South Carolina is a diverse state, and the well-known slogan “from the mountains to the sea” reflects how varied the landscape is across the state’s 20 million acres. One feature that is common across all these landscapes is water. South Carolina has 36 rivers totaling almost 30,000 miles of waterways that can be found in 8 river basins: Broad, Catawba, Edisto, Pee Dee, Salkehatchie, Saluda, Santee, and Savannah. Thousands of miles of streams and thousands of acres of swamps feed the watersheds of these river basins. The National Oceanic and Atmospheric Administration (NOAA) defines a watershed as “a land area that channels rainfall and snowmelt to creeks, streams, and rivers, and eventually to outflow points such as reservoirs, bays, and the ocean .” Multiple watersheds can drain into a single river basin. South Carolina’s surface water accounts for 1.3 million acres, including over 1,600 bodies of water measuring more than 10 acres.
One of the most unique features of South Carolina is the bottomland hardwood forests of the lowcountry. These are the forested swamps in the broad floodplains of streams and rivers. They can vary significantly in their hydrology, from periodic or seasonal flooding to being flooded throughout the year. They serve an essential role in many watersheds since they can store floodwaters, reduce the risk of downstream flooding, and act as a water filtration system. Some researchers have valued these benefits at over $9,000 per acre annually.
The eventual output point for a single raindrop in South Carolina is where all South Carolina rivers end, the Atlantic Ocean. The impacts that a single drop of water can have from the time it falls as rain until it flows into the ocean can be determined by how we manage our forestlands. That is why the state’s 12.9 million acres of forests protect our water quality and maintain water resources for important uses throughout South Carolina, including recreation and drinking water.
Water for Recreation
Outdoor recreation, including water sports and fishing, are an important contributor to South Carolina’s economy. An economic impact study conducted by Clemson University found that in 2005 34% of South Carolinians reported motor boating, 11% said canoeing, kayaking, or rafting was an outdoor sport they participated in, 37% reported freshwater fishing, and 28% reported swimming in a lake or river. While freshwater fishing was not accounted for separately in a more recent study, the South Carolina Department of Natural Resources (SCDNR) reported that the total economic impact of freshwater fishing, hunting, and wildlife viewing in 2012 in South Carolina was over $2.7 billion. The value of clean water for recreational activities and maintaining healthy aquatic populations directly impacts the importance of our water resources to our state’s economy.
Water for Drinking
Less than 1% of the earth’s water is drinkable. And although South Carolina has year-round rainfall and a significant amount of surface and groundwater, a growing concern for our state’s water supply and quality is the availability of clean drinking water. South Carolina’s population is projected to increase by over 450,000 residents between 2025 and 2035. The South Carolina Department of Health and Environmental Control (SCDHEC) reports that over 75% of South Carolina’s residents depend on public drinking water systems, with about 80% of those providers using surface water and 20% using groundwater. Growing populations increase development pressure which in turn threatens forested land. Sixty percent of South Carolina’s surface drinking water passes through a forested watershed, where the trees and forest soils have intercepted, filtered, and stored it.
Threats to Our Water
Site conversion to other uses besides forestland can reduce the quality and quantity of freshwater. This can impact the availability of drinking water, increase water treatment costs, increase the risk of downstream flooding, and reduce recreational opportunities. Bottomland forests have seen some of the most significant impacts of land conversion in the southeast. Over the last 200 years, 60% of these forests have been converted to agriculture, development, and even other forest uses such as pine plantations. Altering the hydrology of these areas by installing drainage systems has eliminated their ability to function as they did before conversion.
Several years ago, SCDNR was tasked with developing an updated state water plan based on regional water plans for each of the eight South Carolina river basins. Models will be used in each basin to evaluate existing surface and groundwater availability and incorporate future use projections to determine threats to our state water supply. The outcome of the state water plan will be updated policy, regulation, and legislation for the state’s water resource management over the next 50 years.
The forested watersheds in these river basins will play a significant role in ensuring clean, drinkable water quality and quantity. Past studies have found that water treatment costs increase by 20% for every 10% reduction in forest cover within a watershed that provides drinking water. Because of this, funding initiatives are being implemented in regions of the state to permanently conserve forested tracts within these watersheds and improve forest management practices. A prime example is the Savannah River Clean Water Fund (https://savannahrivercleanwater.org/). It has brought together municipal water services, state and federal agencies, non-profits, and corporations to support watershed partnerships, conduct outreach activities, hire technical service providers, and raise funding to implement conservation and management practices on private land.
How Forests Protect and Clean Water
Trees stabilize soils. The extensive root systems of trees that anchor and feed them hold the soil surrounding them in place. This is particularly important in sloped areas adjacent to channels, streams, and rivers since forested buffers reduce the amount of sediment entering these waterways. Even during periods of heavy rainfall when the forest soils cannot absorb the water as fast as it is falling, overland flow is slowed and spread by the organic material on the soil’s surface. Tree roots also create open spaces in the soil as their old roots die, allowing water to move into the soil profile before being slowly released into groundwater recharge or moving into channels that feed above-ground water bodies. The water released by one acre of forest is equivalent to the amount coming off 40 acres of impervious surface, like a parking lot, during the same rainfall event.
The above-ground structures of trees also reduce the impact of rainfall on the soil by intercepting and slowing down raindrops. This process is called interception, and it begins in the leaves or needles of the crown, where raindrops are caught as they fall. The drops then move down the tree as stemflow and are gradually absorbed by the forest floor. Even raindrops not intercepted by the crown are slowed down as they fall through the foliage, making less impact than if falling onto a non-forested area. It has been estimated that a deciduous tree can intercept 500 to 750 gallons of rainfall a year, while coniferous trees can intercept five to eight times that amount.
Trees are also giant water pumps, moving water out of the soil and into the atmosphere through transpiration. As the water moves through the tree, it is utilized for processes the tree uses to live and grow, including photosynthesis and the movement of nutrients. Transpiration is essential in the water cycle and returns water to the atmosphere as water vapor. The amount of water a tree can transpire in a year varies by species and age, but large oak trees have been estimated to transpire 40,000 gallons yearly. The impact of transpiration on soil water levels is most apparent during the dormant season in deciduous forests. When the trees are not actively growing and pumping water, seasonal flooding or high-water tables are often evident through standing water or ponding in low areas and soft, mushy soils.
As contaminated water moves through forested soils, trees can remove nutrients such as phosphorous from animal waste and nitrogen from fertilizer. When these nutrients enter freshwater systems at too high levels, they can impact aquatic ecosystems by encouraging the overgrowth of algae. More algal growth, or bloom, than the water system can handle can reduce oxygen availability for fish and other aquatic organisms, leading to fish kills and even creating toxicity issues for humans and animals that contact the water. Forested buffers adjacent to agricultural and livestock areas can filter runoff before it enters adjoining water systems.
Managing Our Forests to Protect Our Water
Properly managed forestland improves the quality of water entering watersheds across the state. To ensure the water from their property is not contributing to sediment or pollution issues, all forest landowners should be familiar with South Carolina’s Best Management Practices (BMPs) for Forestry. The South Carolina Forestry Commission (SCFC) developed these guidelines to protect our state’s water resources by minimizing the impacts of forest operations on our soils. By implementing recommended practices, contamination, soil erosion, and sedimentation into water bodies adjacent to forestry operations can be eliminated, thus maintaining water quality. The SCFC administers the BMP program, and although these guidelines are voluntary, they ensure forestry operations do not violate state and federal regulations related to water quality. The SCFC has foresters around the state who conduct courtesy exams for landowners, contractors, loggers, and forest managers before timber harvesting or other forestry operations to ensure that all BMPs will be implemented adequately on-site. The complete BMP manual can be found at www.scfc.gov/wp-content/uploads/2021/03/best-management-practices-manual.pdf. More information on the SCFC program can be found at https://www.scfc.gov/development/best-management-practices/, including the most recent compliance report for forestry operations across the state and how to schedule a site visit with a BMP forester.
As forest landowners, we need to understand and accept our responsibility for protecting the watersheds our forest management practices impact. Clemson Extension area forestry agents and water resources agents are available to discuss any forested watershed issues or concerns. You can find your local agent by visiting https://www.clemson.edu/extension/about/programs/index.html.
Resources:
Bottomland Hardwoods
https://www.epa.gov/wetlands/bottomland-hardwoods
Ecological Forestry Practices for Bottomland Hardwood Forests of the Southeastern U.S.
https://foreststewardsguild.org/research-and-management-publications/
The Economic Contribution of Natural Resources to South Carolina’s Economy
https://www.dnr.sc.gov/economic/EconomicContributionsSC.pdf
Evapotranspiration and the Water Cycle
https://www.usgs.gov/special-topics/water-science-school/science/evapotranspiration-and-water-cycle
Frequently Asked Questions About Drinking Water
www.scdhec.gov/environment/your-home/drinking-water-protection-program-overview
From Root to Tap: How Trees Ensure Fresh Water Supply
https://www.nationalforests.org/blog/earth-month-watersheds
Healthy Forests for Clean Water
https://ncforestservice.gov/publications/UF0115.pdf
Major Rivers and Lakes of South Carolina
https://www.dnr.sc.gov/water/river/waterbodies.html
Nutrient Pollution: The Issue
www.epa.gov/nutrientpollution
The Role of Trees and Forests in Healthy Watersheds
https://extension.psu.edu/the-role-of-trees-and-forests-in-healthy-watersheds
South Carolina Census Data Center
https://rfa.sc.gov/data-research/population-demographics/census-state-data-center/population-data/population-projections-2000-2035-rev2019
Water Planning Overview
https://hydrology.dnr.sc.gov/water-planning-overview.html
Author
Janet Steele, Cooperative Extension, Forestry and Wildlife Agent
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