Monitoring total phosphorus in lakes

Phosphorus is an essential nutrient for the growth and development of plants and animals. However, elevated phosphorus concentrations in a lake can lead to eutrophication, a process that stimulates algal or aquatic plant growth to nuisance levels. Excessive algal or plant growth, especially when accompanied by cyanobacteria blooms, can impact a lake’s ecological health, recreational and cultural values.

Phosphorus occurs naturally as phosphate bound to rocks and soil, and during weathering processes it is dissolved and released into water in a plantavailable form. Total phosphorus in water includes all dissolved and particulate forms, both in organic and inorganic form. The most biologically available form of phosphorus is ortho-phosphate (PO4 3-), which is commonly expressed analytically as dissolved reactive phosphorus (DRP). Under certain conditions, other forms of phosphorus can also become biologically available.

While phosphorus occurs naturally in rivers, lakes and groundwater, concentrations are generally very low in the absence of land use impacts and contaminant discharges (catchments with volcanic soils are one exception). Unlike nitrogen, most phosphorus attaches to soil particles, such that high phosphate concentrations in surface water are typically associated with high levels of soil erosion and overland runoff. Other sources of phosphorus include phosphate fertiliser and discharges of wastewater or animal effluent.