b'INTERNATIONAL WATERSAcidity or Alkalinity (pH)Dissolved Oxygen Many water managers observeNormal concentrations of DO predictable pH patterns whenvary widely, and are affected by watching for HABs. Like DO,temperature, barometric pressure, pH responds to the growthand salinity. As temperatures of algae, typically increasingincrease, DO decreases; with increased algal growth.as pressure decreases, DO Also, as with DO, pH\'s responsedecreases; as salinity increases, to algal growth is a balanceoxygen solubility decreases. In between photosynthesiswhichgeneral, fish require over 5 mg of consumes dissolved carbon dioxideandoxygen per liter of water to breathe, and respirationwhich generates carbon dioxide. Whileconcentrations below that will place most aquatic live algae are the main consumers of carbon dioxide inunder significant stress. a system, they and all the other organisms respire, generating CO2.Algae have interesting effects on DO in Lake Taihu. Oxygen is a product of photosynthesis, and in As algae consume CO2, less of the gas dissolves intoa balanced diurnal cycle of photosynthesis and the water as carbonic acid. With less of this acidicrespiration, algae generate and consume oxygen. form in the water, the pH will increase during periodsMeanwhile, other organisms continuously consume of high algal growth, especially during daylight hours.oxygen. When algae bloom in Lake Taihu, an Thus, pH can be a highly useful indicator of both theimbalance occurs.rise and decline of an algal bloom in Lake Taihu. It can even reach pH 9 or 10 during severe blooms. During the early and peak growth phases of an HAB, DO can increase significantly in the vicinity Lake Taihus pH levels have also been shown to beof the bloom due to exceedingly high daytime influenced by CO2-generating automobile emissionsphotosynthetic activity. More oxygen is generated that facilitated higher introductions of CO2 into thethan can be consumed by either algae or other water from the atmosphere. This acidification effectorganisms, and sensors may indicate that the water is can counter the acid-reducing effect that high-algalsuper-saturated with oxygen.growth might have.As the bloom fades and dies, photosynthetic activity This dynamic demonstrates that general water qualitydeclines, and further the expired algae become parameters, and what they mean for the purposefood for bacteria and other things that consume of HAB monitoring, are very context-specific andoxygen. The overall effect is that DO levels can a system-level understanding is important beforedrop precipitously. Such anoxic conditions can be conclusions are drawn regarding the stages of andangerous for other life in the water, and is often the algal bloom. It is also the reason that monitoringroot cause of fish kills that occur in the wake ofmultiple parameters is highly valuable. a HAB.Monitoring urban development is equally as important as protecting the historical aspect of Lake Taihu. This buoy is located next to the "Star of Lake Tai" one of the world\'s largest ferris wheels.Whos Minding the Planet? 31'