Mesotrophic Fens Research Articles

Plant functional traits reveal strong effects of anoxia and nutrient limitation on species pool filtering in a riverine rich fen system

ABSTRACTBackground: In fens, plant species composition is predominantly controlled by two environmental factors: root anoxia and low nutrient availability.Aims: We asked how these filters were reflected to the functional structure of plant communities in natural and drained rich fens.Methods: We analysed traits related to species response to anoxia and nutrient availability, using single-trait and multi-trait approaches in fens of a river valley (Biebrza, Poland). We evaluated results concerning multi-trait indices using a null model consisting of simulated communities.Results: Mycorrhizal status and specific leaf area (SLA) clearly distinguished the communities with different levels of anoxia and nutrient deficiency. Mean values, ranges and variance of canopy height showed the differences in the distribution of plant heights among analysed communities.Conclusions: Functional traits distinguish plant communities of the most endangered mesotrophic fens from eutrophic and drained fens. We highlight the role of nutrient and oxygen deficiency in the assembly of fen vegetation and show the impact of the altered environment on the composition of communities in degraded habitats. We demonstrate that single-trait indices are suitable for identifying of environmental filtering in different types of fen communities. We suggest that caution is justified when using multi-trait indices to assess vegetation patterns.

The ecological effects of water level fluctuation and phosphate enrichment in mesotrophic peatlands are strongly mediated by soil chemistry

Since the re-establishment of a more natural water regime is considered by water management in wetlands with artificially stable water levels, the biogeochemical and ecological effects of water level fluctuation with different nutrient loads should be investigated. This is particularly important for biodiverse mesotrophic fens, sensitive to acidification and eutrophication. Mesocosm experiments were conducted to study the interactive effects of water level fluctuation and P-enrichment under controlled summer conditions, using peat cores including vegetation from three fens differing in biogeochemical characteristics.The effects of fluctuating water levels on biogeochemistry and vegetation appeared to be highly dependent on peat chemistry, and more important than the effects of P-enrichment. Only when plant growth was stimulated by a favorable water level regime, P-enrichment led to increased P-consumption by plants. In rich fens with a high soil Ca-content, 7 weeks of lowered water table (−15cm) did not lead to a drop in pH. However, soil subsidence, increased N-availability and decline of the rich fen bryophyte Scorpidium scorpioides give cause to concern. 7 weeks of inundation (+15cm) offered possibilities for restoration in these fens, since alkalinity and Ca-concentrations increased, while soil P-mobilization did not occur. Even P-enrichment did not result in increased P-availability, presumably due to Ca-related precipitation of P. In rich fens with a high soil Fe-content, water table lowering should be avoided as well, because of soil subsidence, increased N-availability, decline of the rich fen bryophyte Calliergon giganteum, plus acidification due to Fe-oxidation. Shallow inundation, however, is also harmful, especially after mowing and with P-rich water, because plant growth was hampered, presumably by toxicity of NH4+ and/or Fe(II). In mineral-poor fens with a high soil P- and S-content, shallow inundation should be avoided, because of tremendous internal P-mobilization. Vitality of the dominant bryophyte Sphagnum palustre, however, was not affected. Low water tables affected neither vegetation, nor biogeochemistry, showing resistance to short-term drought in these fens.Given the strong mediating effect of soil chemistry, risks and benefits of re-establishment of fluctuating water levels with clean or P-rich water need to be considered for different fen types separately in water and nature management.

Production and destruction processes in peatland ecosystems of Vasyugan region

В статье приведены результаты изучения продукционно-деструкционных процессов в болотных экосистемах южной тайги Западной Сибири. Запасы живой фитомассы высоки и колеблются в пределах от 860 до 1710 гС/м 2. Образовавшееся в течение вегетационного сезона растительное вещество в первый год теряет при разложении от 8 до 27% от чистой первичной продукции, что составляет от 14 до 106 гС/м 2 в зависимости от типа экосистемы, чем выше продукция, тем быстрее скорость разложения. Для дальнейшей деструкции и перехода в торф остается до 420 гС/м .2 растительного вещества в богатых продуктивных болотных экосистемах рямов и мезотрофных топей и всего 140 гС/м 2 в бедных олиготрофных мочажинах.

Impacts of water level fluctuation on mesotrophic rich fens: acidification vs. eutrophication

Summary 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. 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. 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 base‐rich water. 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. 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.

Ecology of Testate Amoebae from Mires in the Central Rhodope Mountains, Greece and Development of a Transfer Function for Palaeohydrological Reconstruction

Testate amoebae are useful environmental indicators in ecological and palaeoecological studies from peatlands. Previous quantitative studies have focused on the peatlands of Northern and Central Europe, North America, and New Zealand and have considered a relatively restricted variety of peatland types, mostly ombrotrophic or Sphagnum-dominated while more minerotrophic fens have been less studied. Here we present the first quantitative ecological study of testate amoebae from four small mesotrophic fens (pH 5.5-8.1) in the Elatia Forest, northern Macedonia province, Greece. Relationships with the environmental data were investigated using redundancy analysis and mantel tests. Transfer function models were derived using a variety of techniques. Results demonstrate that as for Sphagnum-dominated mires hydrology is the most important control on amoebae community composition. Transfer function models should enable water tables to be predicted within 2.5 cm, when data selection is used this is reduced to less than 2 cm. pH is also an important environmental control on testate amoebae communities, a transfer function model enables pH prediction within 0.4 pH units. The hydrological transfer function is the best performing such model yet produced in terms of prediction error. This study provides new data on the ecology of testate amoebae in fens, and the transfer function models should allow quantitative palaeohydrological reconstruction.

Phosphorus Retention at the Redox Interface of Peatlands Adjacent to Surface Waters in Northeast Germany

It is demanded currently in public discussions to rewet peatlands and re-establish their function as nutrient sinks. But due to high phosphorus (P) concentrations in the pore water of rewetted peatlands (40–420 μM) it is hypothesized that they can act as a surplus P source for adjacent surface waters and consequently support the eutrophication of such waters. Our detailed investigations of processes at the redox interface in four fens with different geochemical character show the dependence of P retention from the chemistry of the pore water. The precipitation of Fe(III) oxyhydroxide led to high retention of phosphorus and other substances such as DOC and sulphate in the eutrophic fens. When molar Fe/P ratios were larger than about 3 the initially high P concentrations in the anaerobic pore water (20–210 μM) decreased to concentrations below 1 μM under aerobic conditions. Thus, after rewetting high pore water concentrations of P do not automatically result in an increased P load to adjacent surface waters compared to pre-rewetting conditions. An enhanced P export to adjacent surface waters from eutrophic fens can be expected when the Fe/P ratio is smaller than 3 in the anaerobic pore water. In our investigations of natural, oligotrophic to mesotrophic fens the precipitation of Fe(III) oxyhydroxide was inhibited by the formation of stable dissolved Fe ∼ humic complexes. P retention in these fens was only related to the DOC concentrations at the redox interface, so that lower DOC concentrations concurred with higher P retention. The P equilibrium concentrations in an aerobic environment can be higher than that of eutrophic fens with Fe/P ratios larger than about 3 in the anaerobic pore water.

Decomposition of Carex and Sphagnum litter in two mesotrophic fens differing in dominant plant species

Peatlands can be classified into fens and bogs based on their hydrology. Development of fens to bogs is accompanied by the invasion of Sphagnum species. The purpose of this study was to determine how the decomposition process in fens is influenced by the transition from a vascular plant‐dominated system to a Sphagnum‐dominated system. We carried out a reciprocal litter bag experiment, using litter of Carex diandra, C. lasiocarpa, Sphagnum papillosum and S. squarrosum in a fen dominated by Sphagnum species and a fen without Sphagnum. Decomposition rate and nitrogen and phosphorus dynamics of the plant litter were measured in a field experiment for two years. Decomposition rate was highest for the Carex litter types and lowest for the Sphagnum litter types. Surprisingly, decomposition rates hardly differed between the two sites. Nutrient dynamics, however, showed a clear site‐effect: In the Sphagnum site net mineralization was observed for all litter types whereas in the Carex site net immobilization was observed. These results show that carbon and nutrient cycles were coupled in a different way in a Sphagnum‐dominated and a Carex‐dominated site, respectively. Nutrient availability and adaptation of the microbial community to nutritional and other environmental conditions may be the main regulators of carbon and nutrient cycles in these peatlands.

Effects of light competition and litter on the performance of Viola palustris and on species composition and diversity of an abandoned fen meadow

Theeffects of light competition and litter on seedling recruitment and theperformance of established individuals were examined in Violapalustris. This polycarpic perennial plant was a common component ofspecies-rich fen meadows in northwestern Germany until the middle of thiscentury, but today is considered to be regionally endangered. From summer 1996until summer 1998 a bi-factorial field experiment combining three standing croptreatments (mowing, thinning, control) with two litter layer treatments (litterremoval, no litter removal) was carried out in an abandoned fen meadow toinvestigate the effects of these factors both on V.palustris and on aboveground species composition and diversity.MANOVAs (multivariate analysis of variance) revealed significant treatmenteffects for the performance of V. palustris related toexperimental manipulation. Mowing increased vital attributes including thenumber of rosette leaves, the percentage of individuals with chasmogamous andcleistogamous flowers and the number of rhizomes. In contrast, the length of theleafstalk, mean leaf area and the length of rhizomes were negatively associatedwith mowing. Litter removal significantly increased the number of V.palustris seedlings. The removal of the litter layer already resultedin an increase in aboveground species richness in the first year of theexperiment. After three years of experimental manipulation, both abovegroundspecies richness and diversity were positively associated with mowing.Redundancy Analysis showed that typical wet meadow species (Cardaminepratensis, Lychnis flos-cuculi, Lotuspedunculatus) and species of mesotrophic fens (Violapalustris, Agrostis canina, Potentillapalustris) were positively influenced by mowing. It can be concludedthat V. palustris recruitment and growth is promoted by aregular disturbance regime on fen meadows. The conservation of many typicalspecies of wet meadows and fens in northwestern Germany depends on moderategrazing or cutting. These management types prevent successional changes whichlead to an increase in standing crop and the development of a litter layer, bothof which can cause local extinction.

An overview of the Drepanocladus sendtneri complex

The Drepanocladus sendtneri (Schimp. ex H. Müll.) Warnst. complex is revised. Due to much overlap in characters traditionally used to separate taxa within this complex, characters that have not been used in this group before are evaluated. Four species are recognised, Drepanocladus sordidus (C. Müll.) Hedenas, (Hypnum sordidum C. Müll.; syn. D. tenuinervis T. Kop.), occurring in Eurasia and the Americas, D. sendtneri, known from Eurasia and southern Africa, D. brachiatus (Mitt.) Dix., an Australian-New Zealand endemic, and D. latinervis Warnst., known from the arctic parts of Asia and North America. Drepanocladus brachiatus differs from the other three species in being autoicous rather than dioicous, and by always having a relatively low nerve width/leaf length ratio. In addition, it differs from D. sordidus and D. sendtneri in having a 3(−4)-stratose rather than (3−)4–5(−6) stratose nerve. Drepanocladus latinervis differs from the other species by its high median leaf lamina cell length (μm)/leaf length (mm) ratio (37.6–45.6), and the five specimens seen so far were all small (stem leaves 1.1–2.2 mm long). Drepanocladus sordidus and D. sendtneri are the two species most similar to each other. In D. sordidus, the ratio between the median leaf lamina cell length (μm) and the leaf length (mm) has values between 23.3–36.5, and the ratio between median leaf lamina cell width (μm) and leaf length (mm) has values between 1.9–5.9. In D. sendtneri the corresponding values are 17.9–24.4 and 1.5–4.2, respectively. Drepanocladus sendtneri is a species of strongly calcareous wetland habitats, that in some cases dry out temporarily during dry periods, whereas D. sordidus occurs in less mineral-rich wetland habitats, such as mesotrophic fens, or submerged in mesotrophic lakes. The habitats of D. brachiatus and D. latinervis are insufficiently known.

NUTRITIONAL AND PLANT-MEDIATED CONTROLS ON LEAF LITTER DECOMPOSITION OFCAREXSPECIES

We studied the effects of experimentally induced variation in leaf litter chemistry on leaf litter decomposition and leaf litter nutrient release of Carex species from habitats that differ in nutrient availability. Carex diandra, C. rostrata, and C. lasiocarpa are dominant in less productive mesotrophic fens, whereas C. acutiformis is dominant in more productive eutrophic fens. For each species, three types of litter were used: litter collected in the field (FLD); and litter from experimental populations grown at low (LN: 3.3 g N·m−2·yr−1) and high N supply (HN: 20.0 g N·m−2·yr−1). For all the litter chemistry parameters studied there were highly significant interactions between species and litter type. This implies that, due to differential plant-mediated controls on leaf litter chemistry, it is not always possible to predict changes in litter chemistry in response to increased nutrient supply. Litter decay was determined in a long-term (3 yr) field experiment using litter bags. The litter types of each species were incubated at their native growing sites. Contrary to what is generally found, the leaf litter decomposition rate of the species growing at the nutrient-poorest site (C. diandra) was higher than that of the species growing at the nutrient-richest site (C. acutiformis). Only for C. diandra and C. lasiocarpa was the decomposition rate of the litter from the HN treatment higher than that of the field litter. Thus, increased nutrient supply does not necessarily lead to higher litter decomposition rates. Nutrient controls on litter decay changed with time: initial litter decay (≤3 mo) was strongly controlled (high r2 values) by all P-related litter quality parameters, whereas long-term litter decay (>1 yr) was most strongly related with the phenolics : N ratio, the phenolics : P ratio, the lignin : N ratio, and the C:N ratio. Our data suggest that high levels of atmospheric N deposition, such as in the study area (The Netherlands), may lead to a relative shortage of P in the plant-derived substrates for bacteria and fungi. As a result, P-related litter chemistry parameters exert a strong influence on litter decay. Our data did not support the hypothesis that high-nutrient species increase nutrient cycling due to the production of easily decomposable litter with high rates of nutrient release. The leaf litter from Carex acutiformis, the species from the high-productivity fens, decomposed more slowly than that of the other species, immobilized more N and P and had a longer period of net N and P immobilization. However, this species has a higher litter production than the other species and thereby increases the rate of nutrient cycling. At the intraspecific level, increased nutrient supply led to lower amounts of immobilized N and P and faster N and P release from litter in most species, and thereby to a higher rate of nutrient cycling. This positive feedback between nutrient supply rate and the rate of nutrient cycling is reinforced by the increase in litter production in response to increased nutrient supply.

Changes in plant biomass in fens in the vechtplassen area, as related to nutrient enrichment

Species-rich floating fen ecosystems in former turf ponds in the western part of The Netherlands are subject to nitrogen enrichment because of high atmospheric N deposition (50 kg ha−1,Y−1,). and supply of polluted river water in dry summer periods. Further, some fens have become more influenced by rain water because downward seepage to the groundwater has increased due to hydrological alterations. This paper describes changes in plant biomass production by comparing seasonal maximum biomass values for 15 fen sites determined with standard procedures in 1981 and 1988. Fen sites in different polders showed different species composition, which is related to differences in hydrology and history of fen management among the polders. The ‘mid-succession’ fens (type 1) which are characteristically N-limited have shown a biomass increase in spite of the annual mowing regime, which shows that these fens are becoming enriched with nitrogen. There are indications that the role of phosphorus as a limiting factor increases in these fens, and that a shift of N-limited towards P-limited phanerogam growth occurs. This may bring these fens eventually in the ‘late-succession’ stage, as presently found in Het Hol (type 2). The fens in this stage are P-limited and have a different species composition. It was concluded that the mesotrophic fens in the Vechtplassen area, characterized by a species-rich vegetation, can only persist in their eutrophicated environment if they are located in a groundwater discharge area and if they are annually harvested in the summer. If all fens in the area, will eventually become P-limited it is expected that the species composition will change to a more uniform ’late-succession’ vegetation type.

Seasonal Allocation of Biomass and Nitrogen in Four Carex Species From Mesotrophic and Eutrophic Fens as Affected by Nitrogen Supply

1. Allocation of biomass and nitrogen were studied for 1 year in experimental populations of Carex diandra, C. rostrata and C. lasiocarpa (species from mesotrophic fens) and C. acutiformis (a species from eutrophic fens). These species were grown at two levels of N supply (3.3 and 20.0 g N m −2 year −1 , respectively). 2. At low N supply, total biomass did not differ between the species. At high N supply, the total biomass of C. lasiocarpa and C. acutiformis («high-productive species») significantly exceeded that of C. diandra and C. rostrata («low-productive species»)

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.

Dependency of local mesotrophic fens on a regional groundwater flow system in a poldered river plain in the Netherlands

The effect of regional, subregional and local groundwater flow systems on mesotrophic fen ecosystems was studied in the polders of the Vecht River plain that borders the Pleistocene ice-pushed moraine of Het Gooi. Variation in the vegetation and in the habitat factors (groundwater and peat soil) of fens depends whether or not the fens are connected to the outflow of the regional groundwater system. Changes in the regional groundwater flow system, caused by changes in the water management of the polders, are probably responsible for the deterioration of mesotrophic fens. Drastic measures will have to be taken to restore the hydrology on a regional scale if the mesotrophic fens are to be saved from extinction. Hydrological research that integrates the results of regional and local studies is essential if the ecology of fen ecosystems is to be understood.

Comparative emographic study of Carex rostrata stokes, C. diandra schrank and C. acutiformis EHRH. In fens of different nutrient status

A demographic study of dense populations of Carex rostrata Stokes, C. diandra Schrank and C. acutiformis Ehrh. was carried out during two growing seasons in fens of different nutrient status in The Netherlands. The first two species occur in mesotrophic fens and show above-ground biomass maxima between 100 and 350 g m −2, whereas C. acutiformis is found at more eutrophic sites and shows biomass maxima around 550 g m −2. Mean shoot densities (No. shoots m −2) ranged from 210 to 300 for C. rostrata, from 900 to 1700 for C. diandra and from 320 to 760 for C. acutiformis. Mean shoot turnover rates for the three species mentioned (expressed as new shoots formed per shoot present per year) were 1.19, 1,89 and 1.13, respectively, whereas the numbers of leaves produced per shoot per year were 12.4, 9.1 and 12.1. Differences in growth rate over the growing season were proportional to differences in maximum biomass. The total net production divided by the maximum biomass was 2.3 for C. rostrata and C. acutiformis, and 2.7 for C. diandra.

Bryophyte communities in mesotrophic fens in the Netherlands

Seven bryophyte and three vascular plant community types were described from eight small fens in the Vechtplassen area (prov. of Utrecht, the Netherlands). Clear relationships between the species composition of the bryophyte and vascular plant layer were found. The bryophyte species composition shows a gradual change from quaking fens dominated by Calliergon cordifolium to fens dominated by several species of Sphagnum. Fens dominated by C. cordifolium have relatively high pH and conductivity values and are strongly quaking, whereas fens dominated by Sphagnum have relatively low pH and conductivity values and the peat layer is continuous down to the bottom sediment. A comparison of the present‐day vegetation with an earlier successional scheme for this vegetation type (Segal 1966) indicates a raise in nutrient levels and a decrease in the amount of seepage water welling up at the sites, both due to human activities. We suggest that in early successional phases bryophytes react faster to these changes, whereas in later phases vascular plants react faster.

Nutrient dynamics in small mesotrophic fens surrounded by cultivated land : II. N and P accumulation in plant biomass in relation to the release of inorganic N and P in the peat soil.

Release of inorganic N and P in the organic soils of three small quaking fens in The Netherlands was studied by means of in situ incubation of the peat soil in plastic bottles. One of the fens had higher biomass production and lower species richness than the other two. The former fen is located in an area with downward groundwater percolation, whereas the latter fens are situated in an area of upward seepage of groundwater rich in calcium and bicarbonate.Mineralization of N proved to be slow in the low-productive fens, and 6 times faster in the highly productive fen. In the latter fen the amount of N mineralized during a certain period exceeded by far the amount accumulated in that period in the above-ground parts of the vegetation.The release of inorganic P was extremely slow in the two low-productive fens and rapid in the highly productive fen. The release rates were not related to the total P content of the soils. The slow P release in the low-productive fens may be due to the continuous inflow of groundwater rich in Ca, Al and Fe compounds.It can be concluded that the soil is a potentially large source of inorganic N and P in quaking fens. The importance of the soil versus other N and P sources is greater in nutrient-rich fens.

Ecological notes on Carex aquatilis communities

Carex aquatilis spp. aquatilis grows in mesotrophic fens and has a boreal circumpolar distribution. The species is most frequent in areas north of the 66° N line. In Europe the southern limits of its distribution is ca 53°N. Here Carex aqualitis is found in eutrophic flood plains. However, mesotrophic communities of C. aquatilis have been reported from these areas as well. Nowadays the peripheral populations in NW Europe appear to be relics of former mesotrophic communities which at present are under heavy pressure from human activities such as drainage and fertilizing. In the northern part of the Netherlands C. aquatilis stands are restricted to areas with a steady supply of cool groundwater. A decreased groundwater discharge has a negative influence on the development of inflorescences. It is expected that further interference with the hydrology will promote a further decline of the peripheral populations. The species will not be able to survive in drained, eutrophic, warmed up habitats.

Nutrient dynamics in small mesotrophic fens surrounded by cultivated land : I. Productivity and nutrient uptake by the vegetation in relation to the flow of eutrophicated ground water.

In a typical Dutch polder landscape the effects of nutrient transport from cultivated grassland to mesotrophic fen communities were studied. In a comparative approach, biomass production and nutrient (N, P and K) uptake were determined monthly in four fens and a hayfield differeing in productivity and species composition. The interstitial ground water was sampled every two weeks for determinations of inorganic nutrient concentrations.The differences in productivity between the fens were clearly reflected in the amount of N, P and K taken up in the above-ground vegetation. N and P proved to be limiting plant growth in the fens, whereas K was the main limiting factor in the hayfield. The ground water welling up from the sandy bottom into the fens proved to be rich in ammonia (3-5 ppm). There are strong indications that this continual seepage leads to a considerable input of N into the fens but not to a higher productivity, as the ammonia is absorbed by the lowermost peat layers covering the sand.At this moment, the differences in productivity between the fens must be caused by differences in the rates of mineralization of the superficial peat layer. The degree of fixation of the floating vegetation mat, determining whether or not low water levels lead to an aerated soil top layer, is important in this respect. Within a period of decades, however, the continuous inflow of ammonia may eventually cause an increase in the productivity and a change in the species composition of the fens.