General changes in the Matsalu Bay reedbeds in this century and their present quality (Estonian SSR)

Aquatic Botany, 35 (1989) 111-120

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Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

GENERAL CHANGES IN THE MATSALU BAY R E E D B E D S IN THIS C E N T U R Y A N D THEIR P R E S E N T QUALITY (ESTONIAN SSR)

TIINA KSENOFONTOVA

Institute of Zoology and Botany of the Estonian SSR Academy of Sciences, Tartu 202400 (U.S.S.R.) (Accepted for publication 14 November 1988)

ABSTRACT Ksenofontova, T., 1989. General changes in the Matsalu Bay reedbeds in this century and their present quality (Estonian SSR). A quat. Bot.: 35:111-120. The slow but constant rise of the trophic level of natural waters in many places in Estonia (including the eastern part of Matsalu Bay) has brought about a considerable expansion of the area covered by reedbeds and abundant growth (increase of productivity) of hydrophytes. During one century the reedbed territory in the eastern part of Matsalu Bay has increased from 10 km 2 (1870) to 27 km 2 (1980) owing to man's activity (the pollution of natural waterbodies with nutrient elements) as well as the neotectonic uplift of the earth's crust. Today, communities with Phragmites australis (Cav.) Trin. ex Steudel, Scirpus lacustris L. and Typha angusti[olia L. cover about 99.5% of the reedbed area. Helophyte communities in the eastern part of Matsalu Bay function as biofilters, in which large quantities of organic matter, produced here and mineral particles, carried by rivers, have been accumulated in the course of time. The rise of the trophic level is accompanied by an increase in the thickness and length of P. australis shoots, together with their weakening. As a result, the quality of P. australis as a raw material for roofs and insulation mats has deteriorated.

GENERAL CHANGES IN REEDBEDS

According to the data of A. Miiemets (Institute of Zoology and Botany, Estonian SSR Academy of Sciences, unpublished data) and the results of enquiries carried out among the population, the general tendency observed in Estonian waterbodies, is the expansion of reedbed areas and the overgrowing of open water patches between helophyte communities during the last three decades. In coastal regions with populations of Ondatra zibethica L. (introduced into Estonia in 1947), the area of helophyte communities has decreased or in some places they even disappeared (N. Laanetu and A. M~iemets, personal communication). The expansion of reedbeds is connected with the eutrophi0304-3770/89/$03.50

© 1989 Elsevier Science Publishers B.V.

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cation of waterbodies, caused mainly by pollution (fertilization) from intensively used agricultural lands and large farms, and/or municipal sewage and waste waters from the food industry. In some places reedbeds have expanded as a result of stopping grazing on the banks of waterbodies (helophytes do not tolerate trampling and constant grazing). STUDY SITE

The shallow eutrophic Matsalu Bay (West Estonia, length 18 km, greatest width 6.5 km) forms the basic part of the Matsalu wetland, a protected area of international significance. Together the estuaries of the Kasari River and several smaller rivers in the eastern part of the bay form the largest territory in the Baltic region occupied by reedbeds (area 27 km2). The catchment area of the rivers flowing into the eastern part of Matsalu Bay is characterized by a sparse population and intensively used agricultural lands. A chain of islets and shoals separates the eastern part of the bay from its main part, blocking the movement of water and waves. The hydrographical and hydrochemical properties of Matsalu Bay, together with the results of chemical analyses of hydrosoils have been presented elsewhere (Ksenofontova, 1988). Figure 1 shows the location of the sites under study in the Kasari River estuary. Sites P1, P2 and P5 are situated within an old stand of Phragmites australis (Cav.) Trin. ex Steud. Sites P3 and P4 represent the invasion-stage community of P. australis along the bayside edge of reedbeds. Site S 1 is located in the middle of the Scirpus lacustris L. spp. lacustris stand bordering the lagoon among reedbeds. Site $2 in the bay, in the 0.7 ha invasion-stage stand of S. lacustris, is surrounded by open water. Site T1 represents the Typha angustifolia L. bed. Samples were collected as follows: Sites P2 and P3 in 1977; Sites P4 and P5 in 1978; Sites P1, S1, $2 and T1 in 1981 and 1982. METHODS

A detailed map of the reedbed vegetation of the eastern part of Matsalu Bay was drawn during 1979-1980. Aerial photographs and a set of transects {with length 26 mm) were used to determine the boundaries between communities. The characterization of P. australis stands was carried out according to the methods proposed for the international comparative study of the production biology of P. australis (Dykyjov~ et al., 1973 ). Samples were collected in summer at the time of early flowering. The above-ground shoots were cut above the surface of the soil usually from five 1-m 2 plots of one stand. The exact location of the plots was determined by random sampling among stands of 20X30 m. CHANGES IN THE EASTERN PART OF MATSALU BAY

According to the data of Kumari (1973), the territory occupied by reedbeds in the eastern part of Matsalu Bay could have comprised about 10 km 2 in 1870;

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ian S S R

I I I

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Fig. 1. Location of study sites in the eastern part of Matsalu Bay: P1, P2, P3, P4 and P5, Phragmites australis stands; S1 and $2, Scirpus lacustris spp. lacustris stands; T1, Typha angustifolia stand. by 1925 the area of estuarine reedbeds had increased to 15 km 2. In 1980, the territory of reedbed communities in the estuary of the Kasari River was registered as 23.5 km2; together with lagoons and inlets between the communities the total area is 27 km 2. Helophytes usually grow as monospecific stands. Phragmites australis appears to be dominant in 79.8% of the territory of reedbed communities, S. lacustris ssp. lacustris in 6.1%, S. lacustris ssp. tabernaemon-

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tani (C.C. Gmel. ) Syme in 2.6% and T. angustifolia in 7.4%. Stands where two or three out of the three mentioned species are co-dominants comprise 3.6% of the reedbed communities, while the communities of Scirpus maritimus L., Glyceria maxima (Hartm.) Holmb. or Acorus calamus L. grow only on 0.5% of this territory. During the present century the bay boundary of the reedbed cover has constantly been shifting towards open sea; the receding of reedbeds from the flood-plain side is generally slower and differs from region to region (Kumari, 1973; Paakspuu and KastepSld, 1985). The staff members of the Matsalu nature conservation area V. Paakspuu and J. Sibul have observed the following changes in the eastern part of Matsalu Bay during the last three decades. First, numerous former open-water patches between helophyte communities are growing over rapidly. Second, the abundance and biomass of submerged and floating-leaved plants occupying openwater areas between helophyte stands extending into the bay have increased significantly. Third, the height and the culm thickness of P. australis have increased and bent shoots are more frequent. The area of P. australis flattened by spring has also increased in comparison with earlier decades. These three complexes of phenomena have also been observed in other Estonian waterbodies. It has been proved that in the case of high quantities of available nitrogen and phosphorus the culms of P. australis become weaker, owing to the decrease in the proportion of sclerenchyma relative to parenchyma (Bornkamm et al., 1980; Sukopp and Markstein, 1981 ). There are several factors involved in the changes in the distribution and the physiognomy of the helophyte and aquatic plant communities in Matsalu. First, owing to the neotectonic uplift of the earth's crust the Matsalu Bay region is rising at about 2.5 mm year-1. Second, the vegetation cover of the estuary has been transformed as a result of dredging former stream beds and establishing new ones on the delta area of the Kasari River during 1927-1937. Before dredging, flooding occurred, not only in spring and autumn, but also in summer. The inundated area on the flood plain of the Kasari River is up to 40 km 2 (Kumari, 1973). During floods, significant amounts of matter, carried down by river water, are deposited on the flood plain. (According to Pork (1968) the composition of deposits on the flood plain within a range of 50-100 m from the river bed at the end of the 1950s contained annually 10-25 kg N, 12-27 kg K20, 4-7 kg P20~, 83-250 kg CaO and 45-82 kg MgO ha-1) In spring, when the effect of shading by tall plants is still weak, some 'of the dissolved nutrients carried by the water are absorbed by abundant algae (Pork, 1973 ). We assume that later, during summer and autumn, active absorbers of nutrients from water on the flood plain are non-photosynthesizing microorganisms, i.e. those which do not require light for existence. From the aspect of mineral cycling it is essential that on wet and inundated eutrophic and hypertrophic habitats denitrifying bacteria should release considerable quantities of nitrogen into the air (Etherington, 1983 ). After dredging the rivers during 1927-1937 the frequency

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and duration of floods fell considerably, the flood plain became drier, the amount of nutrients bound decreased and hay crops decreased. Consequently, the amounts of nutrients and mineral particles carried by water into the reedbeds and the bay have grown. Third, the concentration of mineral elements in the water of the rivers flowing into Matsalu Bay has risen during the last decades, caused mainly by fertilization from agriculture. Of importance also is the circumstance that during the first half of the century a part of the seston carried by rivers was deposited in storage lakes which have, as a rule, been abandoned in this region. Since the middle of the 1960s a great increase in the abundance and biomass of Cladophora glomerata (L.) Ktitz. (Chlorophyta), a species of eutrophic and hypertrophic waterbodies, has been observed in Matsalu Bay (Trei, 1982). On the flood plain adjacent to the river-bed the replacement of previous plant communities (baseline 1959) by new, more nitrophilous ones was registered in 1977 (Pork, 1981). The regularities of the location and temporal alternation of helophyte communities with different dominant species in the Kasari estuary, can be characterized as follows. On the gradually overgrowing flood-plain side of reedbeds there is a belt of P. australis relatively rich in species including Carex which comprises 20.3% of the whole area. Carex disticha Huds. and C. elata Bell. ex All. are the main subdominant species in these communities. At present, the stands of T. angustifolia and S. lacustris are, as a rule, distributed in places which were earlier occupied by lagoons between high helophyte stands. Hydrosoil drills showed that in several places the P. australis stands occurring there now were preceded by Typha and Scirpus stands. Scirpus lacustris spp. lacustris stands border stream beds and extend, together with Scirpus lacustris spp. tabernaemontani far into the open bay serving as outposts of the helophyte communities. Mixed communities were P. australis, S. lacustris or T. angustifolia appear as codominants (3.6% of the area of the helophyte communities) usually grow in places where reedbeds have spread only recently or where helophytes have been damaged by trampling: former river beds and lagoons, territories destroyed by caterpillar tractors during the stocking of reed for silage in the 1960s. In the S. lacustris stands growing on the territory adjacent to the open bay it is characteristic that Phragmites australis starts growing in the central older and sparser part of the circular stands of Scirpus. It is supposed that helophyte communities with several dominant species arise, first of all, in the course of the succession of communities, often on destroyed territories, and are usually relatively short-lived. QUANTITATIVE PARAMETERS CHARACTERIZING PHRAGMITES AUSTRALIS CLONES

The biomass of the above-ground parts of P. australis at the time of early flowering (about equal to the annual production of above-ground parts) for

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Sites P1-P5 were quite close, the average values were 1270-1515 g m -2 of dry mass; at the same time, the densities of various sites differed considerably. At Sites P4 and P5, the average values were 86 and 87 shoots m -2 and at Sites P1, P2 and P3 102-125 shoots m -2. The production values in the case of the above-ground parts of S. lacustris spp. lacustris and T. angustifolia communities also exceeded 1000 g m -2. At Sites P2-P5 all shoot heights were measured. The arithmetical means of generative shoot heights were in the range 2.853.33 m. The tallest shoot found in the Kasari estuary was 4.12-m long. The value of LAI (upper side of the leaf blade) at Site P4 determined with the weight method (Ross, 1975) was 4.39, and at Site P5 it was 4.54. Specific leaf weight (SLW) increased towards higher layers. At Site P4 the value of SLW in the layer 0.61-0.90 m from the hydrosoil surface was 0.48 g dm -2 and in the layer 3.01-3.30 m, 0.80 g dm -2. At Site P5 the corresponding values were 0.44 g dm -2 and 0.69 g dm -2. The N, P, K, Ca and ash contents of various parts of P. australis, and also several morphometrical shoot features are presented by Ksenofontova (1988). T HE ROLE OF REEDBEDS IN T H E MINERAL CYCLE OF T H E EASTERN PART OF MATSALU BAY

The majority of primary production in the reedbed communities of the Kasari estuary is supplied by helophytes. In places Lemnoidea (Lemna minor L., Spirodelapolyrhiza (L.) Schleid. ) occur abundantly while their production is, owing to the small size of the plants, insignificant in comparison with that of the helophytes (this is also supported by measurements carried out in Czechoslovakia: Kv~t and Husak, 1978). The inhibiting factor in the production of algae in helophyte communities is, first of all, the lack of light (Dokulil, 1973 ). Animals who feed on helophytes and destroy the plants while moving and nesting in the area, are Cygnus olor (J.F.Gmelin), Anser anser (L.) and Fulica atra L. (according to the data of T. KastepSld and V. Paakspuu (personal communication) the number of breeding pairs of these birds in the reedbed area during 1980-1986 were 40-66, 130-300 and 500-600, respectively), Alces alces (L.) (elk), Sus scrofa (L.) (wild pig), as well as young cattle on the grazing grounds at reedbed edges. The influence of these animals on the amount of helophyte phytomass (helophytes do not comprise the basic part of their ration ) and productivity is local and insignificant from the point of view of the size of the Kasari estuary. Phragmites australis in the Kasari estuary is infested to a great extent by Giraudiella inclusa (Frfld.) (Diptera, Cecidomyiidae ). For instance, at Site P2 88% of the green shoots ofP. australis revealed galls caused by this species (dry shoots, i.e. 22% of the total number of shoots, were not taken into account because the lack of galls on them). Adult specimens of G. inclusa have also been reported from the coast of Matsalu Bay (Vilbaste et al., 1985 ). In some places the aphid Hyalopterus pruni Geoffr. (Heteroptera, Aphididae) has been observed on the shoots of P. australis, while it was especially

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abundant and widespread in the extremely rainy summer of 1978. Microfungi from the genus Puccinia (Basidiomycota, Uredinales) have also been found on the shoots of P. australis. However, on the basis of the existing data the influence of the above-mentioned invertebrates and fungi on the productivity of helophytes is not great (Durska, 1970; Mook, 1971; Pintera, 1971 ). Of the species significantly affecting the growth of P. australis only Lipara lucens Meig. (Diptera, Chloropidae) has been reported from the Matsalu wetland: shoots damaged by the larvae of this fly have been found in insignificant amounts at the edges of the reedbed. Nearly all the mass of the above ground shoots produced by helophytes in the Kasari estuary annually will pass directly to the decomposers. It has been shown (Davis and van der Valk, 1983; Davis et al., 1983) that the microorganisms on the helophyte litter, poor in nitrogen and phosphorus, posses a great potential to bind these elements directly from the water. In shallow eutrophic waterbodies (supposedly also in the shallow eutrophic eastern part of Matsalu Bay) denitrification appears to be a macroprocess in helophyte communities. In this way, a large amount of nitrogen carried by water can be released back into the atmosphere (Etherington, 1983). As a result of the function of microorganisms and sedimentation of seston and nutrients the content of nitrogen and phosphorus in the fSrna of the accumulation zone of the Kasari estuary increases. Thus, in October the dead standing shoots of P. australis contain 0.52% N and 0.02% P of the dry mass, in July the shoots of the previous year which have stayed under water contain 1.42% N and 0.16% P of the dry mass. At Sites S1, P1, T1 and $2 the thickness of organic and mineral sediments in hydrosoils was registered. Sites S1 and P1 (Fig. 1) are situated at some distance from the river bed; clearly differentiated sand layers (with thickness of 2 and 6 cm, respectively), deposited here before the spreading of reedbed communities, lie under the peat layer Sites T1 and $2 were chosen not far from the inflows of one branch of the Kasari River and three smaller rivers. The thickness of sand, aleurite and pelite deposits at Site T1 is 54 cm, at Site $2 21 cm. Eastern, older reedbed stands are characterized by a thicker peat layer than younger stands: at Site S1 the thickness of the peat layer is 55 cm, at Site P1 42 cm, at Site T1 22 cm, at Site $2 the upper layer of 10 cm is formed by aleurite, pelite and fine sand, together with a small addition of organic matter. Although research has been very limited, it can be concluded on the basis of available data on the chemistry of the water flowing into the reedbed area and the water of the small inlets between reedbed stands (Porgasaar and Viik, 1982; J~irvekiilg, 1983) that during the vegetation period the quality of the water flowing through the reedbed stands in the Kasari estuary is improved to a considerable extent. In the helophyte communities of the eastern region of Matsalu Bay, a part of the mineral particles and organic seston carried by water is deposited, a part

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of the nutrient elements bound by higher plants and microorganisms is accumulated in organic sediments, while a part of the bound nitrogen is released into air in the denitrification process. Therefore, the amount of nutrient elements and seston carried by flowing water into the open bay is small. The present expansion and thickening of the reedbeds functioning as a biofilter in the eastern part of Matsalu Bay is the result of the natural overgrowing process, and the reaction to the rise of the trophic level of the waters flowing into the reedbed area.

USE OF PHRAGMITES AUSTRALIS IN BUILDING AND SMALL-SCALE INDUSTRY

At the beginning of the present century 70-80% of roofs in West Estonia and on Saaremaa and Muhu islands were covered with P. australis (Blumberg, 1934 ). The average duration of the southern side of P. australis roofs is 50-60 years, while the northern side lasts for over a hundred years. The popularity of P. australis roofs has recently grown, since they are durable and warm, look handsome and harmonize well with the rural landscape. Phragmites australis is a suitable material for covering curved surfaces and other complicated parts of roofs. In open-air museums in Estonia and Latvia many thatched roofs have been replaced by roofs made of P. australis which is now more available and does not spoil the general look of exhibition complexes. Phragmites australis has been and is used for making hotbed mats in gardening farms and for covering drainage pipes. From the 1930s to the early 1960s Matsalu P. australis was used for producing insulation building plates. At present the small-scale production of such plates is again under discussion. Phragmites australis for roof material should be even, 1.5 to 2-m high, thin and tough (see also the morphometric characteristics of P. australis above). This P. australis occurs in pure stands (containing as few other helophyte species as possible), which grow primarily on mineral soils (sandy or clayey soil). In order to get high-quality roof material P. australis stands were previously cut above-ground for several autumns so that the stand would grow thicker the following year, its shoots would be more even in height and thickness so that the raw material would not contain old low-quality shoots of the previous year. Phragmites australis of even height and thickness is also used for making woven mats. In connection with the rise of the trophic state of waterbodies the quality of P. australis as a material for roofs and woven mats has deteriorated (the strength of shoots has decreased; there has been an unfavourable increase in their length and thickness; different sized shoots grow together in one stand).

119 ACKNOWLEDGEMENTS

The author is indebted to her colleagues Dr. Aime M~iemets, Dr. V. Paakspuu, Dr. N. Laanetu and to the staff member of the Matsalu State Nature Protection Area J. Sibul for useful talks, to the late Dr. J. Vilbaste for the identification of insects, to Dr. A. Riipais for the identification of aphids and to Mrs. E. Jaigma for translating the manuscript into English.

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120 genes in the water of Matsalu Bay in 1979-1980). Loodusevaatlusi 1980, 1. (Nature Observations 1980, 1 ) Tallinn, pp. 166-177 (in Estonian, with English and Russian summaries). Pork, K., 1968. Flood-plain meadows on the lower reaches of the River Kasari. In: Trud5 gosudanstvennSh zapovednikov Estonskoi SSR. Valgus, Tallinn, pp. 41-55 (in Russian, with English summary). Pork, K., 1973. Kasari jSe alamjooksu luha taimestik (Vegetation of the flood plains in the lower course of the Kasari River). In: O. Renno (Editor). Matsalu maastik ja linnud (Landscape and Birds of Matsalu). Valgus, Tallin, pp. 40-59 (in Estonian, with English and Russian summaries ). Pork, K., 1981. Kasari luha taimkatte arengutendentse praegusajal (Present tendencies in the development of the plant cover of the Kasari flood plain). Loodusevaatlusi 1979, 1. (Nature Observations 1979, 1). Valgus, Tallinn, pp. 36-50 (in Estonian, with English and Russian summaries ). Ross, J.K., 1975. Radiation Regime and Structure of Plant Cover. Leningrad, 344 pp. (in Russian). Sukopp, H. and Markstein, B., 1981. Ver~inderungen von RShrichtbest~den und - - Pflanzen als Indikatoren von Gew~issernutzungen, dargestellt am Beispiel der Havel in Berlin (West). Limnologica, 13: 459-471. Trei, T., 1982. Cladophoraglomerata Matsalu lahes (Cladophoraglomerata in Matsalu Bay). Loodusevaatlusi 1980, 1 (Nature Observation 1980, 1 ). Valgus, Tallinn, pp. 144-152 (in Estonian, with English and Russian summaries ). Vilbaste, J., 1985. Matsalu m~gala maismaaselgrootud (Terrestrial invertebrates of the Matsalu wetland). In: E. Kumari (Editor). Matsalu-rahvusvahelise t~ihtsusega m~irgala (Matsalu - - a wetland of International Importance). Valgus, Tallinn, pp. 140-198, 190, 306 (in Estonian, with English and Russian summaries).