LAUSR

Abstract The purpose of this study was to analyse suspended sediment (SS) transport in a small catchment (13 km2) located in the Polish Carpathians affected by various forms of human activity in the period 1970–2017. This period covers two stages of socioeconomic development with contrasting forms of human activity: the centrally planned economy related to the communist system up to 1989 and the period of a free-market economy following. Analysis indicates increases in grassland and forest areas of the analysed catchment of 90% and 10% respectively and a decrease in cultivated land of 82%. Changes in land use and land cover (LULC) have reduced soil erosion by 74% as calculated using the Revised Universal Soil Loss Equation. At the same time, population, number of buildings, and construction works along the stream increased, and number of cart roads decreased. Hydrometeorological data as well as suspended sediment load (SSL) have not shown a statistically significant trend despite changes in forms of human activity in 1970–2017. In the first three decades of the analysed period (1970–1979, 1980–1989, and 1990–1999), SSL gradually decreased. In 2010–2017, suspended sediment load was the highest in the whole investigated period. Principal component analysis (PCA) confirmed that it was a result of the appearance of new sediment sources associated with intensification of landslides and new forms of human activity, such as construction works. The imposition on these factors resulted in an increase in SSL and masked the effects of rainfall LULC change in the catchment. Analysis shows that proper recognition of changes in sediment sources in the catchment is fundamental for correct interpretation of long-term sediment transport in the streams.