Planktonic primary productivity and respiration in inland floodplain wetlands: patterns and relationships with trophic conditions and organic matter concentrations differ between channel and non-channel habitats

Planktonic processes are part of carbon cycling and transformation in inundated inland floodplain wetlands. However, quantitative measurements of planktonic process rates are rare. We measured planktonic gross primary productivity (GPP) and respiration (PR) in channel and non-channel habitats (marshes, swamps, waterholes and a floodplain lake) in inland floodplain wetlands of New South Wales, Australia. The rates were modeled as a function of total nitrogen (TN), total phosphorus (TP), and dissolved organic carbon (DOC). TN and TP are a measure of trophic conditions and DOC as a measure of organic matter concentrations. The GPP varied from 3.7-405.4 mgC m^-3 h^-1 (mean±standard error: 89.4±9.2 mgC m^-3 h^-1, n=81), PR from 1.5-251.6 mgC m^-3 h^-1 (43.2±5.66 mgC m^-3 h^-1 , n=81), TN from 682.0-14700.0 mg m^-3 (2643.0±241.6 mg m^-3, n=81), TP from 47.9-1405.0 mg m^-3 (316.8±31.4 mg m^-3, n=81), and DOC from 1.9-46.3 g m^-3 (21.8±1.6 g m^-3, n=81). We found that our models of trophic conditions and organic matter concentrations predicted GPP and GPP/PR ratio in channel habitats as a function of DOC; and GPP, PR and GPP/PR in non-channel habitats as a function of TN and/or TP. The ‘best’ predictive models explained between 46-74% of the variation in channel habitats and between 16-87% of the variation in non-channel habitats. We discuss the need to further refine our models that predict GPP and PR to better understand and assess wetland carbon balances during inundation.