Some worthwhile reading:
http://pubs.usgs.gov/circ/1306/pdf/c1306_ch6_c.pdf
http://www.masgc.org/pdf/bab/hmr/Hall.pdf
http://www.wlf.louisiana.gov/sites/d...kish_marsh.pdf
http://dnr.louisiana.gov/index.cfm?m...p=home&pid=297
Plant diversity and soil organic matter content are higher in brackish marsh than in salt marsh. Brackish marsh is typically dominated by Spartina patens (marshhay cordgrass). Other significant associated species include Distichlis spicata (salt grass), Schoenoplectus olneyi (three-cornered grass), S. robustus (salt marsh bulrush), Eleocharis parvula (dwarf spikesedge), Ruppia maritima (widgeon grass), Paspalum vaginatum (seashore paspalum), Juncus roemanianus (black rush), Bacopa monnieri (coastal water hyssop), Spartina alteriflora (smooth cordgrass), and S. cynosuroides (big cordgrass). Two other major autotrophic groups in brackish marsh are epiphytic algae and benthic algae. Generally speaking, vertebrate species population levels are higher in brackish marsh compared to Salt Marsh. Brackish marsh is of very high value to estuarine larval forms of marine organisms such as shrimp, crabs, menhadden, etc. (See Salt Marsh for other functions). Brackish marsh salinity averages about 8 ppt. This community may be changed to another marsh type by shifts in salinity. Intrusion of salt water from the Gulf of Mexico up numerous waterways exerts a major influence in the configuration of the various marsh types. from
http://www.wlf.louisiana.gov/sites/d...kish_marsh.pdf
After some research, my view is that keeping the weirs open all the time is most likely trading good long term productivity of the brackish marshes they protect for increased short term productivity. The marshes behind the weirs need to be maintained as brackish marshes by keeping the weirs closed most of the time when salinity levels on the lake side are too high. If the marshes behind the weirs are allowed to change into salt marshes through increased saltwater intrusion, their potential productivity will be greatly reduced.
This is an area where it is clear that wildlife management is not a zero sum game. Wise management (protecting the brackish marsh) will maintain ecosystem productivity for years to come. Unwise management (keeping the weirs open) will provide higher satisfaction for a year or two or three, but is ultimately degrading a valuable natural resource that will hurt productivity.
The current management scheme of the weirs seems scientifically sound and data driven.