Drier-than-normal conditions set the stage for improved water quality and the rebound of key habitats in the Chesapeake Bay last year, according to a new Bay Program report.

The annual "Bay Barometer," which scores the status of the Bay's health and its restoration efforts based on a variety of indicators, said those efforts had achieved 45 percent of their goal for restoring the Bay.

That score was based on 2009 actions and conditions, and represented a 6 percent increase from 2008.

Water clarity goals were achieved in 26 percent of the Bay, a 12 percent increase from the previous year.

That helped underwater grass beds-critical habitats for many species-expand by more than 9,000 acres. In 2009, underwater grasses covered 85,899 acres, the second greatest amount since annual monitoring began in 1983. Still, that's just 46 percent of the Baywide restoration goal for underwater grasses.

Similarly, the benthic communities on the bottom of the Bay achieved 56 percent of their goal, improving 15 percent over 2008.

In other good news, the Baywide blue crab population, apparently responding to recent management efforts aimed at controlling the harvest, rebounded to 223 million adult crabs in 2009, the highest number since 1993. Striped bass populations remained strong.

In the watershed, 772 miles of forest buffers were planted along waterways last year, mostly in Pennsylvania, and 132,873 acres of land were permanently protected. But the health of watershed streams provided a mixed story: of 10,452 sampling locations around the watershed, 5,459 revealed very poor or poor conditions while the rest were in fair, good or excellent health.

Tempering the Bay uptick, though, is the fact that much of the water quality-related improvements are likely the work of Mother Nature. While rainfall levels were high in much of Maryland and Virginia last year, conditions were drier north of the Mason-Dixon Line, where the Susquehanna watershed contributes about half of the freshwater reaching the Bay.

As a result of those dry conditions, many of the nutrients and sediment that contribute to poor water quality remained on the land rather than having the rain flush them into streams and the Bay. Many of those nutrients could still find their way to the Bay in future years.

In the Bay, nitrogen and phosphorus spur algal blooms, which block sunlight needed by underwater grasses and bottom-dwelling organisms, which often die. As the algae die, they sink to the bottom and are decomposed in a process that draws oxygen from the water, rendering some areas a lifeless "dead zone." Sediment also clouds the water and, when it settles, smothers bottom habitats such as oyster bars.

The Bay Program estimates that about 240 million pounds of nitrogen entered the Bay last year, a drop of 43 million pounds from 2008. The change appeared to be driven largely by rainfall: Flows into the Bay decreased by 17 percent during the year, corresponding with the 15 percent decrease in nitrogen loads.

The report showed only a 3 percent improvement in nutrient reduction efforts during the year, and most of that came from upgrades at water treatment plants.

Rich Batiuk, the Bay Program's associate director for science, said the report shows that when nutrients are reduced in the Bay, its water quality and habitats will rebound.

But he said that more nutrient reductions are needed to ensure that the Bay isn't overwhelmed by nitrogen and phosphorus when riverflow conditions are normal.

"We are not on track right now, given our pollution reductions, to get to the goals we are establishing," Batiuk said. "Clearly, the rate of reducing pollution is, perhaps keeping up with population, but not doing a lot more than that."

That was echoed by Beth McGee, senior scientist at the Chesapeake Bay Foundation. Although some of the Bay improvements are "encouraging," she cautioned that states "need to ramp up and accelerate pollution reduction activities" to meet pollution reduction goals.

A series of four consecutive dry years from 1999 through 2002-which produced drought conditions in some parts of the watershed-also produced some of the best water quality seen in the Bay for decades. But a series of high flow years, driven in part by several hurricanes, erased many of those improvements between 2003-05 before the current drier-than-normal period set in.

In decades past, a vast network of nutrient-absorbing forests, wetlands, floodplains and other features helped to hold back rainfall, giving it a chance to sink into the groundwater rather than be flushed -with its load of nutrients-into the Bay.

Today, Batiuk said, efforts need to continue to restore the hydrologic system that helped protect the Bay from weather extremes, such as planting streamside buffers, restoring wetlands or even establishing green roofs in cities.

"We can do everything we want on the land, in the air or at the end of a sewage treatment pipe, but if we don't build that resilience back along the lines that Mother Nature was doing, we are just not going to get there."

The Bay Barometer can be found on the Bay Program website, www.chesapeakebay.net.