The oldest Czech fishpond discovered? An interdisciplinary approach to reconstruction of local vegetation in mediaeval Prague suburbs

Wet sediments of a former water reservoir were discovered during an archaeological rescue excavation. Vegetation and environmental changes taking place in the mediaeval suburbs of Prague, Czech Republic, from the tenth to the middle of the fourteenth century were investigated. The origin and function of the water reservoir was revealed using a multi-proxy approach that combined the results of macrofossil, pollen, diatom, antracological, archaeo-zoological and sedimentological analyses. Gradual changes of the surrounding vegetation were documented. Field indicators increased in time, whereas proportions of broad-leaf trees and shrubs decreased; proportions of ruderal plants increased continually. A gradual decline of semi-natural hygrophilous vegetation was accompanied by an inverse tendency in trampled vegetation. All these trends indicate an intensification of human activity around the pool. A similar intensification of anthropogenic influence is clearly visible in the development of the aquatic environment. According to the diatom composition, the base of the profile is the result of sedimentation in considerably oligotrophic conditions. A successive deterioration of water quality was documented by various organisms (diatoms, green algae, water macrophyta, fishes and intestinal parasites). The high content of dissolved nutrients, probably connected with anoxia, could have caused the disappearance of both diatoms and fishes.