The effect of conifers on the chemistry and mass balance of two large lysimeters in Castricum (The Netherlands)

Abstract

A comparison of the quality of drainwater from dunesand in a bare lysimeter and in a lysimeter with growing conifers shows significant differences. Over a period of 16 years the vegetated lysimeter plot intercepts 24% more Cl −, SO 4 − and Na + + K + ions from rainwater and aerosols than the bare plot. On the other hand, the conifers reduce the average output of Ca ++ and Mg ++ in drainwater by 13% and the total amount of NO 3 − in drainwater is reduced by a factor of 20. The pH value of drainwater decreases during periods of rainfall, while large amounts of Ca ++ and HCO 3 − are leached out. The percentage of the rainfall which infiltrates through the bare sandy soil remains constant at 80% during 16 years. In contrast the vegetated lysimeter drains 62% of the rain during its first year of operation. Thereafter a continuing decrease occurs over a period of 7 years, coinciding with increased growth and evapotranspiration of the conifers. After 7 years the decrease in volume of recharged rainwater levels off to 25% of the rainfall. From that period on the conifers do not grow nearly as well as the surrounding trees with free access to groundwater.