Temporal variation of elemental stoichiometry in freshwater plankton

Abstract

The balance of elements within aquatic food webs shapes ecosystem productivity, energy transfer, and nutrient cycling, yet how this balance varies across space and time in freshwater systems remain poorly understood. Much of stoichiometric research in freshwater communities has focused on how macronutrients such as carbon (C), nitrogen (N), and phosphorus (P) move through food webs. Far less is known about how environmental drivers shape consumer stoichiometry, and the entire elemental profile of freshwater communities (i.e. the ionome). To address this, we examined temporal dynamics of seston and zooplankton in Tree Top Pond, a small, dimictic, eutrophic lake located within Seven Ponds Nature Center (Dryden, MI, USA), from March to September 2024. Temperature profiles were obtained from loggers deployed from the surface to the bottom of the lake to capture thermal variation through time. Zooplankton were sampled weekly to quantify the elemental composition (C, N, and P) of two taxa, Daphnia and copepods, alongside community composition through time. Seston was sampled weekly at 1m intervals throughout the water column to characterize the ionomic profile. We found that seston composition had inconsistent influence on zooplankton stoichiometry, while temperature had a stronger effect on elemental composition, particularly in Daphnia. Notably, P in Daphnia and copepods converged over the season, suggesting that warming may alter biochemical allocation of nutrients. Seston ionomic dynamics, in contrast, were more strongly structured by spatiotemporal patterns and physical processes. Spring mixing characterized the seston ionome through geochemical influences of sediment-associated elements, such as aluminum (Al), manganese (Mn), and iron (Fe); whereas macronutrients, such as C, N, and P, were more influential. Across these dynamics, temperature significantly correlated with the concentration of many elements. These results demonstrate that consumer stoichiometry is differentially sensitive to temperature, while seston ionomes are largely shaped by temporal lake processes, with implications for nutrient dynamics and lake functioning under a warming climate.