The influences of suspended mussel and infaunal clam cultivation on benthic metabolism and nutrient cycling were compared in Goro lagoon, Italy. Both aquaculture types stimulated benthic metabolism, with sediment oxygen demand (SOD), CO 2 and ammonium effluxes of up to 14, 16 and 1.2 mmol m -2 h -1. However, whilst mussel farming preferentially stimulated anaerobic metabolism and sediment reduction, clam farming did not. The mussel ropes were also large oxygen sinks and ammonium sources, with oxygen consumption and ammonium production rates of 1.4 to 1.5 and 0.18 to 0.43 mmol kg -1 h -1. Consequently, the overall impacts of mussel farming on oxygen and nutrient dynamics were much greater than those of clam farming. There were also differences in nitrate-reduction processes and the nitrate sources that fuelled them. In winter, at high water column nitrate concentrations, highest nitrate reduction rates (~320 µmol m -2 h -1 ) occurred at the mussel farm. Nitrate reduction was driven predominantly by water column nitrate and ~30% of nitrate reduced was recycled to ammonium via dissimilatory nitrate reduction to ammonium (DNRA). At the control and clam farm sites, nitrate reduction rates were lower (~180 µmol m -2 h -1 ), nitrification supplied ~30% of nitrate and denitrification was dominant. In summer under low nitrate conditions, nitrate reduction was highest (~130 µmol m -2 h -1 ) at the mussel farm site, but this activity was completely dependent upon water column nitrate and 95% of nitrate was reduced via DNRA. In contrast, at the clam farm station, DNRA was unimportant and nitrification was the major nitrate source for denitrification. Consequently, whilst nitrate reduction processes eliminated fixed N from the clam farm sediments via coupled nitrificationdenitrification, the dominance of DNRA at the mussel farm site resulted in a net N input to the sediment compartment. These large differences in the impacts of clam and mussel farming can be explained by the fact that infaunal clams stimulate transfer of both organic matter and oxygen to the sediment, whereas suspended mussels enhance only organic matter inputs.

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1. Freshwater ecosystems worldwide are experiencing native fish losses with severe threats to the conservation of freshwater biodiversity and ecosystem functioning, and the debate on whether the cause is biotic or abiotic disturbance is still open. 2. Temporal variation in fish assemblages was analysed over an 18 year period in 14 waterways of the lowland backwaters of the PoRiver in north-eastern Italy, which are important feeding, spawning and nursery sites for native fish. 3. In 1991, 14 native and eight exotic species were collected. In less than 20 years 10 native species underwent local extinction, three of which – Rutilus pigus, Rutilus aula, and Chondrostoma soetta – were endemic to the Padano-Veneto District in northern Italy. 4. Ordination of the data (MDS, CLUSTER, ANOSIM, SIMPER) showed a clear temporal gradient in fish community structure. After the establishment of the exotic predator Silurus glanis, some native species significantly declined in abundance and biomass (i.e. Alburnus arborella and Scardinius erythrophthalmus) or disappeared (i.e. Rutilus aula and Tinca tinca). Moreover, exotic species Cyprinus carpio, Ameiurus melas, and Carassius auratus from previous introductions, underwent significant changes in their abundance and biomass. No correlation was found between fish community structure and water quality parameters (BIOENV). 5. The success of exotic species, particularly S. glanis which thrived in this degraded habitat, seems to have led to the decline of native fish fauna in the canals of the lower portion of the Po River basin. Conservation strategies focusing on the containment of exotic species and habitat restoration are recommended

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Secondary drainage canals have the potential to effectively mitigate excess nitrogen loads from diffuse and point sources. In vegetated (Phragmites australis and Typha latifolia) and in unvegetated canals subjected to diffuse and point pollution, nitrogen removal was evaluated by means of simple in–out mass balance and potential uptake by macrophytes was estimated from biomass data. Results suggest an elevated control of nitrogen in vegetated ditches receiving point source of pollution (average abatement of 50% of the total N load per linear km), whereas removal processes are much less\ud effective in unvegetated ditches. The comparison between net abatement and plant uptake, highlights the presence of other unaccounted for processes responsible for a relevant percentage of total N removal. Overall, results from this study suggest the importance of actions aiming at the appropriate management of emergent vegetation, in order to improve its direct and indirect metabolic functions and maximize nitrogen removal in impacted watersheds