Chair: Ellen Kracauer Hartig (ehartig@giss.nasa.gov)
M. Sondergaard - Climate change, organic matter production and wetland ecology.
The functioning of wetlands is like other ecosystems under the influence of multiple environmental stressors, where climate change may be or become one of the more prominent. Changes in temperature, precipitation and evapotranspiration will affect the hydrology of wetlands and consequently the load of organic and inorganic matter from the catchment. Furthermore, the continued increase in atmospheric CO2 will affect the quantity and quality of the autochthonous primary production as the photosynthesis of most submerged macrophytes and the emergent littoral vegetation (C3 plants) is limited by CO2. The exposure to the atmosphere makes the latter group of plants most suceptible for direct effects. Submersed macrophytes and phytoplankton are thought to be "protected" via the bicarbonate buffering system. The data on submersed macrophytes and phytoplankton with respect to CO2 acclimation are, however, more scarse and conflicting than for the emergent vegetation. Many plants, and most notably C3 plants, acclimate to increased CO2 by a down-regulation of the carboxylating enzyme Rubisco and an increased N use efficiency. On average a 14% reduction of nitrogen in plant tissue and a change in the resource allocation between above- and below-ground components have been found. One consequence of the increase in the above-ground C:N ratio is a reduction in the quality of plant tissue and a possible change in decomposition patterns and nutrient cycling. The changes in organic matter production and decomposition will be demonstrated in a climate change scenario and exemplified with results from experimental work in a sub-boreal lake exposed to 700 ppm CO2.
E.K. Hartig (ehartig@giss.nasa.gov), A.S. Kolker and V. Gornitz - Climate change impacts on saltmarsh morphology in Jamaica Bay, New York City.
As a consequence of global warming, coastal marshes of the northeastern United States may deteriorate due to inundation and erosion within the next few decades if vertical accretion fails to keep pace with sea level rise (SLR) and increased frequency of storm surges. As part of the U.S. National Assessment on Climate Change and Variability, protected marshes in Jamaica Bay, New York City, were analyzed using field observations, historic photographs and global climate models (GCMs). Monitoring of plant productivity, plant community, erosive events, and salt marsh morphology was initiated to develop indicators of local marsh instability. Exposed sites revealed eroding cliffs and ledges with both recently dislodged segments of fresh peat, and residual mounds. Current Spartina alterniflora productivity (1999) ranged from 750 to 1100 gm /m2. Aerial photograph interpretation suggests that selected marshes have diminished in size by 12% since 1959. Future SLR was projected using outputs from several GCMs coupled with data from local tide gauges. The GCM outputs indicated that marshes would need to accrete at rates ranging from 2.5mm/year up to 15mm/yr by 2090, in the worst case scenario, to accommodate future rates of SLR. Wetland policies that enhance opportunities for preservation, restoration, and inland migration, of marshes, may be effective in compensating marsh loss, and increasing climate change preparedness.
V. van Haesebroeck (vero@uia.ua.ac.be), D. Boeye and P. Meire - Ecological effects of climate change in a Belgian rich fen: a microcosm study.
Characterised by a slow growing, low productive, evergreen vegetation, rich fens are amongst the most species rich herbaceous vegetation types of Europe. Indications for changes in the soil chemistry of these groundwater depending ecosystems due to varying hydrology and their effects on the vegetation, formed the basis of this study of Global Change effects on rich fens. By means of microcosm experiments in which intact sods were subjected to artificial drought, the fen vegetation reaction on temporary drought induced acidification and increased P-availability, was observed. Regularly soil solution was sampled, changes in growth and distribution of different plant species were followed and small vegetation fractions were harvested to determine the plant nutrient content. At the end of the experiment, soil and total vegetation were analysed in detail. The results show that drought caused immediate acidification of the soil environment and induced changes in solubility of Ca and Mg (increased) and of Fe and Mn (decreased). After two growing seasons, acid tolerant species (Molinia caerulea) had expanded their growth, while acid intolerant species (Eleocharis quinqueflora) became much less abundant. Changes in plant height and nutrient content were also observed after the experiment. These results are now used to create a model that will make correct estimation of management effects in rich fens possible.
D. Ryder and P. Horwitz - Modeling peat growth and its response to environmental change in south-west Australian wetlands.
The distribution and development of peat soils in Australia have been poorly documented. Within Western Australia, conditions conducive to peat growth are geographically restricted and generally occur in coastal, forested landscapes. Current management regimes in this region such as prescription burning, land clearing and artificial drainage have the potential to alter rates of peat growth. This study quantifies carbon inputs (autochthonous and allochthonous) and losses (CO2 and CH4 ebullition) to construct a carbon budget for three peatlands in south-western Australia. A model of recent (decadal) and long-term (millennial) carbon accumulation is developed using empirical data from carbon budgets, peat bulk density and 14C/210Pb dated profiles. Manipulation of peatland carbon inputs and/or losses within the model to simulate changes in environmental conditions provide invaluable information for predicting the impact of natural and anthropogenic induced changes on peat growth. The low number of parameters and the compartmentalisation of inputs and losses allow this model to be used for examining peat-forming processes in many aquatic systems.
R.A. Chimner (chimner@lamar.colostate.edu) and D.J. Cooper - Using CENTURY model to simulate long-term carbon accumulation in fens.
Peatlands are important global carbon sinks, which are capable of carbon accumulation and sequestration for thousands of years. Despite the importance of peatlands to the global carbon cycle, no attempt has been made to develop an ecosystem model their carbon dynamics. The objective of this research was to evaluate if the CENTURY model could simulate long-term (up to 10,000 years) carbon accumulation in peatlands. CENTURY is an ecosystem model originally developed to simulate soil carbon dynamics in grasslands, but has been used successfully in many diverse ecosystems including, grasslands, temperate and tropical forests, arctic and agricultural sites. But CENTURY has not been tested for a peatland. CENTURY was successfully calibrated using cores from two fens, each with a large number of carbon dates, in the Colorado Rocky Mountains. Model calibration required adjusting nitrogen inputs to simulate net primary production and adjusting anaerobic decay parameters to allow for the low decay rates that occur in Colorado fens. Once calibrated, CENTURY was successful in predicting carbon accumulation in two other Colorado fens. The successful application of CENTURY to simulate long-term carbon accumulation in fens may allow us to better understand carbon accumulation processes and develop scenarios of carbon changes due to disturbances in peatlands.
M.A. Vile (melanie.a.vile.1@nd.edu), S.D. Bridgham, M. Novak and R.K. Wieder - The contribution of sulfate reduction to carbon cycling in Sphagnum dominated peatlands: a global comparison.
The importance of sulfate reduction to anaerobic carbon cycling in peatlands is unknown despite their importance in global carbon budgets. We determined the relative contribution of sulfate reduction to anaerobic carbon cycling in three peatlands representing extremes in atmospheric sulfur deposition ranging from 2 kg S /ha /yr in Alberta, Canada (BLB) to less than 25 kg S /ha /yr in Cervene, Czech Republic to more than 45 kg S /ha /yr in Ocean, Czech Republic. At all three sites, less than 1% of total anaerobic carbon cycled through methanogenesis. Between 50 and 90 % of total carbon production at Cervene and Ocean is due to sulfate reduction, respectively. Despite sulfate reduction contributing little to total carbon mineralization at BLB, carbon flow was greater through the sulfur pathway than through methanogenesis. These results suggest that we should: (1) focus less on methane production as a controlling variable in peatland soil carbon cycling, (2) focus more on sulfur cycling processes in those regions receiving high atmospheric sulfur loads, and (3) begin to focus on fermentation processes in regions receiving low atmospheric sulfur loads if we want to elucidate controls over carbon cycling in peatland ecosystems.
R. Niemi, S. Turtola and T. Holopainen - UV radiation effects on Sphagnum mosses and carbon fluxes of an oligotrophic fen in Central Finland.
UV-B radiation (280-320 nm) reaching earth is estimated to continue increasing in the future. Boreal peatlands are particularly susceptible to UV-B because of their openness and high latitude location. To learn whether UV-stress disturbs an oligotrophic fen ecosystem, we studied the physiology of three Sphagnum moss species, and CO2 and CH4 fluxes of peatland microcosms under control, UV-A and UV-B treatments with an open field lamp system adding 30% to the ambient UV-level. Sphagnum species varied in their response. Amount of UV-B absorbing compounds decreased significantly in S. angustifolium in both UV-A and UV-B treatments but increased in S. papillosum under enhanced UV-B. Chlorophyll a and carotenoid contents decreased slightly in S. papillosum. In S. magellanicum we found no effects on pigment contents but a significant increase in the leakage of calcium and magnesium out of the cells in UV-B treatment. We anticipate to reveal the actual sites of UV damage in an ultrastructural study, which is yet to be accomplished. At the microcosm level UV-B disturbed the carbon balance reducing photosynthesis, respiration and methane production. Our results suggest that enhanced UV-B radiation can alter the functioning of peatlands.
A.R. Aldous (ara4@cornell.edu) - Nitrogen translocation in Sphagnum mosses: response to atmospheric nitrogen deposition.
When plant production exceeds decomposition, peatlands are sinks for carbon and other plant tissue constituents such as nitrogen. The capacity of peatlands to be a net sink for nitrogen declines, however, as nitrogen translocation from senescent tissues to metabolic tissues increases, because nitrogen translocation decreases the amount of new nitrogen required for plant production. Nitrogen translocation has been well-studied for vascular plants with obvious seasonal phenology, but largely ignored for non-vascular bryophytes. Sphagnum mosses have previously been shown to translocate phosphorus and carbon from senescent tissues to the apical meristem. Here I present quantitative data on nitrogen translocation in Sphagnum mosses in bogs receiving different amounts of atmospheric nitrogen deposition. I compared nitrogen translocation in Sphagna in Maine bogs, where nitrogen deposition is low (0.3 g /m2 /year) to Adirondack bogs, where nitrogen deposition is high (1.4 g /m2 /year). I tested the hypothesis that nitrogen translocation is higher where atmospheric nitrogen deposition is lower, because more nitrogen would be required to fulfill plant tissue requirements where nitrogen is at more of a premium. I did not find any significant differences for nitrogen translocation among sites. However, as much as 50% of nitrogen requirements are met by translocated nitrogen. These results suggest that the capacity of bogs to act as nitrogen sinks is much less than previously assumed.
D.J. Nias (dnias@dlwc.nsw.gov.au) - Carbon sources in an Australian temporary floodplain wetland.
Stable isotope analysis was used to examine the sources and fates of carbon entering the food webs of a temporary floodplain wetland on the Goulburn River in Victoria, Australia. This wetland is typically characterised by a six-month dry and wet cycle, and is dominated during the wet phase by Potamogeton tricarinatus , Amphibromus fluitans, and River Redgum (Eucalyptus camaldulensis ), with an understorey of sedges and herbs. Stable isotope signatures for consumers in the aquatic phase spanned the range of aquatic and terrestrial vegetation, and the lack of distinct signatures amongst primary producers created significant uncertainty in determining original carbon sources. However, highly negative carbon signatures (Delta13C -38ä) of mainly grazing consumers suggested the presence of a depleted carbon source. Likely sources included algae (phytoplankton or epiphytes) or autotrophic bacteria. The aquatic food web probably utilises a mixture of algae, vascular plants and bacteria. The length of the wet-phase was found to have an important influence on the carbon signatures of aquatic macrophytes. During the wet-phase, carbon signatures for some aquatic macrophytes became depleted, whilst others became more enriched. Changing and overlapping isotope signatures suggests that highly dynamic aquatic habitats such as temporary floodplain wetlands may not be suitable for stable isotope analysis. Nevertheless, the stable isotope method proved useful for suggesting the existence of hitherto unknown carbon sources in these systems.
