Marine Preservation

The Muddy Waters of Swapping Swamps

Happy American Wetlands Month!  Yes, May is the perfect excuse to don muck boots, load up the kayaks, or at least take a break to daydream about a favorite bog, fen, pocosin, or swamp.  Before you start celebrating, though, a quick question is in order: what exactly is a wetland?

If you’re worried that you wouldn’t know a wetland if knee-high in one, you’re not alone.  The exact definition of “wetland” has been elusive for decades, partly because the habitats are protected by legislation that makes it necessary to define them with the specificity to satisfy attorneys and nuance to appease scientists.  (Good luck on both counts.)  In the US, the 1987 Army Corps of Engineers’ Wetland Delineation Manual is used to legally identify the boundaries of a wetland.  According to the manual, a wetland is identified according to three characteristics: plants, soil, and hydrology.  A professional wetland scientist would therefore visit a site to check for water-tolerant plants, soil types that indicate frequent inundation, and surface- or groundwater.  Wetlands may not always be wet, but plants, soil, and groundwater aren’t going anywhere, so wetlands can be classified based on legal standards virtually any time.

The three pillars of wetland delineation! Image from http://www.watershedco.com/blog/wetland-delineation-or-reconnaissance/

The three pillars of wetland delineation! Image from http://www.watershedco.com/blog/wetland-delineation-or-reconnaissance/

The legal framework surrounding wetlands might be surprising.  Most habitats are rather intuitive: it’s not difficult to envision a desert or prairie.  Wetlands have been afforded their superstar status by extension of the Clean Water Act, with the substantial consequence that one cannot simply bust up a wetland.  If a construction project will harm one, managers must consider all alternative possibilities.  Destroying the wetland may be unavoidable, which can happen, for example, when the property stands in the way of a planned roadway.  In that case, the law demands that managers make amends by facilitating a replacement wetland, a process known as mitigation.  It’s preferred that managers mitigate indirectly, by paying an approved third-party engaged in environmental work or by purchasing credits from large restoration projects known as mitigation banks.

Whew!  When paddling around a swamp, it’s easy to feel completely removed from the frustrating red tape of society, right?  Who knew that legalese bubbles beneath the surface alongside the lilypads and fish?  The idea of obliterating a wetland and replacing it with a brand new one might strike you as vaguely dubious.  Perhaps it recalls your parents offering to get a new dog after the death of your beloved Nacho.  They just don’t understand!  That new dog won’t jump up to catch popcorn, or sprint out the door when you get off the bus, or fit quite so nicely in the dog bed.  How could a new dog ever replace your old one?  In the decades following the establishment of wetland mitigation, scientists have been asking that same question about wetlands, albeit with less emotion than your average bereaved middle schooler.

This wetland is part of a mitigation bank in Mississippi. Entities can purchase credits from these large constructed wetlands to compensate for destruction elsewhere. Image from http://www.wildlifemiss.org/Habitat/Mitigation.aspx

Jordan Jessop and colleagues at the University of Illinois at Urbana-Champaign recently tackled this question of wetland replacement.  The team visited 30 mitigation wetlands in Illinois, surveying parameters like decomposition rates, plant cover and density, soil organic matter, and diversity of birds and frogs.  They sussed out their data using a statistical analysis that shows correlation among the variables measured at each wetland.  The data collected in the field were therefore translated into broad conclusions pertaining to all the sites- and likely many other mitigation wetlands.  You can check out their analysis and a map of their study sites in their Biological Conservation paper.

Turns out wetlands are a lot like us: they can’t have it all.  Parameters such as soil organic matter and denitrification potential clumped together in the stats analysis, directly opposite frog and bird diversity values.  Jessop and colleagues interpreted this as signs of a “tradeoff” between nutrient cycling and biodiversity.  In other words, some of the wetlands studied had a high potential for facilitating nutrient cycling, particularly nitrogen.  Others hosted a great diversity of birds and frogs.  But most wetlands did not enjoy both benefits, despite the assumption implicit in wetlands legislation that mitigation translates to replacement.

A mitigation wetland in Pecatonica, IL. This is an example of the type of central IL wetland that may have been included in Jessop's study. Image from https://publish.illinois.edu/matthewslab/projects/.

A mitigation wetland in Pecatonica, IL. This is an example of the type of Illinois wetland that may have been included in Jessop’s study. Image from https://publish.illinois.edu/matthewslab/projects/.

The surveyed wetlands were restored 10-21 years before the study, so it’s highly likely that they will continue to evolve, for better or worse.  In the meantime, though, the surrounding environment may experience reduced nutrient removal or biodiversity compared to the services provided by an established wetland.  The study’s authors recommended that future mitigation wetlands be designed with awareness of this tradeoff.  It’s likely too optimistic to assume that mitigation wetlands perfectly replicate the functions lost by an established system.  On the brighter side, the study did demonstrate that mitigation wetlands provide environmental benefits that would have otherwise been completely lost.  This and other research in the growing field of restoration ecology can help scientists and managers pinpoint smarter ways to design mitigation wetlands for maximum function.

Wetlands sit at an exciting intersection between science, policy, and adoration (for some of us, at least).  Regulations in the US have slowed wetland loss, and ongoing research continues to explore ways that mitigation can better compensate for habitat loss.  Those are both very good reasons to make sure that May is swamped with all things marshy!

For more info:

Jessop J, Spyreas G, Pociask GE, Benson TJ, Ward MP, Kent AD, Matthews JW.  2015.  Tradeoffs among ecosystem services in restored wetlands. Biological Conservation 191: 341-348.

Association of State Wetland Managers’ 2016 American Wetlands Month activities

US Fish & Wildlife American Wetlands Month info

Cover photo of the Emiquon Preserve in Lewistown, IL, from http://www.experienceemiquon.com/

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