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Bay Blog: river flow

Jun
14
2011

Scientists predict moderate to poor oxygen levels in Chesapeake Bay

The Chesapeake Bay is expected to have moderate to poor dissolved oxygen conditions during the early part of the summer, according to a team of scientists with Chesapeake Eco-Check.

The early summer dissolved oxygen forecast (called an “anoxia forecast”) is based on nitrogen loads to the Bay during winter and spring, as well as high river flow in May due to heavy rainfall. According to scientists, the Bay’s 2011 low-oxygen area – commonly called the “dead zone” – could be the fourth-largest since 1985.

The annual summer ecological forecast uses data such as nitrogen loads, wind direction and sea level to predict dissolved oxygen levels in the Bay’s mainstem. The forecast is split into early summer (June to mid-July) and late summer (mid-July to September) because scientists have observed a significant change in oxygen levels following early summer wind events.

The forecast is supported through research at the Chesapeake Bay Program, Johns Hopkins University, Old Dominion University, and the University of Maryland Center for Environmental Science Horn Point Lab.

For more information about the dissolved oxygen forecast, visit Chesapeake Eco-Check’s website.



May
09
2011

Health of Chesapeake Bay's streams and rivers slowly improving, but still degraded in many areas

Nutrient pollution in the majority of the Chesapeake Bay region’s freshwater streams and rivers has decreased over the last 25 years, according to data from scientists with the U.S. Geological Survey (USGS) and the Chesapeake Bay Program.

Almost 70 percent of the watershed’s 32 monitoring locations show decreasing nitrogen and phosphorus levels, meaning fewer of these harmful nutrients are entering the Chesapeake’s local waterways. Approximately 40 percent of the sites show decreasing trends for sediment pollution.

Although this data may indicate long-term improvements in the health of the Bay’s streams and rivers, pollution loads to the Bay were higher in 2010 due to more rain, snow and river flow.

“These long-term trends indicate that pollution reduction efforts, such as improved controls at wastewater treatment plants and practices to reduce nutrients and sediment on farms and suburban lands, are improving water quality conditions in many areas,” said USGS scientist Scott Phillips. “However, nutrients, sediment and contaminants will need to be further reduced to achieve a healthier Bay and streams.”

Each day, billions of gallons of fresh water flow through thousands of streams and rivers that eventually empty into the Bay. This fresh water is known as “river flow.” In general, as river flow increases, more nutrient and sediment pollution is carried downstream to the Bay. Pollution levels in rivers vary greatly from year to year because they are influenced by rainfall. Scientists make adjustments to remove the effects of weather variations, allowing consistent measurement of pollution levels over time and better evaluation of long-term changes.

In the 2010 water year (October 2009-September 2010):

  • Average river flow was 52 billion gallons per day. This is 11 billion gallons per day more than in 2009.
  • Approximately 278 million pounds of nitrogen reached the Bay. This is 43 million pounds more than in 2009.
  • Approximately 16 million pounds of phosphorus reached the Bay. This is 7 million pounds more than in 2009.
  • Approximately 9 million tons of sediment from non-tidal rivers reached the Bay. This is a 7 million ton increase from 2009. Two large runoff events in January and March of 2010 in the Potomac River basin are believed to have generated this sediment load, which is one of the highest in the last 20 years.

The Bay Program’s goal is to have a long-term average of 186 million pounds of nitrogen and 12.5 million pounds of phosphorus entering the Bay from streams and rivers.

In a different, shorter-term study conducted between 2000 and 2008, the health of individual freshwater streams across the watershed showed mixed conditions. Of the 7,886 stream sites sampled, more than half (55 percent) were found to be in very poor or poor condition. The remaining 45 percent were found to be in fair, good or excellent condition.

This study uses data on the tiny, bottom-dwelling creatures that live in freshwater streams and rivers as an indicator of overall stream health. This method provides a uniform evaluation of the health of local waterways across state lines and throughout the entire Bay watershed.

The USGS estimates how much river flow enters the Bay each year, monitors pollution loads in the Bay’s major rivers, and works with the Bay Program to estimate how much pollution reaches the Bay. To learn more about the USGS’s Chesapeake monitoring activities, visit http://chesapeake.usgs.gov.



Apr
27
2011

Chesapeake Bay health receives C-minus on latest report card

The Chesapeake Bay has received a C-minus on the University of Maryland Center for Environmental Science’s (UMCES) 2010 Bay Health Report Card. The 2010 grade is a 4 percent decrease from 2009, when the Bay’s health received a C.

Higher rainfall – which led to increased stormwater runoff from the land – drove down scores for water quality and biological heath indicators. Researchers believe that two closely timed, large-scale weather events in winter 2010 played a role in the decrease.

The Bay’s health is affected by many factors, including human activities and natural variations in rainfall, which is the major driver of runoff from farms, cities and suburbs. Even as pollution is reduced, higher rainfall and associated runoff can mask the effects of these improvements.

“One of the main drivers of annual conditions in Chesapeake Bay is river flow related to weather patterns,” said UMCES-EcoCheck scientist Dr. Heath Kelsey. “While efforts to reduce pollution have been stepped up in recent years, nature overwhelmed those measures in 2010 and temporarily set the Bay back a bit.”

The declines are the first observed since 2003 and are on par with conditions observed in 2007. Annual weather-related variability in scores, even as more pollution-reduction measures are put into place, is to be expected in a highly complex ecosystem like the Bay, according to Dr. Kelsey.

Overall, the Lower Bay’s health score stayed relatively steady from 2009, while the Mid- and Upper Bay regions declined slightly. Results were fairly consistent in that declines were seen in most indicators.

  • Grades improved in just two reporting regions: Virginia’s James and York Rivers.
  • Scores declined in nine regions: Lower Eastern Shore (Tangier Sound), Maryland’s Lower Western Shore, Mid Bay, Patapsco & Back Rivers, Potomac River, Rappahannock River, Upper Bay, Upper Eastern Shore and Upper Western Shore regions.
  • For the first time since 1996, two regions scored an F: the Patapsco and Back Rivers and Lower Western Shore (Maryland) regions.

The report card, based on data collected by state and federal agencies through the Chesapeake Bay Program, provides an independent analysis of Chesapeake Bay ecosystem health. It is expected that Bay Health Index scores will increase over time, as restoration and pollutant reduction activities are increased.

The report card analysis is conducted through the EcoCheck partnership between UMCES and the NOAA Chesapeake Bay Office. In addition to the Bay-wide reportcard, UMCES works with local watershed organizations to develop river-specific report cards to give residents a creek-by-creek look at their local waters.

For more information about the 2010 Chesapeake Bay Health Report Card, including region-specific data, visit the Chesapeake EcoCheck website.



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