Gianpaolo Salmoiraghi

Leaf Bags and Natural Leaf Packs: Two Approaches to Evaluate River Functional Characteristics

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.

Macroinvertebrate communities and the changing Italian rivers

Abstract Rivers have been considered for a long time simply as vehicles transporting water and not as ecosystems. In Italy there has been a massive transformation of the lotic habitats, particularly with regard to the riparian zones and to the quality of waters. The structure and function of the populations and communities of organisms represent indicators of the changes which take place in the environment. Numerous indices, based on the study of the macroinvertebrate communities, have been proposed for evaluating the quality of the river environments in Europe. In Italy, a concrete result of the river monitoring programme, based on analysis of the macroinvertebrate communities, is the biological quality maps of hydrographic networks. The macroinvertebrate communities play an important role in the process of transforming the organic material input and as indicators of the quality and structural and functional integrity of the lotic environment.

Decomposition processes of alder leaves downstream of the Ridracoli Dam (Apennines, Italy)

The categorisation of stream macroinvertebrates in to functional feeding groups is a crucial factor in the study of leaf decomposition in a stream. Nevertheless, several authors reported difficulties in allocating macroinvertebrates to trophic groups many taxa are capable o f modifYing their diet an d consuming a wide range of available food sources, thus appearing to be generalists or opponunists (BouLTON & BooN 1991, PALMER et al. 1993). Shredders are reputed to feed directly on CPOM, thus hastening leaf disintegration, and they undoubtedly play an important role in leaf breakdown (STEWART & DAVIES 1989, STEWART 1992). However, changes in feeding behaviour occur during life cycles. Therefore, the small larvae of shredders (particularly Plecoptera in first life stages), being nor yet effective in leaf shredding, should be considered as collectors (CASAS 1996). Leptophlebiidae are another questionable point several authors consider them to be collectors (IMBERT & Pozo 1989, CHAUVET er al. 1993), but according to others they are likely to directly affect leaf decomposition (RoWE et al. 1996). The structure and composition of the macroinvertebrate community may be altered by the presence of impoundments. Sedimenrarion of particulare organic matter within the reservoir, f!ow regularion and modified thermal regimes alter habitat features and food availability for benrhic macroinvertebrates downstream of rhe impoundment (PErrs 1984). The aim of this study was to analyse leaf decomposirion and macroinvertebrate colonization in rwo regulared streams. Hence three quesrions were addressed: l. Can an impoundmenr modifY leaf decomposition and rhe community srrucrure of leaf substratum? 2. Are shredders rhe only functional group affecring leaf breakdown? 3. How much does seasonality influence leaf decomposition processes in similar leaf-packs? Study area

Leaf colonization by aquatic macrobenthos: a comparison between Alpine and Apennine streams

Headwaters are characterized by heterotrophic metabolism, mainly supported by leaf litter input from riparian vegetation (BENFIELD 1997, PosT & eRuz 1977). A multispecific riparian vegetation is of great importance for the macrobenthic con:munity, because i t provides a continuous supply o f h1gh q_uality food throughout the year: autumnal leaf lmer input follows a specific temporal sequence, according to abscission periods, and different species have different decomposition rates (PETERSEN & euMMINS 1974; WEBSTER & BENFIELD 1986). In spring, additional leaf litter input is sometimes represented by green leaves lost from trees during storms (LEFF & McARTHUR 1990) or by partially decomposed leaves transported by run-off (MERRITT & LAwsoN 1992). Naturalleaf-packs are thus usually multispecific in contrast with artificialleaf-packs, often used in studies in lotic environments (eAsAs 1997, VouGHT & LANNERSTAD 2000). It is likely that a naturally heterogeneous pack supports a more abundant and varied colonizing fauna than monospecific packs (BOVLTON & BooN 1991). Several studies have been carried out with artificialleaf-packs, but the environmental variables that affect the structure of the benthic community in naturalleaf-packs are still not well known. The present survey was carried out within the framework of the European eommission project ERMAS I! and with the aim of studying the influence of riparian vegetation and geographical factors on colonization of the in-stream leaves.