Holocene landscape changes in response to sea level oscillations and agricultural intensification in a coastal plain of southeastern South America

This study identified landscape changes in response to variations in mean sea level (MSL) and anthropogenic intervention, from the Early to Late Holocene in Southestern South America. Ananalysis based on palynology and sedimentary bacterial DNA from two sediment cores from the Patos-Mirim System (PMS) is introduced for the first time, to achieve an integrated paleoenvironmental and ladscape reconstruction. The data indicated an east-west migration of the freshwater and forest environments set in the lowlands during the transgressive period (6000–5000 cal yr BP) and an increase in external total biomass input during this MSL rise. A consolidated vegetation onset was inferred, especially of forest environments, after the Holocene Climatic Optimum (5000 cal yr BP). During the last century, landscape changes especially associated with anthropogenic factors were clearly identified from the palynological assemblages. That is, an alternation between Poaceae and Cyperaceae, the first occurrence of Pinus spp. and an increase in the influx of herbs and trees flagged the increase in cultivated areas due to the agricultural and agroforestry intensification. Extreme values of palynological influx appear to be a good proxy for the impact of El Niño events on the sedimentary record, which were associated to increased precipitation. The study also clearly demonstrates the high environmental stress generated by human activities, e.g. loss of plant diversity and changes in the bacterial abundance due to the higher agrochemicals input.