Diatom ecological guilds display distinct and predictable behavior along nutrient and disturbance gradients in running waters

Three diatom ecological guilds were distinguished based on their potential to tolerate nutrient limitation and physical disturbance, i.e. a low profile, high profile, and motile guild. The guild distributions were examined along nutrient and flow disturbance gradients and across habitats in two extensively sampled streams. The guilds showed distinct distributional patterns, i.e. the low profile guild was favored in nutrient-poor and high disturbance habitats; the high profile guild reached a maximum in nutrient-rich sites and in conditions of low flow disturbance; and the motile guild increased along the nutrient gradients and decreased along the disturbance gradient. Guild distribution was habitat-specific: the low profile guild dominated the epipsammon, the high profile guild showed preference for epilithon and epiphyton, and the motile guild—for epipelon. The highest guild diversity was observed at high nutrient levels across all habitats, at higher flow disturbance levels, and in the epipelon and epiphyton. Comparisons of species, guild, and environmental distances, derived from species counts, guild abundance, and physico-chemical data, respectively, revealed high congruence between species–environment and guild–environment correlations. The predictable behavior of the three ecological guilds along nutrient and disturbance gradients, and across major benthic habitats elucidates the functional value of different diatom growth morphologies in species–environment interactions and suggests a potential use in ecological assessments of human-impacted ecosystems.     

Developing and Testing Diatom Indicators for Wetlands in the Casco Bay Watershed, Maine, USA

Diatom indicators of wetland condition were developed and tested by assessing human disturbance, water chemistry, and species composition of benthic, epiphytic, and planktonic diatoms from 20 wetlands sampled for 2 years. One sample from each site was randomly selected to form a development data set, while the rest were used as the test data set. Human disturbance indicated substantial differences among wetlands in hydrologic modification, impervious surface, and potential for non-point source contamination. These landscape alterations were related to increases in pH, non-nutrient ions, and nutrients and decreases in dissolved organic carbon and water color. Pre-existing diatom indicators, calculated with autecological information from lakes and aquatic habitats, correlated highly to relevant water chemistry and human disturbance scores. Weighted average models (WAM) of Cl⁻, conductivity, pH, and alkalinity derived with the Maine development data set correlated to relevant water chemistry and human disturbance of the test wetlands. Diatom assemblage attributes that correlated with human disturbance were selected to combine into a multimetric index of biotic condition (IBC). IBCs and WAMs from benthic and epiphytic diatoms were usually more precisely related to relevant environmental factors than planktonic diatoms. These results showed that human disturbance alkalized wetlands, enriched them with nutrients, and diatom assemblages responded to these changes. Indicator development protocols for streams can be readily adapted for use in wetlands.     

Macroinvertebrates as unreliable indicators of human disturbance in temporary depression wetlands of the south-western Cape, South Africa

Macroinvertebrates have a successful history of use as indicators of human impact in lotic environments. More recently, macroinvertebrate indices have been recommended for use in certain wetland types. Yet some authors do not recommend macroinvertebrates indices of wetland condition in areas with pronounced natural environmental heterogeneity. Our study provides a preliminary assessment of the feasibility of using macroinvertebrates for bioassessment of temporary isolated depression wetlands in the south-western Cape region of South Africa. We expected natural environmental heterogeneity among wetlands to exert a stronger influence on macroinvertebrates than human disturbance factors. Partitioning of the variation in macroinvertebrate assemblage composition that could be attributed to human disturbance factors (within and adjacent to wetlands), environmental variables and spatio-temporal factors indicated that environmental and spatio-temporal factors independent of human disturbances largely determined assemblage composition, whilst human disturbance played a relatively minor role. Linear regressions of taxon richness/diversity measures, individual families and a collation of metrics against measures of habitat transformation around wetlands and scores from a rapid assessment index of human disturbance revealed poor relationships. The univariate and multivariate patterns observed in this study do not lend themselves to the creation of a macroinvertebrate index of human disturbance for temporary wetlands in the region.     

Ecological diatom guilds are useful but not sensitive enough as indicators of extremely changing water regimes

Classification of taxa into ecological guilds is based on the relation of respective taxa to nutrient enrichment and their resistance to physical disturbance. We hypothesized that ecological guild’s proportion and their taxa composition were strongly effected both by extremely changing water regime and nutrient contents. Diatom composition, guild dynamics and the diatom-based ecological status assessment index were studied in the Sebes-Körös River (South-East Hungary) in a year with extremely changing water regimes. There were highly pronounced changes in species composition during the whole vegetation period including the formation of running and standing water segments in autumn. While the proportions of ecological guilds showed no significant correlations with the studied environmental parameters, they were more balanced in high water discharge period than in the low water discharge period. Taxa compositions of segments were mainly determined by the preferences and strategies of a respective species and/or genera, regardless to their guild affiliation. These results point out that ecological guild characterisation should be refined using ecological knowledge at the subgenus level. We suggest to establish several subdivisions within the guilds to consider the differences in life strategies (CSR model) and life forms, and to implement the accumulated knowledge of nutrient preferences/indication of a respective taxa.     

Combined eco-morphological functional groups are reliable indicators of colonisation processes of benthic diatom assemblages in a lowland stream

Classifying benthic diatom taxa based on ecological and morphological features became increasingly important in recent years due to the demand of understanding the dynamics and functioning of diatom assemblages. The great potential in using these functional classifications in diatom ecology involves further refinement of current classification. In our experimental study, colonisation processes of diatom assemblages were studied in a typical small lowland stream, using both diatom guilds and cell size categories. We also tested newly proposed combined eco-morphological functional groups (ecological guilds combined with cell size categories) in the study of the colonisation process in benthic diatom assemblages. We hypothesised that (i) there is a decrease in the proportion of low profile guild, while an increase in that of high profile and motile guilds in time with the decreasing rate of physical disturbance; (ii) the presence of small size categories will be pronounced at the beginning of the colonisation processes, while proportion of larger size categories will be higher in the latter phases of colonisation; and (iii) the relationship between taxa and environmental factors are better reflected by the use of combined eco-morphological functional groups than by the sole analyses of rough guilds or cell size categories. The first hypothesis was not confirmed, and our second hypothesis was only partially confirmed by the results. We found that the relationship between environmental factors and guilds, as well as cell size categories was not appropriate to reveal the relationship between abiotic factors and taxa composition. In contrast we found that compositional changes in colonisation were appropriately reflected by the newly defined combined eco-morphological functional groups. In the combined eco-morphological functional groups, such kind of taxonomical and ecological features can be prevailed which are hidden in guilds or cell size categories separately. Thus these combined eco-morphological functional groups could help to come one step closer to develop a widely used ecological classification in diatom researches.     

时空变化视角下北京市湿地优先保护格局

气候变化通过改变湿地水文过程等影响湿地的空间分布,城市化进程加剧了湿地破碎化程度并导致湿地生境退化,构建连续的湿地生态保护网络体系有利于应对气候变化和城市发展带来的负面影响、提高生物多样性保护水平。北京市现有湿地空间分布呈现斑块面积小、破碎化程度高等特点,为优化湿地保护区格局并应对气候变化和城市发展对北京市湿地生物多样性的影响,基于系统保护规划方法,以Marxan作为空间优化模型,结合PLUS模型和MaxEnt模型,模拟预测北京市湿地优先保护格局、识别湿地保护空缺并构建湿地分级保护区格局。研究表明:2020年北京市湿地存在80.15km²的保护空缺、2035年和2050年优化后湿地保护区占比分别为87.54%和85.95%,在满足本研究预设的生物多样性保护目标的前提下符合北京市湿地保护规划对湿地保护率的要求。为最优化资源分配,综合时空变化对湿地保护区空间分布的影响,构建了湿地分级保护区格局,将湿地保护区分为湿地永久保护区、湿地一级临时保护区和湿地二级临时保护区三个等级,以期为北京市分期建设湿地保护区、优化湿地生态保护网络体系和保护湿地生物多样性提供依据。     

Regional assessment of wetland plant communities using the index of plant community integrity

The Index of Plant Community Integrity (IPCI) was developed to assess wetland plant communities in the Prairie Pothole Region. The IPCI evaluates the condition of wetland plant communities based on disturbance level and multiple community attributes. However, the index was developed for seasonal wetlands from limited spatial and temporal data. We tested the index for seasonal wetlands and developed an index for temporary and semi-permanent wetlands by evaluating vegetative composition of wetlands throughout the Northern Glaciated Plains and Northwestern Glaciated Plains Ecoregions of South Dakota, North Dakota, and Montana. In 2003 and 2004, we selected wetlands based on classification and type of disturbance, ranging from little disturbance (native rangeland) to heavily disturbed (cropland). We analyzed the data using the IPCI vegetation metrics developed for seasonal wetlands, and further analyzed using nonmetric multidimensional scaling and cluster analyses. All vegetation metrics tested were significant in indicating disturbance level. Based on data analysis, five biologically significant groups related to intensity of disturbance (Very good, Good, Fair, Poor, and Very poor) were determined for seasonal wetlands, and three condition classes (Good, Fair, and Poor) for temporary and semi-permanent wetlands. Score ranges were assigned to the metrics according to the determined classes. Using the IPCI method, wetlands throughout the Northern and Northwestern Glaciated Plains of South Dakota, North Dakota, and Montana may be placed into disturbance classes. This data can then be used for ecological purposes and mitigation needs such as monitoring trends on reclaimed or restored wetlands, regional inventories, and for evaluation of ecological functions.     

Characteristic community structure of Florida’s subtropical wetlands: the Florida wetland condition index for depressional marshes, depressional forested, and flowing water forested wetlands

Land use and land cover change has a marked affect on wetland condition, and different wetland types are affected differentially depending on many abiotic and biotic variables. To assess wetland condition, we have developed a Florida wetland condition index (FWCI) composed of indicators of community structure in the diatom, macrophyte, and macroinvertebrate assemblages for 216 wetlands (n = 74 depressional marsh, n = 118 depressional forested, n = 24 flowing water forested wetlands). Depressional wetlands located along a human disturbance gradient throughout Florida were sampled for each assemblage. Forested flowing water wetlands were sampled for macrophytes only. The landscape development intensity index (LDI) was used to quantify the human disturbance gradient. In general, human disturbance in adjacent areas had the greatest impact on depressional herbaceous wetlands, followed by depressional forested wetlands. Forested flowing water wetlands (i.e., forested strands and floodplain wetlands) were less affected by local conditions, with most of their changes in wetland condition correlated with alterations at the larger watershed scale. Strong correlations between the FWCIs and LDI index scores suggest that changes in community structure can be detected along a gradient of human land use activities adjacent to wetland ecosystems.     

近20年白洋淀湿地水文连通性及空间形态演变

水文连通性是表征湿地格局和功能稳定性的重要指标,连通性的降低通常意味着湿地生态功能的退化,内部能量流动和养分循环的扰乱。选取京津冀最具典型性的白洋淀湿地为案例,将形态学空间格局分析模型(MSPA,Morphological Spatial Pattern Analysis)与连通性指数(IIC,Integral Index of Connectivity;PC,Probability of Connectivity)相结合,从时空两方面分析了白洋淀湿地水文连通性的变化,总结出水文连通性变化的空间形态演变规律。结果表明,1990—2015年间,白洋淀湿地整体连通性较差,以2005年为节点呈现先降低后逐步恢复的趋势;根据MSPA功能类型的变化,将白洋淀湿地空间形态演变分为消退期与恢复期两个阶段。消退期主要表现为核心斑块逐步分裂为分支、环岛、桥接、孤岛等细碎斑块,然后逐渐消退的过程;恢复期各类型主要表现为核心湿地面积逐渐增加,分支向桥接转变的过程。其中核心湿地的面积由1990年的8974.90 hm2,最低下降到2005年2092.97 hm2,到2015年又恢复到4122.14 hm2。整体而言,核心湿地的变化对白洋淀湿地水文连通性变化起主导作用。白洋淀湿地水文连通性降低的影响因素主要有上游补给水量的多少,土地利用变化以及气候变化等因素。研究将MSPA模型与连通性指数相结合的方法,能较好揭示湿地水文连通性变化过程中水文形态组织和运行变化的规律,可为其他地区湿地相关研究提供方法上的借鉴。     

Functional traits,spatial patterns and species associations: what is their combined role in the assembly of wetland plant communities?

Studies of community assembly focus on finding rules that predict which species can become member of a plant community. Within a community, species can be categorized in two ways: functional groups classify species according to their functional traits, whereas generalized guilds group species based on their (co-)occurrence, spatial distribution and abundance patterns. This study searches for community assembly rules by testing for coherence among functional groups and generalized guilds, as well as for correlations between the individual functional traits and assembly features, in two wetland plant communities in South Africa. The classifications of functional groups and generalized guilds were not consistent. However, rhizome internode length was related to fine-scale spatial pattern, suggesting that in systems dominated by clonal species (including wetlands, where recruitment sites are strongly limited) community assembly may be strongly linked to colonization ability. Functional groups do not predict guilds in wetland plant communities, precluding their use as the basis for assembly rules. However, an explicit consideration of clonal strategies and their effect on species’ spatial patterns appears to be important for understanding community assembly in systems dominated by clonal plants.     

The ecological condition of geographically isolated wetlands in the southeastern United States: The relationship between landscape level assessments and macrophyte assemblages

Geographically isolated wetlands (GIWs) are common features of the Dougherty Plain physiographic region in southwestern Georgia. Due to lack of protection at the state and federal levels, these wetlands are threatened by intensive agricultural and silvicultural land uses common in the region. Recently, the ecological condition of such GIWs was assessed for the southeastern United States using the Landscape Development Intensity Index (LDI), a practical assessment tool that relies on remotely sensed land use and land cover (LULC) data surrounding isolated wetlands to rapidly predict wetland condition. However, no assessments have been attempted for GIWs in the Dougherty Plain specifically. Our goal was to develop a framework to guide and refine remote assessment of wetland condition within this agriculturally intense region of the southeastern USA. In this study, we characterized human disturbances associated with isolated wetlands in the Dougherty Plain, and paired the rapid assessment of GIWs using LDI with an intensive assessment of wetland plant communities. Specifically, we: (1) examined how macrophyte assemblages and vegetation metrics vary across a human disturbance gradient in the Dougherty Plain; (2) compared multiple condition assessment outcomes using variations of the LDI method that differed in spatial extent and resolution of LULC categories; and (3) determined the predicted condition of GIWs in the Dougherty Plain as indexed by LDI and compared with region-wide assessments of GIWs of the southeastern USA. Generally, the relationship between wetland plant communities and surrounding land use supported the assumptions of the LDI index in that wetlands surrounded by agricultural land use classes featured distinct plant communities relative to those surrounded by forested land use classes. Our results indicated that finer spatial resolution of LULC data improved the predictive ability of LDI. However, based on incongruence between wetland vegetation composition and LDI scores in some forested landscapes, this study identified limitations of the LDI assessment method, particularly when applied in regions in which prescribed fire is an important ecological driver of vegetation and habitat. Thus, we conclude that LDI may be biased toward an overestimation of reference condition GIWs, even though the habitat may be functionally degraded by the absence of natural processes such as fire. Regardless, relative to the assessment of the entire southeastern US, a greater proportion of total GIWs of the Dougherty Plain were identified as impaired due to the intensity of irrigated agricultural land use.     

A quantitative hydrogeomorphic approach to the classification of temporary wetlands in the Doñana National Park (SW Spain)

A quantitative hydrogeomorphic approach was applied to an extensive survey of temporary wetlands in the Doñana National Park (SW Spain) in search for quantitative thresholds for wetland classification. Twenty freshwater ponds on the aeolian sand mantle and 46 sites on silty-clay substrate, located in the southern marshland, were surveyed during the heaviest rainy period so far recorded (October 1995–September 1997). On average, temporary ponds showed higher water depth, longer flooding period, lower conductivity (<0.5 mS cm^?1), lower pH (6.7), lower phosphate concentration (0.4 μM) and a more balanced proportion of Ca²⁺/Na⁺ than temporary marshes. During floods, marshland sites exhibited higher water transparency, pH (9.5), alkalinity (3.5 meq l^?1), conductivity (8.2 mS cm^?1), phosphate concentration (0.7 μM), Na⁺ and Ca²⁺ concentrations (97.2 and 3.5 meq l^?1, respectively) than ponds. Study sites were significantly segregated (ANOSIM test: R = 0.88, P < 0.01, n = 92) in relation to water depth and conductivity. A conductivity of 1.6 mS cm^?1 is proposed as a threshold between marshland sites and ponds during floods. Marshland sites were further segregated into two groups (ANOSIM test: R = 0.777, P < 0.01, n = 23) according to the Na⁺/Ca²⁺ ratio (in meq l^?1) at a threshold value of 25. An ordination by PCA showed that five variables grouped 81.4% of the total variance in two axes. The first PCA axis (60.7% of variance) separated temporary wetlands into ponds and marshland sites according to variables related to substrate and hydrology (Na⁺/Ca²⁺ ratio, conductivity, water depth and flooding period). Other variables (e.g., water transparency, alkalinity, pH, submersed macrophyte biomass, phosphate, nitrate and planktonic chlorophyll concentrations) did not produce a significant segregation between marshland and pond sites during floods. Further discrimination within each wetland type was thus not achieved.     

Seasonal and spatial hydrological variability drives aquatic biodiversity in a flood‐pulsed,sub‐tropical wetland

1. Flood‐pulsed wetlands make vital contributions to local and global biodiversity. However, the patterns and controls of spatial and temporal variation in aquatic biodiversity in flood‐pulsed wetlands are not well understood. We analysed the relationship between variation in hydrological regime and the patterns of aquatic biodiversity in a large pristine flood‐pulsed wetland, the Okavango Delta, Botswana. 2. Surveys of water chemistry, diatoms and macroinvertebrates were conducted over the seasonal phases of the flood pulse. Hydrological variables of flood frequency and hydroperiod class were collated from 16 years of satellite images. Multivariate regression trees and generalised least squares regression were used to determine the chief controls of community composition and taxon richness. 3. Hydroperiod class, phase of the flood and conductivity explained 32% and 43% of the variation in diatom and invertebrate taxon richness, respectively. There was a negative relationship between hydroperiod class and invertebrate taxon richness on the rising, peak and receding flood, whereas at low flood there was no significant relationship. Multivariate regression tree analysis revealed hydroperiod class, phase of the flood and conductivity as the dominant forces shaping invertebrate and diatom community composition. 4. Seasonal and spatial variation in hydrological conditions are the principal drivers of variation in aquatic biodiversity in flood‐pulsed wetlands. In pristine flood‐pulsed wetlands, increased productivity caused by the arrival of the flood waters appears to override disturbance and connectivity in shaping taxon richness and community composition. Thus, these data suggest that the maintenance of a rich mosaic of habitats covering a broad range of hydroperiod is the key to preserving aquatic biodiversity and natural ecosystem function in flood‐pulsed wetlands.     

哀牢山湿性常绿阔叶林地生、树干及树枝 附生苔藓生活型组成及其水分特性

为探讨林内不同垂直高度生境下及不同生活型苔藓植物水分特征的差异,该文对哀牢山湿性常绿阔叶林内地生苔藓、林下树干附生和林冠层树枝附生苔藓优势或常见种的生活型组成、持水力、失水特征和水分利用效率进行了研究。结果表明:地生、树干附生和树枝附生苔藓植物类群分别以交织型、扇型、悬垂型苔藓植物占据优势;地生、树干附生、枝条附生苔藓植物的饱和持水率分别为476%DW、210.98%DW、238.95%DW;地生苔藓植物的持水率和失水速率均高于附生苔藓,树干附生苔藓植物持水率低于树枝附生苔藓,而失水速率高于树枝附生苔藓。在不同生活型苔藓的水分特性上,交织型苔藓具有较高的持水率和失水速率,保水性能较弱,其次为悬垂型苔藓,扇型苔藓的持水率最小,失水速率也较快;地生和树干附生苔藓的水分利用效率均显著高于树干附生苔藓,交织型和扇型苔藓的水分利用效率显著高于悬垂型苔藓。在三种生境下,地生苔藓持水力高,水分利用效率较高而保水能力低;枝条附生苔藓持水力低,水分利用效率低而保水能力较高;树干附生苔藓水分利用效率较高而持水力和保水能力均较差。因此,不同生境下苔藓植物生活型组成及其水分变化特性在一定程度上反映了它们对不同生境的适应策略。     

Using diatom life-forms and ecological guilds to assess organic pollution and trophic level in rivers: a case study of rivers in south-eastern France

The European Union’s Water Framework Directive has set a target of achieving good ecological status for all aquatic environments in Europe by 2015. In order to determine the quality of aquatic environments, biological indicators such as diatoms are often used. However, biotic diatom indices can be difficult and time consuming to use because of complexity of species determination. We investigated whether the biological traits of diatoms in rivers (life-forms, size classes and ecological guilds) could be used to assess organic pollution and trophic level. We worked on a data set comprising 315 diatom species, determined at 328 river stations of south-east France and a variety of parameters. The abundances of some biological traits differed significantly between the different organic pollution and trophic levels, particularly stalked diatoms, and the motile and low-profile guilds.     

Hyporheic invertebrates as bioindicators of ecological health in temporary rivers: A meta-analysis

Worldwide, many rivers cease flow and dry either naturally or owing to human activities such as water extraction. However, even when surface water is absent, diverse assemblages of aquatic invertebrates inhabit the saturated sediments below the river bed (hyporheic zone). In the absence of surface water or flow, biota of this zone may be sampled as an alternative to surface water-based ecological assessments. The potential of hyporheic invertebrates as ecological indicators of river health, however, is largely unexplored. We analysed hyporheic taxa lists from the international literature on temporary rivers to assess compositional similarity among broad-scale regions and sampling conditions, including the presence or absence of surface waters and flow, and the regional effect of hydrological phase (dry channel, non-flowing waters, surface flow) on richness. We hypothesised that if consistent patterns were found, then effects of human disturbances in temporary rivers may be assessable using hyporheic bioindicators. Assemblages differed geographically and by climate, but hydrological phase did not have a strong effect at the global scale. However, hyporheic assemblage composition within regions varied along a gradient of higher richness during wetter phases. This indicates that within geographic regions, hyporheic responses to surface drying are predictable and, by extension, hyporheic invertebrates are potentially useful ecological indicators of temporary river health. With many rivers now experiencing, or predicted to experience, lower flows and longer dry phases owing to climate change, the development of ecological assessment methods specific to flow intermittency is a priority. We advocate expanded monitoring of hyporheic zones in temporary rivers and recommend hyporheic invertebrates as potential bioindicators to complement surface water assessments.     

Use of diatom life-forms and ecological guilds to assess pesticide contamination in rivers: Lotic mesocosm approaches

The persistence of pesticides in the environment and their effects are a cause of concern to more and more people, and so in 2009 the French government announced plans to reduce pesticide use in agriculture over the next 10 years. Water managers are to monitor the beneficial impact of this reduction on aquatic environments. It has been suggested that diatoms may be good indicators of pesticides, and more particularly of herbicides, in water. Diatoms have been routinely used to assess organic and nutrient pollution for more than 10 years. The general approach is to develop a diatom-based tool to assess pesticide contamination. Diatom indices are usually based on specific pollution sensitivity. Other metrics, such as life-forms, ecological guilds, or cell size offer other advantages. For instance, the relationships between trends in these metrics and environmental gradients are more robust, and make it easier to establish ecological hypotheses. We have therefore opted for this approach.To develop such a tool, outdoor, lotic mesocosm experiments lasting about 2 months were conducted from 2006 to 2008. Herbicides (diuron) and fungicides (azoxystrobin, tebuconazole) were tested at environmental concentrations (sum of pesticides concentrations from 1.11 to 3.01 μg L^?1 for chronic pollutions and from 20.25 to 29.50 μg L^?1 for short-term acute pollutions). Diatom communities in artificial channels were analyzed by light microscopy using standard European methods. The various parameters structuring diatom communities were assessed, and colonization time appeared to be the most important. However, pesticide contamination was the second most important, and had a more significant impact on the composition of ecological guilds than on species composition. Some metrics did not display any significant trends (benthic/planktonic, colonial, pedunculate, pioneer), but others looked promising for use in pesticide contamination assessment: the abundances of motile guild, low-profile guild and mucous tubule diatoms all increased in contaminated channels, whereas high-profile diatoms showed the opposite trend. Some possible explanations, such as a protective effect of the exopolysaccharide matrix, can be advanced: diatoms living inside a mucous tubule may be shielded from dissolved pesticides, as are motile diatoms, which have a micro-habitat preference for thick matrices which also allows them to withstand higher levels of water contamination. In the same way, high-profile guild diatoms are exposed to dissolved pesticides to a greater extent, and this could explain their lower abundance in contaminated channels.     

Are landscape-based wetland condition indices reflected by invertebrate and diatom communities?

Assessments of wetland condition are generally based on measures of variables related to plants or large animals (birds, fish), and catchment or landscape features. This approach ignores the considerable biodiversity and functional values of small aquatic organisms. The aim of this study was to assess the correspondence between landscape-based indices of wetland condition and the community composition of both aquatic invertebrates and diatoms across a broad range of wetlands in the West Coast region of New Zealand. Aquatic invertebrates and diatoms were sampled from 29 lowland wetlands subject to varying degrees of catchment modification. Wetland condition was assessed independently using two methods: a field-based method to give the Wetland Condition Index, and a GIS-based method that gave an Index of Ecological Integrity. Strong relationships existed between community composition and pH, so we partitioned the community data into groups according to wetland pH. We found only weak relationships between wetland condition scores and invertebrate and diatom communities within each pH group. In most cases, data describing the nutrient status of the water had the strongest influence on invertebrate and diatom communities. Lack of strong associations between measured wetland condition indices and either diatom or invertebrate community composition suggests that neither index was dominated by variables directly influencing the aquatic component of wetland biota. The challenges now are to identify the critical variables, and to develop complementary wetland scoring systems that better reflect the status of small aquatic organisms.     

Diatom flora in Mediterranean streams: flow intermittency threatens endangered species

In the context of global environmental changes, Mediterranean rivers are considered highly endangered. Temporal and spatial increases of the dry stretches during the summer lead to the loss of river tridimensional connectivity, which represents a major threat for freshwater biodiversity. In this study, we aimed at exploring the response of diatom communities to summer droughts by analyzing taxonomical composition, specific ecological requirements, ecological guilds and percentages of endangered species. The evolution of diatom communities was monitored under both intermediate and intermittent flows, with traditional and innovative sampling procedures, i.e. collecting diatoms from transects and microhabitats, respectively. Microhabitats differed in terms of water velocity, substrate, isolation and presence of macrophytes. Diatom flora was mainly composed of β-mesasoprobous taxa. We highlighted an increase of species considered as aerophilous and planktonic in sites characterized by intermittent flow. In general, ecological guilds did not respond to hydrological disturbance as expected. Statistical models identified the maintenance of a minimum of 0.20 m/s flow velocity as the main factor influencing the abundance of endangered species. Conversely, flow instability, lentification and habitat fragmentation represented the major threats for endangered species. In conclusion, diatoms can provide useful information to improve river management practices when faced with an increasing water scarcity scenario. Water stability and river habitat heterogeneity strongly favor the presence of endangered diatom species. In the absence of these conditions, isolated pools surrounded by dry riverbed are very important habitats to be preserved, representing the only refugia for benthic diatom communities during summer.     

Vegetation and environmental conditions in recently restored wetlands in the prairie pothole region of the USA

How closely the vegetation of restored wetlands resembles that of comparable natural wetlands is a function of the probability of propagules of wetland species reaching reflooded wetlands and how similar environmental conditions in the restored wetland are those in the natural wetlands. Three years after reflooding, we examined the vegetation composition, water level fluctuations, soil organic carbon content, and soil bulk density as well as surface water pH, alkalinity, conductivity, and calcium and magnesium concentrations of 10 restored and 10 natural wetlands. In the restored wetlands, more species of submersed aquatics colonized than were found in natural wetlands, and they rapidly spread to form extensive beds that were larger than those found in natural wetlands. Emergent and wet meadow species in restored wetlands, however, were found in only sparse stands as were a variety of annuals. The vegetation of natural wetlands was predominantly large stands of emergent species. Fluctuations in water storage volume and basin surface area were similar for both restored and natural wetlands. The surface water in restored wetlands had higher pH and lower alkalinity, conductivity, and calcium and magnesium concentrations than that in natural wetlands. Soils of restored wetlands have a lower organic carbon content and higher bulk density than do those of natural wetlands. Our results suggest that for submersed aquatics, dispersal of propagules to restored wetlands is rapid and environmental conditions in restored wetlands are very suitable for their establishment. For other guilds of wetland species, e.g., sedges and other wet meadow species, dispersal to restored wetlands is likely much slower and may pose a serious problem for the re-establishment of these species in restored wetlands. Even if dispersal is not limiting, low surface organic carbon and high bulk density may prevent the establishment of these species in restored wetlands.