paleonet New Orleans effluent and fossilization

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As water is pumped out of New Orleans into Lake Pontchartrain, where will it
go and what will it do to the environment? Will it leave a recognizable
geologic signature?

I don't know how far east the effluent will travel, but here is a historical
item that may help to cast light on the question. In 1890, before many of
the modern changes to the Mississippi Delta were made, flood discharge
through Lake Pontchartrain reached at least as far east as Dauphin Island at
the mouth of Mobile Bay, Alabama. As the original publication is somewhat
hard to find, I repeat the words of E. A. Smith et al. here (1894, 'Report
on the Geology of the Coastal Plain of Alabama', p. 30-32). Please note that
this flood did not include wastewater or toxins. 

Andrew K. Rindsberg
Geological Survey of Alabama

++++++

"Not often within historical times has the Great River extended its arms as
far as the Alabama coast, but in the spring of 1890 it made an effort to do
so, and though with comparatively slight effect, sufficiently it is thought,
to throw a strong light upon the process which, in times not very long past,
geologically considered, has built up the ground work of four of our
southern counties, at least one of western Florida, and the southern
portions of Mississippi and Louisiana. ... On the 13th of March, 1890, the
levee at the Nita Plantation, about two miles above Convent on the left bank
of the Mississippi River, gave way before the flood then at its height. ...
[T]his point is 21 feet above mean high tide. ... 

"The flow of the current at the crevasse during the period of high water was
at the rate of 15 miles per hour. Yet, not until March 22nd, (9 days after
the break), did Lake Maurepas become filled up and the current begin to set
into Lake Pontchartrain through the Pass of Manchac. By April 13th, the
boundary lines of these lakes were obliterated and there was one turbulent
sea of yellow water from the 28th mile post on the I. C. R. R. out of the
city, to the 46th, 18 miles in width, poured through the outer lakes into
the Mississippi Sound. By the first of May, old fishermen of New Orleans and
Biloxi declared they could perceive a distinct current passing eastward
beyond Ship Island; and by color and taste, the effect of the fresh water
was appreciable as far as Grant's Pass, on the every entrance into Mobile
Bay. 

"Whether perceptible or not to the fishermen, the presence of crevasse water
was very appreciable to the fish: it drove them all out of the Sound and
from the Chandeleur Banks. From the eastern part of this district, about
Dauphin Island and Petit Bois, the fish were not long absent, but as late as
the 1st of June, the Sound was distinctly muddy at Mississippi City and Gulf
Port; and seining parties, instead of pompono, sheep head, Spanish mackerel
and red fish, took Mississippi cat fish and buffalo. 

"Of late years a considerable industry had grown up in the cultivation and
canning of oysters, and all the banks or reefs as they are called locally,
along the shores of Lake Bourgne and the Sound were becoming planted with
the highly valued bivalves. To a very great extent the oyster beds as far
east as Ship Island are ruined as well as all on both sides of Cat Island.
... 

"The interest geologically is that the invading floods from the crevasse
brought vast amounts of mud. It was this solid matter held in suspension,
and not the freshness of the water, that drove out the fish accustomed to
the clear medium of ocean streams, for the silt clogged up the delicate
organs of aeration, the gills, and they and the other marine creatures upon
which they depended for food, beat a hasty retreat. But escape was not
possible to the sedentary molluscs, and very soon, or about the 1st of
April, oysters brought into Gulf Port were found to be uneatable and canning
of them had to cease. Those who saw it say there would be pellets of mud in
the folds of the mantle. By the last of April, it was discovered that the
oysters on many of the "reefs" were dead, and the stench from them was
intolerable to those passing over them in boats. This destruction of life
was due to the sediments deposited upon the banks; oysters and their fellow
colonists, unable to get away were covered up -- literally fossilized.

"The floor of the Sound has always been famous for its fine sandy bottom,
the delight of bathers. The seining parties above alluded to, as early as
the middle of May, reported the bottom from ankle deep to knee deep in a
soft yellowish brown ooze. ... [T]housands of acres of the [oyster] banks
are covered many inches deep in a brown muddy sediment. ... In 1872, and
1874 the Bonnet Carré Crevasse produced similar effects upon the fishing and
oyster banks of the Sound, yet the mud laid down by that, (which continued
open eight or ten years), was soon covered up by ocean sand. The report of
Maj. Whenery the able engineer of the N. E. R. R., upon the structure of the
bottom of the Mississippi Sound, shows that it consists of alternate thin
layers of sand and of a soft bluish or brownish clay: for such a process as
described above has been going on for ages."

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