Algae elemental composition

Lakes, of course, are more transient in their chemical and biological characteristics than oceans. A stoichiometry of the nutrients can be observed in the elemental composition of the algae as well as in the concentration depth profiles (see Figure 15.8). 

The chemical composition of all organisms is similar. For example, the elemental composition of algae in terms of carbon, nitrogen, and phosphorus is given by the following ratio of atoms (Redfield etal., 1963) Q06N16P. 

A few studies have been carried out on the trace element composition of nonvascular plants. Schwarz (835) has reported briefly on the selenium content of yeast, and Wey (993) used activation analysis to determine the Mn and Cu contents of chlorella cells. Marine algae have been analyzed for As, Ba, Br, Cs, Co, Ca, I, Hg, Mo, Rb, Re, Sr, U, V, and W by Fukai and Meinke (302,303), Hamaguchi et al. (384), Lunde (572) and Stevenson et al. (919). Merlini and co-workers (609,610) report on the use of nondestructive activation analysis to determine some of these elements in microplankton from fresh water aquatic systems. 

The presence of nutrients and any change of their concentration will influence the growth of higher plants and algae in bioassays. It is a prerequisite to know the elemental composition of the test material. Analysis of the degradation matrix for the main nutrients is always helpful for the interpretation of biotest results and for building relationships to the controls. 

We will illustrate some of the processes involved in a eutrophic lake. Points of interest are the factors that determine the speciation of copper and zinc, the role of biologically produced ligands, how copper and zinc are bound in the settling particles, and whether the settling particles reflect the composition of algae with respect to trace elements. 

Although nitrogen is the element primarily controlling eutrophication in estuaries and coastal seas, and phosphorus is the element primarily controlling eutrophication in lakes, other elements can have a major influence on the community structure of aquatic ecosystems and can influence the nature of the response to eutrophication. A key element in this regard is silica (silicon), an element required by diatoms. The availability of silica in a water body has little or no influence on the overall rate of primary production, but when silica is abundant, diatoms are one of the major components of the phytoplankton. When silica is in low supply other classes of algae dominate the phytoplankton composition. 

Biogeochemical explanations of variations in phytoplankton floristic composition work at two levels. The first level is qualitative, and concerns the crude distinctions between algae that require silicon (diatoms and some others) and those that don t, or between cynaobacteria able to assimilate N2 and all other pelagic photoautotrophs. The second level is quantitative, and concerns the idea that optimum ratios of the nutrient elements required for growth may... 

---