Alkalinity contributes at least a third of annual gross primary production in a deep stratified hardwater lake

In alkaline freshwater systems, the apparent absence of carbon limitation to gross primary production (GPP) at low CO2 concentrations suggests that bicarbonates can support GPP. However, contribution GPP has never been quantified in lakes along seasons. To detect origin inorganic maintaining GPP, we analyze daily stoichiometric ratios CO2–O2 and alkalinity–O2 a deep hardwater lake. Results show aquatic withdraws bicarbonate from alkalinity pool for two-thirds year. Alkalinity rather than is dominant source throughout stratified period both littoral pelagic environments. This study sheds light on neglected role cycle an annual cycle.