Peter Roberts of water specialists Hydroscape Systems Ltd, asks “what will happen to our lakes and ponds as flood water recedes”?
The Christmas of 2013 and New Year of 2014 will be remembered by many, for some of the worst weather experienced in the UK in living memory, with the country being continuously battered by storm force winds, heavy and prolonged periods of rain and high tidal surges, as the jet stream drove wave after wave of low pressure weather patterns across the Atlantic to reach our shores.
Pond before and after Pond Floc Log Installation.
The result was that large areas of the country became submerged, in some cases under several feet of water due to severe flooding. People lost their homes, possessions and more, as rivers and streams burst their banks and the surrounding land became completely saturated, leaving nowhere for the flood water to escape.
Nature however has a way of redressing the balance and flood water will eventually receded, percolating into the aquifer through natural drainage, or evaporating back into the atmosphere. But as the land dried out, much of the flood found it’s way in to our rivers, streams, lakes and ponds, particularly from either surface run off or from man made land drainage systems.
The problem for us in managing either ornamental bodies of water or irrigation reservoirs within our turf environment, is that this runoff and drainage water will tend to be loaded with sediment in the form of minute particles of silt and clay, together with nutrients in the form of phosphorous and nitrates that are bound to the sediment particles, which will present us with a longer term water management headache.
In slow moving bodies of water and in particular, lakes and ponds, much of the ‘sediment and nutrient loading’ will be held in suspension throughout the water column, increasing what is known as ‘turbidity’, which reduces water clarity, making the lake or pond water appear cloudy or murky, or in the worst cases, producing an almost muddy appearance.
However the visual appearance, bought about by a lack of water clarity, is the least of our problems. What is going to cause us the biggest headache, is that increased water turbidity will greatly impact the overall quality of our lake and pond water, which will likely lead to a major reduction in dissolved oxygen levels throughout the water column, with severe ongoing consequences. High turbidity levels will create this problem in a number of ways:
Suspended sediment particles that cause the water turbidity will absorb large amounts of the sun’s rays. When these rays are absorbed by dark colored particles, radiated energy is released as heat, much in the same way as asphalt will heat up in the summer.
Due to this light absorbing property, a body of water with high turbidity will become heated more rapidly by the sun than clearer water.
As water warms up, it becomes less dense, reducing its ability to hold dissolved oxygen. Also higher water temperatures impact the rates of metabolism and growth of aquatic organisms, rate of plants’ photosynthesis and organisms’ sensitivity to disease, parasites, and toxic materials. At a higher temperature, plants grow and die faster, leaving behind organic matter that requires oxygen for decomposition. Consequently high turbidity can lead to a dramatic decrease in oxygen levels through its impact on water temperatures.
Turbidity and Nutrients
The tiny sediment particles that have been washed into the lake or pond have originally come from the land. These particles are likely to contain nutrients particularly Phosphorous and Nitrates, that when combined with water and sunlight can cause an explosive growth of algae.
When this algae dies and decomposes, the decomposition involves a biological process that uses up significant quantities of oxygen. In this way, turbidity can cause lower levels of dissolved oxygen in water by causing algal blooms.
Increased Biological Oxygen Demand
The various substances contained within the sediment, that has caused turbidity, can have a high ‘biological oxygen demand’ (BOD), which is a measure of the amount of oxygen used to decompose a substance. Increased turbidity is therefore associated with increased BOD and decreased oxygen levels.
Reduction in Healthy Biological Activity
All bodies of water contain billions of microscopic bacteria, which naturally break down and digest dead organic materials. Where high dissolved oxygen levels are present the process known as ‘aerobic digestion’ occurs, producing a healthy body of water and aquatic environment. However as oxygen levels are depleted the healthy ‘aerobic bacteria’ count is reduced, being replaced by ‘anaerobic conditions’ and bacteria that does not require oxygen to break down organics.
This process is far less efficient creating organic sludge, leading to the release of ammonia and other obnoxious substances into the water column. Organic sludge coupled with sediment will gradually build up on the lake or pond bed reducing the water depth and the lake or pond will rapidly go into decline.
All in all, high levels of turbidity in water, if left unchecked will create both short term issues of increased algal blooms, coupled with longer term lake or pond degradation.
So What Can Be Done?
Firstly we need to reduce the levels of turbidity and improve water clarity. One of the ways this can be accomplished is through the use of Hydroscape Systems Ltd ‘Pond Floc Logs’
Pond Floc Logs are semi-hydrated, polyacrylamide blended flocculating blocks that are positioned either in the water inlet, if a lake or pond is fed from a stream, or if not, used in conjunction with conventional water movement equipment, such as floating display aerators, fixed fountains, lake bed aeration systems, lake circulators or decorative waterfalls, which will create the agitation needed to introduce and circulate the flocculants throughout the entire water body.
Pond Floc Logs slowly dissolve, adding blends of natural polymers into the body of water, which flocculate suspended particles of colloidal sediment materials, together with phosphorous, forming these into larger aggregates that precipitate out of the water column and become locked up on the pond or lake bed.
As sediment particles and phosphorous are removed from the water column, water clarity improves reducing water temperatures and algal cells are starved of their food source, reducing algae growth by as much as 70%, allowing the lake or pond to return to a healthy state.
Pond Floc Logs are non toxic and completely environmentally safe. Each log will treat up to 1,500m³ of water with multiple numbers of logs used for larger water bodies, for a period of 3 to 4 months before needing replacement.
Pond and Lake Aeration
Secondly, to ensure that good dissolved oxygen levels are maintained, the installation of a properly designed aeration system should be seriously considered, be it through the use of a floating or fixed aerator, surface spray unit, or through the installation of a lake bed diffused aeration system. An aeration system will relieve the natural symptoms of lake degradation, by increasing the rate of dissolved oxygen input and increasing a lakes’ aerobic respiratory capacity.
Aeration affects almost all aspects of a lake in:
- Nutrient cycling.
- Heat distribution.
- Aerobic (good) bacteria populations that break down sludge on the pond bottom.
- Decreased phytoplankton populations that block the sun’s rays.
- Increased population and health of Aquatic life species.
Aeration allows the pond to breathe and speed up aerobic digestion (good digestion) or help the pond respire and ensure achievement of aerobic benefits.
Lake and Pond owners can choose from many mechanical aeration and circulations options available today.
Surface aerators are floating units with a pump or motor mounted beneath the float.
They are efficient as an emergency aerator or for use in shallow bodies of water to keep a constant oxygen supply and circulate the water body.
In a deeper body of water, a surface aerator may need the addition of a “draft tube” to draw water from the lower levels of the lake up to the surface.
As a rule of thumb, a typical “Display Aerator” with a draft tube requires 1-1.5hp per surface acre for proper aeration.
Lake bed diffused aeration is a method of compressing atmospheric air and pumping it to the lake bed, allowing it to flow through a series of lake bed positioned ‘air diffusers’, which create micron-sized bubbles that rise to the surface creating an airlift effect.
The misconception with lake bed diffused aeration is that oxygen is transferred to the water through contact with the bubbles. In reality, less than 5% of oxygen is transferred this way.
As bubbles rise through the water column they expand. Cascading bubbles entrain cold dense oxygen starved water and lift it to the surface, allowing the hydrogen sulfide and carbon dioxide gases to escape to the atmosphere.
At the same time, atmospheric oxygen is absorbed into the surface water and eventually circulated throughout the entire water column. The bottom of the lake or pond becomes aerobic and metals such as iron are oxidized and precipitated out of the water column, whilst phosphates are locked up on the lake bed becoming unavailable for algae to use as a food source.
Unlike surface units, lake bed aeration uses an unconfined airlift technique and the amount of energy required to circulate the entire volume of the lake or pond is greatly reduced, saving on both energy and operating costs.
To size a system using this technique, the entire water volume of the water body is calculated together with the number of bottom placed diffusers to “turnover” the entire water volume a minimum of once per day .
A lake or pond and its aquatic life depend on oxygen to live. Just like you and me. If the Oxygen supply is cut off for even 15 minutes, fish will die or at the least become severely stressed and susceptible to disease.
As low oxygen conditions continue, the build up of harmful gasses continues, thermal stratification will become worse and the potential of a deadly mixture that can result in a fish kill increases.
A heavy accumulation of sediment and high levels of turbidity can also draw more oxygen than the fish. This combination may result in seeing dead fish spread across your lake or pond.
Here are some actual numbers:
- 1kg. of fish will consume about 0.3 grams of oxygen per hour.
- Ten thousand liters of ‘green water’ caused by high levels of phytoplankton will consume about 190 Grams of oxygen per hour.
- Sediment oxygen demand for a mucky or turbid pond is 2.27 grams per square metre.
- With no mechanical aeration and relying solely on the wind, still water rate of oxygenation from the atmosphere at night is about 0.0075 grams per square metre, per hour.
In summary, if left alone, a combination of high turbidity and low oxygen levels will allow nature to begin the process of turning your lake or pond into a marsh land.
You have the ability to slow down and even reverse that process, through improving water clarity and installing an efficient aeration system, be it a display aerator, or lake bed aeration system as the life support for your lake/pond.
For more information on lake and pond management products and aeration systems contact: Hydroscape Systems Ltd on 01425 476261 or email: [email protected]