THE SPECIES RICHNESS OF THE FLORA OF SELECTED SECTIONS OF THE MIETIU Ł KA RIVER IN THE POLESIE NATIONAL PARK

The aim of the study was to conduct an environmental evaluation of 6 selected sections of the improved Mietiułka River, which included an inventory and analysis of the vascular flora associated directly with this watercourse. The results of the study have shown that the flora of the study area is diverse in taxonomic, syntaxonomic and ecological terms, and that it comprises both typical aquatic plants and species characteristic of the habitats surrounding the river. In the flora found in the study sectors, a total of 114 vascular plant species was identified, which come from 42 botanical families, 15 syntaxonomic classes and belong to different ecological groups. Hemicryptophytes, spontaneophytes, species neutral to continentality as well as species included in the phytochorion with boreal elements: Euro-Siberian subelement, were clearly predominant in the species composition of the flora of all the study sectors. The macrophytes commonly found in Poland had the largest proportion. One species with a small number of stands in the country – water dropwort (Oenanthe fistulosa) – as well as two species threatened with extinction, Sagittaria sagittifolia and Hypochoeris glabra, were recorded.


INTRODUCTION
The Mietiułka River is a small, anthropogenically transformed watercourse, flowing through the northern part of the Polesie National Park (PNP).This river is situated on the eastern side of the watershed running through the Park (in the Bug River basin), and its catchment area is estimated to be 3,965.8ha.The river originates in the area of Pieszowola, right by the Park boundary, and it feeds into the Włodawka River upstream of Lake Wytyckie.The total length of the river within the Park is 9. Little direct information on the Mietiułka River itself can be found in literature.The typically anthropogenic nature of its channel is a result of land drainage improvements carried out in the second half of the 20th century (Ł o ś , 1992; 1995).The Mietiułka belongs to the rivers in which the banks have been levelled out and most of the river bank shrubs, which protect against overheating in the summer period and overcooling outside the growing season, have been removed (K o r n i j ó w , 1999).Due to the location of the river in a natural depression in the land surface and agricultural use of the area around the Park, the waters carried by the Mietiułka River are characterized by a high content of dietary minerals and anthropogenic substances, which has a negative effect on its natural values (J a n i e c , 1994; M i c h a l c z y k et al. 1999).
It was only in 1994 that the Mietiułka River, together with its adjacent area, was included in the Polesie National Park.Since that time, renaturalization work has been carried out, designed to gradually increase water storage and to improve the quality of the waters.The aim of these efforts is to create appropriate habitat conditions for different flora and fauna species in the river and within the area adjacent to the river channel (C h m i e l e w s k i and S i e l e w i c z , 1994; P i a s e c k i , 2005).
The aim of the presented pilot study was to conduct an environmental evaluation of 6 selected sections of the improved Mietiułka River, which included an inventory and analysis of the vascular flora associated directly with this watercourse.

MATERIALS AND METHODS
The pilot field study was carried out in May and July 2006 in the Polesie National Park.The study area covered the northern part of the Park, through which the Mietiułka River flows.
During the first stage of the field investigations, a site visit was conducted in the study area, which was designed to make a preliminary identification of vegetation cover and its variation along the studied watercourse.Subsequently, six study sectors were established (I -VI; Fig. 1), each with a length of 25 m.The selection of the location of the sectors was guided by the variation in the vegetation cover and the habitats bordering the investigated watercourse (Figs 2,3,4).
The status of the flora in particular study sectors was documented, by making and analysing species inventories.The plant species were identified using the key of R u t k o w s k i ( 2001).Botanical nomenclature followed M i r e k et al. (2002).The plant species present in the study sectors were assigned to syntaxonomic classes (M a t u s z k i e w i c z , 2001).In office investigations, Ekologiczne liczby wskaźnikowe roślin naczyniowych (Ecological indicator values of vascular plants) (Z a r z y c k i et al. 2002) was used to determine the proportion of species of different ecological groups, life forms and the degree of their endangerment.The species were assigned to historical-geographical groups and range groups according to C h m i e l (1993).Jaccard's formula (W y s o c k i and S i k o r s k i , 2002) was used to calculate the index of species similarity in the flora of the study sectors.

RESULTS
In the phytocoenoses of all the study sectors, a total of 114 vascular plant species was identified, representing 42 botanical families.The most numerous was the group of species from the families Poaceae (14 species) and Asteraceae (10 species).The greatest species richness of the vascular flora was noted in sectors I and II (47 species in each -52.8% of all the taxa).In sector I, Calluna vulgaris, Vicia cracca, Arrhenatherum elatius, Lysimachia vulgaris as well as Filipendula ulmaria occurred in greatest numbers.Carex rostrata, Equisetum fluviatile, Stratiotes aloides, and Lemna minor predominated in sector II (Table 1).
The lowest species richness was noted in sector IV (19 species), which was attributable to extensive shading of the surface of this sector's area by the forest neighbouring with the watercourse in question.There was noted a clear dominance of Urtica dioica on the slopes of the watercourse, as well as of Lemna minor and Spirodela polyrhiza in the water.
The species such as Elodea canadensis, Lemna minor, Filipendula ulmaria and Urtica dioica were found in all the study sectors.The species similarity index for the flora in most of the study sectors was low (between 0.09 and 0.38); only the phytocoenoses of sectors V and VI showed a significant similarity at a level of 0.57 (Table 2).
The species of the syntaxonomic class Molinio-Arrhenatheretea were clearly predominant in the species composition of the flora in sector I; this class had twice more representatives in this sector than the second ranking Phragmitetea.Almost a half of the taxa found in sector II belonged to the class Molinio-Arrhenatheretea.In sector III, the classes Phragmitetea and Molinio-Arrhenatheretea were represented in greatest numbers.The species of the class Lemnetea minoris had a large proportion in the phytocoenosis of this sector (11.8%), similarly in sector IV (10.5%).It was likewise in the case of the class Potametea (the proportion of the characteristics species in the flora of sector III -11.8%, in sector IV -21.1%).
In sector IV, the largest number of species was recorded from the class Potametea (21.1%).There were fewer representatives of the following classes (15.8% of each class): Phragmitetea, Molinio-Arrhenetheretea and Querco-Fagetea (with no clear dominance of the species of any of these classes).In sectors V and VI, the species characteristic of the classes Molinio-Arrhenetheretea and Phragmitetea clearly dominated.
The results of the analysis of the floristic composition and the proportions of particular species in the flora of the investigated sites did not allow an exact classification of the syntaxa to be made due to the absence of characteristic combinations of species.The associations of the aquatic macrophytes Lemno-Spirodeletum polyrhizae, encountered in sectors III, V and VI, were the only exception.
The analysis of the life-form spectrum of the flora showed that it was typical of this geographical zone.Hemicryptophytes (plants with perennating buds at the soil surface) clearly dominated in the species composition of the flora of all the sectors located on the Mietiułka River.Geophytes (plants with perennating buds lying in dry ground), together with hydrophytes and helophytes classified as cryptophytes (plants with perennating buds lying beneath the ground or submerged under water), accounted for a relatively small percentage of the taxa identified.The taxa belonging to phanerophytes (plants with perennating buds borne on aerial shoots) occurred only in three sectors, with the most numerous group noted in sector IV (Table 3) Few chamaephytes (plants with perennating buds borne close to the ground) occurred in five sectors, and the only recorded representative of woody chamaephytes was Calluna vulgaris.
In addition to the life-forms distinguished by Raunkiaer, with reference to the adaptation of plants to survive the unfavourable season (S z a f e r , 1964; F a l i ń s k a , 2004), the classification adopted for the purpose of the analysis (Z a r z y c k i et al. 2002) also comprised other groups, including semi-autrotrophs, the only representative of which is Melampyrum pratense (a species also belonging to the group of therophytes) found in sector II.The analysis of the flora of the study sectors as an indicator of continentality showed that the species neutral to continentality were by far predominant (Table 4).
Spontaneophytes, the species which arrived or are native to the area and can exist there without human intervention, had the largest proportion (88.6%) in the flora of the study area.Anthropophytes, synanthropic plant species of foreign origin in a given area, occurring both in secondary, artificial habitats formed as a result of human activity and in semi-natural or natural habitats, accounted for 5.3% of the studied flora (Table 3).
Based on the classification adopted by Chmiel (1993a), the plant species found in the study sectors   4).
In the phytocoenoses of all the study sectors, the macrophytes commonly found in Poland had the largest proportion.In sectors V and VI, one species with a small number of stands in the country -water dropwort (Oenanthe fistulosa; Table 5) -was recorded.In sectors IV, V and VI, the occurrence of Sagittaria sagittifolia was noted, whereas in sector I Hypochoeris glabra, species threatened with extinction (Z a r z yc k i et al.The number of stands and dynamic trends for the species comprising the flora of the studied sections of the Mietiułka River

DISCUSSION
The flora of the studied sections of the Mietiułka watercourse is diverse in terms of species as well as in syntaxonomic and ecological terms.It is a mixture of typically aquatic vegetation and vegetation characteristic of the habitats surrounding the river.The species identified in the study area account for 11% of the entire flora of the Polesie National Park (if we accept the total number of vascular plant species in the PNP following F i j a ł k o w s k i and I z d e b s k i ( 2002) -1027 taxa).The section of the river which is subjected to continuous human activity is characterized by the lowest floristic diversity, which can be attributable to the initial stage of secondary succession at which the vegetation of this area is.
The results of the study conducted in 2006 were confronted mainly with the results of the studies by B a n a c h et al. ( 2006) and B a n a c h (2007,2008,2009), who had analysed the species composition of the drainage ditches of the Polesie National Park.The nature of the habitats of the drainage ditches is comparable to the habitats formed by the Mietułka River, primarily due to its anthropogenic nature and the absence of a visible flow of water, rather its stagnation.
In the plant communities of the drainage ditches investigated in the years [2003][2004][2005][2006], in twelve 100 m long sections (1200 m), the occurrence of 222 higher plant species, belonging to 58 botanical families, was noted.The largest group comprised the species of the following families: Poaceae and Asteraceae, as well as Cyperaceae, Rosaceae and Fabaceae.
Among the macrophyte taxa identified in the flora of the studied sections of the Mietiułka watercourse, the botanical family Poaceae was also represented in greatest numbers, whereas in the western course of the river it was the family Asteraceae.From among the species recorded in all the sectors studied in 2006, 34 species were not found in any of the sections of the drainage ditches investigated by B a n a c h et al. ( 2006) and B a n a c h (2007,2009).
In the phytocoenoses of all the study sectors located both in the western and eastern part of the Mietiułka River, the taxa belonging to two syntaxonomic classes, Molinio-Arrhenatheretea and Phragmitetea, were predominant.The proportions of representatives of the other classes were relatively small and they varied.Similar proportions of the species of different syntaxa were documented by B a n a c h ( 2007) during her study of the phytocoenoses of the drainage ditches, as well as by S a w i c k a ( 2004) during her study of the plant communities found in the drained "Pociągi" nature sanctuary in the Polesie National Park.
U r b a n and R a d w a n (2000) noted a large proportion of the communities with a dominance of Glyceria fluitans and Glyceria notata as well as Leersia oryzoides in the drainage ditches and in other small water streams in the Łęczna-Włodawa Lakeland.In the study sectors situated on the Mietiułka River, no occurrence of the abovementioned species was noted at all, and B a n a c h (2007,2009) confirms the occurrence of only one of them in the plant associations of the drainage ditches of the PNP.
Ś w i ę s and W r z e s i e ń (2000) mention that the plant patches with the participation of Urtica dioica within the Park area are exceptionally commonly widespread on the slopes of the old canals and ditches.B a n a c h (2007,2009) confirmed these observations founding that common nettle occurred almost at all the study sites, forming more or less dense aggregations mainly on the slopes of the ditches.On the slopes of the Mietiułka River, the occurrence of this species was also recorded in all the study sectors, however, the most numerous population of Urtica dioica was observed in the watercourse section which had been subjected to the most intense improvements.The occurrence of this nitrophilous species in great abundance at the places where the river regulation works were carried out is caused by a large amount of nitrogen compounds which are released from extracted organic deposits (stored on the edges of the watercourse) undergoing the process of humification and mineralization.
Among the species identified, 19 species were noted in the study area as strongly or totally invasive species, similarly to common nettle (C h m i e l , 1993a).Elodea canadensis and Urtica dioica occurred in all the study sectors, and Potentilla anserina in five of them.
In order to evaluate the diversity of communities, the so-called biological spectra are used (the number of life forms and life strategies) (F a l i ń s k a , 2004).Among the plant life-forms occurring in the studied sections of the Mietiułka River, hemicryptophytesthe species characteristic of the temperate zone -dominated by far.The studies of B a n a c h (2007,2009) also indicated the dominance of this group in the habitats of the drainage ditches, and according to S z a f e r (1964), this group accounts for more than a half of the species found in the whole of Poland.The proportions of hydro-and helophytes as well as of therophytes in the investigated phytocoenoses of the eastern part of the Mietiułka River were higher than the proportions of these groups in the phytocoenoses of the western part studied in 2006.The abovementioned groups of species accounted for approx.24% of all the plant species inhabiting the drainage ditches of the Polesie National Park (B a n a c h , 2007; 2009).
The analysis of the flora of the Mietiułka River sections as well as of the drainage ditches and their neighbourhood (B a n a c h , 2007; 2009) as an indicator of continentality showed that the species neutral to continentality were by far predominant.They account for more than 90% of the flora of the studied habitats.
The qualitative and quantitative proportions of species belonging to different historical-geographical groups can be used as an indicator of the naturalness of the studied flora (C h m i e l , 1993a, 1993b).Spontaneophytes -the taxa which arrived or are native to the study area and can exist there without human intervention -had the largest proportion in the flora of the Mietiułka watercourse studied in 2006 (88.6% of species) and of the drainage ditches described by Banach (approx.90% of species; 2009).Anthropophytes -the species which were introduced in a given area and function there only by human activity, accounted for nearly 2% in the flora of the drainage ditches of the Polesie National Park, and in the investigated sections of the Mietiułka River their proportion in the flora was only slightly higher, since it was 5.3%.In spite of the fact that drainage ditches are a typically anthropogenic habitat, according to B a n a c h (2007), the lack of maintenance of the channels of the ditches and, in the first place, the establishment of the national park decided about the natural character of the flora of the studied habitats.But the Mietiułka River was significantly transformed by hydraulic works and it flows through the areas with different land uses, including agriculturally used land, hence the habitat differentiation promoting the persistence of both natural and synanthropic species.
The geographic distribution of species is primarily related to their tolerance to the variability of environmental factors in time and space (C h m i e l , 1993a).The Euro-Siberian species were the dominant range element of the flora of the studied sections of the Mietiułka River, likewise in the flora of the drainage ditches described from the same area located within the Polesie National Park (B a n a c h , 2007; 2009).
The floristically richest phytocoenoses are those functioning in the heterogeneous environments, since no species has an absolute dominance in them (F a l i ń s k a , 2004).Such a situation is observed in the habitats which are formed by the channel and slopes of the Mietiułka River.The favourable habitat conditions create advantageous conditions for the functioning of the diverse flora, in whose species composition rare and protected species can also be encountered.
25 km (C e b r y k o w et al. 2001; M i c h a l c z y k et al. 2002).
different plant life-forms and historical-geographical groups in the flora of the studied sections of the Mietiułka geographical (range) elements and groups of species with different continentality indicators in the flora of the study area Rating for the number of stands (

Fig. 4 .
Fig. 4. Sector VI -the mouth section of the Mietiułka River M i c h a l c z y k Z., B a r t o s z e w s k i S., C h m i e l S., D aw i d e k J., G ł o w a c k i S., Tu r c z y ń s k i M., 2002.Zasoby wodne Poleskiego Parku Narodowego.[In:] Poleski Park Narodowy.Monografia Przyrodnicza.S. Radwan (ed.).Wydawnictwo MORPOL, Lublin.M i c h a l c z y k Z., B a r t o s z e w s k i S., Tu r c z y ń s k i M., C h m i e l S., D a w i d e k J., G ł o w a c k i S., Z i e l i ń s k a B., 1999.Plan ochrony PPN.Operat ochrony zasobów i ekosystemów wodnych.Cz.I -Zasoby wodne.The Polesie National Park conservation plan.A conservation appraisal of water resources and aquatic systems.Part I -Water resources.Maszynopis w Poleskim Parku Narodowym.Warszawa (in Polish).M i r e k Z., P i ę k o ś -M i r k o w a H., Z a j ą c A., Z a j ą c M., 2002.Flowering Plants and Pteridophytes of Poland.A Checklist.W. Szafer Institute of Botany, Polish Academy of Science, Kraków.P i a s e c k i D., 2005.Historia powstania i 15 lat działalności Poleskiego Parku Narodowego.[In:] T. J. Chmielewski (ed.), 15 lat Poleskiego Parku Narodowego.Monografia.Wydawnictwo PPN, Warszawa, Lublin, Urszulin (in Polish).R u t k o w s k i B., 2001.Klucz do oznaczania roślin naczyniowych Polski niżowej.Państwowe Wydawnictwo Naukowe, Warszawa (in Polish).S a w i c k a A., 2004.Analiza zmian warunków hydrologicznych i środowiskowych na obiekcie "Łąki Pociągi" na obszarze Poleskiego Parku Narodowego.Praca magisterska.Maszynopis w Poleskim Parku Narodowym./ An analysis of the changes in the hydrological and environmental conditions at the "Pociągi Meadows" site in the Polesie National Park area.Master's thesis.The manuscript at the Polesie National Park.Warszawa (in Polish).S z a f e r W., 1964.Ogólna geografia roślin.Państwowe Wydawnictwo Naukowe, Warszawa (in Polish).Ś w i ę s F., W r z e s i e ń M., 2000.Ekosystemy synantropijne w Poleskim Parku Narodowym.[In:] S. Radwan, Z. Lorkiewicz (eds), Problemy ochrony i użytkowania obszarów wiejskich o dużych walorach przyrodniczych.Wydawnictwo UMCS, Lublin: 263-277 (in Polish).U r b a n D., R a d w a n S., 2000.Ekosystemy torfowiskowe.[In:] T. J. Chmielewski (ed.), Międzynarodowy Rezerwat Biosfery "Polesie Zachodnie".PPN, Lublin: 43-45 (in Polish).W y s o c k i C., S i k o r s k i P., 2002.Fitosocjologia stosowana.Wyd.SGGW, Warszawa (in Polish).Z a r z y c k i K., T r z c i ń s k a -T a c i k H., R ó ż a ń s k i W., S z e l ą g Z., W o ł e k J., K o r z e n i a k U., 2002.Ecological Indicator Values of Vascular Plants of Poland, W. Szafer Institute of Botany, Polish Academy of Science, Kraków.

Table 1
The species composition of the vascular flora of the phytocoenoses of particular study sectors