Encyclopedia of Environmental Science and Engineering, Volume I and II

LIMNOLOGY 611

the amount of phosphorus released from the sediments to the

water column. In general, lake water quality will improve as

the magnitude of sedimentation increases because higher sedi-

mentation means there is less phosphorus in the water column

to stimulate overgrowth of aquatic plants (for more details, see

section on eutrophication). The change in storage accounts for

changes in the total amount of phosphorus in the lake water

column between the beginning and end of the year.

Phosphorus concentration differs from phosphorus load-

ing. Phosphorus loading to a lake is calculated on the basis

of the water budget for the lake and measured phosphorus

concentrations in the lake, its inlets, its outlets, precipita-

tion, surface water runoff, and groundwater. Loadings are

based on concentrations and flow rates and most accurately

express the relative impacts of various watershed sources on

lake water quality. For example, a stream that is an inlet to a

lake may have a high concentration of phosphorus. This does

not necessarily mean that the stream is a major contributor to

the lake phosphorus budget. If the stream has a low flow, it

will contribute a relatively low annual phosphorus loading.

The concept of phosphorus loading can be illustrated with

an analogy to a grocery bill as shown in Table 1. For each

Cottage Lake

Creek

11%

Internal

29%

Daniels Creek

51%

Basin C5-

Subsurface

5%

Basin C5-Surface

2%

Precipitation

2%

Inputs

Outputs

Sedimentation

36%

Cottage Lake Creek

64%

FIGURE 2 Cottage Lake total phosphorus inputs and outputs.

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