I Speak for the Trees…and the Stormwater

By Jenny Molloy

Most people have a vague recollection, perhaps from a brief fourth grade poetry unit, of the opening lines to Joyce Kilmer’s poem Trees: “I think that I shall never see a poem as lovely as a tree.” Less well remembered is Kilmer’s characterization of a tree as one “who intimately lives with rain.”

An often overlooked fact about trees is that they also do a great job of preventing and reducing stormwater runoff.  Depending on the type of tree and the intensity of rain events, trees can intercept as much as 30% of total annual rainfall before it even reaches the ground.

When precipitation does reach the ground, trees’ extensive root systems drink it up. The transpiration rates of trees (or how much water evaporates from the trees) vary notably, but some of the thirstier species can transpire dozens or even hundreds of gallons per day.

That adds up. A New York City study estimated that one tree reduces stormwater runoff by 13,000 gallons per year. That means the 500,000 existing trees in the city reduce runoff by 6.5 billion gallons per year, and 300,000 new trees could remove another 3.9 billion gallons from the overburdened NYC sewer systems.

In Washington, D.C. a similar study estimated that simply using larger tree boxes could reduce annual stormwater runoff by 23 million gallons, and that increasing the use of trees could provide reductions of 269 million gallons per year.

Trees also provide other benefits: shading and cooling that ultimately provide energy savings; carbon sequestration; wildlife habitat; enhanced property values; air quality improvements; community health and safety. And of course, as Kilmer noted, there are aesthetic advantages as well.

Example output from the National Tree Benefit Calculator

Example output from the National Tree Benefit Calculator

Communities who do the math now see trees as a win-win in wet weather management. While trees require capital investment and maintenance, compared to other stormwater controls (which are costly to build and maintain but don’t provide benefits beyond stormwater), trees are often an obvious component of the solution.

The U.S. Forest Service public domain i-Tree family of tools now provides now standard approaches to quantifying the benefits. So for municipal planners, utility managers, regulators and anyone else with a role in controlling the consequences of wet weather, trees no longer need be considered supplemental or boutique elements. They are on the A-list of options.

You too can estimate the value of that oak or poplar in your yard with the National Tree Benefit Calculator: Enter your zip code, choose from a drop-down list of over 200 species, enter the tree diameter and voila! The calculator provides an estimate of overall annual value in dollars, and also breaks that down into specific benefits: stormwater, property value, electricity, natural gas, air quality and carbon dioxide.

Which brings to mind another childhood standard: Shel Silverstein’s The Giving Tree, an allegory illustrating not only the multiple benefits of trees, but also conveying that with a little care those benefits can be realized for a very long time.

Jenny Molloy has been working in Clean Water Act wet weather programs at the state and federal level for nearly 20 years, and has been at EPA for the last 9. She was EPA’s first Green Infrastructure coordinator, and just completed a 2-1/2 year detail to Region III and the Chesapeake Bay Program Office focusing on the stormwater permitting program. She’s an active member of her son’s high school band program just so she can fulfill a life-long dream of being able to say “I’m with the band”.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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Plant a Tree, Save a River!

Riparian Buffer in an agricultural areaBy Christina Catanese

Since this is the Healthy Waters Blog, you might be wondering why we’re concerned about forests.  But unlike Vegas, what happens on the land doesn’t stay on the land – it affects streams and rivers, especially if the land is right next to the water.  It turns out that having forests right next to waterways (as opposed to developed or tilled agricultural land) is highly beneficial to water quality, ecosystems, and humans.  These vegetated strips of land are often referred to as “riparian buffers.”

I have always been astounded at the amazing power of trees and plants to provide so many benefits to our environment and communities.  Forested stream banks act like a sponge, filtering out excessive nutrients, sediment, and other pollutants that run off from the land that would be damaging if they entered a stream.  Shrubs and trees are also able to prevent stream bank erosion by anchoring the soils, keeping the banks stable and excess sediment out of the stream.  Buffers can even help mitigate flooding by absorbing and slowing down surface runoff.

Forested streams also provide enhanced habitat for wildlife.  Leaves, twigs, and other natural plant litter that fall into the stream provide food and habitat for organisms in the water, and the corridors of natural vegetation along stream banks allow land-based mammals and birds to thrive.

Riparian forest buffers also aid greatly in maintaining cool stream temperatures.  You know how much better it feels to stand in the shade of a tree on a hot day rather than out in the hot sun?  Well, stream organisms prefer their streams to be shaded as well.  Studies have shown that removing the canopy can cause the stream’s temperature to rise by as much as 15 degrees.  Warmer streams can’t carry as much dissolved oxygen, and some organisms can’t survive in these conditions.

That’s all nice for the fish, but what about people?  Riparian buffers also benefit human communities.  Wouldn’t you rather fish and swim in a healthy, forested, shady stream?  I know I would.  Forested streams stimulate local economies by enhancing fisheries and recreational opportunities.  The presence of riparian buffers can also result in higher property values in communities and add aesthetic value.  The water quality improvements from buffers also enhance the quality of our drinking water, so by preserving forests, we actually protect our water supply.The Delaware River Basin, for example, provides high quality drinking water to nearly 15 million people from New York to Delaware, largely because of the mature forest canopy that has been maintained upstream.  Preserving forests in the headwaters contributes to water quality both upstream and downstream water quality.  Another plus: buffer preservation and restoration are pretty cost-effective strategies for managing nonpoint source pollution.

Seems almost common sense given all the benefits, doesn’t it?  But there can be obstacles to implementation, like funding, competing land-use practices, political will, or lack of awareness of the benefits.  EPA encourages buffers as a best management practice through its Nonpoint Source Program,with tools and resources to incorporate buffer restoration in regional planning.

Reforesting streams in the Chesapeake Bay is also an important strategy for the basin’s nutrient pollution diet.  Learn how the Bay program and the basin states are working to restore 10,000 miles of riparian forest in the Bay’s watershed, and see how the states have incorporated riparian reforestation into their Watershed Implementation Plans. Watch a video by the Chesapeake Bay Program Office to hear more about how forests and the Chesapeake Bay are related, and what makes a forest healthy.

What do you think about forested versus unforested streams?  Have you noticed if streams and rivers in your area have trees or not?  Do you know of any initiatives to create and preserve riparian buffers?

About the Author: Christina Catanese has worked at EPA since 2010, and her work focuses on data analysis and management, GIS mapping and tools, communications, and other tasks that support the work of Regional water programs. Originally from Pittsburgh, Christina has lived in Philadelphia since attending the University of Pennsylvania, where she earned a B.A. in Environmental Studies and Political Science and an M.S. in Applied Geosciences with a Hydrogeology concentration. Trained in dance (ballet, modern, and other styles) from a young age, Christina continues to perform, choreograph and teach in the Philadelphia area.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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Science Wednesday: Into the Woods, Exploring Mercury in Northeastern Forests

Each week we write about the science behind environmental protection. Previous Science Wednesdays.

About the author: Jason Townsend is a Ph.D. student in Conservation Biology at the State University of New York College of Environmental Science and Forestry. His work is funded by an EPA Science to Achieve Results (STAR) Graduate Research Fellowship.

Scientists have known for some time that mercury is accumulating in America’s waterways and the ocean. Emissions from coal-fired power plants contribute significant amounts of mercury to the atmosphere. Mercury-laden precipitation is especially severe in parts of the northeastern U.S. directly in the line of prevailing winds from Midwestern, coal-powered power plants.

Accumulation of this potent neuro-toxin poses a threat to wildlife and people through consumption of contaminated fish.

We do not know, however, the extent to which mercury is accumulating in non-aquatic environments—forested areas of the Northeast, for example. It is possible that mercury-laden precipitation is accumulating in leaves, soils, and leaf-litter on the forest floor. This could lead to contamination of land-bound wildlife with unknown effects on their reproduction.

Accumulation of mercury in forested areas might also contribute to waterways for many years to come because the mercury might slowly run off the land and leach into watersheds.

My study is designed to compare mercury accumulation in several forest types in New York’s Catskill Mountains. The study takes place in the heavily forested Ashokan Reservoir watershed, an area that provides drinking water to approximately nine million people in and around New York City.

Image of man entering data into laptop in the woodsI am currently collecting samples of soils, leaves, leaf litter, insects that live in the leaf litter, salamanders that eat the insects of the leaf litter, and blood samples from birds that consume both insects and salamanders. In this way I will be able to identify the amount of “biomagnification” in the forest – the extent to which any mercury that is deposited by rainfall is increasingly concentrated in organisms higher and higher up the food chain. The study takes place at multiple elevations, from the banks of the Ashokan Reservoir at 600’ elevation to the headwater streams at the top of the Catskill’s highest peaks at over 4000 feet.

This information will be critical for identifying “biological hotspots” – areas that exceed the mercury levels deemed safe for human and wildlife populations. It will also provide monitoring information to help regulators determine the magnitude of mercury emissions reductions that will be necessary in the coming decades.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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