Water Hyacinth Decrease Or Increase Biology Essay


Geography and bio are both subjects that I take and in both I have been taught about the affect of fertilizers in water bodies and how the added nutrients from crop runoff has caused algal bloom and ultimately eutrophication and the death of all living aquatic organisms in that water body. I have decided to research the affect of nutrient content on the length of root of water hyacinth. I am interested in how the plant will adapt and either grow or minimize the length of the root for optimal nutrient absorption. This research could be used to educate farmers on the effect of fertilizers in water bodies and to show them, with data, the growth of these plants with added nutrients in the water. Therefore this research could be used to educate farmers about the effect of artificial fertilizers on water hyacinth in close by water bodies as well environmentalists who will study the impact of the water hyacinth to that ecosystem and how the nutrient content increase has aided or hinder the growth of hyacinth.

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- Scale bucket (10 litre line already marked on bucket)

- 5 identical tubs (80 litre)

- 15 identical size water hyacinth plants

- Water

- iron chelates (8g per 80 litre tub = 40g)

- Fertiliser (24g per 80 litre tub = 120g+25g+50g+75g+100g = 370g)

- 30cm ruler

- Camera

- 15 pieces of coloured ribbon (to tie around the individual hyacinth plants)

- Scale

- Permanent marker pen

- 10 plastic bags


1. Measure out, using a scale, 8g iron chelates for each tub (A,B,C,D,E) and place the iron chelates in 5 separate plastic bags.

2. Measure out, using a scale, 24g fertiliser for tub A (control) and place in a plastic bag marked A, 49g fertiliser for tub B and place in a plastic bag marked B, 74g fertiliser for tub C and place in a plastic bag marked C, 99g fertiliser for tub D and place in a plastic bag marked D, 124g fertiliser for tub E and place in a plastic bag marked E.

3. Fill 5 tubs with 80 litres water.

4. Label the tubs A, B, C, D, and E.

5. Add the iron chelates and fertiliser to the corresponding tubs.

6. Take initial readings of the root length (cm) of the longest root of each plant. Record in table.

7. Add three identical sized water hyacinth plants to each tub.

8. Tie a ribbon around all the plants in the tubs.

9. Once a week measure the root length of the longest root of all 15 plants. Record in table.

10. Repeat step 9 for 4 weeks.

11. When all data has been recorded in the table, draw a bar graph to represent the data.

Data Collection Plan:

There will be an initial reading which will be taken before the water hyacinth plants are added to the water tubs. The measurements will be the length of the longest root of the water hyacinth plant. The root will be measured from where the root meets the stem to the tip of the root. The length will be measured with a 30 cm ruler and the measurements will be recorded in a table.

The lengths of the roots will be measured once a week for 4 consecutive weeks. By measuring the lengths of the roots of the water hyacinth plants, it will determine if the length of the roots increase as the nutrient content (fertiliser) increases.

This is quantitative data that will be collected and will be represented, first, in a table which will show root length (cm) of the longest root versus the dry mass of fertiliser in the tub of water. The data will then be represented by a bar graph to emphasise the results collected. The data will then be analysed to indentify any trends in the data and to see if the hypothesis, the root length of a Water Hyacinth plant will decrease as the nutrient content in the water body increases, is correct.

This research project will remain scientifically objective and data will be reported honestly with no distortion whatsoever and therefore the data will not be altered in any way. I will acknowledge any assistance and sources from which I have borrowed information and any information that I have used will be cited and referenced. Any herbicides used will be disposed of appropriately as not to cause any negative impact to the environment. The hyacinth plants will be replaced into the main pond once I have concluded my investigation and in this way other students will be able to use the water hyacinth again without having to growth more.

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Literature Review:

The aim of this research task is to investigate the change in root length of water hyacinth as the nutrient content of the water body is increased. The nutrient content refers to the fertiliser that will be added to the water tubs. If the hypothesis, the root length of a Water Hyacinth plant will decrease as the nutrient content in the water body increases, is proven correct then it will reinforce the studies which have shown that water hyacinth flourishes in water bodies with high nutrient content from fertilisers that have been washed into water bodies from farms. By analysing different sources, both secondary and primary, it will determine the various results and points of view on this particular topic.

Water Hyacinth (Eichhornia Crassipes) originates from Central and South America it is a free-floating or mud-rooted aquatic plant which ranges in size from a few centimetres to almost a metre in height (stem length). The water hyacinth is capable of rapid reproduction by means of side shoots which break off and grow to be separate plants. Stirton (1978) stated that, in optimal conditions, a group/colony of these plants can double in size every eleven to eighteen days. Bromilow (2001) states that this plant was originally introduced into South Africa just before 1910 and is now "well-established in all four provinces of South Africa." (Stirton, 1978, p.68). The roots of the plant are feathery and long and this helps to balance the plant while the stalk is a swollen, air-filled structure that keeps the plant buoyant. According to Bromilow (2001), the water hyacinth infests lakes, dams and rivers and it becomes impossible to navigate, fishing and increase evaporation. Both these sources give identical facts about the plant and both sources are written in a scientific and unbiased manner.

The tubs of water will have to be filled with a "base" of nutrients which will be a fixed mass of iron chelates and fertiliser. Unknown author (website: http://www.smart-fertilizer.com/articles/iron) states that, "Chelates are compounds that stabilize metal ions (in this case - iron) and protect them from oxidation and precipitation. Iron chelates consist of three components: Fe3+ ions, a complex, such as EDTA, DTPA, EDDHA, amino acids, humic-fluivic acids, citrate and sodium (Na+) or ammonium (NH4+) ions." The iron chelates and fertiliser will allow the plants a source of nutrients. The information given by my teacher states that, "7:1:3 fertiliser and iron chelates to be added to the water in a ratio of 3:1. 8g iron chelates and 24 g of fertiliser to be added to 80 litres of water." All of the 5 tubs will be given this "base" nutrient content and there will be a variation in the dry mass measurement of fertiliser that will be added to four out of the five tubs of water. This change in fertiliser content is the independent variable.

Eutrophication falls into this research topic (nutrient content versus growth of plant). Moore, Garnett and Shaw (nd) state that eutrophication is the process whereby nutrients are added to natural bodies of water such as rivers, lakes and dams. Moore, Garnett and Shaw also state phosphorous and nitrate play a role in algal growth. This statement links fertilisers, which contain nitrates and phosphorous. Both these compounds are essential for plant growth and development. If fertilisers are washed into water bodies, it will be in favour of the aquatic plant life, which will benefit from these nutrients. There will be a chain reaction of events. First there will be a flourish in algal bloom such as water hyacinth. This will cause a decrease in dissolved oxygen in the water and decreased light penetration. This eventually leads to the death of marine life in the water body. In my experiment, I am using fertiliser and investigating the effect of added nutrients on the plants, specifically the roots of the plant. The experiment done by Xie, An, Yao and Xiao (2005) offers evidence that my hypothesis is correct. "Increase of nutrient availability in sediment or water led to increased plant N (ranged from 2.47 to 4.77 mg g−1) and P concentrations (ranged from 42.8 to 62.0 mg g−1). These results indicate that considerable variation in root morphology of V. natans exists in response to the fertility of the sediment it is rooted in." (Xie, An, Yao and Xiao, 2005). This experiment tested the type of soli the plant was rooted in versus root growth. This experiment is very similar to mine because it focuses on nutrient content.

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The conclusion that I have come to is that nutrient content in the water body definitely has an effect on the growth of the plant. I have not been able to find an article or research that has confirmed that root length decrease as nutrient content increases. This inverse relationship is due to the surface area: volume ratio that exists. I believe that the plant will extend its length in order to increase the surface area so more nutrients are absorbed when the water body has decreased quantities of nutrients.


Bromilow, C. (2001). Problem Plants of South Africa. Pretoria: Briza Publications.

Iron Nutrition in Plants. (n.d.). Retrieved February 6, 2013, from http://www.smart-fertilizer.com/articles/iron.

Shaw, GR., Moore, DP. & Garnett, C. (n.d.). Eutrophication and Algal Blooms. Queensland: National Research Centre for Environmental Toxicology.

Stirton, CH. (1978). Plant Invaders. Cape Town: Department of Nature and Environmental Conservation of the Cape Provincial Administration.

Xie, Y., An, S., Yao, X. & Xiao, K. (2005). Short-time response in root morphology of Vallisneria natans to sediment type and water-column nutrient. China: University and Wuhan Nanjing University.