Date created: Apr 21 2014 / Download
Up until 2013, submerged aquatic vegetation (SAV, also known as bay grasses) acreage totals for the Chesapeake Bay were aggregated into three zones: Upper Bay, Middle Bay and Lower Bay. For 2013, it was decided to report the totals by the four salinity zones found in the Bay: tidal fresh, oligohaline, mesohaline and polyhaline. Since different species of SAV are generally found in waters of a specific range of salinity, tracking changes in SAV abundance by salinity could help track changes in species abundance more easily.
Bay grasses, also known as submerged aquatic vegetation, are an integral part of the Chesapeake Bay ecosystem. Lee Karrh from the Maryland Department of Natural Resources (DNR) explains what bay grasses need to grow and why their survival is important to Bay critters.
Produced by Matt Rath
Music: “A Moment of Jazz” by Ancelin
What is submerged aquatic vegetation, and why is it important to the Chesapeake Bay? Commonly known as “bay grasses” they among the most critical inhabitants of the Bay’s ecosystem. Find out more about submerged aquatic vegetation, and see what people around Baltimore’s Belvedere Square had to say about it.
Produced by Matt Rath
Music: “Neapolitan song” by Astrid & Ruediger Kramer
“2 percenter” by Williamson
“All of Me” by Double F
Underwater grasses provide significant benefits to aquatic life and serve many critical ecological functions in the Bay and its tributaries, such as:
Scientists believe that having more grasses in the Bay and rivers will dramatically improve the entire ecosystem. The expectation is that as nutrient and sediment pollution decrease and water clarity improves, underwater grass acreages should expand. Experts closely monitor underwater grasses because their well-being is dependent on good local water quality. Therefore, their abundance is an excellent measure of the Bay’s health.
Long-term trend (1984-2013)
Short-term trend (2004-2013)
Change from previous year (2012-2013)
2013 Changes to Zones
When the annual Bay-wide aerial survey started in 1984, the Bay was divided into 3 geographic zones, based on prominent features:
These zones covered a wide range of salinities and didn’t account for underwater grass communities (groups of species).
It makes ecological sense then to report underwater grass acreages by each of these communities, which makes it easier to find patterns on how underwater grasses are growing.
Based on an analysis of the distribution and long-term trends of underwater grass species in Chesapeake Bay done by VIMS (Moore et al., 2000; Orth et al 2010) there are three or four distinct underwater grass communities that can be delineated by salinity range. These correspond roughly to the four salinity zones used in the Bay Program segmentation scheme (EPA, 2004),
These four salinity zones will be used to aggregate the segments in a manner that is more ecologically relevant.
*2013 Changes to Goals
The segment-specific goals associated with three previously reports geographic zones (upper, middle and lower bay) have been re-aggregated to the four new salinity zones.
Changes to Goals Expected in 2014
The CBP SAV workgroup is in the process of recommending changes to the segment-specific goals to align them with water quality standards adopted by Bay jurisdictions. This will result in revisions to the salinity zone goals and the baywide total goal.
Historic Bay Grass Data
Review of photographs from a number of sites dating back to 1937 suggests that close to 200,000 acres of bay grasses – also called submerged aquatic vegetation or SAV – may have once grown along the Bay’s shorelines. However, by 1984, bay grass acreage had fallen to a low of about 38,000 acres. More nutrient and sediment pollution in the water has choked or eliminated bay grasses in many areas, contributing to declines in SAV acreage throughout the Bay.
Collecting Bay Grass Abundance Data
The aerial SAV survey is flown from late spring to early fall. The photography is processed in the fall and winter, and preliminary area totals are usually available the following spring. Visit the Virginia Institute of Marine Science website for additional information about the aerial survey and for segment-specific survey results.
Setting Bay-wide Goals for Bay Grass Restoration
In 1993, the Bay Program agreed to work to restore bay grasses to historic levels. It set an interim restoration goal of 114,000 acres – the total area vegetated at one time or another since the early 1970s. Based on recovery rates at that time, the goal was expected to be achieved by 2005.
In the Chesapeake 2000 agreement, the Bay Program recommitted to the existing goal of protecting and restoring 114,000 acres of bay grasses. They also agreed to “revise SAV restoration goals and strategies to reflect historic abundance, measured as acreage and density from the 1930s to the present.”
In 2003, the Bay Program adopted the Strategy to Accelerate the Protection and Restoration of Submerged Aquatic Vegetation in the Chesapeake Bay. The strategy included a new Bay-wide restoration goal of 185,000 acres by 2010. This acreage represents approximate historic abundance from the 1930s to present.
Scientists believe that having more bay grasses in the Bay will dramatically improve the entire ecosystem. As nutrient and sediment pollution decreases and water clarity improves, bay grass acreage should expand.
Virginia Institute of Marine Science