Although drought conditions ruled much of the Bay watershed though summer and early fall, figures from the U.S. Geological Survey show that the 12-month "water year" that ended Oct. 1 was almost the long-term average.
According to the USGS, the Bay's tributaries discharged an average of 79,500 cubic feet of water per second into the estuary during the water year. That was slightly more than the long-term average of 78,600 cubic feet per second.
The water year coincides with the annual hydrologic cycle. After dry summer months, streamflow typically increases from October until spring, when it begins a slow decline.
Although the 2007 water year was "average" overall, water flows were widely variable during the year. Except for February, freshwater flows were near or above average every month from October 2006 through April.
Flows were below average every month starting in May, reflecting a lack of rainfall that led to drought conditions in much of the watershed and near record-low stream flows in some areas.
Although scientists are still poring over this year's data, they say the varied weather brought mixed results for the Bay. Some of them include:
High spring flows and their associated nutrient concentrations led to an oxygen-starved dead zone in the deep portion of the Bay. The area of oxygen-depleted water disappeared in July-apparently because of strong winds-but rebounded in August and September. Overall, scientists say the summer dead zone will end up being the third smallest since monitoring began in 1985.
Water clarity was poor in many areas, and this year sparked a series of unusually intense algae blooms, many consisting of harmful species such as the potentially toxic Karlodinium. Scientists are still trying to understand what triggered so many blooms-many of which resulted in fish kills.
But they say it's likely the quick switch from wet to dry conditions in late spring may have prevented nutrients from being flushed from the tributaries where many blooms took place.
Underwater grasses are expected to increase slightly in the Bay. While poor water clarity hampered growth in many areas, water clarity in upstream tidal-fresh areas tended to be good and helped grass growth. Eelgrass in the lower Bay appears to be continuing its comeback in many areas after a die-off in 2005, although it still will not approach levels seen in past years.
Meanwhile, dry conditions are expected to remain at least for a while.
The National Oceanic and Atmospheric Administration's Climate Prediction Center in October predicted the southern half of the Bay watershed to be drier than normal through February. The northern half of the watershed had equal chances of being wet, dry or normal, according to the prediction center.
Temperatures are expected to be warmer than normal throughout the watershed.