Tidal effects on net ecosystem exchange of carbon in an estuarine wetland

One year of continuous data from two eddy-flux towers established along an elevation gradient in coastal Shanghai was analyzed to evaluate the tidal effect on carbon flux (F_c) over an estuarine wetland. The measured wavelet spectra and cospectra of F_c and other environmental factors demonstrated that the dynamics of F_c at both sites exhibited a tidal-driven pattern with obvious characteristics at scales between 10 and 20 days (256–512-h). Environmental factors exerted major controls on the carbon balance at finer temporal scales. F_c was more sensitive to tides at the low-elevation site than at the high-elevation site. Overall, the mean nighttime F_c during spring tides was lower than that during neap tides, indicating suppressed ecosystem respiration under inundation. Larger differences were observed at the low-elevation site due to longer inundation durations. In contrast, daytime F_c was more variable since plants reacted differently in different growth periods and under different tidal elevations. The amplitudes of diurnal F_c during tidal periods were larger than those reported for other wetland types, implying a great potential for future carbon sequestration. Whilst tides would also transport organic matter to nearby estuaries and hence may incur carbon emission in the receiving ecosystems. Thus, further study on lateral carbon transport is required to investigate the tidal effect on the carbon sink/source role of the wetland.     

浙东固废拆解区污水灌溉对土壤多氯联苯含量的影响研究

在对浙东沿海某典型固废拆解区的水-土壤-农作物系统进行系统调查和分析的基础上,重点探讨了污水灌溉对土壤多氯联苯（PCBs）含量的影响程度,并通过建立数学模型,对污灌区土壤PCBs含量进行了预测。结果表明,研究区土壤、水体、底泥乃至农作物均检测出相当水平的PCBs,对当地的生态安全影响较大;经因子分析和对比分析发现,约有67.3%的土壤PCBs污染是由污水灌溉引起,污水灌溉对土壤污染的影响显著;在现有农田灌溉模式不变的情况下,污灌区的土壤PCBs含量将呈上升趋势,50a后含量将增加1倍。     

Effect of soil matric potential on tomato yield and water use under drip irrigation condition

Field experiment was carried out to investigate the effect of soil matric potential (SMP) on tomato yield, evapotranspiration (ET), water use efficiency (WUE) and irrigation water use efficiency (IWUE) under drip irrigation condition in North China Plain. The experiment included five treatments, which controlled SMP at 0.2 m depth immediately under drip emitter higher than −10 (S1), −20 (S2), −30 (S3), −40 (S4) and −50 kPa (S5), respectively, after tomato plant establishment. The results showed that different SMP affected irrigation amount and tomato ET. Irrigation amount decreased from 185 mm (S1) to 83.6 mm (S5) in 2004, and from 165 mm (S1) to 109 mm (S5) in 2005, respectively. The ET decreased from 270 mm (S1) to 202 mm (S5) in both years. However, it was found that SMP did not affect the tomato yield significantly, for the range of SMP investigated. Both WUE and IWUE increased as SMP decreased. The maximum WUE (253 and 217 kg/ha mm) and IWUE (620 and 406 kg/ha mm) were for S5 in 2 years, whereas the minimum WUE (178 and 155 kg/ha mm) and IWUE 261 and 259 kg/ha mm) were for S1 in 2004 and 2005. Based on the above results, therefore, it is recommended that if the tomatoes are well irrigated (SMP is higher than −20 kPa) during establishment, controlling SMP higher than −50 kPa at 0.2 m depth immediately under drip emitter can be used as an indicator for drip irrigation scheduling during following period of tomato growth in North China Plain.