AQUATIC METABOLISM IN 4 NEWLY CONSTRUCTED FRESH-WATER WETLANDS WITH DIFFERENT HYDROLOGIC INPUTS

To determine the effect of two different hydrologic flows on aquatic metabolism in constructed freshwater riparian marshes, we measured diurnal changes in dissolved oxygen concentrations during two growing seasons. Average gross primary productivity of water column producers (phytoplankton, periphyton, and submerged macrophytes), estimated from the daily shift in dissolved oxygen concentration, was generally higher in the high-flow wetlands (84 kJ m(-2) d(-1) in 1990; 69 kJ m(-2) d(-1) in 1991) than in the low-flow wetlands (73 kJ m(-2) d(-1) in 1990; 46 kJ m(-2) d(-1) in 1991). Detailed comparisons of one high-flow and one low-flow wetland at 16 sample sites in each wetland showed twice the solar efficiency in the high-flow wetland (0.6 vs. 0.3%). Depth profiles indicated that dissolved oxygen concentration decreased by as much as 60% from 15 cm below the water's surface to 50 cm below. Chlorophyll a concentration did not correlate to productivity. Water column primary producers contributed an estimated 17 to 67% of the net aboveground carbon production of each wetland.