农田溪流深潭营养盐滞留及对人为干扰的响应

摘要

为解析溪流深潭地貌格局的营养盐滞留能力及其对人为干扰的响应,2015年11月~2016年4月,在巢湖流域南淝河某一深潭地貌特征明显的农业源头溪流,选择NaCl为保守示踪剂,NH4Cl和KH2PO4为添加营养盐,开展了9次野外示踪试验,其中人为干扰试验4次,并据此计算水力学参数和养分螺旋指标。结果表明：试验渠段水流属于缓流类型,且在整个试验阶段始终处于湍流状态；人为干扰情形的深潭Sw-NH4下降幅度较自然情形明显,数值由331~3304m下降为232~609m,而Sw-PO4则略有增大,即由232~609m上升为301~1100m；人为干扰时平直渠段Sw-NH4下降显著,数值由4812~58895m下降为2463~13955m,而Sw-PO4下降更为显著,由6242~75285m下降到1792~11432m；人为干扰情形的平直渠段 Sw-NH4、Sw-PO4下降幅度显著高于深潭渠段,意味着平直渠段受人为干扰影响很大,响应更明显；与自然情形相比,深潭和平直渠段的 Vf-NH4、Vf-PO4基本都有不同程度的增大,有利于滞留效应的发生。总体上,从整个试验渠段来看,人为干扰对于提高农田溪流深潭地貌格局的营养盐滞留能力是可行和有效的。%FromNovember 2015 to April 2016, nine field tracer experiments including four human disturbance scenarios were conducted in an agricultural headwater stream of Nanfei River, located in Chaohu Lake basin. To explore the nutrient retention efficiencies and its response to human disturbance for multi-pool morphological pattern in streams, conservative (NaCl) and non-conservative (NH4Cl and KH2PO4) solutes were co-injected at a constant rate. Based on the tracer experiments, hydraulic parameters and nutrient spiraling metrics were calculated. Test stream reach displayed striking turbulence characteristics through the nine tracer experiments and its flow belonged to subcritical flow. The decrease of Sw-NH4(NH4+ uptake lengths) in the deep pool under human disturbances was significant with a drop from 331∼3304m to 232∼609m, while the PO43- uptake lengthsSw-PO4 increased slightly with a raise from 232∼609m to 301∼1100m.The Sw-NH4 decreased sharply from 4812∼58895m to 2463∼13955m, and theSw-PO4 also dropped markedly from 6242∼75285m to 1792∼11432m, in the straight sub-reach in the case of human disturbances. The falling ranges ofSw-NH4 andSw-PO4 in the straight sub-reach greatly exceeded that in the pool sub-reach under human disturbances, suggesting that the straight sub-reach was highly affected by the human disturbance. Compared with the natural situation, the values ofVf-NH4 and Vf-PO4 both in straight and pool sub-reaches under human disturbances had an increase, which would be helpful to nutrient retention. From the point of the whole test stream, the effectiveness of human disturbance was feasible and effective for the improvement of nutrient retention efficiency.