Lake Atitlan, Guatemala and the Cyanobacteria
Morning at Lake Atitlan, Guatemala April 2 2010Introduction: Guatemala City - In December 2009 we published a series of articles about the causes and solutions for the cyanobacteria Lyngbya hieronymusii bloom in Lake Atitlan.
Morning at Lake Atitlan, Guatemala April 2 2010Introduction:
Guatemala City - In December 2009 we published a series of articles about the causes and solutions for the cyanobacteria Lyngbya hieronymusii bloom in Lake Atitlan.
To update the information about Lake Atitlan, we have been interviewing scientists and environmental experts about the newest findings that explain the phenomenon and to verify the original hypothesis that we presented: Too much nutrients flowing constantly into Lake Atitlan, plus little rain, plus little wind and hot weather, produced the conditions necessary for the blooming of the cyanobacteria. Basically the hypothesis about the cause of the blooming has been confirmed by international and national scientists.
However, the local population, the general public in Guatemala, NGO´s, government officials and scientists of different institutions in Guatemala are still struggling to understand the problem. A lot of additional research is required to obtain key information to take the appropriate decisions concerning the solution of the problem. It is probably the lack of this much needed research that causes the misconceptions and views of the people involved in addressing the problem. The general recovery plan for Lake Atitlan is good, it just requires some fine tuning according to the new research that will help to explain the problem better, and of course it has to be implemented.
The most important misconception at the moment is that the cyanobacteria has disappeared - "se desapareció", because it is no longer visible on the surface of the lake. People do not understand that the lake is a complex water body and ecosystem and that the most important events take place beneath the surface and are not visible from above.
Under the lake surface a lot of things are happening, in this article we try to explain what happens under the surface and how the different elements interacts and produce a healthy lake or a lake that can bloom again.
Background information on the Cyanobacteria
As a taxonomic group, Cyanobacteria, also called blue green algae, exist in basically all water bodies in the world as well as in deserts, soils, Antarctic ice and as dust in the air. They are one of the oldest life forms on earth, if not the oldest and they have been developing for over 3 billion years. We often see them as a nuisance or treat, but the fact is that they often do more good than bad. It is believed that cyanobacteria are the reason why we have air to breathe, as they have been producing a big part of the atmospheres oxygen and thereby contributing to the 20% oxygen part of what we call air. It is also one of Mother Nature's first lines of defense if a body of water is contaminated for one or other reason. Most cyanobacteria have a tremendous possibility to absorb nutrients like Nitrogen and Phosphor compounds in water as well as carbon in different forms.
As the Lyngbya, Lyngbya hieronymusii is little known we are assuming that they behave similar to other species of fresh water Lyngbya such as L. wollei and others that live in the benthic zone of a lake. The benthic layer is the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers.
Another characteristic is that Lyngbya is buoyancy neutral or slightly negative but lack direct buoyancy control as is normal to other cyanobacteria such as Microcystis sp. It could however float to the surface on external gas bubbles formed by oxygen release trough the photosynthetic process or from gas bubbles formed by decaying biomass beneath the live Lyngbya.
Some scientists believe that L. hieronymusii has the ability to regulate its buoyancy trough gas vesicles and that they might be able to do Nitrogen fixation. Other scientists and studies contradict these findings. This will probably be clarified soon as more scientific studies are being undertaken.
Why are people so upset about the Cyanobacteria in Lake Atitlan?
First, at the end of 2009, the Lyngbya, specifically, which is a fast growing cyanobacteria under the right circumstances, was outgrowing itself and mass death occurred due to lack of light. The Lyngbya was growing on top of each other and the lower layers of Lyngbya died of lack of sun light
These mats of dead and alive Lyngbya or pieces of it, started to float to the surface, creating, with lack of better words, an ugly looking stinking mess.
Is the Cyanobacteria toxic?
Yes and no, it all depends on the type of Cyanobacteria. Some types of Cyanobacteria are sold at high prices as health medicine or food supplements like Spirulina.
The Cyanobacteria Lyngbya hieronymusii found in Lake Atitlan is toxic according to some sources and non toxic according to others. It still has to be confirmed if the Lyngbya hieronymusii contain cyanotoxins or not.
There are several factors that cause the toxicity to go up or to be lower, such as: stress factors, contact, if the cyanobacteria are alive or dead, the movement of the water, the currents, the level of sun light, level of decomposition, stress exerted on dead or live cyanobacteria. The list goes on and on, more research has to be carried out regarding this issue.
So far, both positions are probably right. One of the first studies of these uncommon cyanobacteria was carried out by the Guatemalan Scientist Pablo Mayorga and his results confused a lot of people and were considered inconclusive. But Mayorga's analysis was right. His findings where that the samples of Lyngbya from the middle of the lake where extremely toxic, as the cyanobacteria used in those samples where alive. The samples collected at the lake shore where dead cyanobacteria and they were slightly or non- toxic. Another source, Dr. Eliska Rejmankova, did her studies and tests (analytical chemistry) at UC Davis and Greenwater Laboratories in Florida and got somewhat different results. They mention that only trace amounts of saxitoxins and cylindrospermopsins are present in samples taken a week after Mayorga's sampling took place.
How can these findings be explained?
When the Lyngbya is alive, they are toxic, to protect itself from predators like fishes, humans and other animals. It releases its toxins when it is eaten or touched in any way. For example, when humans swim in the lake water they disturb the Lyngbya's fragile "bodies", toxins are released and humans can get stomach pain and skin rashes.
So the samples taken from the center of the lake consisted of vigorous Lyngbya and the ones close to shore were dead or dying samples that had lost its sting. This will be explained later in the article under the segment, Physical and geological properties of Lake Atitlan.
The scientific studies concerning the toxicity of the Lyngbya are still in the early stages, what variables have the most impact on the toxicity or non toxicity of the Lyngbya is still not known. Further studies are needed. For instance, some scientists have found that the Lyngbya hieronymusii might have some medicinal properties and a slight phytotoxicity. The bioassay organism (fairy shrimp) used by Mayorga to evaluate the toxicity of the biomass is capable of detecting bioactive products with potential medicinal properties.
lyngbya Lake Atitlan April 3 2010Will the Lyngbya be back at Lake Atitlan?
The answer is: The Lyngbya has never left; it is still there and has been there for probably thousands or millions of years.
The next question is: Will the Lyngbya bloom again?
We should probably say yes. But to answer this and many other questions first we must understand how the Lyngbya lives, why does it multiply, what does it live on, why does it die, etc. We also have to understand a bit of the physics of the lake itself.
Physical and geological properties of Lake Atitlan.
First of all there are a lot of rumors saying that the Lake has turned into a Eutrophic lake as it was blooming. This is not true and Atitlan should still be considered Oligotropic but with certain slightly Eutrophic areas such as the bay of Santiago de Atitlan.
What does Eutrophic and Oligotrophic mean.
* Eutrophic: Having waters rich in mineral and organic nutrients that promote a proliferation of plant life, especially algae, which reduces the dissolved oxygen content and often causes the extinction of other organisms.
* Oligotrophic: Lacking in plant nutrients and having a large amount of dissolved oxygen throughout.
This however doesn't mean that an Oligotrophic lake is clean or that its water is safe to drink. As a matter of fact water from a naturally Eutrophic lake could be safer to drink than from a polluted Oligotropic lake.
Lake Atitlan is a deep lake where the shores in most parts slope steeply down towards the center of the lake. This sets this lake apart from most other lakes in the region. The lake is also surrounded by relatively high mountains and doesn't have any surface water runoffs, no rivers are flowing out of the lake. All this influences the dynamics of the lake.
Normally the Lake has, sometimes strong winds shifting from south to north creating a stirring motion and also moving the water in a north- south shifting current. This is due to weather systems and the topography around the lake. As the Lake is in the tropics, rainfall and cloudy skies form during the rainy season and none or little rain falls during the dry season. This also helps to mix the water in the lake due to different density of cold rain and underlying warmer water in the top layer of the lake during the rainy season.
During the year 2009 in particular, there was little rain and clouds during the rainy season, there where long periods of very little wind at the Lake due to change in climate. Why this happened is out of scope for this article but it is most likely caused by the cyclic phenomenon called El Nino or by Global Climate Change.
The daily wind that lake Atitlan has is called Xocomil, it is a wind that moves from south to north, it starts at approximately 10 am in the bay of Santiago, then it moves across the lake in the direction of Panajachel and increases in speed and force creating big waves in the middle of the lake and then it hits the shores of Panajachel, San Marcos, Santa Catarina and other villages located at the North end of the lake.
The Xocomil in 2009 was weaker; the result was less waves and water movements than usual.
The layers of water and their relationship to the Lyngbya bloom.
Our hypothesis is that the Lyngbya bloom is related to something called stratification. Stratification is caused by the density of water (and air); cold water is denser and has a higher specific weight then warm water. It creates 3 different layers in a lake called:
* Epilimnion - top of the lake.
* Metalimnion (where the Thermocline forms) - middle segment, that may situate at different depths throughout the year and days.
* Hypolimnion - the bottom segment.
These segments are normally broken up to a certain degree and mixed with each other due to currents, wave action, solar radiation and ambient temperature. Some mixing also takes place where thermal wells present at several places in the lake releases, heat at the bottom and hot water rises to the surface.
The Epilimnion segment (top of the lake) is the most active segment as it contains most of the life in a lake and is exposed to factors such as solar radiation, wind and rain.
The Thermocline segment is a relatively thin segment separating the mixed Epilimnion segment from the calm and stagnant Hypolimnion segment (bottom of the lake) from each other and could be seen as an invisible blanket between the two.
The Hypolimnion segment of lakes located in the temperate zones of the planet is the coolest part of the lake in the summer and the warmest part in the winter. This does not apply to tropical lakes such as Lake Atitlan. In Lake Atitlan the Hypolimnion (the bottom segment) is always the coolest segment in the Lake. The bottom segment of water is also by far the largest volume of water in a deep lake like Atitlan.
Figure 1. The lake in a normal partially mixed state, with a weak thermocline segment. The Lyngbya only grows on the sloping bottom down to the dept of usable light penetration.
Our Hypothesis is that the climate in 2009 didn't permit any or little mixing of the 3 different layers, therefore the stratification was more pronounced than normal and the Epilimnion segment (top segment) got warmer due to lack of circulation, evaporation and to strong absorption of solar radiation.
Remember the Thermocline segment? This segment of the lake also got more pronounced due to greater temperature difference between the other two other layers and acted like an invisible (false) bottom in the lake.
This had several effects.
The Lyngbya normally lives on the benthic bottom layer of the lake close to the shore and down to a dept where light can penetrate. In a deep lake like Atitlan its habitat is therefore limited to a relatively small area where it has to compete with other plants and phytoplankton for light and nutrients.
According to our Hypotesis this was changed in 2009. Due to the stratification, the nutrients collected above and on the Thermocline segment (which acted as a physical barrier) and as the Lyngbya could use this layer as a substrate or "false bottom"; it quickly spread out over most of the lake using this layer as its substrate for growth and nutrient collection. In short a false nutrient rich bottom was created where the Lyngbya could grow.
This was further aggravated by the good light penetration in the crystalline waters of Lake Atitlan creating perfect condition for the Lyngbya to grow rapidly and over a greater area.
Figure 2. The lake with a pronounced Thermocline segment creating a "false bottom".
Proof of this was as a matter of fact shown by the Lyngbya itself. On satellite pictures from NASA we can see that the Lyngbya forms a pattern like the clouds in a tornado or hurricane. This indicates that the Epilimnion segment is swirling around and is not forming the traditional band like streaks caused by waves and currents. This swirling motion of waters are often observed in wide and shallow lakes during warm weather but seldom seen in deeper lakes. This indicates that the strong stratification made the Epilimnion and to certain extent the Thermocline segment act as a wide and shallow lake on top of the Hypolimnion. This swirling motion also made nutrients and alive and growing Lyngbya to be drawn to the center of the lake and decaying and dead debris of Lyngbya was pushed closer to the shores due to their differences in specific weight.600lagodeatitlan_ast_200932
Figure 3. Cyanobacteria Bloom Lake Atitlan
hurricane clouds NASA
Figure 4. Hurricane Clouds compare with the swirling Cyanobacteria
(green patterns in the blue water) in Figure 3.
What has changed in the last years:
The climate conditions have probably existed many times during the history of the lake, but one factor has increased enormously in the last couple of years.
That factor is the impact of human life and activities around the lake with increased release of nutrients into the lake as a result. The increase of nutrient inflow is caused by deforestation, permitting more nutrients from the soil being washed out into the lake, agriculture in form of extensive use of fertilizers, and last but not least the release of sewage from Cities, Towns and industries around the lake, this is probably the biggest source of nutrient release and the main reason for the Lyngbya bloom.
How come? Remember it was raining less, so less fertilizer and soil was washed out in the lake. But people around the lake where dumping as much sewage as usual in the top Epilimnion layer, and it stayed and probably accumulated as a benthic layer there due to stratification for the Lyngbya to use.
Our Hypothesis is that this Lyngbya is growing extremely fast under the right conditions but is more limited than most of its cousins that can control the buoyancy better and survive hovering in the water, like the common cyanobacteria, Microcystis sp.
So why did we end up with the stinking and ugly mess floating on the surface of the lake?
We will explain that shortly but first we need to mention another important factor. Phytoplankton are excellent absorbers of not only visible light for the photosynthesis but also act as mini solar collectors absorbing heat further heating up the Epilimnion and the Thermocline segments.
Because of the explosive growth the layer of Lyngbya became thicker and thicker, finally blocking out the light for underlying and older layers which died due to lack of light and possible lack of nutrients. When the natural decomposition started, gases are released and get trapped in the dense mat of Lyngbya and the whole mat starts to float to the surface where more and faster decomposition occurs due to ultraviolet light radiation (Lyngbya is particularly sensitive to this) and more gases are released sometimes creating a pungent aroma. The gas formation also occurs under normal conditions due to the release of oxygen from the photosynthesis in the Lyngbya and can be observed around the lake on most sunny days. This normally causes the release of small "balls" of Lyngbya that floats to the surface and are probably part of the reproduction cycle as it distributes the Lyngbya to different locations of the lake.
The color of the Lyngbya also changes due to lack of light and the decomposition, from green to brown and sometimes purple or red. This color absorbs even more heat from solar radiation, further heating up the surface water which promotes an even faster decomposition.
When the light is blocked to underlying mats of Lyngbya and other phytoplankton and plants, they die and float to the surface adding more fuel to the fire. The decomposition also consumes a lot of oxygen and kills oxygen generating plants and phytoplankton. Acute lack of oxygen could therefore occur in and near these mats.
For many people the most important question is: Will this happen again? The answer is YES. It has happened before (although in a smaller scale) and will happen again in a bigger scale than this time, due to the fact that more and more nutrients are released into the lake.