Identifying patterns of forest hydrologic and biogeochemical fluxes using weather map classification in a Mid-Atlantic deciduous forest

Abstract:

The partitioning of precipitation within the forest canopy into throughfall and stemflow is controlled by biotic and abiotic factors, which include storm characteristics (e.g., intensity, duration, and magnitude) and canopy structural parameters. Our research uses novel applications of weather map classification to relate synoptic scale weather patterns to the surface environment. A daily synoptic calendar was developed in the Mid-Atlantic (USA) to categorize the subcanopy hydrologic and biogeochemical fluxes during storm events in an eastern deciduous forest. Synoptic classification identified 6 low pressure systems, 4 high pressure systems, 1 cold front, 3 northerly flow regimes, 3 southerly flow regimes, and 5 weak patterns across 4 seasons. The low pressure systems were commonly associated with the largest average flux-based enrichment ratios of solutes in throughfall and stemflow compared to rainfall solute concentrations. Low pressures such as the Weak Coastal Low, centered off the Mid-Atlantic coast with easterly winds over the study region, were associated with large rainfall events with moderate intensities falling over a long period of time. This combination of meteorological conditions allowed complete washoff of antecedent atmospheric deposition and maximum canopy leaching as storm systems of this magnitude were able to wet the entire canopy. The lowest flux-based enrichment ratios occurred during the passage of cold fronts and under weak southwest flow regimes, which were both characterized by moderately high rainfall amounts that occurred over short periods of time (i.e., < 0.5 days) with high intensities (i.e., > 5 mm h^-1). As a result, the water from these storm systems passed through the forest canopy very quickly and with minimal contact time thus resulting in minimal enrichment of throughfall and stemflow. The distinct chemical signatures of synoptic types provide evidence that this novel application of storm classification in forest hydrology is useful for estimating hydrologic and nutrient fluxes in eastern forests and modeling forest water and nutrient budgets in response to changing precipitation characteristics in the region.