闽江河口咸淡水混合过程中营养盐含量的变化特征

为研究闽江水体营养盐等物质的输运作用,于2009年11月(秋季),分3个航段(北支、南支及闽江河口区)同步对闽江下游及其河口区表、底层水的盐度、营养盐、悬浮物含量等进行观测,并在北支流、南支流交汇处的19站(罗星塔附近)进行了一个潮周期的连续观测.调查期间闽江表层水体中无机氮含量变化范围在0.640～3.873 mg/dm3之间,平均值为1.789 mg/dm3;活性磷酸盐含量变化范围在0.011～0.059 mg/dm3之间,平均值为0.027 mg/dm3;可溶性硅酸盐含量变化范围在0.82～7.10 mg/dm3之间,平均值为3.77 mg/dm3;总氮含量变化范围在0.67～3.91 mg/dm3之间,平均值为2.39 mg/dm3;总磷含量变化范围在0.027～0.289 mg/dm3之间,平均值为0.087mg/dm3.水体各营养盐含量的平面分布呈闽江北支流的含量均高于南支流,其高值区受陆源输入的影响集中出现在21～23号站区间.受城市污水影响的北支流水体与南支流水体交汇后,近海河段水体营养盐含量迅速降低.在一个潮周期内,涨潮时,随着外海水占比的提高,营养盐含量呈现随着盐度升高而逐步降低的趋势;在退潮时,陆源冲淡水的作用逐渐加强,营养盐在河口表现为随着盐度降低而逐步增高的趋势.闽江河口水体活性磷酸盐含量与盐度没有显著的相关性,为非保守要素;而无机氮、可溶性硅酸盐和总氮整体表现为保守要素.同时,发现在闽江河口盐楔端浊度最大值的"滤器"滞留区,总氮含量受其富集的影响在底层产生一个高值区.

Variation characteristics of nutrient content in the process of fresh and salt water mixing in Minjiang Estuary

In Nov.2009,3 surveys were carried out simultaneously in the north tributary（NT）,the south tributary（ST） and the estuary areas（ET） of Minjiang River.Salinity,nutrients,particulate matters and other factors were observed both in upper and bottom water.Moreover,a station（19#）,closer to Louxing Tower at the intersection of 3 tributary,was set for a tidal cycle observation.In the survey,inorganic nitrogen content were measured between 0.640～3.873 mg/dm3 with average 1.789 mg/dm3,labile phosphate content between 0.011～0.059 mg/dm3 with average 0.027 mg/dm3,silicate content between 0.82～7.10 mg/dm3 with average 3.77 mg/dm3,total nitrogen（TN） content from 0.67 to 3.91 mg/dm3 with average 2.39 mg/dm3,total phosphorus（TP）content from 0.027 to 0.289 mg/dm3 with average 0.087 mg/dm3.NT has higher nutrient concent than ST horizontally.However,NT was affected by terrestrial input at stations 21～23.After affected by urban sewage at the intersection of ST and NT,a rapid decay of nutrient content happened in river towards the sea.At high tide,nutrient content decreased due to intrusion of sea water.At low tide,the role of land source fresh water became strengthened.Therefore,the inorganic nutrients content trend to increase gradually.In Minjiang Estuary,there was no obvious correlation of phosphate content with salinity while phosphate appeared to be non-conservative for its buffer-based behavior.Inorganic nitrogen,silicate and TN behaved as conservative elements in the whole process.Around the tip of the salt wedge there is a distinct zone of estuarine turbidity maximum（ETM） and it is very likely that there existed an effective estuarine filter in the lower reach of Minjiang River,where it resulted in a high TN area in the underlying zone due to the filtering effect.