乌苏里江洪泛湿地蜻蜓目幼虫对水文连通阻断的生态响应

大型底栖动物的群落组成完整性能够指示和预测水生态环境的健康程度和变化趋势,已经在大量研究中得到验证.然而,群落水平的全部样品采集过程的复杂性并不利于它们的便捷应用.蜻蜓目幼虫是大型底栖动物中相对易于捕捉和识别的类群,并且拥有特别的两栖生命周期,它们的多样性特征以及对水体性质变化的敏感反应,使其成为湿地生态系统中非常广泛...     

贵州草海岩溶湿地水体不同形态氮的时空分布特征

为揭示贵州草海岩溶湿地水体中不同形态氮时空分布特征及其变化规律,通过网格布点法采集了该湿地丰、枯水期表层水,并对其不同形态溶解性氮含量进行了测定,运用ArcGIS统计模块分析了草海不同形态氮的时空分布特征,并分析了各形态氮与环境因子之间的相关性.结果表明:草海水体丰、枯水期TN的平均含量分别为(0.96±0.52)、(...     

Methane emissions from wet grasslands on peat soil in a nature preserve

The area of wet grasslands on peat soil in the Netherlands is slowly increasing at the expense of drained, agriculturally used grasslands. This study aimed (i) to assess the contribution of wet grasslands on peat soil to methane (CH₄) emissions, and (ii) to explain differences among sites and between years in order to improve our understanding of controlling factors. For these purposes, a field study was conducted in the period 1994–1996 in the nature preserve Nieuwkoopse Plassen, which is a former peat mining and agricultural area. Net CH₄ emissions were measured weekly to monthly with vented closed flux chambers at three representative sites, and at ditches near these sites. Three-years average of CH₄ emissions was 7.9 g CH₄ m^–2 yr^–1 for Drie Berken Zudde, 13.3 for Koole, and 20.4 for Brampjesgat. Ditches near the sites emitted 4.2–22.5 g CH₄ m^–2 yr^–1. The time-course of CH₄ emissions for all experimental sites and years was fit with a multiple linear regression model with ground water level and soil temperature as independent variables. Lowering or raising the ground water level by 5 cm could decrease or increase CH₄ emissions by 30–50%. Therefore, ground water level management of these grasslands should be done with care.     

Quantitative analysis of bacterial communities from Mediterranean sapropels based on cultivation-dependent methods

Microbial communities of ancient Mediterranean sapropels, buried sediment layers of high organic matter, were analyzed by most probable number (MPN) approaches. Mineral media containing different carbon sources in sub-millimolar concentrations were used. MPN numbers were elevated in sapropels and at the sediment surface, which mirrored total cell count distributions. Highest MPN counts were obtained with a mixture of different monomeric and polymeric substrates, with amino acids or with long-chain fatty acids as sole carbon sources. These values reached up to 2 x 10(7) cm(-3), representing 3.3% of the total cell count. A total of 98 pure cultures were isolated from the highest positive dilutions of the MPN series, representing the most abundant microorganisms culturable by the methods used. The strains were identified by molecular biological methods and could be grouped into 19 different phylotypes. They belonged to the alpha-, beta-, gamma-, and delta-Proteobacteria, to the Actinobacteria and the Firmicutes. However, about half of the number of isolates was closely related to the genera Photobacterium and Agrobacterium. Regarding the high cultivation success, these organisms can be assumed to be typical sapropel bacteria, representing a substantial part of the culturable indigenous microbial community.     

The Effects of Infrared Loading and Water Table on Soil Energy Fluxes in Northern Peatlands

Increased radiative forcing is an inevitable part of global climate change, yet little is known of its potential effects on the energy fluxes in natural ecosystems. To simulate the conditions of global warming, we exposed peat monoliths (depth, 0.6 m; surface area, 2.1 m²) from a bog and fen in northern Minnesota, USA, to three infrared (IR) loading (ambient, +45, and +90 W m^–2) and three water table (–16, –20, and –29 cm in bog and –1, –10 and –18 cm in fen) treatments, each replicated in three mesocosm plots. Net radiation (Rn) and soil energy fluxes at the top, bottom, and sides of the mesocosms were measured in 1999, 5 years after the treatments had begun. Soil heat flux (G) increased proportionately with IR loading, comprising about 3%–8% of Rn. In the fen, the effect of IR loading on G was modulated by water table depth, whereas in the bog it was not. Energy dissipation from the mesocosms occurred mainly via vertical exchange with air, as well as with deeper soil layers through the bottom of the mesocosms, whereas lateral fluxes were 10–20-fold smaller and independent of IR loading and water table depth. The exchange with deeper soil layers was sensitive to water table depth, in contrast to G, which responded primarily to IR loading. The qualitative responses in the bog and fen were similar, but the fen displayed wider seasonal variation and greater extremes in soil energy fluxes. The differences of G in the bog and fen are attributed to differences in the reflectance in the long waveband as a function of vegetation type, whereas the differences in soil heat storage may also depend on different soil properties and different water table depth at comparable treatments. These data suggest that the ecosystem-dependent controls over soil energy fluxes may provide an important constraint on biotic response to climate change.     

The Salton Sea as critical habitat to migratory and resident waterbirds

Concern about the Salton Sea ecosystem, based on potential impacts of increasing salinity, contaminants, disease outbreaks, and large die-offs of birds, is heightened because of tremendous prior loss and degradation of wetland habitat in western North America. In 1999, we used a variety of survey methods to describe patterns of abundance of birds at the Salton Sea and in adjacent habitats. Our results further documented the great importance of the Salton Sea within the Pacific Flyway to wintering, migratory, and breeding waterbirds. Exclusive of Eared Grebes, we estimated about 187000 individual waterbirds at the Salton Sea in January, 88000 in April, 170000 in August, and 261000 in November. Additional surveys of Eared Grebes in November and December suggested the total population of all waterbirds was about 434000 to 583000 in those months, respectively. We also documented breeding by about 14000 pairs of colonial waterbirds. Waterbirds were particularly concentrated along the northern, southwestern, southern, and southeastern shorelines and river deltas. By contrast, some species of wading birds (Cattle Egret, White-faced Ibis, Sandhill Crane) and shorebirds (Mountain Plover, Whimbrel, Long-billed Curlew) were much more numerous in agricultural fields of the Imperial Valley than in wetland habitats at the Sea. Various studies indicate the Salton Sea is of regional or national importance to pelicans and cormorants, wading birds, waterfowl, shorebirds, and gulls and terns. Important taxa are the Eared Grebe, American White Pelican, Double-crested Cormorant, Cattle Egret, White-faced Ibis, Ruddy Duck, Yuma Clapper Rail, Snowy Plover, Mountain Plover, Gull-billed, Caspian, and Black terns, and Black Skimmer. Proposed restoration projects should be carefully assessed to ensure they do not have unintended impacts and are not placed where large numbers of breeding, roosting, or foraging birds concentrate. Similarly, plans to enhance opportunities for recreation or commerce at the Sea should aim to avoid or minimize disturbance to birds. Future research should focus on filling gaps in knowledge needed to effectively conserve birds at the Salton Sea.     

Ecosystem CO2 exchange and plant biomass in the littoral zone of a boreal eutrophic lake

• 1 In order to study the dynamics of primary production and decomposition in the lake littoral, an interface zone between the pelagial, the catchment and the atmosphere, we measured ecosystem/atmosphere carbon dioxide (CO₂) exchange in the littoral zone of an eutrophic boreal lake in Finland during two open water periods (1998–1999). We reconstructed the seasonal net CO₂ exchange and identified the key factors controlling CO₂ dynamics. The seasonal net ecosystem exchange (NEE) was related to the amount of carbon accumulated in plant biomass.
• 2 In the continuously inundated zones, spatial and temporal variation in the density of aerial shoots controlled CO₂ fluxes, but seasonal net exchange was in most cases close to zero. The lower flooded zone had a net CO₂ uptake of 1.8–6.2 mol m^?2 per open water period, but the upper flooded zone with the highest photosynthetic capacity and above‐ground plant biomass, had a net CO₂ loss of 1.1–7.1 mol m^?2 per open water period as a result of the high respiration rate. The excess of respiration can be explained by decomposition of organic matter produced on site in previous years or leached from the catchment.
• 3 Our results from the two study years suggest that changes in phenology and water level were the prime cause of the large interannual difference in NEE in the littoral zone. Thus, the littoral is a dynamic buffer and source for the load of allochthonous and autochthonous carbon to small lakes.

     

Evaluation of biotracers to monitor effluent retention time in constructed wetlands

AIMS: With concern surrounding the environmental impact of chemical tracers on the aquatic environment, this paper presents the initial evaluation of biotracers used to determine the effluent retention time, an important performance indicator, in a Free Water Surface Constructed Wetland. METHODS AND RESULTS: Production of the biotracers, coliphage MS2, and the bacteriophage of Enterobacter cloacae and antibiotic resistant endospores of Bacillus globigii is described in detail. Their subsequent use in three separate tracer experiments - January, March and June (2000) - revealed the variability of retention time with respect to effluent flow. The biotracer MS2 showed the constructed wetland had a retention time of 8-9 h at a mean discharge of 0.9 l s-1, increasing to 10-12 h at a mean discharge 0.3 l s-1. A similar retention of 9-10 h at a mean discharge of 0.3 l s-1 was calculated for the Ent. cloacae phage. In contrast, use of endospores revealed considerably longer retention times at these mean discharge rates; 12-24 h and 36-48 h, respectively. CONCLUSION: Biotracers could provide a useful and environmentally friendly technique to monitor effluent retention in constructed wetlands. At this stage the phage tracers appear particularly promising due to ease of isolation and recovery. SIGNIFICANCE AND IMPACT OF THE STUDY: Initial results are encouraging and have highlighted the potential of biotracers as alternatives to chemical tracers, even in microbially-rich waters.     

Changes in cell structure during the formation of root aerenchyma inSAGITTARIA LANCIFOLIA (Alismataceae)

In many wetland species, root aerenchyma is produced by the predictable collapse of root cortex cells, indicating a programmed cell death (PCD). The objective of this study was to characterize the cellular changes that accompany this PCD in the marsh species Sagittaria lancifolia. Structural changes in membranes and organelles were examined during development of root cortex cells to compare with previous examples of PCD. The organization of cortical microtubule (CMT) arrays in root cells from S. lancifolia was also evaluated as a possible predictor of cell lysis. Nuclear fragmentation and condensation were the earliest changes observed in cells undergoing lysis. Breakdown of the tonoplast and other organelles and disruption of the plasma membrane followed. After loss of cytoplasm, cells collapsed to form gas spaces. These results were compared to collapse of root cortical cells of Zea mays and Oryza sativa during aerenchyma development. Changes in the appearance of the cytoplasm of all three species were similar at later stages of aerenchyma development. The relative timing of disintegration of the tonoplast and middle lamella appeared to differ among the three species. Changes in the organization of CMT arrays did not appear to be a predictor of PCD in S. lancifolia. Aerenchyma production in plants involves a type of PCD that is morphologically distinct from PCD described from many animals.     

Ski slope vegetation at Snoqualmie Pass, Washington State, USA, and a comparison with ski slope vegetation in temperate coniferous forest zones

Ski slope vegetation at Snoqualmie Pass in Washington State, USA, was surveyed in order to identify community types and to compare it with vegetation development patterns in Japan. Ski slopes in Japan, most of which were constructed after 1960, underwent heavy land recontouring, while those at Snoqualmie Pass were constructed before 1950 with less modification. Three points apply to Japanese ski slope vegetation and differentiate these slopes from those at Snoqualmie Pass: (i) grasslands of introduced species are widespread and persistent; (ii) unvegetated patches are uncommon; and (iii) wetland vegetation has developed. These differences are mainly derived from the intensity of human impact, history of the slope and its scale: namely, ski slopes in Washington are older and larger than those in Japan. Ski slope vegetation in Washington was primarily differentiated by a soil moisture gradient. The large size of Washington ski slopes permitted the inclusion and development of wetland habitats, whereas most ski slopes in Japan are constructed on ridges and do not contain wetlands. Most introduced species in Japan are eliminated soon after seeding. In contrast, the long-term management of ski slopes decreased soil erosion and/or unvegetated patches in Washington and created relatively permanent grasslands composed of introduced species. Tsuga heterophylla and Abies amabilis were found established on the ski slopes in Washington, whereas in Japan the pioneer tree species are shade-intolerant broadleaved species. These differences may be a result of the different disturbance histories of ski slopes in the two countries. In addition, along with the conifers, early successional forbs such as Anaphalis margaritacea and Epilobium angustifolium are well established on Washington ski slopes. Results show that disturbances created by ski slope development greatly affect the vegetation, even on older, less heavily impacted ski slopes.