Invertebrate differentiation in various microhabitats of small and medium lowland rivers

Transcription

1 The Functioning and Protection of Water Ecosystems R. Gołdyn, P. Klimaszyk, N. Kuczyńska-Kippen & R. Piotrowicz (eds) Department of Water Protection, Faculty of Biology, Adam Mickiewicz University, Poznań 2008 Invertebrate differentiation in various microhabitats of small and medium lowland rivers PAWEŁ OGLĘCKI Warsaw Agriculture University, Department of Environmental Management, Warsaw, Nowoursynowska 159, Abstract Detailed hydrological and biological surveys were carried out on chosen reaches of some small and medium lowland rivers (both regulated and close-to-nature). Typical, repeatable types of microhabitats of peculiar parameters were singled out and the relationships between the microhabitat types and invertebrate taxa were studied. The paper shows the results of such analyses and points out the fact that some microhabitats (irrespective of the fact of river regulation or not) are especially important for the mosaic of riverbed eco-systems since they provide essential lifeconditions for different and important invertebrate taxa. Key words: invertebrates, lowland rivers, microhabitats, biodiversity Introduction One of the most important aspects to consider when conducting river surveys is the connection between different abiotic (bottom substrate, water velocity etc.) and biotic factors (plants, invertebrates, fish) especially in the riverbed zone. Such connections have been presented in different papers (Rabeni & Minshall 1977, Cummings et al. 1966, Berkman et al. 1986, Tolkamp 1980, Beisel et al. 2000), but with reference to elements (factors) of the environment, not to microhabitats as repeatable environmental structures. It is commonly known that various invertebrate taxa are of varying importance for river eco-system activity and stability. It depends on their position in the food

2 90 P. Oglęcki web and their specified ecological group (Lampert & Sommer 1993). The strict impact of every species or even higher taxons on the community or eco-system is usually very hard or even impossible to determine, but describing the environmental preferences of basic taxonomical groups seems to be the first step just to know which microhabitat types are of the highest importance for specific invertebrates (and fish or other vertebrates as consequence). This is especially important in the light of different human activities in the riverbed zone (maintenance, reclamation, renaturation, revitalisation). Study area and Methods The studies were carried out on five Polish lowland rivers the middle Wkra (90 kilometres of surveyed reaches), the Jeziorka (70 kilometres), the upper Wieprz (30 kilometres), the upper Słupia (30 kilometres) and the lower Kwacza (10 kilometres). In total 230 kilometres were surveyed, of which 100 kilometres may be classified as close-to-nature and 130 as regulated, although in many cases the regulation had been performed in an environmental friendly way and the general look of the reach is similar to natural one (quotation marks because of the fact that according to many authors strictly natural rivers do not exist). Seventeen repeatable microhabitats of specific hydrological parameters were singled out 10 (termed N ) were typical for close-to-nature reaches and often for the regulated ones as well; 7 (termed R ) only for regulated ones. In every season over five years the samples were collected in all microhabitats (regularly on Wkra and Jeziorka, more occasionally on the other 3 rivers; sample coverage 1 4 m 2 ) more than 1400 samples were taken in total, not less than 50 samples from a particular microhabitat. The samples were collected by means of a triangular dip net, plankton tow, mosquito dipper and Ekman grab. The invertebrates were classified immediately in the field or in the laboratory with professional guidebooks and sometimes with the help of specialists. Results The following types of riverbed microhabitats were singled out on the ground of collected hydrometrical and hydrological data: N-type typical for close-to-nature reaches, but present also on regulated ones (especially in environmental friendly way) N-1: flat, sandy bottom; water velocity not differentiated, N-2: flat, sandy bottom; water velocity differentiated, N-3: flat, mixed (sandy and muddy) bottom, water velocity not differentiated,

3 Invertebrate differentiation in various microhabitats of small 91 N-4: flat, mixed (sandy and muddy) bottom, water velocity differentiated, N-5: muddy bottom, stagnant water on outer river bend, N-6: muddy bottom, flat bank (water-hole), N-7: deep pool on the inner side of the bend, N-8: coarse-grained riffle, N-9: fallen tree or pile of branches, also the sections upstream and downstream, N-10: small tributary or drainage ditch mouth R-type typical for regulated reaches R-1: a weir, slabs protecting the slopes upstream or downstream, R-2: weir backwater, R-3: stony bottom downstream of a weir, R-4: stony bottom upstream of a weir, R-5: the border line between concrete slabs and natural bottom upstream or downstream of a weir, R-6: bridge piers, R-7: river bar and the river section upstream and downstream. Seventy eight invertebrate species were identified 65 on the reaches of mixed (sandy and muddy) bottom, 55 on the reaches of muddy bottom and 42 on the reaches of a sandy bottom. Just 3 species were found only in microhabitats connected with regulated reaches (type R). The N-7 microhabitat type was most abundant with invertebrates (51 species). On the other hand the poorest ones were: N-8 (11 species), R-5 (8 species) and R-6 (10 species). In other microhabitats species were collected (statistical differences not significant). Sponges (Ephydatia fluviatilis and Spongilla fragilis) were found only in N-9, R-1 and R-4 microhabitats. The only member of hydrozoans group (Hydra attenuata) inhabited the R-2 and R-4 sites. The largest number of planarians (4 species) were found in the N-7 microhabitat, lack of those invertebrates was typical for R-3 and R-5. Aquatic earthworms (maximal species number in microhabitat 3) were absent in N-8, R-2, R-3 and R-5. The highest number of leeches (5 species) were collected in the N-5 microhabitat, 4 species in N-7, 3 species in N-1, N-3, N-9 and R-1. Arthropods were present in all microhabitats 4 species in N-10 and R-6, 3 species in N-1, N-3, N-9 and R-1. Stonefly larvae (3 species maximally) were found only in the N-1, N-7 and R-1 microhabitats, mayflies (2 species maximally) in N-1, N-2, N-7 and N-9; dragonflies (3 species maximally) in N-5, N-6 and N-7. The highest number of caddisfly species (4) was identified in the N-7 microhabitat, 3 species in N-3. Members of this group were absent in N-9, N-10 and all R type microhabitats. The maximal number of water bug species (4) was typical for N-1, N-2 and N-9 microhabitats, members of this group were absent in N-10 and R-5. The same results were obtained for beetles. Diptera (midges, mosquitoes, gnats and flies) were most abundant in the N-7 microhabitat

4 92 P. Oglęcki (6 species; 4 species in N-1, N-2 and N-9). Molluscs were not only found in the R-6 microhabitat, the highest number of species (4) were collected from the N-3 and N-5 sites. Snails were present in all microhabitats (minimally 2 species, maximally 6 in N-7 and N-9). Discussion The surveys, carried out on the reaches of various rivers allowed rich comparative material to be gathered, helpful for the studies of lowland river biodiversity and activities connected with watercourse conservation or renaturation. It is well known that various taxa of different ranges are of specific importance for the functioning of communities and eco-systems and consequently for biological system stability not only in the river itself, but in the valley as the whole. Experts need to know as much as possible about the environmental necessities of various species and ecological groups (such as shedders) and the collected data seems to be helpful. The author would like to stress the fact that none of the singled out microhabitats was preferred by all invertebrate groups. Without doubt the peculiar importance for invertebrate diversity in the riverbed should be attributed to deep pools on the inner side of the bends, where most planarians, leeches, molluscs and snails were found. But even the poorest microhabitat (the bridge piers) proved to be a record holder in the case of arthropods. It is also worth mentioning that the artificial microhabitats, connected with hydrotechnical structures, were inhabited by sponges and the hydrozoan Hydra attenuata (not collected in any microhabitat on close-to-nature reaches!). The author does not attempt to convince anybody of the necessity of river regulation, but some of the positive aspects of such activities may be well worth noting. The results confirmed the fact that riverbed differentiation is the key for maintaining watercourse biodiversity. Some material for subsequent analyses was gained, but more detailed surveys on the environmental preferences of various invertebrate taxa seems to be necessary. Conclusions 1. Different microhabitats may be singled out in small and medium-sized lowland riverbeds. 2. All microhabitat types are characterized by particular invertebrate fauna. 3. The most preferable (abundant with taxa) microhabitat is the deep pool on the inner side of the bend. 4. Microhabitats connected with hydrological structures may be used by environmentally valuable invertebrate species, sponges for example.

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