl: 100 m2; G2:225 m2; G3:400 m2; G4:625 m2; G5:900 m2; G6:1225 m2; G7:1600 m2) and pure understory of a 39-year-old masson pine plantation in a hilly area of the upper reaches of Yangtze River. The results showed that in the early stage of gap formation, the gap size had significant effect on NH4+-N, the season changes on NP3--N, and the interaction effect of gap size and seasonal variation on NH4+-N and NO3--N. The difference of NH4+-N and NO3--N between the gap center and gap edge was not significant. (I) The NH4+-N content was 4.30-11.99 mg kg-1, and NO3--N content was 2.57-10.81 mg kg-1. There was no obvious difference in NH4+-N and N03--N among gaps of different size in early or late growing seasons, when both increased first and decreased afterwards in the middle of growing season. The gaps of 100∼400 m2 area had a higher content of available nitrogen. (2) The seasonal dynamic differed between NH4+-N and NO3--N, with the former lower in middle growing season whereas the latter higher in the middle growing season but lower in the end of growing season. The soil NH4+-N was higher than NO3- -N in the early and late periods, but lower in the middle period. (3) The soil NH4+-N and NO3--N in parts of gaps were lower than understory in the early and late growing season. (4) Correlation analyses showed that NH4+-N had significant positive correlation with microbial biomass nitrogen (MBN), and NO3--N with soil temperature, MBN and organic matter. But the impact of soil water content on available nitrogen was not significant. These results suggested that soil temperature and microbial activity variation caused by gap harvesting are the main factors affecting soil available nitrogen content of Pinus massoniana plantations. 相似文献
152.
Mike Hutchins Carlo Fezzi Ian Bateman Paulette Posen Amelie Deflandre-Vlandas 《Environmental management》2009,44(2):256-267
A case study of the Yorkshire Derwent (UK) catchment is used to illustrate an integrated approach for assessing the viability
of policy options for reducing diffuse nitrate losses to waterbodies. For a range of options, modeling methods for simulating
river nitrate levels are combined with techniques for estimating the economic costs to agriculture of modifying those levels.
By incorporating spatially explicit data and information on catchment residence times (which may span many decades particularly
in areas of groundwater discharge) a method is developed for efficient spatial targeting of measures, for example, to the
most at-risk freshwater environments. Combining hydrological and economic findings, the analysis reveals that, in terms of
cost-effectiveness, the ranking of options is highly sensitive to both (i) whether or not specific stretches of river within
a catchment are regarded as a priority for protection, and (ii) the criterion of nitrate concentration deemed most appropriate
as an indicator of the health of the environment. Therefore, given the focus under European legislation upon ecological status
of freshwaters, these conclusions highlight the need to improve understanding of mechanistic linkages between the chemical
and biological dynamics of aquatic systems. 相似文献
153.
The urban landscape is comprised of many land uses, none more intensively managed than turfgrass; however, quantification of nutrient losses from specific land uses within urban watersheds, specifically golf courses is limited. Nitrate (NO(3)-N) and dissolved reactive phosphorus (DRP) were measured on a golf course in Austin, TX, USA from April 1, 1998 to March 31, 2003. NO(3)-N and DRP concentrations measured in storm flow were significantly greater exiting the course compared to those entering the course. Significant differences were also measured in baseflow NO(3)-N concentrations. The measured loading from the course was 4.0kg NO(3)-Nha(-1)yr(-1) (11% of applied) and 0.66kg DRPha(-1)yr(-1) (8% of applied). The resulting concentrations contributed by the course were 1.2mgL(-1) NO(3)-N and 0.2mgL(-1) DRP. At these levels, NO(3)-N poses minimal environmental risk. However, the DRP concentration is twice the recommended level to guard against eutrophication. 相似文献
154.
Gupta DK Tripathi RD Rai UN Mishra S Srivastava S Dwivedi S Maathuis FJ 《Environmental monitoring and assessment》2007,134(1-3):479-487
Growth and metal accumulation were investigated in two Cicer arietinum L. varieties (var. CSG-8962 and var. C-235) when grown in various combinations of fly ash (FA) amended with garden soil (GS),
press mud (PM) or saw dust (SD). In addition, the levels of photosynthetic pigments, nitrate reductase (NR) activity, cysteine,
non-protein thiols (NP-SH), and ascorbic acid were studied. FA amended with GS or PM led to a 5–10 times increase in biomass
compared to FA control and was most pronounced in the less metal tolerant variety CSG-8962. Amendment of FA with either GS
or PM only moderately increased the contents of some essential metals whereas the non-essential Cd and Cr remained similar
or decreased slightly compared to FA control. FA combined with either GS or PM increased the amount of photosynthetic pigments
and was largely absent when SD was added to FA. Improved nitrogen availability led to increased nitrate reductase (NR) activity
with all amendments but less so with SD. Metal stress indicating parameters were generally reduced (cysteine and non-protein
thiols) or unchanged (ascorbic acid). In conclusion, of the tested ameliorants both GS and PM greatly improved growth of C. arietinum making FA a suitable component of plant growth substrates. 相似文献
155.
A kinetic study of nitrate reduction by green rust (GR), a group of layered Fe(II)-Fe(III) hydroxide solids, was performed using a batch reactor system. The reduction rate of nitrate by GRs was affected by the anion content in the interlayer of GRs. GR containing F- (GR-F) showed the fastest reduction rate while GR-SO4 showed 9 times slower reaction rate than GR-F. The addition of 1 mM Pt or Cu to GR that contained 85 mM Fe(II) improved the reduction kinetics of nitrate by up to 200 times. Pt was an effective activating agent for all GRs. The sequential step reaction model that we proposed appropriately simulated the experimental data. The fastest nitrate reduction by GR-F with Pt was achieved at pH 9 among 7.5 to 11. At that condition, 1 mM nitrate transformed completely into ammonium within 23 min. 相似文献
156.
The present study investigates the performance of the zero valent iron (ZVI, Fe0) packed bed bipolar electrolytic cell for nitrate removal. The packing mixture consists of ZVI as electronically conducting material and silica sand as non-conducting material between main cathode and anode electrodes. In the continuous column experiments for the simulated groundwater (initial nitrate and electrical conductivity of about 30 mg L−1 as N and 300 μS cm−1, respectively), above 99% of nitrate was removed at the applied potential of 600 V with the main anode placed on the bottom of reactor. The influx nitrate was converted to ammonia (20% to maximum 60%) and nitrite (always less than 0.5 mg L−1 as N in the effluent). The optimum packing ratio (v/v) of silica sand to ZVI was found to be 1:1-2:1. Magnetite was observed on the surface of the used ZVI as corrosion product. The reduction at the lower part of the reactor in acidic condition and adsorption at the upper part of the reactor in alkaline condition are the major mechanism of nitrate removal. 相似文献
157.
S. R. Silva P. B. Ging R. W. Lee J. C. Ebbert A. J. Tesoriero E. L. Inkpen 《Environmental Forensics》2013,14(2):125-130
Ground and surface waters in urban areas are susceptible to nitrate contamination from septic systems, leaking sewer lines, and fertilizer applications. Source identification is a primary step toward a successful remediation plan in affected areas. In this respect, nitrogen and oxygen isotope ratios of nitrate, in conjunction with hydrologic data and water chemistry, have proven valuable in urban studies from Austin, Texas, and Tacoma, Washington. In Austin, stream water was sampled during stremflow and baseflow conditions to assess surface and subsurface sources of nitrate, respectively. In Tacoma, well waters were sampled in adjacent sewered and un-sewered areas to determine if locally high nitrate concentrations were caused by septic systems in the un-sewered areas. In both studies, sewage was identified as a nitrate source and mixing between sewage and other sources of nitrate was apparent. In addition to source identification, combined nitrogen and oxygen isotopes were important in determining the significance of denitrification, which can complicate source assessment by reducing nitrate concentrations and increasing i 15 N values. The two studies illustrate the value of nitrogen and oxygen isotopes of nitrate for forensic applications in urba areas. 相似文献
158.
Zhijun Liu Xi Luo Senlin Shao Xue Xia 《Frontiers of Environmental Science & Engineering》2023,17(4):40
159.
160.
Nitrates in concentrated brines can be electrochemically reduced in the cathodic chamber of a split-cell electrochemical reactor
with formation of ammonium (and small amounts of nitrite). Fortunately, ammonium may be electrochemically oxidized to nitrogen
gas in the anodic reaction chamber if a coupled sequential process is used. The presence of chloride in the brine waste is
an important consideration in oxidative electrochemical processes, however, because it cycles through oxidized and reduced
states at the electrode surfaces and in the bulk solution. Electrochemical oxidation converts chloride ions to “active chlorine”
species with additional oxidizing capability (chlorine, hypochlorous acid and hypochlorite – essentially bleach), as well
as to chlorates, depending on the reaction conditions. The production of these active species improves treatment performance
in the ammonium oxidation phase since oxidation is no longer limited to the electrode surface. However, the process must be
engineered to minimize loss of process efficiency due to parasitic side reactions (chloramines and chlorate). In this study,
two-stage batch electrolysis was conducted using a three-electrode (copper anode, platinum-coated titanium cathode, silver/silver
chloride reference) electrochemical cell, with the anodic and cathodic chambers separated by a Nafion 117 membrane. Treatment
of nitrate and ammonium was tested with and without the presence of chloride in the waste. No significant difference was observed
in cathodic nitrate reduction with chloride present or absent. However, the presence of chloride in the solution favored overall
soluble nitrogen elimination upon oxidation. Increasing applied current increased production of undesirable byproducts (especially
chlorate). 相似文献