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Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Coastal Erosion and Nutrient Balance of the Arctic
Vladimir S. Stolbovoi1
1Forestry Project, International Institute for Applied Systems Analysis, Schlossplatz 1 , Laxenburg, A-2363 , Austria, Phone +43-223-680-753, Fax +43-223-680-759, stolbov@iiasa.ac.at
Background: Siberian Russia belongs mainly to the Arctic basin. Natural processes, including alterations in climate and vegetation disturbances, drive the environmental changes in this huge area. This territory is poorly populated and sporadically used for mining minerals, oil and gas. Most of the territory has a mean annual temperature that is below 4-6oC, which coincides with the zone of sporadic and continuous permafrost. In spite of the projected warming in the future, climate conditions in the region remain too severe for agriculture and current land use is not expected to change.
Climate warming is thought to affect the permafrost and stimulate thermo abrasion of the costal zone. It is reported that on a global average nearly 85% of marine organic carbon (C) originates from the photosynthetic activity of phytoplankton, the remaining 15% comes from the land (Artemyev, 1996). A lot of observations have been done on the reverin discharge in Russia (Vinogradov et al., 1999; Romankevitch and Vetrov, 2001). Latest investigations have found that due to intensive thermo abrasion coastal sediment input into the Arctic is larger than globally observed and even exceeds that of rivers (MacDonald et al., 1998; Rachold et al., 2000). These observations contribute to understanding the marine biology of RussiaÅfs Arctic seas, e.g., relatively low biological activity and limited fish resources. However, to assess the effect of thermo abrasion a better knowledge of the biogeochemical land-ocean interactions and coastal environment is needed.
Objectives: The overall goal of the study is to describe the biogeochemical cycle of the coastal ecosystems along the Eurasian coastal line and to estimate the possible nutrient flux in the Arctic from coastal erosion.
Materials and Discussion: The study is mainly based on data from the CD-ROM “Land Resources of Russia” (Stolbovoi and McCallum, 2002). Among numerous land characteristics the latter contains spatially explicit databases on soils and their chemical composition, vegetation and C content in the phytomass fractions. Data on the Nitrogen content in vegetation and hydrochemistry of river transport is derived from a literature search.
The length of Russia’s segment of the Arctic coastal line is defined as approximately 40 000. Various subzones of the tundra dominate along this line, e.g., polar (13%), arctic (24%), northern (14%), and southern (16%). However, bogs (6%), northern taiga (5%), and halophytic meadows (3%) are insignificant. The C density in phytomass of the coastal ecosystems varies from 0.65 kg m-2 (average for the tundra) to 1.87 kg m-2 (average for forest tundra and northern taiga). The most widespread soils (30%) are Histosols (international FAO nomenclature) with shallow peat (about 0.3-0.5 m), and Histosols with deep peat (more than 0.5 m) occupy about 6% of the coastal zone. Histic Gleysols represent about 30% of the zone, whereby coarse textured Podzols (15%), Histic Fluvisols (10%) play a minor role. The share of Calcaric soil units is considerably less than 1%. The effective soil depth is about 0.5 m and is limited by shallow ground water, hard rock and permafrost. The average organic C density for topsoil (0.3 m) of the tundra biome is about 12 kg m-2; the forest-tundra and northern taiga comprise about 13 kg m-2 (Stolbovoi, 2002). The concentration of organic C in the topsoil of the coastal zone is much higher due to the dominance of Histosols (21 kg m-2) and Gleysols (18 kg m-2). The organic content in the topsoil of excessively drained Podzols is 6.7 kg m-2. The formation of the Histic horizon in the coastal zone soil is caused by cold climate, waterlogging, deteriorated decomposition rate and the quality of vegetation residues in recalcitrant compounds (moss, lichen, vascular plants, etc.). The total ecosystem C content (soil depth 0.5 m) in the coastal zone is approximately 10-12 kg m-2 for well-drained and 35-40 kg m-2 for poorly drained sites. The segments along the coastal line have very different soil-vegetation associations depending on the height above sea level, texture and mineralogy of parent materials, depth to ground water, permafrost, etc.
The littoral deposits contain some 3.8 million tons (about 1%) of organic and 4-5 million tons (about 1.5%) of inorganic C. These concentrations of C do not match the above-mentioned organic C pools of the coastal ecosystems that are subjected to degradation. Clearly, processes of coastal sea erosion are different from that of the terrain due to the excessive amount of water. The latter causes the separation of C substances on heavy and light weighted fractions. The heavy weighted fraction tends to deposit in the littoral zone, which comprises mainly minerals, including carbonates relatively accumulated in the sediments and some organo-mineral compounds. The latter are not common for permafrost-affected soils with a limited humification rate. This explains the relatively low concentration of organic C in the sediments. The light weighted fraction contains vegetation fresh tissues, raw underdecomposed residues, peat, etc., and floats on the surface of the sea. This fraction comprises up to 99% of the C pool of coastal ecosystems and is transported out of the coastal zone.
The contribution of shore abrasion to the organic C flux from the Eurasian continent to the Arctic Basin comprises about 20-25% (4-5 *106 t a-1) of river transport (about 23 *106 t a-1, Vinogradov et al., 1999). These data illustrate a relatively higher contribution of the coastal zone to the C balance of the Arctic. However, this role would be considerably more significant if the transport of the other essential nutrients was considered. As noted above, the materials delivered by coastal erosion consist mostly of the products of destruction of terrestrial ecosystems of the onshore zone, e.g., living vegetation and its dead residues, underdercomposed peat, soil humus, etc. These products are highly biologically active. For example, the concentration of nitrogen in organic matter transported by rivers is 2-3 times less than that of soil organic horizons and vegetation. Taking this difference into account, we estimate that contributing about 20-25% of C of the reverin discharge the coastal erosion supplies nearly half organic nitrogen. Clearly, degradation of the huge amount of low molecular weighted fresh and underdecomposed organic matter derived by coastal erosion requires a considerable amount of oxygen and seriously effects the nutrient budgets by releasing dissolved ions of Nitrogen and Phosphorus. The input of underdecomposed substances supports formation of anoxic water within the estuarine zone in which the bacterial activity and chemical processes drastically modify the speciation of some nutrients. All of the above-mentioned play a principal role in ocean biogeochemistry and biology, which is poorly understood at present.
Conclusions: (1) climate change is expected to accelerate the thermo abrasion of the Russian Arctic coast and will increase the transportation of vegetation residues and underdecomposed organic matter of soils with a high nutrient content; (2) the scenario is that an intensification of the supply of underdecomposed organic matter might increase the extent of anoxic water and deplete the biological activity in the ocean; and (3) the dynamics of the coast and associated ecosystems should be better understood so as to assess the magnitude of a possible change in the Arctic.
References
Artemyev, V. E. (1996). Geochemistry of organic matter in river-sea systems, Kluver Academic Publishers, Dordrecht, the Netherlands, 204.
MacDonald, R.W., Solomon, S.M., Cranston, R.E, Welch, N.E., Yunker, M.B., Gobiel, C. (1998). A sediment and organic carbon budget for the Canadian Beaufiort Shelf. Mar. Geol. 144, 255-273.
Rachold, V., M., Grigoriev, F., Are, S., Solomon, E., Reimnitz, H., Kassens, M., Antonov (2000). Coastal erosion vs riverine sediment discharge in the Arctic Shelf seas. Int. J. Earth Sciences 89, 450-460.
Romankevitch, E.A. and A.A., Vetrov (2001). Cycle of Carbon in the Russian Arctic Seas. Nauka, Moscow, 302 (in Russian).
Stolbovoi, V. (2002). Carbon in Russian soils. Climatic Change. 55, Issue 1-2, Kluver Academic Publishers, the Netherlands, 131-156.
Stolbovoi V. and I. McCallum (2002). CD-ROM “Land Resources of Russia”, International Institute for Applied Systems Analysis and the Russian Academy of Science, Laxenburg, Austria. Available at the: http://www.iiasa.ac.at/Research/FOR/.
Vinogradov, M.E., E.A., Romankevitch, A.A., Vetrov, V.I., Vedernikov (1998). Carbon cycle in the arctic seas of Russia. In: Carbon turnover on Russia territory (ed. G.A. Zavarzin), Moscow branch of SSRC WGD Ministry of Education of Russia, (in Russian).
Abstract Categories: Coastal Processes
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