Analysis of Total Phosphorus in Harvested Aquatic Plants.

Phosphorus is an environmental concern because this P often promotes weed and algae growth in bodies of fresh water.  The decomposition of the weed and algae material reduces dissolved O₂ levels.  This phenomenon can lead to odors, death of fish, and a general degradation of the aesthetic and recreational value of the.  Point and non-point sources of P are of concern for the water quality monitoring, but the P outputs from a body of water are also important for a complete picture of a P budget.  At Pewaukee Lake, near Milwaukee, Wisconsin, aquatic plant (weed) harvesting has been a consistent component of lake management.  The plant material is then applied as a soil amendment.  The impact of the harvesting, in terms of P removal, was determined in order to facilitate on-going P and plant monitoring.  The plant material was collected at various locations and times and analyzed for total P.  Phospho-molybdate colorimetric analysis followed P extraction.  A comparison of two different extraction methods was made: a) by sulfuric acid digestion (wet digestion: Nelson, 1987) and b) by muffle furnace (dry digestion: Plank, 1992).  With this data and the volume of harvested plant material, the P removal is calculated as a component for the P budget.