Ecosystem Research Sites Research Articles

Relationship between aerodynamic roughness length and bulk sedge leaf area index in a mixed‐species boreal mire complex

AbstractLeaf area index (LAI) is an important parameter in natural ecosystems, representing the seasonal development of vegetation and photosynthetic potential. However, direct measurement techniques require labor‐intensive field campaigns that are usually limited in time, while remote sensing approaches often do not yield reliable estimates. Here we propose that the bulk LAI of sedges (LAIs) can be estimated alternatively from a micrometeorological parameter, the aerodynamic roughness length for momentum (z0). z0 can be readily calculated from high‐response turbulence and other meteorological data, typically measured continuously and routinely available at ecosystem research sites. The regressions of LAI versus z0 were obtained using the data from two Finnish natural sites representative of boreal fen and bog ecosystems. LAIs was found to be well correlated with z0 and sedge canopy height. Superior method performance was demonstrated in the fen ecosystem where the sedges make a bigger contribution to overall surface roughness than in bogs.

Ground vegetation monitoring in Swiss forests: comparison of survey methods and implications for trend assessments

At Swiss long-term forest ecosystem research sites, ground vegetation was assessed during the period 1994-2003/2008 following two approaches: (1) visual assessment of the cover of species occurring in sixteen 1 m(2) quadrats, distributed over a 43 × 43 m area, and (2) phytosociological relevés in concentric circular plots of 30, 200, and 500 m(2). We first compared the two approaches with respect to diversity assessment. The number of species recorded in the 16 quadrats was in general higher than in the 30 m(2) plot and it represented 42% to 108% of the number of species recorded in the 500 m(2) plot. In a second step, we tested whether any temporal trends were apparent. In a few cases, a decrease or increase in Landolt's mean indicator values for light, nitrogen availability, soil pH, soil moisture, or temperature was found to be significant. However, these changes were usually restricted to one approach or one area. The only clear trend was detected in an unmanaged former coppice beech stand, for which all survey approaches indicated canopy closure. At another site, vegetation reacted to the local opening of the canopy following windthrow. In a third step, we compared the leaf area index (LAI), measured with an LAI-2000 instrument (Licor, Inc.) over each quadrat, with the indicator value of the vegetation for light (L). Within a site, there was no clear relationship between LAI and L values per quadrat. In contrast, across all sites, the relationship between LAI and L, averaged per site for all available years, was highly significant.

Observations of particle formation and growth in a mountainous forest region in central Europe

In the summers of 2001 and 2002, particle formation and growth were observed at a forest ecosystem research site in the “Fichtelgebirge” mountain range in NE Bavaria, Germany. Atmospheric nucleation events, identified through detailed analysis of the time evolution of submicron particle size distributions, differed considerably from nonevent days with respect to ultrafine particle concentrations and meteorological parameters. Particle diameter growth rates, as quantified through the geometric mean diameter development of the 3–60 nm particle fraction, ranged from 2.2 to 5.7 nm h−1. While H2SO4 concentrations typically explained less than 10% of the observed growth rates, a significant fraction of particle growth may be explained through condensation of organic vapors from α‐pinene oxidation. On several days, cocondensation of H2SO4 and α‐pinene oxidation products was sufficient to fully explain the observed growth dynamics. While BVOC emissions from the tree vegetation may contribute to particle formation, the forest also acts as an effective sink for particles. This is reflected in the dominance of particle deposition to the forest over emission, with the strongest deposition fluxes occurring during particle formation events.

Atmospheric phase distribution of oxidized and reduced nitrogen at a forest ecosystem research site

Atmospheric concentrations of gaseous NH3 and HNO3 and of particulate NH4+ and NO3- were measured during various seasons at a forest ecosystem research site in the "Fichtelgebirge" mountains in Central Europe. Air masses arriving at this site were highly variable with respect to trace compound concentration levels and their concentration ratios. However, the distributions of NH4+ and NO3- within the aerosol particle size spectra exhibited some very consistent patterns, with the former dominating the fine particle concentrations, and the latter dominating the coarse particles range, respectively. Overall, the particulate phase (NH4+ + NO3-) dominated the atmospheric nitrogen budget (particulate and gas phase, NH4+ + NO3- + NH3 + HNO3) by more than 90% of the median total mixing ratio in winter, and by more than 60% in summer. The phase partitioning varied significantly between the winter and summer seasons, with higher relative importance of the gaseous species during summer, when air temperatures were higher and relative humidities lower as compared to the winter season. Reduced nitrogen dominated over oxidized nitrogen, indicating the prevailing influence of emissions from agricultural activity as compared to traffic emissions at this mountainous site. A model has been successfully applied in order to test the hypothesis of thermodynamic equilibrium between the particulate and gas phases.

Chemical classes of atmospheric aerosol particles at a rural site in Central Europe during winter

Ambient atmospheric particles were studied at an ecosystem research site in the Fichtelgebirge mountains in Central Europe by single-particle analysis and bulk impactor measurements. Fuzzy clustering analysis of mass spectra of individual aerosol particles allowed chemical classification of the atmospheric aerosol. During the campaign, inorganic salts, mineral particles, and carbonaceous particles, with varying degrees of secondary components, were identified. These chemical classes exhibited preferential size ranges leading to a characteristic pattern of relative abundances with respect to particle size. A more detailed analysis revealed that 65–80% of all particles were assigned almost exclusively to one chemical class. These particle populations are assumed to be externally mixed with respect to the identified chemical classes. The temporal variations of the ratio of nitrate to ammonium (ranging between 0.37 and 0.81) determined by both impactor measurements and single-particle analyses were in good agreement. Through Monte-Carlo-type simulations, confidence intervals of the mean NO 3 −/NH 4 + ratio were calculated for sub-samples of the total particle population.

Summertime fog chemistry at a mountainous site in central Europe

In this paper, 1997 atmospheric visibility data as an indicator for the presence and density of fog at our ecosystem research site in the Fichtelgebirge mountains, Central Europe, are presented. At this location (about 800 m a.s.l.), fog occurred on 50% of the days and added up to a total fog duration of 1158 h in 1997. Using the visibility as a determining parameter, an automatic system for the collection of fog water was developed, including an automatic sampler, and sampling on an event basis. The data from the summer 1997 season exhibit a large variability in the chemical composition of fog. Easterly winds were associated with fog with higher concentrations of the major ions (NH 4 +, NO 3 −, SO 4 2−) and metals than westerly winds. Although the H + concentrations are lower than concentrations measured between 1983 and 1988 in NE Bavaria, it is not clear from our data alone if the negative trend over time is significant. A simple parameterization of fog deposition shows that fog plays an important role in the water balance of our forests. However, more detailed studies are needed to quantify this input, and the input of pollutants and nutrients to the ecosystems through fog deposition.

Trends of air pollution in the Fichtelgebirge Mountains, Bavaria

We analyzed 13 years of hourly measurements of SO(2), NO(x), and O(3), at forest ecosystem research sites in SE Germany. A quasi-continuous data record was obtained by combining data sets from two locations. Before interpreting trends in the combined data set, we analyzed if the change of location introduced a systematic bias. We employed autocorrelation functions, Hurst statistics, complexity analysis, and recurrence quantification and found that the partial data sets exhibited no indication of the presence of any bias. For SO(2), we also compared the data from the forest sites with data obtained in nearby cities and also found no indications for any systematic effects. Applying nonparametric trend statistics we found a significant decrease of the SO(2). Most of the observed decrease is due to the reductions of SO(2) emissions in eastern Germany, but reductions in western Germany and the Czech Republic also played important roles. For O(3), we observed a significant increase, the causes of which are unclear from our data alone. No trend was identified for NO(x).