Biota of Lakes and Reservoirs - Hydro-Environmental Analysis: Freshwater Environments - page 422

Planktonema lauterbornii

Pediastrum simplex

Staurastrum

Asexual
reproduction

Oocystis spp.

Staurastrum sp.

FIGURE 15.10 Some of the more common groups of green algae in the Great Lakes. (From NOAA and
Ohio University.)

inputs. They are able to ix nitrogen to form inorganic nitrogen, commonly a limiting nutrient, so
while they can use inorganic forms if available, they can also make their own if necessary. They
can also take up more phosphorus than immediately required for growth and store it for later use,
known as luxury uptake. They have gas vacuoles, which enable them to regulate their buoyancy
(Oliver and Walsby 1984). As a result, they can rise to the surface to compete for light and nutrients,
creating unsightly scums that can be several feet thick (Smith 2001). In addition to occurring in
large mats, they produce substances that cause strong tastes and odors, which cannot be removed by
conventional water treatment, causing drinking water problems. When these large blooms die-off,
their decay often results in hypoxia. They are also fairly inedible, so they are not a good food supply
to support the food chain of lakes. Finally, as discussed in the following section, certain species may
also release toxins into the water so that blooms of these, and comparable algae, are referred to as
harmful algae blooms (HABs). A result of HABs is often lake closure, such as for the 2010 bloom in
Grand Lake St. Marys, western Ohio (Figure 15.11), where reports indicated that people were suf-
fering from “stomachaches, rashes and numbness” and that “one man, whose dog died after a swim
in the lake, was hospitalized last week after he gave the dog a bath. Within days, the 43-year-old
man began having trouble walking and lost feeling in his arms and feet.”

15.3.1.1.2 HABs
While not a taxonomic grouping, there are a number of phytoplankton groups that, cause harm
when they occur in excess (algal blooms); their blooms are classiied as HABs. The harm may be
due to populations being large enough to block light and to deplete oxygen. More commonly, HABs
are focused on those phytoplankton that release toxic materials into waters, impacting human or
ecosystem health. Many of the organisms responsible for toxic releases are found in estuarine or
ocean environments (e.g., those causing “red tides”).
In freshwater lakes, the primary organisms responsible for HABs are the Cyanobacteria.
Cyanobacteria have a number of characteristics that make them problematic. For one, they may
occur in large populations and are buoyant, so that they may form dense surface mats, like dense
green paint, on the water surface up to several feet thick. Also, when they die, their decomposition
results in hypoxia, taste, odor, and other problems. Cyanobacteria can produce a factor that inhibits