Summer is the time of year where we start seeing various shades of green, blue, red and brown in Dallas area water bodies.
These different colors are typically
associated with different types of algae.
Algae is a generic term that covers many different organisms from single
cell bacteria to large, multi-celled organisms.
Algae may appear as pond scum, long fibers, or cause the water color to suddenly change.
What ties them all
together? They all get their energy
from the sun through photosynthesis and get their nutrients from the water.
What is an algae
bloom? Algae is always present in Dallas
area waters. They are a critical
ecosystem component, in that they provide food and through photosynthesis, help
with oxygen in the water. However,
through the process of eutrophication (enrichment of a water body with
excessive nutrients), some species of algae can flourish to nuisance and
dangerous levels. How fast this happens
is driven by nutrient levels, ph of the water, increased water temperature, the
amount of sunlight hitting the water, mixing by the wind, and area water/land
management practices. In other words,
during a Texas summer, it can happen very rapidly. As the algae starts to use up the nutrients,
it begins to turn brown and die. When
algae starts to die, combined with warmer water temperatures, the dissolved
oxygen content of the water drops quickly.
This is the oxygen available to fish, and as the level drops, we start
to see fish kills.
What is a cyanobacterial
bloom? Cyanobacteria is also known
as blue-green algae. With the right
combination of nutrients (nitrogen and phosphorus), water temperature and
sunlight, a “cyanobacteria bloom” can occur.
Some species of cyanobacteria, like Microcystis
sp., can produce what is known as a cyanotoxin. This toxin can make humans sick, but is
potentially VERY dangerous to dogs that may drink or swim in the water. This is the type of algae bloom currently
(June/July 2017) being seen in Lake Cliff Park.
The bright neon green, and general pea soup appearance of the water is
characteristic of this type of blooming event.
Where do the
nutrients come from? The main
nutrients in question are nitrogen and phosphorus. Nitrogen can get into the parks’ lakes from
many sources, and not just close to the lakes.
The lakes in Dallas parks are often the recipient of large amounts of
stormwater runoff. That runoff may
contain leaves and grass clippings which can decompose, dog and wildlife fecal
matter, and fertilizer. All of these add
to the nitrogen getting into the water.
Phosphorus tends to bind tightly to soil. This is why sediment from erosion becomes a
major water quality issue. As the soil
settles into a water body, the phosphorus slowly leaches off of the soil and
into the water. Algae blooms are often
driven by the amount of phosphorus that has gotten into a water body. A particularly rainy Spring/Summer, with high
volume rain (ie flooding) events may help trigger algae blooms as the water
heats up in the summer.
How does the Dallas
Park and Recreation Department minimize the potential for algae blooms? The Dallas Park and Recreation Department
takes several steps to help minimize and the react to algae blooms if
- Through Integrated Pest Management (IPM)
practices, the department works to minimize the amount of fertilizer and other
chemicals that are used on park properties.
- Where practical, a 5-7 foot vegetated buffer
strip is maintained along shorelines to help act as a filter for nutrients and
help control erosion.
- Ponds and lakes are chemically treated as part
of routine maintenance, with EPA approved chemicals that help keep nutrient
levels in check. This does not prevent
algae from occurring, but minimizes the chances of a nuisance or harmful algal
bloom (HAB). It is important to note
that following large amounts of rain, the nutrient load may exceed what is
normally taken care of through routine maintenance.
- Park Department staff monitor park ponds and
lakes for the presence of algae, and will report to and work with other city
and state agencies when an issue is noted.
This may lead to additional and/or more extensive water quality testing,
and additional water treatment if needed.
- Encouraging park users to pick up dog
waste. Dog waste can be a significant
contributor to nitrogen levels. This is
extremely important around dog park areas and near bodies of water.
- Where appropriate, water display fountains are
installed. These fountains help
circulate the water and keep the dissolved oxygen content up in the water.
- If a potentially hazardous condition occurs, the
department will take steps to minimize the hazard to the general public.
How can YOU help with
minimizing algae blooms in Dallas? There
are multiple ways you can help minimize algae issues in Dallas.
- Work to maximize the efficiency of fertilizer in
your yard. That means the fertilizer
stays in your yard. Test your soil so
you only put the nutrients your yard needs.
Make sure whatever fertilizer you may use is carefully watered in so
that it does not end up getting washed away in a big rain event.
- Do not sweep your yard clippings into the
street. As much as possible, mulch your
- PICK UP YOUR DOG’S WASTE and properly dispose of
it. This is especially important around
the dog parks.
DO NOT FEED THE WATERFOWL AROUND THE LAKE. This tends to concentrate the ducks and geese
to one small area, and significantly increases the nutrient load in that
area. They will find food without you
- Watch for significant soil in runoff water,
especially around construction projects.
Soil is a major contributor to phosphorus levels. If you see significant amounts of soil
leaving a specific site, please submit a report to 311.
- If reports and signs are put up regarding HAB
conditions at a particular pond or lake, please avoid contact through swimming
(not allowed anyway), fishing or allowing your dogs to have contact with the
water until otherwise notified.
We can never completely stop an algae bloom from happening
in an ecologically responsible manner.
However, we can take steps to minimize the chances of them
occurring. If an algae bloom does occur,
there are steps that can be taken to minimize potential health and ecological
hazards. Also remember, most algae
blooms are more of a nuisance and not a health hazard.