Pond Boss Forums GENERAL QUESTIONS Water chemistry High Phosphorus Levels

Hello all. We had a water analysis & fish shocking performed last fall at our local Sportsmen's club (2 acre lake). Water results came back as follows:

PH: 7.8
Dissolved O2: 7.5 ppm
Alkalinity: 188.1 ppm
Hardness: 171 ppm
Nitrate Nitrogen: 0.4ppm
Ortho Phosphate: 0
Total Phosphorus: 0.27ppm

Water temp was 63 when the sample was conducted. The fisheries biologist noted nitrate levels were low and that the phosphorus levels were high. We spent a lot of time and effort last year getting our weeds & algea knocked back for the first time in the last 5 years. The pumped trailing hose system I set up worked really well on the elodea and algea problems we had, however the warm spring last year hurt us getting out in front of them. We killed a large mass of weeds & algea last year over a 1-1/2 month span late may and june.
We added bottom diffuser aeration, feeding, multiple structures added etc... I believe I have us pointed the right direction however what can we do to lower the phosphorus levels in the lake? My understanding is that high phosphorus levels will encourtage algae & weedgrowth which we are looking to keep at at bay. I can see bottom algae already with the surface temps only in the mid 40's.

Thanks for any help or literature links on this issue.

Water Fowl

Sorry for the delay in answering. That level is high. I think that it would be a good candidate for an aluminum sulphate treatment. It binds with P and sinks to the bottom, locking it in place there. The only other option that I can think of is to use a suction dredge to remove the muck from the bottom of the pond. I'd bet there is a good buildup of organic matter there. That route wouldn't be cheap tho. I checked into it for a pond about half that size and it figured out to be in the $30 - $40 per cubic yard of muck removed range.

I read in a study where the EPA recommends that phosphate levels be kept below 0.1mg/l and nitrate levels be kept below 10mg/l (USGS 1996-1998).

WF In looking at your ortho P are you saying "zero" was the reading or that it was not tested. Algae and aquatic plants use only the ortho PO4 form and your Total Phosphorus reading may be somewhat misleading.Also was your NO3 (nitrates) a representative sample as often if tested in the upper area you will have lower levels and bottom water will have higher levels (due to decay)

Thanks for the responses guys.
Ted, The Ortho P reading was listed as "0" on the water report we received. I will send the biologist a question on it however I am assuming this was a tested level.
All but the dissolved oxygen level were only taken at the surface. So the nitrate level listed above would be a surface reading. Dissolved oxygen levels at very bottom of the lake (10') was 5.67ppm.
Would it be advisable for us to take a soil and/or water sample from the bottom of the lake and have it tested? Is there a preferred or proper way to go about this to ensure accurate data back?

WF, I would retest the water after you have been aerating for 24/7Let the system circulate for at least a week and then just get a sample in the boil area(s) as it should be representative.I would do a muck depth sampling to see what the organic load is. This will also give you a baseline for how well your aerobic bacteria are doing from circulation from your aeration .Map it and log in the depths. After you have more of an accurate composite water sample then answers to your question will be more specific.Also note water temp and time of day sunny cloudy etc when you sample.How many lifts per day is your aeration system providing?