In the northern hemisphere, variability in hydrological conditions was suggested to increase as a consequence of climate warming, which may result in longer droughts than the area has experienced before. Due to their predominately anoxic conditions, peatlands are expected to respond to changes in hydrological conditions, such as successive drying and rewetting periods. As peatlands are rich in organic matter, any major changes in water table may influence the decomposition of it. The hydrological conditions may also influence release of nutrients from peat profiles as well as affect their transport to downstream ecosystems. In our mesocosm experiment, artificial water table fluctuations in pristine peat profiles caused an increase in dissolved organic nitrogen (DON) and ammonium concentrations, while no response was found in drained peat profiles, although originating from the same peatland complex. 1. Introduction High latitudes are expected to experience considerable climatic warming during the 21st century [1]. As a response to climatic change, the position of the water table in boreal and subarctic peatlands will be modified [2], and heavy precipitation events and number of wet days are expected to increase in northern Europe [3]. Climate change predictions for northern Europe, and specifically for Finland, indicate an increase in precipitation by 5–40% and in air temperature by 2–7 degrees Celsius (°C) by the 2080s, depending on the climate model and scenario used [4]. Variation in hydrological processes in both space and time causes changes in nutrient transport from land to surface waters [5]. Modelling studies predict that plausible high climate change scenarios will increase the annual N fluxes in small, forested watersheds in Finland. Increase in 30 years in dissolved inorganic nitrogen can be as high as 25% [6]. Holmberg et al. [7] predicted that an increase in total nitrogen load in 40 years can be 26%. Studies concerning the effects of fluctuating water table on N compounds and their concentrations in soil water in peatlands are scarce. Even though anaerobic bacteria are involved in the nitrogen cycle in various ecosystems [8], N mineralization in peatlands is usually more effective in aerobic than in anaerobic conditions and not least in bogs [9]. Therefore, rewetting after a dry period brings an interesting aspect for understanding nutrient dynamics in a changing climate. Also at high latitudes, where annual rainfall is predicted to increase, there may be heavy rainfall events which follow exceptionally dry seasons. For example, in
References
[1]
M. C. Serreze and J. A. Francis, “The arctic amplification debate,” Climatic Change, vol. 76, no. 3-4, pp. 241–264, 2006.
[2]
J. Pastor, J. Solin, S. D. Bridgham et al., “Global warming and the export of dissolved organic carbon from boreal peatlands,” Oikos, vol. 100, no. 2, pp. 380–386, 2003.
[3]
E. Kjellstr？m, “Recent and future signatures of climate change in Europe,” Ambio, vol. 33, no. 4-5, pp. 193–198, 2004.
[4]
K. Jylh？, H. Tuomenvirta, and K. Ruosteenoja, “Climate change projections for Finland during the 21st century,” Boreal Environment Research, vol. 9, no. 2, pp. 127–152, 2004.
[5]
M. Stieglitz, J. Shaman, J. McNamara, V. Engel, J. Shanley, and G. W. Kling, “An approach to understanding hydrologic connectivity on the hillslope and the implications for nutrient transport,” Global Biogeochemical Cycles, vol. 17, no. 4, pp. 16–1, 2003.
[6]
K. Moore, E. Jennings, N. Allott et al., “Modelling the effects of climate change on the supply of inorganic nitrogen,” in The Impact of Climate Change on European Lakes, D. G. George, Ed., Aquatic Ecology Series 4, pp. 179–197, Springer Science+Business Media B.V., 2010.
[7]
M. Holmberg, M. Forsius, M. Starr, and M. Huttunen, “An application of artificial neural networks to carbon, nitrogen and phosphorus concentrations in three boreal streams and impacts of climate change,” Ecological Modelling, vol. 195, no. 1-2, pp. 51–60, 2006.
[8]
B.-L. Hu, L.-D. Shen, X.-Y. Xu, and P. Zheng, “Anaerobic ammonium oxidation (anammox) in different natural ecosystems,” Biochemical Society Transactions, vol. 39, no. 6, pp. 1811–1816, 2011.
[9]
S. D. Bridgham, K. Updegraff, and J. Pastor, “Carbon, nitrogen, and phosphorus mineralization in northern wetlands,” Ecology, vol. 79, no. 5, pp. 1545–1561, 1998.
[10]
K.-H. Knorr and C. Blodau, “Impact of experimental drought and rewetting on redox transformations and methanogenesis in mesocosms of a northern fen soil,” Soil Biology and Biochemistry, vol. 41, no. 6, pp. 1187–1198, 2009.
[11]
M. Reiche, A. H？drich, G. Lischeid, and K. Küscl, “Impact of manipulated drought and heavy rainfall events on peat mineralization processes and source-sink functions of an acidic fen,” Journal of Geophysical Research G, vol. 114, no. 2, Article ID G02021, 2009.
[12]
D. Zak and J. Gelbrecht, “The mobilisation of phosphorus, organic carbon and ammonium in the initial stage of fen rewetting (a case study from NE Germany),” Biogeochemistry, vol. 85, no. 2, pp. 141–151, 2007.
[13]
E. Ylitalo, Ed., Finnish Statistical Yearbook of Forestry, Finnish Forest Research Institute. Vammalan Kirjapaino Oy, Sastamala, Finland, 2010, Finnish.
[14]
S. Eurola, A. Huttunen, and K. Kukko-oja, Oulanka reports 14—Suokasvillisuusopa, University of Oulu, Oulanka Biological Station, Oulu, Finland, 1995, Finnish.
[15]
E. Lappalainen, C.-G. Stén, and J. H？iki？, Turvetutkimusten MaastO-Opas, Opas N:O 12, Geologian tutkimuskeskus, Espoo, Finland, 1984, Finnish.
[16]
Anonymous, SAS/STAT, 9.2 User's Guide, SAS Institute, Cary, NC, USA, 2008.
[17]
R. Clymo, “The Limits To Peat Bog Growth,” Philosophical Transactions of the Royal Society of London, vol. 303, no. 1117, pp. 605–654, 1984.
[18]
J. J. M. Geurts, A. J. P. Smolders, A. M. Banach, J. P. M. van de Graaf, J. G. M. Roelofs, and L. P. M. Lamers, “The interaction between decomposition, net N and P mineralization and their mobilization to the surface water in fens,” Water Research, vol. 44, no. 11, pp. 3487–3495, 2010.
[19]
D. J. Dowrick, S. Hughes, C. Freeman, M. A. Lock, B. Reynolds, and J. A. Hudson, “Nitrous oxide emissions from a gully mire in mid-Wales, UK, under simulated summer drought,” Biogeochemistry, vol. 44, no. 2, pp. 151–162, 1999.
[20]
J. J. Kieckbusch and J. Schrautzer, “Nitrogen and phosphorus dynamics of a re-wetted shallow-flooded peatland,” Science of the Total Environment, vol. 380, no. 1–3, pp. 3–12, 2007.
[21]
L. Arvola, M. J. J？rvinen, and I. Hakala, “Nutrient export from small boreal catchment areas: the influence of annual and seasonal hydrology,” in International Association of Theoretical and Applied Limnology—Proceedings, J. Jones, Ed., vol. 29, pp. 2031–2034, 2006.
[22]
K. Kalbitz and S. Geyer, “Different effects of peat degradation on dissolved organic carbon and nitrogen,” Organic Geochemistry, vol. 33, no. 3, pp. 319–326, 2002.
[23]
R. Cooper, V. Thoss, and H. Watson, “Factors influencing the release of dissolved organic carbon and dissolved forms of nitrogen from a small upland headwater during autumn runoff events,” Hydrological Processes, vol. 21, no. 5, pp. 622–633, 2007.
[24]
S. Glatzel, S. Lemke, and G. Gerold, “Short-term effects of an exceptionally hot and dry summer on decomposition of surface peat in a restored temperate bog,” European Journal of Soil Biology, vol. 42, no. 4, pp. 219–229, 2006.
