巢湖沿岸典型圩区油菜-小麦生长季营养盐输出特征

Nutrient Export from a Typical Polder Area Around Lake Chao During Rape and Wheat Growing Period

选择巢湖沿岸某典型圩区在油菜和小麦生长的秋、冬、春季,通过系统的野外调查、进排水观测、取样和室内水质分析,探讨圩区面源营养盐的输出特征。结果表明,圩区08-09季(2008年10月-2009年5月)和09-10季(2009年10月-2010年5月)2个油麦季降水量分别为412,704mm,排灌站总排水量分别为141,249mm,排水总氮浓度分别为0.7～17.0mg/L和0.9～33.3mg/L,总磷浓度分别为0.005～0.44mg/L和0.013～0.87mg/L,表现出比较大的变化幅度和年际差别,其流量加权平均浓度均超过了水体富营养化水平。氮的输出以可溶性无机氮(铵态氮和硝态氮)为主,其中硝态氮浓度高于铵态氮,可溶性磷占总磷比例年际差别较大。总氮与硝态氮表现出较一致变化规律,且其逐月变化与施肥较一致,而磷指标动态变化与磷肥的施用时间并不一致,这与输送过程中沟渠的滞留作用及磷的迁移转化有关。圩区沟渠水质空间变化表明减量化施肥对减少氮磷流失有一定的效果。08-09和09-10的2个油麦季总氮净输出通量分别为6.1,21.0kg/hm2,总磷的净输出通量分别为0.14,0.35kg/hm2,分别相当于氮、磷总施肥量的3.1%,10.5%和0.6%,1.4%。秋、冬、春季由于温度较低且并不是水体水华的爆发时期,但是由于油麦季长,排水营养盐浓度较高,营养盐净输出负荷大,大量的营养盐在受纳水体的累积作用对随后夏季巢湖水体富营养化的贡献不容忽视。可通过充分、合理地利用沟渠的滞留作用减少实际排入到受纳水体营养盐的总量。

This research intended to study nutrient export from a polder around Lake Chao, where agricultural activities dominant, during rape and winter wheat growing seasons from October to May of the next year. The outflow and inflow from and into the polder were measured and sampled, and the ditch water was also sampled to analyze for total nitrogen（TN）, ammonium（NH4＋ -- N）, nitrate（NO3 -- N）, total phosphorus （TP） and dissolved phosphorus（DP）. The results showed that there were totally 141, 249 mm outflow and 412, 704 mm of total precipitation for the 2008--2009（i.e. from Oct. 2008 to May 2009） and 2009--2010 （i. e. from Oct. 2009 to May 2010） seasons respectively. The inflow was very limited and could be neglected. The concentrations of TN varied between 0.7-17.0 mg/L, 0.9-33.3 mg/L, and the concentrations of TP varied between 0. 005-0.44 mg/L, 0. 013-0. 87 mg/L respectively for the 2008--2009 and 2009--2010 seasons, indicating great variation in terms of value ranges and interannual differences. Water flow weighted concentrations of TN and TP attained eutrophic-hypereutropic status. Nitrogen was mainly exported in dissolved forms（NH4＋ --N and NO]- --N）, of which NO[ --N demonstrated much higher level than NH4＋ --N. TN and NO;- --N fluctuated accordingly of which higher concentrations were usually observed after fertilization. That was not the case for phosphorus for which the ditch transport and retention processes might play a more important role. Nutrient production from fields to ditches might be abated under reduced fertilization. The net loads were 6. 1 kg/hm2and 0. 14 kg/hm2 （2008--2009） and 21.0 kg/hm2 and 0. 35 kg/hm2 （2009--2010） respectively for TN and TP during the two growing seasons, representing 3.1% and 0.6% （2008-- 2009） and 10. 5% and 1.4 % （2009 -- 2010） of nitrogen and phosphorus fertilizer input. Although algal blooms do not happen during the rape and wheat growing season because of the low temperature, the exported nutrients might be accumulated in the receiving water and are potential treats for eutrophication of Lake Chao in the following summer. Measures could be taken to make full use of the retention capacity of the drainage ditches inside the polder to reduce both concentration and loads of nutrient export.