A Study of the Decomposition of Reed (Phragmites australis ) as a Possible Source of Aquatic Humic Substances by Measuring the Natural Abundance of Stable Carbon Isotopes

Abstract

A Study of the Decomposition of Reed (Phragmites australis)as a Possible Source of Aquatic Humic Substances by Measuring the Natural Abundance of Stable Carbon Isotopes key words: litter breakdown, DOC, water colour, humic acids fulvic acids AbstractThe decomposition of leaf and steam litter of reed (P. australis) was measured both in the field and in the laboratory. The breakdown rates, the total carbon and the stable carbon isotope dynamics of reed litter were determined. The stable carbon isotope ratios of isolated humic substances (fulvic and humic acids) were also analysed. The δ 13 C value in reed remains increased from -26‰ to -24‰ for stems and from -27‰ to -26‰ for leaves. The dissolved fulvic and humic acids isolated from the experimental bottles (mean δ 13 C was -27.6‰) and the reservoir water were depleted in 13 C (mean δ 13 C was -28.6‰) relative to the reed remains. The results show that reed litter is an important source of coloured aquatic humic substances. IntroductionThe shallow lower Kis-Balaton reservoir is located in a former peat-marshy area in the catchment area of the Zala River in Hungary. It was constructed for the water quality management of Lake Balaton. It was flooded in 1993 following the flooding of the upper reservoir in 1985. Large amounts of humic substances have been exported from this area into the western basin of the lake (V. -BALOGH and VÖRÖS, 2001).According to the dominant view that supported the creation of the reservoir, the peatmarshy soil -as the main source of humic sunstances -would be exhausted in a few years. We, on the other hand, have the opinion -shared by some others -that the release of humic substances from the reservoir would remain unchanged, as humic substances can be derived not only from soil/sediment (i.e. formerly degraded plants) but also from freshly degraded plants, even more so as 80% of the reservoir's surface is covered in emergent macrophytes, mainly reed (Phragmites australis). This study tests that hypothesis.Aquatic macrophytes release large amounts of dissolved organic matter during their decomposition, some of which have humic characteristics (WETZEL, 1990). Humic substances from aquatic macrophytes may provide a significant source of fresh and degradable humic matter in some lakes (WETZEL, 1992).The decomposition process of Phragmites australis (CAV.) TRIN. ex. STEUD. has been studied with different objectives by several authors (POLUNIN, 1982;KUFEL and KUFEL, 1988;TANAKA, 1991; VAN DER VALK et al., 1991;WRUBLESKI et al., 1997; DENWARD and Internat. Rev. Hydrobiol. 91 2006 1 15-28

Vegetation persistence and carbon storage: Implications for environmental water management for Phragmites australis

“…[] propose that up to 1.5‰ decrease in δ 13 C value may be attributed to decreases in atmospheric 13 C since the beginning of the eighteenth century due to industrialization and associated burning of fossil fuels, also known as the “Seuss effect.” However, the degree of 13 C enrichment in this case is greater than can be attributed to the Seuss effect alone, particularly in sections of cores more than a century old. Similarly 13 C enrichment has been demonstrated in 100 year old archived soil material from the Russian steppe [ Torn et al ., ]. P. australis organic material is enriched in 13 C as it decomposes [ V.‐Balogh , ]; perhaps influenced by preferential use of lighter carbon sources in metabolic reactions of decomposer microbes [ Dümig et al ., ]; differential loss of components of organic matter by microbial decomposers (e.g., lipids, lignin, protein) with different δ 13 C values [ Benner et al ., ; Hobbie and Werner , ]; or increase in microbial components in residual SOM [ Boström et al ., ]. Incorporation of alternative sources of autochthonous carbon. Water couch ( Paspalum distichum ) is a widely distributed C 4 grass found in the southern Macquarie Marshes, and is enriched in 13 C compared to the dominant C 3 plants including P. australis and Eucalyptus camaldulensis .…”

“…. P. australis organic material is enriched in 13 C as it decomposes [V -Balogh, 2006][Benner et al, 1987;Hobbie and Werner, 2004]; or increase in microbial components in residual SOM [Bostr€ om et al, 2007].…”

Effects of macrophytes and terrestrial inputs on fluorescent dissolved organic matter in a large river system

“…3). The former contain higher proportions of structural tissues (Wetzel, 1990;Balogh et al, 2006), which aid in the formation of humic and fulvic acids in soils (McKnight and Aiken, 1998).…”

Effects of pH on aquatic biodegradation processes

“…(1). For simplicity, the possible precipitation of Mg-calcite is neglected, as well as the possible influence of dissolved constituents such as Ca 2+ -binding complex ligands (fulvic and humic acids) (Cizkova et al, 1999;Reitner et al, 1999;Balogh et al, 2006). The specific electrical conductivity (EC) indicates the degree of dilution of the dissolved electrolytes.…”