Surprisingly small increase of the sedimentation rate in the floodplain of Morava River in the Straznice area, Czech Republic, in the last 1300 years
Abstrakt
Sediment profiles from the floodplain of Morava River in the Czech Republic have been collected from exposed river banks (4-6 m long sections) and cores (2-4 m deep) and investigated using a set of geochemical proxies validated by granulometry and conventional geochemical analysis, outlined in our previous paper. The work was conducted to evaluate the increase in sedimentation rate during Medieval and modern time periods.
Correlation of sediments along the current channel belt allows identification of two most important synchronous changes in the channel structure over the past 1300 years: in the 13th century and at the end of the 16th century. These changes could be related to central European climatic extremes rather than to land cover/land use practises.
Analysis of the pollen record in peaty deposits at the floodplain edge allows excluded dramatic deforestation in Medieval times. Maps of the area from the last five centuries revealed direct and indirect signs of past avulsions and clearly show how the original multichannel system was transformed into a single meandering channel in the early 20th century.
The extrapolated aggradation rate (net vertical accretion of floodplain fines except for levee sediments) increased from 0.2-0.3 cm/year in 700 AD to 0.3-0.4 cm/year in 2000 AD depending on the grain size of the sediment. This is the smallest yet reported enhancement of siliclastic deposition, although Morava River watershed has been intensively used for agriculture and its land cover has changed in a manner similar to west and central European rivers.