b"INTERNATIONAL WATERSWhich water quality parameters matterfor Harmful Algal Bloom (HAB) events?Growth-stimulating nutrients are a cause of harmful algal blooms and thus an obvious thing to monitor for, but certain types of organic matter often accompany those nutrients and can be valuable surrogates to monitor as well. Salinity is interesting particularly in coastal environments, where freshwater incursions might introduce algae into a system, at the same time reducing salinity. Most algae, such as the red tide-former Karenia brevis, have specific salinity ranges at which they can grow. The dynamics of a system and objectives of a monitoring program will dictate whether these water quality parameters will be valuable. In almost all scenarios, however, certain water quality parameters are a must-have: namely algal pigments, pH, DO, and temperature. This has proven to be true for the expansive Lake Taihu monitoring network. Understanding HAB events is key to the monitoring program.TemperatureAlgal Pigments Warming waters in Lake Taihu, dueAlgae have unique pigments that to climate change, seasonal shifts,they use for photosynthesis, the or thermal pollution, favor theprocess of using sunlight and proliferation of most blue-greencarbon dioxide to grow. All algae that form HABs. algae, from blue-green algae to red-tide algae to seaweed, Like most life forms, algae have ause the pigment chlorophyll for preference for specific temperaturephotosynthesis.ranges. While it affects algal growth, temperature isnt affected by algae, distinguishing itLake Taihu's blue-green algae have additional from pigments, DO, and pH.pigments that are useful to monitor and help distinguish the types of algae that are less likely to be One shouldnt fall for the notion that an HAB canttoxic. The pigment phycocyanin is a unique indicator occur in cool waters. Some species of algae areof blue-green algal growth in freshwater systems, and more prone to bloom in springtime, when watersa similar pigment called phycoerythrin is an indicator are slightly cooler (such as Anabaena in Northof blue-green algal growth in marine systems. America), while others favor summer waters (such as Microcystis, virtually anywhere it is found!). ThereUsing in-situ sensors for algal pigments can reduce have even been algae blooms under ice (such astime and expense required for manually collecting some species of Planktothrix). water samples, whether those samples are used for pigment extractions, cell counting and algae As a general rule, HABs have a predictable seasonspeciation, or toxin analyses. Sensors also can help in most source waters, and this is true for Lake Taihumanagers to identify when to apply treatments, saving where Microcystis often dominates. Changes intime and money. While clearly powerful technology, temperature are good indicators that one should bealgae pigment sensors of any type are most valuable on alert for.when paired with DO, pH, and temperature. 30 MISSION: WATER"