Abstract

Low primary production in the Bay of Bengal (BoB) could not be explained as this region receives nutrients from atmospheric deposition, rivers, eddies, and mixing due to depression/cyclones. In addition to nutrients, BoB also receives significant amount of suspended particulate matter (SPM) from the major rivers and their concentrations are in an order of magnitude higher than elsewhere in the open ocean region. Here we show that the removal of phosphorus (P) through adsorption on SPM may be a potential mechanism to decrease in primary production in the northern BoB. Significant fraction of P removal (5–50% of total dissolved inorganic phosphate) in association with SPM was observed in the BoB. The magnitude of removal of P through SPM is linearly related with dissolved inorganic phosphate (DIP), particulate organic carbon (POC) in the water column suggesting that P is removed in association with organic matter. The fraction of P removed from that of DIP showed inverse relation with salinity, and linear relation with SPM concentration suggesting that SPM brought by river discharge removed P from the water column. The P removed by SPM in the mixed layer showed inverse relation with mixed layer integrated primary production in the open sea region but its impact is negligible in the coastal waters. The laboratory experiment by measuring primary production in the presence of different quantities of SPM concentrations confirmed decrease in primary production due to removal of phosphate in the BoB.

Research highlights

• Significant fraction of phosphate adsorbs on to the suspended particles and it is bio-non-available.

• Phosphate severely controls primary production in the northern Bay of Bengal.

• The removal of phosphate is more in the coastal waters, it does not control primary production due to higher input than removal.

• High N/P ratios is caused by phosphate removed on association with suspended matter.

中文翻译：

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通过吸附在孟加拉湾的悬浮物上去除磷酸盐：可能对初级生产产生影响

摘要

孟加拉湾（BoB）的初级生产力低下是无法解释的，因为该地区从大气沉积，河流，涡流和低气压/旋风造成的混合中吸收了养分。除养分外，BoB还从主要河流中接收了大量的悬浮颗粒物（SPM），其浓度比公海地区其他地方高一个数量级。在这里，我们表明通过SPM吸附去除磷（P）可能是减少北部BoB初级生产的潜在机制。在BoB中观察到与SPM结合的P去除率很高（占总溶解无机磷酸盐的5-50％）。通过SPM去除P的幅度与溶解的无机磷酸盐（DIP）线性相关，水柱中的颗粒有机碳（POC）表明P与有机物一起被去除。从DIP去除的P含量与盐度成反比，与SPM浓度呈线性关系，这表明由河水排放带来的SPM从水柱中去除了P。SPM在混合层中去除的P与公海地区混合层综合初级生产成反比，但在沿海水域其影响可忽略不计。通过在不同数量的SPM浓度下测量初级生产的实验室实验证实，由于BoB中磷酸盐的去除，初级生产下降。与SPM浓度的线性关系表明，河流排放带来的SPM从水柱中去除了P。SPM在混合层中去除的P与公海地区混合层综合初级生产成反比，但在沿海水域其影响可忽略不计。通过在不同数量的SPM浓度下测量初级生产的实验室实验证实，由于BoB中磷酸盐的去除，初级生产下降。与SPM浓度的线性关系表明，河流排放带来的SPM从水柱中去除了P。SPM在混合层中去除的P与公海地区混合层综合初级生产成反比，但在沿海水域其影响可忽略不计。通过在不同数量的SPM浓度下测量初级生产的实验室实验证实，由于BoB中磷酸盐的去除，初级生产下降。

研究重点

• 大部分磷酸盐吸附在悬浮颗粒上，因此无法生物利用。

• 磷酸盐严重控制了孟加拉湾北部的初级生产。

• 磷酸盐在沿海水域的去除更多，由于投入比去除高，因此不能控制初级生产。

• N / P比率高是由于与悬浮物结合去除的磷酸盐引起的。