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Underwater Bay Grass Abundance in Four Salinity Zones

  • Tidal Fresh Salinity Zone: 13,990 acres in 2013 achieving 68 percent of zone goal.
  • Oligohaline Salinity Zone: 5,590 acres in 2013 achieving 54 percent of the zone goal.
  • Mesohaline Salinity Zone: 25,579 acres in 2013 achieving 21 percent of the zone goal.
  • Polyhaline Salinity Zone: 14,768 acres in 2013 achieving 44 percent of the zone goal.






SAV Salinity Zones

Map: SAV Salinity Zones

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.




May 05, 2011

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



May 05, 2011

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

Importance

Underwater grasses provide significant benefits to aquatic life and serve many critical ecological functions in the Bay and its tributaries, such as:

  • Providing shelter for young striped bass, blue crabs and other species
  • Improving water clarity by helping suspended sediment particles settle to the bottom
  • Adding oxygen to the water
  • Reducing shoreline erosion

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.

Goal

  • The goal for the tidal fresh salinity zone is 20,602 acres.*
  • The goal for the oligohaline salinity zone is 10,334 acres.*
  • The goal for the mesohaline salinity zone is 120,306 acres.*
  • The goal for the polyhaline salinity zone is 33,647 acres.*

Long-term trend (1984-2013)

  • Tidal Fresh Salinity Zone: increased from 6,911 to 13,990 acres.  Acreage has averaged 12,399 and ranged from 25,481 acres to 6,900 acres.
  • Oligohaline Salinity Zone: increased from 653 to 5,590 acres.  Acreage has averaged 6,680 and ranged from 13,919 acres to 653 acres
  • Mesohaline Salinity Zone: increased from 15,636 to 25,579 acres.  Acreage has averaged 27,851 and ranged from 48,444 acres to 15,636 acres
  • Polyhaline Salinity Zone: decreased from 15,027 to 14,768 acres.  Acreage has averaged 17,887 and ranged from 24,016 acres to 9,959 acres.

Short-term trend (2004-2013)

  • Tidal Fresh Salinity Zone: decreased from 14,464 to 13,990 acres.  Acreage has averaged 18,350 and ranged from 25,481 acres to 12,148 acres.
  • Oligohaline Salinity Zone: decreased from 13,616 to 5,590 acres.  Acreage has averaged 10,515 and ranged from 13,919 acres to 5,511 acres
  • Mesohaline Salinity Zone: decreased from 28,987 to 25,579 acres.  Acreage has averaged 25,359 and ranged from 31,268 acres to 19,251 acres
  • Polyhaline Salinity Zone: decreased from 15,879 to 14,768 acres.  Acreage has averaged 14,156 and ranged from 17,570 acres to 9,959 acres.

Change from previous year (2012-2013)

  • Tidal Fresh Salinity Zone: increased from 12,148 to 13,990 acres.
  • Oligohaline Salinity Zone: increased from 5,511 to 5,590 acres. 
  • Mesohaline Salinity Zone: increased from 19,619 to 25,579 acres.
  • Polyhaline Salinity Zone: increased from 10,917 to 14,768 acres.

Additional Information

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:

  • Above the Chesapeake Bay Bridge was zone 1
  • From the bridge to the mouth of the Potomac River was zone 2
  • Zone 3 was from the mouth of the Potomac River to the mouth of the Bay 

These zones covered a wide range of salinities and didn’t account for underwater grass communities (groups of species).

  • These communities change as salinity increases going from the head of rivers to the mouth of the Bay.  Just like you expect to find different species of fish as the water gets saltier, you find different species of plants as you go from the fresh water areas of the Bay to almost ocean-like saltiness. 
  • These various underwater grass communities respond differently over time and to specific events (storms, drought, heat etc).

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),

  • Tidal Fresh Salinity Zone (no salt)
  • Oligohaline Salinity Zone (slightly salty)
  • Mesohaline Salinity Zone (moderately salty)
  • Polyhaline Salinity Zone (very salty)

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.

Source of Data

Virginia Institute of Marine Science

410 Severn Avenue / Suite 112
Annapolis, Maryland 21403
Tel: (800) YOUR-BAY / Fax: (410) 267-5777
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