|Title||The tight coupling of photosynthesis and respiration during base flow in the Australian Wet-Dry Tropics|
|Publication Type||Conference Participation|
|Year of Publication||2010|
|Authors||Townsend, S, Webster, I, Schult, J|
|Keywords||4: Material Budgets|
The rates of photosynthesis (P) and respiration (R) were calculated at 4 high order river sites during the dry season in tropical Australia when discharge is supplied by groundwater. The rivers were shallow, clear, and had low concentrations of nutrients. Increased irradiance at the riverbed, warmer water temperatures, and an increase in primary producer biomass over the dry season contributed to an approximate doubling of P. We surmise that most photosynthesis resulted in the production of dissolved organic carbon, rather than the growth of primary producer biomass which was nutrient limited. Respiration exceeded photosynthesis (P/R ~0.5), and increased approximately linearly with P (r2 =0.79–1.00). Bacterial metabolism of photosynthetically produced dissolved organic carbon (PDOC) could partially explain the tight coupling of respiration and photosynthesis, though cannot account for the river’s overall net heterotrophy. The co-metabolism of recalcitrant dissolved organic carbon, such as humic acids, by bacteria, which is made possible by the presence of readily degraded PDOC, provides an explanation for the river’s heterotrophy and the tight coupling between P and R.