Jos T. A. Verhoeven

PLANT-MEDIATED CONTROLS ON NUTRIENT CYCLING IN TEMPERATE FENS AND BOGS

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

Nitrogen- or phosphorus-limited growth in herbaceous, wet vegetation : relations with atmospheric inputs and management regimes

Herbaceous vegetation under temperate climatic conditions generally shows nitrogen- or phosphorus-limited plant growth, which creates conditions for a high botanical diversity. Is nitrogen (N) or phosphorus (P) the most important limiting factor, or are both generally in short supply? What are the consequences of Increased N and P inputs that result from anthropogenic disturbances? A new indicator of N or P limitation, that is, the vegetation N:P ratio, allows us to address these questions for a range of mires, dune slacks and moist grasslands.

Wetlands for wastewater treatment: Opportunities and limitations

This paper gives some introductory information on the use of wetlands for wastewater treatment. It focuses mainly on the functioning of constructed wetlands, in particular surface-flow and infiltration wetlands. The various processes which lead to water purification are briefly explained, in relation to the factors which influence their efficiency. The possibilities for optimization of the design and management of such systems are illustrated with data on the functioning of a wastewater infiltration wetland in The Netherlands. In general, constructed wetlands can be designed to remove more than 90% of BOD, COD, suspended solids and bacteriological pollution from the through-flowing wastewater. Removal of N and P remains, however closer to 50% in most cases.

BIOMASS N:P RATIOS AS INDICATORS OF NUTRIENT LIMITATION FOR PLANT POPULATIONS IN WETLANDS

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...

The ecology of Ruppia-dominated communities in western Europe. I. Distribution of Ruppia representatives in relation to their autecology

Abstract This paper contains the first of three parts of a study of the ecology of Ruppia -dominated communities. After introductory remarks on the problematic subdivision of the genus Ruppia and on its distribution in the world, a detailed picture is given of the distribution of the European Ruppia taxa in three study areas at different latitudes (Finland, The Netherlands, S. France), in relation to important environmental factors, e.g. salinity, size and permanence of the water body, substrate type. Ruppia cirrhosa (Petagna) Grande appeared to be characteristic for medium and large permanent water bodies with an annual mean salinity between 2 and 35‰ Cl − (total range 1.5–60‰ Cl − ). Ruppia maritima var. maritima L. proved to occur mainly in small and medium-size permanent water bodies with an annual mean salinity between 0.5 and 8‰ Cl − (total range 0.3–15‰ Cl − ), whereas R. maritima var. brevirostris (Agardh) Aschers. Graebn. proved to be characteristic for temporary waters of various sizes (salinity range 1–42‰ Cl − ). An examination of the ionic content of the water of 8 Ruppia habitats in The Netherlands revealed that the minor components of salinity (K + , Ca 2+ , Mg 2+ , SO 4 2− ) showed considerable variations, resulting in conspicuous differences in proportional ionic compositions in different waters. The Na, K, Mg and Ca contents of Ruppia taxa were measured in material from several natural habitats. The metal contents of Ruppia cirrhosa proved to be similar to those found for Zostera marina L. R. maritima var. brevirostris differed greatly from the other two Ruppia taxa regarding the metal content and showed similarities to fresh water species in this respect. The development of the Ruppia taxa in their natural habitats is described in detail. The switch from winter quiescence to exponential growth is temperature-determined in both Ruppia species. In contrast, the moment of biomass decrease is determined by plant properties: after 4 months of exponential growth, long stems decompose near their base resulting in easy detachment of above-ground parts of the vegetation. In The Netherlands, a further decay is followed by quiescence, whereas in S. France another period of exponential growth can start from the remaining horizontal runners. Further, the biomass decrease is strongly influenced by mechanical damage due to wind action and by bird and macrofauna grazing. Ruppia maritima var. brevirostris is capable of completing its entire life cycle in a few months and is therefore well-adapted to temporary environments. In Finland, it also occurs on exposed shores in moving sandy sediments. The results of outdoor culture experiments carried out in The Netherlands with the three Ruppia taxa are discussed. Both Ruppia species had a better development on soft mud than on sand and showed a decreased growth rate in water containing 18.5‰ Cl − compared with 3.5‰ Cl − . In 28‰ Cl − , only Ruppia cirrhosa survived, but little growth was observed. The similar reaction of the two species was rather surprising. The taxonomical characters proved to be very constant in the cultures. A principal difference in pollination mechanism between R. cirrhosa and R. maritima proved to exist: the pollination of R. cirrhosa takes place at the water surface; consequently, the peduncles have a length significantly related to water depth. R. maritima has an under-water pollination mechanism in which an air-bubble envelops the pistils; the pollen freed from the same inflorescence floats on the surface of the bubble and causes self-pollination. The characteristics of R. maritima var. brevirostris proved constant even after 2 subsequent generations cultivated from seeds. In a final evaluation, the importance of plant properties to the distribution and the strategy for survival of the Ruppia taxa is discussed.

Nitrogen and phosphorus mineralization in fens and bogs

The release of inorganic nitrogen and phosphorus in ten mires in The Netherlands with different vegetation and hydrology was measured by incubating soil in situ in polyethylene bottles at depths of 10 and 25 cm. At the same time, cellulose decomposition was estimated by means of tensile strength loss of in-situ cotton strips. The size of the inorganic N pool was not related to depth, mire type or the presence of a Sphagnum cover. The labile inorganic P pool was significantly larger in Sphagnum-dominated bogs than in phanerogram-dominated fens (...)

Decomposition of Carex and Sphagnum litter in fens: Effect of litter quality and inhibition by living tissue homogenates

Abstract Decomposition of fresh litter of Carex diandra , originating from a base-rich fen, and Sphagnum fallax , originating from a base-poor fen, was investigated in field experiments with litter bags and laboratory experiments with aerobic incubators. The Carex litter decomposed significantly faster than the Sphagnum litter in all experiments. Further, both litter types decomposed faster in the base-rich than in the base-poor fen. The addition of a small amount of homogenized S. fallax capitulums to litter of both types in the laboratory experiments significantly slowed down the rate of weight loss. The addition of homogenized C. diandra leaves did not influence the decay rate. These results suggest that the slow litter decomposition in Sphagnum -dominated mires is due to the chemical composition of the litter itself and the antibiotic effect of a substance leaching from living Sphagnum cells. Literature on the biochemistry of Sphagnales suggests that ‘Sphagnum acid’, a phenolic compound found in all Sphagna tested, is responsible for these differences.

Linkages between Aquatic Sediment Biota and Life Above Sediments as Potential Drivers of Biodiversity and Ecological Processes

A deal of attention has been given to declining species diversity in terrestrial systems, and certainly the rate of species loss in tropical forests is staggering. Recently, increasing attention has been focused on the loss of species in aquatic ecosystems. Indeed, Ricciardi and Rasmussen (1999) report that freshwater extinctions in North America far exceed extinctions in terrestrial environments. For example, an increasing number of freshwater fish and bivalves are being added to endangered species lists (Angermeier and Schlosser 1995, Strayer et al. 1996). In contrast to our knowledge of fish and bivalves, information on species extinctions or even inventory lists are lacking for most inhabitants of the bottom sediments of lakes, streams, ground waters and wetlands, even though these “invisible”habitats harbor diverse and abundant biota (e.g., estimated at more than 100,000 species of sediment invertebrates globally, 10,000 species of algae, and more than 20,000 species of protozoans and bacteria; Palmer et al. 1997). Although the local and global environmental

Agricultural use of wetlands: opportunities and limitations

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 worlds 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 flood-tolerant 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.

Control of plant growth by nitrogen and phosphorus in mesotrophic fens

A fertilization experiment was carried out in 3 mesotrophic fens to investigate whether plant growth in these systems is controlled by the availability of N, P or K. The fens are located in an area with high N inputs from precipitation. They are annually mown in the summer to prevent succession to woodland. Above-ground plant biomass increased significantly upon N fertilization in the two “mid”-succession fens studied. In the “late”-succession fen that had been mown for at least 60 years, however, plant biomass increased significantly upon P fertilization. The mowing regime depletes the P pool in the soil, while it keeps N inputs and outputs in balance. A long-term shift occurs from limitation of plant production by N toward limitation by P. Hence, mowing is a suitable management tool to conserve the mesothrophic character of the fens.