Pond Boss Forums AQUATIC VEGETATION Controlling unwanted plants Seine for removing algae?

Knobber. Plants are very efficient at scavenging phosphorus from the water column. While the number .06 mg/L may be a high number (where more frequently one may test much lower numbers) ... that amount of phosphorus in the water column isn't a very high amount. There are around 6.774 million liters of water in 5.5 acre-feet. And so there are 406,438 mg of phosphorus at the first test. This equates to .406 kg of orthophosphate in the entire pond. around 0.44 lbs/acre.

Based on your description of weeds crops, there is much more than that weight of phosphorus in the pond ... but not in the water column. Biological action on sediments releases phosphorous, nitrogen, and other important nutrients including CO2. This happens throughout out the year and much more than .44 lbs/acre of phosphorous are being recycled annually. It is just as the pond weeds grow ... they metabolize and use the phosphorous. IOWs they consume it and sequester it in their living tissue. This is why the treatments are not removing all that much phosphorous from your pond.

I don't know how much active ingredient is in 3.5 gallons of Meta-floc. But I do question the weight of phosphate the active ingredients can make bio-unavailable to your pond plants. I don't think it is near enough to make a big impact. Now removing the living plants to decay outside the drainage of your pond would have a much larger effect provided you removed a sufficient weight of them. A decent rule of thumb is .4-1 lb of phosphorus for each 100 lbs of dry matter you remove. An interesting exercise that could help a lot of members is good measurement of your removal of plants and associated effects to guage the effectiveness of nutrient removal by this method. You wouldn't need to measure the dry weight of all but if you could track the volume of the drained but wet weed removed you could dry a small sample to get a conversion factor for your methods of removal. That dry sample could be tested for nutrients (just like hay) if you wanted to track the nutrients removed each season. If you remove 10 tons of weed that have 1 ton of dry matter that contain 0.8 lbs of phosphorus per 100 lbs ... then you would remove 16 lbs of phosphorus or 8 lbs of phosphorus per acre.

Let's say that a ton of dry weight weed were removed in 2026. This would remove 16 lbs of phosphorus from the nutrient pool. But it is important to note that the effect you will see will be no more than 10 lbs reduction of annual phosphorus mobilization in 2027. This is because only a little over 60% of the nutrients will be recycled in 2027. Each year the effect of removing weeds in 2026 will decline. For example, in 2028, expect 3.6 lbs of phosphorus reduction in that year's mobilization of phosphorus. The point here is that you will need to maintain removal each year where after 5 years the full benefit will be seen (which will be a reduction of 16 lbs of phosphorus annually per ton of dry matter removed --- this of course depends on the phosphorus content of the dry weed --- here assumed to be 0.8 lbs per 100 weight).

Other considerations ...

There are other sources of nutrients that will accumulate in the pond each year. For example, atmospheric deposition of nitrogen and phosphorus ... organic deposits brought in from rain ... deposits from avian visitors ... deposition by wind of things like grass cuttings and leaves ... and finally ... the deposition that you can effectively control ... feed and/or fertilizer. All of these sources are new annual inputs of nutrients and so if one is removing living plants as a means of nutrient control ... it should at least match the input to keep conditions the same and exceed it to improve conditions.