Do storm synoptic patterns affect biogeochemical fluxes from temperate deciduous forest canopies

Abstract

The volumetric quantity and biogeochemical quality of throughfall and stemflow in forested ecosystems are influenced by biological characteristics as well environmental and storm meteorological conditions. Previous attempts at connecting forest water and nutrient cycles to storm characteristics have focused on individual meteorological variables, but we propose a unified approach by examining the storm system in its entirety. In this study, we use methods from synoptic climatology to distinguish sub-canopy biogeochemical fluxes between storm events to understand the response of forest ecosystems to daily weather patterns. For solute inputs tied to atmospheric deposition (NH4+, NO3−, SO42−, Na+, Cl−), stagnant air masses resulted in high inputs in rainfall (273.42, 81.81, 52.30, 156.99, 128.70 μmol L−1), throughfall (355.05, 130.66, 83.24, 239.55, 261.32 μmol L−1), and stemflow (338.34, 182.75, 153.74, 125.75, 272.88 μmol L−1). For inputs tied to canopy exchange (DOC, K+, Ca2+, Mg2+), a clear distinction was observed between throughfall and stemflow pathways. The largest throughfall concentrations were in the Great Lakes Low (1794.80, 352.96, 72.75, 74.37 μmol L−1) while the largest stemflow concentrations were in the Weak Upper Trough (3681.78, 497.34, 82.36, 72.46 μmol L−1). Stemflow leaching is likely derived from a larger reservoir of leachable cations in the tree canopy than throughfall, with stemflow fluxes maximized during synoptic types with greater rainfall amounts and throughfall fluxes diluted. For flux-based enrichment ratios, water volume, storm magnitude, antecedent dry period, and seasonality were important factors, further illustrating the influence of synoptic characteristics on wash-off, leaching and, ultimately, dilution processes within the canopy.