Thanks for this twist on the difficulties of nutrient management, specifically phosphorus, in our ponds, jpsdad.
This begs the question of what else can we remove/harvest to diminish P? Say we target unnecessary vegetation. I pull FA and elodea each summer from our 1/4 acre BOW, as in many hundreds of pounds wet weight. This probably helps. It would be informative to understand just how much benefit we are achieving through this unpleasant task.
I think it definitely helps much more than removing fish from a population that one is maintaining balance. The wet % of many aquatic plants are in the 90ish range but with say 800 lbs from your 1/4 acre bow we are talking in the neighborhood 80 lbs dry or 320 lbs dry weight to the acre. Compare that to 15 lb weight fish harvest (60 lbs/acre) where the dry weight is 12 lbs/acre. Plants require phosphorus so you know you are removing at the very least what it took to grow the amount you removed. To be certain you could weigh a sample, then sun dry it to understand it's dry weight content. This sun dried sample could be sent to your state's agriculture lab for analysis just like you can do for hay. This would be a way to make a very good estimate of phosphorus content removed from a wet volume or a wet weight measurement. Alfalfa hay has ~0.21 % phosphorus and so I think that might be starting place to make a roughish estimate. I may have underestimated the wet weight of what you are removing. A quarter acre could grow much, much more than that. I read the other day an author's estimate of phytoplankton production in catfish production ponds over the growing season. It was in the tens of tons per acre. So a lot of detrital rain are in these heavily fed production ponds. Zooplankton are just not able to keep up with it..
What else could a pond owner remove other than fish, crayfish, and bottom muck to lessen the nutrient loading? We pull some thousands of gallons of water from the pond each year for irrigation purposes, replenished by rather infertile Dolores river water. There is no irrigation runoff returning to the pond.
I love strategies that use the nutrients. For example, I think your use of the enriched water for irrigation is a great idea. I like organisms that prevent the accumulation of muck. Such organisms like crayfish and TP are literally able to convert this material into edible flesh. I like that too. At sufficient density, these organisms expose sediments to help get nutrients suspended in the water column. So together with flushing they certainly have potential. Though your pond may be too cold for TP when the Dolores water comes through it ... TP are absolutely amazing. You can't hurt a pond by taking them out at the end of growing season so the only limit is how much the pond can grow. They will reach harvestable size ~6" in as little as 90 days from hatching. So TP (in monoculture) can produce up to 1500 lbs of fish just on rich water. They can grow in cages at remarkable rates ... unfed ... except for green water flowing through the cage. 1500 lbs/acre, if fully harvested, will remove 300 to 350 lbs dry weight/acre AND make a lot of meals. If the feed is 1% P and TP 1.5% P then this is like removing 450 to 525 lbs/acre of feed from the nutrient store of a pond. The effect would be greater if the dry weight percent of P in tilapia is greater than 1.5% ... and the probably are. Any organism that feeds very low on the food chain and can achieve high biomass is a candidate for such nutrient sequestration. In essence, you are already doing this at the primary level by removing primary production biomass of elodea and FA.
Thanks again for your scientific analyses of many topics on this forum. I'm able to follow along, and to gain insight into all the subjects you consider.
I appreciate this. I would just say something that I have said before. I have taken much more from here than I have given. Pretty much everyone here has shared experience that I value in the same way. Your comment encourages me and it lets me know participating is worthwhile. Thank you for that.
