When we think of biomes, it's really easy to think of extreme sides of the spectrum.  We know our forests covered in canopies of boundless trees.  We know our oceans with water as far as the eye can see.  We know our deserts, a challenge for anything to thrive in.  Sometimes we get environments that aren't so clear-cut though.  Sometimes we get habitats that seem to blend with others around it.

Probably the greatest example of such a place is the wetland biome.  Definitively a middle ground between land and water yet with gray areas through and though, with variety such that even experts can disagree on what types of wetland they're viewing at a glance.  Especially given the world's many region-specific qualifications for what a wetland is.

And identifying them is really just the tip of the iceberg.  These ecosystems are both complex to understand and one of the most difficult to restore once they've gone out of balance.  Regardless, they are an integral part of our planet, and our topic here today!

By Abrget47j - Own work, CC BY-SA 3.0, Link

Let's dive in!

What is a Wetland

As mentioned, wetlands are a blend of land and water.  A lot of habitats deal with holding some amount of water, but what makes it cross the threshold from forest or grassland into wetland?

The key qualifier that we use in ecology is whether the ecosystem is capable of holding that water long enough to sustain aquatic plant life.  This doesn't mean that standing water has to be permanent.  It just has to be around enough such that these aquatic plants can take hold and thrive even when the water isn't around.  Some of the best examples of these ephemeral, or temporary, wetlands are known as vernal pools.  They're generally seasonal ponds, but when the water is dried up, the plants can still thrive, go into dormancy, and reemerge when the water has returned.  Really neat stuff!

Wetlands serve as an important ecotone, a connector ecosystem, between land and water

These wetlands aren't tied to being freshwater either.  While it tends to be much easier to identify an inland wetland, there are saltwater and brackish (salty, but not too salty) wetlands too.  One such saline example is the lagoon, which is a smaller section of water separated from a larger body, usually by sandbars or barrier reefs.  This isn't to say that all lagoons are saltwater either.  Lagoons can also have inflow from freshwater sources, making them what is considered brackish.

You're probably seeing by now that wetlands classification is almost always a "yes...but!" scenario.  When they're not isolated all their own, wetlands tend to be ecotones from marine to terrestrial ecosystems, making them an inherent planetary blend!

Marshes and swamps primarily differ by presence of woody plants.

Marshes are wet grasslands and swamps are wet woodlands.

Types of Wetlands

While there are a wide variety of wetlands, such as the ones we've gone over, there are 4 main variants that cover a majority of the world's wetlands.  Let's take a bit of time to check out each one and see how they differ.  Believe it or not, these aren't as synonymous as you might think!

Marsh

​The first variety we'll look at is the marsh.  Marshland is differentiated from other wetlands by its noticeable lack of trees and other woody plants.  Marshes are dominated by herbaceous plants like grasses, sedges, and typha instead.  These plants are highly attuned to thriving in muddy conditions, typha especially, which are known more commonly as cattails.  There are a handful of marsh types mostly dependent on where they form, which can range from beside oceans to alongside lakes and streams.

Swamp

Swamps, on the other hand, are dominated by woody plant species instead of herbaceous ones.  While not a requirement for swamps, they tend to be more saturated with water than marshes throughout the year as well, to the point of retaining standing or slow-moving water for a good duration of time.  The trees and shrubs have to be quite water tolerant to survive in these conditions.  With these woody species also comes more animals that can call these places home.

Bog

​The next two types share a commonality (and a difference from marshes and swamps), and that's the presence of peat.  Peat is an accumulation of decayed or organic plant matter. In the case of bogs, that is mostly moss, specifically Sphagnum moss.  This peat layer forms over a standing or slow-moving water over years, slowly replacing deeper waters with a spongy surface.  This accumulation also impacts the pH of the water in the acidic direction.  This leads to one of the most uniquely diverse ecosystems that the planet has to offer, giving rise to plants that needed to survive in harsh environments.  Such plants that evolved to fit the ecosystem are rare carnivorous plants which adapted to consuming insects for nutrients.  Bogs are also predominantly fed by precipitation.  Ones that are completely inundated by rainfall are called ombrotrophic, or cloud-fed.

Fen

As with bogs, fens are a type of mire, or peatland.  While the abundance of peat can succeed a fen into a bog, the difference that keeps the two distinct is the source of water and acidity.  Fens are mostly fed from surface or groundwater with a high mineral content.  Plant nutrients in the water are low, and the high mineral nutrient content results in a neutral or alkaline water chemistry.  This allows for a broader range of plants and animals to thrive in a fen, but the alkaline water chemistry has also resulted in carnivorous plants evolving to pull nutrients from places other than the ground.

Where are Wetlands

Based on the need for water, and knowing most of our water is in our oceans, you might think that wetlands are mainly found in our tropical and subtropical regions, but you'd be surprised!  Wetlands are among the few ecosystems that manage to thrive on all of Earth's continents, including Antarctica.  While recent research has shown that Antarctica has a massive system of wetlands under its ice, it also supports wetlands above the ice as well.

Bogs and fens are some of the most challenging environments for plants to thrive based on their unique water chemistry.

Some plants even evolved to get nutrients from insects rather than water and soil!

Perhaps one of the most prominent examples would be found in the Earth's tropical regions: the Amazon River Basin.  Given its strong connectedness to the Amazon Rainforest, a sizable part of this wetland is considered a swamp, where the dense tree canopy allows very little light to reach the wetland floor.

Those examples aren't to say wetlands only favor extremes either.  Another major wetland is the West Siberian Plain which ranges from temperate to arctic climates.  Considered one of the world's largest lowland plains, it also ranks among the largest stretches of marsh in the world.

And wetlands don't have to be natural either.  If you live around urban environments, you might notice constructed wetlands in the from of stormwater drainage land.  If you happen to see large pipes seemingly ending in a lowland grassy area, these may be designed and built to mimic wetland functions that let nature take care of wastewater filtration and reintroduction to the water cycle.

Wetlands take centuries or longer to naturally occur and provide many valuable ecosystem services to the entire planet

Importance of Wetlands

Riding that thought a bit further, even in urban planning, we have found that wetlands serve a number of functions that benefit the Earth, including humans, if we want to keep living here.  The water purification we mentioned is but one of the functions that wetlands can provide.  Our coastal and river-side wetlands offer shoreline stabilizing trees, roots, and reef systems.  This relationship also doubles as flood mitigation by providing a large amount of water storage.  This buffer prevents flooding from occurring in ecosystems, constructed and natural, that may not be as suited to dealing with large amounts of water.  Peatlands also serve as one of the most effective carbon sinks that the Earth has to offer.  On top of all that, wetlands are among the most biodiverse ecosystems on the planet, providing homes to some of the most strangely adapted plants and animals around.

Yet, despite all of this, we don't tend to see them around too much.  Wetlands are, of course, fairly counter to humanity's desire to live on and grow crops on as much land as possible.  Well, at least until humans found out how good wetland soil was for agriculture.  Over the past century, we've seen massive destruction, degradation, and draining of wetlands to make room for human use, without taking into account all of the good they do for this planet's systems along the way.

In recent years, as more research is done around wetlands, people and groups around the world have discovered just how key these ecosystems are and more efforts are now in place to conserve and restore these fascinating locations.  Though, all this learning has shown that wetlands are among the most complex ecosystems to design and restore, requiring expertise from engineers to landscape architects to ecologists to hydrologists to biologists.  And of course the money and resources to do the work.  And doing it wrong can do more harm than good to the surrounding environment.  As it turns out, ecosystems that take hundreds of years to form and balance naturally are quite difficult to piece together by hand.

Wetland restoration is a truly collaborative effort, requiring expertise ranging from landscape architecture to hydrology

One silver lining to think about here is that the need for new ideas, fresh minds, and a broad spectrum of talent means that there is always room to jump in and help with knowing and aiding our planet.  We're all in this together, and learning while taking action together is how we help ensure magnificent places like our wetlands continue to exist and work with us for eons to come.

~ And, as always, don't forget to keep wondering ~

Sources
* Classification and Types of Wetlands | US EPA. US EPA. (2020). Retrieved 19 July 2020, from https://www.epa.gov/wetlands/classification-and-types-wetlands.
* Romanowski, N. (2010). Wetland habitats : A practical guide to restoration and management. Retrieved from https://ebookcentral.proquest.com

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