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Mangroves are valuable ecosystems for coastal protection, carbon sequestration and storage, and they provide habitat, refuge and rearing areas for many important marine species. To control mosquito outbreaks in coastal regions, mangroves were often impounded and managed using a variety of techniques that ranged from the application of insecticides to water level manipulation. Since continuous impounding had been shown to have negative effects on mangrove vegetation, other techniques have been used to manage hydrology in impoundments. A recent technique is called rotational impoundment management (RIM) and it involves flooding impoundments in summer and spring, the reproductive season of the mosquitos. In this study, we assessed the effects of 5 years of RIM management on mangrove vegetation in an impoundment on the east coast of Florida. We compared mangrove vegetation in the RIM impoundment with an adjacent impoundment that was not managed. We created a map of leaf area index (LAI) to assess vegetation productivity and its change in the two impoundments. We classified color-infrared aerial photographs from 2008 to 2010 and a WorldView-2 satellite image from 2014 to measure the extent of mangrove vegetation types and temporal changes in the two impoundments. We found a 38% increase in cover of dense mangrove vegetation after five years for the RIM-impounded area. Classification accuracy was around 80% for all imagery. The increased growth of plants and cover of dense mangroves in the RIM impoundment was corroborated by observed leaf area index values. Overall, the study demonstrates that vegetation in the RIM impoundment is becoming denser and in the near future will probably become similar to an impoundment that is open to tidal exchange or mangrove dominated areas that are not impounded.

Both environmental filtering and dispersal filtering are known to influence plant species distribution patterns and biodiversity. Particularly in dynamic habitats, however, it remains unclear whether environmental filtering (stimulated by stressful conditions) or dispersal filtering (during recolonization events) dominates in community assembly, or how they interact. Such a fundamental understanding of community assembly is critical to the design of biodiversity conservation and restoration strategies. Stream riparian zones are species-rich dynamic habitats. They are characterized by steep hydrological gradients likely to promote environmental filtering, and by spatiotemporal variation in the arrival of propagules likely to promote dispersal filtering. We quantified the contributions of both filters by monitoring natural seed arrival (dispersal filter) and experimentally assessing germination, seedling survival and growth of 17 riparian plant species (environmental filter) along riparian gradients of three lowland streams that were excavated to bare substrate for restoration. Subsequently, we related spatial patterns in each process to species distribution and diversity patterns after 1 and 2 years of succession. Patterns in initial seed arrival were very clearly reflected in species distribution patterns in the developing vegetation and were more significant than environmental filtering. However, environmental filtering intensified towards the wet end of the riparian gradient, particularly through effects of flooding on survival and growth, which strongly affected community diversity and generated a gradient in the vegetation. Strikingly, patterns in seed arrival foreshadowed the gradient that developed in the vegetation; seeds of species with adult optima at wetter conditions dominated seed arrival at low elevations along the riparian gradient, while seeds of species with drier optima arrived higher up. Despite previous assertions suggesting a dominance of environmental filtering, our results demonstrate that non-random dispersal may be an important driver of early successional riparian vegetation zonation and biodiversity patterns as well. Synthesis. Our results demonstrate (and quantify) the strong roles of both environmental and dispersal filtering in determining plant community assemblies in early successional dynamic habitats. Furthermore, we demonstrate that dispersal filtering can already initiate vegetation gradients, a mechanism that may have been overlooked along many environmental gradients where interspecific interactions are (temporarily) reduced. Our results demonstrate and quantify the strong roles of both environmental and dispersal filtering in determining plant community assemblies in early successional dynamic habitats. Furthermore, we demonstrate that dispersal filtering can already initiate vegetation gradients, a mechanism that may have been overlooked along many environmental gradients where interspecific interactions are (temporarily) reduced.

In peatland ecosystems, plant communities mediate a globally significant carbon store. The effects of global environmental change on plant assemblages are expected to be a factor in determining how ecosystem functions such as carbon uptake will respond. Using vegetation data from 56 Sphagnum-dominated peat bogs across Europe, we show that in these ecosystems plant species aggregate into two major clusters that are each defined by shared response to environmental conditions. Across environmental gradients, we find significant taxonomic turnover in both clusters. However, functional identity and functional redundancy of the community as a whole remain unchanged. This strongly suggests that in peat bogs, species turnover across environmental gradients is restricted to functionally similar species. Our results demonstrate that plant taxonomic and functional turnover are decoupled, which may allow these peat bogs to maintain ecosystem functioning when subject to future environmental change., Peatland plant communities are expected to be affected by environmental change, though how assemblages respond is not fully understood. Here, Robroek et al. show that peatland species occur in two distinct clusters, and functional identity and redundancy was maintained under taxonomic turnover.

Mangroves are important for coastal protection, carbon sequestration and habitat provision for plants and animals in the tropics and subtropics. Mangroves are threatened by habitat destruction and sea level rise, but management activities such as impounding for mosquito control can also have negative effects. We studied the effects of Rotational Impoundment Management (RIM) on nitrogen dynamics in impoundments dominated by three types of Black mangrove (Avicennia germinans) stands along the Indian River Lagoon (Florida). RIM, designed for noxious insect control, involves pumping estuarine water into impoundments in this area during spring and summer to raise water levels by 30 cm. We compared aspects of the nitrogen cycle before and after the start of the RIM and measured the same variables in an impoundment without RIM management. RIM led to the accumulation of ammonium in the substrate which coincided with a lowering of nitrification rates and decreased denitrification rates. Salt pan habitats dominated by dwarf mangroves became less saline following RIM initiation. Shoot growth of mangroves increased in response to higher nitrogen availability and lower pore water salinity. Mangrove responses were greatest in areas with dwarf and sparse mangrove cover. Overall, RIM resulted in lower nitrification and denitrification leading to lower nitrogen losses and increased Black mangrove growth, all benefits of RIM beyond those associated with noxious insect control.

Dutch fens, subjected to high nitrogen (N) deposition levels with reduced N (NHy) highly dominating over oxidised N (NOx), have since the second half of the past century seen a significant decline of Scorpidium and other characteristic brown moss species, while several Sphagnum species have increased rapidly. This promotes acidification and the transition from rich to poor fens. In line with the outcomes of previous short-term water culture experiments, we hypothesised that Scorpidium growth is negatively affected by NHy due to ammonium toxicity, but not by NOx deposition, and that Sphagnum grows equally well on both N forms. To test this hypothesis under field conditions, we carried out a 4-year N addition experiment (5.0 g N m−2 year−1, applied either as NO3 −-N or as NH4 +-N) on natural mixed Scorpidium revolvens–Sphagnum contortum stands in a rich fen with relatively low background N deposition. After 4 years, ammonium addition had significantly reduced Scorpidium growth, while Sphagnum had not significantly been affected by N additions. Increased ammonium levels were directly toxic to Scorpidium, while Sphagnum was not affected. Furthermore, N addition (in particular nitrate) also indirectly influenced moss growth through promoting vascular plants. Our study confirms that it is ecologically relevant to consider the specific form in which N enrichment occurs, i.e. the ratio of NHy vs. NOx. We conclude that in rich fens, the risk of rapid transition of the moss layer to dominance of poor-fen species is strongly promoted by increased deposition of reduced N.

This study assessed the risk of decomposition-driven soil subsidence in drained peat soils in the Netherlands, contrasting in peat origin and current land use. In a full factorial design, fen peat and bog peat were sampled from sites in use for nature conservation and for dairy farming, which contrast in history of drainage and fertilisation. In these four peat types, which frequently occur in the Netherlands, the microbial activity and respiration dynamics were studied in samples from superficial oxic peat layers by measuring Substrate Induced Respiration (SIR) and Substrate Induced Growth Response (SIGR). Total and active microbial biomass, microbial growth potential and potential exo-enzyme activities were determined in unamended samples and after nitrogen and/or glucose amendments. Remarkably, peat origin and land use did not affect basal respiration rates. In contrast, land use affected microbial biomass and potential growth rates as they were quadrupled in dairy meadows compared to nature reserves. This may be attributable to the pulses of organic and inorganic fertiliser that are being supplied in agricultural peatlands. Potential activities of oxidative exo-enzymes (phenol oxidase, POX, and phenol peroxidase, POD), in contrast, depended more on peat type, indicating a difference in peat substrate quality. Basal respiration rates and enzyme activities were not related. Phosphorus enrichment was identified as a potential driver of increased peat decomposition. The activity of the oxidative enzyme phenol oxidase and the concentration of phenolic compounds, which are considered to be the main regulators of peat decomposition according to the enzymic latch theory, were not related to respiration rates. It was concluded that decomposition theories like the enzymic latch theory (attributing a main role in the regulation of decomposition to phenolic compounds and phenol oxidase) were not supported by our research in the drained peat soils in the Netherlands.

Background Eutrophication of aquatic environments is a major environmental problem in large parts of the world. In Europe, EU legislation (the Water Framework Directive and the Marine Strategy Framework Directive), international conventions (OSPAR, HELCOM) and national environmental objectives emphasize the need to reduce the input of nutrients to freshwater and marine environments. A widely used method to achieve this is to allow water to pass through a created or restored wetland. However, the large variation in measured nutrient removal rates in such wetlands calls for a systematic review. Methods Searches for primary studies were performed in electronic databases and on the internet. One author performed the screening of all retrieved articles at the title and abstract level. To check that the screening was consistent and complied with the agreed inclusion/exclusion criteria, subsets of 100 articles were screened by the other authors. When screening at full-text level the articles were evenly distributed among the authors. Kappa tests were used to evaluate screening consistency. Relevant articles remaining after screening were critically appraised and assigned to three quality categories, from two of which data were extracted. Quantitative synthesis consists of meta-analyses and response surface analyses. Regressions were performed using generalized additive models that can handle nonlinear relationships and interaction effects. Results Searches generated 5853 unique records. After screening on relevance and critical appraisal, 93 articles including 203 wetlands were used for data extraction. Most of the wetlands were situated in Europe and North America. The removal rate of both total nitrogen (TN) and total phosphorus (TP) is highly dependent on the loading rate. Significant relationships were also found for annual average air temperature (T) and wetland area (A). Median removal rates of TN and TP were 93 and 1.2 g m−2 year−1, respectively. Removal efficiency for TN was significantly correlated with hydrologic loading rate (HLR) and T, and the median was 37 %, with a 95 % confidence interval of 29–44 %. Removal efficiency for TP was significantly correlated with inlet TP concentration, HLR, T, and A. Median TP removal efficiency was 46 % with a 95 % confidence interval of 37–55 %. Although there are small differences in average values between the two quality categories, the variation is considerably smaller among high quality studies compared to studies with lower quality. This suggests that part of the large variation between studies may be explained by less rigorous study designs. Conclusions On average, created and restored wetlands significantly reduce the transport of TN and TP in treated wastewater and urban and agricultural runoff, and may thus be effective in efforts to counteract eutrophication. However, restored wetlands on former farmland were significantly less efficient than other wetlands at TP removal. In addition, wetlands with precipitation-driven HLRs and/or hydrologic pulsing show significantly lower TP removal efficiencies compared to wetlands with controlled HLRs. Loading rate (inlet concentrations × hydraulic loading rates) needs to be carefully estimated as part of the wetland design. More research is needed on the effects of hydrologic pulsing on wetlands. There is also a lack of evidence for long-term (>20 years) performance of wetlands.

Annual sulfate mass balances have been constructed for four low-lying peat polders in the Netherlands, to resolve the origin of high sulfate concentrations in surface water, which is considered a water quality problem, as indicated amongst others by the absence of sensitive water plant species. Potential limitation of these plants to areas with low sulfate was analyzed with a spatial match-up of two large databases. The peat polders are generally used for dairy farming or nature conservation, and have considerable areas of shallow surface water (mean 16%, range 6-43%). As a consequence of continuous drainage, the peat in these polders mineralizes causing subsidence rates generally ranging between 2 and 10mmy-1. Together with pyrite oxidation, this peat mineralization the most important internal source of sulfate, providing an estimated 96kgSO4ha-1mm-1subsidencey-1. External sources are precipitation and water supplied during summer to compensate for water shortage, but these were found to be minor compared to internal release. The most important output flux is discharge of excess surface water during autumn and winter. If only external fluxes in and out of a polder are evaluated, inputs average 37±9 and exports 169±17kgSha-1y-1. During summer, when evapotranspiration exceeds rainfall, sulfate accumulates in the unsaturated zone, to be flushed away and drained off during the wet autumn and winter. In some polders, upward seepage from early Holocene, brackish sediments can be a source of sulfate. Peat polders export sulfate to the regional water system and the sea during winter drainage. The available sulfate probably only plays a minor role in the oxidation of peat: we estimate that this is less than 10% whereas aerobic mineralization is the most important. Most surface waters in these polders have high sulfate concentrations, which generally decline during the growing season when aquatic sediments are a sink. In the sediment, this sulfur is reduced and binds iron more strongly than phosphorus, which can be released to the overlying water and potentially fuels eutrophication. About 76% of the sampled vegetation-sites exceeded a threshold of 50mgl-1SO4, above which sensitive species, such as Stratiotes aloides, and several species of Potamogeton were significantly less abundant. Thus high sulfate concentrations, mainly due to land drainage and consequent mineralization, appear to affect aquatic plant community composition.

Background and aims: Due to the production of large amounts of tannins and phenolics by Rhizophora mangle, it was hypothesized that the invasion of this mangrove species in salt marshes due to global warming will result in changes in the cycling of carbon and nitrogen. Methods: Leaf litter and/or seedlings of R. mangle were placed into 1-m2 experimental plots in a Distichlis spicata-dominated salt marsh on the Atlantic Coast of central Florida (USA). An additional litter decomposition experiment was conducted in all plots by adding litter bags containing 10 g of dried D. spicata shoot litter. Seedling growth was measured yearly. One and four years after the start of the experiment, soil samples were collected to determine physical and chemical soil conditions, potential nitrification and denitrification activities and abundances of genes that are related to microbial processes in the nitrogen cycle. Results: Growth of R. mangle seedlings was stimulated in the presence of R. mangle litter, while decomposition rates of D. spicata litter were lower in plots with R. mangle litter and seedlings. The presence of R. mangle litter and/or seedlings had no significant effect on potential nitrification and denitrification activities and on the abundances of genes. Conclusion: The colonization of R. mangle into D. spicata-dominated salt marshes will affect the carbon cycle, but not necessarily the nitrogen cycle, which is likely due to the pre-existing nitrogen-limited conditions in the salt marsh.

Nitrous oxide (N2O) is a powerful greenhouse gas and the main driver of stratospheric ozone depletion. Since soils are the largest source of N2O, predicting soil response to changes in climate or land use is central to understanding and managing N2O. Here we find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3−), water content and temperature using a global field survey of N2O emissions and potential driving factors across a wide range of organic soils. N2O emissions increase with NO3− and follow a bell-shaped distribution with water content. Combining the two functions explains 72% of N2O emission from all organic soils. Above 5 mg NO3−-N kg−1, either draining wet soils or irrigating well-drained soils increases N2O emission by orders of magnitude. As soil temperature together with NO3− explains 69% of N2O emission, tropical wetlands should be a priority for N2O management., In a global field survey across a wide range of organic soils, the authors find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3–), water content and temperature. N2O emission increases with NO3– and temperature and follows a bell-shaped distribution with water content.

1. Nature conservation and restoration traditionally focus on protecting individual sites. In parts of the world where the natural landscape has been severely altered for agricultural or urban use, individual patches are too small and isolated to ensure effective nature protection. Spatial processes, such as metapopulation dynamics, are disrupted and natural linkages in the landscape, such as water flows, are severed by modifications in the landscape and hydrology. 2. We propose the identification of Operational Landscape Units (OLUs), which are defined as combinations of landscape patches with their hydrogeological and biotic connections, as a tool to facilitate wetland restoration in catchments with a high degree of fragmentation and strongly altered hydrology. The combined consideration of biotic (i.e. dispersal, transports of organisms) and hydrological connections (flooding events, groundwater flowpaths) is a new approach. 3. We developed criteria for the delineation of OLUs in regional wetland restoration initiatives. The key elements for delineation are definition of the restoration objectives, identification of spatial landscape mechanisms and information on historic and present land uses and hydrologic management. 4. As a case study, we delineated an OLU by applying these criteria in a restoration initiative for a large agricultural area that used to be a floodplain until the early 1950s in N.E. Twente, The Netherlands. The OLU encompassed not only the floodplain area to be restored but also a relatively remote nature reserve upstream as well as the stream connecting both areas. By restoring the historic water regime, flooding events would become a regular feature in the two areas and organisms including seeds would flow from the nature reserve to the restored floodplain. 5. Synthesis and applications. Discussions of the proposed Operational Landscape Units with stakeholders (water authorities, nature conservation agencies, farmers) resulted in shared insights which will lead to modifications of the original management plan for the area. We believe the OLU approach will make natural resource managers aware of the importance of spatial processes and connectivity in landscapes and, if properly applied, will lead to more natural and more successful restoration projects. © 2008 The Authors.

Biodiversity in freshwater ecosystems – rivers, lakes and wetlands – is undergoing rapid global decline. Major drivers are land use change, eutrophication, hydrological disturbance, climate change, overexploitation and invasive species. We developed a global model for assessing the dominant human impacts on inland aquatic biodiversity. The system consists of a biodiversity model, named GLOBIO-Aquatic, that is embedded in the IMAGE model framework, i.e. linked to models for demography, economy, land use changes, climate change, nutrient emissions, a global hydrological model and a global map of water bodies. The biodiversity model is based on a recompilation of existing data, thereby scaling-up from local/regional case-studies to global trends. We compared species composition in impacted lakes, rivers and wetlands to that in comparable undisturbed systems. We focussed on broad categories of human-induced pressures that are relevant at the global scale. The drivers currently included are catchment land use changes and nutrient loading affecting water quality, and hydrological disturbance and climate change affecting water quantity. The resulting relative mean abundance of original species is used as indicator for biodiversity intactness. For lakes, we used dominance of harmful algal blooms as an additional indicator. The results show that there is a significant negative relation between biodiversity intactness and these stressors in all types of freshwater ecosystems. In heavily used catchments, standing water bodies would lose about 80% of their biodiversity intactness and running waters about 70%, while severe hydrological disturbance would result in losses of about 80% in running waters and more than 50% in floodplain wetlands. As an illustration, an analysis using the OECD ‘baseline scenario’ shows a considerable decline of the biodiversity intactness in still existing water bodies in 2000, especially in temperate and subtropical regions, and a further decline especially in tropical regions in 2050. Historical loss of wetland areas is not yet included in these results. The model may inform policy makers at the global level in what regions aquatic biodiversity will be affected most and by what causes, and allows for scenario analysis to evaluate policy options.

Summary Recruitment processes are critical components of a plant's life cycle. However, in comparison with later stages in the plant life cycle (e.g. competition among adults), relatively little is known about their contribution to the regulation of plant species distribution. Particularly, little is known about the individual contributions of the three main recruitment processes – germination, seedling survival and seedling growth – to community assembly, while quantitative information on these contributions is essential for a more mechanistic understanding of the regulation of plant species distribution and biodiversity. Riparian zones along streams provide a globally-relevant case study for evaluating the importance of the different stages of plant recruitment. The natural hydrological gradients of stream riparian zones are currently being restored after a period of world-wide habitat degradation. To identify how recruitment contributes to vegetation patterns and biodiversity in riparian zones, we carried out field experiments at restored lowland streams. We quantified the germination of introduced seeds, and survival and growth of introduced seedlings of 17 riparian plant species across a gradient from the stream channel to upland. The hydrological gradient of riparian zones acted as a strong environmental filter on all three recruitment processes, through imposing an abiotic limitation (excess water) at low elevations and a resource limitation (water shortage) at higher elevations. Other variables, such as soil organic matter content and nutrient availability, only affected recruitment marginally. Species-specific patterns of environmental filtering initiated niche segregation along the riparian gradient during all three recruitment processes, but particularly during germination and seedling growth. These recruitment niches appeared strongly related to indicator values for adult distribution optima, suggesting that at least some riparian plant species may have evolutionary adaptations that promote recruitment under favourable hydrological conditions for adult growth and reproduction. Our results suggest that strong environmental filtering during germination and seedling growth plays an important role in determining later adult distributions, by forming the spatial template on which all subsequent processes operate. In addition to well-known mechanisms, such as competitive exclusion at the adult stage, environmental filtering during early recruitment stages already strongly affect plant distribution and diversity.

We evaluated the effect of four hydraulic retention times (HRT, 0.3, 0.8, 2.3, and 9.3 days) on pollutant removal in a surface-flow wetland system for polishing tertiary effluent from a sewage treatment plant (STP). The removal efficiency of pollutants at these HRTs was based on mass budgets of the water inputs and outputs in parallel ditches, which together with a presettling basin, made up the wetland system. Fecal coliform and N-removal efficiencies in the ditches were enhanced by increasing the HRT, with only little removal of fecal coliforms during spring-summer at a HRT of 0.3 days. A HRT of 4 days turned out to be required to meet the desired bathing water standard for fecal coliforms (103 cfu 100 ml-1) and the future standard of ammonium (1 mg N 1-1) all year. An annual N-removal efficiency of approximately 45% can be accomplished in the ditches at this HRT, corresponding to an annual N mass loading rate of 150 g N m-2 yr-1. Annual P removal was not improved by increasing the HRT even up to 9.3 days, largely because of the still high P mass loading rate (14 g P m-2 yr-1) in combination with relatively low P input concentrations. Substantial P removal can probably only be achieved at HRTs longer than 15 days, which will not be feasible for the situation investigated because of the large land area that would be required to reach such long HRTs. The future P standard (1 mg P 1 -1) can therefore only be met by additional chemical P removal. In a densely populated country such as the Netherlands, adequate polishing of tertiary STP effluent in surfaceflow wetlands with similar goals as for this wetland is restricted to small and medium-sized STPs. The simultaneous use of these treatment wetlands for other functions, such as nature conservation, recreation, and flood control, however, would permit the use of relatively larger land areas.

Wetlands perform functions that support the generation of ecologically, socially and economically important values. European legislation has increasingly recognised the importance of preserving wetland ecosystems. The Water Framework Directive (WFD) embodies many of the existing directives that have implications for wetlands. The EU funded EVALUWET project (European valuation and assessment tool supporting wetland ecosystem legislation) aims to develop and implement an operational wetland evaluation decision support system to support European policy objectives. A multidisciplinary approach is adopted combining expertise from natural and social scientists. The region of Noord-Hollands Midden is selected as the Dutch case study within EVALUWET. This region north of Amsterdam is a typical Dutch landscape with drained peat meadows in polders below sea level. Important stakeholders are: agricultural organisations, recreation, nature conservation organisations, and provincial/regional authorities. Water levels are controlled in the area. Changes in water regimes are proposed (National Policies, WFD) which will have an impact on the performance of functions such as agriculture, nature and residential and recreation opportunities. In this case study, three alternatives will be compared: (1) modern peat pasture (current), (2) historical peat pasture and (3) dynamic mire. Impacts of these alternatives on a number of criteria relevant to EU policy are assessed. Spatial evaluation techniques in combination with multicriteria methods are used to support evaluation. This provides a better insight into the consequences of alternative water regimes on the performance of the wetland functions and is used to support stakeholders participating in the decision process. The system is based on the following software components: impact assessment is performed by a rule-based knowledge base implemented in NetWeaver. Spatial evaluation and map presentation are handled in ArcView and ArcMap. Multicriteria analysis is performed using the software package DEFINITE. © 2004 Elsevier Ltd. All rights reserved.

A surface-flow wetland system designed for polishing effluent from a sewage treatment plant (STP) on the island of Texel, The Netherlands, was studied between April 1996 and March 1997. The wetland system was composed of a sequence of several units with different water depth, hydraulic retention time and vegetation. The system had a relatively short hydraulic retention time of 2.4 days (hydraulic loading rate 25 cm day−1). The wetland system showed 92% removal of faecal coliforms (3.7 × 1010 cfu m−2 yr−1), a 26% reduction of nitrogen (126 g N m−2 yr−1) and less than 5% reduction of phosphorus (5 g P m−2 yr−1). The oxygen concentration, which was less than 3 mg l−1 in the STP effluent, showed a strong increase during passage through the wetland all year with a clear diurnal shift between 1 and 12 mg l−1 in summer. Turbidity of the surface water doubled, but the suspended solids changed from sewage sludge particles at the beginning of the system to microscopic biota characteristic for a wetland at the end. A presettling basin produced substantial reductions of faecal coliforms (11 × 1010 cfu m−2 yr−1) and also intercepted incidental peaks in organic N and P load. N removal was highest in the shallow front sections of the subsequent parallel ditches (240 g N m−2 yr−1), largely owing to denitrification. These ditch sections contained Phragmites australis or Typha latifolia. The increase of the oxygen dynamics predominantly occurred in the rear, deeper sections of the parallel ditches, due to the presence of submerged macrophytes, macro-algae and periphyton. The treatment of the wetland resulted in water with acceptable faecal coliform concentrations that closely resembled the quality of the receiving surface water. However, the removal of nutrients was insufficient to meet the criteria for good ecological quality, probably due to the short hydraulic retention time.

To estimate the nutrient and organic matter (Biological Oxygen Demand (BODs) and Chemical Oxygen Demand (COD)) removal capacity of a constructed vertical-flow wetland in The Netherlands, a water and nutrient budget study was conducted. Also bacterial water quality enhancement was measured. The system had a Phragmites australis vegetation and comprised four parallel compartments of 0.25 ha each, which were loaded sequentially with sewage from recreational facilities. Annual loading rates were moderate and were estimated to be 16700 kg COD ha-1; 6700 kg BOD5 ha-1; 2400 kg N ha-1; and 335 kg P ha-1. The removal efficiencies for COD (81%) and BODs (96%) were high. Almost all Escherichia coli and F-specific RNA bacteriophages (> 99%) were removed from the wastewater during transport. The removal efficiencies for nitrogen (30%) and phosphorus (24%) were much lower. Nutrient removal was the result of plant uptake and harvesting (15% of total N input, 10% of total P input), denitrification (8% of total N input), sedimentation and accumulation of organic matter in the soil (7% of N total input, 14% of total P input). Removal efficiencies for N and P could be increased by harvesting the Phragmites vegetation in October, rather than the current harvesting practice in December. This vertical-flow wetland appeared to be P-saturated after 15 years of operation. The use of sandy sediments with better P-adsorbing properties is advocated as a critical issue for the design of these systems. Further, the groundwater eutrophication resulting from the poor functioning of the drainage systems has shown that a good hydraulic separation of vertical-flow systems from the subsurface is an important prerequisite for their proper functioning.

Alteration of natural flow regime is considered a major threat to biodiversity in river floodplain ecosystems. Measurements of quantitative relationships between flow regime change and biodiversity are, however, incomplete and inconclusive. This hampers the assessment of human impact on riverine floodplain wetlands in global biodiversity evaluations. We systematically reviewed the scientific literature and extracted information from existing data sets for a meta-analysis to unravel a general quantitative understanding of the ecological consequences of altered flow regimes. From 28 studies we retrieved both ecological and hydrological data. Relative mean abundance of original species (mean species abundance, MSA) and relative species richness were used as effect size measures of biodiversity intactness. The meta-analysis showed that alteration of a natural flow regime reduces the MSA by more than 50 % on average, and species richness by more than 25 %. Impact on species richness and abundance tends to be related to the degree of hydrological alteration. These results can be used in strategic quantitative assessments by incorporating the relationships into global models on environmental change and biodiversity such as GLOBIO-aquatic.

Information on ecological qualities can play an important role in land-use planning. This information is not always in a form that is suitable to support planning and negotiation among stakeholders. In this paper we describe an approach that uses ecological information based on expert knowledge in combination with spatial multicriteria analysis. Important elements of this approach are selection of evaluation criteria, assessment of scores, standardization, weighting, and aggregation. The approach was tested as part of the land-use planning process of the Bodegraven polder, a peat meadow area in the Netherlands. An interactive mapping device (the ‘touch table’) was used to support a series of interactive workshops with the various stakeholders to generate, assess, and discuss land-use plans for the Bodegraven polder. This paper shows the use of ecological information to support decision making and negotiation. Keywords: ecological qualities, spatial ecological evaluation, multicriteria analysis, interactive decision support

Mangrove forests are sites of intense carbon and nutrient cycling, which result in soil carbon sequestration on a global scale. Currently, mangrove forests receive increasing quantities of exogenous nutrients due to coastal development. The present paper quantifies the effects of nutrient loading on microbial growth rates and the mineralisation of soil organic carbon (SOC) in two mangrove soils contrasting in carbon content. An increase in SOC mineralisation rates would lead to the loss of historically sequestered carbon and an enhanced CO2 release from these mangrove soils. In an incubation experiment we enriched soils from Avicennia and Rhizophora mangrove forests bordering the Red Sea with different combinations of nitrogen, phosphorus and glucose to mimic the effects of wastewater influx. We measured microbial growth rates as well as carbon mineralisation rates in the natural situation and after enrichment. The results show that microbial growth is energy limited in both soils, with nitrogen as a secondary limitation. Nitrogen amendment increased the rate at which labile organic carbon was decomposed, while it decreased SOC mineralisation rates. Such an inhibitory effect on SOC mineralisation was not found for phosphorus enrichment. Our data confirm the negative effect of nitrogen enrichment on the mineralisation of recalcitrant carbon compounds found in other systems. Based on our results it is not to be expected that nutrient enrichment by itself will cause degradation of historically sequestered soil organic carbon in nitrogen limited mangrove forests.

The distribution of species of aerobic chemolitho-autotrophic microorganisms such as ammonia-oxidizing bacteria are governed by pH, salinity, and temperature as well as the availability of oxygen, ammonium, carbon dioxide, and other inorganic elements required for growth. Impounded mangrove forests in the Indian River Lagoon, a coastal estuary on the east coast of Florida, are dominated by mangroves, especially stands of Black mangrove (Avicennia germinans) that differ in the size and density of individual plants. In March 2009, the management of one impoundment was changed to a regime of pumping estuarine water into the impoundment at critical times of the year to eliminate breeding sites for noxious insects. We collected soil samples in three different Black mangrove habitats before and after the change in management to determine the impacts of the altered hydrologic regimes on the distribution of 16s rRNA genes belonging to ammonia-oxidizing betaproteobacteria (β-AOB). We also sampled soils in an adjacent impoundment in which there had not been any hydrologic alteration. At the level of 97% mutual similarity in the 16s rRNA gene, 13 different operational taxonomic units were identified; the majority related to the lineages of Nitrosomonas marina (45% of the total clones), Nitrosomonas sp. Nm143 (23%), and Nitrosospira cluster 1 (19%). Long-term summer flooding of the impoundment in 2009, after initiation of the pumping regime, reduced the percentage of N. marina by half between 2008 and 2010 in favor of the two other major lineages and the potential ammonia-oxidizing activity decreased by an average of 73%. Higher interstitial salinities, probably due to a prolonged winter drought, had a significant effect on the composition of the β-AOB in March 2009 compared to March 2008: Nitrosomonas sp. Nm143 was replaced by Nitrosospira cluster 1 as the second most important lineage. There were small, but significant differences in the bacterial communities between the flooded and non-flooded impoundments. There were also differences in the community composition of the bacteria in the three Black mangrove habitats. N. marina was most dominant in all three habitats, but was partly replaced by Nitrosospira cluster 1 in sites dominated by sparsely distributed trees and by Nitrosomonas sp. Nm143 in sites characterized by taller, more densely distributed Black mangrove trees.

Wetlands are terrestrial ecosystems characterized by high and fluctuating water tables. The spatial and temporal differences in the degree to which wetland soils are waterlogged create a very dynamic soil environment with, on average, lower oxygen concentrations than unsaturated soils. Wetland soils are characterized by gradients in redox conditions from totally oxidized to extremely reduced. These conditions require special adaptations for the plant and microbial species in the wetland. Wetland plants, particularly in wetlands with strongly fluctuating water tables, need adaptations to the shortage of oxygen in the root zone, but also to extended periods of dry conditions during low-water phases. Microbial communities are strongly coupled to redox cycles, in which alternative electron acceptors are used, for example nitrate, iron, manganese, sulphate and carbon dioxide. Plant–microbe interactions add to the complexity of the functioning of the wetland soil system. This Highlight section of Annals of Botany addresses the adaptations of plants and microbes in wetlands with fluctuating water levels, following a broad perspective. It contains three review papers and three primary scientific papers with experiments and field comparisons. The review by Parolin et al. gives an overview of adaptations of wetland plants in Amazonian floodplains to drought. The annual water cycle in these wetlands is quite predictable but shows an amplitude of 8 m, giving rise to a long flooded period as well as a long dry period each year. Previously, most emphasis in the evaluation of plant adaptations in these environments had been on the wet phase, focusing on the difficulty of overcoming long periods of waterlogged soil and (partial) submergence of the above-ground parts of plants. This paper for the first time evaluates plant adaptations to the dry period, in the context of the total annual cycle. The review paper by Laanbroek investigates how methane emission from wetland systems is controlled by microbial processes and influenced by wetland vegetation. The complex coupling of the various microbially mediated redox cycles, the leakage of oxygen from the internal plant gas system and the ‘escape’ of methane through this gas system to the atmosphere are evaluated. The review by Verhoeven and Setter deals with human control of water levels in wetlands to promote agricultural use. The emphasis is on the difference between sustainable and non-sustainable uses of wetlands for agriculture. Drainage of peatlands has led to severe soil subsidence and greenhouse gas emissions, whereas floodplains and rice fields are suitable for a more sustainable agricultural use. Developments in crop science, leading to increasingly waterlogging-tolerant crops are also discussed in this context. The paper by Sorrell and Hawes evaluates the importance of convective gas flow in the lacunae of helophytes for the occupation of relatively deep-water habitats. In their study, plant species lacking convective flow occurred in very shallow water only, whereas species with high rates of convective flow were able to grow in deep water, even in eutrophic habitats where the organic soil has a high oxygen demand. Li et al. carried out an experiment with Typha domingensis to test the ability of this species to grow in nutrient-rich, strongly reduced sediments. Growth was adversely affected by low redox potentials, but high availability of phosphates moderated this negative effect. The results are discussed in the context of competitive replacement of Cladium jamaicense by Typha domingensis in parts of the Everglades affected by high agricultural run-off. Finally, Yu and Ehrenfeld have studied the way in which the plant and microbe community structure was affected by water-level fluctuations and soil characteristics in New England forested wetlands. Both median level and variability in water tables turned out to affect plant and microbe communities; however, soil genesis, a result of both water-table position and geologic history, appeared to be even more important.

Questions: Which nutrient(s) limit(s) vegetation productivity in Calthion grasslands? Is phosphorus release a bottleneck for restoration of species-rich Calthion grasslands on rewetted dairy meadows? Location: Three species-rich Calthion grasslands in the Western Peat District in the Netherlands. Methods: We conducted a field fertilization experiment with nitrogen (N), phosphorus (P) and potassium (K) in three existing Calthion grasslands to evaluate the potential for restoration on rewetted dairy meadows. Responses of above-ground biomass, tissue nutrient concentrations and nutrient ratios were determined after 2 yr of fertilization. Results: Biomass increased with fertilization with Nonly and K-only but did not react to P-only additions. Comparisons of tissue nutrient concentrations and nutrient ratios also gave indications of N and K limitation. Conclusions: The strong P release expected after rewetting should not necessarily interfere with restoration of Calthion communities on rewetted dairy meadows. It is concluded that for successful restoration management measures should focus on reducing N and/or K availability. Potassium might be an overlooked bottleneck in the restoration of species-rich grasslands.

A major threat to freshwater taxon diversity is the alteration of natural catchment Land use into agriculture, industry or urban areas and the associated eutrophication of the water. In order to stop freshwater biodiversity loss, it is essential to quantify the relationships between freshwater diversity and catchment Land use and water nutrient concentrations. 2. A literature survey was carried out on biodiversity data from rivers and streams. Fish and macroinvertebrates were selected as focal groups as they are widely used as indicator species of river and stream health. Only published data were selected that (a) compared data found at impaired sites with a pristine reference situation (either in time or space), (b) clearly defined the stressors studied (Land use cover and/or nutrient concentrations), and (c) clearly defined biodiversity (number of native species, species lists or IBI-scores). 3. The number of native taxa found in each study was transferred in an index of relative taxon richness (RTR) ranging from 0 (severely altered) to 100 (pristine reference conditions). Only those taxa were included that were (at least) present in the most pristine situation. This made it possible to combine, compare and analyse results from different studies. Catchment Land use was expressed as the percentage of non-natural Land use (agriculture, industry, housing or mining). As a measure of nutrients, the concentrations of NO3, NH4, PO4, total N and total P in the river and stream water were used. 4. Over 240 published articles have been studied, but only 22 met the criteria described above and could be used for further analysis. 5. This study showed that altered catchment Land use has a major effect on freshwater biodiversity and that the rate of species loss is serious; on average every 10% of lost natural catchment Land use cover leads to a loss of almost 6% (±0.83) of the native freshwater fish and macroinvertebrate species.

In the framework of rehabilitation efforts to enhance the ecological value of closed-off estuaries, we studied the effects of restoring a tidal movement and seawater incursion on soil nitrogen conversion rates and vegetation response of semi-natural and agricultural grasslands in an outdoor mesocosm experiment. Intact soil monoliths including vegetation were collected in June 2004 on two locations on the shores of the Haringvliet lagoon in the south-western part of the Netherlands, which used to be a well-developed estuary before closure in 1970. For more than 1 year, soil monoliths were continuously subjected to a full-factorial combination of tidal treatment [stagnant/tidal (0.20 m amplitude)] and water type [(freshwater, oligohaline (salinity = 3)]. Soil, soil moisture and water nitrogen concentrations were monitored for a year, as well as vegetation response and nitrogen conversion rates in the soil. As expected, nitrogen mineralization rates were enhanced by the tidal treatment in comparison with the stagnant treatment. Denitrification rates however, were much less affected by tide and were even lower in the tidal treatments after 3 months in the agricultural grassland soils, implying that in general, soils were more oxic in the tidal treatments. Oligohaline treatments had virtually no effect on soil nitrogen conversion rates compared to freshwater treatments. Vegetation performance, however, was lower under saline conditions, especially in the semi-natural grassland. No further significant differences in response to the tidal and oligohaline treatments were found between the two soils although they differed strongly in soil characteristics. We conclude that if the rehabilitation measures in the former Haringvliet estuary are carried out as planned, drastic changes in soil nitrogen processes and vegetation composition will not occur.

Climatic change has great impacts on stream catchments and their ecology. Expectations are that more extreme climate events will result in undesired flooding in stream catchments. In the Netherlands, former floodplains with a history of agricultural use are put into use again as flooding areas for the purpose of water retention. This study focuses on the effects of winter flooding on various plant site conditions in the soil, such as redox, nutrient, pH, and base status. We compared the effects on groundwater- and rainwater-dominated floodplains. Water chemistry (pH, EC, HCO3, SO4, Cl, Ca, Mg, Na, K, pCO2, NO3, NH4, and PO4) and soil nutrients (Total N and P, and bio-available P) were monitored for one year, including a 3-4 month period with winter flooding. In both floodplains no direct effect of the flood-water chemistry was detected in the pore water, because the soil pores had become saturated with groundwater or rainwater, respectively, just before flooding, flood-water did not penetrate the soil. We found that the increase in pH and ammonium concentration in the rainwater floodplain were due to changes in redox status, resulting from the completely water-filled state of the soil pores during the flooding event. Furthermore, we noticed an increase in soil nutrient contents and a shift in plant species composition in the rainwater floodplain: the vegetation included more plant species characteristic for N-richness. Finally, we conclude that winter flooding has more drastic effects on biogeochemical conditions and vegetation composition in the atmotrophic conditions characteristic for low-order subcatchments than in lithotrophic conditions in the larger, higher-order subcatchments of the stream basin. © 2007 Springer Science+Business Media B.V.

Plant and Soil, 287 (1-2), ISSN:0032-079X, ISSN:1573-5036

18 páginas, 6 tablas, 9 figuras., Plant uptake and denitrification are considered to be the most important processes responsible for N retention and mitigation in riparian buffers. In many riparian buffers, however, nutrients taken up by plants remain in the system only temporarily and may be gradually released by mineralization later. Still, plants increase the residence time of nutrients considerably by reducing their mobility. We investigated the importance of plant N uptake and N immobilization in litter for N retention in riparian buffers. Nitrogen uptake in vegetation and N dynamics in litter were measured over a two-year period in a range of forested and herbaceous riparian buffers along a climatic gradient in Europe, receiving different loadings of N-enriched groundwater. Plant production, nitrogen uptake, and N retention were significantly higher in the forested buffer sites compared to the herbaceous buffer sites. However, in herbaceous buffers, periodic harvesting of herbaceous biomass contributed considerably to the N retention. No relationship between lateral N loading and plant productivity or N uptake was observed; this indicated that plant growth was not N-limited. In the winter period, decaying leaf litter had a small but significant role in N retention in a majority of the riparian ecosystems studied. Moreover, no responses to the climatic gradient were found. Generally, we can state that annual N retention in the vegetation and litter compartment is substantial, making up 13–99% of the total N mitigation., This study arose from the European program: Nitrogen Control by Landscape Structures in Agricultural Environments, NICOLAS, which was supported by an European grant from the Environment and Climate Program no. ENV4-CT-97-0395.

This paper reports on patterns in plant-mediated processes that determine the rate of nutrient cycling in temperate fens and bogs. We linked leaf-level nutrient dynamics with leaf-litter decomposition and explored how the observed patterns were reflected in nutrient cycling at the ecosystem level. Comparisons were made among growth forms (evergreen and deciduous shrubs and trees, graminoids and Sphagnum mosses) and between mire types (fens and bogs). A literature review showed that the predominant growth form was more important as a determinant of leaf-level nutrient-use efficiency (NUE) than mire type (fen vs. bog). Evergreens had the highest N and P use efficiency. The growth form differences in NUE were mainly determined by differences in N and P concentrations in mature leaves and not by differences in resorption efficiency from senescing leaves. Sphagnum leaves had lower N and P concentrations than the other growth forms, but because of a lack of data on nutrient resorption efficiency the NUE of thes...

1 We tested the influence of geographical gradients upon nutrient dynamics in the root environment of the vegetation of mires in north-eastern Poland and the Netherlands. The study areas show differences in the water level fluctuations, and atmospheric nitrogen deposition (the Netherlands, 50kg N ha-1 year-1; Poland, 5 10kg N ha-1 year-1). 2 Nitrogen and phosphorus mineralization, decomposition, denitrification and nitrous oxide emission were studied during 6 weeks in May June and correlated with characteristics of the interstitial water and the soil. Five types of mires (herbaceous bog, forested bog, herbaceous rich-fen, river marginal fen and alder fen forest) were compared. 3 Inorganic N as well as P release were faster in the Dutch than in the Polish mires of the same type. Denitrification and nitrous oxide emission were also faster in the Dutch mires, with the exception of the Polish alder forest, where denitrification was high because of high N richness and a strongly falling water table. 4 Principal component analysis of 18 physical and chemical soil and interstitial water variables resulted in four components: I, 'soil redox status'; II, 'soil base status'; III, 'interstitial water nutrient richness': IV, 'soil P richness'. In multiple regressions, N mineralization correlated positively with component III, P release with components III and IV, and cellulose decomposition with components II and IV. Both denitrification and nitrous oxide emission correlated positively with components I and II. 5 It was concluded that the lower P release rates in the Polish compared to the Dutch mires were due to higher calcium levels and lower summer water tables, which was partly attributed to the Polish continental climate. The higher rates for N mineralization, denitrification, nitrous oxide emission and cellulose decomposition in the Dutch sites were attributed to the high N deposition in the Netherlands.

1. An ecological and physiological study ofI. chelipes from Lake Veere, The Netherlands, was made. 2. Both osmoregulatory capacity and survival decrease with increasing temperature as well as with decreasing salinity. 3. Respiration experiments suggest that the need of energy by osmoregulatory activity may be supplied at the cost of other physiological processes, at any rate at temperatures of 10°C and higher. 4. It may be expected that, if temperatures higher than 15°C and salinities lower than 8‰ coincide, the population ofI. chelipes will be affected negatively.

The responses of dwarf black mangroves (Avicennia germinans) and components of the microbial community to the addition of nitrate over a 2-year period were examined. The field study was conducted in the Indian River Lagoon (Florida) in a mangrove-dominated impoundment that was established for purposes of mosquito control. The responses of mangroves to the regular addition of nitrate were insignificant or relatively minor compared to responses of the components of the microbial community. Denitrification rates, measured in the field and laboratory, increased significantly in fertilized plots and nitrous oxide emission rates were almost six times higher in fertilized plots. Nitrogen fixation was significantly lower in fertilized plots. Results suggest that mangrove systems in the N-limited Indian River Lagoon are likely to be long-term sinks for any increases in N loading.

It is generally known that the water quality of shallow lakes can be influenced significantly by marginal wetlands. In order to study the efficacy of constructed littoral wetlands in the IJsselmeer area (The Netherlands) for water quality improvement, a field survey was carried out in 2003. Vegetation, soil, pore water and surface water characteristics were measured in spring and summer in two types of littoral zones: natural and constructed for 8–16 years. The study showed that constructed wetlands perform well and are suitable to enlarge the vegetated littoral zone in the IJsselmeer area. In both natural and constructed sites vegetation biomass varied between 2,200 g m−2 for helophyte vegetation and 1,300 g m−2 for low herbaceous vegetation. Nutrient concentrations in the pore water of constructed sites tended to be higher than in natural sites. \( {\text{PO}}^{{3 - }}_{4} \) and \( {\text{NH}}^{ + }_{4} \) concentrations in pore water were much lower when vegetation was present, probably as a result of plant uptake. The N and P accumulation rate in the soil of constructed wetlands was 20 g N m−2 y−1 and 3 g P m−2 y−1 in vegetated plots; without vegetation the rate was much lower (8 g N m−2 y−1 and 1.8 g P m−2 y−1). We conclude that concerning their effect on water quality, constructed sites may replace natural sites, at least after 8–16 years. Principal component analysis showed a relationship between vegetation biomass and flooding, and nutrient concentrations in soil and pore water. Biomass was negatively correlated with extractable nutrients and positively with soil total N and P content. Flooding duration was negatively related to pore water salinity and positively to pore water nutrients. Due to their high biomass, helophyte stands retained significantly more nutrients than low pioneer vegetation and are therefore more suitable for improving water quality.

Littoral zones are characterized by gradients in depth and vegetation biomass, influencing nutrient retention capacity. A field experiment was conducted in a Phragmites australis dominated littoral zone to investigate nutrient retention and its effect on surface water quality. Measurements were done in mesocosms where water levels could be manipulated. Nutrient status was investigated along a gradient perpendicular to the shore during two growing seasons, one with a stable water level and one with a gradually decreasing water level. Nutrient concentrations in sediment, soil pore water and surface water were significantly lower in the vegetated than in the unvegetated zone. The negative correlations of nutrients in sediment and water, with nutrient contents of the vegetation suggest a direct effect of the vegetation. Nutrient uptake and biomass of the vegetation was higher in continuously flooded soils than in seasonally emerging sediments higher along the littoral gradient, probably due to the increased salinity in drained zones. Denitrification rate was highest in the unvegetated zone and was positively related to water level. Flooded littoral zones did result in a higher nutrient retention than drained zones. On small scale, for an optimal nutrient retention a fluctuating regime is not necessarily better suited than a stable water level, but on a larger scale it can substantially increase the width of the vegetated zone. It is important to optimize conditions for helophyte growth since the positive effect of vegetation on nutrient retention, at least at local scale, has been demonstrated in this study.

Elevated carbon dioxide (CO2) and in- creased nitrogen (N) availability generally increase deciduous tree biomass and alter green and yellow leaf stoichiometry. This paper investigates whether this also applies to Betula pendula (Birch). The effects of elevated atmospheric CO2 (600 ppmv) and increased N availability (50 and 100 kg N ha −1 year −1 ) of differential inorganic nitrogen type (am- monium, nitrate and ammonium nitrate) on net primary production (NPP) and green/yellow leaf C:N of Betula pendula saplings were studied for 3 years. The combination of both factors raised NPP, but elevated CO2 alone did not. In green leaves, increased N availability raised N concentrations, outweighing decreases caused by elevated CO2. After senescence, increased N concentrations were found at 100 kg N ha −1 year −1 , also leading to a lower C:N ratio. Al- though a lower C:N ratio may increase the decompo- sition rate during early decomposition, it may have the opposite effect during later decomposition stages. This, in combination with increased biomass production and possibly lower soil pH values, might increase soil C storage. However, due to the complexity of soil C formation and related processes this remains unsure.