Productivity floodplain wetland Kakadu

Abstract

Tropical floodplains are one of the most productive ecosystems on Earth. Studies on floodplain productivity have mainly focused on trees and macrophytes because of their high biomass. However, epiphyton –algae and bacteria attached to the submerged portion of aquatic macrophytes- has been recognized as the main source of energy in many tropical floodplains. Epiphyton productivity rates are unknown for most tropical floodplain wetlands, and spatial variability is not well understood. In this study, we measured primary productivity of epiphyton within relatively undisturbed tropical floodplain wetlands in Kakadu, Northern Australia, and estimated their relative contribution to the total production of the floodplain wetlands. We sampled sites dominated by different macrophyte structures: vertical emerging, horizontal emerging, submerged, and attached with floating leaves. Epiphyton productivity was highly influenced by the dominant macrophyte structure, with highest potential productivity per weight measured on epiphyton growing on macrophytes with floating leaves and emerging horizontal grasses (1.52  0.53 and 1.82  0.61 mgC dw g epiphyton-1 h-1, respectively) and lowest in submerged and emerging vertical grasses (0.57  0.26 and 0.66  0.47 mgC dwg epiphyton-1 h-1, respectively). When considering the areal biomass of the macrophyte and the amount of epiphyton attached, epiphyton on emerging horizontal and submerged plants had productivity values about ten times higher (45-219 mgC m-2 d-1) compared to those on vertical and floating macrophytes (2-18 mgC m-2). Epiphyton contributed between 2 to 13% to the total production of these tropical floodplain wetlands.