Paleoenvironmental analysis of a late-holocene subfossil Coleopteran fauna from Starks, Maine

The Sandy River in central Maine Is flanked along much of its length by low terraces. Approximately 100 kg of sediment from one terrace in Starks, Somerset County, Maine was wet-sieved in the field. Over 1100 subfossil Coleoptera were recovered representing 53 individual species of a total of 99 taxa. Wood associated with the fauna is 2000 +/-80 14C Yr in age (1-16,038). The fauna is dominated by species characteristic of habitats apparent in modern central Maine. The subfossil assemblage is indicative of a wide vartety of environments including open ground (e.g., Harpalus pensylvanicus), dense forest (e.g., pterostichus honestus), aquatic environments (e.g., Gyrinus, Helophorus), riparian environments with sand and gravel substrates (e.g., Bembidion inaequale, Schizogenius lineolatus), and moist, organic-rich terrestrial environments (e.g., Micropeplus sculptus). The ecological requirements for each taxon permit an environmental reconstruction suggesting an area vegetationally, climatically, and ecologically similar to that of the Sandy River today. The lowest terraces apparently represent the modern-day floodplain of the Sandy River. An average sedimentation rate of l.00 to 1.04 mm per year has been inferred based on radiocarbon dates here and elsewhere on the Sandy River. The Coleopteran fauna suggests that sand and gravel were distinctly abundant, and that the aggradation of point bars, as seen today, contributed to the flood history. Lateral bank erosion of the modern Sandy River accelerated after the State of Maine mandated cessation of bar removal in 1975: flood severity has dramatically increased since that time. Implications suggest that mining of the bars may be necessary to minimize future flooding problems.