About Stream Buffers
What Does Buffer Do for Suburban Streams?
Stream buffer helps control stormwater run-off—the water that rushes off lawns and streets during downpours. Run-off is an enormous but largely hidden environmental problem in urban and suburban landscapes.
Because so much of suburbia consists of buildings, roads, parking lots, and bulldozer-compacted turf, our landscape now absorbs relatively little water, compared to what it once did when it was less paved and more forested. When it rains on the ‘burbs, a much smaller proportion of the water is now retained by plants and soils, and a much larger proportion runs into the streams. (It’s true that storm sewers capture a large share of run-off, but that only delays its movement into the streams. Stormwater systems are not surrogate forests: They cannot return large quantities of water to either the atmosphere or the soil, the way riparian forests and meadows do.)
All this run-off contaminates streams with pollution from roads and lawns. It also washes in eroded soil and erodes the stream channels themselves, sometimes dropping them so low that they lose their natural connection to their flood plains. Run-off also raises stream water temperatures, because run-off is usually warmer than groundwater, which is the natural source of most stream water. This “thermal pollution” makes streams uninhabitable for many native aquatic organisms. There are secondary effects too. For example, the thermal pollution reduces the amount of oxygen dissolved in the water, as does the nitrogen and phosphorous pollution from lawn fertilizer, animal waste, and eroded soils. (Such “nutrient pollution” promotes algal growth; subsequent decomposition of algae consumes oxygen.)
Taken together, the pollution, deposition of sediment, erosion, warming, and oxygen depletion have had a ruinous effect on suburban stream ecology. In many parts of the DC area, our streams are becoming little more than stormwater ditches.
Riparian buffer can help absorb, diffuse, and filter run-off. Unfortunately, suburban streams often have very little buffer, and sometimes none at all. Many streams in the DC area are bordered for parts of their length by nothing but mowed turf, a highly unnatural condition. Even where buffer remains, it is often badly infested with invasive alien plants, which suppress native plants and compromise the development of forests and meadows.
Of course, buffer restoration cannot, on its own, return damaged streams to health. The volume of run-off is too great for that—and buffer-planting space is too small. But buffer restoration does reduce, to one degree or another, all of the run-off problems mentioned above. (The degree of benefit depends on site conditions and the buffer’s density and width.)
Buffer restoration confers other benefits too. Buffers expand our native forests and meadows. Buffers create more habitat for both terrestrial and aquatic wildlife. And buffers are very cheap to install and maintain, compared to other forms of stormwater management.
Rural Streams Need Buffer Too
You might think that rural streams are bound to be in better shape than suburban ones, because the rural landscape has more forest and meadow—and fewer buildings and parking lots. This smaller proportion of impervious surface does mean less of a run-off problem but, unfortunately, that advantage doesn’t always translate into healthier streams.
Many rural streams also lack buffer, especially on farmland. On dairy or beef farms, for example, pasture often extends all the way to the stream bank—a condition that is no more natural than suburban turf-to-bank conditions. Streams that flow through pasture are often damaged by cattle. In such places, a great deal of manure usually ends up in the stream, and the cattle trample the channel. The trampling disturbs the stream bed, contributes to erosion, and tends to widen the channel; the wider channel, in turn, increases the water’s exposure to sunlight, thereby raising the water temperature. Many farmland streams are badly damaged by this combination of stream-bed disturbance, erosion, nutrient pollution, and thermal pollution.
Here too, buffer restoration can help. Buffer can reduce erosion, absorb nutrient pollution, and cool the water by shading the channel. And because rural drainages have less in the way of impervious surface, rural buffer projects may create stream conditions that are more natural than is possible in suburbia. Better conditions may allow for the return of native organisms that cannot tolerate suburban streams, no matter how well buffered—organisms like eastern brook trout, or certain native mussels. By buffering their streams, farmers can create big opportunities for conservation.
Where to Find More Information
For an account of the Sangha’s stream-buffer activites, read the Stream-Buffer Plantings page and look at the slide shows listed in the links panel of the main Stream-Buffer page. For recent activities, check the Stream-Buffer News.