**5. Conclusions**

Data obtained from various sediment analyses yield a high temporal resolution of the sediment stratigraphy. In 1920 the sedimentation rate was 2.1 cm/a; then came a slight rise,

Lake Mladotice in the Western Czech Republic – Sediments as a Geoarchive

**7. References** 

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reaching 2.7 cm/a after 1963. Because this increase cannot be attributed to greater frequency or amplitude of big floods, we conclude that the switch to collective agriculture was responsible for the increase in sediment entering the lake. If we disregard the extraordinary event layers when calculating sedimentation rates, greater importance then attaches to the "change in land use" factor. The differences in sedimentation rates are smaller, but still remain (Fig. 10).

Collectivisation led to larger units of farmland. According to Janský (1976, 1977) and Janský & Urbanová (1994), the enlargement process was most active during the 1960s and 1970s and was accompanied by the removal of field terraces. In consequence, slopes became steeper and the fine colluvial material that had collected above the terraces over decades or centuries was easily remobilised. From then on, the bigger fields were worked by larger and heavier agricultural machinery, thus increasing soil compaction and erodibility. All three parameters (greater slope length, steeper slope angle, modified farming practices) intensify average soil erosion according to the Universal Soil Loss Equation (Wischmeier & Smith 1978). A substantial increase in sediment input and deposition might be expected, but did not occur to the anticipated extent.

These results may be interpreted in two ways. 1. The amount of soil erosion from the parts of the drainage basin used for agriculture corresponds to the sediment increase in the lake and the additional transport through the lake. 2. Soil erosion has increased much more than is indicated by the lake's sedimentation rates, because a (large) proportion of the sediments was deposited in colluvial, alluvial and lake inflow areas. If the latter is the case, such sinks are likely to provide relevant information.

In 31 years 37,471 m³ of sediment accumulated in the lake basin. This represents a sedimentary deposit of 1,209 m³ per year on average. If we consider the current volume of the lake basin of 103,910 m³, this means that – under the existing dynamics of sedimentation - the lake would be entirely filled up within the next 86 years! In addition to the speed of sedimentation, the lake's drainage could also play a significant role in its future development. Over time, the outflowing creek will cut deeper and deeper into the lake's dam. During extreme floods, the drainage channel could be markedly deepened. This would mean the lowering of the water level and the quicker disappearance of the lake.

Processes of sedimentation in Lake Mladotice could be slowed by implementing thorough anti-erosion and soil protection measures throughout the entire catchment area draining to the lake along with changes in land use (with preference given to permanent grasslands and decreases in arable land).
