Environmental Engineering Reference
In-Depth Information
ular areas can alter relative nutrient availability. For example, phosphorus
can be amply available in watersheds with P-rich volcanic ashes on sedi-
mentary deposits of opatite. Variation in surface concentration of total P
shows areas that are higher in phosphorus than other places in the United
States (Fig. 16.5). These P-rich areas are associated primarily with high
densities of human population or intensive agricultural activity. Thus,
knowledge of nutrient supply in a specific groundwater aquifer, wetland,
lake, or stream requires detailed knowledge of the geological and land-use
characteristics of the specific watershed, including point and nonpoint
sources of nutrients.
Nutrient Limitation
Growth is limited by the factor or factors present in the lowest rela-
tive supply that is required for synthesizing the cellular constituents. The
initial application of this idea to aquatic sciences utilized the concept of
Leibig's law of the minimum:
The rate of a process will be limited by the
rate of its slowest subprocess. The original statement of the law was based
on crop production. It stated that a single constituent would eventually dis-
appear and leave the land barren if successive crops were planted in one
area with no nutrient amendments.
Consider an automobile construction plant as an analogy for Leibig's
law. The plant utilizes parts shipped from suppliers all over the world. Dif-
ferent amounts of various parts are required for each car (e.g., four tires
per car, 1 transmission, and 6 engine cylinders). If 400 tires, 100 trans-
missions, and 540 cylinders are supplied each month, only 90 cars (540/6)
can be constructed, even though sufficient tires and transmissions are avail-
able for 100 cars per month. The rate at which the cylinders are supplied
FIGURE 16.5
Spatial map of total phosphorus concentrations in surface waters of the
United States (Omernick, 1977). Darker areas have more phosphorus.
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