This data set reports the chemistry of porewater in the S3 peatland that was collected at the Marcell Experimental Forest (MEF) in Itasca County, Minnesota. Porewaters at four depths (0 to 1 m depths) have been collected about monthly from three different nest of piezometers since 2013, though never when samplers were frozen. Samples are measured for pH, specific conductivity, anions (chloride, sulfate), cations (calcium, magnesium, potassium, sodium, aluminum, iron, manganese, strontium), silicon, nutrients (ammonium, nitrate, soluble reactive phosphorus, total nitrogen, total phosphorus), and total organic carbon. The MEF is operated and maintained by the USDA Forest Service, Northern Research Station.