One of the unique approaches the St. Johns River Water Management District takes to improve water quality in some central and northeast Florida lakes is removing bottom-feeding gizzard shad.
The District is conducting an experimental project in Newnans Lake east of Gainesville, and Alachua County recently posted a video about the process on its Web site. Details about the Newnans Lake project and gizzard shad removal in general are available on the District’s shad harvesting Web page.
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3 comments:
What are these bubbles and how much do they disterb? The sediment is so close to the surface, it cooks and makes gas bubbles. These bubbles must be re-animating total P and total N to a certain extent. Since it is so extensive It could be a major contributer, There is a greater probability more so than the shad.
http://www.youtube.com/watch?v=rXXjJfbSGmo
Mike,
Thanks for your comments.
Bubbles from organic sediments in water bodies such as Newnans Lake are produced by microbes in the sediments and can consist of a variety of gases, including methane, nitrogen and carbon dioxide. This bubbling activity can facilitate exchange between the sediments and lake water. Nitrogen bubbles are an important way to remove excess nitrogen from the lake.
The gizzard shad harvest is one way to reduce the exchange of nutrients between the sediments and lake water. Gizzard shad feed on organic matter in lake sediments, resuspending sediments in the lake water. After digesting the organic matter from the lake sediments, gizzard shad excrete a form of phosphorus into the water that is easily assimilated by phytoplankton that cause lake water to become murky and green rather than clear and tea-colored. Removing large numbers of gizzard shad from a lake can reduce resuspension of lake sediments and reduce recycling of nutrients from sediments.
Thanks Jeff for your helpful answer. I find the shad story a bit confusing though. Shad are filter feeders the second part of their life, but what they filter is algae from the water not from the sediment. The sediment would clog their filter system of a baleen type structure in their mouth. Besides algae needs light and could only grow on top of the sediment not mixed in as you imply. If I understand the species correctly, they filter feed in open water near the surface.
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