Plankton respiration and biomass as functional indicators of recovery in restored prairie wetlands

Reliable ecological indicators of wetland integrity are necessary for assessing recovery of restored wetlands; yet, little consensus currently exists on which indicators are most appropriate. We employed indicators derived from simple, standard measures of ecosystem function selected on the basis of ecological succession theory developed by [Science 164 (1969) 262; Bioscience 35 (1985) 419], which suggests that respiration:biomass ratios should increase in disturbed systems due to the diversion of energy from growth to maintenance. This hypothesis holds potential for the development of a simple ecological indicator and therefore was tested among prairie wetlands restored after drainage disturbance. No difference was observed in respiration:biomass ratios in restored wetlands and reference wetlands designated as controls. Plankton respiration or biomass may be poor indicators of disturbance because plankton responds quickly to re-establishment of a wetland hydrology regime and/or because different plankton species may have redundant function. We suggest employing more revealing assessment techniques that employ simultaneous examination of ecosystem structure and function to better characterize subtle or lingering effects of wetland disturbance after restoration.     

Potential for total nitrogen removal by combining vertical flow and horizontal flow constructed wetlands: A full-scale experiment study

To improve total nitrogen removal, a full-scale experimental study was conducted on a hybrid constructed wetlands plant designed for 100 person equivalents. The plant was composed of a first stage of vertical filters (fed with raw wastewater), followed by a second stage of horizontal filters. It was monitored over one year, measuring hydraulic conditions, physico-chemical conditions, gas emission, oxygen levels in the gas phase as well as regular treatment performance by 24-h composite samples. Different vertical filter configurations (media depth, intermediate and passive aeration system) were tested as well as two horizontal filter designs. Nitrogen removal is discussed in terms of the efficiency of each stage in relation to the season and the load applied. This study indicates limits for systems configuration and suggests some design avenues for hybrid systems to reach high and regular levels of nitrogen removal with reasonable surface area per person.     

大气中CO2、O3浓度升高对银杏成年叶片气孔数量特征的影响

利用开放式气室(OTC)持续观测了2个生长季(2005-2006年).在每年9月30日停止供气后,采样1次.观测高浓度CO2和O3处理的银杏(Ginkgo biloba)成年叶片气孔数量的变化规律.结果表明:在700 μmol·mol-1CO2处理条件下,叶片气孔的长度、宽度、周长和面积均明显高于对照(P<0.05);在80 μmol·mol-1O3处理条件下,气孔的长度、宽度、周长和面积却显著低于对照(P<0.01);成年叶片气孔在高浓度CO2影响下,气孔密度略有升高(P>0.05),而气孔指数显著减少(P<0.05);大气O3浓度升高对气孔密度影响不大(P>0.05),气孔指数显著减少(P<0.05);银杏成年叶片气孔的长度、宽度与气孔比密度存在一定的负相关关系,可用一元二次曲线方程较好地描述.     

小区生活污水处理模式的研究进展

分析了小区生活污水处理模式的现状,指出了集中式处理模式和分散式处理模式的不足.依据人工湿地、地下渗滤为主的土地生态处理技术的特点,提出小区污水处理采取土地生态处理模式的构想.通过分析污水土地生态处理技术的特征及其运行局限性,建议土地生态处理技术应重视强化预处理,采取低进水污染物浓度,高水力负荷的运行方式.     

杭州西溪湿地植物组成及其与水位光照的关系

 杭州西溪湿地是在自然湿地基础上,并在一千多年农渔耕作用下形成的城市边缘次生湿地。随着工业化和城市化,它的面积急剧萎缩,植被受 干扰,生态脆弱,不久前成立的西溪国家湿地公园已经将保护提上日程。该文在报道这类特殊湿地植被结构和物种多样性的基础上试图回答下 列问题：何种小生境利于保护本地和湿地植物多样性？入侵种在各种小生境中的影响如何？怎样防控？根据调查,将西溪湿地草本层的小生境 分成5种类型：强光高基、弱光(有树遮光)高基、强光低基、强光高渚和强光低渚。采用分层和随机取样相结合的方法调查这5种小生境下的植 物群落组成,以重要值作为变量来计算物种多样性指数并排序。共26个地点,约234 m²的样方。结果显示在农渔耕的背景下,水位高低及光照 等自然因子对植物组成具有一定的选择作用。强光高基生境物种丰富度最高,其中本土、木本和豆科植物数量最多,而入侵种、湿生物种数量 最低;强光低渚生境的情况正好相反。强光高基生境有利于保持本土植物多样性,降低入侵种的竞争能力,但不利于湿地植物的存在;强光低 基有中度本土植物多样性及抵御入侵种的能力,有较大的草本比例和湿地植物比例,是一个保持良好的湿地环境。有利于湿地植物的低湿生境 目前在西溪比例较低,湿地植物偏少,这主要与西溪先前人类从事农业和渔业活动有关。在去除影响景观、影响本土物种多样性的入侵种的同 时,可考虑增加低湿的生境,并补种湿地物种。     

Constructed Wetland Habitat for American Avocet and Black-Necked Stilt Foraging and Nesting

Abstract In 1994, a 117-ha wetland was designed, constructed, and operated by the Tulare Lake Drainage District (TLDD), California, USA, to provide foraging and nesting habitat for American avocets (Recurvirostra americana) and black-necked stilts (Himantopus mexicanus). The wetland was operated seasonally in compliance with regulatory requirements to compensate for impacts to stilts, avocets, and other wildlife exposed to elevated selenium concentrations, fluctuating water levels resulting in nest flooding, and high nest-predation rates at the TLDD agricultural drainage evaporation basins. Water supply for the wetland was from low-selenium (typically <2 μg/L) saline agricultural drainage water, although the facility also had capability to blend and use freshwater and saline supplies. Coincident with wetland construction, 2 evaporation basins totaling 1,174 ha were physically modified and operated to discourage their use by shorebirds. In the first year of wetland operation (1995), American avocet and black-necked stilt nest construction at the wetland was 17.6 nests/ha. This compares to a preproject (1994) combined density of 1.9 nests/ha at the evaporation basins. From 1995 through 2004, annual nesting attempts by American avocets and black-necked stilts at the wetland averaged 2,896 per year (24.8 nests/ha). American avocets and black-necked stilts represented 91% of the nests observed at the wetland. Over the 10-year monitoring period, nest success at the wetland averaged 82% for American avocets and 75% for black-necked stilts. We estimated nest predation rates at the constructed wetland to be <1%. During the same period, American avocet and black-necked stilt nesting at the evaporation basins declined from 2,266 in 1994 to 9 in 2004. The constructed wetland has proven to be effective in attracting and providing suitable nesting habitat for large numbers of avocets and stilts. Results of this long-term study confirm the validity of management recommendations for American avocets and black-necked stilts and suggest that agricultural drainage can be successfully managed to provide highly productive managed wetlands.     

Wetland degradation leads to homogenization of the biota at local and landscape scales

1. We examined whether the anthropogenic degradation of wetlands leads to homogenization of the biota at local and/or landscape scales and, if so, what specific factors account for such an effect. We compared 16 isolated wetlands (Michigan, U.S.A.) that varied in surrounding land use: half had developed, and half undeveloped, riparian zones. Samples of macrophytes, epiphytic diatoms, zooplankton, macroinvertebrates and water chemistry were collected along three transects in each wetland. 2. Developed wetlands were more nutrient‐rich with higher Cl concentrations. The plant community at developed sites was dominated by Lemnaceae (duckweed), while undeveloped wetlands were dominated by rooted, floating‐leaved vegetation and sensitive plant species. Undeveloped wetlands contained heterogeneous and species‐rich plant communities, greater species richness of zooplankton and diatoms, and heterogeneous zooplankton distributions as compared to developed sites. 3. A comparison among wetlands showed that diatom and zooplankton assemblages in developed wetlands were nested subsets of richer biota found in less developed wetlands. Conversely, plant communities were more heterogeneously distributed among developed wetlands at the landscape level. This may be attributable to patchy invasions by exotic species, which were a feature of the degraded wetlands within developed landscapes. 4. Our results indicate that several taxonomic groups showed similar, probably inter‐dependent, responses to wetland degradation and habitat homogenization at both the local and landscape scales. This change in community structure from a species‐rich and heterogeneous community dominated by floating‐leaved plants in undeveloped wetlands, to nutrient‐rich wetlands dominated by duckweed may represent a shift to an alternate stable state.     

Snail–periphyton interactions in a prairie lacustrine wetland

This study examined the effects of nutrients and macrophytes on snail grazers and periphyton in a prairie wetland food web. Snails (Gyraulus circumstriatus) and periphyton in large enclosures in a lacustrine wetland, Delta Marsh, MB, Canada were subjected to two experimental treatments, nutrient addition (nitrogen, phosphorus) and macrophyte exclusion (using a porous geotextile carpet) during July and August. Snail biomass and periphyton biomass (on both artificial substrata and submerged macrophytes) increased over time in all treatments, representing seasonal growth. Snail biomass was three times higher on macrophytes than on artificial substrata. In response to nutrient addition, snail biomass was significantly elevated over time on macrophytes but not on artificial substrata. Conversely, periphyton biomass was higher on artificial substrata but not on macrophytes in response to nutrient addition. Snail biomass and periphyton biomass on artificial substrata showed no response to macrophyte exclusion. Snail biomass on all substrata was inversely correlated with turbidity, whereas periphyton biomass showed no relationship with turbidity. Timing of nutrient additions to wetlands may influence whether the response occurs primarily in phytoplankton or in periphyton and macrophytes.     

North African wetland lakes: characterization of nine sites included in the CASSARINA Project

Exploitation of land and water resources has increased rapidly in North Africa during the 20th century, paralleling regional population growth. As part of the CASSARINA Project (see Flower, 2001), the environmental status of nine wetland lakes in Morocco, Tunisia, and Egypt was evaluated. All are conservationally important habitats and several are Ramsar Sites (internationally recognized bird reserves) and several support significant fisheries. All are shallow (<2 m in depth) but vary greatly in area.Where available, documentary information on relevant 20th century changes is given. Survey transects for aquatic vegetation were established and used to provide baseline ecological information on the aquatic plant communities during 1997–1999. Unusually, one site (Tunisian Megene Chitane) supported acidophilous vegetation (some taxa being nationally rare). Aquatic macrophytes declined catastrophically at two sites during the 1990s. Merja Bokka was drained in 1998 and, at Garaet El Ichkeul, fringing Phragmites and Scirpus spp. were lost, mainly as a result of salinity changes. Elsewhere, fringing macrophytes remain (extensively so in the Nile Delta lakes) common, despite major land reclamation and water quality problems, or are degraded by grazing (Merja Zerga). Marginal vegetation during 1997/98 changed markedly at Megene Chitane due to water level lowering.Documentary records indicated that throughout the 20th century, reclamation and hydrologic modifications, mainly for agricultural purposes, affected all nine sites. The loss of lake area by reclamation is substantial for the Nile Delta lakes (Edku, Burullus and Manzala). For the western sites, some data indicate increasing salinity in the most recent decade but the Delta lakes have become generally fresher during the 20th century, as supply of Nile water for irrigation increased.Despite intense human disturbance, many of the remaining CASSARINA sites still support regions of high aquatic diversity. Spatial scale monitoring of the larger sites for seasonal and inter-annual changes in open water area and in aquatic plant abundances is a key requirement for integrated environmental change assessment in the 21st century.     

Restoration of Freshwater Intertidal Habitat Functions at Spencer Island, Everett, Washington

In November 1994 dikes were breached around Spencer Island, restoring tidal inundation and connections to the Snohomish River estuary, Washington. Approximately 23.7 ha (58.5 ac) of palustrine wetlands previously dominated by Phalaris arundinacea (reed canarygrass) now experience diurnal tides and are in the process of transition to a freshwater tidal system. It was expected that brackish water would accompany the return of tidal influence to the site, but post‐project monitoring has revealed little evidence of salinity. Pre‐ and post‐project monitoring of changes in habitat function included aerial photography, vegetation and fish sampling, and benthic prey studies. To date site changes include (1) die back of pre‐project vegetation, development of tidal mudflat, and emergent wetland habitats, with recruitment of vegetation typical of freshwater tidal wetlands; (2) presence of juvenile coho, chum, and chinook salmon that feed on invertebrate prey typical of the site; (3) presence of three distinct benthic invertebrate assemblages in the project area; and (4) some invasion by Lythrum salicaria (purple loosestrife). The unexpected freshwater conditions, the lack of published information about tidal oligohaline marshes in the Pacific Northwest, the use of the site by endangered salmonid species, and the invasion by an undesired plant species underscore the importance of long‐term monitoring at the site.