The turbidity of the water indicates the amount of soil suspended in the water – i.e., the more intense the erosion of the fields, the more turbid the water. When the turbidity reaches 1,000 FTU, a litre of water holds approximately one gram of soil. Turbidity also describes the amount of phosphorus bound in the soil: when the turbidity reaches 1,000 FTU, a litre of water contains approximately 1.4 milligrams of phosphorus. Gypsum is expected to reduce erosion and thus have an impact on the turbidity of the water.
In general, turbidity increases as the water flows faster, and a turbidity value of 1,000 FTU is only likely during intense autumn rains or during the melting of the snow. It is impossible to deduce the streamflow data directly from the sensor results, but the height of the water level provides some indication: the higher the water, the more water is flowing in the Savijoki river.
The fluorescence of the humus indicates the amount of dissolved organic matter. Some organic matter is always washed away into the waterways, which can be reflected in the brown colour of the water. The leaching of organic matter should be minimised, as organic matter improves the structure of the soil. In addition, when organic matter leaches into the water, it dissolves faster than it would on land, leading to increased greenhouse gas emissions. Once the link between fluorescence and the amount of dissolved organic carbon as indicated by laboratory testing from the Savijoki river has been determined, the results will be expressed directly in terms of carbon amounts. Fluorescence is expected to drop as a result of gypsum application, as the increase in the ionic strength of the soil will also promote the retention of organic matter.