Eutrophication of Natural Waters

In practice the measured content of P species in fresh and marine waters is higher than dissolved carbon species. This apparent inconsistency arises from sources of nutrient supply. We have seen (Chapter 3, Sections I and 2), that carbonate can be re-supplied by atmospheric CO2. A similar explanation applies to nitrogen since this element can be fixed by blue-green algae with corresponding increasing of dissolved nitrogen species in waters. 

Thus we can see that the interactions of biogeochemical cycles in natural waters and relevant ratios between nutrients in various aquatic living organisms determine the productivity of freshwater and marine ecosystems. 

Equally, many species have looked at grazer nutrient recycling, generally for N in marine waters and for P in freshwaters, but rarely were both nutrients taken into account or their relative recycling rates looked at. 

Microbial mats are communities in surface water ecosystems where bacteria and bacterial processes dominate. In microbial mats dissolved nutrients and metabolites are transformed by one-dimensional (vertical) molecular diffusion. The distinction between microbial mats and biofilms is not sharp. By definition (Fenchel et al, 1998), microbial mats are typically stratified vertically with respect to different functional types of bacteria. Microbial mats are thicker (often several millimeters) than biofilms. In microbial mats various types of filamentous prokaryotes are the most conspicuous part and they are responsible for the mechanical coherence of the mat. The mechanical stability of microbial mats is reinforced by the bacterial excretion of mucous polymers, producing a gelatinous matrix. 

Requirements for the development of microbial mats include a sufficient energy supply and conditions that more or less exclude eukaryotic activity, especially grazing and mechanical disturbance (bioturbation). Microbial mats are widely distributed in spice of the somewhat special conditions required for their formation and integrity. In most places they are transient or seasonal phenomena of limited extension. They grow at most a few millimeters in thickness. 

---

Eutrophication of Natural Waters and Toxic Algal Blooms... 

Figure 835 Mean Eh-pH values for various types of seawaters. A = normal oceanic waters B = oxidized surface waters C = euxinic basins D = eutrophic waters. Dashed line field of natural waters according to Baas Becking et al. (1960).

In summary, it can be reported that toxic cyanobacteria can produce neurotoxic, hepatotoxic, and dermatotoxic compounds that are a direct threat to animal and human water supplies. This threat increases as water bodies become more eutrophic, thus supporting higher production of toxic and nontoxic cyanobacteria. Presence of these potent natural product toxins poses an increasing threat to the maintenance of quality water supplies for agriculture, municipal, and recreational use. 

Cultural eutrophication Overgrowth of algae in natural waters caused by runoff of fertiflzers from land-based applications. 

The potentially harmful effects of exposure to high concentrations of nitrates in drinking water result from reduction to nitrites, which combine with haemoglobin to form methaemoglobin (blue baby disease). Additionally, nitrosamine formation can cause cancer and hypertension. In nature, high levels of nutrients, such as nitrates, lead to eutrophication of water sources, which in, severe cases, lead to the extermination of the other aquatic life due the decreased levels of oxygen and luminosity. 

---