【作者】 曾立雄；

【导师】 肖文发；

【作者基本信息】 中国林业科学研究院 ， 生态学， 2010， 博士

【摘要】 三峡库区的水土流失和水体富营养化是水库安全的巨大威胁。对三峡库区小流域养分循环过程的研究,有利于了解三峡库区水体富营养化的原因,探索森林植被恢复对养分流失的控制机制、过程和作用。本文选取兰陵溪小流域为研究对象,收集有关历史资料,结合大量实地调查和取样,全面分析了小流域的降雨特征及土壤性质的时空分布,通过对小区尺度、坡面尺度和小流域尺度养分运移过程的连续监测,对比不同尺度下养分运移特征及影响因子,对小流域养分流失的发生过程和控制策略进行了研究和探讨。该小流域地处库区干流,为国家退耕还林示范区,2000年退耕还林以来,500 m以上全部分布为林地,500 m以下主要为茶园、板栗和柑橘,农田只占流域面积的2.91 %。居民主要集中在海拔300 m左右的盘山公路附近。本小流域人为干扰严重,在三峡库区具有典型的代表性。人类活动的长期干扰会对土壤的理化性质的时空分布产生重要影响。土壤含水量(SWC)和有效磷(AP)的空间分布受人为干扰较少,空间自相关性较强;全磷(TP)和PH成中度的空间自相关,其空间分布在受到结构性因素影响和随机因素的综合影响;土壤铵态氮(NH4+-N)、硝态氮(NO3--N)和总氮(TN)的空间自相关性非常弱,其空间分布受到了非常强烈的人为干扰。土壤PH、AP和TP随土壤沙粒含量的升高而增加,而土壤NH4+-N、NO3--N和TN则是随着土壤沙粒含量的升高而降低。土壤PH、AP和TP含量的分布受土壤沙粒含量影响较大,而各种型态N的敏感性则相对较小。地形和土地利用分布格局是小流域的养分分布与运移的主要控制因素。流域土壤的渗透性与地形关系密切,在0-5和5-10 cm层,土壤的初渗速率随着坡度的增加先增加后降低,坡度在20~25°时为最高值,达到10.78mm/min和6.07 mm/min。土壤的初渗速率和稳渗速率都随着坡位的降低而减慢。土壤渗透速率与土壤非毛管孔隙度成极显著的正相关关系,与土壤毛管孔隙度和总孔隙度成显著正相关关系;各土地利用类型土壤NH4+-N、NO3--N和TN的含量都随土层的加深而降低。而AP和TP的垂直分布规律则与坡位有关,处于上坡土壤的AP和TP含量随着土层的加深而增加,中坡土壤的AP和TP含量随土层的增加是先降低后增加,而中下坡土壤的AP和TP含量则是随土层的增加而降低;地形(坡长与坡度)、土地利用类型和用地类型的分布格局都对坡面土壤养分的迁移产生了重要影响,在用地类型单一的茶园坡面,土壤PH、AP和TP都是随坡位的降低而减少,土壤NH4+-N、NO3--N和TN随坡位的降低而增加,而在土地利用复杂的坡面,土壤PH、AP和TP都是随坡位的降低而在整体上也有减少趋势,但会在中坡附近出现了峰值,居民区是磷素的重要“源”景观,而林地对磷表现出较强的拦截吸附能力。土壤N素在下坡位具有显著的累积效应。退耕还林之后各土地利用类型的泥沙流失量只有农田的5-20 %,小流域2009年泥沙流失量为279.4 m3。本流域养分流失以N素为主,其中硝态氮占总氮的40-60 %。各养分流失负荷主要受少数几个因子控制,正磷酸盐和总磷的流失负荷主要受灌草盖度和植被总盖度的影响。硝态氮和总氮的流失负荷都随乔木层盖度的增加而减少。作为养分的载体,小流域内水的时空特征对养分运移具有明显调控作用。只有当日降雨量达到4.4-10 mm时,各土地利用类型才会有地表径流产生。土壤前期含水量高会使地表径流较早形成峰值,加快养分的流失。高强度降雨是磷素流失的主要降雨类型,主要是以颗粒态随地表径流流失。氮素更容易随地下水流失。正磷酸盐、总磷、铵态氮、硝态氮、亚硝态氮和总氮的流失负荷均与径流量正极显著的线性关系。流域全年总氮和总磷的输出负荷分别为1498.19 kg/a和41.67 kg/a,总氮的流失量要远远高于总磷。基于三峡库区退耕还林小流域养分空间分布和运移的基本规律,初步提出了“三带——网状”模式以有效控制三峡库区养分流失。同时认为,鉴于试验地区是国家和地方的新农村建设示范基地,采取“参与式”的生态建设和环境保护策略具有良好的基础,也十分重要。通过“参与式”培训和教育,提高民众的环境保护意识,在发展过程中平衡“经济”和“环保”的关系,有利于从根本上降低养分流失的潜在威胁。更多还原

【Abstract】 Analyzing consecutive processes and mechanisms of non-point source was helpful to study the forming cause of the eutrophication, and provided the basis for controlling measure in Three Gorges Reservoir Area. Experiments were conducted in a conversion of cropland to forest watershed—Lanlingxi watershed in Three Gorges Reservoir Area. Historical data collection, watershed investigation, rainfall-runoff events monitoring and sampling activities were carried out all along. Temporal and spatial distribution of soil nutrient was analyzed, comparative researches on nutrient transfer via surface runoff at plot-scale, slope-scale and catchment-scale were also discussed. Finally, the controlling suggestions for agricultural non-point source pollution in Three Gorges Reservoir Area were given. The main results were showed as following:1. Infiltration was impacted by terrain factor greatly. The soil water infiltration rates showed a single-hump curve with slope gradient, the tip appeared in 20-25°, the peak in layer 0-5 cm and 5-10 cm were 10.78 and 6.07 mm/min, respectively. Initial and stable water infiltration rate both slowed down with decreasing altitude. The correlation between the soil water infiltration rates and non-capillary porosity was very significant positive, the correlation between the soil water infiltration rates and capillary porosity was significant positive, and the total porosity was the same.2. Spatial heterogeneity and spatial dependence were apparent in SWC、pH、AP、TP、NH4+-N、NO3--N and TN, the ratio of random variance(nugget) to total variance (sill) were 6-50 %、50 %、7-50 %、30-50 %、100 %、40-100 % and 63-100 % for them in different seasons, respectively. SWC and AP less involved by human activity, NH4+-N、NO3--N and TN more involved human activity, spatial variability of pH and TP were mainly affected by a co-working of the structural factors with random factors. pH, AP and TP of soil decreased sharply as SWC increased, while NH4+-N、NO3--N and TN of soil increased slowly as SWC increased. pH, AP and TP of soil increased sharply as soil SPC increased, while NH4+-N、NO3--N and TN of soil decreased slowly as SPC increased. 3. Phosphorus loss decreased after conversion of cropland to forest because of the silt loss considerably reduced as well. Nitrogen loss was the chief form of agricultural non-point pollution in Heigou watershed and nitrate nitrogen accounted for 40-60% of total nitrogen. The order of total phosphorus loss loading of different land use was that: farmland(521.55 g/hm2)>citrus park(80.66 g/hm2)>tea garden (67.30 g/hm2)>bamboo forest(63.58 g/hm2) > chestnut forest(47.16 g/hm2) > woodland (43.78 g/hm2), The order of total nitrogen loss loading of different land use was that: tea garden(2598.99 g/hm2)>farmland(2267.03 g/hm2)> citrus park(1679.7 g/hm2)> bamboo forest(1151.66 g/hm2)>chestnut forest(550.47 g/hm2)> woodland(426.10 g/hm2). Orthophosphate and total phosphorus loss loading were effect by shrub -herbous layer and total coverage. The higher of soil ammonium nitrogen the ammonium nitrogen loss loading was more. Total nitrogen and nitrate nitrogen loss loading decreased with the tree layer coverage increased, slightly related with soil properties.4. The soil pH was correlated positively with soil depth. Ammonium nitrogen, nitrate nitrogen and total nitrogen of soil decreased as soil depth increased, exceeding fertilizer application leaded to leaching phenomenon of nitrogen in soil. Distribution characteristics of phosphorus in soil profiles under different land use closely related with slope position. Along the soil depth, available phosphorus and total phosphorus of soil increased at upper slope, increased at beginning and then decreased at middle slope, decreased at lower slope. Terrain factors (slope and slope length), land use type and distribution had important effect on the transfer ability of soil nutrient in slope scale. At single-land-use slope, the higher of slope position the soil PH, available phosphorus and total phosphorus were less, and the soil ammonium nitrogen, nitrate nitrogen and total nitrogen were more. At different-land-use slope, because of residential was the important“sink”landscape and the phosphorus adsorption capacity of woodland was great, soil PH, available phosphorus and total phosphorus decreased at beginning, increased at middle slope, and then decreased again as slope position deceased. Migration and leaching leaded to the accumulation of nitrogen in soil at lower slope.5. The higher of the antecedent moisture contents of the soil the peak of surface runoff appeared earlier. Phosphorus loss occurred mainly during strong rainfall processe, the particle phosphorus was the dominant form. Nitrogen loss by groundwater occurred more easily than phosphorus loss. There was a good linearity relationship between runoff volume and loss load of orthophosphate, total phosphorus, ammonium-N, nitrate-N, nitrite-N and total nitrogen. The annual total nitrogen and phosphorus exported from Heigou watershed were 1498.19 kg/a and 41.67 kg/a, respectively.6. Based on the mechanisms of non-point source in Three Gorges Reservoir Area, the control pattern of source area of controlling key source-reducing surface runoff-intercepting nutrient was presented firstly.更多还原