Freshwater from Louisiana’s proposed $800 million Mid-Breton Sediment Diversion might pose a big risk to oysters and different fisheries in Mississippi Sound, in response to a brand new examine commissioned by the Mississippi Division of Marine Sources.

When the diversion’s water is added to a median of Mississippi River, Lake Pontchartrain and different Mississippi coast rivers and bayous obtained from an 11-year document of water flows, salinity ranges in parts of the western Mississippi Sound close to Bay St. Louis the place oysters are grown drops to unsafe ranges for as a lot as 50 days or extra, stated Jerry Wiggert, lead writer of the examine, and affiliate director of the College of Southern Mississippi Faculty of Ocean Science and Engineering.

Oysters are usually in a position to tolerate salinity ranges of between 5 and 15 elements per thousand.

Nevertheless, the peer-reviewed examine carried out by Wiggert and different USM researchers was based mostly on Louisiana’s authentic plan for the diversion that referred to as for a most stream charge of 75,000 cubic toes per second. In 2021, the state introduced it was decreasing the diversion’s most stream to 50,000 cfs.

Wiggert stated his staff has not checked out that decrease most stream charge, however expects it might end in as a lot as 21 days of salinity ranges under 4 elements per thousand within the western sound, which might nonetheless be a risk to oysters.

The diversion can be constructed simply south of Wills Level on the east financial institution of the Mississippi River in Plaquemines Parish in hopes it can add 31 sq. miles of latest land in Breton Sound by the top of fifty years, with a key objective of decreasing the results of storm surge on the world’s east financial institution levee methods, along with including fish and wildlife habitat.

It’s one in all two large-scale diversions presently transferring towards development because the state seeks to gradual coastal land loss. The opposite, the Mid-Barataria Sediment Diversion on the alternative facet of the river at a price of greater than $2 billion, is predicted to start development later this yr.

The Mid-Breton diversion’s gates can be open when the Mississippi River’s stream at Belle Chasse reaches 450,000 cfs, and would attain its most stream when the river exceeds 1 million cfs. It could be anticipated to function for as a lot as 9 months in the course of the yr, although not often at its most stream. As much as 5,000 cfs would stream into the diversion channel when the gates are formally closed.

The Louisiana Coastal Safety and Restoration Authority, which might construct the diversion, stated that it deliberate to look into the USM examine, however expressed concern it was not contacted to assist design the mannequin utilized by the researchers or their investigation plans.

“There are key items of technical data we might have offered that will have improved the rigor of the modeling software and the ensuing evaluation, and that will have essentially altered the conclusions put ahead,” the assertion stated.

That included the decrease stream degree, which the state stated it had shared with Mississippi officers in conferences on the diversion.

“From the modeling that we’ve carried out in assist of the undertaking’s environmental affect assertion, salinity impacts are diminished considerably with that capability discount,” the assertion stated. “The USM examine additionally centered solely on modeling present circumstances, and didn’t think about the 50-year evaluation interval CPRA modeled for the undertaking, which is supposed to fight future points like saltwater intrusion and emergent wetland loss from rising sea ranges.”

Sea ranges alongside the Mississippi coast are anticipated to be at the least a foot greater on the finish of fifty years, which might seemingly enhance salinity of within the sound.

The report’s outcomes have prompted reactions from Mississippi Sound oyster growers and different fishers, and from Mississippi state officers.

“This proposed diversion is an ecological demise sentence,” stated Tac Carrere, govt director of the Mississippi Sound Conservancy, which represents quite a lot of fishery and different customers of the sound. “Having witnessed first-hand bodily the destruction to the Mississippi Sound that resulted from the Bonnet Carre Spillway opening, it’s utterly apparent how the proposed Breton Sound diversion if applied as deliberate might be catastrophic.”

Carrere stated Louisiana ought to refocus its funds to initiatives that construct new wetlands with dredged sediment.

Mississippi Secretary of State Michael Watson stated the examine reveals the necessity for the Corps to incorporate impacts to the Mississippi Sound in its environmental evaluation of the diversion and for representatives from his state to be concerned in figuring out what hurt it might trigger. However Watson additionally stated he acknowledged Louisiana’s want to contemplate constructing it.

“Due to the fragile steadiness present in our shared ecosystem with our neighbor, we will’t ignore the existential land-loss downside Louisiana is dealing with within the Mid-Breton Sound and Biloxi Marsh,” he stated in an announcement. “As wholesome marsh lands proceed to vanish throughout what’s left of the crow foot delta, we should decide what the long-term impacts to the (sound) might be when they’re gone. Whereas we now have proof of the detrimental impacts (the diversion) might have on the (sound) beneath the studied operational parameters, a course of no motion on Louisiana’s half might even have disastrous results on the Mississippi Gulf Coast.”

Wiggert stated his staff already is discussing extra mannequin runs utilizing the 50,000 cfs most now proposed by Louisiana.

The USM examine additionally checked out what impact working the diversion at most capability would have had in 2019, a yr with near-record stream down the Mississippi River that resulted within the Bonnet Carre Spillway being opened for a document 123 days. That yr, the utmost stream by Bonnet Carre was 207,000 cfs, greater than 4 instances the utmost stream of the diversion.

The eventual stream of that water into Mississippi Sound added to excessive flows from rivers and bayous alongside the Mississippi coast, together with the Pearl and Pascagoula rivers, destroyed the sound’s oysters and triggered dangerous algae blooms that killed different fish and disrupted tourism to the tune of about $200 million.

The examine concluded that working the diversion that yr would have had little impact on salinity within the sound, because the water stream out of Lake Pontchartrain and rivers alongside the coast would have saved its waters from transferring north, and their freshwater was greater than sufficient to kill the oysters.

The spillway has been opened six instances within the final 15 years, in comparison with a median of solely as soon as each 10 years between its opening in 1932 and 2008. The repeated openings triggered lawsuits by Mississippi and the state’s native governments, together with one which ended with the Corps being ordered to seek the advice of with the Nationwide Marine Fisheries Companies earlier than future openings.

However in 2007, Mississippi officers had been so involved about salinity ranges within the sound threatening oysters and different fisheries that then-U.S. Sens. Trent Lott, R-Miss, and Mary Landrieu, D-La., inserted language in laws authorizing development of a freshwater diversion close to Violet. That diversion was by no means constructed.

The state has utilized to the Corps for permits for the Mid-Breton diversion, and research by the Corps, together with a complete environmental affect assertion, are barely underway. A Corps spokesperson stated the state has knowledgeable it of the plan to maneuver to 50,000 cfs, however has not but amended its allow requests.