Aquatic ecosystem stoichiometry, structure, and function in response to latitudinal gradients of atmospheric nitrogen and phosphorus deposition

Lindsey Pett and Nicholas J. Gotelli, Biology, University of Vermont, Burlington, VT, Angelica L. Gonzalez, Department of Biology, Rutgers University, Camden, NJ

Background/Question/Methods
Atmospheric nutrient deposition of nitrogen and phosphorus varies greatly on the east coast of the United States, nitrogen ranging from <1 to 20 kg/ha and phosphorus ranging from 0 to 0.3 kg/ha. These gradients of nutrient deposition can have major impacts on aquatic ecosystems, potentially leading to eutrophication. As nutrient concentrations and ratios continue to get altered atmospherically, these loads can change ecosystem stoichiometry, structure, and function. To determine the impacts of gradients of atmospheric nitrogen and phosphorus deposition a survey of the model system Sarracenia purpurea (Northern pitcher plant) occurred in the summer of 2019 from the Florida panhandle to Northern Maine. S. purpurea was utilized as a model system because it contains an entire aquatic ecosystem in its tubular shaped leaves, contains complex trophic dynamics similar to larger aquatic ecosystems, and lives in nutrient poor habitats, so a majority of the nutrients it receives is from atmospheric deposition. 28 bogs were surveyed, in which 15 plants were sampled at each bog for stoichiometry in each ecosystem component (pitcher fluid, plant tissue, invertebrates, detritus, algae, and microbial communities). As well as structure of obligate invertebrates, prey, and plankton and function in the form of fluid parameters (pH, DO, EC, TDS) and biomass for each component was also recorded.
Results/Conclusions
From the latitudinal survey we found no significant interaction between atmospheric N deposition and the amount of nitrogen found in S. purpureas plant tissue, detritus, microbial community, obligate invertebrates, or prey. We did find a significant relationship between atmospheric phosphorus deposition and the amount of phosphorus found in the plant tissue (p <0.01). We also found significant positive relationships between the N:P ratio from atmospheric deposition and the N:P ratio found in pitcher fluid as well as plant tissue (p<0.001). The strongest relationship found from the survey was in regard to latitude/growing season length and the amount of P present in the plant tissue. Northern plants with smaller growing seasons had higher amounts of phosphorus in their tissue and significantly lower N:P ratios. Northern plants were also found to be larger in biomass, have larger pitcher openings, and contained higher amounts of prey but lower detrital biomass. As for community structure we did find that as nitrogen deposition increased so did Wyeomyia smithii(mosquito) abundance, while Fletcherimyia fletcheri (flesh fly) abundance decreased. For ecosystem functioning we found that as nitrogen deposition increased pH decreased while dissolved oxygen increased.