What is algae and what causes it ?
The term "algae"
refers to a wide variety of photosynthetic organisms. Algae range in size from
microscopic phytoplankton to giant marine kelp that may grow to 60 meters long.
During periods of excessive growth, or algal blooms, of one, two or more
species which may cause certain problems for other organisms and degrade water
quality. Large amounts of decaying algae consume oxygen in the water, causing
fish kills if oxygen levels drop too low. A scum of algae floating on the
surface can shade out beneficial plants that provide habitat for fish and
wildlife.
Like all plants, algae
require nutrients to grow and reproduce. Algae are free-floating, so they must
get their nutrients from the water. They do not have the ability to obtain
nutrients from the pond bottom. The higher the nutrient level in the pond, the
more algae you will have. Also, the older a pond gets, the more nutrients it
will have accumulated and the more susceptible it will be to algae problems.
The runoff from fertilized lawns and gardens, fields, pastures, feedlots, septic tanks and leach fields will
accelerate algae growth in the pond.
The amount and type of
nutrient loading in your pond can determine the type of algae that will grow.
At slightly higher nutrient levels, the algae community is often dominated by
filamentous algae. This is particularly true during summer. But with very high
nutrient levels, the algae blooms are typically composed of planktonic algae
rather than filamentous algae. In nature, algal blooms are usually short-lived,
on the order of a month or two, typically because of the combined effects of
nutrient depletion and "grazing" by planktivores. Algal blooms are often
successional, i.e. a green algae bloom can be followed by a blue-green algae,
cyanobacteria bloom. Or for example, when the N:P ratio exceeds 29, there is a
shift in dominance from the blue-green cyanobacteria to green algae and diatoms
(Smith 1983).
Algal production is
correlated to the levels and ratios of nitrogen (N) and phosphorous (P) in the
water. Generally, a phosphate concentration of 0.01 mg./l will support
plankton, while concentrations of 0.03 to 0.1 mg./l phosphate or higher will
likely trigger blooms (USEPA, 1986; Dunne and Leopold, 1978).
How does nutrient reduction help reduce algal blooms
?
The ultimate goal is
to prevent noxious algal blooms (e.g., dinoflagellates and blue-green
cyanobacteria) by nutrient manipulation. The growth of algae can be manipulated
by nutrient dynamics. This is can be achieved through bioaugmentation in a
process called biological nutrient removal (BNR).
Based on the
stoichiometric composition of algae, typically, either nitrogen (N) or
phosphorous (P) is the element present in the algal environment that, when
supplied at a rate less than needed, can limit the growth of algae; this is the
limiting element. This is important in managing eutrophication-related
water-quality impairment.
The bacteria used in
bioaugmentation are selected specifically for their ability to degrade organic
material and detritus, and nitrify ammonia and because of the high CFU counts
(colony forming units) do so at an accelerate rate. These bacteria consume the
nutrients in the water. The microbes ingest carbon, nitrogen, phosphorous at a
ratio of 100:10:4. In the presence of calcium carbonate and high pH, an
insoluble phosphorous particulate is created by the death of the microbes. This
reduces the amount of bioavailable nutrients that are then available for the
algae.
Oxygen
While facultative anaerobes may
function in the presence or absence of oxygen, aerobic activity is the
preferred method for many contaminants. When bacteria have available oxygen,
and hence function aerobically, they produce roughly eighteen times as much
energy as anaerobic activity yields. This results in faster, more aggressive
remediation.
Nitrogen
Nitrate and ammonia
are typically available forms of Nitrogen. If the bioaugmentation process is
targeted for ammonia, and the ammonia is reduced,
then we have in effect altered the ratio of nutrients in the water. The ratio
of nitrogen to phosphorous has been disturbed and ceases the production of
algae.
Phosphorous
Phosphorous occurs in nature and is
critical to the support of life. However, excess phosphorus can cause a severe
environmental impact in both fresh and marine ecosystems. Algae blooms are
caused by an over abundance of nutrients and phosphorus is often the limiting
nutrient in the growth of algae.
As little as 15 parts per billion
of total phosphorous can encourage excessive production algae. Undesirable
aquatic plant growth results from additions of phosphorus to the water. The net
result of the eutrophic condition and excess plant growth in water is the
depletion of oxygen in the water due to the heavy oxygen demand by
microorganisms as they decompose the organic material. It severely impacts the
lakes natural ability to support aquatic life.
Types of Algae common in Ponds
Filamentous algae
Filamentous algae, or
commonly referred to as "pond scum" or "pond moss" forms greenish mats upon the
water's surface. The stringy, fast-growing algae can cover a pond with slimy,
lime-green clumps or mats in a short period of time. This algae usually begins
its growth along the edges or bottom of the pond and "mushrooms" to the
surface. Individual filaments are a series of cells joined end to end which
give the thread-like appearance. They also form fur-like growths on bottom
logs, rocks and even on the backs of turtles. Some forms of filamentous algae
are commonly referred to as "frog spittle" or "water net".
Some common types of
problem filamentous algae :
- Spirogyra - bright green and
slimy to the touch
- Cladophora - has a cottony feel
- Pithophora- often referred to
as "horse hair" algae because its coarse texture resembles that of horse hair
and it may feel like steel wool.
Spirogyra spirogyra (SPIRE oh ji ruh)
Spirogyra is a
free-floating genus of filamentous algae belonging to the division Chlorophyta.
It is a photosynthetic algae with impressive long bright grass-green filaments
with spiral-shaped chloroplasts. It is sometimes known as "green silky-strand
algae". It is bright green in the spring but deteriorates to yellow. Spirogyra
grows in running streams of cool freshwater, and secretes a coating of mucous
that makes it feel slippery. This freshwater algae found in shallow ponds,
ditches and amongst vegetation at the edges of large lakes. Under favorable
conditions, Spirogyra forms dense mats that float on or just beneath the
surface of the water. Blooms cause a grassy odor and clog filters especially at
water treatment facilities. Masses of it are very slippery. It is most abundant
in the spring.
O. Siphonocladales pithophora pithophora
Pithophora belongs to the family of
filamentous green algae. Pithophora is a common mat-forming species, commonly
referred to as "horsehair algae", that inhabits ponds, and is especially
troublesome in Florida. It clogs waterways and lakes with its large mats and
filaments.
Pithophora may range in color from
lime green to a dark green or greenish brown. It is often described as
resembling a tangled mass of steel-wool or wool-like growth which is very
course to the touch. Individual filaments show extensive branching. It may be
found growing on the bottom in a mat or in a column, with large sections
reaching for the surface of the water forming dense mats on the surface. It's
growth is quite prolific. These algae possess the ability to fix and store
nitrogen for growth, and out compete other vegetation.
Pithophora grows on the bottom,
attached to the substratum by holdfasts, and sporadically surfaces. When it
becomes dense enough, the plant produces gas bubbles that become trapped. In
warmer water, it becomes buoyant and it floats to the surface. Disturbance of
these mats by high wind or heavy rain events may cause them to temporarily sink
to the bottom. This often gives a false impression that the growth has
"disappeared", only to have it return to the surface within several days.
Pithophora pithophora resembles
cladophora and the two are difficult to distinguish. If, after a normal
treatment with copper sulfate, there is algae remaining that does not appear to
be affected, or disappears for a few days, but then bounces back, then it may
be pithophora.
Cyanobacteria - Blue-Green Algae
Cyanobacteria
(technically a bacteria, not an algae) comprise a single class, Cyanophyceae.
Cyanobacteria is often mistakenly classified as algae (Blue-green algae)
because of the chloroplasts contained within the cells.
This diverse group of
cyanobacteria can exist in all settings from freshwater to terrestrial settings
and from oligotrophic (low nutrient) to hypereutrophic (very high nutrient)
environments.
Changes in the ratio
of nitrogen to phosphorus (N:P ratio) can affect algal species composition
within a given lake. Some species of cyanobacteria (blue-green algae) have a
competitive advantage over other algae by having the ability to fix nitrogen,
whereas other types of algae cannot. Nitrogen fixation is the process of
converting unusable nitrogen (atmospheric nitrogen) into usable nitrogen
(ammonia). This characteristic allows these species to exist in areas where low
nitrogen availability inhibits growth. Therefore, under phosphorus-rich
conditions, when nitrogen may be limited, blue-green cyanobacteria algae have a
competitive advantage because they can utilize ("fix") nitrogen directly.
Cyanobacteria can
also successfully compete against other groups of such as green algae and
diatoms because they can store phosphorus for later use, and are not preferred
as food by zooplankton (microscopic animals), larval fish and other animals
that graze on many kinds of algae.
In fresh water
systems, many blooms are due to members of the cyanobacteria family. They can
grow so profusely that they can impart an objectionable odor, taste, and
appearance to the water. Many of these cyanobacteria release toxins into the
water, causing health concerns in both animals and humans. People exposed to
the cyanobacteria, blue-green, algal blooms by swimming in affected lakes or
rivers have experienced skin irritations, allergic reactions, gastrointestinal
symptoms, and respiratory problems.
Planktonic
Cyanobacterial Ecology require:
- physical stability: turbulence
or fluctuating conditions prevent/eliminate blooms
- common in extreme (but stable)
habitats
- prefer neutral to acidic water
- efficient buoyancy
regulation
- dominance aided by high
organics, high P:N ratio (due to N2-fixation ability), low metals
- some produce potent
hepato-/neurotoxins of unknown ecological role
- not preferred food of
microcrustaceans; protists, rotifers, tropical cichlids (Tilapia) &
flamingos
- may be dormant for years,
germinate when favorable
- typically produce these blooms
are planktonic, or free-floating organisms, that can become distributed
throughout the water body
The most common
troublesome algae are species of cyanobacteria are:
- Oscillatoriales - filamentous,
non endo/exospore-producing; incl. Oscillatoria, Lyngbya, Anabaena, Nostoc.
- Microcystis
- Cylindrospermopsis
- Aphanizomenon
Nostoc: A fine,
filamentous cyanobacteria that can form spherical colonies
Oscillatoria: Long blue-green, unbranched
filaments that oscillate naturally. Most tolerant of organic pollutants.
Oscillatoria spp. often inhabit depths of thermally stratified lakes in which
gradients of physical and chemical factors occur. Often found with Euglena in
waters with high nitrogen levels. Common in farm ponds and lagoons where sewage
is treated. O. rubescens is a red species that can form conspicuous red blooms
in eutrophic lakes. Some species of Oscillatoria are known to produce toxins.
These include both neurotoxins called anatoxins and hepatotoxins called
microcystins. Anatoxins can block the transmission of signals from neuron to
neuron and neuron to muscle, while microcystins cause bleeding in the liver.
The threat is more to livestock then to humans.
Lyngbya
A species which is
particularly troublesome to control using traditional copper sulphate and
chelates. They grow in colonies forming small spongy masses of mucilage. These
blue-green, black or gray clumps made up of thousands of individual cells will
lay on the bottom or float to the surface. Because of its protective mucilage,
chemical control is difficult.
Lyngbya is one of the
groups of cyanobacteria that are of special concern. This long, hair-like
organism is a filamentous alga that can form large benthic (on the bottom) and
surface mats (blooms). Lyngbya normally grows in dense mats at the bottoms of
nutrient enriched lakes and spring fed systems. These mats produce gasses
during photosynthesis that often causes the mats to rise to the surface. At the
surface, winds pile the algal mats against shorelines or in navigation
channels; these mats can be several acres in size. Lyngbya, is one of the
cyanobacteria that is known to release toxins into the water. These three
toxins, debromoaplysiatoxin, aplysiatoxin and lyngbyatoxin have been found to
be a major cause of dermatitis.
Anabaena (ann uh BEE nuh) This cyanobacteria is
capable of causing odor even in small numbers. It can form surface scums, where
concentrated cells can be drunk by livestock. Produces toxins that can cause
skin rashes in humans and has been know to cause death to livestock drinking
infected water.
Microcystis (MIKE row sis' tis) is an important
bloom-forming cyanobacter. This spherical, unicellular algae can form a colony
(group of cells). Though microscopic in size, when in bloom proportions, it
will turn the water a blue-green color and may form surface scums. Some strains
of Microcystis have the ability to produce a toxin known as microsystin. In
abundance, this toxin is potentially harmful to animals.
Cylindrospermopsis
This tropical algae,
Cylindrospermopsis, is found in rivers, freshwater lakes and ponds and
reservoirs . This particular species grows abundantly and blooms in subtropical
freshwater lakes and rivers with high levels of phosphorus and other
nutrients.
Unlike Anabaena or
Microcystis, the cells of Cylindrospermopsis are extremely small and do not
form surface scums. It does produce a brown tint to the water, but cannot be
easily distinguished from suspended sediment or other types of algae that also
appears brown, such as diatoms. The algal cell densities may be very high, in
the hundreds of thousands per millilitre, and located in bands several feet
from the surface in a lake, stagnant pond or slow moving water. There is no
taste or odor associated with Cylindrospermopsis or its toxins.
Like others in this
group, Cylindrospermopsis produces oxygen by photosynthesis and can fix
nitrogen from the air and so can live without relying on nitrogen sources in
the water. In recent years, this species has begun replacing other
bloom-forming algae as the dominant alga following the nutrient enrichment of
lakes, reservoirs, and rivers. There is now evidence that it appears to be
moving into more temperate climates.
Cylindrospermopsis is
very small, even in comparison to other microscopic algae, and is made of a
filament that is either linear or coiled and composed of rectangular cells with
basal heterocysts (nitrogen fixing cells).
Cylindrospermopsis,
when found in large quantities, can produce several substances that show
toxicity, including:
- (1) cylindrospermopsin, which is
mainly toxic to the liver, but can affect the kidneys, heart and other organs,
and may be carcinogenic and genotoxic;
- (2) saxitoxin, which is a
neurotoxin that can cause paralytic fish poisoning leading to paralysis and
respiratory distress in fish eaters; and
- (3) anatoxin-a, which is a
neuromuscular agent that can result in paralysis, respiratory distress and
convulsions.
Case study of Algae reduction - Lake in central
Florida
Pond
and Lake management - bioremediation products
Typical
example of a lake remediation project - case study
If you you are considering having
a pond company quote on cleaning your pond - here are a list of factors that
should be addressed Ponds - questions for successful
projects
