EXERCISE 26
Special Lake Types
Certain of the vast number of lakes distributed
over the surface of the Earth have speciallimnological characteristics. Bog lakes in the northern
latitudes, reservoirs, anthropogenically acidified
lakes in Scandinavia and eastern North America
and below strip-mining operations, meromictic
lakes, playa lakes in arid regions, and alpine
RESERVOIR ECOSYSTEMS
lakes, provide examples of a diversity of exceptional conditions that add to the fascination and
enjoyment of limnological studies. We suggest
you explore as many of these diverse habitats in
your local area as possible. A discussion of
several examples follows.
Reservoirs are created when water runoff from the land, such as a river, is accumulated
in a basin by an impounding structure, usually a dam. Reservoirs are created
predominantly in regions where large natural lakes are sparse or unsuitable (e.g., too
saline) for human exploitation. In these regions the climate tends to be warmer than is
the case for many natural lakes and results in somewhat higher average water
temperatures, longer growing seasons, and precipitation inputs that are closely
balanced to, or less than, evaporative losses (Wetzel, 1990a). Drainage basins of
reservoirs are much larger in relation to the lake surface areas than is the case among
most natural lakes. Because reservoirs are formed almost always in river valleys and at
the base of the drainage basins, the morphometry of reservoir basins is usually
dendritic, narrow, and elongated (see Exercises 1 and 5).
These physical characteristics affect biological processes in many complex ways, the
most important of which are light and nutrient availability to aquatic organisms
(Wetzel, 1990a). Reservoirs receive runoff water mainly via large streams, which have
high energy for erosion, large sediment-load carrying capacities, and extensive
penetration of dissolved and particulate loads into the recipient lake water. Because the
inflows are primarily channelized (along the prior river course before it was inundated)
and often not itercepted by energy-dispersive and biologically active wetlands and
littoral interface regions, runoff inputs to reservoirs are larger, more directly coupled to
precipitation events and extend much farther into the lake per se than is the case in most
natural lakes. All of these properties result in high, but irregularly pulsed, nutrient and
sediment loading to the recipient reservoir.
331
Special Lake Types
Certain of the vast number of lakes distributed
over the surface of the Earth have speciallimnological characteristics. Bog lakes in the northern
latitudes, reservoirs, anthropogenically acidified
lakes in Scandinavia and eastern North America
and below strip-mining operations, meromictic
lakes, playa lakes in arid regions, and alpine
RESERVOIR ECOSYSTEMS
lakes, provide examples of a diversity of exceptional conditions that add to the fascination and
enjoyment of limnological studies. We suggest
you explore as many of these diverse habitats in
your local area as possible. A discussion of
several examples follows.
Reservoirs are created when water runoff from the land, such as a river, is accumulated
in a basin by an impounding structure, usually a dam. Reservoirs are created
predominantly in regions where large natural lakes are sparse or unsuitable (e.g., too
saline) for human exploitation. In these regions the climate tends to be warmer than is
the case for many natural lakes and results in somewhat higher average water
temperatures, longer growing seasons, and precipitation inputs that are closely
balanced to, or less than, evaporative losses (Wetzel, 1990a). Drainage basins of
reservoirs are much larger in relation to the lake surface areas than is the case among
most natural lakes. Because reservoirs are formed almost always in river valleys and at
the base of the drainage basins, the morphometry of reservoir basins is usually
dendritic, narrow, and elongated (see Exercises 1 and 5).
These physical characteristics affect biological processes in many complex ways, the
most important of which are light and nutrient availability to aquatic organisms
(Wetzel, 1990a). Reservoirs receive runoff water mainly via large streams, which have
high energy for erosion, large sediment-load carrying capacities, and extensive
penetration of dissolved and particulate loads into the recipient lake water. Because the
inflows are primarily channelized (along the prior river course before it was inundated)
and often not itercepted by energy-dispersive and biologically active wetlands and
littoral interface regions, runoff inputs to reservoirs are larger, more directly coupled to
precipitation events and extend much farther into the lake per se than is the case in most
natural lakes. All of these properties result in high, but irregularly pulsed, nutrient and
sediment loading to the recipient reservoir.
331