Univ. Bordeaux, EPOC, UMR 5805, F-33400 Talence, France.
Environ Sci Process Impacts. 2013 Mar;15(3):585-95. doi: 10.1039/c2em30874f.
Dissolved oxygen (DO) is a fundamental parameter of coastal water quality, as it is necessary to aquatic biota, and it provides an indication of organic matter decomposition in waters and their degree of eutrophication. We present here a 7 year time series of DO concentration and ancillary parameters (river discharge, water level, turbidity, temperature, and salinity) from the MAGEST high-frequency monitoring network, at four automated stations in the central and fluvial regions of the macrotidal Gironde Estuary, one of the largest European estuaries. The spatio-temporal variability of DO at different time scales was first related to the migration and position of the maximum turbidity zone in this extremely turbid estuary. Since 2005, the Gironde Estuary has recorded several borderline hypoxic situations (DO close to 2 mg L(-1)) and a 7 day-long hypoxic event (DO < 2 mg L(-1)) in July 2006. Summer hypoxia occurred exclusively in the fluvial, low salinity, and high turbidity sections of the estuary and was significantly more pronounced in front of the large urban area of Bordeaux (715 000 inhabitants). Detailed analysis of the data at the seasonal, neap-spring and semi-diurnal tidal time scales, reveals that hypoxia in this area occurred: (i) in the maximum turbidity zone; (ii) during the spring to neap tide transition; (iii) at highest water temperature; and (iv) at lowest river discharge; there was also evidence of an additional negative impact of sewage treatment plants of Bordeaux city. Enhancement of respiration by turbidity, temperature and inputs of domestic biodegradable organic matter and ammonia, versus renewal of waters and dispersion of reduced pollutants with the river discharge, appeared as the dominant antagonist processes that controlled the occurrence of summer hypoxia. In the context of long-term environmental changes (increase in temperature and population, decrease in summer river discharge), the occurrence of severe hypoxia could not be excluded in the next decades in the upstream reach of the Gironde Estuary.
溶解氧 (DO) 是沿海水质的基本参数，因为它对水生生物群系是必要的，并提供了水中有机物分解及其富营养化程度的指示。我们在这里介绍了来自 MAGEST 高频监测网络的 7 年 DO 浓度和辅助参数（河流流量、水位、浊度、温度和盐度）时间序列，该网络在吉伦特河口中部和河流区域的四个自动化站进行监测，吉伦特河口是欧洲最大的河口之一。首先，根据该极其浑浊的河口最大浊度带的迁移和位置，将 DO 的时空变化与不同时间尺度相关联。自 2005 年以来，吉伦特河口记录了几次边界缺氧情况（DO 接近 2 毫克/升）和 2006 年 7 月长达 7 天的缺氧事件（DO < 2 毫克/升）。夏季缺氧仅发生在河口的河流、低盐度和高浊度区域，在波尔多（715 000 名居民）的大型城市区域更为明显。在季节性、小潮和半日潮时间尺度上对数据进行详细分析，表明该区域的缺氧现象：(i) 在最大浊度带；(ii) 在小潮到大潮的过渡期间；(iii) 在最高水温时；(iv) 在最低河流流量时；波尔多城市污水处理厂的影响也有证据表明存在额外的负面影响。与河流流量更新水和分散还原污染物相比，浊度、温度和输入的可生物降解有机物质和氨的呼吸增强，似乎是控制夏季缺氧发生的主要拮抗过程。在长期环境变化（温度和人口增加，夏季河流流量减少）的背景下，在接下来的几十年中，吉伦特河口的上游区域可能会发生严重的缺氧现象。
