Size structure and body mass of Chironomid larvae in the regulated subalpine Lake Maggiore (NW Italy)

An appropriate water management strategy could contribute to solve problems of water availability both from a biodiversity and a socio-economic point of view. Further, water level manipulation (WLM) may well mitigate the adverse impact of extreme events on the distribution and ecology of macroinvertebrates. This is particularly true for chironomids, the largest family of aquatic insects dominating lakes, where their assemblages seemed to be influenced by amplified water level fluctuations. However, knowledge of how the distribution, diversity and size structure of chironomids change under different water level regimes is still fragmentary. Here, we report our preliminary results of the chironomid assemblage obtained from a study within the INTERREG Project "Parchi Verbano Ticino" aimed to understand the impact of water level fluctuations on the macroinvertebrate community structure in the littoral zone of Lake Maggiore, the second largest lake in Italy regulated from mid-March to mid-September through the Miorina Dam placed at the lake's outflow (River Ticino). Samples were collected in 2019 and 2020, from July to September, in three sampling sites following the north-south axis of the lake and characterised from different WLMs (high/low) and depths (deep/intermediate/shallow). Biometry, biomass and relative abundance of each detected chironomid species are presented here, and for the most common species, length-mass regression models were developed to predict the dry mass. Alterations in size structure and length-mass relationships for populations of the same species relative to different WLMs and depths are investigated as potential consequences of the impact of water level regulation in Lake Maggiore.