河岸缓冲带植被布局对氮流失的影响

河岸缓冲带（Rriver Buffer Strips，RBSs）已被证明能有效拦截水流并去除氮，该研究旨在揭示不同配置缓冲带对脱氮效果的影响。实地布置河岸植被缓冲带，开展地下径流试验。缓冲带设置3种不同植物种类（水曲柳，五叶枫，杨树），和不同宽度（0、5、10、20、30 m），河岸坡度为3%，树木密度为540株/hm2。在此条件下，研究各类河岸植被缓冲带对地下径流铵态氮、硝态氮和总氮的截留效果。结果表明：20 m宽度河岸植被缓冲带能很好地截留各形态氮素。30 m宽度下，河岸植被缓冲带径流水中的铵态氮、硝态氮和总氮的截留率最高，分别为70.4%、67.7%和69.1%。在不同植物种类缓冲带比较中，杨树可显著降低径流铵态氮和总氮浓度，水曲柳可显著降低径流硝态氮浓度。在宽度与不同植物种类的交互关系中，20 m宽度杨树缓冲带对铵态氮和硝态氮的截留率最高，30 m宽度杨树缓冲带对总氮的截留率最高，为62.1%。研究结果可为东北地区中小型河流河岸缓冲设计最大化截留径流氮污染物提供参考。

Effects of riparian buffer zone vegetation layout on nitrogen loss

Abstract: To study the nitrogen retention efficiency of riparian vegetation buffers of small and medium-sized rivers, the common broad-leaved species in Northeast China were slected on the slope of Hejiagou, Harbin in Northeast China. Four riparian planted woodlots of 15 m long by 30 m wide were prepared for the different species experiment, namely bare ground, water willow or ash, five-leaf maple, and poplar riparian vegetation buffers. The bare ground riparian buffers served as controls. The effects of different riparian buffer widths (0, 5, 10, 20, and 30 m) and different plant species above on nitrogen retention in subsurface runoff at 20 and 40 cm depth were analyzed under the condition of riparian slope (3%) and tree density (540 trees/hm2). At the test sites, PVC pipes with a diameter of 10 cm and a 4-mm partial subsurface runoff intake hole on the left side were used to collect subsurface runoff at soil depths of 20 cm and 40 cm. The PVC pipes were buried when the trees were planted. At the four riparian buffer plots from 0 to 0.5 m, the compound fertilizer was evenly applied using a small fertilizer spreader to simulate nitrogen loss conditions. The fertilizer was applied before rainfall, and the ratio of flow-producing compound fertilizer collected after rainfall was 24:6:35 for nitrogen: phosphorus: potassium, with fertilizer application rate of 61 kg/hm2. When sampling, the upper clear liquid in the tube was pumped out with a small pump, and then all the turbid liquid in the tube was pumped out and drained at the far end of the test site to avoid affecting the experimental results, the clear liquid was sampled into 300 mL plastic bottles and stored in a -4-0 ℃ refrigerator for determination of the nitrogen content of the water samples. The ammonium nitrogen in the runoff was determined spectrophotometrically by the nano reagent, the nitrate nitrogen was determined by a UV spectrophotometry, and the total nitrogen was determined by a UV spectrophotometry using the alkaline potassium persulfate elimination method. The statistical analysis results showed that the depth of subsurface runoff did not significantly interact with riparian buffer width and vegetation type. Therefore, the nitrogen values at 20 and 40 cm soil depth were averaged for the followed analysis on the effects of different widths, different vegetation types and different widths × different vegetation types on nitrogen retention. The results showed that the concentrations of runoff ammonium and nitrate nitrogen gradually decreased in riparian vegetation buffers of 0, 5, 10, and 20 m in width. Thus, the riparian vegetation buffer with a width of 20 m could retain all forms of nitrogen well. The 30 m width riparian vegetation buffer had the highest retention of ammonium nitrogen, nitrate nitrogen, and total nitrogen in runoff with 70.4%, 67.7%, and 69.1%, respectively. in the comparison of different plant species buffer zones, poplar could significantly reduce the runoff ammonium nitrogen and total nitrogen concentrations, and water willow could significantly reduce the runoff, the poplar significantly reduced runoff ammonium and total nitrogen concentrations, and ash significantly reduced runoff nitrate-nitrogen concentrations. In the interaction between width and plant species, poplar buffer strips of 20 m width had the highest retention rate of ammonium nitrogen and nitrate nitrogen, and the poplar buffer strips of 30 m width had the highest retention rate of 62.1% for total nitrogen. The results of the study can provide valuable information for the design of riparian buffers to maximize the retention of runoff nitrogen pollutants in small and medium-sized rivers in Northeast China.