USING MACROZOOBENTHOS TO ASSESS THE ECOLOGICAL CONDITION OF THE STARZYC LAKE (NORTH-WEST POLAND)

In the summer of 2008–2009 species composition and quantity of macrozoobenthos in deposits samples collected with Ekman gripping device at 4 points of Starzyc Lake was studied. Lake Starzyc also called Chociwel is located in West Pomeranian Voivodeship and is adjacent to the town of Chociwel from South and South East of the city. In the collected material of the analysed lake macrozoobenthos organisms from the following classes were found: Oligochaeta, Hirudinea, Crustacea, Insecta and Bivalvia. The Insecta class was the most numerous one in respect of species found, including larvae of the following orders: Ephemeroptera ( Leptophlebia sp., Ephemera sp., Caenis macrura (Stephens)), Trichoptera (Limnephilidae, Leptoceridae, Cyrnus sp.) Diptera and Megaloptera ( Sialis lutaria L.). The density and biomass distribution in the analysed Starzyc Lake demonstrates the occurrence of unfavourable changes which may lead to eutrophication in the shallowest layers of the body reservoir and in the zone at the depth of 4.9 m. The littoral zone of the studied lake features high density and significant benthic fauna biomass with low values of PIE biodiversity index.

These alarming changes gave an impetus to taking suitable legal actions for the protection of water resources. European Union issued a series of regulations, the so-called "water directives", yet it recognized the need for introducing a coherent framework regulating the acts of law aimed at conservation of water resources in all EU member states [1-6, 9-17, 21-23, 36-40, 48-53].
Directive 2000/60/EC, the so-called Water Framework Directive (WFD), which entered into force in December 2000, constitutes such an integrated act of law [1-6, 9-17, 21-23, 36-40, 48-53]. The main objective of the WFD is providing access to good quality water to present and future generations as well as enabling the use of water by, inter alia, industry and agriculture, while simultaneously preserving and conserving the natural environment [6-17, 21-23, 36-40, 48-53].

EXPERIMENTAL
Lake Starzyc, also called Chociwel, is located in West Pomeranian Voivodeship and is adjacent to the town of Chociwel from South and South East of the city [28]. Starzyc is the second largest lake in the municipality of Chociwel. Has an area of 59.2 ha, its length is approximately 3000 m and the width of the average 200 m, its depth is 9 m. The Lake is located at 68 m above the sea level. flows through the settlements not Krąpiel River [28].
Research was carried out in the years 2008-2009, in the period from July. At the place of sampling pH was determined (Fig. 1). Benthic material (sediments) along with benthic fauna was collected with Ekman-Brige grab sampler (surface of 225 cm 2 ). Following that, the type of sediment and depth of the bottom were determined (Table 1). Benthic fauna was collected during two summer months from 6 sampling stations located in the littoral and profundal zone (altogether 4 samples).
The location of research stations resulted from tributary positions and water reservoir morphometry. At each station 2 sub-samples were collected.
The collected material was rinsed on a sieve with a mesh size of 0.5 mm and it was conserved in 4% formalin solution. Animals were segregated macroscopically and under a stereomicroscope (PZO make) into individual taxa, and their concentration was referenced to 1 m 2 of the surface of the lake bottom. Benthic fauna taxa collected from individual stations were weighted with an accuracy of 0.01 g after having been dried on filter paper. Fauna biomass was presented in grams of wet mass per 1 m 2 of the bottom. Dominance index (D) was calculated from the following formula: where: S(a) -is a sum of individuals belonging to taxon "a", S -is a total biomass of individuals of macrozoobenthos in all samples.
The dominance index and frequency values were interpreted in accordance with the criteria specified by Kasprzak and Niedbałe (1981).
PIE biodiversity index was determined through the application of the following formula: At work, particular attention has focused on a comparison of the two zones -litoral, profundal of the Starzyc Lake.

RESULTS AND DISCUSSION
The results of the Starzyc Lake are presented in Tables 1 to 7.
In the collected material of the analysed lake macrozoobenthos organisms from the following classes were found: Oligochaeta, Hirudinea, Crustacea, Insecta and Bivalvia. The Insecta class was the most numerous one with respect to the species found, including larvae of the following orders: Ephemeroptera (Leptophlebia sp., Ephemera sp., Caenis macrura (Stephens)), Trichoptera (Limnephilidae, Leptoceridae, Cyrnus sp.) Diptera and Megaloptera (Sialis lutaria L.), (details are presented in Tables 2 to 5).
Average concentration of total benthic fauna in the summer of 2008 in Starzyc Lake amounted to 685 ind.·m -2 , whereas average biomass -6.6 g mm /m 2 (Tables 4 and 6). The Oligochaeta, Hirudinea and the Chironomidae larvae were of the greatest significance in the littoral zone, constituting 92% of benthic fauna density, whereas only representatives of the Oligochaeta and the Chironomidae larvae were found in the profundal zone. Average concentration of total benthic fauna in the summer of 2009 in Starzyc Lake amounted to 694 ind.·m -2 , whereas average biomass -7.3 g mm /m 2 (Tables 5 and 6). The Oligochaeta, Hirudinea and the Chironomidae larvae were of the greatest significance in the littoral zone, constituting 94% of benthic fauna density, whereas only representatives of the Oligochaeta and the Chironomidae larvae were found in the profundal zone.
The study of 2008 in macrofauna frequency related to the benthic zone showed that the sand-eating Oligochaetes and the Chironomidae larvae (F = 100%) were the most commonly found, and they were categorized according to Tischler's classification as dominant species. Chironomus f.l. plumosus (F = 100%) were the dominant species among the Chironomidae larvae, while Procladius sp. and Chaoborus sp. are categorized as accessoric species.
The remaining identified species of benthic fauna were accidental species F = 25%.
In 2009 attendance related macrofauna test bed showed that the most common they were mudeating and larvae chironomids, oligochaeta (F = 100%), which consisted of Tischlera classification of the species is absolutely solid. Among larvae of Chironomidae the species is absolutely integral Explanation: F -Turnout.     Comparison of average density of benthic fauna in the studied lake to the studies of benthic fauna of selected lakes in north-western Poland shows substantial changes in the density of the analysed taxa (details are presented in Table 7). Against this background, Starzyc Lake features a significant macrozoobenthos density, since higher values were found only in Lakes Gardno, Lubowidzkie [43] and Krzynia Lake [23] (details are presented in Table 7).
In relation to other lakes, a large number of taxa occur in Starzyc Lake, however, as a result of its non-harmonic distribution, it does not translate into the value of PIE biodiversity index (details are presented in Tables 4 to 7).
On the basis of the summer analyses of macrozoobenthos studies in the lakes of northern and western Poland presented by Piór-Zasada 1997, Gostomczyk 2005, Obolewski 2006 conclusion arises that the Oligochaeta develops with high intensity in Starzyc Lake (details are presented in Tables 6 and 7).
The dominance of the Oligochaeta, the Chironomidae larvae and a high number of Chaoborus sp. in north-western Poland lakes demonstrates the eutrophication processes in those water bodies (details are presented in Tables 6 and 7).
The density and biomass distribution in the analysed Starzyc Lake demonstrates the occurrence of unfavourable changes which may lead to eutrophication in the shallowest layers of the body reservoir and in the zone at the depth of 4.9 m (details are presented in Tables 1 to 5). The littoral zone of the studied lake features high density and significant benthic fauna biomass with low values of PIE biodiversity index (details are presented in Tables 4 to 7). These conditions may have been caused by contamination inflow from the farming fields surrounding the lake as well as by intensive tourist traffic. Favourable trophic conditions in Starzyc Lake are found at the depth of 2.1 m, where high macrozoobenthos density and biomass are accompanied by the highest biodiversity index (details are presented in Tables 6 and 7).

CONCLUSION
During the summer stagnation the benthic fauna of Starzyc Lake was qualitatively poor, what constitutes a proof of its significant biological degradation.
The Oligochaeta dominated in the macrozoobenthos of the studied lake in respect of its density, while the Chironomidae larvae dominated in respect of wet mass. It is a situation typically found in eutrophicated water reservoirs.