Jan G M Roelofs

• Radboud University

Isoetids are slow growing ecosystem-engineers that maintain an oligotrophic environment through high radial oxygen losses (ROL) from their roots. This ROL could potentially reduce methane (CH4) emission by maintaining sediment redox conditions unfavourable for methanogenesis. Isoetids have declined in many European countries as an effect of eutroph...

Zeolite minerals are able to bind ammonium ions (NH4 +) and simultaneously release cations due to their ion-exchange properties, making them promising to mitigate for the increased atmospheric nitrogen deposition. In pilot experiments, the ammonium removal of different zeolites was tested (vulkamin, actionine, optizec) when applied to an ammonium n...

Water hyacinth is able to sequester large amounts of carbon dioxide (CO2) in wetlands. At the same time, the high production of organic matter combined with the plant’s capacity to limit the diffusion of oxygen from the atmosphere into the water creates favorable conditions for the production of methane (CH4). The combination of these mechanisms ch...

Water hyacinth is able to sequester large amounts of carbon dioxide (CO 2) in wetlands. At the same time, the high production of organic matter combined with the plant's capacity to limit the diffusion of oxygen from the atmosphere into the water creates favorable conditions for the production of methane (CH 4). The combination of these mechanisms...

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 determi...

Aim The formation of a local vegetation mosaic may be attributed to local variation in abiotic environmental conditions. Recent research, however, indicates that self‐facilitating organisms and negative species interactions may be a driving factor. In this study, we explore whether heterogeneous geohydrological conditions or vegetation feedbacks an...

Water soldier is an aquatic macrophyte characterised by alternating floating and submerged life stages. Because of its ability to form dense, floating mats and produce high amounts of organic matter, water soldier is an important species in the process of terrestrialisation and the succession of fens. Throughout the Netherlands, the species decline...

With the current risks caused by sea level rise and increased extreme weather events, the study of natural coastal systems has never been more important. Erosion and anthropogenic forcing led to disappeared of the majority of coastal bogs in Europe. Here, we report on case study of a unique bog remnant still under influence by seawater which floats...

As a result of altered land use, water shortage and eutrophication, aquatic and semi-aquatic biodiversity in minerotrophic peatlands has severely declined in The Netherlands. After the improvement of surface water quality following hydrological and other measures, biodiversity is now increasing again in many reserves including former peat extractio...

Deterioration and restoration of minerotrophic waters in the Dutch peat landscape As a result of altered land use, water shortage and eu- trophication, aquatic and semi-aquatic biodiversi- ty in minerotrophic peatlands has severely declined in The Netherlands. After the improvement of surface water quality following hydrological and other meas- ur...

As a result of altered land use, water shortage and eutrophication, aquatic and semi-aquatic biodiversity in minerotrophic peatlands has severely declined in The Netherlands. After the improvement of surface water quality following hydrological and other measures, biodiversity is now increasing again in many reserves including former peat extractio...

The addition of iron and calcium rich sludge from groundwater extraction processes, in the restoration of black alder carrs on abandoned rewetted agricultural lands, was investigated in a small-scale field experiment divided over three nature reserves differing in hydrology. We applied three different treatments with sludge to the (partly excavated...

Methane (CH4) strongly contributes to observed global warming. As natural CH4 emissions mainly originate from wet ecosystems, it is important to unravel how climate change may affect these emissions. This is especially true for ebullition (bubble flux from sediments), a pathway that has long been underestimated but generally dominates emissions. He...

Research rationale: Groundwater-fed fens are known sources of methane (CH4 ) emissions to the atmosphere, but these are known to be mediated by vegetation. In a fen located in the Bale Mountains, Ethiopia, we assessed the effects of a cushion plant (Eriocaulon schimperi) and a sedge species (Carex monostachya) on rhizosphere biogeochemistry. Cent...

Given the bioremediation potential of peat, natural capping of landfills in wetlands with a “peat cap” could provide a sustainable addition to regular capping methods using basal liners with limited life-spans and sand. It is unknown, however, which initial conditions optimise growth of this “peat cap” on top of a sand layer. Here, we tested the co...

The sequestration of nutrients from surface waters by aquatic macrophytes and sediments provides an important service to both natural and constructed wetlands. While emergent species take up nutrients from the sediment, submerged and floating macrophytes filter nutrients directly from the surface water, which may be more efficient in constructed we...

Woekerende waterplanten in stromende wateren zorgen voor veel hoofdbrekens bij waterbeheerders. Ze staan ecologische doelen in de weg en zorgen bovendien voor hoge onderhoudskosten. Een minder productieve vegetatie is dus om meerdere redenen wenselijk. Dit artikel gaat nader in op de rol van de waterbodem hierbij. Onderzoek aan waterbodems in Oost-...

Die anhaltende Stickstoffdeposition lässt die Böden versauern und verändert deren Basensättigung. In der Folge haben es Eichen und Gemeiner Wacholder schwer. Neue Forschungen aus den Nieder- landen erlauben Einblicke in die Wirkung von Stickstoffdeposition und Bodenversauerung auf diese und andere Pflanzen auf schwach gepufferten Böden.

Die anhaltende Stickstoffdeposition lässt die Böden versauern und verändert deren Basensättigung. In der Folge haben es Eichen und Gemeiner Wacholder schwer. Neue Forschungen aus den Nieder- landen erlauben Einblicke in die Wirkung von Stickstoffdeposition und Bodenversauerung auf diese und andere Pflanzen auf schwach gepufferten Böden.

The construction and restoration of riparian (temporarily flooded) wetlands as water storage and flood protection areas plays a central role in climate-adaptive water management. In general, arable and ex-arable lands are used for this type of water storage. However, inundation may lead to problems, as excess phosphorus (P) stored in these soils ma...

Eggs of theWestern spadefoot toad (Pelobates cultripes) reached a 100%mortality in all 29 clutches deposited at a pH below 5.0 in a temporary pond of the Doñana National Park (SWSpain) throughout the wet season of 2006– 2007. A similar trend was detected in a neighbouring pond. The proximity of these two ponds to a groundwater pumping area (b1.5 km...

There is growing evidence that species are able to coexist in communities through niche separation, and that consistent community structuring can take place at the biogeographical scale, as the same biotic interactions can determine species’ fate at large scales. In this study, we document niche differentiation at a larger scale within a specific p...

Inputs of salt spray to the blanket bogs, due to their proximity to the coast and the predominant westerly winds from the Atlantic Ocean. To test this hypothesis we carried out an ecohydrological field study at a large blanket bog in the western part of Connemara, Ireland. We described peat profiles in two transects and sampled pore water from peat...

Acidification has been recognised as a serious environmental problem in Scandinavia since the 1970s, and liming has been the main strategy to counteract negative effects on biota by improving water quality. We studied the short‐ and long‐term effects of liming on sediment and water quality, as well as macrophyte development, by comparing five limed...

Azolla spp. rank among the fastest growing plants in the world. Increased atmospheric CO 2 concentrations can be expected to have a strong impact on the biomass production of this fast growing floating fern, especially at northern latitudes. We investigated the growth of the northernmost occurring species, A. filiculoides , under past (Eocene), pre...

The direct contribution of microbial activity to the formation of iron-oxide minerals is difficult to prove in wetlands due to the high reactivity of solid iron phases with different compounds and the variety of redox processes that may occur at each oxic-anoxic boundary. Here, we propose an explanation for the formation of iron-oxide films in wetl...

Globally, coastal lowlands are becoming more saline by the combined effects of sea level rise, land subsidence and altered hydrological and climatic conditions. Although salinization is known to have a great influence on biogeochemical processes, literature shows contrasting effects that challenge the prediction of future effects. In addition, the...

Peatlands play an important role in the global carbon (C) cycle due to their large C storage potential. Their C sequestration rates, however, highly vary depending on climatic and geohydrological conditions. Transitional mires are often characterised by floating peat with infiltration of buffered groundwater or surface water. Sphagnum mosses grow o...

Structural diversity formed by dense, floating Stratiotes aloides stands, generates hotspots of biodiversity of flora and fauna in wetlands. However, only part of the populations become emergent and provide this important facilitation. Since it has been hypothesised that its buoyancy depends on the rates of underwater photosynthesis, we investigate...

In March 2013 we investigated two small peatlands in the Bale Mountains in central Ethiopia. The mires are located on the Sanetti Plateau at an altitude of approximately 4000 metres above mean sea level (a.m.s.l.). Their vegetation is dominated by tussocky Carex species and locally also by a cushion plant Eriocaulon schimperi, which occurs elsewher...

Internal phosphorus (P) mobilisation from aquatic sediments is an important process adding to eutrophication problems in wetlands. Salinisation, a fast growing global problem, is thought to affect P behaviour. Although several studies have addressed the effects of salinisation, interactions between salinity changes and nutrient cycling in freshwate...

Fens represent a large array of ecosystem services, including the highest biodiversity found among wetlands, hydrological services, water purification and carbon sequestration. Land-use change and drainage has severely damaged or annihilated these services in many parts of North America and Europe; restoration plans are urgently needed at the lands...

In wetland soils and underwater sediments of marine, brackish and freshwater systems, the strong phytotoxin sulfide may accumulate as a result of microbial reduction of sulfate during anaerobiosis, its level depending on prevailing edaphic conditions. In this review, we compare an extensive body of literature on phytotoxic effects of this reduced s...

In remote, tropical areas human influences increase, potentially threatening pristine seagrass systems. We aim (i) to provide a bench-mark for a near-pristine seagrass system in an archipelago in East Kalimantan, by quantifying a large spectrum of abiotic and biotic properties in seagrass meadows and (ii) to identify early warning indicators for ri...

Eutrophication is an important problem in aquatic environments in Europe. In the Netherlands, many aquatic macrophytes have strongly declined while, at present their former habitats are characterized by non-rooting species such as Lemna species, Spirodela polyrhiza (L.) Schleiden and Azollla filiculoides Lamark. The experiments reveal that processe...

The water fern genus Azolla has been found in marine sediments, showing that ancestral species grew in marine ecosystems during the Eocene. Modern Azolla species, however, only live in freshwater. Besides aiming to elucidate experimentally the conditions that prevailed over the Arctic Ocean and adjacent Nordic seas during the Eocene, studies on tol...

Climate buffers, natural areas specially designed to reduce the consequences of climate change, can be achieved in different ways. There is a distinction between the storage or retention of surface water (water storage) and the retention of rain water. The latter can, particularly in peatlands, be combined with the recovery of Sphagnum dominated pe...

Biogeochemical processes affecting surface water quality in ditches and ponds of Dutch peat meadows are described and applied under two scenarios: low and high water table. Dutch peat meadows are generally sulphur-rich due to marine influences in the past. In addition the peat top-layer (0-50 cm) is overloaded with phosphorus due to agricultural ac...

During spring storms massive uprooting of Littorella uniflora occurred in a shallow Dutch softwater lake. The aim of this study was to test whether changes in plant morphology and sediment characteristics could explain the observed phenomenon. Uprooting was expected to occur in plants having a high shoot biomass and low root to shoot ratio (R:S), g...

In order to understand the physicochemical mechanisms that could explain the massive growth of Azolla arctica in the Eocene Arctic Ocean, we carried out a laboratory experiment in which we studied the interacting effects of rain and wind on the development of salinity stratification, both in the presence and in the absence of a dense Azolla cover....

Minimum water temperature ( C±SE) in the top water layers and the bottom water layers of the freshwater and brackish water basins and the minimum air temperature (°C) at 10 cm above ground level during the mesocosm experiment. (TIF)

Nutrient concentrations (µM ± standard error) in the freshwater and brackish water basins during the mesocosm experiment. A) Calcium concentrations, B) Magnesium concentrations, C) Sodium concentrations, D) Potassium concentrations and E) Sulphate concentrations in the top, middle and bottom water layers of the basins. (TIF)

Oxygen concentrations (mg L−1±SE) in the top water layers and the bottom water layers of the freshwater and brackish water basins during the mesocosm experiment. (TIF)

The increase in alkalinity and SO4 2− in softwater lakes can negatively affect pristine isoetid population because the increase in alkalinity and SO4 2− can stimulate sediment mineralization and consequently cause anoxia. The consequences of increased sediment mineralization depend on the ability of isoetids such as Lobelia dortmanna to oxidize the...

The majority of studies on rhizospheric interactions focus on pathogens, mycorrhizal symbiosis, or carbon transformations. Although the biogeochemical transformations of N, S, and Fe have profound effects on vegetation, these effects have received far less attention. This review, meant for microbiologists, biogeochemists, and plant scientists inclu...

Isoetids, as indicators of near-pristine softwater lakes, have a high priority in national and international (European Water Directive Framework) assessments of ecological lake quality. Our main goal was to identify the most important environmental factors that influence the composition of plant communities and specifically determine the presence a...

QuestionDoes liming mitigate carbon limitation to the original submerged vegetation of Norwegian softwater lakes? LocationDybingsvatn (Dalane region, Southern Norway). Methods Eight plots (1 m2) were permanently marked in the deeper part (1.5 m) of the littoral zone of Dybingsvatn in 1994. Half of the plots were limed four times with dolocal (1 kg...

1. Populations of marine megaherbivores including green turtle (Chelonia mydas) have declined dramatically at a global scale as a result of overharvesting and habitat loss. This decline can be expected to also affect the tolerance of seagrass systems to coastal eutrophication. Until now, however, simultaneous effects of top–down control by megaherb...

Selecting an appropriate variable subset in linear multivariate methods is an important methodological issue for ecologists. Interest often exists in obtaining general predictive capacity or in finding causal inferences from predictor variables. Because of a lack of solid knowledge on a studied phenomenon, scientists explore predictor variables in...

Sphagnum-bog ecosystems have a limited capability to retain carbon and nutrients when subjected to increased nitrogen (N) deposition. Although it has been proposed that phosphorus (P) can dilute negative effects of nitrogen by increasing biomass production of Sphagnum mosses, it is still unclear whether P-addition can alleviate physiological N-stre...

Land use changes in tropical regions such as deforestation, mining activities, and shrimp farming, not only affect freshwater and terrestrial ecosystems, but also have a strong impact on coastal marine ecosystems. The increased influx of sediments and nutrients affects these ecosystems in multiple ways. Seagrass meadows that line coastal marine eco...

Seagrasses have declined at a global scale due to light reduction and toxicity events, caused by eutrophication and increased sediment loading. Although several studies have tested effects of light reduction and toxicants on seagrasses, there is at present no information available on their interacting effects. In a full-factorial 5-day laboratory e...

In remote, tropical areas human influences increase, potentially threatening pristine seagrass systems. We aim (i) to provide a bench-mark for a near-pristine seagrass system in an archipelago in East Kalimantan, by quantifying a large spectrum of abiotic and biotic properties in seagrass meadows and (ii) to identify early warning indicators for ri...

This chapter discusses and explains various peat bog restoration strategies relating to peat quality, water chemistry and hydrology based on case studies from the Netherlands. Inundation of bog remnants can lead to a rapid redevelopment of (floating) Sphagnum vegetation, usually when poorly humified Sphagnum peat is still present. After inundation,...

• Vascular wetland plants may substantially increase methane emissions by producing root exudates and easily degradable litter, and by providing a low-resistance diffusion pathway via their aerenchyma. However, model studies have indicated that vascular plants can reduce methane emission when soil oxygen demand is exceeded by oxygen released from r...

Soaks (areas of mesotrophic/minerotrophic vegetation within acid bog) add to the overall heterogeneity and biodiversity of raised bog landscapes due to the presence of flora and fauna communities not typically associated with acid bog systems. A field experiment was set up to investigate the potential to restore the minerotrophic and aquatic commun...

This study aimed to assess AMF diversity in various plant species in lakes with low and relatively high P concentrations to elucidate possible correlations with environmental factors in order for better understanding the functioning of mycorrhizal fungi in submerged plants. A considerable diversity of AMF communities was observed in the lakes with...

As a result of the high deposition of ammonium compounds in The Netherlands the forest trees are under a severe nitrogen stress. Effects of increasing amounts of ammonium on the major nutrient fluxes by Scots pine seedlings have been studied. In addition, the effect of mycorrhization of the roots has been taken into account. With nitrate-N nutritio...

Twenty-six macrophyte species were studied for their degree of tolerance to extremely acid conditions. They are characteristic of soft water on sandy soils in The Netherlands. These species were divided into two groups based on their recent distribution by pH and alkalinity. The first group consists of the species that can (at least temporarily) su...

To investigate whether there is a relation between the availability of nitrogen and the incidence of damage caused by the parasitic fungus Sphaeropsis sapinea (Fr.) Dyko & Sutton in Corsican pine (Pinus nigra ssp. laricio (Poir.) Maire) stands, needle and soil samples were taken in 29 stands in spring and early summer of 1986. The infected stands p...

Het hoogveenareaal in Nederland is door ontginning, turfwinning, boekweitbrandcultuur en verdroging sterk gereduceerd. De water- en nutriëntenhuishouding van de hoogvenen zijn sterk verstoord door deze aantastingen en bovendien door de neerslag van atmosferisch stikstof (N). Verder is door deze aantastingen de variatie in terreincondities die aanwe...

1. Despite real improvement in the water quality of many previously eutrophic lakes, the recovery of submerged vegetation has been poor. This lack of recovery is possibly caused by the accumulation of organic matter on the top layer of the sediment, which is produced under eutrophic conditions. Hence, our objective was to study the combined effects...

In the last decades, eutrophication has become a major cause for concern in aquatic ecosystems worldwide. Apart from external nutrient loading, release of dissolved nutrients from sediment pore water into the water layer contributes importantly to eutrophication. Theory implies that pore water HCO3- and nutrient mobility are linked, because anaerob...

Changes in macrophyte communities have occurred over the past decades in many oligotrophic softwater lakes with low carbon availability. Slow-growing isoetid species have been replaced by faster-growing elodeid species. Commonly, these changes are explained by anthropogenic nutrient enrichment or acidification of the lake water. Here we present a m...

Metallophyte vegetation along the River Geul has been almost completely replaced by grasses during the last decades. Field investigations indicated that this was accompanied by higher alkalinity and phosphate availability in the soil, related to the closure of the metal industry and intensification of agricultural practices. An experiment with a fu...

Biodiversity in urban areas is affected by a multitude of stressors. In addition to physico-chemical stress factors, the native regional species pool can be greatly reduced in highly urbanized landscapes due to area loss and fragmentation. In this study, we investigated how macrophyte composition and diversity in urban water systems are limited by...

1. The growth of submerged macrophytes in softwater lakes is often assumed to be carbon limited. Isoetid species are well adapted to grow at low carbon availability and therefore commonly dominate the submerged macrophyte vegetation in softwater lakes. In many such lakes, however, large-scale invasions of fast-growing elodeid species, replacing the...

The long term effects of salinity stress on the growth, nutrient content and amino acid composition of the Azolla filiculoides - Anabaena azollae association was studied in a laboratory experiment. It was demonstrated that the symbiosis could tolerate salt stress up to 90 mM NaCl, even after a 100 day period of preconditioning at salt concentration...

Increased phosphorus availability may provoke serious eutrophication problems in wetlands. Strong evidence indicates that sulphate induced mobilization of phosphate (internal eutrophication) has been responsible for a strong decline of the biodiversity in wetlands during the last decades. It is currently underestimated, however, that the wide sprea...

Worldwide, fens and peat lakes that used to be peat-forming systems have become a significant source of C, N and P due to increased peat decomposition. To test the hypothesis that net nutrient mineralization rates may be uncoupled from decomposition rates, we investigated decomposition and net mineralization rates of nutrients in relation to sedime...

The spatial structure of seagrass landscapes is typically ascribed to the direct influence of physical factors such as hydrodynamics, light, and sediment transport. We studied regularly interspaced banded patterns, formed by elongated patches of seagrass, in a small-scale intertidal ecosystem. We investigated (1) whether the observed spatial patter...

The impact of atmospheric N-deposition on succession from open sand to dry, lichen-rich, short grassland, and tall grass vegetation dominated by Carex arenaria was surveyed in 19 coastal dune sites along the Baltic Sea. Coastal dunes with acid or slightly calcareous sand reacted differently to atmospheric wet deposition of 5–8kgNha−1y−1. Accelerate...

1. Softwater lakes are generally dominated by slow growing, small, isoetid plant species that are adapted to the carbon‐ and nutrient‐limited conditions in these lakes. We investigated the strategy of a fast growing species, Sparganium angustifolium , for occupying softwater lakes. A field survey was carried out in Norwegian carbon‐limited Isoëteto...

The worldwide observed dramatic decline of seagrasses has typically been attributed to multiple stressors such as eutrophication, disease, sedimentation, and toxicity events. Using principal component analysis and (multivariate) logistic regression, we investigated the importance of 30 commonly measured variables in explaining the presence and abse...

The worldwide observed dramatic decline of seagrasses has typically been attributed to multiple stressors such as eutrophication, disease, sedimentation, and toxicity events. Using principal component analysis and (multivariate) logistic regression, we investigated the importance of 30 commonly measured variables in explaining the presence and abse...

The water quality of urban drainage ditches in lowlands in the Rhine-Meuse delta was analysed with principal component analysis (PCA) during a dry period and a rain storm, and related to the seepage of polluted river water and effective impervious area (EIA). This was done in order to test the hypothesis that seepage of river water and storm water...

The northwest European heathland landscape with its characteristic communities of nutrient-poor and acidic soils has a high nature value, because of its locally high biodiversity and the distinct site conditions. In order to conserve and restore the heathlands, numerous rehabilitation projects have been performed, although with varying success. Thi...

1. During the past century, isoetid vegetation types in softwater lakes have often been invaded by faster-growing elodeids. In these C-limited systems, this may be related to rising aquatic CO2 levels. 2. In a laboratory experiment we tested the growth response of two elodeid species, Myriophyllum alterniflorum and Callitriche hamulata, at four dif...

The peat and pore-water biogeochemistry of an Irish oceanic raised bog are reported with a view to understanding the origin and development of a minerotrophic soak contained within an ombrotrophic bog. Depth profiles of electrical conductivity, pore-water chemistry and peat chemistry were recorded from the mire surface down to a maximum depth of 10...