Abstract
Dissolved nutrient uptake and metabolism by periphyton in a central North Island gravel‐bed river were investigated using recirculating in‐situ chambers. Dissolved inorganic nitrogen (DIN) uptake was correlated with photosynthesis and chlorophyll but N uptake and carbon fixation were partly de‐coupled indicating storage. Dissolved reactive phosphorus (DRP) uptake was only weakly correlated with photosynthesis. Diatoms and green algae relied on DRP in the water, but Cyanobacteria met part of their P needs from storage. Dissolved organic nutrients were excreted in both light and dark incubations, with approximately 50% of DIN uptake during photosynthesis excreted as DON. To simulate diurnal variations in nutrients, oxygen and pH existing computer models need to de‐couple photosynthesis from nutrient uptake, allow for variable stoichiometry and better quantify recycling of organic nutrients.