School of Natural Resources & Environment, University of Michigan, Ann Arbor, Michigan 48109-1041, United States.
Environ Sci Technol. 2012 May 15;46(10):5489-96. doi: 10.1021/es204481a. Epub 2012 May 1.
Stratification and nutrient loading are two primary factors leading to hypoxia in coastal systems. However, where these factors are temporally correlated, it can be difficult to isolate and quantify their individual impacts. This study provides a novel solution to this problem by determining the effect of stratification based on its spatial relationship with bottom-water dissolved oxygen (BWDO) concentration using a geostatistical regression. Ten years (1998-2007) of midsummer Gulf of Mexico BWDO measurements are modeled using stratification metrics along with trends based on spatial coordinates and bathymetry, which together explain 27-61% of the spatial variability in BWDO for individual years. Because stratification effects explain only a portion of the year-to-year variability in mean BWDO; the remaining variability is explained by other factors, with May nitrate plus nitrite river concentration the most important. Overall, 82% of the year-to-year variability in mean BWDO is explained. The results suggest that while both stratification and nutrients play important roles in determining the annual extent of midsummer hypoxia, reducing nutrient inputs alone will substantially reduce the average extent.
分层和营养物负荷是导致沿海系统缺氧的两个主要因素。然而，当这些因素在时间上相关时，很难将它们的单独影响隔离和量化。本研究通过使用地质统计回归，根据分层与底层水溶解氧（BWDO）浓度的空间关系，确定分层的影响，为解决这一问题提供了一种新方法。利用与空间坐标和水深相关的趋势，对 10 年（1998-2007 年）墨西哥湾盛夏 BWDO 的分层指标进行建模，这些指标可以解释个别年份 BWDO 空间变异性的 27%-61%。由于分层效应仅能解释 BWDO 年均值变化的一部分，其余变化由其他因素解释，其中 5 月硝酸盐加亚硝酸盐河浓度最为重要。总体而言，82%的 BWDO 年均值变化可以得到解释。结果表明，尽管分层和营养物在确定盛夏缺氧的年度范围方面都起着重要作用，但单独减少营养物的输入将大大降低平均范围。
