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27BioClimLand, 2014 No. 2,4-14
UDC 58:574.46
Ob river floodplain mire
N.P. Mironycheva-Tokareva, E.K. Vishnyakova, N.P. Kosykh
Institute of Soil Science and Agrochemistry of SB RAS, (Novosibirsk, Russia) This work was done with financial support from a BIO-GEO-CLIM Mega-grant of the Ministry of Education and Science of the Russian Federation and Tomsk State University (No 14.B25.31.0001). The photos by Wulf Hahne, Grejfsvald University, Germany, are used in the paper.
Mires occupy 40% of the Ob river floodplain within the taiga zone. Their forming started about 8 or 9 thousand years ago. Floodplain mires are highly productive ecosystems. Total standing crop is 4.0 or 6.5 t*ha-1. Standing crop of living phytomass takes 50-60% of the total standing crop. The peak of living phytomass (4.5 t*ha-1) is registered in sedge-brownmoss fen, the minimum (4.3 t*ha-1) is in pine-shrub ridge. Net primary production (NPP) is 2.7 t*ha-1*yr-1 in sedge-brownmoss fen, it decreases to 2.0 t*ha-1*yr-1 in pine-shrub ridge. Above-ground production (ANP) takes 7-10% of NPP, below-ground production (BNP) is 75%, brown mosses production is 15-18%. Mass losses of litter have changed from 25 to 85% in the last two years depending on fraction and species. Brownmoss litter losses about a quarter during one-year decomposition. Herewith element losses are following: 90% for Na and K, 73% for Mg and 3% for Ca.
Keywords: floodplain mire, standing crop of phytomass, above-ground production, below-ground production, decomposition, element losses.
Introduction
Mires occupy about 35-40% of the Ob river floodplain within the taiga zone of Western Siberia. The Ob valley consists of 4 or 5 terraces formed during the Late Pleistocene and Holocene periods [1]. Peat layer of 5-8 m thick was formed in the Holocene and is deposited on the youngest terrace. Clay and silt layers occur inside the peat as a result of river flooding. Mire nutrient base are outlets of ground waters rich in calcium and moisture going into the floodplain from the higher valley levels. Additional water sources are spring river overflow and precipitation. Bed streams often play indirect role ponding local terrace water during the high water [2].
Under the long-term surface and ground overmoistening in the near-terrace flood-plain part and in the central part of depressions eutrophic peatlands are formed. Available radiocarbon dates show that the floodplain mires within the taiga zone started forming about 8 or 9 thousand years ago [3]. Distinct micro-relief is formed with sedge hummocks and mire herbs take a great part in the vegetation cover. In the mire near-terrace part open herb-reed community (Fig. 1), sedge-brownmoss fens and rich ridge-fen complexes are spread. Dwarf birch-sedge-brownmoss communities of high flooding are specific to the places of abundant ground water outlets. Birch-Carex cespi-
Figure 1. Herb-reed (Phragmites australis (Cav.) Trin. ex Steud.) community.
Figure 2. Vegetation communities of the Ob mire transect (Schipper et al., 2007): I -herb-reed community, II - bogbean-sedge-brownmoss fen, III - rich ridge-fen complex, IV - sedge-brownmoss fen, V - willow-sedge community.
1 2 3 4 5 6 7 KM
Figure 3. Vegetation communities and peat types of the Ob mire transect (Lapshina, 1987): I - herb-reed community, II - bogbean-sedge-brownmoss fen, III - rich ridge-fen complex, IV - sedge-brownmoss fen, V - willow-sedge community. Peat types: 1 - brownmoss peat, 2 - sedge radicel-brownmoss peat, 3 - wood peat, 4 - sedge radicel peat, 5 - wood-sedge radicel peat, 6 - sedge radicel eutrophic peat, 7 - clay.
Figure 4. Birch-shrub-sedge-brownmoss fen.
Figure 5. Location of the study area.
Figure 6. Bogbean (Menyanthes trifoliate L.) - brownmoss fen. Pine-shrub ridge with
birch is behind the fen. birch is behind the fen.
Figure 7. Sedge-brownmoss fen with Carex lasiocarpa Ehrh. and Cicuta virosa L.
Figure 8. Vegetation community with Carex appropinquata Schumach. and Typha latifolia L.
A B C
Figure 9. The Cyperaceae species: A - Carex rostrata Stokes, B -C.lasiocarpa Ehrh., C - C.chordorrhiza Ehrh.
ABC
Figure 10. The Orchidaceae species: A - Dactylorhiza incarnata (L.) Soo, B -Epipactis palustris (L.) Crantz, C - Herminium monorchis (L.) R. Br.
Figure 11. The brown mosses: A - Helodium blandowii (F.Weber & D.Mohr) Warnst., B - Drepanocladus aduncus (Hedw.) Warnst., C - Plagiomnium ellipticum (Brid.) T.J.Kop.
A
B
C
Figure 12. Mire herbs: A - Polemonium caeruleum L., B - Ranunculus lingua L., C - Lysimachia vulgaris L.
Figure 13. Pine-shrub ridge with birch.
Figure 14. Standing crop in rich ridge-fen complex.
tosa L. and birch-willow-C. cespitosa communities are spread in the central part of the mire. Stripe-shaped C. cespitosa communities bound mires on the side of near-bed bank (Fig. 2, 3, 4).
The transverse profile of the present floodplain surface is characterized with the highest marks at the mire terrace bottom, lower central part and slightly raised near-bed bank. As for mineral mire bed, it is on the level of the present river low water. Floodplain peat-lands are characterized with asymmetric peat body shifted towards the near-terrace part with maximum deposit thickness at the terrace bottom and its gradual decreasing towards the river bed. Asymmetry is also seen in the deposit stratigraphy in the peatland near-terrace, central and periphery (near-bed) parts [4].
The aim of the given investigation is to reveal the present state of the floodplain mire productivity and the peculiarities of standing crop distribution and structure within the taiga zone.
Study Sites, Sampling and Analyses
The study site is the Ob mire (56°30' N — 84°01' E). The mire stretches approximately 150 km along the Ob terrace in the northern part of its upper flow on the left bank near Melnikivo, Tomsk region. The mire system width fluctuates from 1 to 5 km (Fig. 5).
The vegetation of the Ob mire is a combination of rich sedge-brownmoss, bogbean-sedge-brownmoss (Fig. 6), shrub-sedge-brownmoss fens and stretched ridges with sparse trees. The ridges run parallel to the Ob river. Wide sedge-brownmoss fens occupy the most part of the Ob mire (Fig. 7). Dominating species of such communities are Car-ex lasiocarpa Ehrh., C.rostrata Stokes, Menyanthes trifoliate L. and Thelypteris palustris Schott. Thick hummocks of Carex appropinquata Schumach. and small sedges of Carex limosa L., C.diandra Schrank and C.chordorrhiza Ehrh. also occur (Fig. 8, 9). Orchids of Dactylorhiza incarnata (L.) Soo, Epipactispalustris (L.) Crantz and Herminium monorchis (L.) R. Br. play their role in fen vegetation diversity as well (Fig. 10).
Inflorescences of Cicuta virosa L. and Rumex aquaticus L. rarely rise above this vegetation cover. Brownmoss cover is mainly presented by Drepanocladus aduncus (Hedw.) Moenk., Helodium blandowii (F. Weber & D. Mohr) Warnst., Plagiomnium ellipticum (Brid.) T.J. Kop. and Bryum pseudotriquetrum (Hedw.) P. Gaertn., B. Mey. & Scherb. (Fig. 11). Brown mosses form round pillow-shaped hummocks of 30-50 cm diameter. Galiumpalustre L., G. uliginosum L., Parnassiapalustris L., Saxifraga hirculus L. and other small herbs grow above brownmoss surface. Schrubs of Betula fruticosa Pall., Salix ros-marinifolia L., S. cinerea L. and S. lapponum L. of 0.5-2.0 m high occur among the fens. Here and there Betula nana L. grows thicker. Lysimachia vulgaris L., Naumburgia thyrsi-flora (L.) Rchb., Cicuta virosa, Polemonium caeruleum L., Ranunculus lingua L. and Rumex aquaticus L. occur sporadically (Fig. 12). While going towards the river bed the fens change their aspect. Abundance of shrub willows and birch increases forming thickets in the near-bed mire part. In the herb tier sedge hummock Carex appropinquata and C. cespitosa take greater part and Phragmites australis (Cav.) Trin. ex Steud. appears as well (Fig. 1, 8).
The ridges of 250-300 m long and 5-7 m wide rise to 50-80 cm over fens with distance 300-500 m from one ridge to another making several rows from the near-terrace flood-plain part to the river bed (Fig. 2). First Pinus sylvestris L. and Picea obovata Ledeb. with addition of Betulapubescens Ehrh. dominate in the ridge wood tier (Fig. 13). While going from the terrace, conifers on the ridges gradually change to birch. The distinct ridge shrub
Figure 15. Net primary production (NPP) in rich ridge-fen complex: ANP - above ground production, BNP - below ground production
Figure 16. Litter decomposition over two years in sedge-brownmoss fen: 1 - leaf litter, 2 - roots and rhizomes, 3 - brownmoss litter.
Figure 17. Element losses are during litter decomposition in sedge-brownmoss fen over one year: total circle is initial element content (100%), white sector is percentage of element loss, gray sector is percentage of element remain. 1a - leaf litter of Carex lasiocarpa, 1b - roots and rhizomes of Carex lasiocarpa, 2a - leaf litter of Menyanthes trifoliata, 2b - roots and rhizomes of Menyanthes trifoliata.
tier in the near-terrace mire part is presented with Lonicera pallasii Ledeb., Ribes hispidu-lum (Jancz.) Pojark. and Rosa acicularis Lindl. and on the ridges more distant from the terrace it is presented with shrub willows. The ridge herb cover under coniferous canopy is presented with taiga small herbs of Maianthemum bifolium (L.) F.W. Schmidt, Moeh-ringia lateriflora (L.) Fenzl, Pyrola rotundifolia L. and Poa palustris L. On the ridges with birch domination in the wood tier small herbs change to mire vegetation of Menyanthes trifoliata, Thelypterispalustris, Equisetum fluviatile L. and different sedge species.
Results
Standing crop of phytomass and net primary production
During two vegetation periods standing crop of phytomass and structure were assessed for sedge-brownmoss fen and pine-shrub ridge. The wood tier was not considered and the below-ground phytomass was assessed in the layer 0-20 cm.
Phytomass division into above-ground and below-ground layers for mires is generally done on moss cover. Above-ground phytomass only takes 10% of total standing crop. The brownmoss cover structure of fen is rather complex. Thick brown mosses hummocks have slightly prominent surface and are consist mostly of some species [5].
First 3-5 cm deeper from the brownmoss hummock surface are occupied with a pho-tosynthetic layer. Brownmoss litter, i.e. moss dead parts keeping their structure are located lower. Brownmoss litter is the substrate where vascular plant roots grow. Brownmoss amount decreases at 20 cm lower. Below-ground parts of herbs and shrubs are presented with the following fractions: roots, rhizomes, sedge stem bases and shrub stems. Living below-ground parts of vascular plants are mostly concentrated within 0-30 cm. Roots and rhizomes of sedges, ferns and some other plants form something like quagmire on densely interlacing. Dead roots share increases sharply at 30-cm depth.
The horizon of 20-40 cm has more friable structure than the upper and lower horizons. At this depth a whole system of hollows filled with mire water is formed. It is noteworthy that the peat deposited into this mire ecosystem mainly consists of sedge and fern root residues (radicel peat).
Standing phytomass in the described communities is unequally distributed. Total standing crop of living and dead phytomass is on average 6.5 t*ha-1 and fluctuates during vegetation season and from year to year in each phytocenosis. Living phytomass takes 50-60% of total standing crop. It gets greatest values of 4.5 t*ha-1 in the fen in the middle of the vegetation period (Fig. 14).
Net primary production of the fen is of 2.7 4.5 t*ha"1*yr"1 average (Fig. 15). The most important role in the fen structure belongs to herbs. Rich herbs cover that mainly consists of perennial plants gives on average 0.2 t*ha"1*yr"1 (7%) of above-ground production and 2.7 t*ha"1*yr"1 (74%) of below-ground production. Herb below-ground production is 10 times greater than the above-ground one.
The second in production value in fen phytocenosis is brownmoss tier. Brown mosses are more subjected to the influence of mire water level fluctuations than perennial plants. With a high level of mire water most part of moss hummocks are flooded and brownmoss production decreases to 0.3 t*ha"1*yr"1 while in low-flow years it can reach 0.6 t*ha"1*yr"1 (18%).
A quite different situation is observed in the pine-shrub ridge. Small taiga herbs grow under wood canopy. The ridge soil is a thick well-decomposed peat. Standing crop of liv-
ing phytomass reaches the greatest value of 4.3 t*ha-1 in July. Net primary production of 2.0 t*ha"1*yr"1 in the ridge is 25% less than that in the fen. The percentage of production compounds is similar to that of the fen. The largest part of 1.5 t*ha"1*yr"1 (75%) goes to below-ground production and the smallest one of 0.2 t*ha"1*yr"1 (10%) belongs to photosynthesizing phytomass fraction of vascular plants. 0.3 t*ha"1*yr"1 (15%) goes to brownmoss production (Fig. 14, 15).
Decomposition and element losses
Fen depositing of root peat is connected with high root production and incomplete root decomposition. Plant residues decomposition results from microorganisms and other soil invertebrates' activity. A complete decomposition is only possible under certain consecutive substitution of some microorganisms for other ones. The succession of plant residues mineralization is stipulated by nutrient elements available for the following groups and mainly depends on the plant chemical composition.
The investigation results of litter decomposition rate showed that bogbean leaves, roots and rhizomes were subjected more than other plants in sedge-brownmoss fen (Fig. 16). Bogbean litter losses of the mass were 75-85% over two years. The half of sedge root initial mass decomposed over two years. Sedge leave litter decomposed more (65% over two years). Betula nana leave litter, Thelypterispalustris litter and roots, brownmoss litter mass losses were about a third of their initial mass over two years [6]. In the following years herb leave litter and brownmoss litter decomposition continued at slow-down rate. A specific chemical composition of sedge and fern roots prevents their complete decomposition and contributes to radicel peat deposition (Fig. 3).
The rate of macroelements carry-over under plant residues decomposition decreases in K, Na, Mg and Ca row (Fig. 17). Bogbean roots and rhizomes have greatest losses in all four investigated elements - 92-99% of their initial amount. The lowest sodium losses are recorded for below-ground parts of Carex lasiocarpa (34%); the losses of the rest fractions are rather great and similar to potassium losses. The lowest magnesium losses of 22% under decomposition are revealed for Carex rostrata roots and rhizomes that are close to calcium losses of the fraction. Great magnesium loss of 73% is recorded for brownmoss litter. Calcium loss is less than other investigated macroelements and most fractions lose from 20% to 33%. The smallest calcium losses (3%) are recorded under brownmoss litter decomposition.
Conclusions
Global and regional ecological problems are often related to irreversible environment changes. The disorder in the flood regime of the Ob upper stream causes a decrease in nutrient elements' supply to fen ecosystems, which results in the changes in vegetation distribution over the profile from the terrace to the near-bed bank. Associated investigations of phytomass growing and peat accumulation processes in the floodplain mires enable us to reveal functional connections between certain structure blocks of biological cycle and their quantity characteristics.
Floodplain mires are highly productive ecosystems with a fast carbon cycle. Total standing crop of living and dead phytomass are 6.5 — 7.0 t*ha-1 average and vary during vegetative season and from year to year for each phytocenosis. Average standing crop of living and dead phytomass for the fen are 7.0 t*ha-1 and 14% less for the ridge that is 4.5 t*ha-1. Living phytomass takes 50-60% of the total standing crop. Floodplain mire stand-
ing crop of living phytomass change a little from 4.0 to 4.5 t*ha-1. It gets its maximum growth (4.5 t*ha-1) in the fen in the middle of vegetation period.
The average fen net primary production is of 2.7 t*ha"1*yr"1 and that of the ridges is 2.0 t*ha"1*yr"1 than for 25% less. Herbs play the most important role in the fen structure. Rich herbs cover that mainly consists of perennials plants gives on average 0.2 t*ha"1*yr"1 (7%) of the above-ground production and 2.7 t*ha"1*yr"1 (75%) of the below-ground one. The below-ground production is 10 times greater than that of above-ground. The second in production of the fen phytocenosis is brownmoss tier. Brown mosses are more subjected to fluctuations of mire water level than herbs. With a high level of mire water most part of hummocks are flooded and brownmoss tier production decreases to 0.3 t*ha"1*yr"1 while in low-flow years it can reach 0.6 t*ha"1*yr"1 (18%).
Decomposition goes very intensively in floodplain mire ecosystems, especially in the fen. Plant residues are completely mineralized over 2-3 years, except for roots. The greatest decomposing rate and macroelement losses are registered for all bogbean (Menyanthes trifoliata) fractions. A part of leave litter not decomposed over the first year is completely decomposed in the second one. The slowest decomposition rate is registered for fern (Thelypterispalustris) rots of 25% over two years. Brownmoss litter loses about a quarter of its initial mass in the first year decomposition process. Herewith elements losses are 90% for Na and K, 73% for Mg and 3% for Ca. Vascular plants lose about 40% of ash elements on average a year and brown mosses lose 15% of them.
References
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About
Mironycheva-Tokareva Nina P. — PhD, chief of laboratory of Biogeocenology, Institute of Soil Science and Agrochemistry, Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia. E-mail: [email protected]
Vishnyakova Evgenia K. — PhD, junior researcher, Institute of Soil Science and Agrochemistry, Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia. E-mail: zhenya1579@rambler. ru
Kosykh Natalya P. — PhD, senior researcher, Institute of Soil Science and Agrochemistry, Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia. E-mail: [email protected]
