Geography, Trajectories, and Controls of Coastal Water Quality: More Rapid Improvement in the Shallow Zone of the Chesapeake Bay

Many coastal ecosystems
have suffered from cultural eutrophication
and dead zones. In the Chesapeake Bay, water quality degradation is
manifested in low dissolved oxygen, poor water clarity, and decreased
submerged aquatic vegetation acreage. This research combines long-term
monitoring data, science-based assessment methods, and novel data
analysis approaches (i.e., machine learning) toward understanding
the geography, trajectories, and controls of water quality in the
Chesapeake Bay, which provides an example for the assessment and management
of complex coastal ecosystems. Results showed that the attainment
of water quality standards has improved in both the deep zone and
the shallow zone since 1985, but the shallow zone has improved more
rapidly. In addition, the attainment trajectory has been affected
by mainly external drivers (i.e., nutrient reductions) and, to a lesser
extent, internal drivers (i.e., water temperature and stratification).
Reductions in nutrient loads would improve attainment, whereas warming
and stratification would decrease attainment. Furthermore, scenario
analyses demonstrated the importance of managing both nitrogen and
phosphorus loads. Overall, the deep zone and the shallow zone showed
different trajectories and controls, emphasizing the importance of
geographical targeting with management actions.