Chesapeake Bay - Forests of the Watershed

Forested waterways have it made in the shade
Bay Naturalist / By Kathy Reshetiloff - Bay Journal

I learned a lot about streams and rivers the summer of 1983 when I was a summer intern analyzing water samples throughout Maryland.

I spent most of my days bent over a petri dish, trying to identify and catalog the aquatic animals in each sample. Some samples were full of a variety of minnows, crayfish, insects and insect larvae. Others had very little variety or were suspiciously devoid of life. I soon discovered from field work that these latter samples consistently came from streams or creeks that ran through barren or nearly barren landscapes.

It has been estimated that when colonists first arrived in the Chesapeake Bay region, 90 percent to 95 percent of the watershed was forested. This means that at one time, forests lined both sides of almost every stream, creek and river draining into the Bay. These streamside forests, also known as riparian forests, made up a huge filtering system that helped to maintain the water quality of local waterways and the Chesapeake.

Because of the fertile nature of floodplain soil, many riparian areas and their forests were cleared for agriculture. As more people moved into the region, riparian forests were also cleared to make room for development. Today, only about 59 percent of the watershed is forested. A little more than half of all waterways in the watershed still have riparian forests of 100 feet or more bordering them on both sides.

As a transition area between aquatic and terrestrial environments, riparian forests help to maintain water quality by acting as buffers that reduce the amount of pollutants reaching streams and rivers.

By increasing the infiltration of water into the ground, forests reduce runoff that may contain such pollutants as sediment, nutrients and chemicals. Infiltration rates are 10 percent to 15 percent higher in forests than turf grass fields and 40 percent higher than plowed fields.

Nitrogen and phosphorus are nutrients that are essential for the growth of plants. But, an overabundance of either of these in water systems can cause a rapid growth of algae that block sunlight needed by underwater grasses. Bacteria that decompose this overabundance of algae use up large amounts of oxygen, which is critical to the survival of fish and other aquatic organisms.

Trees and other vegetation absorb these nutrients. Streamside forests remove nitrogen through plant growth. Bacteria in the forest floor convert nitrate to nitrogen gas that is then released into the atmosphere.

Water runoff often contains large amounts of sediment that can cloud the water and cover critical aquatic habitat. As runoff moves through a forest, the physical structure of the vegetation filters out soil particles so that the forests acts as a sediment trap.

Phosphorus, which is usually attached to soil particles, is also filtered out with the sediment. Trees growing along streams and rivers hold soil in place with their roots, thus stabilizing streambanks. They reduce flooding by slowing the erosive force of rain and floodwaters.

Many riparian forests also contain forested wetlands, which can temporarily hold floodwater and release it slowly over time. Even fish, crayfish, aquatic insects and other aquatic organisms derive benefits from riparian forests. Streamside vegetation helps to control water temperature. Without shade, temperatures would be higher in the spring and summer. This shade is especially important for maintaining healthy fish populations, as temperature is a major factor controlling fish spawning.

Warmer water also retains less oxygen and elevated water temperatures can accelerate the growth of algae.

In addition, riparian forests contribute to the food cycle in a waterway. Plant material that falls into the water or is washed in by rains is a source of food. Aquatic insects, crayfish and other invertebrates break down plant material into smaller particles. Bacteria and fungi break it down even further into tiny particles called detritus. Detritus is food for many small aquatic animals and insect larvae which, in turn, are food for small fish. Minnows, aquatic insects and insects that fall into waterways provide food for larger game fish.

Riparian forests are important to many life stages of aquatic, as well as terrestrial, life.

Much of our wildlife depends on forests for their habitat. Forests provide food, cover, nests and nursery areas. Bears, deer, foxes, raccoons, beavers, snakes, turtles and frogs are just a few of the animals that can be found in riparian forests. Temporary pools that form in these areas in late winter and spring are important breeding areas for frogs, toads and salamanders.

The unbroken riparian forests also offer protective pathways through which wildlife can move. Forest corridors are especially critical for migrating neotropical songbirds.

In addition, people regularly use riparian forests for hunting, fishing, nature study, birdwatching, camping and hiking.

When we lose these forests, we also lose the functions they provide: the reduction of nonpoint source pollution and erosion; the protection of adjacent land and water from flood damage; food and habitat for fish and other wildlife; and recreational opportunities for people.

Riparian forests are often considered a stream's last defense against pollution and dwindling biodiversity.

What I learned almost 15 years ago still holds true and is even more important today.



Kathryn Reshetiloff is with the U.S. Fish and Wildlife Service’s Chesapeake Bay Field Office in Annapolis.




Forested waterways have it made in the shade
Chesapeake Bay Forests article from Bay Journal - March 1998