This article is excerpted from Wave Maker’s News, our quarterly update on all things water in the Gulf of Mexico, check out the full newsletter here.A thoroughly rotten submersed soil section from the collapsed marsh.In February, GRN was invited to a site visit of Four Mile Marsh by Ed Boedeker, a longtime resident of the area. Four Mile Marsh is located not far from Hammond, Louisiana and this once thriving marsh has been a site of some controversy lately due to the role it plays in treating sewage waste from nearby communities. Since 2006, the marsh has been part of the Hammond Wetland Assimilation project, a project that attempts to use the marsh to finish treating waste from a nearby sewage treatment plant. In that time, tens of acres of freshwater marsh that are being exposed to undertreated sewage water have collapsed and now rot beneath a large pond of open water. Ed spent his childhood walking and trapping in Four Mile Marsh, but, in good portions of the marsh, those days are over. Instead, we made our way through the disappearing marsh on a pirogue, a flat-bottomed canoe.At three different locations, Ed cut into the ground and down into a section of roots. In the first spot, Ed was digging beneath the water, and dug up a large clump of former Cattail roots. The root mat was thoroughly rotted and came apart easily, squishing in our hands. At the second location, to the east, Ed dug into an area along the border of a marsh dominated by wiregrass and pulled out a much sturdier root system. Sadly, this section of marsh, which has not collapsed, will probably eventually succumb to the same accelerated decomposition that rotted away the marsh to the west. If the undertreated waste water caused the rapid decomposition to the west, isn’t it only a matter of time before this eastern portion collapses?The third soil section was taken from a marsh area that isn’t being exposed to poorly treated waste. Ed picked this area because it looks like the collapsed marsh used to look. This root mat was tough– we couldn’t tear it much. Rapid decomposition of the Cattail root layer has not happened here, where the effluent does not flow.There are different ideas about what caused the collapse of Four Mile Marsh. Nutria are not very abundant in the area, but, attracted to tasty Cattails and fresh marsh plants, they may be playing a role in the collapse. However, the role of the polluted water itself cannot be overlooked. Freshwater wetlands need to drain like any other, and the constant effluent from the sewage plant caused Four Mile Marsh to be flooded for too long. If the roots rot faster than the shoots grow, open water is the result.Wetland assimilation is an exciting concept that works in some situations. But the Hammond treatment plant enjoys relaxed pollution standards because it is assumed that the wetland plants will help treat the water. In this situation, this discharge from the Hammond sewage treatment plant is not being “assimilated,” it appears to be a direct or indirect driver of the collapse of this wetland system. In any case, the treatment plant should have to maintain higher anti-pollution standards.Scott Eustis is GRN’s Coastal Wetlands Specialist.