What are the most harmful pollutants to the Bay?
The current degraded state of water quality and living resources in the Chesapeake Bay can be attributed to over enrichment of nutrients (nitrogen and phosphorus), an excess amount of sediment and the presence of toxic substances like heavy metals in sediments in localized areas such as Baltimore Harbor and the South River.
All of the plants and animals that inhabit the Bay’s waters need a certain amount of nutrients to live and reproduce. However, problems occur when more nutrients are present than can be moved up the food chain from microscopic plants (algae) that consume them, to microscopic animals and filter feeders such as oysters and menhaden that feed on the algae.
When algae are present in excess of what can be consumed, large algae blooms can form that reduce the depth to which sunlight can penetrate the water. Reduced light penetration makes it difficult for underwater grasses to grow. When algae die in large numbers and settle to the bottom of the Bay they decompose and consume oxygen needed by crabs, oysters and fish, which can result in fish-kills. Sediment is harmful because it reduces light available for grasses and can smother bottom dwelling organisms like oysters and clams.
The Maryland Department of Natural Resources has monitored nutrients, sediments, chlorophyll (a measure of algal density), dissolved oxygen and water clarity in the Bay and its tributaries since the mid-1980s. These data are displayed, in real time, on the Department’s “Eyes on the Bay” web site: http://mddnr.chesapeakebay.net/eyesonthebay/index.cfm