Pond Boss Forums INTRO Questions & Observations perch pond

Russ - You bring up a topic of minimizing weed growth with pond depth that has no easy answer nor one answer for all situations. IT ALL DEPENDS and in this case it depends on light penetration depth (water transparency) in YOUR situation.

Pond depths of 15'to 16" are standard around me (NWest OH) in limestone based soils. Very few plants grow in alkaline water around here deeper than 8'to 10'. But.....

Tiny particles in the water, usually phytoplankton, but not always, develop densities similar to fog in the air. These suspended particles disperse light and LIMIT the depth light penetrates into the water. Once light intensity decreases to about 1% of the surface intensity this is the depth where most plants do not grow. Some plants need slighty more light than 1% of surface intensity. So water clarity then determines how deep plant (rooted types, attached algae and phytoplankton) will grow in your pond. Some plant species inherently require more light for growth than others.

The depths that I mentioned in my March 05, 10:00pm post were just generalizations for typical pond depths where plants are typicially LIGHT limited in MY region. Depths were primarily educated guesses, and I used notes from the Michigan Pond Mgmt Booklet for Trainwreck's situation. In some of Michigan's nutrient poor conditions, ponds could have water visibilities down to 20 ft. However sometimes in the Upper Peninsula of Michigan brown water (tannins) is common in ponds and varying amounts of these stains puts limits on sunlight penetration. But in some situations it is sometimes not feasable, economical or sometimes not possible to dig a deep pond. Plants in very clear water situations have to be dealt with by other means than water depth.

The increased water clarity of your pond after the suspended solids settled from pond filling was a common "new pond" character. Water clarity in a new pond is usually and ultimately determined by how many nutrients and their ratios were in the fill water. Ponds almost always contain the fewest nutrients once the pond is filled. From that point in time thepond begins accumulating MORE nutrients to make it more nutrient rich - this is called eutrophication. Nutrient ratios and water hardness will determine weather phytoplankton or filamentous algae develops first in the new pond setting. Sometimes not much plant growth at all grows in a new pond which means fill water was low in most all macronutrients. However as the nutrients accumulate and collect in the pond over time then the plant growth often responds by increasing accordingly.

Your pond is behaving like some relatively low nutrient first filled ponds in my region. After initial settling, waters clear, and going into winter, during winter and for a while after ice off the water is very, very clear; visibilities down to 10' to 15ft or more. Numerous fertile ponds in my area get quite clear as ice cover approaches. After ice thaw and as water warms to 39-42F the wind starts mixing the water column and very light fluffy particles can get resuspended into the water column. Wave action on the banks can also result in suspended sediments which get mixed by the wind and weak resulting currents. Surface runoff can also contain soil clay particles that contribute to water cloudiness soon after spring- summer rain showers.

Warming waters and longer day lengths also stimulate phytoplankton and zooplankton growths. Amount of that growth depends on water fertility. Ponds frequently get more cloudy as spring conditions proceed. So expect your pond to get a little cloudier as spring progresses.

If your water stays clear, and with water visibility still quite clear down to 8 ft by Memorial Day and or 2nd wk into June then this is a sign that your pond needs to be deep to suppress rooted plant growth. You should then have depths of 18' to 22' if possible.

Typically it is hard for pond builders with bulldozers to get real deep in a real small pond due to steepness of side slopes and lack of working space in the basin. A bulldozer physically has a hard time digging and compacting a pond with slopes greater than 2:1, which means a pond has to be at about 82 ft wide to be 18 ft deep when dug with a dozer (36' wide for each side and 10 bottom width).

In the small pond, there are ways to reduce water clarity and resultant rooted plant growth in a shallower pond with perpetually clear water.

1. You can limit growth of rooted plant in very clear water by using Aquashade. The concentration of Aquashade (darkness or amount of apparent blue) affects how deep the light penetrates. So you can sort of control how deep the rooted plants and phytoplankton will grow in your pond by how concentrated the Aquashade is. Ligher doses will result in deeper plant growth.

2. In a small pond you can also decrease the water clarity by agitating the bottom sediments while running your aerator. This will mix the fine particles throughout the pond and make it cloudier. When my pond gets clear I use a Lake or Pond Rake and remove some of the rooted weed growth. This clouds the water for several days or weeks depending on amount of agitation and when the aerator is operated in relation to the raking activity.

3. You can feed the fish pellets and the added manure-nutrients will usually stimulate additional phytoplankton growth and organic particulates and or bacterial levels.

4. Stock grass carp/white amur and their nutrient laden manure from eating plants will stimulate phytoplankton -zooplankton growth.

5. If your water is clear and you desire phytoplankton growth, remember to follow the basic guidelines for fertilizing a pond; check your alkalinity concentrations. Low alkalinity levels are not conducive to growing phytoplankton. Sometimes all one needs to do is to increase the akalinity and a mild phytoplankton bloom will occur naturally if some nutrients are present.

6. If the pond is not bottom aerated and thermal stratification is in place, and the upper warm layer is very clear, the benthic water can still be somewhat light limited. A dense thin layer of suspended solids develops in a zone of the upper thermocline. This layer is very cloudy and acts as a strong light penetration barrier. Light intensity is low below this layer and plant growth can be suppressed.

I have used up a lot of space for a simple answer to you. If it was my pond in NY and soil depth and compostion was adequate then I would deepen it to 18'. Keep in mind that there is not a lot of dirt volume to be moved once you are at 15' and the bottom of a pond 80x110. This is the smallest depth contour of your pond, the bottom.

Deeping 3 extra feet should not take a lot of time or extra money due to the small amount of dirt to be moved. Extra depth in NY snowy winters will be a benefit for 1. oxygen reserves, 2. very few weeds if any should grow in 17' of water. 3. Steep sides with hard packed slopes will have a somewhat of a negating affect of growth of rooted plants. 4. Added depth will still provide good depth to the pond even after 20 - 30 years and in the presence of the always increasing accumulations of sedimented organics - muck layering which could be easily 12" to 18" thick - depending.