洱海近岸不同种植类型农田沟渠径流氮磷流失特征

摘要

In order to explore effect of planting pattern on nitrogen and phosphorus losses with ditch runoff, one typical ir?rigation and drainage unit each was selected in a sapling nursery, vegetable garden and a tract of rice paddy field on the west bank of Lake Erhai as objects in the study, nitrogen and phosphorus concentrations in the irrigation water flowing into and ditch runoff flowing out of the irrigation and drainage units were monitored for analysis of effects of planting pattern on nitrogen and phosphorus concentrations in ditch runoff and their relative contribution. Results show that in terms of N and P concentrations of N and P in ditch runoff, the three types of farmlands exhibited an order of vegetable garden>rice paddy field > sapling nursery. The ditch run?offs at the outlets of the ditches from the test units in the paddy field and the sapling nursery were higher in TN but lower in TP than the criteria for Class IV surface water set by GB 3838-2002, while the ditch run?off from the vegetable garden was far above the criteria for Class V surface water in both TN and TP and higher than the irrigation water in concentration of various forms of nitrogen and phosphorus. The situation in the sapling nursery was just the contrary. In the paddy field the ditch runoff was higher than the irrigation water in concentration of various forms of N and P in May and June, while it went opposite in the other months. Inorganic nitrogen and dissolved total phos?phorus ( DTP ) were the main N and P forms in the ditch runoff under all the three planting patterns, accounting for 70. 32%-81. 49% of TN and 70. 33%-79. 33% of TP, respectively, and NO3-?N was the major fraction of inorganic ni? trogen, accounting for 75. 13%-84. 75%. In terms of contribution to TN, NH4+?N, NO3-?N, TP and DTP in the ditch run?offs, the three types of farmlands followed an order of vegetable garden ( 56. 41%, 85. 81%, 44. 61%, 66. 17% and 64. 80%, respectively) > rice paddy field (-4. 50%, -15. 14%, -10. 01%, -0. 85% and -0. 29%, respectively) >sapling nursery (-89. 88%, -64. 81%, -96. 49%, -72. 11% and -69. 69%, respectively ) . All the findings in this study demonstrate a strong need for optimizing spatial distribution of planting in the areas offshore of Lake Erhai to reduce agricultural N and P losses and protect Erhai Lake from eutrophication.%为研究不同种植类型对沟渠径流氮磷流失的影响,以洱海西岸苗木地、菜地和稻田3种种植类型农田内的典型灌排单元为研究对象,通过监测沟渠径流流入和流出灌排单元断面的氮、磷浓度,分析不同种植类型对沟渠径流氮、磷浓度的影响及相对贡献.结果表明,不同种植类型农田沟渠出水径流氮、磷浓度从大到小依次为菜地、稻田和苗木地,其中稻田和苗木地沟渠出水口径流总氮(TN)浓度大于GB 3838—2002《地表水环境质量标准》Ⅳ类水,而总磷(TP)浓度低于地表Ⅳ类水标准,菜地沟渠出水口径流TN、TP浓度远大于地表V类水标准.菜地沟渠出水口径流中各形态氮、磷浓度均大于沟渠入水口,苗木地则相反.5、6月稻田沟渠出水口径流各形态氮、磷浓度大于沟渠入水口,其他月份则相反.3种种植类型下沟渠径流氮磷的主要形态为无机氮和可溶性总磷(DTP),分别占TN和TP浓度的70.32%~81.49%和70.33%~79.33%,NO3-?N占无机氮浓度的75.13%~84.75%.不同种植类型对沟渠径流TN、NH4+?N、NO3-?N、TP和DTP浓度的贡献率从大到小依次为菜地(56.41%、85.81%、44.61%、66.17%和64.80%)、稻田(-4.50%、-15.14%、-10.01%、-0.85%和-0.29%)和苗木地(-89.88%、-64.81%、-96.49%、-72.11%和-69.69%).