Trophic status and lake depth play important roles in determining the nutrient-chlorophyll a relationship: Evidence from thousands of lakes globally.

A fundamental problem in lake eutrophication management is that the nutrient-chlorophyll a (Chl a) relationship shows high variability due to diverse influences of for example lake depth, lake trophic status, and latitude. To accommodate the variability induced by spatial heterogeneity, a reliable and general insight into the nutrient-Chl a relationship may be achieved by applying probabilistic methods to analyze data compiled across a broad spatial scale. Here, the roles of two critical factors determining the nutrient-Chl a relationship, lake depth and trophic status, were explored by applying Bayesian networks (BNs) and a Bayesian hierarchical linear regression model (BHM) to a compiled global dataset from 2849 lakes and 25083 observations. We categorized the lakes into three groups (shallow, transitional, and deep) according to mean and maximum depth relative to mixing depth. We found that despite a stronger effect of total phosphorus (TP) and total nitrogen (TN) on Chl a when combined, TP played a dominant role in determining Chl a, regardless of lake depth. However, when the lake was hypereutrophic and/or TP was >40 µg/L, TN had a greater impact on Chl a, especially in shallow lakes. The response curve of Chl a to TP and TN varied with lake depth, with deep lakes having the lowest yield Chl a per unit of nutrient, followed by transitional lakes, while shallow lakes had the highest ratio. Moreover, we found a decrease of TN/TP with increasing Chl a concentrations and lake depth (represented as mixing depth/mean depth). Our established BHM may help estimating lake type and/or lake-specific acceptable TN and TP concentrations that comply with target Chl a concentrations with higher certainty than can be obtained when bulking all lake types.

Sulfate radical oxidation combined with iron flocculation for upgrading biological effluent of coking wastewater.

Because the components of the coking wastewater was biologically toxic and hence inhibit the actions of microorganisms in conventional biological treatment processes,the biological effluent of coking wastewater (BECW) still remains much recalcitrant pollutants. In the current work, we set out to explore the feasibility of using a proposed advanced oxidation method, involving the persulfate-activated zero-valent iron system (PS/ZVI), to realize a deep treatment of BECW. The efficiency levels at which sulfate radical oxidation combined with iron flocculation removed pollutants, specifically TOC, phenolic compounds (PCs), cyanide, and suspended solids (SSs), as well as removing colour were investigated in batch tests. Increasing the persulfate concentration generally resulted in improved pollutant removal, with maximum removal efficiency levels of 58.5%, 68.4%, 61% 99.9% and 91.04% for TOC, PCs, SS, cyanide and colour, respectively. Note that the coexisting inorganic ions CO3 2- and HCO3 - were strong competitors of the radical consumption of TOC, but this interference was eliminated by adjusting the pH to 4.5. Also, flocculation of the generated Fe3+ ions from the radical reaction significantly enhanced SS removal. GC-MS analysis showed that the compositional diversity of the BECW decreased after oxidation. Meanwhile its biodegradability increased, indicating less bio-toxicity reaching the natural water body. This study suggests that the PS/ZVI system may be an alternative safer and more efficient method than Fenton's method for carrying out an advanced treatment of coking wastewater.

Fast Detection of Carbonate and Bicarbonate in Groundwater and Lake Water by Coupled Ion Selective Electrodes / 分析化学

The content of bicarbonate ( HCO-3 ) and carbonate ( CO2-3 ) ions in groundwater and lake water reflects a broad set of carbon cycling reactions associated with decomposition or synthesis of organic compounds with mineral dissolution or precipitation, which indicates the local geochemical environment. However, the content of HCO-3 and CO2-3 changes easily under the influence of pH, temperature, atmosphere pressure in the process of sampling, transportation and storage, so it has been a worldwide problem to determine the real content of HCO-3 and CO2-3 ions in groundwater and lake water. This article proposed a new way to solve the problem by fast field detection of HCO-3 and CO2-3 ions through the use of pH electrode combined with carbon dioxide electrode. Studies showed in the base solution of pH=4. 8 ± 0. 1, the detection range of HCO-3 ion was 0. 027-570 mg/L and that of CO2-3 was 1. 25 ×10-8-39. 7 mg/L. In the most case, the coexisting ions and weak acid ( K+, Na+, Mg2+, Cl-, SO2-4 <100 mg/L;HSO-3 , NO-2 , HOAc<50 mg/L) did not interfere with the analysis. The method was validated for real water samples and the recoveries were in the range of 95. 2%-99. 2% with the relative standard deviations (RSDs) of 2. 6%-3. 7%. Compared with the acid-base titration method, the accuracy of this method had proved to be good. However, the method could be affected by temperature, so the standard solution and samples should be measured at the same temperature. Above all, this method is suitable for fast field analysis for HCO-3 and CO2-3 ions in the nature water as it is sensitive, fast, economical, and the electrodes are easy to carry and operate. It has been successfully applied in the determination of HCO-3 and CO2-3 in groundwater and lake water in Qinghai Province. Experiment showed that the pH of the groundwater samples from Haidong district was 6 . 4-7 . 4 , with 234-4096 mg/L HCO-3 and 0. 16-1. 89 mg/L CO2-3 . The pH of the lake water samples was about 8. 7, with 1. 36-1. 86 g/L HCO-3 and 32. 3-43. 9 mg/L CO2-3 , which was consistent with the previous results.