Dynamics of dissolved organic carbon after a cyanobacterial bloom in hypereutrophic Lake Taihu (China)

Abstract

a b s t r a c tTo establish the influence of the cyanobacterial bloom collapse on the characteristics of dissolved organic carbon (DOC) in Lake Taihu, high-molecular-weight dissolved organic matter (HMW-DOM), with sizes between 1 kDa and 0.5 m, were collected using cross-flow ultrafiltration, from three different eutrophic regions. Isolated HMW-DOM was further characterized by atomic carbon to nitrogen ratio and neutral sugars composition by gas chromatography and mass spectrometry. The results indicated that the cyanobacterial cell lysis induced by nitrate depletion is the likely mechanism for DOC release. The relatively high DOC level was associated with the high chlorophyll a concentration in Meiliang Bay, one of the most eutrophic bays in the northern part of the lake. However, no significant correlations were observed between chlorophyll a concentration and HMW-DOC concentration during the demise of the cyanobacterial bloom in Lake Taihu. No significant differences were found in the HMW-DOC concentration among the three sampling sites, which were selected to represent different eutrophic status. However, a significant difference in the HMW-DOC concentration was found between October 2009 and January 2010 in all three sampling sites (p = 0.02). The HMW-DOC release may be attributed to the cyanobacterial cell lysis after the peak of summer bloom. The similarity in neutral sugar composition between the HMW-DOM and cyanobacterial exopolysaccharides suggests that the cyanobacterial bloom is the source of HMW-DOM. However, the significant correlation between the carbon to nitrogen ratio in HMW-DOM and chlorophyll a concentration was only observed in Meiliang Bay, which implies that apart from the cyanobacteria-derived DOC, a fraction of DOC was from riverine input. The decline of the cyanobacterial bloom also changed the overall DOM pool, leading to a shift in the component of HMW-DOM from a C-enriched material to an N-enriched material, as revealed by the variation in the carbon to nitrogen ratios. Overall, these results demonstrate that the quantitative and qualitative DOM is affected by the post-cyanobacterial bloom in Lake Taihu.

Transformations in DOC along a source to sea continuum; impacts of photo-degradation, biological processes and mixing

“…Measured DOC increases for single water types in Experiment B suggest that production of DOC outweighs photo-degradation under certain conditions when particulates and microorganisms are present. The size of the DOC pool in natural waters can increase by lysis of plankton cells and excretion of photosynthates by algae and cyanobateria (Brock and Clyne 1984;Malinsky-Rushansky and Legrand 1996;Ye et al 2011). These products are considered to be a major source of DOC, particularly in marine environments (Lee and Henrichs 1993) and to be a significant driver of heterotrophic bacterial growth (Brock and Clyne 1984;Teira et al 2001).…”

Dynamics of dissolved organic carbon in eutrophic Lake Taihu and its tributaries and their implications for bacterial abundance during autumn and winter

“…Phytoplankton are the main source of DOC-supporting bacterial communities, and approximately 50% of daily primary production can be released by phytoplankton as DOC (Karl et al 1998) as a result of cell lysis or direct exudation (Nagata 2000). Highmolecular-weight DOC (Ye, Shi, Wu, Zhang, et al 2011) was found to be released via phytoplankton cell lysis in autumn and winter in Lake Taihu. However, we found no significant correlation between Chl a and DOC concentration in the present study, consistent with previous results .…”

“…The water quality in the southern region is comparatively good relative to the polluted northwestern regions (Zhu 2008). In addition, frequent phytoplankton blooms occur in the northwestern region and large amounts of DOC are released upon the lysis of phytoplankton cells (Ye, Shi, Wu, Zhang, et al 2011). Finally, the northern part of the lake is the drinking water source for Wuxi City.…”

“…Zhang et al (2011) suggested that the contribution of allochthonous CDOM (chromophoric dissolved organic matter) decreased in the dry season due to low discharge. It was also shown that DOC quality and quantity are affected by the phytoplankton bloom collapse in Lake Taihu in autumn and winter Ye, Shi, Wu, Zhang, et al 2011). Nevertheless, the relationships among DOC dynamics and sources, the chemical and spectroscopic properties of DOC, and BA and water characteristics of Lake Taihu and its tributaries in autumn and winter remains unknown.…”

Effect of algal flocculation on dissolved organic matters using cationic starch modified soils

“…During algal blooms, high DOM accumulation is often observed due to the release and lysis of algal cells, which is an important nutrient pool in eutrophic waters (Nguyen et al, 2005;Ye et al, 2011). The co-removal of algal cells (particulate nutrients) and DOM (dissolved nutrients) may maximize the nutrient reduction and benefit the ecological restoration in eutrophic waters.…”