Nitrate leaching in forest ecosystems is related to forest floor C/N ratios

Relationships between nitrogen (N) output with seepage water and forest floor C/N ratios were analysed by use of three independent datasets: (i) a compilation of input-output studies in temperate forest ecosystems in Europe; (ii) a seven-year national Danish survey of nitrate concentrations in forest soils; and (iii) a similar one year Dutch survey. Nitrate leaching and nitrate concentrations were negatively correlated with forest floor C/N ratios in all three datasets, though the correlation was weak in the Dutch dataset. Sites with a C/N ratio below 25 leached nitrate or had elevated nitrate concentration in the three datasets. Nitrate was not present in the subsoil at sites with C/N ratios above 30 in the European and Danish data. In the less intensively monitored Dutch forest soils nitrate concentrations at C/N ratios above 30 were variable. Forest floor C/N ratios may be used to assess risk for nitrate leaching in conifer stands using>30, 25 to 30, and <25 to separate low, moderate, and high nitrate leaching risk, respectively.