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Chesapeake Bay water quality improvements hit wall

February 2, 2023

Nutrient reduction threshold slows rehabilitation.

According to the University of Maryland’s Center for Environmental Science researchers, rehabilitation of the Chesapeake Bay may require twice as much effort to respond to nutrient load changes after reaching a certain threshold of nutrient reductions.

The new study of water quality over time revealed the estuary’s historical response to nutrient reduction efforts and persistent challenges. Professor and co-author Ming Li said that once the threshold is crossed and “the system enters a eutrophic state, it will take (a) much larger reduction to return to the original state.”

The analysis “may partly explain the modest reduction in Chesapeake Bay hypoxia since the implementation of nutrient management strategies in the mid-1980s,” commented Li.

Excess nutrient management try to minimize hypoxia, or low-oxygen zones, that primarily result from agriculture runoff and wastewater effluent. Examination of pollution control strategies was outside the scope of this study.

This study examined the 39-year expansion of dead zones, from 1950 to 1989 when the amount of nitrogen pollution in the Chesapeake Bay doubled. Previous analysis showed that the large expansion of hypoxia between the 1950s and the 1980s correlated with increased nutrient pollution from rivers.

Habitat degradation on the bottom of the Chesapeake Bay may have changed the estuary’s capacity to filter nutrients and sediment. (Temperature) warming, sea level rise, changing precipitation patterns and river flows — together with associated changes in runoff — may alter key baselines impacting the functioning of coastal systems and their responses to excess nutrients, observe the study’s authors.

“Looking into the future, nutrient reduction strategies will need to be considered in the face of accelerated warming and sea level rise,” said Li.