Dissolved components in precipitation water percolated through forest litter

Abstract

Leaves lying on the forest¯oor are a major source of dissolved organic substances in soil and surface waters, and these substances have important effects in those environments. We used zero-tension lysimeters to study the chemical characteristics of water percolating through litter from various species of forest trees. The leaching rates were greatest in the autumn and declined rapidly thereafter, especially for deciduous litter. During an annual cycle, 2.5±17% of the initial contents of the carbon in the litter was recovered as dissolved organic carbon in percolates. Humus-like substances, hydrophilic acids and hydrophilic neutral compounds constituted the major fractions of dissolved C. Leachates from deciduous leaf litter were only partly biodegradable, and those from spruce needles were scarcely biodegradable.Low molecular weight organic acids constituted 0±12% of the dissolved organic carbon in the percolates of the ®rst autumn sampling and decreased over time. Acetic and formic acids were present at the largest concentrations, up to 30 "mol l ±1 per g litter, and gluconic, pyruvic, fumaric, oxalic and citric acids were also frequent in signi®cant concentrations. Among the aromatic acids, p-hydroxybenzoic acid was identi®ed in four out of ®ve autumn samples. The organic components in litter leachates are important for the microbial activity in soil and surface waters. The organic acids enhance weathering and translocation of metals by their ability to form complexes. Litter is also a source of inorganic ions in soil solutions. The dominant cations in the percolates were K + , Ca 2+ and Mg 2+ , and spruce litter also yielded large quantities of Al and Fe.

Amounts of carbon mineralised and leached as DOC during decomposition of Norway spruce needles and fine roots

“…20 mL of sample was added to each flask. Aqueous samples with more than 10 mg C L À1 were diluted before incubation to avoid overgrowth of microorganisms (Hongve et al, 2000) and to minimise concentration effects on DOM biodegradation (Zsolnay, 2003). Nutrients (equal weights of NH 4 NO 3 and K 2 HPO 4 ) were added in order to adjust the C:N ratio to about 10:1 and facilitate DOM biodegradation (McDowell et al, 2006).…”

Would Forest Litter Cause a Risk of Increased Copper Solubility and Toxicity in Polluted Soils Remediated via Phytostabilization?

“…First, a decrease in the pH values of soils after the application of acidic forest litter resulted in an intensive desorption of copper into soil solution [9,18]. Secondly, released copper was bound by low molecular weight organic acids (formed as a result of litter decomposition in biochemical processes) and transformed into the complexed forms [4,6,19] Fig. 3) in the lasts days of incubation.…”

“…Such a treatment may, however, create hazards associated with an increase of copper solubility in afforested areas caused by the influence of organic matter that derives from forest litter. Copper has a high affinity to organic matter [1][2][3] and can be complexed by low molecular weight organic acids produced from decomposing litter [4][5][6]. Moreover, microbiological decomposition of litter leads to acidification of the soil environment, which may directly contribute to enhanced desorption of copper into soil solution.…”

Hydrophobicity of Sparta Sand under Different Vegetation Types in the Lower Wisconsin River Valley

“…Doerr et al (1998) did a similar experiment with leachates of pine needles and found an increase of soil hydrophobicity in the treated soils. Hongve et al (2000) found that percolates from deciduous and coniferous litter contained large fractions of hydrophobic compounds, with coniferous litter having the greatest concentrations. These experiments with pine leachates are in agreement with findings of soil water repellency in unburned pine forests (Richardson and Hole, 1978;Scott, 2000;Doerr et al, 2009).…”