Deposition signatures in Onondaga Lake, New York: Observations from a 28-year sediment-trap study
Limnol. Oceanogr., 57(5), 2012, 1531-1543 | DOI: 10.4319/lo.2012.57.5.1531
ABSTRACT: We tested paradigms and models that relate deposition of phytoplankton constituents to lake metabolism based on analyses of long-term sediment-trap collections (28 yr of the 1980–2010 period) from a dimictic urban lake, Onondaga Lake, New York. There were major changes in a number of important drivers of deposition, including decreases in the concentration of a divalent cation (Ca2+), nutrient loading and primary production, and variations in food-web effects. The summertime downward fluxes of particulate organic carbon (DFPOC), particulate nitrogen, particulate phosphorus (P), and chlorophyll were greater than values reported in the literature at the start of the program and decreased > 70% in response to decreases in Ca2+ and P loading. Results include (1) the positive dependence of DFPOC on primary production, (2) the positive dependence of the rate of hypolimnetic oxygen depletion on DFPOC, (3) the negative effect of Daphnia grazing on DFPOC under eutrophic and hypereutrophic conditions, and (4) the dependence of the stoichiometry of depositing material on particle origins and nutrient status of the phytoplankton community. The relationship between the export ratio, the fraction of gross primary production lost to deposition, and primary production reported in the literature was extended based on inclusion of Onondaga Lake data, and described by a nonlinear (polynomial function) relationship.