Pond Boss Forums GENERAL QUESTIONS Water chemistry nutrient overload??

Q - Is that normal for everything to be so uniform especially if one sample was taken so close to a source like the fish cages? It all depends. If there is good mixing due to current, wind or mechanical aeration then water chemistry can be fairly uniform in many of the areas. Unmixed areas will show higher and lower concentrations.

Results. I assume the testing laboratory was certified and knew what they were doing regarding the tests and proper collection and storage of samples.
Nitrate is vulnerable to biological activity thus the test should be started promptly after collection. If the sample is to be stored it should be keep just above freezing with or without preservatives such as sulfuric acid.

Phosphate. These sample should not be collected in plastic due to P can absorb on to the walls of the bottle. If samples are not analyzed immediately then storage should be slightly above freezing or preserved with mercuric chloride to stabilize the sample. If total P only is to be tested no special storage is necessary.

I consider your P values lower than expected for your situation. Total P and ortho P values can fluxuate quite a bit due to production and condition of plants which absorb ortho P (reactive). Ortho P of cage operation is twice that of control which indicates more reactive P regardless of the amount of error in sample collection or analysis. I assume that the P values are in mg/L. It is best to analyze P values with accuracy in micrograms/liter (parts per billion).

I consider your values for P and N in error. Typically total nitrogen is 12 to 35 times more abundant the total P. Total P typically ranges over the trophic range from lows of 10ug/L to 100ug/L or 0.01 - 0.1 mg/L. There are instances where N can be limiting and quite low while ortho P is still available. In these cases certain types of algae will bloom.

pH values will not have much bearing on what you are trying to do which I assume is determine the impact of cage operation on water quality.

Making evaluations or judgements from a one time sampling is very risky because the condtions are constantly changing and often the changes can be quite dramatic depending on the prevailing conditions.