Lake and Reservoir Management 22(4):293-302, 2006 © Copyright by the North American Lake Management Society 2006 Limnological Characterization and Flow Patterns of a Three-coupled Reservoir System and Their Influence on Dreissena polymorpha Populations an

Navarro, E., M. Bacardit, L. Caputo, T. Palau and J. Armengol. 2006. Limnological characterization and flow pat-terns of a three-coupled reservoir system and their influence on Dreissena polymorpha populations and settlement during the stratification period. Lake and Reserv. Manage. 22(4):293-302. During summer 2001, zebra mussels (Dreissena polymorpha Pallas) were found (500 adults m-2) in the coupled res-ervoir system composed by Mequinenza, Riba-Roja and Flix (Ebro River, Northeast Spain). Two years later, mussels achieved densities of 4000 adults m-2, representing the first record of successful colonization by zebra mussels in the Iberian Peninsula. An August 2003 study investigated the environmental conditions that support the successful settlement of the zebra mussel populations during the stratification period. Flow patterns in the whole system and mussel populations near the dam were characterized. Chemical characteristics of water inputs, not the usual thermal stratification, determine the deep circulation of the Ebro River along the Riba-Roja reservoir, whereas water input from one tributary into Riba-Roja flows along the top of the water. Physico-chemical stratification of the water column seems to control the observed vertical distribution of zebra mussel biomass. Larger biomass and mean body size were found in the epilimnion, while meta- and hypolimnetic individuals were smaller in size and composed a lower biomass. Moreover, to know the influence of the water drawn off for electricity production in the settlemen