**3.6 Range of phosphorus soluble in water**

To understand the extent of eutrophication caused by phosphorus in water, it is crucial to measure the total phosphorus concentration instead of just orthophosphate. This is because orthophosphate concentrations can rapidly change within minutes under enriched conditions. Laboratory studies indicate that the concentration of phosphate required for balanced algae growth ranges from 0.003 to 0.8 μg/L. However, in Lake Michigan, it was observed that a concentration of 15 μg/L significantly increased carbon fixation and chlorophyll concentration. While a few micrograms per liter of phosphorus can enhance algae growth in most water systems, there is no agreement among researchers on the exact concentration that causes eutrophication. Some researchers suggest that a concentration between 0.01 and 0.03 mg/L of phosphorus can lead to excessive growth of harmful algae, while others propose a threshold of 0.02 mg/L for accelerated eutrophication. It is essential to note that the appropriate threshold for phosphorus concentration depends on the specific area being studied.
