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101.
《Process Safety and Environmental Protection》2014,92(6):903-916
In this paper we investigated the use of three different methods for determining the rate constants for degradation of winery effluent within a sub-surface flow constructed wetland (CW). These methods comprised of using a dispersed plug flow (the Peclet) equation; a tanks-in-series (TIS) equation; and analysing the residence time distribution (RTD) directly. The last of these is described by the convolution integral (CI). We demonstrated self-similarity of the RTDs, which meant that the system's hydraulics were similar throughout the CW. We therefore extrapolated the RTD data to develop a more complete understanding of the hydraulic properties of the CW and examine how they affected the kinetics of degradation. We found that whilst both the Peclet and the TIS equation were able to predict concentration within the CW, this required the optimisation of more than one variable at the same time rendering a result that was more of a modelling exercise than a useful design tool. The CI method could be applied to predict system parameters effectively. We used it to measure rate constants of removal for both ethanol and potassium (key species for tracking the degradation/treatment of the effluent). Acetic acid, however, did not degrade implying that the CW operated aerobically. The concentration of sodium increased very slightly, indicating that it is not bioremediated/removed and that there are some minor evapotranspirative effects. The rate constant found for the biodegradation of COD was found to have significantly more uncertainty associated with it than the measurement of the rate of degradation individual components and we therefore posit that it is better to describe the processes of degradation by tracking individual components rather than lumped parameters. 相似文献
102.
An ongoing debate in ecology is the relationship between community or ecosystem structure and function. This relationship is particularly important in restored ecosystems because it is often assumed that restoring ecosystem structure will restore ecosystem functioning, but this assumption is frequently not tested. In this study, we used a novel application of structural equation modelling (SEM) to examine the relationship between ecosystem structure and function. To exemplify how to apply SEM to explore this relationship, we used a case study examining soil controls on denitrification potential (DNP) in two restored wetlands. Our objectives were to examine (1) whether both restored wetland soil ecosystems had similar relationships among soils variables (i.e. similar soil ecosystem structure) and (2) whether the soil variables driving denitrification potential (DNP) were similar at both sites (i.e. the soil ecosystems were functioning in a similar manner). Using the unique ability of SEM to test model structure, we proposed a SEM to represent the soil ecosystem and tested this structure with field data. We determined that the same model structure was supported by data from both systems suggesting that the two restored wetland systems had similar soil ecosystem structure. To test whether both ecosystems were functioning in a similar way, we examined the parameters of each model. We determined that the drivers of DNP function were not the same at both sites. Higher soil organic matter was the most important predictor of higher DNP at both sites. However, the other significant relationships among soils variables were different at each system indicating that the soils were not functioning in exactly the same way at each site. Overall, these results suggest that the restoration of ecosystem structure may not necessarily ensure the restoration of ecosystem functioning. In this study we capitalize on an inherent feature of SEM, the ability to test model structure, to test a fundamental ecological question. This novel approach is widely applicable to other systems and improves our understanding of the general relationship between ecosystem structure and function. 相似文献
103.
An ecological risk assessment model for a pulsed contaminant emission into a wetland channel flow 总被引:1,自引:0,他引:1
As a continuation of the modelling on ecological degradation and hydraulic dispersion of pollutant emission into an idealized two-dimensional free-surface wetland flow (Zeng, L., Chen, G.Q., 2009b. Ecological degradation and hydraulic dispersion of contaminant in wetland. Ecol. Model., doi:10.1016/j.ecolmodel.2009.10.024), an ecological risk assessment model for the typical case of a pulsed contaminant emission into a realistic three-dimensional wetland channel flow is presented in this paper for the fate of cross-sectional mean concentration under environmental dispersion. An environmental dispersion model for the mean concentration is devised as an extension of Taylor’s classical analysis on dispersion in fluid flows. The velocity distribution and the environmental dispersivity in the fully developed steady flow through the wetland is found and illustrated with limiting cases covering various known solutions for the porous media flow between parallel plates, flow in a shallow wetland, sweeping flow in a densely vegetated wetland, and single phase flow in a channel. Obtained by Aris’s method of moments, the environmental dispersivity is shown characterized with multi-scale asymptotic time variations with stem dominated stage, transitional stage, and width-depth-stem dominated stage. Based on the solution for the evolution of contaminant cloud in the wetland channel flow, critical length and duration of the contaminant cloud with concentration beyond given environmental standard level are concretely illustrated for typical pollutant constituents in wastewater emission. Under the same emission intensity and environmental standard, the duration of contaminant cloud in the wetland channel is revealed shorter than that in a free surface wetland, due to the lateral effect. 相似文献
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109.
洞庭湖区湿地生物多样性保护及其可持续利用 总被引:9,自引:0,他引:9
洞庭湖区是我国最大的淡水湖泊湿地之一,复杂多样的湿地类型和生态环境蕴含了丰富的生物资源,但长期以来由于人类不合理的开放利用,导致了洞庭湖区湿地面积和景观结构发生了很大变化,湿地生态功能也遭到严重破坏,生物多样性不断减少,本文分析了洞庭湖区湿地生物多样性现状及保护的意义,湿地生物多样性面临的威胁,并提出了洞庭湖区湿地生物多样性保护及其可持续利用的主要对策。 相似文献
110.
介绍了大小兴安岭地区湿地生态环境的形成,就湿地植被形成的主要因素─—气候和地貌进行了论述,分析了大小兴安岭湿地类型主要属低位、中位和高位沼泽类湿地及其自然演替过程,指出了湿地现有生态系统所存在的问题并对其保护对策提出合理建议。 相似文献