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The conservation of biodiverse wetland vegetation, including that of rich fens, has a high priority at a global scale. Although P-eutrophication may strongly decrease biodiversity in rich fens, some well-developed habitats do still survive in highly fertilized regions due to nutrient filtering services of large wetlands. The occurrence of such nutrient gradients is well-known, but the biogeochemical mechanisms that determine these patterns are often unclear. We therefore analyzed chemical speciation and binding of relevant nutrients and minerals in surface waters, soils and plants along such gradients in the large Ramsar nature reserve Weerribben-Wieden in the Netherlands.P-availability was lowest in relatively isolated floating rich fens, where plant N:P ratios indicated P-limitation. P-limitation can persist here despite high P-concentrations in surface waters near the peripheral entry locations, because only a small part of the P-input reaches the more isolated waters and fens. This pattern in P-availability appears to be primarily due to precipitation of Fe-phosphates, which mainly occurs close to entry locations as indicated by decreasing concentrations of Fe- and Al-bound P in the sub-aquatic sediments along this gradient. A further decrease of P-availability is caused by biological sequestration, which occurs throughout the wetland as indicated by equal concentrations of organic P in all sub-aquatic sediments.Our results clearly show that the periphery of large wetlands does indeed act as an efficient P-filter, sustaining the necessary P-limitation in more isolated parts. However, this filtering function does harm the ecological quality of the peripheral parts of the reserve. The filtering mechanisms, such as precipitation of Fe-phosphates and biological uptake of P, are crucial for the conservation and restoration of biodiverse rich fens in wetlands that receive eutrophic water from their surroundings. This seems to implicate that biodiverse wetland vegetation requires larger areas, as long as eutrophication has not been seriously tackled.

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.

This chapter presents and discusses the soil–sediment–river connections and summarises the pressures at the basin scale from their causes (natural and anthropogenic drivers) to their consequences (impacts on biophysical status). Nine important pressures on river basins are evidenced with respect to their temporal and spatial scale of occurrence and their impact on the river basin at the basin scale and concerns: erosion, sealing, compaction, hydromorphological changes, salinisation, contamination, changes in water quantity, acidification and reduction of soil organic matter. Each pressure can affect the biophysical status, and the simultaneous presence of pressures can have cumulative or compensatory impacts on biophysical status through propagation. Eight biophysical statuses were identified (concentration of chemicals, trophic status, biota status, buffering capacity, salinity, suspended matter and sediment, water level, morphology and pedology), and the pressures are described in this chapter in the sense of impacts on these biophysical status.

Summary 1. Water levels in areas with intensive agriculture have often been strictly controlled for decades. Recently, more natural fluctuating water levels have been propagated to improve the ecological quality of wetlands in these areas. This study investigated the effects of water levels on protected base-rich mesotrophic fens during winter and summer. 2. We used a mesocosm approach to simulate water level fluctuations under winter and summer conditions (light and temperature) to test the effects of water level on the biogeochemistry and vegetation of two highly endangered fen types with the brownmosses Scorpidium scorpioides and Hamatocaulis vernicosus as dominant mosses. 3. Both species showed decreased photosynthetic capacity at lower water levels. These levels also resulted in decreased alkalinity due to oxidation processes in the moss layer. High water levels led to increased pH and alkalinity, due to reduction processes and infiltration of baserich water. 4. For the P-limited S. scorpioides mesocosms, high water levels did not lead to P mobilization or to significant changes in biomass production, P uptake and N:P ratios. However, for the mesocosms with H. vernicosus, where P limitation was not obvious, high water levels did result in P mobilization and increased P availability due to iron reduction. The lower P mobilization for S. scorpioides appeared to be related to lower total soil P content and higher Fe:P and Ca:P ratios. Although high water levels resulted in the accumulation of ammonium under winter conditions, this did not happen under summer conditions, making ammonium toxicity unlikely. 5. Synthesis and applications. Our results suggest that low water levels could hamper protected brownmosses in rich fens, especially during the summer. In contrast, inundations may have a positive effect on rich fens by increasing the alkalinity. However, inundations may lead to eutrophication due to internal P mobilization in soils with a high total P content and low Fe:P ratio. Therefore, we recommend that soils with high total P content and low Fe:P ratios should not be flooded.

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

Scorpidium scorpioides (Hedw.) Limpr. is a characteristic species of rich fens, where its chemical environment is one of high pH, calcium content, alkalinity, and conductivity. It often forms a dominant component of rich fen peat deposits. When grown under experimental conditions, Canadian plants of this species respond differently than plants from The Netherlands. Canadian plants respond best when grown in extreme-rich fen waters, while plants from The Netherlands respond best in waters from moderate-rich fens and in nutrient enhanced conditions. Saline waters yield no or limited growth responses from plants in both areas. The results suggest ecotypic variation between plants from the two continents. Also, the results suggest that chemical factors (i.e., saline water) affect the presence and growth of S. scorpioides. These chemical factors may have had an influence on the past distribution of the species. Abstract. Scorpidium scorpioides (Hedw.) Limpr. is a characteristic species of rich fens, where its chemical environment is one of high pH, calcium content, alkalinity, and conductivity. It often forms a dominant component of rich fen peat deposits. When grown under experimental conditions, Canadian plants of this species respond differently than plants from The Netherlands. Canadian plants respond best when grown in extreme-rich fen waters, while plants from The Netherlands respond best in waters from moderate-rich fens and in nutrient enhanced conditions. Saline waters yield no or limited growth responses from plants in both areas. The results suggest ecotypic variation between plants from the two continents. Also, the results suggest that chemical factors (i.e., saline water) affect the presence and growth of S. scorpioides. These chemical factors may have had an influence on the past distribution of the species. Abstract. Scorpidium scorpioides (Hedw.) Limpr. is a characteristic species of rich fens, where its chemical environment is one of high pH, calcium content, alkalinity, and conductivity. It often forms a dominant component of rich fen peat deposits. When grown under experimental conditions, Canadian plants of this species respond differently than plants from The Netherlands. Canadian plants respond best when grown in extreme-rich fen waters, while plants from The Netherlands respond best in waters from moderate-rich fens and in nutrient enhanced conditions. Saline waters yield no or limited growth responses from plants in both areas. The results suggest ecotypic variation between plants from the two continents. Also, the results suggest that chemical factors (i.e., saline water) affect the presence and growth of S. scorpioides. These chemical factors may have had an influence on the past distribution of the species. Brown mosses, composed of species in the genera Calliergon, Calliergonella, Campylium, Cratoneu- ron, Drepanocladus s.l., Meesia, Scorpidium, and Tomentypnum-along with a few of the more hy- grophytic species of Brachythecium and Hypnum - are characteristic of rich-fen habitats, peatlands characterized by minerotrophic, alkaline (see Wet- zel 1975) water. Nutrients, especially nitrogen and phosphorus, are present in the surface waters in low amounts. However, due to seasonal flow of water, plants are able to take up more nutrients than are present in oligotrophic bogs; thus rich fens are me- sotrophic ecosystems (Vitt & Kuhry 1992). Three types of base-rich (Ca, Mg, or Na) fens occur in boreal western Canada. Moderate-rich fens are characterized by pH's between 5.5 and 7.0, small amounts of bicarbonate, somewhat seasonally vari- able water tables, and no marl deposition. Char- acteristic species include Brachythecium mildean- um (Schimp.) Schimp. in Milde, Calliergonella cuspidata (Hedw.) Loeske, Drepanocladus aduncus (Hedw.) Warnst., D. aduncus var. polycarpus (Bland. ex Voit) G. Roth, D. lapponicus (Norrl.) Smirn., D. vernicosus (Mitt.) Warnst., and Helodium blandowii (Web. & Morh) Warnst. (Chee & Vitt 1989). Ex- treme-rich fens have pH's higher than 6.5, large Brown mosses, composed of species in the genera Calliergon, Calliergonella, Campylium, Cratoneu- ron, Drepanocladus s.l., Meesia, Scorpidium, and Tomentypnum-along with a few of the more hy- grophytic species of Brachythecium and Hypnum - are characteristic of rich-fen habitats, peatlands characterized by minerotrophic, alkaline (see Wet- zel 1975) water. Nutrients, especially nitrogen and phosphorus, are present in the surface waters in low amounts. However, due to seasonal flow of water, plants are able to take up more nutrients than are present in oligotrophic bogs; thus rich fens are me- sotrophic ecosystems (Vitt & Kuhry 1992). Three types of base-rich (Ca, Mg, or Na) fens occur in boreal western Canada. Moderate-rich fens are characterized by pH's between 5.5 and 7.0, small amounts of bicarbonate, somewhat seasonally vari- able water tables, and no marl deposition. Char- acteristic species include Brachythecium mildean- um (Schimp.) Schimp. in Milde, Calliergonella cuspidata (Hedw.) Loeske, Drepanocladus aduncus (Hedw.) Warnst., D. aduncus var. polycarpus (Bland. ex Voit) G. Roth, D. lapponicus (Norrl.) Smirn., D. vernicosus (Mitt.) Warnst., and Helodium blandowii (Web. & Morh) Warnst. (Chee & Vitt 1989). Ex- treme-rich fens have pH's higher than 6.5, large Brown mosses, composed of species in the genera Calliergon, Calliergonella, Campylium, Cratoneu- ron, Drepanocladus s.l., Meesia, Scorpidium, and Tomentypnum-along with a few of the more hy- grophytic species of Brachythecium and Hypnum - are characteristic of rich-fen habitats, peatlands characterized by minerotrophic, alkaline (see Wet- zel 1975) water. Nutrients, especially nitrogen and phosphorus, are present in the surface waters in low amounts. However, due to seasonal flow of water, plants are able to take up more nutrients than are present in oligotrophic bogs; thus rich fens are me- sotrophic ecosystems (Vitt & Kuhry 1992). Three types of base-rich (Ca, Mg, or Na) fens occur in boreal western Canada. Moderate-rich fens are characterized by pH's between 5.5 and 7.0, small amounts of bicarbonate, somewhat seasonally vari- able water tables, and no marl deposition. Char- acteristic species include Brachythecium mildean- um (Schimp.) Schimp. in Milde, Calliergonella cuspidata (Hedw.) Loeske, Drepanocladus aduncus (Hedw.) Warnst., D. aduncus var. polycarpus (Bland. ex Voit) G. Roth, D. lapponicus (Norrl.) Smirn., D. vernicosus (Mitt.) Warnst., and Helodium blandowii (Web. & Morh) Warnst. (Chee & Vitt 1989). Ex- treme-rich fens have pH's higher than 6.5, large