三峡库区规模化顺坡沟垄果园氮、磷输出过程及流失负荷

通过对三峡库区顺坡垄沟构型的规模化柑橘园集水区次降雨过程径流氮、磷进行动态监测,分析典型降雨事件氮和磷流失负荷,并探讨了规模化柑橘种植对土壤氮磷流失及入库河流水环境的影响.结果表明:①顺坡沟垄柑橘园集水区径流氮和磷年流失负荷分别为13.43 kg·(hm~2·a)~(-1)和1.26 kg·(hm~2·a)~(-1),春季施肥及强降雨冲刷是集水区污染物高负荷的主要原因;②集水区全年总氮(TN)和总磷(TP)的EMC为8.49 mg·L~(-1)和0.87 mg·L~(-1),超过发生水体富营养化含量标准;③春季施肥后的2场典型降雨中,长历时暴雨径流硝态氮(NN)和溶解态磷(DP)负荷为4.94 kg·hm~(-2)和0.28 kg·hm~(-2),分别占TN和TP流失负荷的92.90%和64.69%;短历时大雨径流NN和DP负荷为0.52 kg·hm~(-2)和0.05 kg·hm~(-2),分别占TN和TP的65.92%和74.88%,溶解态氮和磷是顺坡沟垄坡面果园径流氮和磷流失的主要途径;④集水区氮磷流失表现出显著的"初始冲刷效应",初期20%的地表径流流失了58.0%的TN, 57.0%的DN, 58.5%的NN, 79.0%的AN, 62.0%的TP, 63.5%的DP和60.0%的PP,控制初期地表径流对降低入库径流养分具有重要作用.

Dynamic Process of Nitrogen and Phosphorus Export and Loss Load in an Intensive Orchard with Ridge and Furrow Plantation in the Three Gorges Reservoir Area

To comprehend the runoff load of nitrogen (N) and phosphorus (P) and the impact on the receiving river in an agricultural area with an intensive orchard plantation and a longitudinal ridge and furrow morphology in the Three Gorges Reservoir Area, the runoff and N and P concentrations were dynamically monitored in a typical citrus orchard catchment in Wanzhou Country, Chongqing, China. The results showed that the nutrient concentration in runoff water from the intensive citrus planting catchment was very high. The average annual event mean concentrations (EMC) were 9.31 mg·L^-1 for total nitrogen (TN), 8.11 mg·L^-1 for dissolved nitrogen (DN), 5.66 mg·L^-1 for nitrate nitrogen (NN), 0.51 mg·L^-1 for ammonium nitrogen (AN), 0.87 mg·L^-1 for total phosphorus, 0.56 mg·L^-1 for solved phosphorus (DP), and 0.32 mg·L^-1 for particulate phosphorus (DP). In addition, the annual loss loads were 13.43, 12.20, 8.77, 0.75, 1.26, 0.84, and 0.42 kg·(hm²·a)^-1 for TN, DN, NN, AN, TP, DP, and PP, respectively. The annual average concentrations of TN and TP were 8.49 mg·L^-1 and 0.87 mg·L^-1, respectively, which exceeded the category V values of the surface water quality standards (GB3838-2002) by 4.25 times and 2.2 times, respectively, and also exceeded the internationally recognized thresholds for the eutrophication of waterbodies. The TN and TP loss load from storm runoff was one of the main reasons for the degradation of the river water quality, thus suggesting the need to treat surface runoff and control runoff nutrient losses, especially during the first storm events after fertilization. During two typical long-duration springtime rainfall events after fertilization, the loads of nitrate nitrogen (NN) and dissolved phosphorus (DP) were 4.94 kg·hm^-2 and 0.28 kg·hm^-2, respectively, which accounted for 92.90% and 64.69% of the total annual TN and TP loss loads, respectively. The loads of NN and DP in a short-duration high-intensity rainfall event were 0.52 and 0.05 kg·hm^-2 respectively, which accounted for 65.92% and 74.88% of the total annual TN and TP loss loads, respectively. The DN and DP were the main forms of nitrogen and phosphorus losses from the intensive citrus orchard with a longitudinal ridge and furrow morphology. Meanwhile, the catchment showed a significant first-flush phenomenon during a typical rainfall event, with a total of 58.0%, 57.0%, 58.5%, 79.0%, 62.0%, 63.5%, and 60.0% of the mass of TN, DN, NN, AN, TP, DP, and PP in the initial 20% of the runoff, respectively. Hence, controlling the surface runoff at the early runoff stage plays an important role in reducing nutrient losses.