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Thread: Understanding String Algae

  1. #21
    Sansai almostgeorgia's Avatar
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    Quote Originally Posted by MikeM View Post
    The individual filaments are more able to take in CO2 and nutrients, and both CO2 and nutrients are more available at the molecular surface due to the continual flow over the surface of the filament. Studies have shown that string algae that was utilizing bicarbonates as a carbon source in low current conditions was able to decrease reliance on bicarbonates and directly use more dissolved atmospheric CO2 as currents were increased. This was perhaps due to the greater availability of CO2, and it being a more efficient source of carbon than the more complex bicarbonates formed in water.

    So, with more efficiency in absorbing available nutrient, and increased availability of efficiently used nutrient, string algae thrives in currents. It is not that highly oxygenated water is preferred, oxygen is a waste product of photosynthesis. Rather, it is increased availability of CO2 and other nutrients along the outer cell membrane that seems to generate higher growth rates.
    The theory that moving water creates the opportunity for string algae to more efficiently utilize carbon sources and other nutrients makes sense. But my understanding of basic photosynthesis is the 'throwing off' oxygen is only half the story. That process occurs during daylight hours, but the reverse is true at night, when plants actually re-absorb oxygen out of the water column. This is one of the classic dangers of planted bodies of water in that oxygen levels can drop to dangerously low levels by early morning in ponds and aquariums. If my admittedly basic understanding of the photosynthesis process is correct, would it not stand to reason that filamentous algae also gains a competitive advantage by placing itself where it can absorb the most available oxygen, directly in a more agitated, oxygen rich 'stream' of water? Some of my casual observations of string algae in the wild are of luxuriant growths noted in oxygen rich mountain streams where that gas, due to the tumbling action of the water over rocks and cobbles, is at or near saturation levels.

    Just trying to get to the bottom of why string algae appears to manifest itself most frequently in moving water structures such as waterfalls, near TPR vents, etc., in a pond.

  2. #22
    Tategoi powerman's Avatar
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    Quote Originally Posted by MCA View Post
    I wonder if you find it in ponds with low TDS (<100) and high ORP (>300mV).
    I know it grows great in ponds with low tds.. my pond runs a tds of 74 to 76..

    the string algae that I get seems to do really good in areas of high flow, waterfalls, under the bakki shower but also attaches to all pond surfaces eventually

  3. #23
    Daihonmei MikeM's Avatar
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    Light

    We all know that plants need light to live. It is essential to photosynthesis. Some plants prefer shade. Some prefer full sun. Put a shade plant in full sun and it will be scorched and eventually die. Put a sun-loving plant in deep shade and it will wither over time. These are simple observations we have all learned in our personal experiences. We tend to categorize all plants in this manner. However, some are adaptable to a very broad range of light exposure. There has been a great deal of study of the relationship of light and photosynthesis in string algae. (I guess it is an easy lab subject, because otherwise I do not know why so much attention has been given to it.) Although there have been a lot of inconsistent results, one theme that rings true throughout is that Cladophora exhibits positive photosynthetic activity at low light levels even in cool water. One study found that even in water as cold as 5C [41F], there was net positive photosynthesis at light levels as low as 35 uE, and even lower light levels have been sufficient at slightly higher temperatures. [The light studies use a measure of photosynthesis-irradiance that is rather too complex to explain here. It focuses on how many millioniths of a mole of photons reach a square meter of surface in one second, which I refer to as a uE (micro-einstein). These measurements are helpful for comparative purposes and focus on light in the spectral range useable by plants. There is something like 2,000 uE hitting the surface of the earth at noon at the equator on a perfectly clear, cloudless day in a desert (i.e., no humidity), and probably more like 1,400 if you leave the desert, add a normal haze and humidity. So, 35 uE is rather weak light.] The main points I gain from these studies is that string algae is well-adapted not only for tree-lined streams, but also for weak winter sun. It will still be growing, albeit very slowly, when almost nothing else is.

    There have been efforts to identify optimal light levels, but I have found these fairly useless from a practical pondkeeper perspective because the results are so inter-related with temperature, nutrient availability and all sorts of other factors. As one might expect, as temperature rises, the optimal light level increases (until temperature is quite warm, interfering with plant metabolism). So, as water warms in the Spring, and the sun intensity is increasing, the string algae can use the increased light intensity for highly efficient growth.

    There are also many studies trying to identify saturation points, the intensities at which additional light does not produce additional growth; and studies on photo-inhibition, trying to learn the light levels at which photosynthesis is reduced due to the light being too intense. Again, the results vary significantly according to numerous factors. However, one aspect that seems to hold true is that photo-inhibition rarely occurs, even when light intensities are quite higher than the saturation point. This low level of photo-inhibition has led to consideration of how string algae protects itself from too much sun. It seems to be that it can simply endure a lot of very intense light. It's growth habit also assists. In Nature, currents result in light being very unevenly distributed within the water, with the result that exposure to overly intense light would have to be measured in fractions of seconds. Clumps of filaments are also self-shading as they continuously wave through the water, over one another. And, the epiphyte community colonizing the surfaces provide shading. When photo-inhibition has been observed, it has involved high stress conditions, such as extreme temperatures, increased salinity, low available nutrient.

    One group of studies I have found interesting concern string algae blooms in the Great Lakes that were mystifying observers because they were occurring in areas where nutrient pollution was significantly lowered. Why would string algae experience a population explosion when nutrient was reduced? The answer appears to be the proliferation of the freshwater mussels that have invaded as exotics carried by ships. In areas where the mussels are well-established, water clarity has greatly improved. The mussels are filter feeders, and eliminate turbidity otherwise present. In some areas, water clarity has increased from visibility limits of a couple of feet, to depths of dozens of feet. As clarity increased, string algae residing on rocks on the lake bottom became robust, and deeper areas of lake bottom became suitable habitat. The bloom was not caused by nutrient pollution, nor decreasing pollution, but by increased water clarity. I find it ironic that as we pondkeepers work to create clear water, using UV to get rid of the unicellular greenwater algae, adding media to entrap fines, we are improving conditions for string algae to fully use what nutrient is available.

    Once again, that bothersome question comes to mind: With all we do make nutrient available and conditions near-perfect for string algae, and as adaptable as it is, why doesn't it overwhelm our koi ponds all the time?

  4. #24
    MCA
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    why doesn't it overwhelm our koi ponds all the time?
    exclusion. other types of algae are a better fit for your ponds sunlight, nutrients, surface area...etc.

  5. #25
    MCA
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    I know it grows great in ponds with low tds.. my pond runs a tds of 74 to 76.

    ORP over 300mV?

  6. #26
    Daihonmei MikeM's Avatar
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    Temperature

    Since light and temperature appear to work in tandem when it comes to the rate of photosynthesis in string algae, it seems logical to address temperature at this point. There are a number of studies that report findings concerning the optimal temperature range for Cladaphora glomerata growth. However, they differ. An often repeated finding is that 15C-25C (59F-77F) is optimal. Studies of string algae growth in particular lakes often have somewhat different findings. One Great Lakes study came in at significantly lower temperatures, 10C-22C; and another established a range of 13C -17C. The problem I have with all of the 'optimal range' conclusions is that they may well be accurate for the particular study, but without having every parameter affecting growth measured, one cannot be sure what to attribute to temperature. Even in controlled laboratory experiments, the spectral range of the lighting is a variable that may alter results from one lab to another. What does come through clearly is that 'optimal temperature' is directly related to light. One study demonstrated this very dramatically. String algae grown at 10C (50F) at a particular irradiance level had only a negligibly lower rate of photosynthesis compared to string algae grown at the same irradiance level at 15C (59F). When the light irradiance was cut in half, the string algae grown at 10C had a photosynthesis rate of less than half of the string algae grown at 15C. Similar relationships have been found at other light and temperature levels in other studies. So, at low light levels, like the weak sun of winter, string algae will grow more if the water is warmer. Shading will reduce growth compared to what it otherwise would have been, but as water warms the extra shading may do no more than maintain the rate of growth the algae had at lower water temperatures.

    The studies I have seen reach differing conclusions on the upper temperature limits for string algae. There is consistency in finding that at some high temperature level, string algae populations collapse. The multiplicity of factors that make the 'collapse point' 29C (84F) in one study and over 35C (over 95F) in another, have not been figured out as far as I am aware. The inconsistencies include one study where maximal growth was reached at 30C (86F), a temperature point where populations had collapsed in other studies. Nonetheless, there are repeated findings that photosynthesis rates and efficient utilization of nutrient go into decline as the water temperature exceeds 25C (77F), and some studies where the decline began at temperatures as low as 23C (73.4F). My conclusion from this is that results will vary from pond to pond, but there will be a temperature point where decline sets in. Hopefully for the pondkeeper, that temperature point will be one consistent with the well-being of the fish.

    An interesting observation made in studies of string algae in natural waterbodies in various parts of the world with temperate climates, that is, where there are true seasonal changes, is that string algae dies off in mid-summer. What I find interesting is that midsummer in northern Michigan is nothing like mid-summer in the Grand Canyon. (I also notice that the term 'midsummer' does not have a universal meaning. For some, midsummer is in late June. For others, it is in mid-August.) It makes me think there are factors involved which have not been identified.

    I'll toss out a thought for folks to tuck in the back of their minds. Consider the destructive process of production of zoospores, which results in irreparable rupturing of cell walls. There are many plants in my garden which come into bloom according to the duration of the day, or the angle of sunlight. I have a clump of Vriesea (a type of bromeliad) growing in the garden where some plants bloom in May and some bloom in November, while other Vrieseas grown in the garden bloom during one period of the year only. The blooming habit of this one clump seems to makes no sense until one realizes that plants of sufficient maturity in the clump reliably bloom two months after the equinox, whether it is the Spring or Fall equinox. There may be an analogous trigger for zoospore production, with the population collapses observed in relation to increasing temperatures also being in relation to maturation and reproductive cycles, which are reached in that vague summer time period in Nature. Of course, temperature is directly involved in the growth and maturation process in all plant forms that I know about, so some correllation would certainly exist.

    As a purely personal observation, I have not had string algae proliferate at water temperatures below 68F (20C). The usual seasonal growth usually begins in April with water temperatures in the range of 70-72F, and typically dies back by June when water temperatures are generally around 75-78F (24-26C). The bloom is generally a 6-week wonder, minor some years and substantial other years. In our ponds, of course, we do all sorts of things that create a very unnatural environment.
    Last edited by MikeM; 06-03-2013 at 02:13 PM. Reason: typo

  7. #27
    MCA
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    Our pond is finally at 70F due to a relatively cool wet spring. So are we heading into string algae alley? Not so far......fingers crossed.

  8. #28
    Sansai almostgeorgia's Avatar
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    There are a couple of reasons for the proliferation of highly specific scientific studies of late on algae in general, and string algae in particular. First, it continues to draw interest as a natural water purification tool due to it's ability to draw out and 'fix' a number of pollutants and trace elements. And second, it receives continuing interest from the bio-fuels industry, with string algae being particularly easy to harvest due to its growth habits.

    And I agree with MCA in that much like a tropical rainforest, I suspect our ponds annually go through a series of growth cycles as different species of algae and microscopic life rapidly reproduce, then diminish as their specific niches of optimum temperature, light, nutrients, etc., wax and wane, only to be supplanted by another species of algae or life form better suited to the new, ever-changing environment. As a pond keeper and from our admittedly biased point of view, I suppose the short but dense 'carpet algae' which so luxuriantly covers our walls in mid-summer is the true 'climax' or apex plant life in our ponds.

  9. #29
    MCA
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    Our pond definitely has green velvet on all the walls.

  10. #30
    Daihonmei MikeM's Avatar
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    Impacts on Water

    Since studies about use of string algae have been mentioned, that seems like a good starting point for today's post. And, yes, there are a lot of such studies going on.

    Some years ago the focus was on string algae as a means for removing excessive nitrogen and phosphorous from polluted water, such as sewage plant effluent. It lost out to water hyacinths, but not because it was less effective. To the contrary, string algae was repeatedly found to be much more effective and more effective in a wider range of conditions. However, success in water purification requires removal of the pollutants through harvesting the plants used. String algae is just too difficult to harvest. Water hyacinths win the competition as a water purifier because of the comparative low cost of harvesting. Also, water hyacinth can be turned into a livestock feed ingredient more readily than the heavy masses of wet algae. For pondkeepers, of course, our goal of reducing nitrogen and phosphates in our pond water is as much about preventing excessive algal growth as anything else. But, string algae does reduce the ammonia, nitrite and nitrate that would otherwise affect our fish.

    The more recent focus has been on the use of string algae to deal with industrial pollution. A lot of the studies come out of eastern Europe and China, where communist regimes did little to protect the environment, leaving some truly horrible contamination sites. These studies have established that string algae has an astounding ability to remove heavy metals from water, particularly lead, cadmium, chromium, copper and nickel. In optimal conditions, upon harvesting the algae has been found to contain as much as 400 times the concentration of lead as the water in which it was placed, nearly 500 times as much nickel, and almost as high a concentration of other dangerous metals. However, the rate of adsorption is highly dependent on pH and the chemical properties of the water. The most effective adsorption rates have been attained at pH levels far more acidic than koikeepers would ever want, with a pH of 4.0 being very effective. Water that acidic would challenge even such acid-loving aquarium fish as Discus. At a pH of just 6.0, significant decreases in adsorption occur. At the pH ranges we normally have in a koi pond, string algae will remove heavy metals (although much of the metals would precipitate and not be a bother anyway), but not at the amazing rates that make it a subject for studying as a contamination cure. The pH factor raises a point to consider. If in doing water changes there is an upward shift in pH, metals adsorbed by the string algae may be released. I emphasize 'may'. I am not aware of studies focused on the relatively small pH shifts koikeepers would experience. It would be more concern for those pondkeepers who do a once-per-year pond cleaning, which so often involves replacing water that has become acidic with water that is of a high pH. (But, of course, they have other more serious issues than heavy metals.) It should also be noted that calcium ions block the uptake of metals (by a type of competitive exclusion). Since calcium-based materials are often used for maintaining alkalinity, these will impact the extent to which metals are removed. So, altogether, it seems string algae has some beneficial impact on the water in our ponds through removal of heavy metals, but folks should not get overly excited by the idea.

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