The last post described the physical methods to control microbial populations, either by bursting microbes, altering their chemical structures within the cells with radiation, by burning them with heat or by slowing their replication by taking heat away (Physical Methods to Kill Microbes or Taking Microbes by Force). Microbes, like the pond enthusiast or any living being for that matter, rely on water for life. This post will go over water quality and how it can affect life in a pond and the overall quality of a pond.
Several criteria are considered for gauging the water quality in a pond or body of water. Here are listed the nine factors of water quality by the United States National Sanitation Foundation. They developed standardized tests and implemented them in 1970 in order to determine water quality.
• Dissolved oxygen.
• Fecal coliform bacteria numbers.
• Five day biochemical oxygen demand.
• Total phosphates.
• Total nitrates.
• Total solids.
The first criterion for gauging water quality is the temperature. The temperature is a blanketing characteristic of water and the environment and it will change frequently as the weather does. The temperature of water will affect almost all of the other criteria of water quality. For example, the solubility of certain substances, like oxygen, phosphates, nitrates and organic molecules will increase or decrease depending on the temperature of the water into which these substances are dissolved. This will affect microbial growth and numbers due to the availability of nutrients. Finally, microbial growth itself will be affected by the temperature since higher temperatures will generally increase microbial growth to a point. Increased microbial growth will also change the demand and availability of nutrients in the water. The effect of the temperature will also be elaborated on with regards to each criterion as they are described.
Dissolved oxygen is important to keep at high enough levels in the pond to ensure life of the plants and fish present. Oxygen is required by these life forms, and by many bacteria which utilize oxygen in the nitrification process of one’s pond for example, which will later be described with the nitrogen cycle. Oxygen is crucial to a large number of biological processes. The amount of oxygen that can be present in water will depend on many factors, but one is the temperature of water, as alluded to earlier. Less oxygen is capable of being dissolved in water as the temperature increases. This is why fish kills, due to algal blooms, are more common when the water is warmer. Warmer temperatures increase the growth of algae, thus increasing the oxygen demand, but less oxygen will be available in the first place due to the lower oxygen saturation in warmer water. It is generally considered that the saturation point of oxygen in water is 15ppm (parts per million), or the point where no more oxygen can be dissolved into water. A healthy range of oxygen in a pond will be 5-10ppm, and less than 3-4ppm will result in an unhealthy pond. As mentioned before, fish kills can occur at this point, and other signs of low oxygen in a pond will include unpleasant odours. These odours are created when aerobic bacterial replication and metabolism of nutrients present in the pond becomes reduced, and anaerobic bacteria and their processes increase. These bacteria will create the odoriferous gases of methane and hydrogen sulphide. Oxygen generally enters ponds by way of photosynthesis; a biological process of converting light and carbon dioxide into oxygen and sugars (mentioned in the post “Phycology: The Forgotten Field of Study and the Pond” and this will be elaborated in the next blog entry), wind, waves, and aeration.
The third criterion is the number of coliform bacteria, which are less important for water quality in the pond, but play a huge role in drinking water quality. Coliform bacteria are a type of bacteria found in large numbers in the feces of warm blooded animals and assist in digestion, which is why they are usually referred to as fecal coliform bacteria. They are rod shaped in appearance and are incapable of forming the protective spores that some bacteria can employ, which was described in the last post (Physical Methods to Kill Microbes or Taking Microbes by Force). Coliform bacteria include such microbes as Escherichia coli, but the larger problem with coliform bacteria is that some types can be a lot more harmful than others. One example is the strain of E. coli, O157:H7, which caused the outbreak in Walkerton, Ontario, where at least seven people died and about 2500 became infected in the year 2000. These bacteria, when ingested, can cause illnesses such as diarrhoea and even life threatening bloody diarrhoea in extreme cases (also known as enterohemorrhagic diarrhoea). It goes without saying that zero numbers of these microbes are ideal for drinking water.
Although there is little tolerance for microbes in drinking water, microbes will be present in all other types of water, including pond water. The numbers of microbes present will affect the biochemical oxygen demand (BOD). The BOD is the amount of dissolved oxygen necessary for aerobic microbes to break down the organic substances in a body of water at a certain temperature over a certain period of time. The time period of five days was selected due to the fact that a large enough amount of oxygen was used in this period of time to convert organic matter in the pond without affecting the reproducibility of the results. Generally, 68% of the BOD is used in five days at 20°C and larger amounts of the BOD will be converted in 10 (90%) and 20 days (99%). However, the microbial population will shift to nitrifying bacteria, which will affect the results of the test. Nitrifying bacteria are the bacteria that use oxygen to convert toxic ammonia compounds to nitrates in the nitrogen cycle, which will be described in greater detail. Since BOD measures the amount of oxygen used up in an amount of time by microbes in the water, it is a gauge for the degree of organic pollution present. This is because of the fact that the more organic compounds that are present for microbial reproduction, the more demand there will be on oxygen, and the BOD will increase. BOD will not be able to be measured accurately if the water may contain products that may hinder microbial reproduction, such as antibiotics, sanitizers, chlorination, or odour control formulations, which can be found in certain waste waters, depending on the source. BOD is generally not used for determining the quality of drinking water, but rather for waste water for example, from waste water treatment plants or from rivers, lakes and streams. Pristine rivers will have a BOD of less than 1mg of oxygen consumed per litre of sample (1mg/l) during five days, at 20°C. Treated sewage will have a BOD below or equal to 20mg/l, and untreated sewage, generally has a BOD of in the range of hundreds of mg/l of water.
A ubiquitously important quality of water, whether it is inside organisms involved in their biological processes or in the environment, is pH. The pH is a measure of the relative acidity of water. Water, and compounds that dissolve in it, have a natural tendency to ionize, which means that a small fraction of water will dissociate and form ions:
Figure 1: The dissociation of water (H20) into a positively charged hydronium ion (H3O+) and a negatively charged hydroxide ion (OH-).
Compounds that dissolve in water will also dissociate and ionize. The ion concentrations will affect the relative acidity of the water. Hydronium (H3O+), in larger numbers, will make the water more acidic. The pH of the water will change depending on what is dissolved in the water, be it an acid, such as sulphuric acid (H2SO4):
Figure 2: The dissociation of sulphuric acid (H2SO4) into water. Ionized products on the right (HSO4 and H3O+) will form when dissolved in water.
Or a base, such as ammonia (NH3), which can accept hydrogen from a hydronium ion found in the solution:
Figure 3: The dissociation of ammonia (NH3) into water. Ionized products on the right (NH4+ and OH-) will form when dissolved in water.
For example, water that is exposed to air is generally mildly acidic because it absorbs the carbon dioxide (CO2) in the air, which is slowly converted to carbonic acid (H2CO3), and will further be converted into the ionized products (HCO3- and H+) thus making the solution more acidic.
Figure 4: Carbon dioxide dissolving in water. First, carbonic acid is formed (H2CO3), then the ionized products are dissolved in the solution (HCO3- and H+).
Pure water with no acidity or alkalinity is considered to be neutral at a pH of 7 at 25°C. The pH is charted on a logarithmic scale, which is exponential, so a difference of one pH unit is equal to a tenfold difference in the hydronium ion concentration. The scale goes from 0-14, where values below 7 are acidic and those above 7 are basic or alkaline. Alkalinity, however, is not always interchangeable with the term basic. Whereas the pH will always measure the quantitative number of hydronium ions dissolved in water, alkalinity is the capacity of a solution to neutralize an acid or the amount of acid that can be added to a solution before the pH changes drastically. A solution can be alkaline but it does not have to be strongly basic (have a high pH), even though the terms alkalinity and basic are often interchanged. Some factors that can influence the alkalinity of a solution are carbonate, bicarbonate, hydroxide, phosphate, silicate, nitrate, ammonia and sulphide.
Another chemical factor that is important in water quality is the amounts of phosphates and nitrates present, especially where plant and algal growth is concerned. They can speed the growth of algae in the pond and thus disrupt the natural balance of a pond. Waterfowl excrement contains a lot of both compounds, and having even one or two birds contributing to their waste to a pond can disrupt the pond’s ecosystem in certain conditions. The factors that can greatly assist or hinder in this include the size of the pond, the temperature, the circulation, and what microbes are present and whether or not they are part of a bioaugmentation program (as discussed in “You Get More Flies with Honey and You Get Better Microbes with Probiotics”). Phosphates are a large contributor to plant growth. Therefore, they can be found in many plant fertilizers and will also contribute to algal blooms. The water quality is thought to decline when the level of phosphates reaches 0.05-0.1ppm. Phosphates, as well as in waterfowl excrement and in fertilizers, can also be found in pesticides, dead vegetation or landscape debris, and water runoff after rain. Once phosphates are present in a pond, they are quite difficult to remove. One method used to remove phosphates is barley straw. When bacteria break down barley straw, hydrogen peroxide is produced. Hydrogen peroxide is an algaecide and an oxidizing agent that will bind phosphates and remove them from the water. Phosphates can also be removed by the addition of alum (aluminum sulphate or potassium aluminum sulphate). Once the alum binds to the phosphates and forms aluminum phosphate, it will precipitate the phosphates out of the water since aluminum phosphate has a lower solubility than aluminum sulphate. Alum is a widely used method to control phosphate levels in ponds; however, in shallower ponds it is less ideal since it can leave these ponds with a milky appearance.
Nitrate and phosphate levels often go hand in hand, having similar origins in excrement, decomposing plant and animal matter, and water runoff. Though phosphates, as mentioned earlier, are extremely important when contributing to algal growth, nitrogen levels in a pond will also contribute. Nitrogen, like phosphates and oxygen, is extremely important for life, therefore, some nitrogen is necessary for a balanced pond ecosystem, but there can be a point where the ideal nitrogen levels are exceeded, which is above 5-7ppm. Nitrogen is present in large quantities in the atmosphere, 78% of it consists of nitrogen. Though there is a lot of nitrogen available in the atmosphere, there are limited ways for biological creatures to harvest it. The manner in which nitrogen enters the food chain is by nitrogen fixation. Some bacteria, such as Rhizobium species, which live on the root nodules of legumes, and some free living bacteria, such as Azobacter species, have the capability to take nitrogen from the air and incorporate it into biological molecules. In fact, Rhizobium lives in a symbiotic relationship with some legumes contributing nitrogen in the form of ammonia to the plant in exchange for carbohydrates. These bacteria possess an enzyme called nitrogenase that will combine gaseous nitrogen (N2) and hydrogen (H) to produce ammonium (NH4+). This is the start of the nitrogen cycle (Figure 5). It is referred to as fixation, where bacteria take nitrogen from the atmosphere and convert it to compounds such as ammonia, nitrite (NO2-) and nitrates (NO3-). Then the compounds made by the bacteria are absorbed and used by plant life, this is called assimilation. As plants and animals then decompose, ammonium is formed once again. This is the ammonification portion of the cycle. Ammonia then can re enter the food chain being absorbed by plants, or digested by bacteria such as Pseudomonas and Clostridium species. These species, when oxygen is absent, utilize nitrogen instead of oxygen for certain biological processes and will produce nitrogen gas in the step called denitrification. Thus, the nitrogen cycle completes itself by either re contributing the nutrients to plants and bacteria at the base of the food chain, or by reconverting nitrogen to its original gaseous atmospheric form (Figure 5).
Figure 5: The nitrogen cycle. Atmospheric nitrogen (N2) is brought into the ground and the nitrogen cycle by way of bacteria either living symbiotically on the roots of certain legumes, or as free living bacteria in the soil. This step is referred to as nitrogen fixation, which results in the nitrogen being incorporated into ammonium (NH4+). Ammonium is further converted to nitrites (NO2-) and, finally to nitrates (NO3-) by other bacterial species. These nitrates can be absorbed by plants in the process called assimilation, since the nitrogen is in a form that is capable of being utilized by plants. Then, nitrogen can be utilized by herbivores and carnivores. As the plants and animals produce waste, or die and decompose, they produce ammonium to contribute to the ammonification of the nitrogen cycle. Finally, certain bacterial species, in the absence of oxygen, can take certain nitrogen containing compounds, like nitrate, and convert it to gaseous nitrogen. Denitrification therefore completes the nitrogen cycle.
The nitrogen cycle exists in many ecosystems including the pond (Figure 6). Nitrogen enters the pond by the bacterial fixation of nitrogen and will be used and excreted by plants and fish. Then ammonia is produced, which is toxic to these life forms. Then, certain bacteria present will be able to convert ammonia to nitrite, which is equally toxic, and finally to nitrate, a far less toxic substance. Nitrate can then be denitrified in a pond by the denitrifying bacteria. This process though, as mentioned earlier, is an anaerobic process meaning it has to happen in the absence of oxygen. Therefore, in order to keep a healthy pond, a bottom layer of sediment is recommended to facilitate denitrification. Oxygen, as mentioned earlier, is also required for healthy levels of certain nitrogenous compounds and for the continuation of the nitrogen cycle. Without sufficient oxygen, nitrification cannot be completed and the toxic compound, nitrite, will accumulate in a pond.
Figure 6: The nitrogen cycle in a pond. Fixation of gaseous nitrogen and conversion from ammonia to nitrites and nitrates is done by bacterial species. Among them are the Nitrosomonas and Nitrospira species. Nitrates are then utilized by plants for nutrients, which will contribute to the food chain, be it for fish or other organisms in the pond. Once plants and fish die, or produce waste, ammonia is produced which will continue the nitrogen cycle in an aquatic environment.
The final criteria for water quality are turbidity and total solids. Turbidity is the cloudiness of water caused by particulate matter suspended in it. Its effect is similar to that of smoke in the air. Some matter will be large and heavy enough to eventually settle on the bottom, but until then will contribute to the turbidity. Very small solids will settle much more slowly and sometimes not at all if the sample is agitated enough and will remain contributing to the turbidity of the water. The turbidity can be increased by phytoplankton, soil erosion in water runoff and precipitation of certain compounds such as phosphates. The turbidity, as it increases, will decrease the amount of light that can enter the depths of water. This may decrease the levels of photosynthesis from plant life, thus decreasing the oxygen levels. Turbid water also becomes warmer more readily since suspended particles will absorb heat from the sun, which in turn affects many other aspects of water quality. High turbidity can also hinder the ability of fish gills to absorb oxygen. Though high turbidity is often considered bad, some turbidity is beneficial as it indicates some microbial life in the pond and thus a balanced, functional ecosystem. High turbidity, in some cases, serves as protection for certain life forms like juvenile fish in mangroves (Blaber, S.J.M., 2000).
The total dissolved solids are similar to turbidity in that it involves particles being suspended in the water. However, the particles are much smaller, the standard being that the particles should be able to pass through a 2μm filter. The total dissolved solids involve all inorganic and organic substances dissolved in the water, including molecular, ionized and micro-granular suspended forms. Though the source of the total dissolved solids is from water runoff and soil erosion, the same as that of the impurities that increase the turbidity of water, these dissolved solids are generally not associated with health risks and are considered more for aesthetic purposes when considering drinking water. This measure of water quality is exclusively used for fresh water, since salt water includes the ions constituted as total dissolved solids. Some common constituents include calcium, phosphates, nitrates, sodium, potassium and chloride. The United States National Sanitation Foundation standard for drinking water is less than, or equal to, 500mg/l of water.
Once the ecosystem of the pond becomes unbalanced in one form or another, there are methods that one may employ to try and bring back the balance. It is always recommended though to employ these methods as preventative measures to balance an already healthy ecosystem. This is because treatments, though they may suppress surplus growth, like an algal bloom, will only temporarily do so and such imbalances will occur in a cyclical fashion. For example, if a copper compound is added to control algal growth, dead algae will then accumulate and decompose. This will free up nutrients for the next algal bloom. During this process, residual chemicals from the treatment will also accumulate. Therefore, though there are compounds available to control surplus growth of algae, such as copper carbonate and chelated forms of copper, these generally offer only a temporary solution. In the long term, maintaining a balanced ecosystem will be much more beneficial. Chemical treatments may also differ for each pond because of the various aspects of water quality, such as the pH, temperature, and the levels of organic materials will affect the manner in which these treatments function.
A good way to maintain a pond ecosystem is by aeration. Aeration is crucial for ensuring maximal levels of oxygen in the pond, but is also useful for distributing the water chemistry, such as the temperature, pH, nitrates, phosphates, and microbes. There exist a few tools to assist in the aeration of a pond. These include floating fountains, a water pump with an intake at the bottom of the pond, and compressors. Floating fountains can increase circulation and provide aeration, but are designed more for aesthetics and only affect a small area of the pond near the surface whereas, ideally, one would want the whole pond evenly affected by aeration and circulation. Water pumps with an intake at the bottom of the pond affect a larger area, removing and circulating water at the bottom of the pond and discharging it in a fountain or waterfall, however, it will only circulate the water in a channel, leaving dead areas outside of the water flow. Compressors, unlike the other two methods, are designed purely with aeration in mind and not so much aesthetics. These compressors are installed at the surface of the pond with air lines extended to the bottom. The bubbles of air that form then float to the surface and as they do, they transfer oxygen and circulate water throughout all depths of the pond, creating a continuous circulation pattern. These will not affect the appearance of the pond either, since the system is designed to make very small bubbles because smaller bubbles will circulate more water and will transfer more oxygen than larger bubbles. Some methods may be better than others, depending on the pond and the preferences of the pond enthusiast, but combinations of these methods are generally preferred.
Another excellent method of maintaining a pond ecosystem is by bioremediation. This was the topic of the post “You Get More Flies with Honey and You Get Better Microbes with Probiotics”. It includes adding specific microbes in order to obtain balanced pond water chemistry, and to assist in maintaining a proper ecosystem, such as by preventing algal blooms. Sometimes, even with the best of the pond enthusiast’s efforts, a pond can become improperly balanced in its water chemistry. If this is the case, let us at Village Pond and Garden look at the various factors that may contribute to this. Even if it is a healthy pond, we can discuss ways to keep it this way. For we at Village Pond and Garden also believe that prevention is the best method to having a healthy pond ecosystem.
In the next installment →You Light up My Food Chain: The Process of Photosynthesis
• The criteria for gauging water quality set by the United States Sanitation Foundation are the temperature, dissolved oxygen, fecal coliform bacteria numbers, five day biochemical oxygen demand, pH, total phosphates and nitrates, turbidity and total solids.
• The temperature can affect the solubility of compounds that will affect the balance as well as the growth rate of organisms in the pond ecosystem.
• The amount of dissolved oxygen is important to maintain, for it is necessary for many biological processes in the pond.
• The number of coliform bacteria is suited to gauging the water quality of drinking water, since some types of these bacteria can cause quite severe illnesses.
• The five day biochemical oxygen demand is the amount of dissolved oxygen necessary for the microbial population to break down the organic substances in a body of water. It reflects the amount of organic pollution in a body of water.
• The pH is ubiquitously important in many chemical and biological processes. It is a quantitative measurement of the relative acidity of a solution, which is affected by the number of hydronium (H3O+) ions present. Pure water has a pH of 7, acidic solutions have a pH below 7, and basic solutions have a pH above 7. The pH is measured on a logarithmic, exponential scale of 0-14.
• Nitrates and phosphates are necessary to all organisms, but it is important to maintain the levels of these compounds in order to have a balanced pond ecosystem.
• Turbidity is the cloudiness of water caused by particulate matter suspended in it. Turbidity can be increased by phytoplankton, soil erosion and the precipitation of certain compounds.
• Total solids are much smaller particles (≤2μm) suspended in the water and are generally for aesthetic purposes. This is exclusively a criterion for fresh water, since some total solids are actually the regular constituents of salt water.
• Certain treatments exist to aid in controlling imbalances in the pond ecosystem, but such solutions are only temporary, delaying a much larger problem that will eventually occur. Preventative methods are recommended such as bioremediation, circulation and aeration methods.
Blaber, S.J.M, 2000. Tropical estuarine fishes: ecology, exploitation and conservation. Oxford: Blackwell Science.