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CHAPTER 1. ENVIRONMENTAL ASPECTS OF EUTROPHICATION

1.2. Eutrophication as an Environmental Problem

1.2.5. Limiting Factors

Supplies of light and nutrients determine the growth of algae and aquatic vascular plants. Therefore, these resources can be considered limiting factors in the development of the plants. Although one factor seldom consistently limits plant growth under the varying and interacting conditions prevalent in aquatic ecosystems, dominant control, at a particular time and place, often can be attributed to a single factor. Approaches for assessing the role of different nutrients are discussed in section 1.4.1.

Light availability plays a key role in the development of submerged aquatic vascular plants, which are usually rooted and can access sediments for nutrients. Hence, waters made turbid by suspended sediments or algal blooms, or shaded by floating aquatic plants are not conducive to the submerged, aquatic vascular plants. In contrast, floating plants are well positioned to receive sunlight, and depend on nutrient-rich water for the inorganic nitrogen and phosphorus. Phytoplankton abundance and species composition changes as a function of ratios of supplied nutrients and underwater light conditions. Some species of cyanobacteria, which is an algal group with members known to produce noxious conditions, can regulate their buoyancy and often become common as turbidity increases. Apparently, subtle differences in ratios, such as nitrogen to phosphorus or phosphorus to silicon, can alter competitive relations among algal species.

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