Definition of hydrologic regimes in regulated rivers for aquatic biodiversity conservation.

Negative ecological effects of water withdrawal activities from lotic systems have led to the need for the restoration of naturally shaped flow schemes. As a first step in this direction, individuation of sustainable minimum flow volumes can limit extreme alteration of ecosystem structure and functionality. The definition of such minimum flow values, to be released downstream each water diversion structure, must follow the understanding and the quantification of ecological alteration related to flow reduction. This thesis focuses on the study of instream ecological effects of water withdrawal from lowland rivers (Ticino and Adda rivers), with the purpose to define adequate indicators for the identification of ecological effects of hydrological alteration. The application of such indicators should be useful for the definition of environmentally sustainable minimum flow schemes. For this purpose, national protocols for the study of biological communities were applied and critically analyzed. These monitoring criteria and tools appeared inadequate for addressing the hydrological assessment as postulated in this work and for the studied geographical context. Alternative sampling and analysing methods are proposed, following two different directions: (1) a different approach in the use of a common and well known structural indicator (macroinvertebrate fauna) and (2) the integration of such structural descriptors with a functional approach that considers the river quality through ecosystem methabolism measures. Although their widespread use, connected to simple field and laboratory application, macroinvertebrates appeared to be an inadequate tool for hydrological alteration monitoring. However, interesting considerations about relationship between community density and richness and environmental disturbance could be made. Presented data about physico-chemical parameters, collected through the open-channel method, show an influence of flow on ecosystem functional processes, mainly related to influence on aquatic vegetation. Collected data were useful to define an easy method to assess general response of the ecosystem to hydrological modifications, which future application could lead to interesting results and to an alternative approach for the application of WFD (Dir. 2000/60/EC) requirements.