Clearing Suspended Sediment in Ponds

Clearing Suspended Sediment in Ponds

This new BRIEF is curated from a collection of articles on suspended particles in ponds. The articles cover the key elements of clearing ponds of turbidity due to sedimentation. Individually, the articles do not provide a comprehensive set of the key factors on the subject, so this issue of BRIEFS provides a combined summary. With this single BRIEF, you have a resource on the causes of and remedies to turbidity due to sedimentation and the role of aeration in clearing muddy ponds.

This edition of PondHawk BRIEFS is curated from the following articles:

Muddy Water in Ponds: Causes. Prevention, and Remedies. William E. Lynch, Jr. Aquatic Ecosystem Management; Eric R. Norland, Assistant Professor & Extension Specialist, Natural Resources; School of Natural Resources, The Ohio State University Extension
Sedimentation in Ponds. Dr. Claude E. Boyd, Pond Boss, Volume XXVII, No. 6, May – June 2018. Page 22
Clearing Muddy Water. Bob Lusk, Editor. Pond Boss, Volume XXVII, No. 6, May – June 2018. Page 42
Clearing Muddy Ponds. Texas Agricultural Extension Service. Don Steinbach and Billy Higginbotham, Extension Fisheries Specialist and Project Supervisor, Wildlife and Fisheries Sciences, Texas A&M University; and Extension Wildlife and Fisheries Specialist, Prairie View A&M University, The Texas A&M University System. L-2161

KEY TAKEAWAYS FOR POND AERATION

Use properly sized aeration systems. Improperly sized systems cause wave action that may erode the shoreline and cause suspension of particles in the water.
Aeration may be needed with some turbidity remedies to prevent fish kills from decomposing organic material.
In some cases, stopping the use of aeration systems until the particles settle out of the water column may be required.

Ponds are commonly collection basins for stormwater runoff from the surrounding watershed, and they fill in overtime from both internal and external sources. Flowing water suspends loose particles from the watershed and turbulent water maintains the particles in suspension. All small lakes can become muddy from runoff during inclement weather. The particles turn the water chocolate milk brown and depending on the size, composition, and density, the rate suspended particles settle to the bottom varies. The inlets and shores collect the larger particles and the finer silt, clay, and organic matter that remains suspended longer collects in the deeper parts of the pond. While the condition is aesthetically unappealing, it can also impair habitat for aquatic life if it persists. Causes of turbid or muddy ponds: There are two principal causes of suspended particles in ponds and lakes: biological and watershed.

GENERAL TAKEAWAYS

Biological factors: fish and waterfowl
- Aquatic animals can disturb the sediment layer at the bottom of the pond, causing resuspension of particles.
  - Large populations of common carp, goldfish, and bullhead catfish churn up the bottom sediment.
- Waterfowl eat bank vegetation, exposing soil to erosion during rain events.
Watershed factors: Run off that introduces suspended particles into the water from sources uphill and stream.
- Construction activity in watershed can lead to disrupted soil. Employ erosion control products to stop soil erosion and facilitate seed germination. Establish grass in new construction areas as soon as possible.
- Agriculture and livestock can create exposed soils that will be collected by flowing water entering the pond.
- The pond size relative to the watershed can also lead to turbidity. A watershed that is too small for the pond capacity can expose shoreline soil during periods of low rainfall. When the water level increases from a large rain event, the shore soil will be disturbed and particles will enter the water column.
When heavy rain and biological factors are not the cause of the muddy conditions, the cause may be an imbalance in the ionic charge of the particles. Test the water chemistry to determine if this is the case.

Prevention: The best way to maintain a clear pond is to prevent suspended particles from entering the water and eliminating sources of turbulence.

Eliminate the source of erosion in the watershed, dam, and edges
Remove nuisance fish species
Employ dogs or other tactics to keep geese away
Use properly sized aeration systems
Grow grass in bare areas. Install rocks or riprap on shoreline if eroded by wave action or geese.

Remedies:

Time: Typical particles of sand settle at a rate of 1 foot in 3.3 hours; silt 1 foot in 13.7 hours; and clay 1 foot in 1,370 hours.
Employ a “binding” or flocculant to facilitate the consolidation of particles, making them heavier and quicker to sink.
- Dry hay (not straw) – Distribute the hay loosely throughout the shallow area of the pond so it binds with the clay particles.
  - Aeration may be required to prevent fish kills, as a large amount of decomposing organic material can lead to oxygen depletion.
  - Two of the four authors discuss hay in their articles, and they do not agree on its effectiveness. The value of adding decaying biomass to a pond is frequently questioned.
- Agricultural Gypsum – Dissolve gypsum in clean water and spray over the surface on a calm windless day.
  - Chemically neutral. Gypsum does not cause pH issues associated with Alum.
  - Fish friendly. Gypsum does not cause the decaying biomass that leads to fish mortality.
  - Cost effective. Add the minimum quantity to the surface water and wait for a few days to determine if additional quantity is needed.
- Limestone – Dissolve calcium carbonate in clean water and spray it over the surface on a calm windless day.
  - Agricultural limestone is commonly used to remove suspended clay from the water.
- Aluminum sulfate (Alum). This is the most effective material for clearing suspended clay particles from the water column, but it also carries the most risk.
  - Alkalinity and pH should be tested prior to alum application. Alum creates a chemical reaction that impacts the pH (acidity) of the water. The reaction produces a small amount of sulfuric acid, which can decrease the pH to levels that are harmful to aquatic life.
  - If alkalinity and pH are too low, hydrated lime needs to be added simultaneously with the alum to buffer the effects of the acid produced by the alum.
  - Use a minimal quantity and determine if more is required.
Consult article “Clearing Muddy Ponds by Texas Agricultural Extension Service” for details on testing, mixing, measuring and applying for gypsum and alum.
Do not use alum, gypsum or limestone if pond is used for home or livestock drinking.