In lakes, the rates of gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP) are often controlled by resource availability. Herein, we explore how catchment vs. within lake predictors of metabolism compare across lake types. We combined stream loads of dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorus (TP) with lake DOC, TN, and TP concentrations and high frequency in situ monitoring of dissolved oxygen from 16 lakes spanning 39 to 64 ^oN, a range of inflowing streams, and trophic status. We found that stream load stoichiometry was indicative of lake stoichiometry for C:N and C:P (R²=0.74 and R²=0.84, respectively), but not for N:P (R²=0.04). As we found a strong positive correlation between TN and TP, we only used TP in our statistical models. For the catchment model, GPP and R were best predicted by DOC load, TP load, and load N:P (R²=0.85 and R² = 0.82, respectively). For the lake model, GPP and R were best predicted by TP concentrations (R²=0.86 and R²=0.67, respectively). The inclusion of N:P in the watershed model, but not the lake model, suggests that both N and P regulate metabolism and that organisms may be responding more strongly to catchment inputs than lake resources. Our models predicted NEP poorly, though it is unclear why. Overall, our work stresses the importance of characterizing lake catchment loads to predict metabolic rates, a result that may be particularly important in watersheds experiencing changing hydrologic regimes related to global environmental change.

Primary Presenter: Jessica Corman, University of Nebraska-Lincoln (jcorman3@unl.edu)

Authors:

Jacob Zwart, US Geological Survey  ()

Jennifer Klug, Fairfield University  ()

Denise Bruesewitz, Colby College  ()