Environmental Engineering Reference
In-Depth Information
Particulate organic P,
including organisms
Heterotrophy
Leakage, lysis
Dissolved organic P
Phosphatase
Assimilation
Oxic precipitation
Inorganic P
FePO
4
Anoxic dissolution
FIGURE 13.9
A diagram of the phosphorus cycle.
Given the importance of phosphorus in nutrient pollution, numerous
phosphorus budgets have been well documented. Chapter 17 explores the
process of quantification of the effects of phosphorus in lakes and describe
wetlands as systems that remove phosphorus from water.
SILICON, IRON, AND OTHER TRACE NUTRIENT CYCLES
Silicon cycles drive the dominance of diatoms in many surface waters
and can be a primary determinant of algal community structure in lakes and
streams. Iron is intimately tied to the sulfur and phosphorus cycles in addi-
tion to being a water quality variable of concern on its own. Manganese,
molybdenum, and many other nutrients have their own cycles as well.
Silicon
Aluminosilicate minerals are the most abundant in the earth's crust
(Schlesinger, 1997). However, silicate is generally not the major dissolved
ion in natural water because of the limited solubility of silicon-containing
compounds (Stumm and Morgan, 1981). Regardless, clays are composed
mainly of silicon-containing compounds and are a primary component in
turbid aquatic systems and sediments. Sand, composed mainly of silicates,
also forms a major component of the benthic substrata of many aquatic
systems. Silicon can take several forms, including
silica
(SiO
2
) and
silicic
acid
(H
4
SiO
4
). Silicic acid is generally the form dissolved in waters.
Diatoms rely on silicon as a component of their cell walls (frustules),
where it is deposited as opal. The opal is relatively insoluble, so it sinks to
the sediments. The burial of these frustules allows for paleolimnological
determinations of the diatom species present over time in lakes.
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