安庆沿江湿地资源利用与保护对策研究

为了充分发挥安庆沿江湿地资源的优势和潜力,实现区域经济社会发展与生态环境保护的双赢,促进社会主义新农村建设,通过遥感分析和实地调查等方法,深入分析了安庆沿江湿地资源的优势和生态环境面临的问题。从调控湿地生态系统与周边陆域生态系统的耦合关系着手,提出了安庆沿江湿地资源利用与保护的对策:(1)优化农业结构和布局,建立生态保障体系;(2)发展生态水产养殖业,优化湿地生态系统结构;(3)开发湿地生态文化旅游,完善湿地资源保护管理系统。     

Beyond the wetland border: Estimating the impact of roads for two species of water snakes

We used models integrating road maps, traffic volume, and snake movements to examine the potential for roads to contribute to mortality in two species of water snakes that differ in their vagility, use of terrestrial habitats, and conservation status. Road networks and traffic volumes typical of three regions in Indiana, USA, may account for mortality of 14-21% of the population per year in the more vagile, terrestrial, and imperiled copperbelly water snake (Nerodia erythrogaster neglecta) but only 3-5% mortality in the more sedentary, aquatic, and common northern water snake (Nerodia sipedon). The majority (>91%) of road crossings and associated mortality are predicted to occur during overland migrations to other wetlands, suggesting roads bisecting travel routes between wetlands may function as mortality sinks. Our models highlight the proportionately greater risk of mortality for the more vagile and imperiled species, N. e. neglecta, and suggest current wetland conservation strategies that focus on the wetland alone are unlikely to adequately protect wetland biodiversity from certain types of anthropogenic habitat modification. What is needed is a landscape approach to wetland conservation that considers not only the quality of wetlands and nearby terrestrial habitats, but also ensures that terrestrial corridors between wetlands remain permeable and offer safe passage for wildlife.     

How management strategies have affected Atlantic White-cedar forest recovery after massive wind damage in the Great Dismal Swamp

In September 2003 Hurricane Isabel swept through eastern North Carolina and Virginia, destroying most of what formerly ranked among the most extensive remaining stands of Atlantic White-cedar (Chamaecyparis thyoides L., cedar). As Atlantic White-cedar communities are dependent on irregular, large-scale disturbances, the hurricane event can be viewed as an opportunity for perpetuating cedar populations in the Great Dismal Swamp. The success of cedar regeneration in the Dismal Swamp has been influenced by the management strategies employed by Great Dismal Swamp National Wildlife Refuge (active management) and by the adjacent Dismal Swamp State Park (passive management). We investigated the regeneration success of Atlantic White-cedar 5 years following Hurricane Isabel by sampling five stands at the Dismal Swamp State Park withstanding varying impact from the storm and previous windthrow events. We compared our findings to regeneration surveys completed at the adjacent Great Dismal Swamp National Wildlife Refuge. Atlantic White-cedar seedling densities were up to 100 times higher in the actively managed Wildlife Refuge compared to the passively managed State Park. We also determined the seedbank of viable cedar seeds and we described the vegetation at the State Park. The stands at the State Park are now dominated by red maple (Acer rubrum) with a dense shrubby understory. Since viable cedar seeds were still present in the seedbank (>800,000 ha⁻¹), future seedling establishment is possible at the State Park. However, active management is essential for achieving sufficient seedling densities and survival for regenerating a mature cedar stand.     

济南玫瑰湖湿地生物多样性评价研究

在对玫瑰湖湿地物种现状进行统计分析的基础上,建立湿地生物多样性评价指标体系与赋值标准．从物种多样性和生态系统多样性两个指标对玫瑰湖’湿地生物多样性进行了评价。玫瑰湖湿地生物多样性总评分为68．5分,结果表明玫瑰湖湿地生物多样性处于一般水平。     

Relationships between microbial biomass and dissipation of 2,4-D and dicamba in soil

A study was conducted to evaluate relationships between microbial biomass and the dissipation of 2,4-D (2,4-dichlorophenoxy acetic acid) and dicamba (2-methoxy-3,6-dichlorobenzoic acid) in soil. We hypothesized that the size of the microbial biomass should be a strong predictor of the pesticide degradation capacity of a particular soil. Soils with a high microbial biomass should have relatively high levels of general microbial activity and should support a diversity of degradation pathways. In this study, we quantified the degradation of 2,4-D and dicamba in a range of soils with different concentrations of microbial biomass. The herbicides 2,4-D and dicamba were added to similar soils collected from five different land use types (home lawn, cornfield, upland hardwood forest, wetland forest, and aquifer material) and incubated for 80 days under laboratory conditions. Herbicide residue and microbial biomass (C and N) analyses were performed 5, 10, 20, 40, and 80 days following herbicide application. Microbial biomass-C and -N and soil organic matter content were positively correlated with dissipation of 2,4-D and dicamba. The results suggest that there are relationships between the size of the soil microbial biomass and the herbicide degradation capacity of an ecosystem. These relationships may be useful for developing approaches for evaluating and predicting the fate of pesticides in different ecosystems.     

Evaluation of alternative substrates for determining methane-oxidizing activities and methanotrophic populations in soils

The magnitude of methane emission is a net result of methane production and the oxidation rate. The possibility of measuring oxidized products of alternative substrates of methane monooxygenase was examined to determine methane-oxidizing ability of soils, and to count methanotrophic populations in soils. Wetland rice soils were incubated under methane containing air to enirch the methanotrophs. Methane loss and oxygen uptake were inhibited by acetylene, dimethylether, and nitrapyrin (N-Serve). Acetylene was used routinely, because it inhibited methane oxidation even at a low concentration of 0.03 to 0.06 l ml^-1 in the incubation headspace. Propylene at 10 kPa was used as an alternative substrate of methane monooxygenase, and the formation of propylene oxide was measured. When soils were incubated under methane, their methane-oxidizing activity increased. Propylene oxide formation increased simultaneously. Acetylene also blocked propylene oxidation. The results of several experiments and propylene oxide formation (r=0.87 after long-transformation). These results indicate that propylene oxide formation can be used as a semiquantitative measure of the methane-oxidizing activity of soils. The colonies of soluble methane monooxygenase-forming methanotrophs were counted on Cu-deficient methanotroph agar medium by the formation of naphthol from haphthalene. The counts increased from 10⁴ (0 days) to 10⁷ (21 days) g^-1 soil during oxic incubation under methane.     

Spatial and seasonal distribution of organic amendments affecting methane emission from Chinese rice fields

The effect of fertilizers on methane emission rates was investigated using an automated closed chamber system in Chinese rice fields (Human Province). Each of three experiments compared two fields treated with a first uniform fertilizer dose and a second fertilizer dose which was different for each of the two fields. The uniform fertilizer doses for both fields in each experiment comprised mineral (experiment 1), organic (experiment 2) and combined mineral plus organic components (experiment 3). In all three experiments the second fertilizer dose comprised organic amendments for field 1 and no organic amendments for field 2. The rate of increase in methane emission with a given amount of organic manure was found to depend on the total amount of organic manure applied. A single dose of organic manure increased the emission rates by factors of 2.7 to 4.1 as compared to fields without organic manure (experiment 1). In rice fields that had already been treated with organic manure, the application of a second dose of organic manure only slightly enhanced the emission rates in experiment 2 by factors of 1.1 to 1.5 and showed no detectable increase in experiment 3. The net reduction achieved by separation of organic and mineral fertilizers was maximized by concentrating the organic amendments in the season with low emission rates, i.e. early rice, and using exclusively mineral fertilizers on late rice when emission rates were generally higher. This distribution pattern, which was not associated with significant yield losses, resulted in an annual methane emission corresponding to only 56% of the methane emitted from fields treated with blended fertilizers.     

Denitrification losses from puddled rice soils in the tropics

Summary Although denitrification has long been considered a major loss mechanism for N fertilizer applied to lowland rice (Oryza sativa L.) soils, direct field measurements of denitrification losses from puddled rice soils in the tropics have only been made recently. This paper summarizes the results of direct measurement and indirect estimation of denitrification losses from puddled rice fields and reviews the status of research methodology for measurement of denitrification in rice fields. The direct recovery of (N₂+N₂O)-¹⁵N from ¹⁵N-enriched urea has recently been measured at sites in the Philippines, Thailand, and Indonesia. In all 12 studies, recoveries of (N₂+N₂O)-¹⁵N ranged from less than 0.1 to 2.2% of the applied N. Total gaseous N losses, estimated by the ¹⁵N-balance technique, were much greater, ranging from 10 to 56% of the applied urea-N. Denitrification was limited by the nitrate supply rather than by available C, as indicated by the values for water-soluble soil organic C, floodwater (nitrate+nitrite)-N, and evolved (N₂+N₂O)-¹⁵N from added nitrate. In the absence of runoff and leaching losses, the amount of (N₂+N₂O)-¹⁵N evolved from ¹⁵N-labeled nitrate was consistently less than the unrecovered ¹⁵N in ¹⁵N balances with labeled nitrate, which presumably represented total denitrification losses. This finding indicates that the measured recoveries of (N₂+N₂O)-¹⁵N had underestimated the denitrification losses from urea. Even with a probable two-or threefold underestimation, direct measurements of (N₂+N₂O)-¹⁵N failed to confirm the appreciable denitrification losses often estimated by the indirect difference method. This method, which determines denitrification losses by the difference between total ¹⁵N loss and determined ammonia loss, is prone to high variability. Measurements of nitrate disappearance and ¹⁵N-balance studies suggest that nitrification-denitrification occurs under alternate soil drying and wetting conditions both during the rice cropping period and between rice crops. Research is needed to determine the magnitude of denitrification losses when soils are flooded and puddled for production of rice.     

Fate of Azolla spp. and urea nitrogen applied to wetland rice (Oryza sativa L.)

Summary Using ¹⁵N, the fate of N applied to wetland rice either as Azolla or urea was studied in a field at the International Rice Research Institute (IRRI). In bigger plots nearby, yield response and N uptake were also determined with unlabelled N sources. Azolla microphylla was labelled by repeated application of labelled ammonium sulfate. Labelled and unlabelled N were used alternately in applications of Azolla or urea 0 and 42 days after transplanting, in order to determine the effect of the time of application on the availability of Azolla N. The quantities of Azolla N incorporated were 23% more than those of urea N (30 kg N ha^–1) in the isotope plots or 7% less in the yield response plots. Grain yield and total N uptake by the rice plants in the yield-response plots were higher in the urea-treated plots than in the Azolla-treated plots, but the physiological effect of Azolla N (grain yield response/increase in N uptake) was higher than that of rea. The labelled N balance was studied after the first and second crops of rice. Losses of labelled N after the first crop were higher from urea (30%–32%) than from Azolla (0%–11 %). Losses in N applied as a side dressing 42 days after transplanting were less than those of N applied basally. No further losses of ¹⁵N occurred after the first crop. The recovery of Azolla ¹⁵N in the first crop of rice was 39% from the basal application and 63% from the side dressing. The recovery of urea ¹⁵N was 27% from the basal application and 48% from the side dressing. Recoveries of residual N from both Azolla and urea during the second rice crop were similar. Laboratory incubation of the Azolla used and the changes in labelled exchangeable N in the soil showed that at least 65% of Azolla N (4.7% N content) was mineralized within 10 days.     

Ammonium oxidation coupled to dissimilatory reduction of iron under anaerobic conditions in wetland soils

In exploring the dynamics of iron and nitrogen cycling in sediments from riparian forests we have observed a redox reaction that has not been previously described. During incubations of soil slurries under strictly anaerobic conditions, we repeatedly measured an unexpected production of both nitrite () and ferrous iron [Fe(II)]. Using this indirect evidence we hypothesize that, under anaerobic conditions, there is a biological process that uses ferric iron [Fe(III)] as an electron acceptor while oxidizing ammonium () to for energy production. This oxidation under iron reducing anaerobic conditions is thermodynamically feasible and is potentially a critical component of the N cycle in saturated sediments.