Jicheng Zhong

Heterogeneity of archaeal and bacterial ammonia‐oxidizing communities in Lake Taihu, China

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) communities within the surface sediments of Lake Taihu, a large eutrophic freshwater lake in China, were investigated using molecular approaches targeting the ammonia monooxygenase subunit A (amoA) gene. Large intra-lake variability in the composition and the relative abundance of both groups of ammonia-oxidizing prokaryotes was observed. Archaeal amoA far outnumbered bacterial amoA at most sites except those located in the Eastern Taihu Bay. This bay, which is used for intensive pen aquaculture, harboured the most unique AOA communities but was dominated by AOB in terms of relative abundance. Accumulation of organic substances rather than presence of submersed macrophytes significantly influenced the relative abundance of AOA. In contrast, shifts in the abundance of AOB were not found to be significantly related to the investigated environmental parameters. Phylogenetic analysis showed that all archaeal amoA sequences fell within either the Crenarchaeotal Group (CG) I.1b or the CG I.1a subgroup, and all AOB clustered exclusively with the genus Nitrosomonas. These findings represent the first detailed survey of AOA in eutrophic freshwater lake sediments by demonstrating that AOA dominate the ammonia-oxidizing communities, and are negatively correlated with the accumulation of organic substances.

Evaluation of in situ capping with clean soils to control phosphate release from sediments

Evaluation of in situ capping with clean soils to control phosphate release from the sediments of a eutrophic bay in Lake Taihu was performed after 18 months of capping. The concentrations of dissolved reactive phosphate (DRP) in pore waters and DRP resupply from native sediments and capped sediments were determined using high-resolution dialysis (HR-Peeper) and a Zr-oxide diffusive gradients in thin films (Zr-oxide DGT) technique. The adsorption isotherm of these sediments was further investigated using a modified Langmuir model. The results showed low concentrations of DRP in pore waters with a low resupply from the sediments for sustaining pore water DRP concentration after capping. The calculated flux to the overlying water following the capping treatment was approximately half of that for the native sediments, implying that the capping reduced the release of phosphate from the sediments. The low resupply of the sediments after capping was further demonstrated by larger partitioning coefficient (K(p)) values and greater adsorption capacity (Q(max)) values, while zero equilibrium concentrations (EPC(0)s) were similar to those in native sediments. The larger K(p) and Q(max) were attributed to higher active Fe and Al introduced by the capping, indicating that the binding of phosphate onto the active Fe and Al played a critical role in reducing the internal loading of phosphorous.

Effects of hydrodynamics processes on phosphorus fluxes from sediment in large, shallow Taihu Lake

The turnover of phosphorus (P) in lake sediments, a major cause of eutrophication and subsequent deterioration of water quality, is in need of deep understanding. In this study, effects of resuspension on P release were studied in cylindrical microcosms with Y-shape apparatus. The results indicated that there was a positive correlation between flux of suspended substance across sediment-water interface (F(SS)) and the wind speed, and an increasing F(SS) during each wind process followed by a steady state. The maximal F(SS) under light, moderate, and strong wind conditions were 299.9 +/- 41.1, 573.4 +/- 61.7, and 2093.8 +/- 215.7 g/m2, respectively. However, flux of P across sediment-water interface (F(P)) did not follow a similar pattern as F(SS) responding to wind intensity, which increased and reached the maximum in initial 120 min for light wind, then decreased gradually, with maximal flux of 9.4 +/- 1.9 mg/m2. A rapid increase of F(P) at the first 30 min was observed under moderate wind, with maximal flux of 11.2 +/- 0.6 mg/m2. Surprisingly, strong wind caused less F(P) than under light and moderate wind conditions with maximal flux of 3.5 +/- 0.9 mg/m2. F(SS) in water column declined obviously during the sedimentation process after winds, but F(P) varied with wind regime. No obvious difference was detected on F(P) after 8 h sedimentation process, compared with the initial value, which means little redundant P left in the water column after winds.

Seasonal variation of potential denitrification rates of surface sediment from Meiliang Bay, Taihu Lake, China

The regulatory effects of environmental factors on denitrification were studied in the sediments of Meiliang Bay, Taihu Lake, in a monthly sampling campaign over a one-year period. Denitrification rates were measured in slurries of field samples and enrichment experiments using the acetylene inhibition technique. Sediment denitrification rates in inner bay and outer bay ranged from 2.8 to 51.5 nmol N2/(g dw (dry weight) x hr) and from 1.5 to 81.1 nmol N2/(g dw x hr), respectively. Sediment denitrification rates were greatest in the spring and lowest in the summer and early autumn, due primarily to seasonal differences in nitrate concentration and water temperature. For each site, positive and linear relationships were regularly observed between denitrification rate and water column nitrate concentration. Of various environmental factors on denitrification that we assessed, nitrate was determined to be the key factor limiting denitrification rates in the sediments of Meiliang Bay. In addition, at the two sites denitrification rates were also regulated by temperature. The addition of organic substrates had no significant effect on denitrification rate, indicating that sediment denitrification was not limited by organic carbon availability in the sediments. Nitrate in the water column was depleted during summer and early autumn, and this suppressed effective removal of nitrogen from Taihu Lake by denitrification.

Influence of Sediment Dredging on Chemical Forms and Release of Phosphorus

A laboratory experiment was carried out through a six-month incubation of undredged (control) and dredged cores to study the effect of sediment dredging on phosphorus (P) release from the sediment in the Taihu Lake. During the experiment, dredging the upper 30 cm layer could efficiently reduce the interstitial PO34 -P concentration and different P forms in the sediment. The P fluxes of the undredged and dredged cores ranged from −5.1 to 3047.6 and −60.7 to 14.4 μg m−2 d−1, respectively. The fluxes of the dredged cores were generally lower than those of the control. Differences in the fluxes between the dredged and undredged cores were statistically significant (P < 0.05) from March to June 2006. The sediment P in the dredged cores had a lower release potential than that in the control. Dredging can be considered as a useful measure for rehabilitating the aquatic ecosystem after the external P loading in the Taihu Lake catchment was efficiently reduced.

Geochemistry of iron, sulfur and related heavy metals in metal-polluted Taihu Lake sediments

Abstract To understand the geochemical characteristics of iron and sulfur and the extent of iron-sulfide minerals influencing heavy metal behaviour in metal-polluted sediments of Taihu Lake, two sites, in Meiliang Bay (ML) and Wuli Lake (WL), were selected to study the fractionation of iron, sulfur and related heavy metals. There were relatively high concentrations of Fe2+ and low concentrations of total S2− in porewaters, indicating that conditions in these sediments favored iron reduction. The concentrations of acid volatile sulfides in sediments were 1.9–9.6 μmol g−1 at ML and 1.0–11.7 μmol g−1 at WL, both in the range of values detected in unpolluted lakes. Pyrite-S was 10.2–49.4 μmol g−1 at ML and 10.3– 33.0 μmol g−1 at WL, accounting for more than 69% of the reduced inorganic sulfur at both sites. The low degree of sulphidization (

Significance of dredging on sediment denitrification in Meiliang Bay, China: a year long simulation study.

An experiment for studying the effects of sediment dredging on denitrification in sediments was carried out through a one-year incubation of undredged (control) and dredged cores in laboratory. Dredging the upper 30 cm of sediment can significantly affect physico-chemical characteristics of sediments. Less degradation of organic matter in the dredged sediments was found during the experiment. Denitrification rates in the sediments were estimated by the acetylene blockage technique, and ranged from 21.6 to 102.7 nmol N2/(g dry weight (dw) x hr) for the undredged sediment and from 6.9 to 26.9 nmol N2/(g dw x hr) for dredged sediments. The denitrification rates in the undredged sediments were markedly higher (p < 0.05) than those in the dredged sediments throughout the incubation, with the exception of February 2006. The importance of various environmental factors on denitrification was assessed, which indicated that denitrification was regulated by temperature. Nitrate was probably the key factor limiting denitrification in both undredged and dredged sediments. Organic carbon played some role in determining the denitrification rates in the dredged sediments, but not in the undredged sediments. Sediment dredging influenced the mineralization of organic matter and denitrification in the sediment; and therefore changed the pattern of inherent cycling of nitrogen.

Different effects of copper (II), cadmium (II) and phosphate on the sorption of phenanthrene on the biomass of cyanobacteria

Due to the large surface area and high organic carbon content of cyanobacteria, organic contaminants can be readily sorbed on cyanobacteria during algal blooms, and then be transferred to the food web. This process is likely to be affected by the coexisting metals and nutrients, however, the possible impacts remain unclear. Effects of Cu(2+), Cd(2+), and phosphate on the sorption of phenanthrene on cyanobacterial biomass collected from an algal bloom were therefore studied. Continuous decrease in phenanthrene sorption was observed in the presence of low concentrations of Cu(2+), and Cd(2+) (<0.04 mmol L(-1)), because Cu(2+) and Cd(2+) were coadsorbed with phenanthrene on the surface of cyanobacteria as suggested by scanning electron microscopy-energy dispersive X-ray (SEM-EDX) and Fourier transform infrared (FTIR) analyses. Phenanthrene sorption began to increase with the further increase in Cu(2+) concentration, but remained lower than that in the absence of Cu(2+). This increase in sorption was ascribed to the cation-π interaction between Cu(2+) and phenanthrene, as suggested by the enhanced ultraviolet absorbance at 251 nm. In contrast, sorption rebounding of phenanthrene did not occur in the presence of higher concentrations of Cd(2+). The different effects of Cu(2+) and Cd(2+) on phenanthrene sorption were attributed to that Cd(2+) required much more energy than Cu(2+) to form cation-π complexes with phenanthrene in the solutions. Phenanthrene sorption decreased continuously with the increase in phosphate concentration. Phosphate blocked the binding sites, modified the cell morphology, and increased the negative charge as well as the hydrophilicity of the cyanobacterial surface, thereby suppressing phenanthrene sorption. This study indicates that sorption of aromatic organic compounds by cyanobacteria could be significantly alerted by concentrations and properties of the coexisting transition metals and phosphates, which may subsequently affect their transfer to the food web in eutrophic waters.

Evaluation of simulated dredging to control internal phosphorus release from sediments: Focused on phosphorus transfer and resupply across the sediment-water interface

Sediment dredging is an effective restoration method to control the internal phosphorus (P) loading of eutrophic lakes. However, the core question is that the real mechanism of dredging responsible for sediment internal P release still remains unclear. In this study, we investigated the P exchange across the sediment-water interface (SWI) and the internal P resupply ability from the sediments after dredging. The study is based on a one-year field simulation study in Lake Taihu, China, using a Rhizon soil moisture sampler, high-resolution dialysis (HR-Peeper), ZrO-Chelex diffusive gradients in thin film (ZrO-Chelex DGT), and P fractionation and adsorption isotherm techniques. The results showed low concentration of labile P in the pore water with a low diffusion potential and a low resupply ability from the sediments after dredging. The calculated flux of P from the post-dredged sediments decreased by 58% compared with that of non-dredged sediments. Furthermore, the resupply in the upper 20mm of the post-dredged sediments was reduced significantly after dredging (P<0.001). Phosphorus fractionation analysis showed a reduction of 25% in the mobile P fractions in the post-dredged sediments. Further analysis demonstrated that the zero equilibrium P concentration (EPC0), partitioning coefficient (Kp), and adsorption capacity (Qmax) on the surface sediments increased after dredging. Therefore, dredging could effectively reduce the internal P resupply ability of the sediments. The reasons for this reduction are probably the lower contributions of mobile P fractions, higher retention ability, and the adsorption capacity of P for post-dredged sediments. Overall, this investigation indicated that dredging was capable of effectively controlling sediment internal P release, which could be ascribed to the removal of the surface sediments enriched with total phosphorus (TP) and/or organic matter (OM), coupled with the inactivation of P to iron (Fe) (hydr)oxides in the upper 20mm active layer.

Fifteen-year study of environmental dredging effect on variation of nitrogen and phosphorus exchange across the sediment-water interface of an urban lake

Environmental dredging has been applied widely in Chinese lakes to reduce their internal nutrient loads. However, the efficacy of dredging to reduce internal loading of nitrogen (N) and phosphorus (P) and to improve water quality has been questioned by some researchers. In this study, the long-term (∼15 years) effects of dredging to reduce internal N and P loading in a closed, polluted urban lake were investigated. The results showed that the release of soluble reactive phosphorus (SRP) could be suppressed quickly after dredging, and that the dredging effect was sustained for about 18 months. A significant release of NH4+-N was discovered during the first 2-8 months after dredging, followed by maintenance of low-level release rates for about 21-32 months. The continuous inflowing of external pollution loading led to the increase in the release rates of SRP and NH4+-N. The external pollution loading was therefore reduced three years after dredging to strengthen the remediation effect. After that, high diffusive flux from the sediment was observed for both NH4+-N and SRP during summer seasons for about six years, followed by a decreasing trend. The NH4+-N concentration in the overlying water was reduced after the reduction of external loading, while a high concentration of SRP in the overlying water was still observed during summer seasons. In conclusion, the mid-term (<3 years) reduction of internal N and P loading could be achieved by dredging if the external pollution loading were not reduced. Achieving long-term control would require modification of external loading.