Plants as indicators of wetland water source

At the local scale, plant species distribution is determined primarily by the environmental characteristics of a site. In a wetland, water chemistry and hydroperiod are two of the most important of these environmental characteristics. Both are functions of water source. In central Pennsylvania, groundwater input tends to be continuous, while surface water may be permanent or seasonal. The chemistry of groundwater and surface water differs since groundwater is influenced by the substrate through which it flows. Because of these differences, and because of their effects on plant species distribution, it is possible to use vegetation as an indicator of the dominant water source of a site. Plots within 28 wetlands in central Pennsylvania were sampled, and the plots were classified by water source. The three hydrologic categories were groundwater, seasonal surface water, and permanent surface water. The core of the study was the analysis of half of the plots to identify species that were associated with a particular water source. Several groups of indicator species were identified. Some species, including Nyssa sylvatica, were strongly associated with the presence of groundwater. Others, such as Symplocarpus foetidus, were strongly associated with the presence of seasonal surface water. Several aquatic species were associated with permanent surface water. The remainder of the plots were used to test the predictive ability of the indicator species identified. The vegetation of a wetland plot predicted its hydrologic category with 72% accuracy. The identification of more indicator species could lead to the development of a useful tool for wetland research and management, since monitoring hydrology is often both expensive and time-consuming.     

Structure and seasonal dynamics of humid tropical grasslands in Meghalaya,India

Abstract. Four humid grassland communities at three different locations in Meghalaya, India were analysed during 1988 and 1989 for species and life-form composition, diversity and dominance in relation to altitude, soil and prevailing disturbances. Due to the adverse interactive influences of exceptionally high annual rainfall (> 10 000 mm), topography and human interference on soil fertility, the grassland at Cherrapunji, at 1300 m altitude, had a low species diversity (H'= 1.74) and was dominated by three perennial grass species. Similar grasslands, at both higher and lower altitudes on fertile soil and with lower rainfall (ca. 2000 mm), showed higher diversity values (H'= 2.28 at Burnihat and 2.31 at Upper Shillong). The proportion of perennial species and chamaephytes increased with elevation. At the high altitude site a grassland under short-term protection from fires and grazing had a higher species richness, density and basal cover than an unprotected grassland. All grasslands show a clear seasonality, albeit with different patterns, with a maximum in density and basal cover in August. The differences in structure and seasonality are discussed in terms of different levels of stress.     

山东省滨州市湿地水鸟的多样性调查

于2008年3月～2009年4月,采用路线调查法和定点观察法对滨州市区水鸟多样性情况进行了调查,共记录7目15科36属64种。其中国家Ⅰ级保护鸟类1种,国家Ⅱ级保护鸟类2种;冬候鸟10种(15.6%),夏候鸟18种(28.1%),旅鸟28种(43.8%),留鸟8种(12.5%)。区系组成包括:古北界40种(62.5%),东洋界6种(9.4%),广布种鸟类18种(28.1%)。多样性分析显示,滨州市区水鸟的Shannon-Wiener指数H′=2.5655、Pielou指数J=0.6169及G-F指数DG-F=0.6137。在市区3个水库中,北海水库的水鸟多样性指数最高。人类活动和自然环境恶化是该地区水鸟面临的主要威胁。     

The relationship between species richness and standing crop in wetlands: the importance of scale

One of the few important empirical generalizations regarding herbaceous plant systems has been the demonstration that species richness is related to standing crop with maximum richness occurring at moderate levels of standing crop. This relationship is normally demonstrated by comparing among vegetation types (i.e., vegetation with different dominants). We undertook this study to test whether the species richness-standing crop relationship was evident at a finer-grained level of organization, the within vegetation type level. Fifteen wetland sites were sampled in eastern Canada and species richness and standing crop determined in each of 224 0.25 m² quadrats. Each site was relatively homogeneous in terms of the dominant species present and were therefore categorized as single vegetation types. However, as a group, the sites comprised a wide range of vegetation types.A second order polynomial regression indicated a significant bitonic relationship between species richness and standing crop at the among-vegetation types scale, that is, when all 15 sites were combined. At the within-vegetation type level, however, no significant relationships were observed (p>0.05). The results indicate that the model of species richness proposed by Grime has predictive power at a coarse-grained level of organization, among vegetation types, but does not survive the transition to a finer-grained level of organization, the within vegetation type level. Therefore, the higher level processes which structure species richness patterns among vegetation types are not the same processes which determine richness patterns within a vegetation type.     

Variation in structure and diversity in Mediterranean grasslands related to trophic status and grazing intensity

Abstract. The spatial organization of Mediterranean grassland in Spain is described, based on samples from 71 sites covering the existing variation in slope exposition and inclination.The whole set can be regarded as representing a trophic gradient, along which gradual variation in soil, species composition, biomass, and coverage were quantified. Corresponding to other studies from varying habitats, maximal species richness, diversity, and heterogeneity were observed on moderately infertile sites. Maximum species richness, over 60 species, occurred on sites with biomass values from 150–350 g / m². Species richness values are much higher and biomass values are much lower than those found in temperate grasslands. The decrease in diversity towards the mosteutrophic communities is stronger than expected, but can be easily explained by the high grazing pressure here. The variation in diversity observed runs parallel with that in heterogeneity. Zones with a high species richness also have a high heterogeneity, meaning a low amount of dominance. Grazing is understood as abiotic form of disturbance. Differences in grazing pressure may modify the relation between richness and fertility. While the greatest grazing pressure coincides with the most eutrophic communities, decreasing progressively towards the oligotrophic ones, the trend predicted by the resource availability theory is maintained; species diversity will be maximal at intermediate levels of disturbance. Absence of grazing in the eutrophic communities would lead to an investment in the soil of the unconsumed organic matter.     

The effect of mollusc grazing on seedling recruitment in artificially created grassland gaps

Two experiments conducted in spring and autumn 1992 examined the effect of mollusc grazing on seedling regeneration from natural grassland seedbanks by creating artificial gaps in plots in a grassland sward. Molluscs were excluded from half the gaps by application of molluscicide. Mollusc grazing in both the spring and autumn experiment significantly reduced seedling recruitment, though the intensity of grazing was greatest in autumn. Recruitment of five species was markedly influenced by molluscicide application. In spring, plots from which molluscs were excluded contained significantly more seedlings of Chenopodium polyspermum and Ranunculus acris. In the autumn, exclusion of molluscs resulted in increased populations of R. acris, Stellaria graminea and Rumex acetosa. Cerastium holosteoides populations were greatest in autumn grazed plots. Other species, notably the grasses Holcus lanatus and Agrostis capillaris and the legume Trifolium repens were unaffected by molluscicide application. Species diversity was significantly decreased by molluscicide application in the autumn. Gap size significantly affected the recruitment of two species. Ranunculus acris populations were significantly higher in small gaps in both spring and summer, while Chenopodium recruitment in the spring was greater in small gaps. Gap size also significantly influenced the risk of mollusc attack on Ranunculus as molluscs appeared to show an aggregative feeding response in the high seedling density small gaps. Selective grazing of vulnerable seedlings by molluscs may influence the eventual relative proportions of the species present and so provide a potent mechanism in shaping community composition in grasslands.     

西洞庭湖湿地越冬期野生植物多样性

本研究采用定点取样法,于2008～2009年越冬期对西洞庭湖湿地野生植物多样性进行了调查统计分析.结果表明:西洞庭湖湿地野生植物种类共73种,隶属29科,植物种类丰富,其中以菊科、十字花科野生植物为主.西洞庭湖区野生植物群落具有较大的物种丰富度,分布均匀,且不同种之间相遇几率较大,具有较高的物种多样性.为保护西洞庭湖区野生植物多样性提供了科学依据.     

山西湿地维管植物区系多样性研究

山西省湿地有维管植物686种,隶属于308属, 83科。其中蕨类植物8科10属, 18种;双子叶植物56科, 223属, 504种;单子叶植物19科, 75属, 164种。在山西省湿地维管束植物属的分布区类型中,温带性质的属有108属,占主导地位,除去世界分布属,所占比例达76.9%,反映出山西湿地维管束植物的分布与本地所处的气候带相适应。世界分布有74属,占总属数的24%,也是湿地植被的主要组成成分或关键属。特有属匮乏。     

Determining discharges from the Table Mountain Group (TMG) aquifer to wetlands in the Southern Cape, South Africa

The focus of this study was to determine whether coastal wetlands in lowland settings could be dependent on groundwater from the deep circulating confined Table Mountain Group (TMG) aquifer. Groundwater interactions with wetlands are normally perceived to be limited to primary aquifers. A comparative study was done between two endorheic coastal wetlands in the southern Cape. Earlier reports stated that these groundwater dependent wetlands were fed by discharges from the fixed dunes surrounding them. On the basis of a three-dimensional electrical conductivity (EC) interpolation for Groenvlei, a hydrological link between the TMG aquifer and Groenvlei and Van Kervelsvlei was investigated by measuring water level and quality of groundwater and surface water. Water quality parameters used were EC, pH, Na⁺, Fe²⁺ and Cl⁻. The results from this, and an accompanying study, on the basis of water quality and plant nutrient cycling assessments, indicated direct groundwater discharges from the TMG to at least Van Kervelsvlei, with Groenvlei receiving secondary discharges from the TMG via Van Kervelslvlei. These findings significantly affect the current knowledge on which water balance models are based for the determination of groundwater availability for the area. Handling editor: D. Hamilton The first author did the research as part of his PhD in the Department of Earth Sciences of the University of the Western Cape, Bellville, South Africa. Funding is quoted under acknowledgements.     

A hydrologic assessment of the Everglades Nutrient Removal Project, a subtropical constructed wetland in South Florida (USA)

The Everglades Nutrient Removal Project (ENRP), a 1544-ha constructed wetland in south Florida, was intensively monitored throughout its five-year operational history. Water budgets for the ENRP and each of its interior treatment cells were dominated by surface flows (≥85% of inflows; ≥68% of outflows) with smaller contributions from precipitation, evapotranspiration, groundwater flux, and change in storage. The mean water depth, hydraulic loading rate for surface water, and nominal hydraulic retention time for the entire wetland were 0.6 m, 3.1 cm d⁻¹ and 17.7 d, respectively, and were comparable to values anticipated in design. The east flow-way was slightly shallower (0.2 m) and received proportionately more flow (61%) than the west flow-way. The hydrology of other treatment wetlands is often driven by surface flows. All treatment cells in the ENRP were to some extent hydraulically short-circuited. There was net groundwater inflow to the ENRP from Water Conservation Area 1 (WCA-1) resulting from significant head differences between these wetlands. Groundwater outflow to the adjacent farmlands was greatest in Cell 2 and substantially exceeded groundwater inflow. All hydrologic parameters exhibited seasonality to some extent; fluctuation in water depth and groundwater inflows corresponded with the seasonal change in stage in WCA-1. Errors in the ENRP and individual cell water budgets were generally less than 10% and within the range of errors for water budgets from other wetlands.     

河南石山口水库水鸟调查

石山口水库为河南水鸟种类与数量最多的典型湿地,位于大别山西北麓的浅山丘陵地域,属北亚热带向暖温带过渡的大陆性季风气候区,每年的秋末(11—12月)、初春(2—3月)及夏季(6—7月)湿地水鸟的种类与种群数量呈现明显的高峰期。本文共记录石山口水库湿地水鸟计8目、15科、85种,其中国家重点保护种类9种,《中日保护候鸟协定》指定种类55种,《濒危野生动植物种国际公约》(CITES)指定种类10种,省保护种类9种。     

Nitrogen removal in subsurface water by narrow buffer strips in the intensive farming landscape of the Po River watershed, Italy

In many countries buffer strips have become an important management tool widely accepted for controlling the diffuse pollution and supporting the development of more sustainable agriculture. However, there is the need to investigate their role in intensive farming systems where a realistic and shareable proposal to realize buffer strips can only foresee the use of a limited space. We evaluated the nitrogen buffering capacities of two narrow riparian strips (5-8 m) along irrigation ditches located in a typical flat agricultural watershed of the alluvial plain of the River Po (Northern Italy). Subsurface water level and nutrient concentrations were monitored along transects of piezometers installed from crop fields to ditches in two different areas. Spatial and temporal variation in water chemistry and hydrology were investigated to individuate the main processes (biological or physical) leading to groundwater nitrate depletion related to fertilization, pluviometric regime and seasonal variation. The results obtained indicate an elevated nitrate removal efficiency in both riparian areas. Compared to the high mean concentrations measured at the exit of the crop fields (10-90 mg l⁻¹ N-NO₃⁻), nitrate levels within riparian sites can be very low, completely disappearing below the ditches. The patterns of some chemical species (O₂, SO₄²⁻ and HCO₃⁻) and the potential denitrification rates suggest that denitrification plays a predominant role in the N-NO₃⁻ depletion observed in the first few meters of the herbaceous strip. The key factors in the system are the elevated groundwater residence time and the effect of the evapotranspiration. The water uptake by woody vegetation affects the subsurface water to flow through the riparian zone and, at the same time, it contributes to completely remove the nitrate from the groundwater.Our findings also suggest the double role of riparian vegetation both in ecohydrological and biological terms. In fact the water uptake by trees affects the subsurface flow pattern and contributes to completely remove the nitrate in the riparian zone.     

Grazing as a mediator for maintenance of offspring diversity: Sexual and clonal recruitment in alpine grassland communities

To understand the effects of grazing on grassland plants sexual and clonal recruitment, we conducted a demographic field investigation of species recruitment along a grazing gradient in the Tibetan alpine grassland. Grazing intensity had significant effects on quantity and diversity of sexual and clonal recruitment. Sexual recruitment increased significantly, but clonal offspring production decreased significantly with increased grazing intensity. Grazing intensity had different, significant effects on offspring recruitment of the various functional groups in the community, grasses (GG), sedges (SG), legumes (LG) and forbs (FG). Higher grazing intensity reduced offspring recruitment of GG and SG; it increased offspring recruitment of LG and FG. Seedlings were significantly more abundant in lightly grazed, moderately grazed and heavily grazed meadows than in non-grazed grasslands. Offspring diversity from sexual recruitment was significantly higher than that from clonal recruitment in grazed than in non-grazed grasslands. Our studies indicate that moderate grazing had positive effects on seedling recruitment and offspring diversity, but heavy gazing may alter community succession by affecting recruitment patterns among the four plant functional groups.     

Effect of grazing on community structure and productivity of a Uruguayan grassland

Grasslands and their grazers provide some of the most compelling examples for studying the relationship between diversity, productivity, and disturbance. In this study, we analyzed the impact of grazing-induced changes in species composition and community structure upon the productivity of a grassland in the Campos region, Uruguay. We compared three treatments: a continuously grazed area, a 9-year old exclosure to domestic herbivores, and grazing-simulated plots inside the exclosure, which were clipped so that their standing biomass resembled that of the grazed area. We studied the community composition of the grazed and ungrazed situations, and determined biomass and above-ground net primary production (ANPP) of the three treatments during 1 year. Grazed plots had higher species richness and diversity than the exclosure. Grazing resulted in the replacement of some cool-season, tussock grasses by warm-season, prostrate grasses. ANPP was 51% higher under grazing than in the exclosure, but the grazing-simulated plots inside the exclosure were the most productive treatment, 29% higher than the grazed plots. Thus, two components of grazing effect may be postulated for this grassland. The structural component resulted in higher ANPP, probably due to the elimination of standing dead biomass. The species composition component resulted in lower ANPP once the structural component was controlled, probably due to the shift to warm-season phenology and prostrate habit. Our findings contrast with a similar experiment carried out in the neighbouring Flooding Pampa region, which suggests that the relationship between grazing and community structure and function is difficult to generalize.