Size structure and body mass of Chironomid larvae under different water level management in the temperate deep subalpine Lake Maggiore (NW Italy)

The amplified water level fluctuations (WLF) caused by natural and anthropogenic disturbances are recognized as one of the factors that strongly modified the structure and the functioning of the lake ecosystems. This is particularly true for chironomid assemblages, the largest family of aquatic insects dominating lakes. However, knowledge of how the distribution, diversity and size structure of chironomids are altered under different water level regimes is still fragmentary, especially about the temperate lakes. Here, we report our preliminary results on near-shore chironomid assemblages obtained in the frame of a three-year INTERREG Project "Parchi Verbano Ticino" (PVT; ID 481668) aimed to understand the impact of WLF on littoral macroinvertebrate community structure of the deep oligotrophic Lake Maggiore (Italy). The lake is regulated from mid-March to mid-September through the Miorina Dam placed at the lake's outflow (River Ticino). Only samples collected from July to September in 2020, at three sampling sites characterised by different water level regimes (high/low water level) and depths (deep/intermediate/shallow) were detailed. Length-mass regression models for the most common species and subfamilies are presented. Alterations in size, morphological traits, relative abundance and diversity in relation to different water level regimes are considered as possible indicators of water management impact.