首页> 外文期刊>Ambio: A Journal of the Human Environment >Coastal Eutrophication Thresholds: A Matter of Sediment Microbial Processes
【24h】

Coastal Eutrophication Thresholds: A Matter of Sediment Microbial Processes

机译:沿海富营养化阈值:沉积物微生物过程的问题。

获取原文
获取原文并翻译 | 示例
       

摘要

In marine sediments, the major anaerobic mineralization processes are Fe(III) oxide reduction and sulfate reduction. In this article, we propose that the two alternative microbial mineralization pathways in sediments exert decisively different impacts on aquatic ecosystems. In systems where iron reduction dominates in the recently deposited sediment layers, the fraction of Fe(III) oxides that is dissolved to Fe(II) upon reduction will ultimately be transported to the oxic layer, where it will be reoxidized. Phosphorus, which is released from Fe(III) oxides and decomposing organic matter from the sediment, will be largely trapped by this newly formed Fe(III) oxide layer. Consequently, there are low concentrations of phosphorus in near-bottom and productive water layers and primary production tends to be limited by phosphorus (State 1). By contrast, in systems where sulfate reduction dominates, Fe(III) oxides are reduced by sulfides. This chemical reduction leads to the formation and permanent burial of iron as solid iron sulfides that are unable to capture phosphorus. In addition, the cycling of iron is blocked, and phosphorus is released to overlying water. Owing to the enrichment of phosphorus in water, the nitrogen: phosphorus ratio is lowered and nitrogen tends to limit algal growth, giving an advantage to nitrogen-fixing blue-green algae (State 2). A major factor causing a shift from State 1 to State 2 is an increase in the flux of labile organic carbon to the bottom sediments; upon accelerating eutrophication a critical point will be reached when the availability of Fe(III) oxides in sediments will be exhausted and sulfate reduction will become dominant. Because the reserves of Fe(III) oxides are replenished only slowly, reversal to State 1 may markedly exceed the time needed to reduce the flux of organic carbon to the sediment. A key factor affecting the sensitivity of a coastal system to such a regime shift is formed by the hydrodynamic alterations that decrease the transport of O_2 to the near-bottom water, e.g., due to variations in salinity and temperature stratification.
机译:在海洋沉积物中,主要的厌氧矿化过程是还原Fe(III)氧化物和硫酸盐。在本文中,我们提出沉积物中的两种替代微生物矿化途径对水生生态系统具有决定性的不同影响。在新近沉积的沉积层中铁还原起主要作用的系统中,还原时溶解到Fe(II)的部分Fe(III)氧化物最终将被运输到含氧层,在该层将被重新氧化。从Fe(III)氧化物中释放出来并分解沉积物中的有机物的磷将被新形成的Fe(III)氧化物层大量捕获。因此,在水底和生产水层中磷的浓度很低,初级生产往往受到磷的限制(状态1)。相反,在硫酸盐还原占主导的系统中,Fe(III)氧化物被硫化物还原。这种化学还原导致无法形成磷的固体硫化铁形式的铁形成并永久埋葬。此外,铁的循环受阻,磷释放到上方的水中。由于水中磷的富集,氮与磷的比率降低,氮趋于限制藻类的生长,从而有利于固氮蓝藻(状态2)。导致从状态1转换为状态2的主要因素是不稳定有机碳通向底部沉积物的通量增加。在加速富营养化时,当沉积物中的可用Fe(III)氧化物耗尽并且硫酸盐还原将占主导地位时,将达到临界点。由于Fe(III)氧化物的储备只能缓慢补充,因此还原为状态1可能会大大超过减少有机碳通向沉积物的通量所需的时间。影响沿海系统对这种状态变化的敏感性的关键因素是由流体动力学变化形成的,该流体动力学变化例如由于盐度和温度分层的变化而减少了O 2向近底部水的输送。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱:kefu@zhangqiaokeyan.com

京公网安备:11010802029741号 ICP备案号:京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有
  • 客服微信

  • 服务号