Factors Affecting Primary Production
The rate of primary production of a parcel of a marine environment depends on light and on the chemical conditions provided by the physics of water masses. There is thus a complex coupling of physics, chemistry, and biology in marine environments. In this chapter we start in reductionist fashion by examining how light, nutrients, and temperature affect primary producers. We focus on two major variables—light and nutrients—and their role in determining primary production. Grazing and sinking, the other major factors affecting producers, are discussed in Chapters 5 and 10. We end this chapter with some examples of how the motion of water masses affects production in the ocean through its effect on availability of light, nutrients, and temperature.
KeywordsCoastal Water Photosynthetic Rate Particulate Organic Carbon Oceanic Water Phytoplankton Production
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- *.Phytoplankton absorb light primarily at wavelengths about 400 and 700 nm (Fig. 2–11). Water absorbs mainly near 700 nm, while the dissolved organic matter absorbs at wavelengths nearer 400 nm (Yentsch, 1980).Google Scholar
- *.There is some doubt about the validity of estimates of K S obtained by incubation periods as long as hours, such as those in Table 2–1. Ammonium uptake can be very rapid during the first few minutes of exposure to nutrients (Glibert and Goldman, 1981), and slows later. Estimates obtained in exposures longer than 1 hr or so may therefore underestimate K s (Glibert et al., 1982).Google Scholar
- *.Oceanographers express concentrations in gram-atoms of an element per liter, since this makes it clear that, for example, a reported value refers to the nitrogen in nitrate (NO3) and does not involve the oxygen. The actual expression is usually shown as µgat NO3-N liter-1. Concentrations are also often stated in molar (M) units. This is just as convenient a system of units, and µM NO-1 3 is equivalent to µgat NO3-N liter-1 in the case of compounds such as NO3 or NH+ 4, where one atom of the μ element in question is present.Google Scholar
- *.This kind of laboratory experiment is artificial in that sedimentation and grazing losses from the water are curtailed. Further, the regeneration of nutrients provided by grazers is also absent. Nonetheless, such experiments are a convenient, simple description of the situation.Google Scholar
- † There is little evidence that silica by itself limits phytoplankton in freshwater, even though it is a major component of diatom and other phytoplankton (Paasche, 1980).Google Scholar
- *.There are low but detectable concentrations of Si over much of the oceans. In upwelling regions intense bloom of diatoms may deplete silicon, but there are few instances of direct evidence of Si limitations for the sea (Paasche, 1980).Google Scholar
- †.F. Morel (personal communication) proposes that this is because most iron exists as Fe3+ in seawater. Phytoplankton take up Fe2+ more readily than Fe3+ and have to rely on photoreduction of Fe3+ to Fe2+ to be able to take up iron. The iron added in the experiments may have been—or may have been quickly converted to—oxidized iron.Google Scholar