Application of spectral analysis to meteorological and soil solution chemistry data

One of the longest-running forest ecosystem studies in Europe was established at the Solling region in central Germany. It provides a unique database covering more than 25 years of meteorological, throughfall, and soil solution chemistry data. It determines input to the ecosystem at canopy level and infiltration into the soil. These are important parts of water and element flux. Application of time series analysis can detect structures and dynamics in the long-term time series, which are not apparent in the original data. Our study investigates these dynamics, especially their seasonal patterns using spectral analysis. While some meteorological input parameters such as temperature and rain chemistry show pronounced annual seasonality, throughfall data of spruce and beech indicate a transformation of the input signal. Chemical parameters of spruce throughfall behave either half-annual seasonal (NO,-N, S04-S, Ca), or, as chloride, the time series contains both annual and half-annual seasonality. No element of beech throughfall has distinct seasonal behaviour. During infiltration into soil, the next step of flux, most seasonality disappears. Influences of seasonal inputs can be observed down to Ocm (under humus layer) or at most 10cm under beech forest. Only potassium under spruce forest still shows strong seasonality at 100cm soil depth. This appears to be coupled with a biological process.