Quantification of Enrichment Processes in Throughfall and Stemflow in a
Mixed Temperate Forest
Abstract
Forest ecosystems depend on throughfall and stemflow fluxes for both
water and nutrient input. Spatial and temporal variability of
throughfall and stemflow fluxes are large and differ between tree
species. The nutrient fluxes that accompany throughfall and stemflow are
affected by climate, precipitation intensity, the seasonality of dry
deposition, and canopy exchange processes. The interdependence of these
factors make it challenging to quantify changes in throughfall and
stemflow amounts as well as their nutrient content. Here we provide
observation-based evidence from 3.5 years of record with 222 rainfall
events, of the seasonal variability of throughfall and stemflow
magnitude and ion concentrations under a beech (Fagus silvatica)
and spruce (Picea abies) tree. Interception and canopy cover were
seasonally variable, average annual interception was 53% below beech,
61% below spruce and 68% below young spruce canopies. Further we
assess seasonality of ionic nutrients such as NH 4 and
NO 3 as well as Mg, Ca and K and their dependence on
both dry deposition and canopy exchange. Throughfall and stemflow were
enriched compared to precipitation, with large differences between ions
and different months. Antecedent precipitation was a main control on
throughfall and stemflow enrichment. We developed a conceptual model of
the potential drivers of throughfall and stemflow enrichment based on
our observations. While NH 4 and NO 3
enrichment are likely dominated by dry deposition and dew and fog
accumulation, Mg, Ca and K were additionally affected by canopy
exchange. Observation based studies such as this one are needed to
understand precipitation and nutrient partitioning across forests, which
enables to predict how changes in climate and forest composition will
affect local hydrology and nutrient inputs into forest ecosystems.