Mechanisms influencing the circulation and distribution of water mass in a medium residence-time lake

The seasonality of physical structure in a deep, temperate lake (Kootenay Lake) is described in relation to its major river inputs (Kootenay and Duncan Rivers). The lake's volume is 37 km3 and its annual outflow is 25 km3 yr-I, yielding a residence time of about 1.5 years. Water mass distributions are controlled by the interactions of three processes: riverine circulation, mixed-layer dynamics, and internal wave behavior. The riverine circulation is determined by the inflow rate and by the relative density of incoming water and ambient lake water. Mixed-layer structure varies in relation to the combined action of the wind and surface heat flux on both seasonal and synoptic time scales. Internal waves may periodically raise a given stratum of water, such as the riverine layer, to a depth where wind mixing is more intense. Knowledge of these processes, their relative importance, and their time-space variability can aid in understanding the ecology of the lake.