Throughfall nutrient fluxes across a temperate forest fertility gradient

We measured throughfall nutrient fluxes across a gradient of soil
fertility and tree species composition in the northern Lower Peninsula of
Michigan, USA. We collected throughfall from April through November in
2006 and 2007 across five stands ranging from the poorest site on sandy,
infertile outwash sediments dominated by black oak (Quercus velutina) and
white oak (Quercus alba), to moderate-fertility ice-contact origin sites
dominated by red oak (Quercus rubra) and red maple (Acer rubrum), to the
highest fertility site on fertile moraine dominated by sugar maple (Acer
saccharum) and basswood (Tilia americana). Collectors were sampled
whenever cumulative precipitation exceeded 2 cm. At each site we had five,
randomly located throughfall collectors, and a single throughfall
collector in an open field centrally located relative to the five study
sites. All samples were anlyzed for total nirtogen (N), calcium (Ca),
potassium (K), magnesium (Mg) and phosphorus (P). The net
exchange of nutrients in throughfall was calculated for each collector as
the difference in nutrient concentration between the throughfall sample
and the open precipitation collector, multiplied by the volume of
throughfall collected. The data set is organized by site and by sampling
date with throughfall fluxes of N, Ca, K, Mg and P expressed in units of g
of nutrient per m2.