Editing Chesapeake Bay (section)

===Eutrophication and Hypoxia===
European settlers around the Chesapeake Bay in the late 17th and early 18th centuries brought with them industrial agricultural techniques. Land clearance and deep plowing of farmland increased sediment and nutrient loading into the bay, which continued to increase as the area continued to develop (Cooper & Brush 1991). 
[[File:MD State DO Map.jpg|thumb|Dissolved Oxygen Chesapeake Bay 2023]]
The sediment record of the Chesapeake Bay shows a major increase in nutrient levels, suggesting limited availability of oxygen, starting between the 17th and 18th centuries (Cooper & Brush 1991; Zimmerman & Canuel, 2002). The overloading of nutrients into the bay only continued to increase throughout the modern era. Recently deposited sediments in the Chesapeake Bay have 2–3 times greater amounts of organic carbon, and 4–20 times greater amounts of nitrogen and phosphorus input into the bay than the pre-colonial era (Cornwell et al., 1996; Fisher et al., 2006).
The nutrient runoff from land sources causes a huge increase in available nutrients in the water. Algae present in the bay take up those nutrients and rapidly reproduce in algal blooms. As algae sink to the bottom, they are decomposed, consuming oxygen (Long et al. 2014). In the Chesapeake Bay, seasonal stratification typically occurs between Spring and early Fall (Officer et al. 1984; Cerco & Noel 2007). More sunlight, higher temperatures, and less storms and winds during the summer cause strongly stratified water column, with a pycnocline typically 10 meters below the surface (Cerco & Noel; Seliger et al.). As oxygen is depleted from the decomposition of organic matter in bottom waters, but is not able to exchange gas with surface water due to a strong pycnocline, dissolved oxygen levels reach near zero by mid-June and can persist until October (Officer et al.). Organisms living in bottom waters may have some tolerance to hypoxia, but when events exceed their tolerance, ecologically and commercially important crabs, oysters, and mesoplankton become unhealthy and may experience die offs (Kirby & Miller; Officer; Kimmel).