Historical Analysis of Submerged Aquatic Vegetation (SAV) in the Potomac River and Analysis of Bay-wide SAV Data to Establish a New Acreage Goal : Final Report

Throughout most regions of the Chesapeake Bay and its tributaries both direct and anecdotal evidence has indicated that large-scale declines of submerged aquatic vegetation (SAV) occurred in the late 1960s and early 1970s (Orth and Moore 1983). These declines have been related to increasing amounts of non-point inputs of nutrients and sediments in the bay system resulting from development of the bay’s shorelines and watershed (Twilley et al. 1985). Currently there are approximately 89,659 acres of SAV in Chesapeake Bay (Orth et al. 2003). Although it has been estimated that this is approximately 15% of the bay’s historical SAV distribution, most comprehensive analyses have been based on 1971 or later aerial photography and the distributions of SAV prior to this time in many regions are not well known. SAV is a highly valuable resource and its presence serves as an important indicator of local water quality conditions (Dennison et al. 1993). SAV growth and survival can be decreased by high levels of turbidity and nutrient enrichment. Because SAV beds are non-motile, their presence serves as an integrating measure of variable water quality conditions in local areas (Moore et al. 1996). Because of the direct relationships between SAV and water quality, trends in the distribution and abundance of SAV over time are also very useful in understanding trends in water quality. Review of photographic evidence from a number of sites dating back to 1937 suggests that SAV, once abundant throughout the Chesapeake Bay system, have declined from historical levels and therefore water quality conditions may have similarly deteriorated (Orth and Moore 1983)