Oxygen deficiencies in the Schelde and Elbe estuary: same difficulties, different causes

The expansion of oxygen minimum zones (OMZ’s) in estuaries, sometimes also referred to as ‘dead zones’, is catastrophic for ecology and economy (e.g. Diaz, 2001; Conley et al., 2009). At low oxygen levels, benthic invertebrates and fish are physiologically stressed (e.g. Vaquer-Sunyer & Duarte, 2008) while estuarine biogeochemistry is drastically changed (e.g. Middelburg & Levin, 2009). In the Elbe Estuary a minimum oxygen zone can be found around 50km downstream the weir at Geesthacht (Amann et al., 2012), while in the Schelde two minimum oxygen zones can be found, one around 20km downstream the sluice of Merelbeke, and another one around 70km downstream the sluice (Soetaert et al., 2006).