Seasonal changes in aboveground and belowground life history of Carex lacustris were determined and used to study primary production and nutrient cycling in the ecosystem. Seasonal aboveground production was estimated to be about 965 g/m2 per year, with a peak rate of 20.9 g/m2 per day reached in late July. Belowground production was estimated to be 208 g/m2 per year for a total production estimate of 1173 g/m2 per year.Nitrogen, phosphorus, and potassium begin the season with high percentage concentrations in green overwintering shoots but the percentages decline to only about one-third of the original at death in December. Early growth in spring is characterized by a redistribution of these nutrients in the shoots, some translocation from belowground tissues, and uptake from the soil. Calciumand magnesium do not show any important translocation patterns during the year.The yearly budget of uptake and loss of nutrients during a year is estimated to be 15.9 g/m2 nitrogen, 1.9 g/m2 phosphorus, 16.6 g/m2 potassium, 2.9 g/m2 calcium, and 1.5 g/m2 magnesium.