Water Quality Issues 

Sunlight & Temperature 

Sunlight is the primary source of energy. Most of the energy that controls the metabolism of a lake comes directly from the solar energy utilized in photosynthesis. Photosynthesis will occur only in the upper layer of the pond, or euphotic zone, this is the area in the water column that sunlight is able to penetrate. Shallow bodies of water less than 9ft in depth more commonly experience problems such as bottom-rooted weeds or benthic algae.

Thermal stratification or temperature layering occur when the sun warms the surface water, this water becomes lighter than the cooler, denser waters which are trapped at the pond’s bottom. The difference in temperature between the warm surface waters and the colder bottom waters increase all season. As a result the water becomes stratified or separated into layers and the top and bottom layers of the lake do not mix with each other. The area created between the warm and cold layers, called the thermocline or metalimnion, can act as a physical barrier preventing any vertical mixing in the lake, and encourage algae growth throughout the warm surface waters.

Thermal Stratification impacts the water quality in a pond primarily because of its effect on dissolved oxygen levels, (the way we measure how water holds oxygen). Compared to cooler water, warm water has a diminished capacity to hold oxygen, in fact 52 degrees Fahrenheit can hold over 40% more oxygen than water at 80 degrees Fahrenheit. As water temperature increases, the water’s capacity to hold oxygen decreases.

Dissolved oxygen in a lake comes primarily from photosynthesis and wave/wind action. During stratification, bottom waters are removed from both of these sources and an anoxic or no oxygen condition occurs. Aquatic organisms require oxygen to survive; in its absence organisms must move from the anoxic area or die. Anoxic bottom waters lose most if not all of the zooplankton and aerobic bacteria necessary for efficient and effective digestion, while less effective more pollutant tolerant forms of anaerobic bacteria will develop.

The lack of dissolved oxygen sets in motion a series of chemical reactions that further reduce water quality: sulfide is converted to hydrogen sulfide, insoluble iron is converted to soluble forms, suspended solids increase and a severe decrease in the decomposition of waste materials on the pond bottom occur.

Thermal stratification occurs in a seasonal cycle with the thermocline becoming more severe in late summer and late winter. Lakes and ponds in warmer weather regions experience a shorter annual cycle spending more time in late summer and early fall conditions. Shallow ponds, (less than 6ft in depth) tend to be warm allowing for the entire water column to be productive with weed and algae growth.

Nutrients or Load 

The impact of nutrients on the aquatic ecosystem is profound. There is a direct correlation in the level of available nutrients and the populations of algae and

aquatic weeds.

It is important to understand the sources of nutrients and how the nutrients are absorbed and broken down. A diagnosis of a pond’s chemical make up can help you design a preventative program for a problem pond.

Consider the way that organic nutrients are accumulated and digested in the pond. An organic nutrient is a carbon based compound essential to the life of a plant. In pond ecology the macro nutrients we specifically talk of are phosphorus and nitrogen. In fact, phosphorus has been identified as the single greatest contributor to aquatic plant growth; one gram of phosphorous will produce one hundred grams of algal biomass.

As the nutrient level in the water increases so does aquatic plant and weed growth, this leads to severe problems from an environmental and aesthetic viewpoint.

It is beneficial to try to identify the sources of nutrient coming into the pond. The three most common sources are bottom silt and dead vegetation in the pond, runoff water from surrounding turf areas, and the sources of incoming water.

Vegetative life in the pond and sediment at the pond bottom are the primary sources of nutrient. Although they only have a two-week life cycle, blue-green algae can experience cell division and double their population as often as every 20 minutes. At the end of the cycle, the plants simply die and begin to sink to the pond’s bottom, adding to the biomass, or total amount of biological material in the pond. This adds to the “aquatic compost pile” at the bottom, or benthic zone. The layer of dead plant material acts as nutrient for future algae and aquatic weed blooms, a phenomenon called nutrient cycling. Nutrient cycling creates additional demands on the available oxygen in the bottom waters, or hypolimnion, and creates a stress situation.

Sediment, and or sludge can accumulate at a rate of 1 to 5 inches per year in temperate climates. While in tropical climates the rate increases to 3 to 8 inches per year depending on the level of nutrient loading.

At a mid point accumulation rate of 3 inches per year, a one surface acre pond will lose 80,000 gallons of water storage capacity in a single year. Imagine the impact on an irrigation storage pond over the course of ten, twenty or fifty years. Sludge build up can gradually occur, robbing any lake or irrigation pond of its capacity to store water.

The second most common source of nutrients is runoff from surrounding turf areas as well as roads, farms and other outlying areas. The USGA reports that up to 4% of the fertilizers applied to areas adjacent to ponds and lakes may eventually runoff into the ponds, this runoff of fertilizers into ponds is known as nutrient loading. Consider that a golf course may apply up to sixteen tons of fertilizer in a year the possibility for a half-ton of fertilizer to runoff into the lakes or drainage basins exists. Leaves, grass clippings, and other materials will also runoff into the ponds, placing additional burdens on the pond’s natural clean up processes. Ponds and lakes often act as Mother Nature’s “garbage cans.

Nutrient loading can be very high in waters adjacent to green areas or turf grass. As the nutrient levels in the pond increase, the rate of plant growth will increase as well.

A case study presented by the North American Lake Management Society (NALMS) suggests that algae can absorb over 1mgL of phosphorus and over 2.5mgL of nitrogen. Nutrients do have a significant impact on algae and aquatic weed growth; increased nutrient levels usually mean increased plant levels.

Nutrient is also added to lakes and ponds through inlet waters. This inlet water can come from effluent sewage, wastewater treatment plants and leeching from septic systems. Often inlet waters have minimal oxygen and are loaded with phosphorus;

an indication of excess phosphorus is foaming water.

Oxygen 

Oxygen is important to all forms of life in the pond, and supports the food chain. A healthy ecosystem in a pond contains a wide variety of plants and animals including

a natural mechanism to biodegrade organic nutrients. The bottom of the food chain consists of microscopic algae which are consumed by slightly larger zooplankton. This means that a few sport fish depend on a much larger supply of smaller fish, and in turn the smaller fish depend on a large base of plants and algae, and the large mass

of plants and algae require an even larger amount of nutrient to grow. As you can see a healthy food chain can pull a tremendous amount of nutrient out of the water, and oxygen supports this entire system.

Natural decomposition processes in the aquatic ecosystem are oxygen dependent. Aerobic digestion is a fast and efficient way of breaking down nutrients. Moreover,

an abundant supply of dissolved oxygen supports the oxidation and other chemical processes that help keep the lake in ecological balance.

How is a pond supplied with oxygen? From several sources but primarily through photosynthesis, wave and wind action. Aquatic plants and algae produce large amounts of oxygen through the light process of photosynthesis. This is an important source of oxygen in most lakes especially older, or eutrophic lakes. At night plants become oxygen consumers in the dark process of photosynthesis and produce carbon dioxide. The other significant oxygen producer is the oxygen transfer created by wave and wind action. The surface area of the pond is increased by surface waves or ripples caused by wind or other means, the wave action created by the wind creates additional circulation and partially breaks down thermal stratification. Surface waters that have direct contact with the air will be oxygenated through diffusion. And finally, as the rain passes through the atmosphere it picks up free oxygen and deposits it in a dissolved state when it strikes the surface waters of the pond.

Oxygen depletion or stress situations occur for different reasons. Whenever oxygen levels fall below 3 to 4 parts per million an oxygen stress will occur. The most immediate reactions to oxygen depletion would be fish kills or odors. Long-term issues include nutrient build up, sludge accumulation, and a chemical imbalance in the pond.

Nature has provided a clean up process that will metabolize or decompose excess nutrients. This process is called organic digestion. Two types of naturally occurring bacteria are presenting all lakes and ponds, aerobic and anaerobic. The bacteria in

the water will work to break down the nutrient load by feeding on the organic nutrients

and digesting it into non-organic compounds that algae and aquatic plants cannot readily use for food.

The most effective of these bacteria are aerobic bacteria. Aerobic bacteria only live

in the presence of oxygen and they metabolize or break down nutrients respiring or consuming oxygen in the process. They are very efficient, breaking down organic nutrients, carbon dioxide and other materials and are many times faster in organic digestion than anaerobic bacteria.

Anaerobic bacteria also break down organic nutrient and exist in pond water and soils that are oxygen deficient. They are not as effective as aerobic bacteria in the digestion of organic wastes and allow soluble organic nutrients to recycle into the water column. Noxious by-products such as methane, ammonia and hydrogen sulfide are created by anaerobic decomposition. In general, any foul smelling waters can be assumed to be anoxic or oxygen deficient.

Oxidation is a chemical process that is dependent on oxygen. Oxygen has a positive molecular charge, as an oxygen molecule affixes itself to a particle in the water it then starts to oxidize or break down the molecular bonds which hold the particle together. In addition, the positive molecular charge of the oxygen molecule will create an attraction and pull several small particles together, a process known as coagulation. These heavier, coagulated particles now precipitate, or fall out of suspension. In this process soluble substances like phosphorus and iron become insoluble and unavailable for use by aquatic vegetation. A balanced aquatic ecosystem contains a fairly low population of algae and aquatic weeds as well as other forms of nutrient. Aerobic bacteria feed on the organic nutrients and digest it into non-organic compounds that algae and aquatic plants cannot use as readily for food.

Simple water quality tests will indicate the nutrient levels and other valuable information in regards to lakes and ponds. These tests typically monitor dissolved oxygen, biological oxygen demand, alkalinity, pH, phosphorus, nitrogen, and fecal coliform in some situations. Dissolved oxygen is described in either parts per million

or milligrams per liter. Biological Oxygen Demand is referred to as BOD. This testing can be completed by most water testing laboratories and water testing is important

for a complete understanding of the water you are trying to manage.

In Summary 

As a pond ages the level of nutrient rises, this is due to an increase in runoff, organic bottom sediment, or fertilizer used in the surrounding area, and in the amount of algae and aquatic weed growth. As these weeds grow and die they sink to the bottom of the pond to decompose, this will result in a sudden increase in the activity and population of aerobic bacteria due to the large food supply. The depth of the pond will decrease as the biomass at the pond bottom accumulates. Aerobic bacteria will use a large amount of oxygen as they digest organic waste, with primary source of oxygen in the pond coming through surface contact, rainfall and plant photosynthesis.

Due to thermal stratification the top and bottom layers of the pond will not mix and the needed oxygen can not get down to the lake bottom to support aerobic digestion. This will cause an oxygen depletion problem in the lower layers of the lake and may result in nutrient cycling, fish kills and foul odors caused by anaerobic digestion. The problem is caused by poor water quality, that has excessive nutrient levels, poor circulation and low oxygen levels.

Balance is critical to the aquatic ecosystem, without it your pond will suffer. There are many steps that can prevent an imbalance from occurring, and knowing the causes will assist in determining the best solution for your application. Some methods include proper pond construction, including the placement of aquatic plants on the shores of

a pond to assist with the filtering of excessive nutrient, and the addition of oxygen through aeration systems and devices.

EcoSens POD Aerators 

To address the critical requirements of water pollution of ponds and lakes EcoSens Technologies developed a method to improve the rate of dissolve oxygen absorption (mass transfer) in water. It is accomplished through deep draw Venturi circulating water through the POD’s motionless mixing chamber. The total water volume is circulated constantly. This mixing of the water column with the nutrient creates a desirable environment for the aggressive vegetative bacteria to flourish and allow them to digest the nutrient / pollutants left in the water.

The profound difference in EcoSens POD Technologies is the pure speed and volume of the oxygen transfer at the liquid gas interface. Unlike diffusion stones or membrane diffusers (3 to 5 CFM) the motionless mixer concept allows for hundreds of cubic feet of air every minute (CFM) to interface and dissolve into the water column. This level of saturation allows for rapid decomposition of the harmful nutrients and creates a desirable environment for the naturally occurring bacteria to handle the organic load in the water. The effect of the oxygen rich water in turn is delivered to the root zone and helps tremendously with the turfs ability to respirate. It is akin to aerating every time water is applied to the turf. An additional benefit of clean, oxygen rich water is increased percolation and disease control. Pumping low quality water into the root zone will create ” black layer” and ultimately seal off the turf from oxygen.

Oxygen rich water increases the bio availability of fertilizers already applied to turf. The cleaning up of the exchange sites in the root zone will provide a good porous structure for microorganism activity and nutrient generation.

In summary you have the ability to control what ever water quality issues may arise with simple inexpensive equipment and some design expertise. Water quality management is a science. Understanding and applying best practices while prompting Mother Nature to fight the good fight is the most cost effective and complete solution available.