Turner R E, Rabalais N N, Swenson E M, Kasprzak M, Romaire T
Coastal Ecology Institute, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Mar Environ Res. 2005 Feb;59(1):65-77. doi: 10.1016/j.marenvres.2003.09.002.
An 18-year monitoring record (1978-1995) of dissolved oxygen within a region having hypoxia (dissolved oxygen less than 2 mgl(-1)) in the bottom layer was examined to describe seasonal and annual trends. The monitoring location was near or within a well-described summer hypoxic zone whose size has been up to 20,000 km(2). The monitoring data were used to hindcast the size of the hypoxic zone for before consistent shelfwide surveys started, and to predict it for 1989, when a complete shelfwide survey was not made. The concentration of total Kjeldahl nitrogen (TKN) in surface waters and concentration of bottom water oxygen were directly related, as anticipated if organic loading from surface to bottom was from in situ processes. The TKN data were used to develop a predictive relationship that suggested there was no substantial hypoxia before the 1970s, which was before nitrate flux from the Mississippi River to the Gulf of Mexico began to rise. The peak frequency in monthly hypoxic events is two to three months after both the spring maximum in discharge and nitrate loading of the Mississippi River. These results support the conclusion that persistent, large-sized summer hypoxia is a recently-developed phenomenon that began in the 1970s or early 1980s.
对某一区域（底层存在低氧现象，即溶解氧低于2毫克/升）1978 - 1995年长达18年的溶解氧监测记录进行了研究，以描述其季节性和年度变化趋势。监测地点位于一个描述详尽的夏季低氧区附近或区内，该低氧区面积曾达20000平方千米。监测数据用于在全陆架范围一致的调查开始之前推算低氧区的面积，并对1989年（当时未进行全陆架范围的完整调查）的低氧区面积进行预测。正如从表层到底层的有机负荷源自原地过程时所预期的那样，表层水中凯氏总氮（TKN）的浓度与底层水的氧浓度直接相关。利用TKN数据建立了一种预测关系，结果表明在20世纪70年代之前（即密西西比河向墨西哥湾的硝酸盐通量开始上升之前）不存在实质性的低氧现象。月度低氧事件的峰值频率出现在密西西比河春季流量最大值和硝酸盐负荷之后的两到三个月。这些结果支持了这样的结论：持续存在的大面积夏季低氧是一种始于20世纪70年代或80年代初的新近出现的现象。
