The Chesapeake Bay watershed explained

Droplets of rain can follow many routes after falling onto the Chesapeake Bay watershed and winding its way down to the Atlantic Ocean. The water may pass through forests, lawns, farmland, or sidewalks, joining with dissolved nitrogen, phosphorus, and sediment and playing host to phytoplankton – microscopic, free-floating, plant-like organisms that thrive in fresh, salt, and brackish water.

The Chesapeake Bay has grown cloudy in the past few decades – nitrogen, phosphorus, and sediment have been blamed for these changes. Their concentrations rose in the 1950s, 60s, and 70s due to developments and the evolution of the farming process. All these substances play a huge role in the natural functioning of the ecosystem and in small amounts can be harmless – but as they become more commonplace, scientists have noticed algal blooms, oxygen-deprived habitat, and dead zones are becoming more frequent and severe in the area.

While some algae blooms are subtle, the right mix of environmental conditions and species can turn stretches of water green, brown, or red. Their effects are more than just visually striking: several species release toxins which can kill fish and cause other severe damage to the ecosystem. The aerial photograph below, taken by Kimberly Reece of the Virginia Institute of Marine Science, shows tendrils of an algae bloom that discolored the water in the lower Chesapeake Bay on July 31, 2012.

Even non-toxic blooms can cause serious effects. When external conditions shift – such as a change in winds, cloudiness, or temperature – huge numbers of phytoplankton die, sink to the bottom of the Bay, and begin to decompose. This bacteria then sucks oxygen from the water, leaving it severely depleted. The lack of dissolved oxygen in turn kills off more marine life, an environment compared to that of the moon.

In the 1960s and 1970s the dead zones began disrupting Bay ecosystems. Populations of  fish, crabs, and other marine species were plummeted as once-thriving sea grasses withered away.

In an attempt to revive the Bay, a consortium of state and federal agencies, nonprofits, and private sector groups established the Chesapeake Bay Program. Since 1985, the group monitors the clarity and quality of water, tracks the size and scope of phytoplankton blooms, and studies the conditions surrounding the dead zones that emerge each year.

Because blooms and dead zones both are ephemeral and fast-changing, they are a challenge to study. Using the scientists’ current methods, it’s very difficult to discern bay-wide trends or large-scale patterns.

Despite promising results, there are still challenges in gathering data through remote sensing, with various natural occurrences disrupting the data. Scientists studying the area are eagerly awaiting the launch of a next-generation ocean-color sensor that they hope will give them a clearer picture of the goings-on under those murky waters.

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Credit: NASA