Picture of runoff on farm.
The Streamside Forest Transforms Nitrate to Nitrogen Gas

The streamside forest functions as a TRANSFORMER when chemical and biological processes occurring within it change the chemical composition of compounds. For example, under well oxygenated soil conditions, bacteria and fungi in the streamside forest convert nitrogen in runoff Picture of cows grazing on streambank.and decaying organic debris into mineral forms (N03). These forms can then be synthesized into proteins by plants or bacteria. When soil moisture is high enough to create anaerobic conditions in the litter and surface soil layers, denitrifying bacteria convert dissolved nitrogen into various nitrogen gasses, returning it to the atmosphere. Studies have shown that the amount of nitrogen in runoff and shallow groundwater can be reduced by as much as 80% after passing though a streamside forest.

The streamside forest can also function as a TRANSFORMER when toxic chemicals such as pesticides are converted to non-toxic forms. Because of continued improvements in the formulation and management of pesticides, only very small amounts manage to leave the area of application. These residues, borne by runoff, are converted to non-toxic compounds by microbial decomposition, oxidation, reduction, hydrolysis, solar radiation and other biodegrading forces at work in the soil and litter of the streamside forest. while scientists have long understood the biological processes at work in the streamside forest, additional data are necessary to fully quantify their importance with respect to pesticide degradation.

Nature Provides Safe Storage for Nutrients in Biological Cycles

The basic elements that occur in nature move through the environment in a series of naturally occurring chemical and biological states, a process commonly referred to as a cycle. The cycle describes the state, chemical form, and relative abundance of the element at each point along it's route through the environment. There is usually a state, chemical form, and location in the cycle in which nature safely stores the bulk of the element. In the case of the nitrogen cycle, the bulk is stored as nitrogen gas in the atmosphere. Pollution occurs when, through man's interference, an element occurs at some point in the cycle in an inappropriate form or amount, thus disrupting the environmental balance.

Nitrogen and phosphorus, elements essential to plant growth, move through the environment in such cycles. Fertilizers and animal wastes both contain nitrogen and phosphorus. When these elements are applied to crop and pasture lands in amounts in excess of plant needs, they can adversely affect water quality.

Phosphorus, the less mobile of these two nutrients, is quickly bound to soil particles or taken up by plants. Because about 85% of phosphorus is bound to soil and organic particles, eroding sediments and organic materials borne by runoff are the chief sources of phosphorus in water.

In contrast, nitrogen from fertilizer and animal waste is soluble in water as nitrate, and not held by soil particles. Nitrate ions which are not taken up by plants or converted to gaseous forms by microbial action can leach downward through the soil into the groundwater or move laterally with surface and subsurface flow to contaminate surface waters.

Drawing showing effects of nitrogen runoff.
Reference: Maryland Department of Natural Resources
  Graph - Nonpoint source contributions nitrogen, 1980.
Reference: Maryland Department of Natural Resources

Technological Improvements Have Reduced the Impact of Pesticides on the Aquatic Environment

The chemical, physical and biological properties which determine the effect of pesticides on water resources and the fate of these pesticides in the environment have been advanced significantly in the years since Rachel Carson's "Silent Spring". Wide spectrum pesticides, which kill a wide variety of non-target organisms and remain active for a long period of time are no longer used. For example, DDT is a wide spectrum chlorinated hydrocarbon with a half life of ten years (i.e. the time required for one half of a compound to decay). DDT, and other pesticides like it, have been banned in the United States because they concentrate in fatty tissue and tend to accumulate in the food chain where they can interfere with the reproduction and survival of many non-target species.

Truck spraying crop field.Many contemporary insecticides, such as Organophosphate and Carbamate have half lives of only a few days to several weeks, are not fat soluble, and are often much more specific in the targets they affect. While these insecticides do not accumulate up the food chain and are safer environmentally, they are very soluble in water and usually quite toxic to fish.

In contrast, most herbicides currently in use break down by the end of the growing season and are relatively less toxic to fish than insecticides. However, if herbicides reach surface waters, many species of aquatic plants can be killed. Along with shorter half lives, new pesticides utilize more effective stickers, the chemicals which keep them in place, and are thus effective in much lower concentrations. This makes them easier to control and adds less chemical to the environment. In addition, biological controls, viruses and bacteria that occur in nature, are being refined and adopted for use as natural micobial pesticides, such as Bacillus thuringiensis for the control of gypsy moth.

Drawing showing streamside forest buffer.
Sediment, fertilizer and pesticides are carefully managed, Concentrated flows are converted to dispersed flows by water bars or spreaders, facilitating ground contact and infiltration. Filtration, deposition, plant uptake, anaerobic denitrification and other natural processes remove sediment and nutrients from runoff and subsurface flows. Maturing trees provide detritus to the stream and help maintain lower water temperature vital to fish habitat. Debris dams hold detritus for processing by aquatic fauna and provide cover and cooling shade for fish and other stream dwellers.


Drawing showing streamside forest buffer.
Debris dams hold detritus for processing by aquatic fauna and provide cover and cooling shade for fish and other stream dwellers. Tree removal is generally not permitted in this zone. Periodic harvesting is necessary in Zone 2 to remove nutrients sequestered in tree stems and branches and to maintain nutrient uptake through vigorous tree growth. Controlled grazing can be permitted in Zone 3 under certain conditions. Watering facilities and livestock are kept out of the Riparian Zone insofar as practicable.

The Streamside Forest Acts as a Sink by Storing
Nutrients for Extended Periods of Time

The streamside forest can function as a SINK when nutrients are taken up by plants and sequestered in plant tissue. Some estimates indicate that 25% of the nitrogen removed by the streamside forest is assimilated in tree growth which may be stored for extended periods of time in woody tissue and possibly removed as logs or other forest products. Nitrogen and other nutrients may also be passed up the food chain when plant tissues are consumed by animals and converted to animal tissues. In wetter areas, nutrients in leaf litter can be stored for longer periods as peat. Sediments filtered out by the streamside forest remain to become incorporated into the forest soil.

Forest floor leaf litter.
  Orange arrow bullet point. Nutrients can be filtered, transformed or stored by processes taking place in the forest litter.
USDA Forest Service

The Streamside Forest Provides
a Source of Energy for Aquatic Life

Energy for aquatic life is added to streams in the form of leaves and twigs, a part of a mixture called detritus.The streamside forest functions as a SOURCE when it provides energy to streams in the form of dissolved carbon compounds and particulate organic detritus. These materials are critical to processes within the stream itself, helping to restore and maintain nature's equilibrium. In small, well-shaded upland streams, as much as 75% of the organic food base may be supplied by dissolved organic compounds or detritus such as fruit, limbs, leaves and insects that fall from the forest canopy. Benthic detritivores (the stream bottom bacteria, fungi and invertebrates that feed on the detritus) form the basis of the aquatic food chain. They pass on this energy when they are, in turn, consumed by larger benthic fauna and eventually by fish. Thus the streamside forest functions as an important energy source for the entire aquatic food chain from headwaters to estuary.

Orange arrow bullet point.Energy for aquatic life is added to streams in the form of leaves and twigs, a part of a mixture called detritus.
David Funk

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