黄河干流营养盐分布与变化趋势

河流是海洋获取陆源物质的主要途径,河流营养盐含量和结构的变化会对海洋生态环境产生重要影响。为了解黄河干流营养盐的基本情况及影响因素,于2012年7月(汛期)对黄河流域水体和土壤进行了综合调查,并结合历史资料分析了悬浮颗粒物和营养盐等的变化特征及对黄河物质输送的影响。结果表明:各参数受地势和人类活动的影响明显,表现出不同的分布特征。营养盐和悬浮颗粒物在上游浓度较低,在中游相对稳定,下游浓度有一定程度升高;相比于贵德而言,黄河利津段悬浮颗粒物、溶解硅和硝酸盐分别增加了近66%、60%和800%。磷限制是黄河营养盐限制的主要特征,且氮磷比呈升高趋势;与资料对比发现,黄河氮增加约1倍,硅下降60%后相对稳定,而磷略有下降。从目前分析看,支流与干流的氮营养盐构成有显著差异。在沿岸表层土壤营养盐含量较高的区域,河段内营养盐含量也较高。流域人类活动是黄河氮营养盐含量增加的重要因素;流域降水减少、水土保持等导致的物理侵蚀作用减弱是黄河硅和磷减少的重要因素;自1986年后,流域泥沙减少导致河流溶解硅降低了约34%,这值得进一步关注。

TREND AND DISTRIBUTIONS OF NUTRIENT ELEMENTS IN THE HUANGHE (YELLOW) RIVER

Rivers are the primary source of terrestrial materials to the oceans. The input of major biogenic nutrients (N, P, and Si) from land to sea plays a critical role in regulating global oceanic production. We studied nutrient distribution observed in July 2012 and historical data sets in the Huanghe (Yellow) River, focusing on nutrient transport and the influencing factors. Water chemistry parameters showed different distribution characteristics due to topography and human activities in the river reaches. In general, nutrients and suspended particulate matter concentration are low in the upper stream, and relatively stable in the middle and high in low streams of the river. The amounts of suspended particulate matter, nitrate, and dissolved silica were increased by 66%, 60%, and 800% at Lijin Station of the Huanghe River. The ratios of nitrogen and phosphorus showed a rising-up trend in the river. In addition, phosphorus limit is the main feature of nutrient limitation of the river. Human activities shall be responsible for nitrogen increase; and the decreases in precipitation caused less erosion and less silica and phosphorus in the river water. Since 1986, dissolved silicate has been decreased by about one third due to reduced basin sediment, which we should concern about in the future.