The Use Of Vetiver Grass For Stabilization and Remediation Of Farm Ponds.

Commodities

Practices

[caption id="attachment_1172951" align="alignnone" width="225"] Hedgerows of Vetiver[/caption]

Vetiver grass (Chrysopogon zizanioides L. Roberty) is a tropical, fast-growing perennial bunch grass with a fibrous, dense and deep root system. It has been used for hundreds of years and is capable of surviving for decades. It is noninvasive, as it does not produce fertile seed, nor does it have lateral roots. The plant is very adaptable and will tolerate soil with a pH from 3 to 11, temperatures from -15 to +55 degrees C, it is drought resistant and at the same time can survive being submerged in water for 3 to 6 months. It also tolerates soils with up to 9% salinity, most heavy metals, and herbicides except for glyphosate. Vetiver Grass Technology is the use of vetiver grass to prevent soil erosion, conserve water, manage storm water, prevent landslides, and provide phytoremediation. It is used in over 100 countries worldwide and is promoted by Vetiver Network International

 

When planted very closely it forms a dense narrow hedge. Its leaves and stems will grow up to 7 feet tall and its roots will grow downwards from 6 to 12 feet. The roots have a tensile strength of 1/6 that of mild steel, and when planted in hedges they will increase soil sheer strength by up to 45%. Underneath each hedgerow an interlocking and dense root matrix creates vast, dense underground walls that not only reinforces soil structure but will stabilize any associated infrastructure. (Truong,2008) This has been shown to markedly reduce erosion. These hedgerows will capture up to 90% of all sediment behind the row, increase the infiltration rate of water into soil, increase both the soil’s water retention capacity and hydrologic conductivity, and decrease water runoff by up to 70%.(Truong,2008)

 

The pond to be studied has had significant erosion of the banks due to rainfall and effects from wind causing waves against the edges. There has been overflow in heavy rains affecting down sloop areas and the water is contaminated with blue-green algae and e-coli therefore it cannot be used for any agricultural purposes. There is also significant saturation of the soil below the pond indicating possible seepage. The pond continues to have low water levels that indicate water loss from seepage or evaporation.

 

Ponds, particularly small earth-built ponds are vulnerable to wall erosion, overflow, and instability of the spillway. For these ponds it is particularly difficult to protect the walls from erosion because of drawdown and fluctuating water levels. But vetiver grass can survive months of being submerged and therefore is particularly useful in protecting the edges of a pond.(Vetiver) Planting the lower edge of the study pond with vetiver with allow the degree of erosion to be assessed over two years.

 

Phytoremediation is the use of plants with associated soil microbes to reduce the concentration of contaminants in the environment. Vetiver grass is economical and effective in removing pollutants from water (Truong;Danh;Darajeh;Mini;). Vetiver's roots absorb heavy metals and agricultural pollutants from water, and these are then sequestered by the plant's cells and inactivated. The upper edge of the pond is closer to the road and there has been runoff while the lower edge is adjacent to sheep and goat pens, both possibly causing contamination with nitrogen, phosphorus (causing the heavy growth of blue green algae) and effluent (causing the e-coli contamination). These have rendered the pond unusable for agriculture. A study in China examined the effects of vetiver grass hedgerows on the runoff of agricultural pollutants. Following fertilization of fields, the presence of a vetiver grass hedgerow reduced nitrogen and phosphorous in runoff by 94 to 99%(Oshunsanya).  Vetiver is also very effective in reducing e-coli bacterial counts by up to 97 % after only 14 days.(Truong,2015). Placing a vetiver hedgerow along the edges of the pond should reduce any continuing ingress of pollutants.

 

A study in the Philippines looked at using vetiver on pontoons to remediate the water used in the aquaculture ponds. The water was obtained from a nearby river with known ammonia, phosphorous, and heavy metal pollution including copper, chromium, lead, Zinc, and Manganese. Three different water treatments were used, one of which was floating vetiver pontoons in the aquaculture ponds. One of the vetiver treated ponds was 350 m² and 1.5 m deep. This is similar in size to the pond that is being studied. The pontoons used were 1 m² with 12 vetiver bunches per pontoon. The number of pontoons used in this pond is unknown.  After 4 months of treatment copper levels were undetectable, ammonia levels were within acceptable limits, and dissolved oxygen levels had improved. The treatment improved the water quality and the growth of the fish.(Pleto) Another study looked at using vetiver pontoons in a small river for water remediation. These pontoons were 1m² and had 100 vetiver plants on each one. Nine pontoons were deployed Within 500m. A 14% increase in the Water Quality Index was seen within six weeks of the pontoon installation in actual running water. It is difficult to extrapolate this information to what would be needed in a pond with a much lower flow of water.(Kusin)

 

Although there is a significant amount of research on how Vetiver can be used to reduce pond wall erosion and to improve water quality, it is still unknown for small farm ponds how many plants are needed per surface area of pond to achieve improvement of water quality. It is also unknown if the pontoons continue to function or if the plants need to be replaced and if so at what intervals.

 

This solution using The Vetiver System is a well-tested low cost and effective method for improving water quality. It is particularly beneficial to low resource farmers as it does not require heavy equipment to install, it will treat the contaminants that are present in local ponds, and it withstands both drought and inundation. By improving access to water vetiver is capable of increasing crop productivity and maintaining the health of livestock thereby improving the economic outlook for farmers.

This project has four objectives:

1. Measuring bank erosion of the pond through observation.
2. Looking at potential loss of water through the banks of the pond by measuring the moisture level below the vetiver hedge row as compared to the area of the bank that does not have the hedgerow.
3. Measuring how water quality of the pond is affected by the floating vetiver pontoons through serial testing of the water and tissue of the vetiver plants.
4. Measuring the number of vetiver plants needed per surface area of a pond for both complete and continuing phytoremediation.

The first objective of the project is to control the amount of erosion that occurs on the banks of the pond. The pond that is being studied has had fluctuations in the water level with current significant drawdown. Currently, the pond is full after about 5 inches of rain. However, before the rain the level was at least 3 feet lower. Although the use of vetiver to control erosion on hillsides and ponds has been well documented, its ability to function in the soil that is present, and the degree of water saturation of the soil would be important to measure. This objective will be by observation and serial photographs of the area will be used to document how well the vetiver survives on the bank and controls any continuing erosion.

The second objective is to look for indications of continued water loss through and over the lower bank of the pond. Vetiver is known to increase the infiltration of water and to increase hydraulic conductivity of soil. This pond is located uphill of other farming plots. It has been noted that the soil of these plots is highly water saturated and at times inundated. The lower bank of the pond is above grade of these plots. Since it is known that vetiver can increase the hydraulic conductivity of soil and given the way that this pond is situated it is possible that there may be continued or even increased saturation of the plots below the pond with the vetiver hedgerows.  This would be important data to have for future design and planting of other ponds. Multiple moisture readings will be taken along the entire lower edge of the pond prior to any intervention. One half of the lower edge of the pond will be planted with vetiver grass and serial moisture readings will be taken monthly and compared to the unplanted side. In the second year the planting of the lower edge will be completed. The serial moisture readings will be continued and compared to the first year to determine if the quantity of vetiver will affect the soil saturation. Also serial measurements of pond depth will be taken at several sites in the middle of the pond and the level of drawdown at the edges will be measured to help quantify water loss even though this could be due to multiple factors including evaporation along with seepage. In addition, anecdotal records of actual downstream flooding will be collected along with any evidence of flooding over the top of the pond.

[caption id="attachment_1173358" align="alignnone" width="300"] Erosion of the pond banks[/caption] The third objective of measuring how the water quality of the pond is affected by the floating vetiver pontoons will be accomplished through serial testing of the water and testing the tissue of the vetiver plants after deploying a floating pontoon in the pond. Studies have shown that floating vetiver grass pontoons are able to remediate water that is contaminated with agricultural pollutants, bacteria, and heavy metals. Through testing it is known that this pond is contaminated with e-coli, and it is presumed that it has a high level of nutrients given the amount of blue-green algae present. To quantify the actual levels of contamination a water sample will be sent to a certified laboratory before any interventions are started. The pontoons will be built based on the designs that have been found to be the most workable and then planted with vetiver. In these studies, the number of vetiver plants per pontoon vary from 12 to 100. The pontoons used in this study will use 25 plants. A site close to thelocation of the pontoon will be used for all of the water measurements. Serial water samples will be obtained after the pontoon is placed. Studies have shown an improvement within 2 weeks to 2 months. So, the sampling schedule will be 2 weeks, 2 months and 6 months. At 6-months a tissue sample of the vetiver will be obtained. The tissue sample will allow quantification of how much contaminant was taken up by the plant. At 6 months a second pontoon will be built and deployed. The same sampling schedule of 2, 4, 6 months will be used. This will allow an analysis of how much increased benefit could be obtained with an increased number of plants. At the end of the 6 months a third pontoon will be built and deployed. The same sampling schedule will be used. This third pontoon will be used not only to determine if additional plants are needed to remediate the pond but also if there is a decrease in the efficacy of the pontoons over time. All of the pontoons will remain in the pond. Although samples of the grass will be taken from the pontoons present the entire plant will not need to be removed. Therefore this should have a negligible effect on the efficacy of each pontoon.

The fourth objective of determining the number of vetiver plants needed per surface area of a pond for both complete and continuing phytoremediation will be obtained by the serial addition of the vetiver pontoons and the continued water quality sampling. Tissue cultures will be obtained from all the pontoons. This will allow for a comparison of the quantity of contaminants in the plant based on the time that it has been in the water. This can then be extrapolated to the efficacy of the plant over time.