Nature of phosphorus limitation in the ultraoligotrophic eastern Mediterranean

Phosphate addition to surface waters of the ultraoligotrophic, phosphorus-starved eastern Mediterranean in a Lagrangian experiment caused unexpected ecosystem responses. The system exhibited a decline in chlorophyll and an increase in bacterial production and copepod egg abundance. Although nitrogen and phosphorus colimitation hindered phytoplankton growth, phosphorous may have been transferred through the microbial food web to copepods via two, not mutually exclusive, pathways: (i) bypass of the phytoplankton compartment by phosphorus uptake in heterotrophic bacteria and (ii) tunnelling, whereby phosphate luxury consumption rapidly shifts the stoichiometric composition of copepod prey. Copepods may thus be coupled to lower trophic levels through interactions not usually considered.     

肯尼亚水稻土和甘蔗地土壤中~(14)C-六氯苯和~(14)C-滴滴涕的自然消解

氯代持久性有机污染物的农田土壤污染呈现污染浓度低、面积大、新源污染不断输入的特点。农田土壤本身微生物种类丰富,对氯代有机污染物具有较大的降解潜力和未知性。本试验以典型高氯代和低氯代持久性有机污染物——六氯苯(HCB)和滴滴涕(DDT)为研究对象,结合~(14)C同位素示踪技术,研究HCB和DDT在热带水稻土和甘蔗地土壤的矿化现象,同时监测HCB和DDT在两种土壤中的挥发、降解产物以及结合残留。结果表明,经84 d好氧培养,HCB和DDT在两种土壤中的矿化量分别仅为0.14%和3%,低氯代有机污染物DDT的矿化速率显著高于高氯代有机污染物HCB。然而,两种土壤对HCB或DDT的矿化没有显著性差异。HCB或DDT在水稻土中的挥发量略微高于甘蔗地土壤,两种土壤中HCB和DDT的挥发量在0.1%~0.6%之间,表明挥发不是其主要的环境过程。在DDT污染水稻土和甘蔗地土壤中添加1.25%的堆肥增加了DDT在土壤中的矿化与结合残留,减少了DDT的挥发。本研究结果表明土壤在好氧条件下对氯代持久性有机污染物的自然消解能力非常弱,而有机肥的使用有助于土壤中持久性氯代有机污染物的矿化消除。