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

Abstract

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.An important parameter of any natural or man-made lake is its residence time, defined as basin volume divided by outflow rate T, = V/R. In long residence-time systems, wind and local heat exchange are the principal means of setting water in motion (Mortimer 1974;Hollan and Simons 1978). As residence time shortens, the interaction between a lake and its through-flowing river becomes increasingly important, eventually resulting in the so-called run-of-the-river system in which river inputs completely dominate the distribution of properties. In the middle of this spectrum are many lakes whose dynamics are influenced by river through-flow but modified by other physical mechanisms within the lake. As a category, such lakes are still poorly understood. For example, a review of ecosystem modeling of northern lakes by Fox et al. (1979) contains no reference to the processes of lakeriver interaction" We discuss here the annual cycle of mixing and circulation in Kootenay Lake, British Columbia, and show how the seasonal patterns of circulation and water mass distribution are controlled by the interplay of advective and surface-driven processes.

Localized algal blooms induced by river inflows in a canyon type reservoir

“…Seasonal changes experienced by transport and mixing processes affecting river inflows in aquatic systems have been reported by Carmack (1979); Carmack et al (1986) and Pickrill and Irwin (1982). Armengol et al (1999) also described these changes at a seasonal scale and linked them to seasonal changes experienced by phytoplankton communities in a reservoir in northern Spain.…”

Field calibration of a formula for entrance mixing of river inflows to lakes: Lake Taupo, North Island, New Zealand

“…In their study of the Dart and Rees Rivers' inflows to Lake Wakatipu, a large, deep lake in the South Island, New Zealand, Pickrill & Irwin (1982) pointed out that "currents, thermal structure, residence time, sediment transport, and depositional environments are all largely controlled by the way in which river water enters and flows through the lake". River inflows that have a significant effect on basin-scale circulation have also been studied by Hamblin & Carmack (1978) and Carmack et al (1979) in Kamloops Lake, British Columbia; 10 km Johnson & Merritt (1979) in Lake Powell, UtahArizona; and Carmack et al (1986) in Kootenay Lake, British Columbia. Alavian & Ostrowski (1992) studied the effects of river inflows on thermal structure in Tennessee Valley Authority reservoirs.…”

Eutrophication processes regulated by a plunging river inflow

“…A density inflow to a small eutrophic lake generated a net upwelling and associated nutrient transfers through the upper layers of the waterbody (Imberger & Spigel, 1987). The seasonal dynamics of physical structure in Kootenay Lake, British Columbia is substantially influenced by two rivers that at certain times of year penetrate into the lake as plunging inflows (Carmack et al, 1986). At each of these study sites the inflowderived density currents may be expected to have major implications for the ecological dynamics of the lake.…”