Analysis of purification efficiency of pollutants in farmland runoff by the ecological ditch in winter and spring
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摘要:
为有效提高冬春季沟渠的净化效率，在原有土质沟渠中增设耐寒植物黑麦草浮毯与填料透水坝构建生态沟渠，分析生态沟渠对农田径流中主要污染物的削减率，对比沿程不同处理段对污染物的净化效果，估算植物吸收对于污染通量降低总量的贡献。结果显示：在冬春季节，生态沟渠对总氮（TN）、硝氮（${\mathrm{NO}}_ 3^-{\text{-}}{\mathrm{N}}$）、总磷（TP）、化学需氧量（COD）和悬浮物（SS）的总削减率均值分别为29.06%、54.93%、20.76%、54.08%和49.85%。透水坝段的TN和${\mathrm{NO}}_ 3^-{\text{-}}{\mathrm{N}}$沿程削减率最高；植物浮毯+透水坝段的TP和COD沿程削减率最高；植物浮毯段的SS沿程削减率最高，其对${\mathrm{NO}}_ 3^-{\text{-}}{\mathrm{N}}$、TP和COD也有较好的净化效果。在降水量达到10 mm以上的9 d内，TN和TP的污染通量降低总量分别为11.43和0.27 kg；黑麦草吸收的氮、磷量分别约占污染通量降低总量的20.6%和55.6%。大雪融化后气温降至0 ℃以下，可能引起土壤冻融作用，雪水径流中的氮、磷浓度显著升高，此时生态沟渠对径流中氮、磷的净化效果不明显，可利用周边河塘暂存雪水径流，后续结合生态措施对污染物实施强化处理。
Abstract:To improve the purification efficiency of ditches in winter and spring, the ecological ditch was constructed by adding floating blankets with the cold-tolerant plant (Lolium perenne L.) and permeable dams with adsorption filler in the original soil ditch. The removal rates of main pollutants in farmland runoff by the ecological ditch were analyzed, the purification efficiencies of pollutants in different treatment segments were compared and the contributions of plant absorption to the total pollutant flux reduction were estimated. The results showed that the average values of the total removal rates of total nitrogen (TN), nitrate nitrogen (${\mathrm{NO}}_ 3^-{\text{-}}{\mathrm{N}}$), total phosphorus (TP), chemical oxygen demand (COD) and suspended solids (SS) were 29.06%, 54.93%, 20.76%, 54.08% and 49.85%, respectively. The removal rates of TN and ${\mathrm{NO}}_ 3^-{\text{-}}{\mathrm{N}}$ were highest in the permeable dam section of the ecological ditch; the removal rates of TP and COD were highest in the permeable dam section combined with floating blankets; the removal rate of SS was highest in the floating blankets section, and the purification efficiencies of ${\mathrm{NO}}_ 3^-{\text{-}}{\mathrm{N}}$, TP and COD were also better in the floating blankets section. In the nine days with more than 10 mm of rainfall during the experiment, the total reduction amounts of pollutant flux of TN and TP were 11.43 and 0.27 kg, respectively. The nitrogen and phosphorus amounts absorbed by Lolium perenne L. accounted for 20.6% and 55.6% of the total reduction amount of pollution flux of TN and TP, respectively. When the temperature dropped below 0 ℃ after the melting of heavy snow, the concentrations of nitrogen and phosphorus in snow-water runoff increased significantly, which might be due to soil freezing and thawing. Meanwhile, as the purification efficiencies of nitrogen and phosphorus in snow runoff by ecological ditch were not significant, nearby ponds and rivers could be utilized as temporary storage of the runoff, and further enhanced treatment of pollutants could be implemented in combination with ecological measures.
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Key words:
- winter and spring /
- ecological ditch /
- farmland runoff /
- nitrogen /
- phosphorus
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图 1 生态沟渠设置及采样点位分布示意
Figure 1. Setting of the ecological ditch and distribution of the sampling sites
图 2 生态沟渠处理设施布置俯视图及透水坝布设断面
注：图中数字单位为mm。
Figure 2. Vertical view of different treatments in the ecological ditch and sectional view of the permeable dam
图 3 生态沟渠进出水口TN和${\mathrm{NO}}_ 3^-{\text{-}}{\mathrm{N}}$浓度变化及总削减率
注：PR-U为PR段前端采样点，代表生态沟渠进水口；EP-D为EP段末端采样点，代表生态沟渠出水口；Rt为总削减率。全文同。
Figure 3. Variations of TN and ${\mathrm{NO}}_ 3^-{\text{-}}{\mathrm{N}}$ concentrations at inlet and outlet and total removal rates of the ecological ditch
图 4 生态沟渠进出水口TP和$ \mathrm{PO}_4^{3-}\text{-}\mathrm{P} $浓度变化及总削减率
Figure 4. Variations of TP and ${\mathrm{PO}}_ 4^{3-}{\text{-}}{\mathrm{P}} $ concentrations at inlet and outlet and total removal rates of the ecological ditch
图 5 生态沟渠进出口COD和SS浓度变化及总削减率
Figure 5. Variations of COD and SS concentrations at inlet and outlet and total removal rates of the ecological ditch
表 1 试验期间天气、降水量、气温与沟渠内水温、pH及DO
Table 1. Weather, rainfall, air temperature and water temperature, pH and DO in the ecological ditch during the experiment
采样时间（月-日） 天气 降水量/mm 气温/℃ 水温/℃ pH DO 浓度/(mg/L) PR段 PD段 EC段 EP段 PR段 PD段 EC段 EP段 01-27 雨夹雪 10.5 1~4 5.14 8.39 8.92 8.39 8.06 9.67 10.48 10.75 11.05 02-08 雨夹雪 1.0 2~5 6.94 8.31 8.26 8.19 8.09 12.76 12.57 12.91 13.66 02-24 多云 0~10 13.51 8.38 8.15 7.92 7.68 12.11 12.82 13.64 13.33 03-02 多云转晴 6~17 17.51 8.19 8.11 8.10 8.07 11.35 10.14 11.94 11.08 03-17 大雨 40.8 6~9 13.70 7.03 7.26 7.25 7.14 10.43 10.56 11.44 10.73 03-23 小雨 0.2 5~14 16.63 8.54 8.25 8.23 8.19 10.21 11.44 11.16 11.38 04-02 多云转晴 5~17 21.20 8.20 8.54 8.60 8.40 13.02 12.85 13.09 12.44 04-14 多云转晴 12~18 19.10 8.67 8.50 8.65 8.25 12.49 11.30 12.79 11.20 04-29 中雨 10.7 11~15 18.39 8.05 8.13 7.67 7.43 7.79 7.34 8.63 5.95 注：水温数据为沟渠所有采样点的均值，pH和DO浓度数据为沟渠各处理段3个采样点的均值。 
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表 2 生态沟渠各处理段的污染物进水平均浓度与沿程削减率
Table 2. Inlet average concentrations and removal rates of major contaminants of different treatment segments in the ecological ditch
处理段 TN ${\mathrm{NO}}_ 3^-{\text{-}}{\mathrm{N}}$ TP COD SS 进水平均浓度/
（mg/L）削减率/% 进水平均浓度/
（mg/L）削减率/% 进水平均浓度/
（mg/L）削减率 进水平均浓度/
（mg/L）削减率/% 进水平均浓度/
（mg/L）削减率/% PR段 9.63 7.06 3.44 17.96 1.45 0.00 31.35 4.38 38.53 15.99 PD段 8.74 9.61 2.68 28.77 1.48 0.53 24.12 7.88 38.67 21.26 EC段 7.70 3.83 1.81 23.16 1.46 1.43 25.59 19.62 27.67 34.27 EP段 7.70 2.97 1.62 1.95 1.49 7.23 18.90 21.99 22.37 23.18
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表 3 生态沟渠进出水口主要污染物的污染通量
Table 3. Pollutant flux of major contaminants at inlet and outlet of the ecological ditch
kg/d 采样点 TN ${\mathrm{NO}}_ 3^- $ TP ${\mathrm{PO}}_ 4^{3- }$ COD SS PR-U 5.69 2.03 0.85 0.02 18.52 22.77 EP-D 4.42 0.94 0.82 0.01 8.92 10.15 降低值 1.27 1.09 0.03 0.01 9.60 12.62
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表 4 生态沟渠中植物吸收的氮、磷总量
Table 4. Amount of nitrogen and phosphorus absorbed by the plants in the ecological ditch
处理段 单位面积
鲜质量/（kg/m2）单位面积
干质量/（kg/m2）干物质
氮含量/%单位面积
氮含量/（g/m2）吸收氮总量/kg 干物质
磷含量/%单位面积
磷含量/（g/m2）吸收磷总量/kg EC段 5.25±0.12 0.95 3.42±0.21 32.32 1.16 0.20±0.03 1.89 0.07 EP段 5.16±0.09 0.98 3.39±0.11 33.24 1.20 0.22±0.05 2.16 0.08 合计 2.36 0.15
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