PRODUCTIVITY OF PODOSTEMUM CERATOPHYLLUM IN THE NEW RIVER,VIRGINIA

Productivity of Podostemum ceratophyllum, the dominant aquatic macrophyte in the New River, was measured at four sites representing soft- and hardwater reaches of the river. Available dissolved inorganic carbon (DIC) was 4–5 times greater in the hardwater reach. The difference in available DIC was reflected in standing crop and productivity of P. ceratophyllum. Maximum standing crops of P. ceratophyllum at the two hardwater sites (Sites 1 and 2) were 244.8 ± 30.7 g ash-free dry wt (AFDW) m^?-2 and 193.8 ± 18.7 g AFDW m^?-2 compared to 128.5 ± 14.9 g AFDW m^?-2 and 101.3 ± 6.9 g AFDW m^?-2 for the softwater sites (Sites 3 and 4). Productivity, based on differences in standing crops, was: Site 1, 1.08 ± 0.12 g C m^?-2 d^?-1; Site 2, 0.86 ± 0.08 g Cm^?-2d^?-1; Site 3,0.58 ± 0.06 g C m^?-2 d^?-1; Site 4,0.45 ± 0.03 g C m^?-2 d^?-1. Corresponding values for productivity as ¹⁴C uptake were: 2.77 ± 0.44 g C m^?-2 d^?-1; 2.10 ± 0.45 g C m^?-2 d^?-1; 0.34 ± 0.04 g C m^?-2 d^?-1; 0.28 ± 0.03 g C m^?-2 d^?-1. Productivity/biomass (P/B) based on ¹⁴C uptake and standing crop revealed that P. ceratophyllum productivity was inhibited at the softwater sites perhaps due to carbon limitation. Because of its abundance and its high productivity, P. ceratophyllum is hypothesized to contribute significantly to the New River organic matter budget.