What are they?
Submerged aquatic vegetation (often shortened to SAV) is plants that are always under water. The most common native species of SAV in the Hudson River watershed is water celery (Vallisneria americana), but other species include clasping leaved pondweed (Potamogeton perfoliatus), and such non-native plants as curly pondweed (Potamogeton crispus) and Eurasian water milfoil (Myriophyllum spicatum).
Why are they important?
SAV provides important habitat for juvenile fish that can hide within the leaves. Many tidal marshes and vegetated areas of the Hudson River are key nurseries for young fish, which may be more subject to predation in the open river. In addition to fish, SAV beds provide habitat for macroinvertebrates, and food for waterfowl, either by eating the plants themselves or eating the animals living in the plant beds. SAV is an important source of oxygen in the water, which aquatic animals need to survive and is used as a key measure of water quality.
A very common invasive species impacting SAV is water chestnut (Trapa natans), which can be seen in almost every freshwater, slow moving area of the Hudson River in the summertime. Water chestnut creates mats of leaves at the surface of the water, shading out native water celery below. The water underneath water chestnut beds are known to have much lower oxygen levels than other areas. While water chestnut does produce oxygen, they release it into the air through their leaves floating at the top of the water, instead of directly into the water like other aquatic plants would.
Where are they?
SAV beds cover varying amounts of area depending on where you are in the Hudson River. The maximum is from Kingston to Catskill, where SAV covers approximately 20% of the river. Maps of SAV from Hastings-on-Hudson to Troy have been made for the years 1997, 2002, 2007, and 2014, and the latter three inventories are available on the GIS Clearinghouse (see the "Links Leaving DEC's website" on the right sidebar). To map areas that have the potential to support SAV growth, all four inventories have also been combined into one "Hudson River Estuary Documented Submerged Aquatic Vegetation" map, also available on the GIS Clearinghouse.
How are they changing?
The location and amount of SAV beds can change year to year, with one of the most drastic observations occurring in the summer of 2012. Water celery was not found in areas where it was consistently observed in previous years. One possible cause for this decline is that the sediment pulse from Hurricane Irene and Tropical Storm Lee may have inhibited SAV growth by burying stems and blocking light when the paired storms came through the Hudson Valley in the late summer of 2011. Scientists have documented a return of native plant beds in recent years. This recovery will be quantified through the interpretation of 2016 aerial imagery. The resulting GIS maps, when completed by the end of 2018, will provide important additional information on the status and trends of SAV.
The SAV mapping project is funded by the Environmental Protection Fund.
How are we conserving them?
In addition to several regulations protecting SAV from disturbance, restoration planning efforts for the upper Hudson River estuary have focused on restoring lost SAV habitats. Shallow waters where SAV exist were dredged and filled from Catskill to Troy during the construction of the Federal Navigation channel. Nearly 4000 acres of shallows that may have supported SAV were destroyed. Current restoration planning efforts for the upper estuary are looking into opportunities to restore some of the shallows and SAV that have been lost.