Restoration and Management of Lakes and Reservoirs - Hydro-Environmental Analysis: Freshwater Environments - page 475

17.4.6 a rtIfIcIaL c IrcuLatIon
Artiicial circulation typically involves methods to destratify a lake or reservoir, or to remove verti-
cal stratiication. The primary beneit is to improve the overall water column dissolved oxygen con-
centrations, but there may be improvements in algal concentrations too. The most common method
is air injection, although other methods have been used, such as axial low pumps, like a big loating
fan, to “push” the water down into the epilimnion. Some of the alternative methods are illustrated
in Figure 17.5 and are described by Holdren et al. (2001).

17.4.7 o xIdatIon
Similar to aeration, oxidation is used to introduce oxygen to the hypolimnion and sediments, where,
under oxic conditions, nutrient concentrations and release rates from sediments would be reduced.
Unlike aeration when used for artiicial circulation, hypolimnetic oxygen injection is typically
designed not to destratify the lake or reservoir. Hypolimnetic oxidation is a commonly used technique
to improve the quality of reservoir releases and reduce nutrient releases by sediments. There are a vari-
ety of methods to introduce oxygen, including diffusers on the bottom of the lake or reservoir or side-
stream oxygenation, where hypolimnetic water is pumped onto the shore, injected with oxygen, and
then discharged back into the hypolimnion (Fast et al. 1975). Beutel and Horne (1999) reviewed the
effects of hypolimnetic oxygenation on lake and reservoir water quality. NALMS (1990) indicated that
there is little documentation of its successful use to control nuisance algae. However, there is evidence
that sediment oxygenation successfully reduces nutrient releases and Cooke et al. (2005) indicated that
it may be, albeit more expensive, an effective alternative to alum treatment and dredging.

17.4.8 a LGIcIdeS
Algicides kill algae, and the most commonly used are the toxic forms of copper, with copper sulfate
(CuSO 4 ) being the most basic and common form (Holdren et al. 2001). Copper commonly kills many

Water
level

ermocline

Bottom
sediment

Layer
aeration

Diffusion
aeration

Full lift
aeration

Partial lift
aeration

Downdraft or updraft
circulation

(Nondestratifying)

(Impact on stratification
varies)

(Destratifying)

Diffuser (Pneumatic input)

Mechanical pump

FIGURE 17.5 Aeration methods for artiicial circulation. (From Holdren, C., Jones, W., and Taggart, J.,
Managing Lakes and Reservoirs , North American Lake Management Society and Terrene Institute, in
cooperation with the Ofice of Water Assessment and Watershed Protection, U.S. Environmental Protection
Agency, Madison, WI, 2001. With permission.)