Study of the Phosphorus losses from different watersheds in Guilan province

Phosphorus is one of the essential nutrients for plants which is major pollutants originating from non-point sources such as urban runoff, residential, industrial and agricultural areas. Runoff movement and erosion result in Phosphorus loss from watershed and entering the waterbody. The aim of this study was to investigate the Phosphorus release from watersheds under different land-use in Guilan Province .These watersheds included Divshel, Komsar, Jokolbandan, Sangar and Saravan. Samples were taken monthly from the runoff of these watersheds during one year. Then, some properties of runoff including electrical conductivity and acidity of runoff, total solids, total suspended solids and total dissolved solids were measured by weighing method; moreover, three types of phosphorus, total Phosphorus, water-soluble phosphorus and particulate phosphorus were determined as well. The results showed that the highest loss of total phosphorus was relevant to Sangar with forest and agricultural land uses in February (0.228 mg/l). Phosphorus variations in these watersheds were dependent on the amount of monthly precipitation and phosphorus loss was increased with augmenting rainfall. The maximum mean of water-soluble phosphorus losses were related to Jokolbandan with the dominant land use of forest (0.36 mg/l) and Saravan with land uses of forest and industrial activities (0.33 mg/l), respectively. Furthermore, the highest loss of particulate phosphorus was from Sangar in April (0.192 mg/l). The level of phosphorous losses from the studied watersheds was high enough to result in eutrophication of water bodies and consequently water quality decline.