Water clarity is a measure of how much light penetrates though the water column. Water clarity is dependent upon the amount of particles (e.g. suspended sediment and plankton) and colored organic matter present. Water clarity plays an important role in determining bay grasses and phytoplankton distribution and abundance.
Chesapeake Bay - Indicator Details:
Water clarity was measured at approximately 144 stations up to 14 times during the periods of interest (April to October in the tidal fresh, oligohaline and mesohaline regions, and March to November in the polyhaline regions). Secchi depth is the water depth (in meters) that you can just differentiate black and white quarters of a Secchi disc lowered into the water. The proportion of time that water clarity was below the threshold at each station was calculated and then interpolated to provide estimates between the stations.
This map shows average water clarity levels for Chesapeake Bay and the tributaries from March to September 2007. All Chesapeake Bay tributaries exhibited a gradient in water clarity, with lower water clarity (shallowest Secchi depth ? orange-pink shades) in the mid to upper reaches and clearer waters in the lower reaches (deeper Secchi depths ? shade of blue). The Bay's mainstem had a similar pattern, with lower water clarity in the Upper Bay and clearer water in the Mid and Lower Bay regions. Lower water clarity in the mid to upper reaches of the tributaries can, in part, be attributed to the mixing of fresh and saline waters leading to a phenomenon known as a turbidity maximum. While the bay wide patterns of water clarity in 2007 were similar to 2006, there are notable differences in many of the reporting regions. For example, the area of poor water clarity in the Lower Eastern Shore (Tangier) region was much larger in 2007 compared to 2006.
Water clarity was measured at approximately 144 stations up to 14 times during the periods of interest (April to October in the tidal fresh, oligohaline and mesohaline regions, and March to November in the polyhaline regions). Secchi depth is the water depth (in meters) that you can just differentiate black and white quarters of a Secchi disc lowered into the water. Average water clarity (Secchi depth) at each station was calculated and levels between stations were estimated using spatial interpolation software.
Comparison of Bay Health Index scores for 2007 () compared to ()
|0 20 40 60 80 100|
|Upper Eastern Shore|
|Upper Western Shore|
|Lower Western Shore (MD)|
|Lower Eastern Shore (Tangier)|
|Patapsco and Back Rivers|
This figure ranks each region from best to worst water clarity scores for 2007. Overall there was a slight improvement in water clarity in 2007, although this does not reverse the downward trajectory of the water clarity noted in many regions. The Choptank River and Upper Bay region had the highest water clarity score in 2007, while the Lower Eastern Shore, Elizabeth River, and the Patapsco and Back Rivers had the lowest (0).
This graph is dynamic, you can: a) show and hide items by clicking them in the legend, b) select year range (click and drag), and c) export as an image.
|Salinity Regime||Season||Relative Status Thresholds (m)*|
* Lacouture et al., Estuaries and Coasts (2006) & Buchanan et al., Estuaries (2005)