Riparian Isn t Just a Fancy Word for River-Related

The Los Angeles River and its environs is home to a wealth of flora and fauna. This series of posts on Confluence attempts to unveil the hidden wildlife that thrives along the river banks. This series is developed in collaboration with fellow nature lovers working in the sciences.

In this article, we asked Ellen Mackey, Senior Ecologist with the Metropolitan Water District of Southern California, to share some of her expertise on this water system and why it matters.

Merriam-Webster describes the word riparian as anything relating to or living or located on the bank of a natural watercourse. It's a word rarely used outside of ecology textbooks, but will be familiar to Los Angeles River supporters. No educational material or announcement about River Revitalization would probably be complete without the word riparian in it.

The word is so often used that it's gone the way of words like artisinal or bespoke -adjectives plastered on marketing materials only to impress.

For Ellen Mackey, Senior Ecologist with the Metropolitan Water District of Southern California (MWD), the word riparian doesn't just mean a bunch of green space beside the river, it is a beautiful mosaic of plant and animal life that contributes to life on the river. It's less like the staid, evenly trimmed grass on our front lawn and more like a biological Rube Goldberg machine, each plant with its own specific function.

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Diversity is key on the river, not just for wildlife, but for plant life as well. According to Mackey, it's not just the variety of plants that is crucial to the Los Angeles River, but also the form it takes on the river. When I speak of diversity, I also mean diversity in structure, how high or low a plant is, said Mackey.

Much like a vibrant city offers different vantage points-high-rises, multi-story apartments, single-family homes, and parks-for its residents to enjoy, tall trees, tall shrubs, and low shrubs create a landscape mosaic along an intact riparian system. Tall plants give wildlife a place to perch and survey their surroundings. Medium-height plants make great nesting areas. Low plants allow animals access to the water. What's more, like a bustling city, a healthy riparian habitat is always a work in progress.

The Los Angeles River system was historically very dynamic. Big floods would rip out all the tall trees, then the medium-height ones would spurt up then the newly scoured area becomes colonized by tree seedlings. During the next flood, it starts all over again. Some stuff would get pulled out, while others keep growing. There were always plants of different heights, said Mackey.

Uprooted trees along the L.A. River || Photo courtesy of the Los Angeles Public Library

Riparian habitats perform different, interrelated functions.

The most infamous function of the Los Angeles River is probably flood control. Water that rushes out of the canyons hits the lower areas, spreads out and then boulders and gnarly roots from plants by the river help slow down the water, giving it time to be absorbed by the spongy soil. That water then seeps into the ground recharging our local water supplies rather than gushing out into the ocean.

The areas right next to the stream or in between the stream acts as a sponge that soaks up the rainfall, said Mackey.

Intact riparian systems result in high water quality. As water moves through a riparian area, it slows down, giving sediment a chance to drop out and pollutants to filter out, said Mackey, As water moves down the river, it gets cleaner and cleaner.

But apart from floods, riparian habitats perform a more subtle service. Tall trees offer shade, lowering the water temperatures so fish can live in it. Cooler water temperature hold more oxygen, said Mackey.

Wood debris trapped by rocks and boulders within the riparian zone also create microhabitats for insects, which in turn, attract fish and birds.

The river also became a default highway for wildlife, a source of food, water and shelter for any animal making their way from point A to point B.

Perhaps the river's most infamous function, at least when it comes to the Los Angeles River, is flood control.

Normally, a riparian habitat-river meanders, plants of various heights, woody debris, and all-slows the water flow down, so that the ground has enough time to soak up the rainfall. Rainwater would then infiltrate down to the ground, removing pollutants and sediments-a process that results in higher water quality, while adding to our groundwater supply.

Intact riparian habitats also nourish plants by allowing nutrients such as nitrogen, phosphorus, calcium, magnesium, and potassium to be distributed and taken up by shallow and deep-rooted plants, or re-introduced back into the water.

These plants, which flourished thanks to the water then return the favor by shading the water, keeping the waters cool and inviting for fish and other wildlife. If you've ever taken shelter beneath a tree shade while waiting for a Los Angeles bus to come, you know how much of a difference a bit of shade makes.

Leaves, branches, and sometimes whole uprooted trees, can also be carried downstream by the river, which create an obstacle course of sorts throughout the river. This trail of detritus provides food and shelter for wildlife living by the rivers, creating wildlife corridors.

Riparian habitats also provide great places for recreation, as Angelenos already know.

It was a tightly integrated system, until humans had changed it. When you line the river with concrete, you're left with one function: flood control, said Mackey, Everything else that a riparian system is supposed to do isn't being done. Gone is filtering, the energy dissipation; gone is the spongy soil that soaks up water then percolates to groundwater; gone are the plants of diffe

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