Seasonal iron­sulfur interactions and the stimulated phosphorus mobilization in freshwater lake sediments.

Sulfur reduction in freshwater ecosystems has previously been considered as negligible because of often very low sulfate concentrations and generally low sulfate reducing capacity in freshwater sediments. In this study, seasonal variations on three types of sediments from central lake, dredged and algae accumulated areas in a eutrophic lake in China, Lake Taihu, were investigated. The high temperature in summer and the accumulation of algae are conducive to the reduction processes in freshwater lake sediments. Iron reduction was observed as the major anaerobic process in all types of sediments, while sulfate reduction was weak in central and dredged lake areas. However, strong sulfate reduction with increase of sulfate reducing bacteria and sulfides generation (119.5 ± 0.2 µmol L-1) was found in surface sediments in algae accumulated areas. Based on the results of Fe reduction rate and the quantity of Fe reducing bacteria, extensive sulfate reduction in algae accumulated sediments inhibited the microbial Fe reduction, and the ΣS2--mediated chemical Fe reduction (SCIR) dominated instead. Iron was principally stored in the sediments as Fe sulfide compounds, which weakened the rebinding of phosphorus and stimulated phosphorus mobilization. Therefore, attention should be paid to the alteration of Fe cycling and phosphorus mobility caused by the SCIR in algae accumulated sediments and the consequent effects on the eutrophication of freshwater lakes.

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.

Cyanobacteria blooms: A neglected facilitator of CH4 production in eutrophic lakes.

Lakes are regarded as one of the important sources of atmospheric CH4. However, the role of cyanobacteria blooms (CBBs) play in the CH4 production in eutrophic lakes is not fully clear. In this study, the spatial distribution characteristics of CH4 concentrations in surface water and sediment columns were investigated in Zhushan Bay of Taihu lake, China. Results showed that CH4 concentrations in CBBs accumulated zones were much higher than that in the open lake areas, with the highest values of 3.79 µmol·L-1 and 2261.88 µmol·L-1 in surface water and sediment columns, respectively. CH4 concentrations were strongly influenced by various factors. In surface water, the occurrence of CBBs greatly contributed to CH4 productions, as evidenced by the well-predicting for CH4 concentrations using Chl-a and NH4+ concentrations. In the sediments, the Ignition Loss and C:N ratio values were two indicators of CH4 contents, suggesting that the methanogenesis processes were influenced by not only the quantities, but also the qualities of organic matter. The labile substrates produced during the CBBs decomposition processes promoted the CH4 production and migration from sediments to the water column, resulting in the coherence in CH4 concentrations between the sediments and the surface water. The high-resolution determinations of CH4 concentrations in surface water and sediments clarified that the CBBs were a neglected facilitator of CH4 productions, which should be considered in the future estimation of CH4 emissions in eutrophic lakes.

High sulfide production induced by algae decomposition and its potential stimulation to phosphorus mobility in sediment.

This study is devoted to addressing the effects of algae blooms on sulfur cycle and the consequent phosphorus mobility in the sediments of freshwater lake ecosystems. A mesocosm experiment was conducted to investigate these effects through monitoring the dynamics of sulfur (S), iron (Fe) and phosphorus (P) in water and sediments, and their diffusion fluxes at the sediment-water interface (SWI). In addition, the abundance of sulfate-reducing bacteria (SRB) in the water column was also detected. The addition of the algae lead to an increase of SRB, a drastic decline of sulfate and a significant increase of total dissolved sulfide (ΣS2-, the peak value of near 3.0 mmol/L on day 6) in the water column. These results suggest the sulfate reduction was dramatically promoted during algae decomposition. Indeed the ΣS2- was 2 to 3 times of SO42- initial concentration, and higher ΣS2- was produced with higher algal biomass. Moreover, the diffusive flux of ΣS2- at the SWI was negative, indicating that diffusion of ΣS2- from water column toward sediment was occurring. These results indicated that algae decomposition might also be another important source of ΣS2- (termed "algae-derived ΣS2-") in addition to sulfate reduction. The increase of Fe(II) in surface sediment pore-water was slightly delayed compared to the ΣS2- generation in the water column, which illustrated that Fe oxyhydroxides in sediments were transformed into Fe(II) through chemical reduction of ΣS2-. Concomitantly, the vertical distribution of PO43- in high amounts algae group suggested that desorption and release of iron oxides-bound PO43- occurred in sediments. Collectively, algae bloom can boost the lake eutrophication not only through direct release of nutrients but also through the high production of ΣS2-and indirect promotion of phosphorus mobility in sediment.

Agreement between ethnicity recorded in two New Zealand health databases: effects of discordance on cardiovascular outcome measures (PREDICT CVD3).

OBJECTIVES: To assess agreement between ethnicity as recorded by two independent databases in New Zealand, PREDICT and the National Health Index (NHI), and to assess sensitivity of ethnic-specific measures of health outcomes to either ethnicity record. METHOD: Patients assessed using PREDICT form the study cohort. Ethnicity was recorded for PREDICT and an associated NHI ethnicity code was identified by merge-match linking on an encrypted NHI number. Agreement between ethnicity measures was assessed by kappa scores and scaled rectangle diagrams. RESULTS: A cohort of 18,239 individuals was linked in both PREDICT and NHI databases. The agreement between ethnicity classifications was reasonably good, with overall kappa coefficient of 0.82. There was better agreement for women than men and agreement improved with age and with time since the PREDICT system has been operational. Ethnic-specific cardiovascular (CVD) hospital admission rates were sensitive to ethnicity coding by NHI or PREDICT; rate ratios for ethnic groups, relative to European, based on PREDICT were attenuated towards the null relative to the NHI classification. CONCLUSIONS: Agreement between ethnicity was moderately good. Discordances that do exist do not have a substantial effect on prevalence-based measures of effect; however, they do on measurement of the admission of CVD. IMPLICATIONS: Different categorisations of ethnicity data from routine (and other) databases can lead to different ethnic-specific estimates of epidemiological effects. There is an imperative to record ethnicity in a rational, systematic and consistent way.