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| Algae blooms like these have plagued a number of Hill Country creeks and lakes this spring. |
Both rain and sunshine make it grow. It's the basis of the food chain, but too much of it, makes once-clear creeks run thick
and green and can foul the taste of your drinking water. It's algae and it's everywhere this season.
This spring LCRA scientists have reported algae blooms in a number of area creeks as well as lakes Buchanan, LBJ and
Travis.
"I'm driving around looking for it and 90 percent of the time there's algae growing in every body of water you see," John
Wedig, LCRA aquatic science supervisor. "We're hearing from folks calling about algae growing in their bird baths."
Algae are aquatic plants, typically found in small quantities in the water and kept in check by algae-eating fish. Stringy
algae are common in streams and creeks, where it grows attached to rocks, and in lakes along the shoreline. Free-floating
algae are common in the lakes, where the water is more open. Algae blooms occur with warmer temperatures and longer daylight
hours, causing growth so abundant, that it turns the water green.
Tainted taste and smell
If the algae are of the blue-green variety, it makes the water taste and smell musty as it decomposes. For example, the
blue-green algae blooms have tainted the taste and smell of the water in the Sandy Creek arm of Lake Travis. This part
of Lake Travis supplies water to residents of Cedar Park, where the water was being flushed (old water is released to
let new water in) to resolve the problem.
Although algae growth is common this time of year, the blue-green algae usually don't begin to dominate until August
and September, when the weather really heats up.
"What was unique about April's Cedar Park situation is that we don't usually experience these kinds of blue-green algae
blooms this time of year," Wedig said. "But for whatever reason, that Sandy Creek arm had a bunch of blue-greens."
Lick Creek
The proliferation of algae is also apparent on the eastern branch of Lick Creek. Once clear, the creek is now abundant
with the green stuff. Local residents blame a nearby development, which LCRA fined in October for violating its nonpoint-source
pollution ordinance with its sediment discharges. But since the LCRA enforcement action took place, the developer
has complied with specified water quality conditions in the enforcement order. LCRA continues to take and test water
samples to monitor the site, according to Tom Hegemeier, supervisor of watershed engineering and planning.
A more-than-typical amount of nutrients, washed into the water during winter rains, is feeding the growth as well.
Runoff created by land clearing and fertilizer chemicals used for new housing developments may seem to be the logical
source of algae-feeding nitrogen and phosphorous to water in an area like Central Texas, where the population is growing.
However, even rural areas are experiencing algae blooms. Animal feces from ranches and farms contain similar nutrients.
Even turkey manure, a popular organic soil supplement, has a composition that enables algae to thrive in the right conditions.
Other factors
While it is difficult for water scientists to pinpoint the source of nutrients, it is also hard to determine exactly when
the nutrients got into the water. That's why recent residential developments can't always be blamed for the algae.
Nutrients already in the soil need only a good rain to wash them into waterways and begin the algae bloom. Central Texas
experienced those kinds of rains during June and November 2004, making that year the third wettest in more than 100 years.
(The wettest year was recorded in 1919, and the second-wettest occurred in 1900.)
"We can back track to the Thanksgiving flood and other causes that promoted algae growth," Wedig said. "And now that
we've reached springtime, the algae is opportunistic taking advantage of abundant water and sun. We can be certain that
sunlight is playing a large role in the proliferation in algae being seen in Lick Creek."
In addition to longer daytime hours increasing the algae's sun exposure, tree clearing near creeks has benefited algae
growth by intensifying sunshine where there used to be shade, he said. In other words, shade produced by trees and brush
can be a deterrent to the growth of algae.
The algae blooms typically occur naturally and are not harmful to people, but what about aquatic life?
A moderate amount of algae living in water and receiving sunlight facilitates photosynthesis and produces oxygen in the
water, which fish need to breathe. Algae is also eaten by filter-feeders, which swim with their mouths open and eat by
filtering algae from the water, and insects, which are then eaten by fish. However, in the darkened conditions of night,
algae absorb oxygen and when the algae are too abundant, this resulting lack that can kill fish, but only on extremely
rare occasions.
Morales is an LCRA writer specializing in water topics. Have a comment or a story idea? Contact her at info@lcra.org. |
