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1

Populations of fish in relation to riparian ecotone development in the Narew River catchment

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Penczak T.

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nr 1-2

EN

Number of species (S), density (N) and standing crop (B) were investigated in 331 sites in the catchment of the Narew River, the biggest tributary of the Vistula, against 4 categories of riparian ecotone intensity in various-width rivers. All populations were first analyzed together, then within the scope of three most abundant ecological spawning groups. The image obtained is to some extent blurred by anthropogenic alterations as well as humancreated ecotones, yet it is evident that a total lack of bankside trees had a negative impact on the values of S, N and B of all investigated populations. Exceptions are only small streams of the Bialostocka Upland, where at a high percentage of submerged vegetation and occasionally stony bottom (washed away moraine bars), the lack of riparian trees did not cause any decrease in any of the three populational parameters. The uninterrupted compact forestation of the banks was positively correlated with S, N and B only in the lower Narew River, where the river bed was more than 100 m wide, hence where the access of light was not already limited. For lithophilous species a river's naturalness was a more important factor conditioning their abundance than the development of riparian ecotones. Indifferent species displayed a high, positive dependence on the development of ecotones, while phytophils (whose development is vegetation-dependent) formed the most qualitatively and quantitatively abundant populations at a weak, and in some rivers, even medium forestation of the banks.

2

Economic aspects of agricultural area management and land-water ecotone conservation

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Petersen H. G.

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nr 1-2

EN

Today’s management of agricultural areas is hardly in accordance with actual economic and ecological goals. In view of the future risks for the global system a revolutionary change within our current land use systems is essential. The paper gives an example of a workable strategy for agricultural policy baded on the internalization of external burdens into a market price system as well as the expansion of property rights. Then it explains why sensible perspectives do exist, but are still not transformed into practical political measures or reforms.

3

Buffering role of land-water ecotones in the structuring of the fish community of the Sorraia system

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Coelho M. M. , Pires A. M. , Collares-Pereira M. J. , Sousa E. C. , Zalewski M.

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nr 1-2

EN

To test the role of riparian ecotones in fish community dynamics three different sites along the Sorraia system, were selected. Each station has been under distinct anthropogenic pressure, and characterized by a mosaic of habitat conditions. Fish were collected by electrofishing from October 1991 to October 1993 using two distinct sampling scales, (50 m and small sectors defined according to discontinuities in the dominant vegetation). The variation in species abundance and distribution was correlated with physical factors. The results showed the preference of barbel and nase for riparian vegetation and greater depth and of roach for zones with macrophytic vegetation and high current velocity. Fish community of the Sorraia system does not exhibit a consistent pattern of temporal variation, what is usually observed in Southern streams of the Iberian Peninsula. This fact is probably related to the landscape disturbance.

4

Ecotones of riverine ecosystems: Role and typology, spatio-temporal dynamics, and river regulation

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Ward J. V. , Wiens J. A.

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nr 1-2

EN

Natural riverine ecosystems are characterized by a high level of heterogeneity manifest across a range of spatio-temporal scales. Ecotonal habitats are both the result of and contributors to the spatio-temporal dynamics of riverine ecosystems. Natural disturbances play an important rôle in maintaining a diversity of ecotonal habitats. A typology of riverine ecotones is developed that provides an expansive perspective scaled along four dimensions (longitudinal, lateral, vertical, and temporal) and that encompasses environmental gradients and boundaries as well as distinct transition zones between adjacent patches. From this broad perspective it is apparent that riverine ecotones play important rôles relating to speciation, evolutionary invasion of fresh waters, biodiversity, bioproduction, and ecological connectivity. River regulation disrupts the natural disturbance regime downstream, thereby reducing the diversity of ecotonal habitats and their connectivity with the main river channel. The altered rôle of ecotonal habitats induced by regulation is especially pronounced in alluvial floodplaing rivers, which are characterized by a mosaic of habitat patches that collectively occupy a wide range of successional stages. Downstream hydrologic changes, such as truncated sediment transport and reductions in the frequency and intensity of flooding, typically lead to altered successional trajectories, desiccated floodplain waterbodies, severed migration pathways, and reduced exchange rates of nutrients and organic detritus across ecotone boundaries. Effective management of regulated rivers should focus on maintaining or restoring the important rôles of ecotones by re-establishing interactive pathways and by reconstituting a disturbance regime that leads to a diversity of habitat patches and successional stages.

5

Riparian ecotones, invertebrates and fish: life cycle timing and trophic base

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Bretschko G. , Waidbacher H.

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nr 1-2

EN

Riparian ecotones are either within the bankfull lines (instream ecotones) or beyond (bank vegetation and floodplains). Instream ecotones (e.g. gravel bars) are most intimately and permanently interconnected with the stream system. The third order river Melk was channelized some decades ago with devastating effects on the fish fauna. The restoration of instream ecotones and of the riparian vegetation improved the fish population immediately. Instream ecotones are equally important for the fish community in high order streams. Data are given for the 9th order Danube. The duration of floodplain inundation is unpredictable but generally short in the temperate climatic zone. Fish do not migrate far into the inundated terrestrial vegetation but stay in or near to the enlarged backwaters. In backwaters separated from the main stream, a potamal fish population survives in an otherwise rhithral stream section. Floodplain inundation is predictable and lasts over long periods in the tropics. Fish and invertebrates are adapted to use the vast resources of habitats and food by active migration into the inundated forests.

6

The role of the shoreline ecotonal zone in spawning success and early life history of dominant fish species in the lowland Sulejow Reservoir

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Frankiewicz P. , Dabrowski K. , Rucinski W. , Zalewski M.

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nr 1-2

EN

The roach preferred branches of spruce and juniper as artificial spawning substratum rather than pine and birch. Perch preferred birch over conifers. Thus altering the availability of spawning substrata in the littoral zone should be effective in controlling the density and structure of juvenile roach and perch communities in reservoirs. Density dependent processes affects the early life history of fishes. Surveys in the Sulejow Reservoir in 1994 and 1997 provide an example of how increased availability of prey fish in the littoral zone may influence a predator population. During early summer age-0 pikeperch formed two discrete groups, one in the littoral and the other in the pelagic zone. In the littoral pikeperch became piscivorous at c. 3 cm on the numerous juvenile cyprinids, and grew relatively fast (5.2->9 cm by mid-July 1994). Those in the pelagic where prey fish were scarcer fed chiefly on zooplankton and grew relatively slowly (4.2-6.6 cm by mid-July 1994). From the resulting bimodal length distribution the upper modal group (littoral) had a higher probability of surviving their first winter. These data suggest a critical role for the ecotonal habitats in the dynamics of the trophic cascade, and show possibilities for controlling symptoms of eutrophication.