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Riparian Forest Buffers and Agriculture

Thomas R. Weik

Introduction

The Big Problem

The Solution

The Big Question

Recommendations   

Conclusion

References

INTRODUCTION (Back to Top)

 

Riparian Forest Buffers (RFB) are an integral part of the health and subsequent life of streams, rivers, lakes, and estuaries. Their location in general makes them an ideal buffer zone for areas of agricultural and chemical run off located near streams, rivers and other bodies of water. RFBs provide many benefits beside the filtration of water. By providing various habitats, they increase the diversity of life existing in them. This increases the importance of RFBs as part of both marine and terrestrial ecosystems.

 

THE BIG PROBLEM (Back to Top)

 

The pollution of waterways by nutrients, sediments, and other chemicals is damaging to ecosystems and hazardous, if not deadly, to life (including human). "According to a United States Environmental Protection Agency survey released last year [1997], pollution is a serious problem in 21 percent of the nation's 2000 or so watersheds"(Suszkiw p. 4). Although not solely responsible for all the non-point source [not from any one source] pollution of the water resources, it contributes its fair share. "In the U.S., non point pollution from agriculture – mostly in the form of sediment, inorganic fertilizers, manure, salts dissolved in irrigation water, and pesticides – is responsible for an estimated 64 % of the total mass of pollutants entering streams and 57% of those entering lakes"(Miller p.279).

NUTRIENTS

 Aquatic plants, like their land-based relatives, are controlled by the nutrient in shortest supply. This principle is known as Liebig's Law of the Minimum. In salt water, nitrogen is the limiting factor, as phosphorus is the limiting factor in fresh water. Therefore, when excess nutrients from the land enter into a water system, the limiting amount is raised and massive growth of algae and other aquatic plants takes place. This growth explosion is called a "bloom". When a bloom occurs at the surface, it can block sunlight from getting to the plants deeper in the water. These underwater plants, called submerged aquatic vegetation (SAV), will often die out from their inability to carry out photosynthesis.

When the SAV areas start to die, bacteria move in to decompose the vegetative remains. This process of decomposition pulls dissolved oxygen out of the water. Since there is no photosynthesis occurring, oxygen is not being returned to the water. As a result, the dissolved oxygen levels in the water at depth drop rapidly. "The capacity of the organic matter in a sample of natural water to consume oxygen is called its biological (or biochemical) oxygen demand (BOD)"(Baird p. 297). As the amount of dissolved oxygen in the water is lowered, the number of species able to survive in the newly forming aquatic environment is also decreased. "This breakdown of degradable wastes by bacteria depletes dissolved oxygen, which then reduces or eliminates populations of organisms with high oxygen requirements, until the stream is cleansed. The depth and width of the resulting oxygen sag curve, and thus the time and distance required for a stream to recover, depends on the stream's volume, flow rate, temperature, and pH level, as well as, the volume of incoming degradable wastes,"(Miller p. 279). Next, certain organisms which flourish in oxygen deficient environments move in and release chemical substances such as methane and hydrogen sulfide which are toxic to fish and other marine life. Algal blooms in estuaries may cause the death of shellfish beds. In areas where thick beds are present, the blooms may prevent oysters from obtaining necessary food and oxygen, by hampering the oyster's ability to pump water through itself. Also, marine plants that are also part of land based ecosystems may be affected. Certain submerged grasses, which are feeding areas for waterfowl, often die out due to lack of light.

 Excess nitrogen in surface and ground water can pose a health risk to some people and animals if the water is used for drinking. In very young children, nitrates in the water may be converted into nitrites. Large amounts of nitrites has been linked to blue baby syndrome, a process where the hemoglobin, or oxygen carrying part of the blood, gets oxidized to a form which is unable to carry oxygen. As a result, brain damage and possible suffocation may occur due to lack of oxygen transport.

SEDIMENTS

 Sediment pollution occurs when soil and chemicals bound in the soil are eroded off the land surfaces and enter the water system. "By weight this is by far the biggest water pollutant. Sediment clouds the water and reduces photosynthesis; it also disrupts aquatic food webs and carries pesticides, bacteria, and other harmful substances"(ES p. 79). Every year about 1.5 billion tons of soil enter the water systems across the nation, and of that, around 64% came from animal grazing lands and croplands. In addition to the effects previously mentioned, the sediment often fills up lakes, reservoirs and raises the bed level of some streams. This may cause the area to be more susceptible to flood hazards.

THE SOLUTION (Back to Top)

What are RFBs and where are they located?

RFBs are the areas adjacent to some body of water like streams, rivers, lakes or shorelines. This area includes all the trees, shrubs, and grasses that trap and filter sediments and nutrients. RFBs also utilize these sediments and nutrients to provide sources of food and shelter for aquatic and terrestrial wildlife.

What do RFBs really do?

If used, RFBs can play a major part in improving the quality of water by trapping and utilizing large amounts of nutrient runoff and sediments. RFBs can trap or absorb up to 90% of the available nitrogen and 80% of the phosphorus that moves into the water system by shallow through flow or overland runoff. RFBs stabilize stream and riverbank slopes by binding soil particles together and adding to bank integrity with deep root mass. The leaf litter and debris on the forest floor helps to slow the flow of water, which allows for the percolation of water and the deposition of sediments.

In addition to the physical effects on the landscape, RFBs provide suitable habitat for a wide variety of birds and animals. This wildlife will find food and shelter in the forest buffers and help add to the environmental diversity and subsequent stabilization of the area. The water habitat also benefits from the presence of the forests. Not only do the forests remove chemicals and sediments that would be detrimental to delicate ecosystems, but the forest canopy also regulates water temperature by providing shade. This allows the water to hold more dissolved oxygen and therefore a wider diversity of life can reside and reproduce in these waters. RFBs help to lengthen food chains and to diversify food webs, which in turn yield a higher species survival rate.

How do RFBs work?

By now the need for RFBs should be clear but the question of how they work remains. RFBs carry out three specific functions often simultaneously.

  1. Filtration – RFBs have the ability to filter out chemicals and excess nutrients by allowing runoff to pass through a series of different vegetative types. This process allows each plant or tree to take full advantage of the rich nutrient flow and utilize it for growth. RFBs slow the speed of water and allow for sediment to be deposited in the buffer zone. This sediment is often laden with phosphorus that is bonded to soil particles.
  2. Change of Chemical Compounds – Certain organisms in the soil convert the nitrogen in the sediment and runoff into NO3. In this form organisms and plants can use it in the creation of proteins. Also, some bacteria will release nitrogen gases into the air as part of the nitrogen cycle.
  3. Storage – Nutrients taken up from runoff may be stored in plant tissues. These nutrients then become part of the biomass and are not released until the death of the plant. When grazed, plants will pass on nutrients up the food chain.

Nuts and Bolts

In order to function properly, RFBs are divided into zones. Each zone has a specific vegetation and function as a part of the buffer system. The number of zones will depend on the land use of the surrounding soils.

Zone 1 - The section of land immediately adjacent to the water's edge and extending a minimum of 15 to 20 feet inland. The vegetation in this zone is of several types of native streamside trees and shrubs. The use of native plants and trees (if at all possible) is preferred do to the hazard of introducing a foreign species that could damage the ecosystems in place. These trees should be of the hardwood variety, as would be found in old growth forests. These are the trees that will provide the major support for stream and riverbanks. The leaf litter will help to slow overland flow and promote infiltration. This zone is the last line of defense before runoff hits the water so careful planting of trees and spacing of shrubs is essential. Trees in this area should not be harvested except as needed to maintain the zone. Livestock should not be permitted to enter this area.

Zone 2 – This zone starts at the edge of zone 1 and extends a minimum of 20 – 60 feet. The vegetation in this zone closely resembles a transitional forest, with lots of conifers, shrubs and some hardwoods. The primary function of this zone is to provide the necessary amount of contact time so that trees and other vegetation can take up the nutrients from the runoff. This forest zone may have its timber harvested as necessary to maintain the forest. Timbering may be done from time to time as long as the soil stability of the zone is not adversely affected and that zone 1 is not compromised. Discharge pipes should not be allowed to pass through the forest. If discharge of any type is piped through the zone, it must have been cleaned somewhere else prior to its entry into the water system. Livestock must not be permitted to enter this area.

Zone 3 – This zone is only used when the buffer is adjacent to cropland or tilled soils. Grasslands or land that is used for grazing will substitute for a zone 3. This zone, when used, starts at the end of zone 2 and is a minimum of 20 feet. The vegetation in this zone should be made up of dense grasses. These grasses will slow the speed of water over them. This will allow for deposition of sediments and nutrients in this zone. From here the processes of filtration and nutrient uptake begins. This zone is suited to intensive rotational grazing by livestock. If this area is not used for grazing, it must be mowed several times a year depending on climate, grass type, and nutrient load. This regular maintenance is necessary to promote growth and nutrient uptake as well as weed control. Re-vegetation by seeding or sod placement may be necessary in areas of high sediment deposition. In some cases, sediment removal may be necessary, to maintain optimum buffer performance.

Width

The width of the zones and the buffer as a whole are determined by many factors. Some factors may include the slope of the surrounding terrain, permeability and leaching potentials, soil type, and the length and depth of source land (size of field or cropland). As a general rule, zones 1&2 together should make up about one – third of the distance from stream bank to the farthermost point of source land. For protection around ponds and lakes, an area of about one-fifth is used as a general rule. The use of other soil and conservation practices in conjunction with RFBs can reduce the total land width required for optimum function.

THE BIG QUESTION(Back to Top)

 

The problem has been identified and an effective solution has been rendered. So, why doesn't everyone use RFBs to protect our waters?

Economics:

Most farmers view RFBs as relatively permanent changes to their farming practices, especially in comparison to other soil management techniques. For instance, if a farmer has a 10-acre field along a river, 25-33% of the field will be tied up in zones 1&2 if the field is used for grazing. If, however, the field is used for cropland, even more land will have to be set aside for zone 3. This farmer would then have to forego the income that would have been generated by the set aside portions of this field for an extended period of time. In many cases for planning purposes, 20 years is often used as the time required before benefits may be seen from the forest. So in effect the farmer has to fence himself and his animals out of a portion of his own land. In addition, the farmer still pays taxes on this land, and in some cases may actually pay more tax since the land may not qualify for agricultural land use. All of these factors in addition to the cost of seeding, reforesting and maintaining this land add up to the economic cost incurred by the farmer for putting in the RFB.

Government programs available

The USDA-NRCS in Virginia provides a program for the establishment of RFBs. This program is based in the conservation reserve program. It provides a cost share of 50% of the cost of the vegetation planted. In the case of grazing land, it will provide 50% of the cost of fencing needed to keep the farmer and his animals off zones 1&2. The program is based on a 10-year agreement with the landowner that he will continue to maintain the fields as stipulated for a period of 10 years at his expense. USDA will pay a rental payment that is based on the soil type, plus a 20% bonus for the environmental use of the land. These payments are meant to compensate the farmer for the loss of viable farmland.

The payments are made yearly for the duration of the contract.

The base cost to the farmer minus the government payment equals the actual cost to the farmer.

In some cases it may be economically advantageous to the farmer to enroll in an RFB program. However, in many cases the payment received for the land set aside is less than what the farmer could make if the land was kept in agricultural production. Furthermore, the program only lasts 10 years, after which all payments stop. Since it will usually take 20 years before the first of the timber can be harvested, the farmer is faced with only a few options:

  1. The farmer can try to reapply for the program. However, since funding is inadequate to meet first time requests, additional funding is unlikely.
  2. The farmer can let the trees mature for 10 additional years without any payments.
  3. The farmer can remove the trees and revert the land back to full agricultural production.

Obviously, these programs designed to encourage the formation of RFBs are greatly under funded. Plus there is few or no programs available for the long-term maintenance of existing buffers. It would appear to be a waste of government funds to allow the buffers to revert to their former use in 10 years and have the cycle repeat itself.

RECOMMENDATIONS (Back to Top)

 

  1. Increase the incentives: Funding to existing programs must be increased to make RFBs an economically appealing option. The entire riverbank must be buffered not just a part.
  2. Increased education: Educate the landowners about the importance of RFBs and the availability of government programs to help in the establishment and maintenance of the buffers.
  3. Establish long term maintenance programs. Our water sources need to be protected indefinitely. Established buffers must be protected.

 

CONCLUSION: (Back to Top)

 

Agriculture contributes about two-thirds of the non-point source poll entering the water systems across the country. Even though this is a large amount, Riparian Forest Buffers, if used properly, would do a tremendous job of filtering out this pollution and improving our water supplies. An additional benefit would be the improved habitat for aquatic and terrestrial wildlife. With proper education and advertising and improved and adequately funded incentive programs, the American landowner might well give up some of their independence for the greater good and could more easily be brought in as custodians of the land, water and natural resources of the nation.

REFERENCES: (Back to Top)

 

Baird C. 1995. Environmental Chemistry. W.H. Freeman and Company, New York, p.296

Hemphill, R.W., and Bramley, M. E. 1989. Protection or River and Canal Banks. Butterworths, London, p.76-108.

Miller, Jr., G.T. 1997. Environmental Science. 6 th edition. Wadsworth Publishing Company, Albany, p.279

Suszkiw, J., Lee, J., Lyons-Johnson, D., and Adams, S. 1998. Natural Environmental Protection Agents. Agricultural Research, February 1998, p 4-9.

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