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Aquatic Plants

Factors Influencing Aquatic Plant Growth
 
If you have been on Alabama Power Company reservoirs this year, or any reservoir for that matter, you may have noticed an outbreak of aquatic plants. I can’t count the times I’ve heard people say, “I’ve never seen it this bad,” or “This has never been here before.” 
 
Our reservoirs are dynamic ever-changing systems where the aquatic plant communities are influenced by many factors. A few requirements for aquatic plants to grow are sunlight, temperature, nutrients, and water (yes, just like any other plant). Let’s take a look at each of these requirements.
 
Sunlight
 
There are two categories of aquatic plants: emergent and submersed. Emergent plants are rooted in the lake bottom and “emerge” above the water line as they grow to continue their life cycle. Submersed plants, on the other hand, may or may not be rooted to the bottom and stay below the water line during their life cycle.
 
Emergent and submersed each has different sunlight requirements.
 
Emergent plants spend stored energy early in the year trying to “emerge” above the water surface to sprout leaves and begin photosynthesizing to produce more energy. They rarely survive if they are not able to make this transition. Sunlight tends not to be a limiting factor for emergent vegetation, as you can see by the abundance of shoreline vegetation on our lower Coosa lakes such as Lay, Mitchell, and Jordan.
 
Submersed plants, meanwhile, are more easily influenced by sunlight or a lack thereof. They depend on sunlight getting into/through the water column; which has been very easy to do this summer with the clear water that accompanies a drought. Adding to the problem are lower water levels caused by the drought, allowing sunlight to hit the lake bottom, where it rarely reaches. These plants bolstered by abundant sunlight have been spreading like wildfire.
 
Temperature
 
Different plant species respond differently to temperature changes, but almost all thrive in warm conditions. It’s no surprise sustained hot temperatures this summer have contributed to increased plant growth.
 
 We have shifts in the aquatic plant community throughout the growing season and these shifts are often due to temperature requirements of plants. Certain algae prefer cooler water temperatures, such as Spirogyra – a bright green, slimy alga that is often the first to show up in the spring and recedes as water temperatures increase in the summer. Exotic plants thrive in hot conditions because many originate from tropical areas. Water Hyacinth and Water lettuce have high growth rates in the summer months.
 
Water can also act as a buffer from freezing conditions in the late fall/early winter because water has the ability to gain heat and lose heat slower than air. Have you ever jumped into a swimming pool or lake on a summer night and felt how much warmer the water is when compared to the air? It is because the water has retained more heat from the sunlight during the day. Submersed aquatic plants or those that are on the water’s surface often survive longer into the winter than emergent plants because of water’s ability to stay warmer longer.
 
Nutrients
 
The Coosa has a large aquatic plant community because the river system is rich with nutrients. But too much of a good thing can cause unwanted aquatic plant growth. Nutrients enter the river from various sources including municipal and agricultural runoff, improperly designed septic or sewer systems, and over-fertilization of lawns.
 
Fertilizer making our yards lush and green often runs off and affects aquatic plants. Homeowners can avoid adding nutrients to the river by reducing the amount of fertilizer used on lawns, maintaining buffers of natural vegetation along the reservoir, and by not dumping or blowing grass clippings into the lake.
 
As grass and leaves decompose, the nutrients they contain are released back into the water and become available to aquatic plants.  Alabama Power’s Shoreline Management Department has a Best Management Practices (BMP) document with suggestions on responsibly managing the shoreline. This document can be viewed at apcshorelines.com/pdfs/Shoreline_bmp.pdf.
 
Water
 
Some aquatic plant species will have high growth following a drought. Certain plants are considered annuals and reproduce by seeds; some of which lay dormant on the lake bottom for years before they germinate. A drought is considered a “disturbance” event and causes these dormant seeds to germinate when covered with water after the drought.
 
As I mentioned before, our reservoirs are dynamic, ever-changing systems and we cannot assume everything will stay the same. Some years provide better conditions for aquatic plants than others. As reservoirs age, other factors such as sedimentation drive changes. Aquatic plants are often an indicator changes are taking place with the factors mentioned above.
 
If you are reading this article then you are a stakeholder. According to Google, a stakeholder is a person with an interest or concern in something. In this case the “something” is our reservoirs.
​We depend upon you, the stakeholder, to be our eyes and ears on the reservoirs and notify us if something seems unusual. You can do this by calling 205-257-2393 or if you have an aquatic plant concern; visit https://apcshorelines.com/aquatic/ to submit an invasive plant report.
 
Josh Yerby
Environmental Affairs
Alabama Power Company
205-664-6072
jnyerby@southernco.com



​WATER HYACINTH
​Water hyacinth (Eichornia crassipes) is a non-native, floating plant found throughout the Southeastern United States. It is often difficult to pinpoint the exact introduction of a non-native exotic plant, but this is not the case with water hyacinth.  It was introduced to the United States in 1884 at the World’s Fair in New Orleans. Since then it has spread through much of the United States.
 
Identification
Water hyacinth has broad leaves attached to thick, bulbous stalks. Plants have long, feathery roots and bright, lavender flowers. These plants are often seen in clusters, but free-floating single plants may be found.
 
Reproduction/Growth Rates
Water hyacinth has two modes of reproduction: seeds and stolons. The seeds can remain dormant in the soil for decades before germination. Stolonic reproduction is where one plant sends out a stalk, or “stolon,” and at the end of the stalk grows another plant. This type of reproduction allows water hyacinth biomass to increase exponentially throughout the year as, one plant becomes two, two become four, four become eight, etc.  It can double in population within two weeks.
 
Environmental Impacts
Large mats of water hyacinth can cause major issues with navigation, recreation, water intakes and increased mosquito reproduction. These mats block sunlight from reaching the water column, which degrades water quality by reducing oxygen that fish and other aquatic organisms breathe.
 
Control
If found in an early stage of growth, water hyacinth can be controlled most efficiently with herbicides approved for use in water.  As a tropical plant, it cannot withstand a typical winter at our latitude. The growth achieved within one season typically does not carry over to the next season and the next year’s growth usually comes from seeds.
 
What Can We Do?
Be on the lookout for water hyacinth on Alabama Power reservoirs. Report any findings at 205-257-2393. If possible, take a picture and get a GPS coordinate so we can expedite control measures. After traveling on lakes, boats and boat trailers should be cleaned to prevent carrying “hitch-hiker” plants and animals to the next lake.
 

WATER LETTUCE
Water lettuce (Pistia stratiotes) is a non-native, floating plant found throughout the Southeastern United States. Reports vary on the native range of water lettuce but experts agree that it is tropical. The first documentation in Florida was in 1765 and it is thought to have been introduced by shipping commerce between Florida and South America.
 
Identification
Water lettuce is a floating plant and, as its name suggests, it has the appearance of a head of lettuce. Leaves are pale green. Submersed roots are long and feathery. These plants are often seen in clusters, but free-floating single plants may be found.
 
Reproduction/Growth Rates
Water lettuce has two modes of reproduction: seeds and stolons. The seeds can remain dormant in the soil for years before germination. Stolonic reproduction is where one plant sends out a stalk, or “stolon,” and at the end of the stalk grows another plant. This type of reproduction allows water lettuce to increase exponentially throughout the year as one plant becomes two, two become four, four become eight, etc. One study suggests that under optimal conditions water lettuce can double its biomass in three weeks.
 
Environmental Impacts
Large mats of water lettuce can cause major issues with navigation, recreation, water intakes and increased mosquito reproduction. These mats block sunlight from reaching the water column, which degrades water quality by reducing oxygen that fish and other aquatic organisms breathe. Water lettuce can lower biodiversity by crowding out native plant species.
 
Control
Water lettuce can be controlled most efficiently with herbicides approved for use in water.  As a tropical plant, it cannot withstand a typical winter at Alabama’s latitude. The growth achieved within one season typically does not carry over to the next season and the next year’s growth usually comes from seeds.
 
What Can We Do?
Be on the lookout for water lettuce on Alabama Power reservoirs. Visit our website https://apcshorelines.com/aquatic/ to report finding water lettuce or call us at 205-257-2393. If possible, take a picture and get a GPS coordinate so we can expedite control measures. After traveling on lakes, boats and boat trailers should be cleaned to prevent carrying
 “hitchhiker” plants and animals to the next lake.


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