Land use changes and their effect on floodplain aggradation along the Middle-Tisza River, Hungary

Land-use changes and their effect on overbank sediment accumulation were investigated on thefloodplain of Middle-Tisza River. Military survey maps (1783, 1860, 1883 and 1890) and aerialphotos (1950, 1965, 1980 and 2000) were used to evaluate land-use changes and to calculate thevegetational roughness of the area. To determinate the rate of overbank sedimentation sedimentsamples were collected from a pit, the grain-size, content of organic matter, heavy metal content (Pb,Cu, Zn, Ni and Cd) and pH were measured. Until 1950 meadows and pastures were typical on thefloodplain, gallery-forest was along the river, the oxbow-lake and the artificial levee. Notable landuse changes were detected in the second half of the 20th century, as the aerial photo taken in 1965shows extensive forestry in the area. These land-use changes affected the average vegetationalroughness, as it has been doubled since the disappearance of grasslands. Land-use changes highlyaffect the aggradation, as the increased roughness decreases the flood velocity on the floodplain,causing accelerated aggradation. Using Pb marker horizons and grain-size changes the studiedsediment profile was compared to dated profiles (Braun et al. 2003), thus, the sediment accumulationrate could be determined for the periods of 1858-1965 and 1965-2005. According to ourmeasurements the accumulation rate was doubled since 1965, very likely in connection with thedoubled vegetational roughness