Palaeoecological record of natural changes and human impact in a small river valley in Central Poland

The developmental history of a mire located in the Grabia River valley, central Poland, spanning the last 9000 years, was investigated using high-resolution records of pollen, Cladocera, and geochemistry from a 14C-dated core. The study demonstrates the value of Cladocera, palynological, and geochemical methods in research into human impact and natural fluvial activity, particularly for those elements that are difficult to find through sedimentological methods. Our research shows the importance of long-term reconstructions in establishing palaeohydroclimatic conditions and determining the human impact on the mire. We propose that water-level fluctuations were important in modifying biota assemblages. Periods with higher water-levels are synchronous with climatic changes, but in the Subatlantic, they also correspond to phases of human activity in the valley. The probable phases of increased fluvial activity of the Grabia River coincide in general with periods of wet climate, deforestation, and soil erosion. The main phases that show increases in the water level in the lower part of Grabia River valley are estimated at ca. 5800–5500 BC, 4500–4300 BC, 4200–3800 BC, and 400 AD. The water-level changes of 1300 AD, 1500 AD, and 1650 AD, as well as those of the last century, were most strongly influenced by a combination of natural and anthropogenic factors. Anthropogenic events were particularly significant during the Middle Ages and in the last century.