Environmental and land use factors affecting phosphate hysteresis patterns of stream water during flood events (Carpathian Foothills, Poland)

Flood events play a substantial role in the circulation of catchment phosphate (PO43-). The purpose of the research was to analyze the factors determining PO43- hysteresis patterns (direction and width) during four types of floods: short and long rainfall floods and snowmelt floods on frozen and thawed soil. The research took place in small catchments (forested, agricultural, mixed-use) in the Carpathian Foothills in Poland. Anticlockwise hysteresis was identified in the forested catchment during short and long rainfall floods. Under the same conditions, the clockwise direction was observed in the agricultural catchment. In the mixed-use catchment, the direction of PO43- hysteresis loops was various, driven by the share of water flowing from each part of the catchment. For snowmelt floods, the PO43- hysteresis pattern was similar in all the streams studied (usually clockwise). The direction of PO43- hysteresis loops depends on water circulation patterns, which are determined by the different influx times of particular runoff components. The stream recharge mechanism during a flood event is affected both by the factor initiating the event (precipitation, snowmelt) as well as by land use in the given catchment. Hysteresis loop width was determined by the pool of PO43- in a given catchment during the time period immediately preceding a flood event as well as by the quantity of PO43- flushed out of the soil. The greater a catchment's pool of PO43- and the greater its ability to flush PO43- out of the soil and into surface flow, the wider the hysteresis loops. Copyright (c) 2012 John Wiley & Sons, Ltd.