Molecular biomarkers reveal co-metabolism effect of organic detritus in eutrophic lacustrine sediments.

In eutrophic lacustrine ecosystems, drifting algal blooms are easily trapped by emergent macrophytes in downwind littoral zones, potentially altering carbon cycling processes; yet, knowledge remains limited about the mechanisms driving these changes. In this study, Microcystis and Phragmites, two dominant photosynthetic organisms in a hypereutrophic (Lake Taihu, China), were collected to simulate their co-decomposition processes. We demonstrate how molecular-level biomarkers could be used to elucidate the degradation dynamics of these two distinct organic forms in mixtures. Microcystis-derived carbon accelerated the decomposition rate of mixed systems (positive co-metabolism effect), rather than retarding it. The decomposition rate of TOC (total organic carbon) directly measured in the mixed treatments was 14% higher than when the two substrates were incubated alone. The use of specific fatty acid biomarkers facilitated more accurate tracking, demonstrating 1.09 times higher decomposition rates for Phragmites detritus in mixed treatments than in single Phragmites treatments. Furthermore, Microcystis showed 0.98 times higher decomposition rates in mixed treatments than in single treatments. The addition of Microcystis detritus to Phragmites detritus might meet microbial stoichiometric requirements, increasing the abundance of decomposing bacteria in Phragmites detritus, and accelerating decomposition rates, resulting in the co-metabolism of Microcystis and Phragmites carbon. Given the increasing occurrence of algal blooms in eutrophic lakes, the processes documented here might enhance greenhouse gas emissions from lakes with continued global climate warming.

Taste and odor compounds associated with aquatic plants in Taihu Lake: distribution and producing potential.

The odor problem caused by the decay of aquatic plants is widespread in many freshwater lakes. In this study, the spatial distributions of seven taste and odor (T&O) compounds (dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, 2-methylisoborneol, geosmin, ß-cyclocitral, and ß-ionone) in the sediments and overlying water of the east of Taihu Lake were investigated. The effects of plant and physico-chemical parameters on the release of T&O compounds were also analyzed. The results showed that high concentrations of T&O compounds were detected in the area where Eichhornia crassipes was flourishing. Volatile organic sulfur compounds were not found in the water source area, which was not covered by aquatic plants. High plant biomass and aquiculture activities might increase the release of the taste and odor compounds. The correlation between the concentrations of odorous compounds and nutrients in the sediment was also analyzed. The production of odorants was positively correlated with the nitrogen, and they may migrate from sediment to overlying water. The result suggested that controlling the plant density and aquaculture activities could reduce the release of odorous compounds.

Release of taste and odour compounds during Zizania latifolia decay: A microcosm system study.

Organic matter-induced black bloom frequently occurs in a number of large eutrophic shallow lakes; this can result in the release of malodorous compounds and has a negative impact on water quality. In the study, a microcosm system containing Zizania latifolia (Z. latifolia), a common aquatic plant, was established and the release of seven taste and odour compounds, dimethyl sulphide (DMS), dimethyl disulphide (DMDS), dimethyl trisulphide (DMTS), 2-methylisoborneol (MIB), geosmin (GSM), ß-cyclocitral, and ß-ionone, was investigated. The results showed that these compounds were all detected during Z. latifolia decay, and that volatile organic sulphur compounds (VOSCs), such as DMS, DMDS, and DMTS, were the main factors responsible for the strong foul odour (the maximum reached 5.0 µg L-1). The release of odorous compounds was stronger during the initial seven days, and then progressively decreased in the middle stage of the experiment. Furthermore, large amounts of nutrients were released into the overlying water; nutrient concentration increased with increasing plant biomass. A positive correlation was observed between the odorant concentration and plant biomass. These results indicate that the density of aquatic plants should be controlled as part of future management of aquatic ecosystems.