PERIPHYTON PRODUCTIVITY ON ARTIFICIAL AND NATURAL SURFACES IN CONSTRUCTED FRESH-WATER WETLANDS UNDER DIFFERENT HYDROLOGIC REGIMES

Four constructed freshwater marshes in midwestern USA were subjected to two hydrologic regimes of turbid river water. Two wetlands (high flow) received 41 cm of water depth per week and the other two wetlands (low flow) received 6-9 cm week. Periphyton samplers near the inflow and outflow of all four wetlands measured dry weight, organic dry weight and chlorophyll a every 2 weeks for one growing season. We also estimated periphyton growth on the dominant macrophytes (Polygonum amphibium L., Polygonum pennsylvanicum L., Phalaris arundinacea L., Typha angustifolia L. and Typha latifolia L.) three times in all four wetlands. Periphyton growth on artificial surfaces was higher in the high flow wetlands (P < 0.10). Inflow samplers in all wetlands had higher average chlorophyll a (0.4 vs. 0.2 mug cm-2), dry weight (3.0 vs. 1.0 mg cm-2) and organic dry weight (0.7 vs. 0.4 mg cm-2) than outflow samplers (P < 0.10). Epiphyte chlorophyll a, dry weight and organic dry weight, were highest on Polygonum spp. and lowest on Typha spp. (P < 0.10). Net epiphyte productivity ranged from 2 to 85 g carbon m-2 per year and was highest in a high flow wetland. Higher productivity in high flow wetlands and near the inflow was attributed to higher nutrient availability.