造纸废水灌溉对滨海退化盐碱湿地土壤酶活性的响应

经生物塘处理后的造纸废水矿化度低,有机物质含量高,可用来改善滨海盐碱土壤。研究了不同量(每次灌溉深度为5、10、15和20 cm)处理后的造纸废水灌溉对土壤脲酶、磷酸酶、蔗糖酶、脱氢酶和过氧化氢酶活性的影响,通过酶活性的变化来反映对土壤改良的效果并寻求最佳灌溉量。结果表明:5种土壤酶上层(0-10 cm)和中层土壤(10-20 cm)的活性大于下层土壤(20-30 cm),造纸废水灌溉没有改变土壤酶活性在不同土层的分布规律;灌溉造纸废水对土壤脲酶和磷酸酶活性的提高主要发生在表层土壤,而对蔗糖酶、脱氢酶以及过氧化氢酶活性的提高主要发生在上层和中层土壤;20 cm灌溉对下层土壤酶活性的提高最明显。5种酶活性均受温度降雨等因素影响,最大值出现在8月份。总体上,灌溉量的增加能提高酶活性的增加程度,最佳灌溉量为20 cm,土壤脲酶、磷酸酶、蔗糖酶和脱氢酶相对对照分别提高了70.0%、30.9%、56.2%、135.2%和20.84%。酶活性与土壤盐碱度和微生物代谢商(qCO₂)显著负相关,与速效磷和微生物量碳显著正相关,与有机质和速效氮相关性不显著。

Responds of soil enzfyme activities of degraded coastal saline wetlands to irrigation with treated paper mill effluent

Yellow River Delta, which is surrounded by Bohai Sea to the north and Laizhou Bay to the east, is one of the three largest deltas in China. However, large amounts of water and salts that were brought by penetration of water in the Yellow River and encroachment of sea water resulted in the rise of groundwater level and salinization. Under the influence of strong evaporation, the soil degraded into saline soil. Currently, up to around 1670 km² of land have turned into saline soil in the Yellow River Delta. Thus, it is urgent to ameliorate the saline soil for the assurance of ecological security and coordinated development of economy and ecology. Treated paper mill effluent was low in salinity and high in organic matter, and could be used to restore saline soil. Irrigation with treated paper mill effluent could enrich soil nutrients, improve soil activity and leach soil salts, and meanwhile it could solve the disposal problem of paper mill effluent. Thus, different depths (viz. 5, 10, 15 cm and 20 cm) of treated paper mill effluent were irrigated for remediation of saline soil in this study. In addition, anti-waterlogging ditches were built around the plots for discharging leached soil salts. Soil enzyme activities, which can reflect soil fertility, are important parameters for evaluating soil quality. Five enzymes, viz. urease, phosphatase, sucrase, dehydrogenase and catalase, were used to evaluate the effectiveness of saline soil remediation. Under the multi-influences of soil water content, temperature, aeration, nutrients and salts, soil enzyme activities were higher in soil layers of 0-10 cm and 10-20 cm than those in soil layer of 20-30 cm. Irrigation did not change the distribution of soil enzymes in the different soil layers. The improvements of urease and phosphatase mainly achieved in soil layer of 0-10 cm, and those of sucrase, dehydrogenase and catalase mainly achieved in both soil layers of 0-10 cm and 10-20 cm. Irrigation rate of 20 cm was the most effective in improving soil enzyme activities in lower soil layer (20-30 cm). The five enzymes also presented regular seasonal dynamics, all reaching the highest level in August. Irrigation with treated paper mill effluent, salinity (2080 mg/L) of which was very low compared to the present saline soil (2.31%), was effective in reducing soil salinity. Thus, inhibition of soil salinity to enzymes was reduced. In addition, irrigation with treated paper mill effluent introduced abundant of substrates for enzymes. Consequently, all the five enzyme activities were significantly improved. In general, higher irrigation rates were more effective in the improvement of enzyme activities and 20 cm turned out to be the optimum irrigation rate. Compared to the control, the activities of urease, phosphatase, sucrose, dehydrogenase and catalase were improved by 70.0%, 30.9%, 56.2%, 135.2% and 20.84%, respectively. The results also showed that in the studied saline soil, the five soil enzyme activities presented significantly negative correlation with soil salinity, sodicity and microbial metabolic quotient (qCO₂), and significantly positive correlation with available phosphorus and microbial biomass carbon, while no significant correlation with soil organic matter and available nitrogen due to the different dynamics over time after irrigation.