Estimating Evapotranspiration and Seepage for a Sinkhole Wetland From Diurnal Surface‐Water Cycles1

Abstract: This study used measured diurnal surface‐water cycles to estimate daily evapotranspiration (ET) and seepage for a seasonally flooded sinkhole wetland. Diurnal surface‐water cycles were classified into five categories based on the relationship between the surface‐water body and the surrounding ground‐water system (i.e., recharge/discharge). Only one class of diurnal cycles was found to be suitable for application of this method. This subset of diurnal cycles was used to estimate ET and seepage and the relative importance of each transfer process to the overall water budget. The method has limited utility for wetlands with erratic hydrologic regimes (e.g., wetlands in urban environments). This is due to violation of the critical assumption that the inflow/outflow rate remains constant throughout the day. For application to surface‐water systems, the method is typically applied with an assumed specific yield of 1.0. This assumption was found to be invalid for application to surface‐water systems with a noncylindrical pond geometry. An overestimation of ET by as much as 60% was found to occur under conditions of low pond stage and high water loss. The results demonstrate the high ET rates that can occur in isolated wetlands due to contrasting roughness and moisture conditions (oasis and clothesline effects). Estimated ET rates ranged from 4.1 to 18.7 mm/day during the growing season. Despite these large ET rates, seepage (recharge) was found to be the dominant water loss mechanism for the wetland.     

人工湿地处理系统的运行管理与维护

人工湿地作为一种新型的处理技术，在水环境保护中具有重要的意义和广阔的应用前最。随着人工湿地处理工程数量的增多，迫切地需要建立科学的管理制度和维护方法，以充分发挥其美化水环境和提升人文环境的双重作用。本文对人工湿地处理系统中水位控制、进出水装置维护、护堤维护、植物管理、气味控制、蚊蝇控制和野生动物管理等方面进行了分析探讨，系统论述了人工湿地处理系统在运行管理和维护中需要考虑的主要事项。对将来建立完善的人工湿地处理系统的管理体系具有一定的借鉴意义。     

IDENTIFICATION OF AN OPTIMAL SAMPLING STRATEGY FOR A CONSTRUCTED WETLAND1

ABSTRACT: The objective of this investigation was to determine the effect of sampling frequency and sampling type on estimates of monthly nutrient loads and flow‐weighted nutrient concentrations in a constructed wetland. Phosphorus and nitrogen loads and concentrations entering and leaving a subtropical wetland (the Everglades Nutrient Removal Project, ENRP) were calculated on the basis of three sampling frequencies. The first frequency included weekly composite samples (three daily samples composited for one week) and grab samples from August 1994 to July 1997, representing a base‐line condition for comparison with results using reduced sampling frequencies. The second and third sampling frequency included three and two composite samples per month, respectively, drawn from the weekly samples. Total phosphorus and nitrogen loads calculated using two and three samples per month were almost identical to results based on four samples per month (least‐squares regression coefficients ranged from 0.96 to 0.98). Results of monthly mean flow‐weighted nutrient concentrations, obtained using reduced sampling frequencies, also were strongly correlated to concentrations calculated using the base‐line sampling frequency (r²ranged from 0.82 to 0.93). Grab samples did not always provide good estimates of loads or concentrations, particularly at the inflow when data were highly variable. From the results of this study, we can recommend that bi‐weekly composite sampling be used to monitor nutrient concentrations and loads discharged from larger‐scale Everglades Stormwater Treatment Areas (STAs) now under construction. Because there are high costs associated with water sample collection and processing, studies to identify optimal sampling frequencies should be a key feature in the design of any comprehensive wetland‐monitoring program.     

SEASONAL WATER TABLE DYNAMICS OF A SOUTHERN APPALACHIAN FLOODPLAIN AND ASSOCIATED FEN1

ABSTRACT: Appalachian mountain alluvial wetlands include floodplain forests interspersed with fens or bogs. This study evaluates the water table dynamics of an Appalachian mountain flood‐plain which includes a depressional fen. Water table wells and piezometers documented seasonal patterns of the water table and the vertical hydraulic gradient (VHG) in the floodplain and fen areas. Additional water table wells determined the potential sources of water from adjacent hillslopes to the fen area. The water table of the floodplain and the fen exhibited distinct regular seasonal fluctuations. The water table remained near the surface of the fen from late winter through late spring and dropped 20 to 80 cm during the summer between precipitation events. The water table of the floodplain fluctuated more but followed similar patterns and was typically within 40 cm of the surface during late winter and early spring months and greater than 60 cm during the summer months. The water table of the floodplain was more often correlated to precipitation than the water table of the fen. The VHG in the floodplain was highly variable although seasonal patterns of upwelling of water in fall and downwelling in winter were common. The VHG of the fen showed a consistent downwelling of water and suggested that the fen serves as a recharge area for an aquifer. Principal sources of water for the fen appeared to be precipitation, inflow from a shallow aquifer on an adjacent slope plus increased interflow associated with precipitation events from another adjacent slope. The influence of soil texture on water dynamics of the fen or floodplain was not fully ascertained but it appeared to influence horizontal flow from hillslopes and the depth of the water table in the fen.     

DEVELOPMENT AND APPLICATION OF A SPATIAL HYDROLOGY MODEL OF OKEFENOKEE SWAMP,GEORGIA1

ABSTRACT: :The model described herein was used to assess effects of the Suwannee River sill (a low earthen dam constructed to impound the Suwannee River within the Okefenokee National Wildlife Refuge to eliminate wildfires) on the hydrologic environment of Okefenokee Swamp, Georgia. Developed with Arc/Info Macro Language routines in the GRID environment, the model distributes water in the swamp landscape using precipitation, inflow, evapotranspiration, outflow, and standing water. Water movement direction and rate are determined by the neighborhood topographic gradient, determined using survey grade Global Positioning Systems technology. Model data include flow rates from USGS monitored gauges, precipitation volumes and water levels measured within the swamp, and estimated evapotranspiration volumes spatially modified by vegetation type. Model output in semi‐monthly time steps includes water depth, water surface elevation above mean sea level, and movement direction and volume. Model simulations indicate the sill impoundment affects 18 percent of the swamp during high water conditions when wildfires are scarce and has minimal spatial effect (increasing hydroperiods in less than 5 percent of the swamp) during low water and drought conditions when fire occurrence is high but precipitation and inflow volumes are limited.     

广州南沙地区湿地生态系统的特征分析

南沙地区是广州城市空间“南拓”发展战略的重点开发区域,南沙地区湿地资源丰富。南沙建设必须正确处理湿地开发与保护的关系,实现社会经济与生态环境协调发展。本文根据湿地资源调查结果,详细分析了南沙地区湿地生态系统的基本特征,为南沙开发建设中保护与合理利用湿地资源提供科学依据。     

Optimal conditions for chlorothalonil and dissolved organic carbon in horizontal subsurface flow constructed wetlands

The most efficient system of horizontal subsurface flow constructed wetlands (HSSFCW) for removing dissolved organic carbon (DOC) in the presence of chlorothalonil pesticide (CLT) present in synthetic domestic wastewater was determined using the macrophyte Phragmites australis. Two concentrations of CLT (85 and 385 μg L^?1) and one concentration of glucose (20 mg L^?1) were evaluated in four pilot scale horizontal surface flow constructed wetlands coupled with two sizes of silica gravel, igneous gravel, fine chalky gravel (3.18–6.35 mm), coarse gravel (12.70–25.40 mm) and two water surface heights (20 and 40 cm). For a month, wetlands were acclimated with domestic wastewater. Some groups of bacteria were also identified in the biofilm attached to the gravel. In each treatment periodic samplings were conducted in the influent and effluent. Chlorothalonil was quantified by gas chromatography (GC-ECD m), DOC by an organic carbon analyzer and bacterial groups using conventional microbiology in accordance with Standard Methods. The largest removals of DOC (85.82%–85.31%) were found when using fine gravel (3.18–6.35 mm) and the lower layer of water (20 cm). The bacterial groups quantified in the biofilm were total heterotrophic, revivable heterotrophic, Pseudomonas and total coliforms. The results of this study indicate that fine grain gravel (3.18–6.35 mm) and both water levels (20 to 40 cm) can be used in the removal of organic matter and for the treatment of agricultural effluents contaminated with organo-chloride pesticides like CLT in HSSFCW.     

半月周期的潮汐对滨海湿地土壤理化性质的影响

周期性的潮汐是滨海湿地重要的水文特征,为了探讨潮汐的半月周期(包括小潮期和大潮期)对土壤理化性质的影响及可能的机制,于2009年7月中下旬测定了长江口崇明东滩湿地土壤理化性质在小潮期和大潮期交替周期内的变化规律。结果表明,与小潮期相比,由于频繁的潮水淹没,大潮期0～5 cm土壤含水量的增加量从低潮滩向高潮位依次为:44.8%、18.5%、10.9%和14.3%,5～10 cm含水量的增加量从低潮滩向高潮位依次为:19.2%、9.8%、12.6%和16.2%,10～20 cm则依次为:5.6%、6.1%、2.5%和7.3%。大潮期,从低潮滩向高潮滩增加的盐度依次为0.18、0.13、0.10和0.09 ms·cm^-1,增加的硫酸盐依次为0.32、0.21、0.16、0.13 mg·g^-1。与小潮期相比,大潮期氧化还原电位(Eh)显著降低;土壤容重、pH、可溶性有机碳和可溶性氮在大小潮期间无明显差异。此外,在潮汐的半月周期内,低潮滩土壤比高潮滩有更高淹水频率和更长淹水时间,受潮水的影响更明显,大潮期低潮滩土壤含水量、盐度和硫酸盐的增加幅度大于高潮滩,低潮滩土壤Eh降低幅度则小于高潮滩。半月周期的潮汐可以显著影响滨海湿地的部分土壤理化性质,且不同潮位的土壤性质对潮汐的响应程度不同,进而可能会对湿地植物生长和相关生态过程起到重要的调控作用。     

退化过程中翅碱蓬湿地营养元素变化特征研究

在双台子河口选取4块样地,分别代表恢复中、长势良好、退化严重的翅碱蓬湿地和裸露的光滩,于2009年6月、2009年9月、2010年4月(代表夏季,秋季,春季)分别采集表层土壤与植物样品。通过对翅碱蓬生物量、N、P、有机质含量及土壤N、P、有机质含量的测定,分析了翅碱蓬湿地退化过程中土壤及植物营养元素的变化规律。结果表明:春季各种类型翅碱蓬湿地土壤的有机质(分别为1.88%、1.89%、1.19%、1.13%)和总磷(分别为496.30、498.75、435.97、404.57 mg/kg)含量顺序为:长势良好≈光滩>退化中>恢复中,同该类型湿地的演替顺序一致,说明湿地的退化导致土壤C、P素大量损失。翅碱蓬湿地的退化引起翅碱蓬植株生长状态的变化,导致同一种湿地植物植株中N、P、有机质含量在不同退化类型湿地中的分布存在明显差异,说明湿地的退化,已经明显的影响到N、P、有机质的生物地球化学循环。