The most common problem with nutrient pollution is the stimulation of growth of nuisance plants, which can dominate and change the dynamics of an aquatic ecosystem. Phosphate is the compound made up of 1 phosphorus and 4 oxygen atoms. The Streamwatch kit measures phosphate. Here's some info from the latest edition of the Standard Methods Bible Phosphorus occurs in natural waters and in wastewaters almost solely as phosphates. While reactive phosphorus is largely a measure of orthophosphate, a small fraction of any condensed phosphate present usually is hydrolyzed unavoidably in the procedure.
Reactive phosphorus occurs in both dissolved and suspended forms.
Acid hydrolysis at boiling-water temperature converts dissolved and particulate condensed phosphates to dissolved orthophosphate. The hydrolysis unavoidably releases some phosphate from organic compounds, but this may be reduced to a minimum by judicious selection of acid strength and hydrolysis time and temperature. Like reactive phosphorus and acid-hydrolyzable phosphorus, organic phosphorus occurs both in the dissolved and suspended fractions. There are three ways to digest the sample and in Streamwatch we use the 2nd most extreme digestion method, nitric acid-sulphuric acid digestion which is recommended for most samples. Total phosphorus measurements on highly saline samples may be difficult because of precipitation of large quantities of salt as a result evaporation during digestion.