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Rainfall

• Rainfall affects the volume of water flowing into the Bay – or river flow – from its many freshwater streams and rivers.
• River flow impacts the amount of pollution delivered to the Bay, the saltiness of Bay waters, and the vertical mixing of oxygen rich surface waters with deeper waters of the Bay.
• As river flow increases, its potential to carry increased pollutants from the watershed increases as well.
• River flow is generally fast moving and turbulent, mixing the Bay's waters and capturing oxygen from the air.
• Runoff from winter and spring rains deliver loads of sediment and nutrient pollutants to the Bay that drive summer water quality conditions in the Bay. Past observations reveal that summer weather conditions also contribute to summer water quality when intense storms increase erosion, which contributes to poor water clarity and adds to the existing nutrient load in the Bay.
• Not all rain water “runs off” the land. Some water seeps into the soil, carrying nutrients into groundwater. The travel time of nutrients through the watershed ranges from weeks to centuries. This can result in a “lag time” between implementing management actions and improvements in water quality.

Temperature:

• Changes in water temperature influence when plants and animals feed, reproduce, move locally or migrate. Temperature plays a critical role in determining the amount of dissolved oxygen in the Bay's waters. High water temperatures may also affect underwater grass beds.
• Temperature dramatically changes the rate of chemical and biological reactions within the water. Because the Bay is so shallow, its capacity to store heat over time is relatively small. As a result, water temperature fluctuates throughout the year, ranging from 34 to 84 degrees Fahrenheit. These changes in water temperature influence when plants and animals feed, reproduce, move locally or migrate.
• The temperature profile of the Bay is fairly predictable. During spring and summer, surface and shallow waters are warmer than deeper waters, creating two distinct temperature layers. The turbulence of the water can help to break down this layering. In autumn, fresher surface waters cool faster than deeper waters and sink. Vertical mixing of the two water layers occurs rapidly, usually overnight. This mixing moves nutrients up from the bottom, making them available to phytoplankton and other organisms inhabiting upper water levels. This turnover also distributes much-needed dissolved oxygen to deeper waters. During the winter, water temperature is relatively constant from surface to bottom.
• Temperature plays a critical role in determining the amount of dissolved oxygen in the Bay's waters. The colder the water, the more oxygen it can hold. Therefore, the waters of the Chesapeake Bay have a greater capacity to hold dissolved oxygen during the cold winter months than they do during the summer months.
• High water temperatures may affect underwater grass beds. Last year, warmer than average water temperatures may have caused the large scale loss of eelgrass in Tangier Sound. And while high temperatures can negatively affect SAV, they aid in the growth of something not so desirable: algae. These tiny plants flourish in the hot summer sun, soaking up rays and nutrients, but often multiplying to unhealthy proportions. These harmful algae blooms can block out sunlight needed by SAV, or produce toxins that kill fish and sicken humans.

Wind

• Wind also plays an important role by mixing the surface of the water and increasing oxygen levels in the Bay.
• Just as circulation moves much-needed blood throughout the human body, circulation of water transports plankton, fish eggs, shellfish larvae, sediments, dissolved oxygen, minerals and nutrients throughout the Bay. Circulation is driven primarily by the movements of freshwater from the north and saltwater from the south. Circulation causes nutrients and sediments to be mixed and resuspended. This mixing creates a zone of maximum turbidity that, due to the amount of available nutrients, is often used as a nursery area for fish and other organisms.
• Weather can disrupt or reinforce this two-layered circulation pattern. Wind plays a role in the mixing of the Bay's waters. Wind also can raise or lower the level of surface waters and occasionally reverse the direction of flow. Strong northwest winds, associated with high-pressure areas, push water away from the Atlantic Coast , creating exceptionally low tides. Strong northeast winds, associated with low-pressure areas, produce exceptionally high tides.

Peter Tango at 800-968-7229 ext. 875