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Newly constructed wetlands are created to provide a range of ecosystem services, including carbon sequestration. Our understanding of the initial factors leading to successful peat formation in such environments is, however, limited. In a new 100-ha wetland that was created north of Amsterdam (the Netherlands), we conducted an experiment to determine the best combination of abiotic and biotic starting conditions for initial peat-forming processes. Sediment conditions were the main driver of vegetation development, biomass production and elemental composition during the 3-year study period. Overall, helophytes (Typhaspp.) dominated basins with nutrient-rich conditions, whereas nutrient-poor basins were covered by submerged vegetation, which produced about seven times less aboveground biomass than helophytes. The C/N ratios for all plant species and biomass components were generally lower under nutrient-rich conditions and were lower for submerged species than helophytes. Because total basin biomass showed five times higher shoot and ten times higher root and rhizome production for clay and organic than sand sediments, even with some differences in decomposition rates are the conditions in the nutrient-rich basins expected to produce higher levels of initial peat formation. The results suggest that addition of a nutrient-rich sediment layer creates the best conditions for initial peat formation by stimulating rapid development of helophytes.

In a great number of scientific articles on water quality improvement using constructed wetlands (CW) and riparian buffers zones (RBZ) at catchment scale, contradictory results are found. In most cases this is due to underestimating or even ignoring the role of the hydrological factor for water quality improvement. It has often resulted in biased estimates of buffering systems’ efficiency at catchment scale and, consequently, has caused planning and establishment failures, mistakes and inconsistencies in legislative acts and finally, it has influenced stakeholder’s willingness to support these eco-technological measures. In this paper we present a short but critical overview of the potential of CWs and RBZs in water quality improvement at catchment scale and highlight the most important aspects to be considered when planning, establishing and managing these systems.

Surface mining is a global phenomenon. When dealing with the land disturbances caused by surface mining operations, the terms remediation, reclamation, restoration and rehabilitation (R4) are commonly used interchangeably or otherwise vaguely defined. Expectations associated with these terms may differ significantly from one stakeholder to another, however. Regulators, industry, environmental practitioners, local communities and the general public therefore stand to benefit from a precise terminology based on agreed-upon end-goals. The latter range from the avoidance of exposure to pollutants (remediation) to the full recovery of the original ecosystem (restoration). Although frequently claimed as the end-goal, restoration may often not be unachievable, because of altered hydrology, habitat fragmentation, contamination, climate change, prohibitive costs and other environmental and socio-economic boundary conditions. Mostly, the definitions of reclamation and rehabilitation may overlap in their definitions and approaches. Here we attempt the creation of a road-map that can clearly translate end-goals for each of the R4 terms. According to the definitions encountered and exposed here, reclamation, which aims to recover key ecosystem services and biogeochemical functions within a replacement ecosystem or rehabilitation, which implies a repurposing of the landscape, may be the best approaches to deal with surface mining legacies.

This chapter reflects on the most important results presented and their relevance and implications for wetland management and restoration. Overviewing the contents, there are two general areas where this volume will break new ground. The first is the more rigorous underpinning of the two most important regulating wetland ecosystem services, and the second is the presentation and critical discussion of the strong, recent activities in wetland conservation and restoration in China and neighboring countries. The two regulating wetland ecosystem services meant here are (1) the capacity of restored and constructed wetlands to remove nitrogen and phosphorus from through-flowing water and (2) the role of wetlands in cooling or warming the climate as the net balance between carbon sequestration and emissions of methane and nitrous oxide. It is a robust fact that wetlands can be expected to remove 40% of the nitrogen and phosphorus from runoff and groundwater flow in agricultural areas. The area of wetland needed to really make a difference at the catchment level amounts to 10% of the total catchment area. With respect to the cooling/warming function of wetlands, there is now firm evidence that newly originating wetlands start off as having a net warming effect on the climate, because the warming effect of methane emissions surpasses the cooling effects of CO2 sequestration and evapotranspiration. In the course of time, the cooling function will increase due to the persistent cooling of already sequestered carbon. This re-emphasizes the enormous importance of “old” wetlands such as peatlands over newly formed ones in the climate regulation service. On the other hand, climate change effects will enhance the overall primary productivity and carbon sequestration in herbaceous coastal as well as inland wetlands. Increasingly, sea level rise and warming will result in more opportunities for forested wetlands (mangroves, boreal forest), which will enhance the climate cooling service of wetlands worldwide. The book also contains a number of chapters reflecting the large investment in ecological research in wetlands in China and neighboring countries in recent decades. There are chapters on the effects of invasive species on coastal wetlands, on the protection and wise use of coastal wetlands around the Yellow Sea, and on the principles and recent case studies of wetland restoration in this part of the world. The ecosystem services of wetlands definitely play a major role in the motivation and justification of large projects for wetland restoration. The results of these projects so far are most promising.

Wetlands are key locations in the landscape for the production, consumption, and exchange of greenhouse gases with the atmosphere. In this chapter, we review the major controls of wetland greenhouse gas fluxes and consider how wetlands influence global climate. It is a challenge to determine the overall climatic role of a wetland as the conclusion can vary depending on whether one wants to know the radiative balance over a defined period of time, the radiative forcing since 1750, or the lifetime climatic role of a wetland. For many wetlands, it is the long-term accumulation of soil carbon that eventually dominates the overall climatic impact of the wetland, such that wetlands that are hundreds to thousands of years old may have a lifetime cooling effect. Using a dynamic modeling approach, we consider how wetland disturbance, restoration, and mitigation affect wetland climate impacts. When a wetland is degraded, its functioning is reduced and greenhouse gas fluxes can change, thus altering the overall climatic role of the wetland. We demonstrate that disturbances to existing wetlands can cause warming that persists long after a wetland is restored or replaced by a mitigation wetland. Thus, activities that disturb wetlands and lead to the oxidation of sequestered soil carbon should be avoided to the maximum possible extent. Climate regulation is just one ecosystem service provided by wetlands; informed environmental management should consider the full range of wetland services and disservices when developing plans for wetland creation, restoration, and protection.

This introductory chapter defines the key subjects for this volume of ecological studies and briefly presents the common context and the cohesion of the contents of the various chapters. It gives a definition of wetland ecosystem services and outlines briefly the 17 services that have been identified in ecosystems globally and are generally considered as being of major importance. Provisioning wetland ecosystem services such as food chain support, regulating services such as climate cooling, and the enhancement of biodiversity are prime examples. Definitions are also given for wetland character and wise use, as adopted by the Ramsar Convention on Wetlands. New developments in wetland restoration to enhance wetland ecosystem services, as they are described in this volume, are outlined briefly. The overview also pays attention to the chapters on the latest developments of our understanding of water quality enhancement services and climate regulation services of wetlands; on threats and resilience to disturbances such as climate change and invasion of exotic species; on new initiatives for wise use of large, internationally divided wetlands in the Yellow Sea; and on restoration and creation of wetlands in urban environments, in particular in China.

Water quality in freshwater lakes and coastal areas has deteriorated in many densely populated areas with increasingly intensive agriculture. For example, eutrophication of aquatic environments has become a major environmental problem in large parts of the world. Biogeochemical transformations occurring in wetlands generally result in reduced nutrient content of water, but quite commonly these ecosystems have been drained or filled to create new forest and arable land. In recent decades efforts have been made to compensate for the losses of natural wetlands by creating new wetlands or restore drained wetlands. However, the large variation in measured nutrient removal rates in such wetlands has made it difficult to assess the effectiveness of such interventions. In this chapter we discuss the role of created wetlands in regulating water quality at the catchment scale. First, we pay attention to a recent systematic review of nitrogen and phosphorus removal in single wetlands in boreal, temperate and sub-tropical regions. Second, in a more focused case study, we evaluate the efficacy of large numbers of constructed wetlands in southern Sweden to remove nutrients from runoff in the context of the eutrophication of the Baltic Sea. The removal efficiency of total nitrogen and total phosphorus in single wetlands is in general relatively high (median values are 37% and 46%, respectively). However, to make a significant difference on a catchment scale, more and larger wetland areas need to be created, and they need to be wisely placed where nutrient loading rates are high.

Wetlands are being degraded and destroyed at a faster rate than any other ecosystem on earth. Many key functions and values that wetlands provide have already been lost. Since the Ramsar Convention on Wetlands, the crucial benefits of wetland restoration and creation have been recognized by an increasing number of countries around the world. The goal of this chapter is to illuminate the ecological restoration and conservation strategies for marshes and peatlands using case studies. General principles and guidelines based on experience under different settings can offer a useful starting point for new restoration projects. We summarize eight key principles applied to different stages of a restoration project, from early planning to post-implementation monitoring that can be used widely. These principles focus on scientific and technical issues, but as in all environmental management activities, the importance of community perspectives and values should not be overlooked. We present an in-depth look at four different wetland restoration case studies. We acknowledge that every restoration project is unique and that there is no “cookbook” for restoring wetlands. Even so, these case studies provide a general outline regarding the historical causes of wetland degradation, the goal-setting required for successful restoration, and the details involved in significant wetland restoration efforts across different sites. In addition, the valuable lessons and challenges faced by the Chinese government in response to these case studies will be discussed.

Inorganic phosphates (ferric phosphate, calcium phosphate and aluminium phosphate) and organic forms of phosphorus (inosito) hexaphosphate and β-glycerophosphate) were tested as phosphorus (P) sources for the growth of three Carex species from fens differing in productivity- and nutrient availability. Aluminium phosphate and β-glycerophosphate were equally effective sources of P for all three Carex species as KH2 PO4 , which was used as a control treatment. Phosphorus from ferric phosphate and calcium phosphate was also taken up bv Carex acutiformis Ehrh., a species of high productivity from eutrophic fen areas, but not by the other two species. Only Carex lasiocarpa Ehrh., a species from P-limited fens, showed a higher P-uptake when grown with inositol phosphate than in the second control treatment without P. The P-source also affected, with differences between species, the biomass allocation to the below-ground plant parts and the area of absorption surface of the roots. The mobilization of organic sources of P by fen Carex species found in the present study might be an important factor in the P dynamics of fens because of the high contents of organic P in the fen peat soils where these species grow. In the same way, the utilization of inorganic sources of P can play a relevant role in the P-cycle in these systems where the discharge of ground water rich in ions can lead to the fixation of P into inorganic compounds. However, the differing abilities of the various Carex species to mobilize P from P-pools does not explain clearly their preferential presence in different fens in relation to the P-availability.

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.

Floodplain habitats of the Xilin River in Inner Mongolia, China, were overgrazed by sheep and cattle until fencing of the floodplains was implemented in 2000. Carbon cycling of three plant communities of differing floodplain elevation after fencing showed that biomass in low-elevation wetlands increased fastest until reaching its maximum at 20years in the future, while a slower increase in biomass existed in high-elevation and hummock' wetlands. Modelling and field experiments revealed differences between the three plant communities that were primarily attributed to different elevation levels and inundation periods. This study also determined the carbon sequestration capacity of the three floodplain wetland types (0.18kg C m(-2)year(-1) in low-elevation wetlands, 0.09kg C m(-2)year(-1) in high-elevation wetlands, and 0.05kg C m(-2)year(-1) in hummock wetlands). Copyright (c) 2014 John Wiley & Sons, Ltd.

Although 80% of their original area has been lost in the past millennium, Europe's wetlands still cover large areas in the northern part of the continent. Most original wetland types are still represented: bogs and fens are common in the boreal, atlantic and temperate parts of the continent. Riverine wetlands, although strongly reduced in size and functionality, still occur along Europe's streams and rivers. Freshwater tidal wetlands have become very rare in Europe's temperate zone. European wetlands are valued because of their biodiversity and their ecosystem services; their protection and restoration is supported by the Ramsar Convention, EU directives and national legislation for nature protection in the various states. These actions need to be intensified to stop any further degradation of the resource and its many services. The ecosystem services of wetlands should be taken into account in management decisions on land and water use. Multiple wetland restoration initiatives in river catchments and fen areas are good examples of the way forward.

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.

Riparian zones along streams and other small wetlands perform important ecosystem services in agricultural landscapes. They improve water quality by retaining nutrients and sediment from through-flowing water, sequester carbon and attenuate flood peaks at high discharge. At the same time, they have been shown to enhance biodiversity at the landscape as well as regional scale. However, there is concern about loss of biodiversity and enhanced greenhouse gas emissions where wetlands have become overloaded with nutrient-rich surface water or groundwater. This paper discusses conditions for the best performance of riparian zones and other small wetlands in agricultural landscapes in terms of nutrient and greenhouse gas retention and biodiversity. High nitrous oxide emissions have been identified in riparian zones used for N removal and could be a concern which would diminish their overall environmental benefit. However, it has been shown in riparian zones in the Rhine and Scheldt catchment that nitrous oxide emissions mainly occur when soil pH values are lower than 5. Such conditions occur mostly in stream headwater areas only where sandy sediments have a low buffering capacity, whereas higher-order streams and their riparian zones often have fine silty clay or loam sediments with higher pH values, supporting effective denitrification with low nitrous oxide emission. The question whether the nutrient attenuation service comes at the expense of biodiversity losses should be answered differently for existing, (semi-)natural wetlands and for new wetlands created in the agricultural landscape. Existing wetlands are quite vulnerable for nutrient loading, depending on their natural nutrient richness. Oligotrophic and mesotrophic wetlands such as bogs and fens are negatively affected by nutrient loadings > 4 g N m −2 y −1 and 0.5 g P m −2 y −1 , which lead to loss of diversity and characteristic species. Wetlands in riparian zones are naturally more nutrient-rich and can tolerate much higher nutrient loadings without consequences for ecosystem health and diversity, their loading limits are 50 g N m −2 y −1 and 4 g P m −2 y −1 . For nitrogen the relatively high limit is explained by significant denitrification activities in wetlands, transforming nitrate to mostly inert elemental nitrogen gas. There are also indications that only one of the major nutrients needs to be in short supply (i.e. below the limits indicated) in order to avoid major eutrophication problems. In agricultural areas where large numbers of wetlands have been created for N removal and biodiversity enhancement, the experience of this ‘dual purpose’ are generally positive, particularly in landscapes where not much of the original wetland resource remains.

Question How did frequency and local abundance of key bryophytes in Dutch fens change between 1940 and 2000? Location The Netherlands. Methods A total of 1939 vegetation relevés, objectively assigned to the class Parvocaricetea and dating from the period 1940–1999 inclusive, were extracted from a national Netherlands database. From this relevé set, two additional data sets were derived; these were syntaxonomically homogeneous at the association level. One contained 418 Scorpidio-Caricetum diandrae relevés and the other 956 Pallavicinio-Sphagnetum relevés. The following analyses were done for these three data sets: frequency and local abundance change of 13 bryophyte species over three 20-yr periods were described using logistic regression and the nonparametric Jonckheere–Terpstra test, respectively. Results Acidophytic, late-successional species, notably Sphagnum palustre and Polytrichum uliginosum, have replaced relatively early-successional species such as brown mosses, Sphagnum subnitens and Sphagnum squarrosum during the studied period. The results were mostly consistent across the three data sets. Local abundance patterns generally paralleled those of frequency, although cover trends were often less robust. Conclusions Drastic changes have taken place in the bryophyte layer of Dutch fens between 1940 and 2000. Our study has shown that acidophytic, late-successional bryophytes have replaced relatively early-successional brown moss and Sphagnum species. Both hydrological changes and nutrient shifts (in particular phosphorus enrichment and ammonium toxicity) appear to have been responsible for the observed rapid shifts in the bryophyte layer of Dutch fens.

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.

Question: Dutch fen areas have become embedded in intensively used landscapes, resulting in biodiversity loss. Hence, plant species that colonize open water inducing the formation of species-rich floating peat mats have disappeared. Despite many restoration efforts, they have not returned. Is natural succession towards floating mats impeded by site conditions, dispersal limitations or changed biotic interactions? Location: Six Dutch fen reserves: De Deelen, De Weerribben, De Wieden, Westbroek, Molenpolder and Terra Nova. Methods: In 62 fen ponds we determined plant species richness and expansion into open water. We related these to habitat quality (chemical composition of soil and surface water, pond morphology), dispersal potential (distance to remnant populations, likelihood of dispersal) and biotic interactions (presence of muskrats [Ondatra zibethicus L.] and the keystone species Stratiotes aloides). Results: Factor analysis showed that plants expanded further into open water and bank vegetation had higher species richness in areas with older ponds and lower muskrat densities. Locally, high turbidity hampered colonization. Whenever the water was clear, colonization was higher in shallow ponds, and in deep ponds only if Stratiotes was present. Species richness was negatively correlated to nutrient availability in soil and positively correlated to hydrological isolation (decreased sulphate concentrations). We also found that species richness was higher in sheltered banks. Conclusions: Multiple habitat characteristics (turbidity, water depth, nutrient and sulphate concentrations) and the influence of muskrats and Stratiotes all play a role in the lack of restoration success in Dutch fen ponds. Dispersal limitations seem to be overruled by habitat limitations, as colonization often fails even when sufficient propagule sources are present, or when connectivity is high.

Question: High atmospheric nitrogen (N) deposition has been shown to affect productivity and species composition of terrestrial ecosystems. This study focused on the differential effects of the two inorganic N forms in atmospheric deposition (i.e. ammonium and nitrate). Methods and location: Nutrient addition experiments were carried out during 4 years in a mesotrophic fen in a low-deposition area in Ireland. In a factorial design, plots were fertilized with ammonium and/or nitrate, in two doses comparable with 35 and 70kgNha � 1 y � 1 and compared with an unfertilized control. Results: Vascular plant biomass as well as bryophyte biomass were not affected by N dose but showed significantly different responses to the N form. In the ammonium-fertilized plots, vascular plant biomass was higher and moss biomass was lower than the control, while nitrate additions had no effect. Vascular plant species density was high (16 species per 0.49m 2 ) and was not affected by any of the treatments; bryophyte species density was also high (seven species per 0.04m 2 ) but showed a significant decrease upon ammonium fertilization. Conclusion: The vulnerability of the mesotrophic vegetation to enhanced atmospheric N deposition depends strongly on the N form. If N would be mainly deposited as NOx, no detrimental effects on the vegetation will occur. If, however, the deposition is mainly in the form of NHy, the bryophyte vegetation will be seriously damaged, while the vascular plant vegetation will show an increased biomass production with possible shifts in dominance from Carex and herb species to grasses and shrubs.

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.

Sphagnum-dominated peatlands head the list of ecosystems with the largest known reservoirs of organic carbon (C). The bulk of this C is stored in decomposition-resistant litter of one bryophyte genus: Sphagnum. Understanding how Sphagnum litter chemistry controls C mineralization is essential for understanding potential interactions between environmental changes and C mineralization in peatlands. We aimed to separate the effects of phenolics from structural polysaccharides on decay of Sphagnum. We measured aerobic microbial respiration of different moss litter types in a lab. We used chemical treatments to step-wise remove the chemical compounds thought to be important in decay-resistance in three taxonomically distant moss genera. We also focused on the effect of Sphagnum-specific cell-wall pectin-like polysaccharides (sphagnan) on C and N mineralization. Removing polymeric lignin-like phenolics had only negligible effects on C mineralization of Sphagnum litter, but increased mineralization of two other bryophyte genera, suggesting a minor role of these phenolics in decay resistance of Sphagnum but a major role of cell-wall polysaccharides. Carboxyl groups of pectin-like polysaccharides represented a C-source in non-Sphagnum litters but resisted decay in Sphagnum. Finally, isolated sphagnan did not serve as C-source but inhibited C and N mineralization instead, reminiscent of the effects reported for phenolics in other ecosystems. Our results emphasize the role of polysaccharides in resistance to, and active inhibition of, microbial mineralization in Sphagnum-dominated litter. As the polysaccharides displayed decay-inhibiting properties hitherto associated with phenolics (lignin, polyphenols), it raises the question if polysaccharide-dominated litter also shares similar environmental controls on decomposition, such as temperature or nutrient and water availability.

Shifts from N limitation to P or K limitation in wetlands (e.g. due to mowing and high atmospheric N deposition) are reflected by increased N:P and N:K ratios of plant biomass and changes in species composition. So far, the implications of increased N:K ratios for wetland vegetation have hardly been investigated. We examined how the supply of N and K influences the growth of three wetland grass species (Holcus lanatus, Anthoxanthum odoratum, Deschampsia caespitosa) to determine at what N:K ratios growth is likely to be K limited, how N:K ratios influence biomass allocation and nutrient uptake, and whether the responses to high N:K ratios vary among species. Plants were grown in sand at six N:K supply ratios ranging from 0.17 to 40.5 and combined with two levels of fertility in a factorial design. In 15 weeks of growth, plant biomass increased with increasing N:K supply ratios, indicating that growth was mostly limited by N and not by K across the entire range of N:K ratios. However, there were indications of K deficiency at the highest N:K supply ratio, such as increased leaf mortality and strong reduction of K concentrations during leaf senescence. The response of total plant biomass to nutrient treatments did not differ among the three species. However, other plant traits, such as biomass allocation to roots, leaf senescence and N concentrations, suggested that D. caespitosa is better adapted to extremely low K availability than the other two species. The short-term responses of the three wetland grass species to N and K supply were similar to those found in previous experiments testing different N:P supply ratios. In both cases, growth depended mainly on N supply, despite high N:K or N:P supply ratios and very low K or P concentrations in plant biomass. In those previous experiments, P supply became more important in the second year. There are indications that the same could also be true for K in a longer-term experiment. Hence, the so-called ‘critical’ values for N:K ratios of plant biomass in the field might be lower than indicated by our short-term experiment.

Received: 24 February 2009 Returned for revision: 14 April 2009 Accepted: 2 June 2009 Published electronically: 21 August 2009 † Background Wetlands are species-rich habitats performing valuable ecosystem services such as flood protection, water quality enhancement, food chain support and carbon sequestration. Worldwide, wetlands have been drained to convert them into agricultural land or industrial and urban areas. A realistic estimate is that 50 % of the world’s wetlands have been lost. † Scope This paper reviews the relationship between wetlands and agriculture with the aim to identify the successes and failures of agricultural use in different types of wetlands, with reference to short-term and long-term benefits and issues of sustainability. It also addresses a number of recent developments which will lead to pressure to reclaim and destroy natural wetlands, i.e. the continuous need for higher production to feed an increasing world population and the increasing cultivation of energy crops. Finally, attention is paid to the development of more flood-tolerant crop cultivars. † Conclusions Agriculture has been carried out in several types of (former) wetlands for millennia, with crop fields on river floodplain soils and rice fields as major examples. However, intensive agricultural use of drained/reclaimed peatlands has been shown to lead to major problems because of the oxidation and subsidence of the peat soil. This does not only lead to severe carbon dioxide emissions, but also results in low-lying land which needs to be protected against flooding. Developments in South-East Asia, where vast areas of tropical peatlands are being converted into oil palm plantations, are of great concern in this respect. Although more floodtolerant cultivars of commercial crop species are being developed, these are certainly not suitable for cultivation in wetlands with prolonged flooding periods, but rather will survive relatively short periods of waterlogging in normally improved agricultural soils. From a sustainability perspective, reclamation of peatlands for agriculture should be strongly discouraged. The opportunities for agriculture in naturally functioning floodplains should be further investigated. The development and use of crop cultivars with an even stronger flood tolerance could form part of the sustainable use of such floodplain systems. Extensive use of wetlands without drastic reclamation measures and without fertilizer and pesticides might result in combinations of food production with other wetland services, with biodiversity remaining more or less intact. There is a need for research by agronomists and environmental scientists to optimize such solutions.

Chronically nitrate-loaded riparian buffer zones show high N(2)O emissions. Often, a large part of the N(2)O is emitted from small surface areas, resulting in high spatial variability in these buffer zones. These small surface areas with high N(2)O emissions (hotspots) need to be investigated to generate knowledge on the factors governing N(2)O emissions. In this study the N(2)O emission variability was investigated at different spatial scales. Therefore N(2)O emissions from three 32 m(2) grids were determined in summer and winter. Spatial variation and total emission were determined on three different scales (0.3 m(2), 0.018 m(2) and 0.0013 m(2)) at plots with different levels of N(2)O emissions. Spatial variation was high at all scales determined and highest at the smallest scale. To test possible factors inducing small scale hotspots, soil samples were collected for slurry incubation to determine responses to increased electron donor/acceptor availability. Acetate addition did increase N(2)O production, but nitrate addition failed to increase total denitrification or net N(2)O production. N(2)O production was similar in all soil slurries, independent of their origin from high or low emission soils, indicating that environmental conditions (including physical factors like gas diffusion) rather than microbial community composition governed N(2)O emission rates.

Both eutrophication and SO4 pollution can lead to higher availability of nutrients and potentially toxic compounds in wetlands. To unravel the interaction between the level of eutrophication and toxicity at species and community level, effects of SO4 were tested in nutrient-poor and nutrient-rich fen mesocosms. Biomass production of aquatic and semi-aquatic macrophytes and colonization of the water layer increased after fertilization, leading to dominance of highly competitive species. SO4 addition increased alkalinity and sulphide concentrations, leading to decomposition and additional eutrophication. SO4 pollution and concomitant sulphide production considerably reduced biomass production and colonization, but macrophytes were less vulnerable in fertilized conditions. The experiment shows that competition between species, vegetation succession and terrestrialization are not only influenced by nutrient availability, but also by toxicity, which strongly interacts with the level of eutrophication. This implies that previously neutralized toxicity effects in eutrophied fens may appear after nutrient reduction measures have been taken.

Infrequent inundations of river floodplains during the growing season are known to have a stronger impact on plant distributions than annual flooding in the winter and early spring. Growing season responses to flooding may be explained by 1) direct effects of flooding on fully developed plants, and/or 2) indirect effects on vegetation mediated by soil nutrient availability. Nutrient availability, in turn, is the result of the effects of summer flooding on the microbial community that reacts to changes in soil moisture conditions. We employed a mesocosm experiment to test these ideas. Soil monoliths were obtained from a highly modified floodplain on the river Rhine (Netherlands) and a more pristine floodplain on the river Narew (Poland). Vegetation performance and soil nutrient availability were measured in the monoliths, which were exposed to a 14-day summer inundation. Flooding had a negative effect on plant biomass in the Dutch soils, while biomass remained unchanged on soils from the pristine Polish floodplain. This is probably related to the absence of summer flooding in the Dutch floodplains due to intensive river regulation the last century. Summer flooding is still common in the Polish situation where more original hydrology patterns remained. One month after 14-day inundation there was a decrease in species diversity (Shannon’s H) in both systems. This decrease was caused by better performance of a few graminoid species. Pore water phosphate concentrations were higher in Dutch soils and reached the highest levels during inundation. Nitrate concentrations were also generally higher in the Dutch mesocosms, although during inundation concentrations were very low in both soil types. Differences in nutrient availability between soils were reflected in aboveground biomass tissue concentrations, yet biomass response was apparently not related to nutrient availability. We conclude that ecological rehabilitation in the Netherlands, i.e., return to a more natural hydrology, resulting in an increased incidence of summer inundation could lead to a short-term reduction in productivity and changes in patterns of species abundance and dominance.

Summary 1. Globally, freshwater wetlands, including fen waters, are suffering from biodiversity loss due to eutrophication, water shortage and toxic substances, and to mitigate these pressures numerous restoration projects have been launched. Water quality data are generally used to evaluate the chances of reestablishment of aquatic vegetation in fen waters and shallow peat lakes. Here we investigated whether sediment characteristics, which are less prone to fluctuate in time, would result in more reliable predictions. 2. To test if sediment characteristics can indeed be used not only for an easy and early diagnosis of nutrient availability and water quality changes in fen waters, but also for the prognosis of biodiversity response, we recorded the aquatic vegetation and collected surface water, sediment pore water and sediment samples in 145 fen waters in the Netherlands, Ireland and Poland. 3. Endangered macrophyte species were more closely related to surface water chemistry than common species in terms of occurrence and abundance. Sites featuring endangered species appeared to have significantly lower turbidity and pH, and lower concentrations of SO4, PO4, total phosphorus (TP) and NH4 than other sites. 4. PO4 and TP concentrations in the water layer increased markedly at PO4 concentrations above 5–10 μmol L−1 in the sediment pore water. High surface water PO4 and TP concentrations appeared to be SO4-induced and only occurred below certain threshold values for pore water Fe:PO4 (3.5 mol mol−1) and total sediment Fe:P (10 mol mol−1). 5. Interestingly, the occurrence of endangered species also correlated strongly with sediment and sediment pore water ratios; the number of endangered species increased markedly at pore water Fe:PO4 ratios above 1 mol mol−1, whereas their actual abundance had the greatest increase at ratios above 10 mol mol−1. Additionally, endangered species seemed to be more sensitive to accumulation of potentially toxic substances such as sulphide and ammonium than non-endangered species. 6. As an indicator of both biogeochemical processes and biodiversity, pore water Fe:PO4 ratios could be a valuable diagnostic and prognostic tool for the restoration of water quality and biodiversity in fen waters, e.g. for selecting the most promising sites for restoration and for optimization of restoration measures.

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.

Dutch water policy aims for more frequent, controlled flooding of river valley floodplains to avoid unwanted flooding elsewhere; in anticipation of increased flooding risks resulting from climate changes. Controlled flooding usually takes place in winter in parts of the valleys which had not been subject to flooding in the last decades. it may thus affect existing nature with its conservation values. The goal of this study was to clarify the geochemical and hydrological factors determining plant species composition of winter-flooded river valley grasslands. A correlative study was carried out in 43 sites in 13 Dutch river valley floodplains, with measurements of flooding regime, vegetation composition, soil nutrients and soil pH status. With the use of canonical correspondence analysis (CCA) the plant species composition was investigated in relation to the geochemical variables and the winter winter-flooding regime. We found that the distributions of target species and non-target species were clearly correlated with geochemical characteristics and flooding regime. Clustering of sites within the CCA plots has led us to distinguish between four types of winter flooding in our areas: floodplains with (a) accumulating rain water, (b) low groundwater levels flooded with river water, (c) discharging groundwater and (d) high groundwater levels flooded with river water. Our major conclusions are (1) the winter groundwater level of winter-flooded grasslands was important for evaluating the effects of winter flooding on the geochemistry and plant species composition, and (2) winter winter-flooding effects were largely determined by the nature of the flooding. A high frequency of flooding particularly favoured a small set of common plant species. in areas with groundwater seepage, winter flooding may provide geochemical conditions suitable for diverse vegetation types with rare species. Rainwater flooded sites appeared less suitable for most target species. (c) 2008 Elsevier B.V. All rights reserved.

Despite the scientific method's central tenets of reproducibility (the ability to obtain similar results when repeated) and repeatability (the ability to replicate an experiment based on methods described), published ecological research continues to fail to provide sufficient methodological detail to allow either repeatability of verification. Recent systematic reviews highlight the problem, with one example demonstrating that an average of 13% of studies per year (±8.0 [SD]) failed to report sample sizes. The problem affects the ability to verify the accuracy of any analysis, to repeat methods used, and to assimilate the study findings into powerful and useful meta‐analyses. The problem is common in a variety of ecological topics examined to date, and despite previous calls for improved reporting and metadata archiving, which could indirectly alleviate the problem, there is no indication of an improvement in reporting standards over time. Here, we call on authors, editors, and peer reviewers to consider repeatability as a top priority when evaluating research manuscripts, bearing in mind that legacy and integration into the evidence base can drastically improve the impact of individual research reports.

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.

The efficacy and feasibility of annual harvesting of Phragmites australis and Typha latifolia shoots in autumn for nutrient removal was evaluated in a wetland system used for polishing sewage treatment plant (STP) effluent. Aboveground biomass and nutrient dynamics nutrient removal through harvest were studied in parallel ditches with stands of Phragmites or Typha that were mown in October during two successive years. The inflow rate of STP effluent to the ditches was experimentally varied, resulting in pairs of ditches with mean hydraulic retention times (HRT) of 0.3, 0.8, 2.3, and 9.3 days, corresponding to N and P mass loading rates of 122-4190 g N m(-2) yr(-1) and 28.3-994 g P m(-2) yr(-1). Nitrogen and P removal efficiency by harvest of Phragmites and Typha shoots in October increased with increasing HRT, despite the opposite HRT effect on N and P standing stocks. This removal through harvest appeared to be useful in treatment wetlands with N and P mass loading rates lower than approximately 120 g N m(-2) yr(-1) and 30 g P m(-2) yr(-1), corresponding to a HRT of roughly 9 days in the ditches of this wetland system. At the HRT of 9.3 days, the annual mass input to the ditches was reduced through the harvest by 7.0-11% and 4.5 -9.2% for N and P, respectively. At the higher nutrient mass loading rates, the nutrient removal through harvest was insignificant compared to the mass inputs. The vitality of Phragmites and Typha, measured as maximum aboveground biomass, was not affected by the annual cutting of the shoots in autumn over two years. The Typha stands yielded higher N and P removal efficiencies through shoot harvest than the Phragmites stands, which was largely the result of lower decreases in N and P standing stocks between August and October. This difference in nutrient standing stocks between the two species was caused by a combined effect of greater decreases in nutrient concentrations largely due to higher nutrient retranslocation efficiencies of Phragmites plants and greater reductions in shoot Phragmites biomass because of leaf fall and mass resorption. Nutrient removal by harvesting Phragmites shoots can probably be doubled without a reduction in vitality of the stands by advancing the harvest date to mid-September, which would at least approach the nutrient removal by harvesting Typha shoots in October. Phragmites also may be more profitable in very low-loaded wetland systems because the vigor of Typha stands seemed to be more sensitive to a lower nutrient availability at N and P mass input rates lower than the range indicated.

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.

Summary 1. Restoration of formerly species-rich wet heaths and matgrass swards has not always been successful. The constraints on this restoration process are not yet fully understood and need further investigation, particularly the accumulation of ammonium in the soil after sod cutting, i.e. the removal of the vegetation and topsoil layer. This accumulation is known from sod cutting experiments in dry heaths, but had not previously been studied in wet heaths and matgrass ecosystems. 2. In 2000, sods were cut from two degraded Dutch wet heaths. Soil chemistry and germination in the sod-cut plots were measured at irregular intervals between April 2000 and August 2001. To test the influence of ammonium on germination and survival, a glasshouse dose‐response experiment was conducted with two endangered wet heath plant species. 3. In both wet heaths, an accumulation of KCl-extractable ammonium up to 600 µ mol kg − 1 dry soil was found in the upper 10 cm of the soil within the first year after sod cutting. These high ammonium concentrations lasted for about 10 months. Germination was very low in the sod-cut plots in 2000 and 2001, and few target species were found, although they were present in the vicinity. 4. The dose‐response experiment indicated a significant, negative correlation of both germination and survival with increasing ammonium addition for both plant species. Mean soil ammonium concentrations of the control, 100 and 250 µ  ammonium treatments were significantly lower than those of the 500 and 1000 µ  ammonium treatments (47, 45, 70, 144 and 252 µ mol kg − 1 dry soil, respectively). 5. Maximum concentrations of KCl-extractable ammonium in the field corresponded to water-extractable concentrations that were higher than those found to be limiting germination and growth in the glasshouse experiments. The low germination in the field is likely to have been adversely affected by high concentrations of ammonium as a result of sod cutting. 6. Synthesis and applications . High ammonium concentrations occur in wet heaths following sod cutting. Low rates of germination of restoration target plant species occur under such conditions. To increase the success of wet heath restoration, the accumulation of ammonium after sod cutting should be prevented by additional measures, such as liming. Because sod cutting is also applied as a restoration measure in the restoration of other ecosystems, such as fens, the effects on increased soil ammonium concentrations need further attention.

The conservation or restoration of seminatural vegetation often involves measures that influence the availability of nutrients and consequently the plant species composition. The ability to predict effects of modified nutrient availability on species composition would therefore help to choose appropriate management strategies. The aim of this study was to test whether short-term effects of nitrogen or phosphorus enrichment can be predicted from nutrient ratios in plant biomass. At 11 species-rich sites in Dutch fens and dune slacks, small plots were fertilized with N, P, N + P, or not fertilized (control). The aboveground biomass, N and P concentrations, and N:P ratios were compared between fertilized and control plots for all sufficiently abundant plant populations in the summers preceding and following fertilization. Of 121 populations, only 45 had their biomass enhanced significantly by fertilization. Populations enhanced by P fertilization had on average higher biomass N:P ratios than those enhanced b...

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.