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Temporal trends in DOC concentration and flux were investigated at two geochemically distinct forested catchments in western Czech Republic. Mean discharge-weighted DOC concentrations averaged 18.8 mg L(-1) at the acidic Lysina catchment, and 20.2 mg L(-1) at base-rich and well-buffered Pluhuv Bor. Between 1993 and 2007 DOC in streamwater increased significantly in both catchments: the mean annual increase was 0.42 mg L(-1) yr(-1) (p < 0.001) at Lysina and 0.43 mg L(-1) yr(-1) (p < 0.001) at Pluhuv Bor, resulting in cumulative increases of 64 and 65%, respectively. These long-term increases in streamwater DOC were correlated with only modest increases in stream pH in both catchments, but large declines in ionic strength (IS), that resulted from declining atmospheric deposition. Neither catchment has undergone changes in soil-water pH, yet DOC concentrations tripled in the soil-water of both catchments. We conclude that changes in ionic strength of soil-water and streamwater, rather than acidity, are the primary drivers of changes in streamwater DOC in this region. Temperature, precipitation and discharge show no statistically significant trends during the study period, suggesting that climate change has played no role in the changes in DOC that we have observed.

We compared two adjacent mature forest ecosystem types (spruce vs. beech) to unravel the fate of assimilated carbon (C) and the cycling of organic and inorganic nitrogen (N) without the risk of the confounding influences of climatic and site differences when comparing different sites. The stock of C in biomass was higher (258 těha-1) in the older (150 years) beech stand compared to the younger (80 years) planted spruce stand (192 těha-1), whereas N biomass pools were comparable (1450 kg·ha-1). Significantly higher C and N soil pools were measured in the beech stand, both in forest floor and mineral soil. Cumulative annual CO2 soil efflux was similar among stands, i.e., 9.87 t·ha-1·year-1 of C in the spruce stand and 9.01 t·ha-1·year-1 in the beech stand. Soil temperature explained 78% (Q10 = 3.7) and 72% (Q10 = 4.2) of variability in CO2 soil efflux in the spruce and beech stand, respectively. However, the rather tight N cycle in the spruce stand prevented inorganic N losses, whereas losses were higher in the beech stand and were dominated by nitrate in the mineral soil. Our results highlighted the long-term consequences of forest management on C and N cycling. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon and nitrogen (DOC and DON) produced in the forest floor are important for ecosystem functions such as microbial metabolism, pedogenesis and pollutant transport. Past work has shown that both DOC and DON production are related to litterfall and standing stocks of C and N in the forest floor. This study, conducted in spring, 2003, investigated variation in forest floor water extractable DOC (WEDOC) and DON (WEDON) and forest floor C and N as a function of lignin, cellulose and N contained in live canopy foliage across eight Picea abies [L.] Karst stands in northern Bohemia. Based on Near Infrared Spectroscopy (NIR) analysis of foliar materials, lignin:N and cellulose:N content of the youngest needles (those produced in 2002) were positively and significantly related to WEDOC ( R 2 = 0.82–0.97; P<0.01) and to forest floor C:N ratio ( R = 0.72–0.78; P<0.01). Foliar N was strongly and negatively related to WEDOC and C:N ratio ( R = −0.91 and 0.72; P<0.05) among our study sites. WEDON was positively correlated to foliar lignin:N ( R = 0.48; P<0.05; n=40). Forest floor C pools were not positively correlated with foliar lignin and cellulose and forest floor N pools were not positively correlated with foliar N. Instead, a significant negative correlation was found between forest floor N pools and foliar cellulose ( R=−0.41; P<0.05), and between forest floor C pools and foliar N ( R = −0.44; P<0.05). From a remote sensing standpoint, our results are important because canopy reflectance properties are primarily influenced by the most recent foliage, and it was the chemistry of the most recently produced needles that showed a stronger relationship with forest floor WEDOC and C:N ratio suggesting forest floor production of WEDOC can be calculated regionally with remote sensing. [ABSTRACT FROM AUTHOR]

Forests play a primary role in the cycling and storage of mercury (Hg) in terrestrial ecosystems. This study aimed to assess differences in Hg cycling and storage resulting from different vegetation at two adjacent forest stands - beech and spruce. The study site Načetín in the Czech Republic's Black Triangle received high atmospheric loadings of Hg from coal combustion in the second half of the 20th century as documented by peat accumulation rates reaching 100 μg m −2 y −1 . In 2004, the annual litterfall Hg flux was 22.5 μg m −2 y −1 in the beech stand and 14.5 μg m −2 y −1 in the spruce stand. Soil concentrations and pools of Hg had a strong positive relation to soil organic matter and concentrations of soil sulfur (S) and nitrogen (N). O-horizon Hg concentrations ranged from 245 to 495 μg kg −1 and were greater in the spruce stand soil, probably as a result of greater dry Hg deposition. Mineral soil Hg concentrations ranged from 51 to 163 μg kg −1 and were greater in the beech stand soil due to its greater capacity to store organic carbon (C). The Hg/C ratio increased with depth from 0.3 in the O-horizon to 3.8 μg g −1 in the C horizon of spruce soil and from 0.7 to 2.7 μg g −1 in beech soil. The Hg/C ratio was greater at all mineral soil depths in the spruce stand. The organic soil Hg pools in beech and spruce stands (6.4 and 5.7 mg m −2 , respectively) were considerably lower than corresponding mineral soil Hg pools (39.1 and 25.8 mg m −2 ). Despite the important role of S in Hg cycling, differences in soil Hg distribution at both stands could not be attributed to differences in soil sulfur speciation. [ABSTRACT FROM AUTHOR]