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A DORMANT FEN: The underestimated value of dead organic matter metabolism in wetland functioning and restoration Wojciech Puchalski A method of biogeochemical assessment Pracownia Natury - The Nature Laboratory ul. Sosnowa 8 PL-95-050 Konstantynów, POLAND Introduction The dormancy period in wetlands is usually considered unimportant in their metabolic balance and system biogeochemistry, hence only few research data exist and only data from the vegetation period are used for restoration planning. In early spring flows of water between upland areas, floodplain wetlands and rivers or lakes often are at their peak intensities. The quality of water from wetlands then affects algal blooms and macrophytes in water bodies, and indirectly other functions of the whole aquatic ecosystem. Examples are given how local hydrologic cons trains and plant species as a source of dead organic matter influence processes of oxygen consumption and nutrient uptake or release. Results are important for decisions concerning the water level and its dynamics. 1600 No add. +PO4 +NH4 +NO3 +Corg +CNP 1200 P-PO4 w P-PO4 d Contr. A simple assessment method has been developed. It is based on exposition of freshly collected material (sediments, algal/microbial mats, decaying plant debris) in water (preferably also taken from the site, or artificially prepared) in stoppered bottles during one day. Different bottles with the same material may be amended with higher nutrient concentrations, or a concentration gradient can be prepared. Control bottles contain only water, without any solid material. After exposition in temperature and light conditions resembling natural ones, nutrient uptake or release (negative values) are calculated from differences in nutrient amounts between sample and control bottles, divided by exposed material weights and exposition time. In the same set, differences in oxygen concentrations may be measured with an oxygen probe, and its consumption calculated. Also, by initial deoxygenation of water in bottles, anoxic conditions can be established. A short, one-day period of exposition produce no drastic changes in function of microbial communities. This appeared to be a rapid method of functional monitoring, suitable for assessment of important biogeochemical processes, where sediments, live plants or particular organic matter are involved. 2400 N-NO3 w N-NO3 d 2000 N-NH4 w N-NH4 d Examples of contrasting sediment types in a lowland floodplain 1200 800 1600 1200 800 400 800 400 400 0 s. fen imp. sedge fen Rn-A imp. Rn-A F-A imp. F-A s. fen imp. sedge fen Rn-A imp. Rn-A F-A imp. F-A 0 s. fen imp. sedge fen Rn-A imp. Rn-A F-A imp. F-A 0 Metabolic properties of sediments in different floodplain communities during early spring, in dry and wet years. Uptake pf phosphate, ammonia and nitrate in Fraxino-Alnetum, Ribeso nigri-Alnetum and a sedge fen, in nonimpounded and impounded reaches of the Skotawa river, N. Poland. 250 600 P-PO4 consumption 200 400 April June 150 700 N-NH4 consumption 600 June 200 500 June 400 300 0 -400 22-42 cattail, n+ reed, n- cattail, n+ reed, n+ cattail, n- reed, n- 1.5 coarse, n+ fine, n- coarse, n- coarse, n+ fine, n- Do eutrophic conditions may advance the nutrient release switch in spring? Recalculated data from Robinson & Gessner (2000): decay of alder (Alnus viridis) leaves in an alpine headwater stream The presence of emergent plant litter seems to be a necessary condition for germination and early development of a rare aquatic fern, Salvinia natans. Accumulation of plant debris after a flood enables abundant occurrence of this chaotic species. 14 14 14 birch pine oak 12 12 12 12 10 10 10 10 below reed belt 6 6 6 6 4 4 4 4 2 2 2 2 0 0 0 0 stems leaves reed stem prisms wet reed floor -20 -15 -10 -5 0 g.g-1.d-1 5 w 0 50 100 150 g k l w p 60 g k l p 60 alder w g k l 60 birch w p 40 40 40 40 reed stem prisms reed stem prisms 20 20 20 20 wet leaf zone wet leaf zone 0 0 0 0 w stems ref.: stems leaves ref.: g k l p w g k l p w g k l k l p pine high water level below reed belt g 60 oak high water level below reed belt water 22-42 below reed belt ref.: flooded sedim. 9-22 8 -25 15 0-9 8 -1 m.salv.dried days from start 8 -1 20 N uptake / release 8 g.g .d m.salv.lake 0 wet leaf zone wet reed floor 25 5 wet leaf zone reed stem prisms no.salv.dried 0.5 alder reed stem prisms stems leaves 30 10 20.00 10.00 0.00 -10.00 -20.00 -30.00 -40.00 -50.00 -60.00 high water level ref.: 35 no.salv.lake 1 14 reed stem prisms 2 dry reed wet reed wet reed wet seepage unflood. unflood. Glyceria sedim. sedim. Late spring: the switch from nutrient uptake to releasedepends on plant species and trophic conditions. (N- low trophy, n+ eutrophic conditions) The litter of emergent macrophytes, after its initial leaching in autumn, appears to be an important consumer of dissolved nutrients during early spring, when live plants are still dormant and nutrientrich waters of upland origin enter the floodplain. Dissolved nutrients are assimilated by decomposing microorganisms, as C:N and C:P ratios in plant debris are extremely high. With the progress of decomposition in late spring, previously absorbed nutrients become partially released, but this occurs during period of intensive development of macrophyte stands, which may use this available nutrient supply for their growth. Mechanical removal of plant litter during the end of nutrient uptake period in spring might serve as more effective way of exporting surplus nutrient load then removal of mowed sedge hay in summer. high water level 40 A250 lake 0 0 cattail, n+ reed, n+ cattail, n- reed, n- -2.00 coarse, n- 100 -800 45 A250 dried 9-22 no release reed, n+ release -150 plant litter added 2.5 -1.00 release -600 -100 0-9 50 fine sediments added -4.00 cattail, n- -50 200 3 -3.00 50 -200 3.5 days from start 0.00 100 0 P uptake / release 1.00 April Sulfur purple bacterial mat - highly reductive, denitrification, Fe and SO4 = reduction present Decomposing plant debris in spring 2.00 N-NO3 consumption April Diatom mat- oxidative, P-consuming, enabling nitrification w p -20 -20 -20 -20 -40 -40 -40 g k l p leaves reed stem prisms reed stem prisms -40 wet reed floor wet reed floor 12 -1 -1 g.g .d -1 -30 -20 -10 0 -1 g.g .d 10 forest bog 10 -50 0 50 100 Phosphate (upper graphs) and ammonia (lower graphs) uptake/release by reed litter in early spring, under low (left) and high (right) nutrient content, in littoral reed stands of Lake Kwiecko, N. Poland, characterized by frequent water level changes. forest ecot. 8 6 forest stream 4 agric. ecot. 2 0 w 200 150 C[P-PO4] +PO4 C[N-NO3] C[N-NH4] +NH4+ +DOM 100 150 C[P-PO4] 100 N upta ke P-PO 4 upt ake 50 50 0 0 2 4 6 8 10 12 14 16 -1 -50 -1 Oxygen consumption, mgO2.g .d 0 2 4 6 8 10 12 14 16 Oxygen consumption, mgO 2.g -1.d-1 agric. streaml k p Natural floodplains of rivers are characterized by a well developed mosaic of patches, where various redox values create conditions for different biogeochemical reactions and microbial processes. Distribution of such patches and intensity of their functions are much more stable than in low-order streams. This, in turn, create conditions for development of various plant species and communities, according to their specific environmental demands. -50 -100 0 g Oxygen consumption (upper graphs) and phosphate uptake (+) or release (-) (lower graphs) between autumn (fallout of leaves) and late summer next year. Differences are related not only to tree species, but also to aquatic habitat type where the decomposition of fallen leaves does occur. Mosaic floodplain structure enables a greater complexity of metabolic processes where coarse allochthonous organic matter is involved. -150 -200 Relationships between P, N and oxygen uptake P-PO4 uptake related to O2 consumption, intensities depend on availability of P and DOM. No clear pattern for nitrogen (both ammonia and nitrate) metabolizm Biogeochemical constrains should be considered in floodplain restoration or protection projects, when the maintenance or reintroduction of particular plant communities is desired. Also, these floodplain processes are important in nutrient transformations, their entrapment and storage or release to river water, thus regulating trophic conditions in the river channel and lakes or seas receiving riverine inflows. In low trophic conditions, nutrients are available from decomposition of last year's plant litter, which was enriched with nutrients during cold season. Optimising plant litter decay in spring may lead to establishment of healthy and stable emergent plant communities in floodplains.