休耕对抚仙湖周边农田土壤剖面和浅层地下水中氮累积的影响

减少外源氮投入能有效降低农田土壤氮累积和地下水氮污染,休耕是减少外源氮投入的重要措施之一.为探讨农田休耕对土壤剖面和浅层地下水中氮累积的影响,以抚仙湖周边农田土壤剖面和浅层地下水为研究对象,分析了休耕前（2017年12月）和休耕后（2020年8月和2021年4月）农田0~100 cm土壤剖面氮累积和浅层地下水中氮浓度的变化及其两者的关系.结果表明:休耕显著降低了土壤剖面氮含量和储量,休耕后0~30、30~60和60~100 cm土壤剖面TN、ON、DTN、NO₃ ^--N和NH₄ ⁺-N含量分别降低18.4 %~36.5 %、16.1 %~26.8 %、54.0 %~130.2 %、59.5 %~90.8 %和60.1 %~110.6 %.休耕前0~100 cm土壤TN、ON、DTN、 NO₃ ^--N和NH₄ ⁺-N储量分别为（17.20 ±0.97）t·hm^-2、（15.50 ±1.23）t·hm^-2、（0.68 ±0.06）t·hm^-2、（266.8 ±31.17）kg·hm^-2和（18.7 ±3.04）kg·hm^-2,休耕后各形态氮储量分别下降了25.5 %、23.3 %、44.7 %、80.1 %和59.9 %.休耕也改变了浅层地下水中氮浓度和形态构成,休耕后地下水中TN、ON、NO₃ ^--N和NH₄ ⁺-N浓度分别下降了88.4 %、82.7 %、92.1 %、65.8 %,ON/TN和NH₄ ⁺-N/TN从休耕前的26 %和6 %升高至休耕后的39 %和17 %,而NO₃ ^--N/TN从休耕前的61 %降至休耕后的41 %.地下水氮浓度和形态变化与休耕前后土壤中DTN、NH₄ ⁺-N、NO₃ ^--N和地下水中pH、ORP、DO等因素密切相关.可见,休耕有效降低了农田土壤剖面氮累积,缓解了浅层地下水氮污染,有利于防止高原湖泊的水质恶化.     

Risk assessment in Nile tilapia (Oreochromis niloticus) and African mud catfish (Clarias gariepinus) exposed to cassava effluent

Toxicity of cassava effluent in water on aquatic lives was examined via acute and chronic bioassay experiments on Clarias gariepinus (I) and Oreochromis niloticus (II) under laboratory conditions, using standard procedures. The effluent cyanide concentration exceeded the WHO limit for wastewater. Fish body weights and haematological parameters (HMP) significantly decreased with increasing effluent concentration at p≤0.05. Toxicity on HMP for the respective (I) and (II) varied from 5.4 to 52.8; 4.8 to 51.9% for packed cell volume, 4.1 to 43.9; 5.3 to 64.0% for red blood count, 0.0 to 15.7; 0.0 to 61.4% for white blood count, 3.6 to 45.9; 5.2 to 49.5% for haemoglobin, 11.6 to 71.9; 28.4 to 63.8% for total protein, 11.5 to 75.5; 15.0 to 58.2% for albumin and 11.8 to 75.0; 46 to 83.9% for globulin. Acute exposure yielded 96-h LC₅₀ values of 0.45% for (I) and 0.25% for (II) and chronic exposure caused reduced growth and poor blood quality.     

不同种植制度对稻田旱作季节CH4和N2O排放的影响

通过大田试验研究了稻田旱作季节几种典型种植制度对CH4和N2O排放的影响,包括休闲（fallow）、油菜对照（OR-ck）、小麦对照（W-ck）、油菜施N（OR-N）和小麦施N（W-N）5个处理。试验结果表明,稻田旱作季节N2O排放明显,CH4排放量较低,甚至表现为弱的CH4汇。稻田旱作季节N2O排放除受到N肥和种植制度影响外,还受土壤含水量影响,施N处理显著促进了N2O排放,降雨后N2O排放明显。小麦和油菜施N处理N2O平均排放通量分别为18.51和13.47μg·m^-2·h^-1,季节累积排放量分别为87.31和59.48 mg·m^-2,均显著高于对照和休闲处理。不同作物种类间N2O平均排放通量无显著差异,N2O季节累积排放量则表现为小麦显著高于油菜。各处理综合温室效应（100 a）依次为：OR-N〉W-N〉W-ck〉fallow〉OR-ck。各施N处理综合温室效应以N2O为主,但各无N处理则以CH4为主,也不容忽视。     

Biogas plants efficiency in purifying Indian sago factory waste water with wide C/N ratios: strategies for process water reuse

Cassava tubers produced under hot, dry and monsoon governed climate in the Salem region, Tamil Nadu, South India, consume together with the about 1000 starch extracting industries daily, 9 millions of litres of groundwater which have to be pumped from a depth of 80 m below ground level. Because of water shortage, adjacent fields are irrigated with organically highly enriched sago factories wastewater and the land becomes unproductive. One-third of the wastewater is presently channelled through a few installed biogas plants with a purification efficiency, biological oxygen demand, of only around 30%. Microbiologically and chemically analysed in- and effluents of biogas plants exhibited nutrient contents sufficient to maintain a rice crop and significantly higher population densities of fermenting bacteria and methanogenic archaea, despite C/N ratio of about 250. CO₂ and CH₄ emissions from aerobic and anaerobic incubated sago factory biogas plants in- and effluents indicated that the present purification efficiency of 30% can be further enhanced. This investigation has given clues for designing a purification system that connects the already installed biogas plants with a well-aerated, hydro-cultured, constructed wetland and a Stirling motor device for electric power gains and heat distillation, for enabling reuse of process water and saving groundwater.