We studied zooplankton dynamics in a groundwater-fed, montane lake during four consecutive years and assessed the importance of water residence time for zooplankton dynamics. Crustacean abundance and biomass were significantly correlated with water residence time and temperature, but showed no significant correlation with phytoplankton biovolume. We hypothesised that temperature depended on water residence time (t), and therefore we further investigated the functional relationship of crustacean dominance with the latter by logistic regression analysis. Water residence time values above a threshold value (t = 193 days) determined crustacean biomass dominance while values below determined rotiferan dominance. Our results indicated that water residence time was an important factor structuring zooplankton succession in this lake that showed large fluctuations of t values (median 263 days; range 23 -786 days for the four year period) compared to other lakes. We suggest that crustacean biomass was directly controlled through water residence time as found for riverine systems, whereas rotifer biomass was controlled through exploitative competition with crustaceans for phytoplankton. The importance of water residence time may have been underestimated in lakes when explaining zooplankton community structure and succession, because studies usually focus on other factors such as temperature, predation, or food limitation.

The principal environmental factors influencing the seasonal dynamics of phytoplankton were examined from September 1997 to July 1998 in three stations along a 26-km stretch of the lowland course of River Adige (northeast Italy). Nutrient concentrations did not appear to be limiting for the phytoplankton growth. Annual minimum concentrations of reactive and total phosphorus, and dissolved inorganic nitrogen were 22 lg P l -1 , 63 lg P l -1 and 0.9 mg N l -1 , respectively. The most critical forcing factors were physical variables, mainly water discharge and other variables related to hydrology, i.e. suspended solids and turbidity, which acted negatively and synchronously by diluting phytoplankton cells and decreasing light availability. Higher algal biomass was recorded in early spring, in conditions of lower flow velocity and increasing water temperature. In late spring and summer, higher water discharge caused a decrease in phytoplankton biomass. Conversely, low algal biomass in late autumn and winter, during low discharge, was mainly related to low water temperatures and shorter photoperiod. Physical constraints had a significant and measurable effect not only on the development of total biomass, but also on the temporal dynamics of the phytoplankton community. Abiotic and biotic variables showed a comparable temporal development in the three sampling stations. The small number of instances of spatial differences in phytoplankton abundance during the period of lower flow velocity were related to the increasing importance of biological processes and accumulation of phytoplankton biomass.

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An extensive knowledge of the functional characteristics of rivers is of basic importance to develop precise management plans with specific aims, e.g. to rehabilitate riparian ecotones or increase the retention capacity of streams. In this study man‐made leaf bags (LB) and natural leaf accumulations (NLP) were used. The first method was useful in calculating breakdown rates and the second one in understanding the effective litter composition, which does not always reflect the composition of the riparian canopy. The assemblages of macroinvertebrate colonizing both LB and NLP were divided into functional feeding groups and compared. Are both methods (Leaf Bags and Natural Leaf Packs) necessary and complementary to analyse the functional characteristics of an upland river? The study was carried out in three different sites on the upper reaches of the Adige River. The breakdown rates were very similar in all three study sites but litter quality and quantity were very different. Although, in the two upper sites, the composition of invertebrates colonizing LB and NLP was the same, abundance and biomass values coincided only in the first stage of the colonization process of LBs. In the third site no invertebrates using litter as a trophic resource were found. Both NLP and LB methods are needed in the evaluation of rehabilitation programs as they take account of the different aspects of the dynamics and the composition of CPOM.

A model of analysis and environmental evaluation was applied to 11 stretches of the Adige River, where an innovative procedure was carried out to interpret ecological results. Within each stretch, the most suitable methods were used to assess the quality and processes of flood plains, banks, water column, bed, and interstitial environment. Indices were applied to evaluate the wild state and ecological quality of the banks (wild state index, buffer strip index) and the landscape quality of wide areas of the fluvial corridor (environmental landscape index). The biotic components (i.e., macrozoobenthos, phytoplankton and zooplankton, interstitial hyporheic fauna, vegetation in the riparian areas) were analysed by both quantitative and functional methods (as productivity, litterprocessing and colonisation). The results achieved were then translated into five classes of functional evaluation. These qualitative assessments have thus preserved a high level of precision and sensitivity in quantifying both the quality of the environmental conditions and the integrity of the ecosystem processes. Read together with urban planning data, they indicate what actions are needed to restore and rehabilitate the Adige River corridor.

The faunistic research carried out in the Adige basin, often together with ecological researches, has underscored the following aspects: 1) the faunistic composition as the «historical memory» of the evolution of the river environment, its loss of biodiversity, and the worsening of water quality; 2) the contribution made by faunistic studies to the methods of the biological evaluation of the quality of running waters and, vice versa, the contribution made to faunistic studies by the use of these methods; 3) the support given by faunistic studies in formulating and verifying the basic concepts of the fluvial ecosystem.

No abstract

This research is a contribution to an integrated overview of the alpine low-order river ecosystem. We associated the results obtained from colonization and breakdown processes (functional aspects, i.e. colonization of natural and artificial leaf packs and of artificial inorganic substrates), with the morphohydrological features of the river bed, with density and biomass of benthic invertebrates and with banks quality. We studied the Ausor stream, North-East Italy, a natural alpine stream with a narrow steep gradient channel.The applied monitoring methods allowed us to point out the total biodiversity, the seasonal and regional heterogeneity of macrobenthos and of habitats and the efficiency of breakdown and colonization processes. The integrated overview, achieved from the comparison of results, showed that diversity and variability of habitats are connected with the natural morphological development of the river bed and of riparian areas. Furthermore, heterogeneity and variability of habitats are essential in supporting biodiversity and the functional processes occurring in a natural environment.