How Does The Oxygenation Level Of The Water Affect The Number Of Stonefly Larvae

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This research project was designed to investigate the affects of oxygenation levels the number of stonefly larvae in fast flowing rivers and streams. Stonefly larvae are an invertebrate that makes its home in fast flowing streams and rivers all over the world. Sampling different places in a stream or river and counting the number of stonefly larvae in that area carried out the test.

Experimental Hypothesis

I expect there to be more stonefly larvae in water with a high concentration of oxygen compared with water of a lower concentration of oxygen.

Null Hypothesis

There will be no difference between the amount of stonefly larvae in water with a high concentration of oxygen compared with water of a lower concentration of oxygen.

Research

This experiment was designed to research how oxygenation levels in water affect invertebrates that live in it, especially stonefly larvae.

There are many different factors which help or hinder life for aquatic animals. I will be conducting my experiment in fast flowing streams and rivers. The main factors that affect aquatic life are things like; temperature of the water, velocity of the water the substrate and the oxygenation levels of the water. The substrate of the river is what kind of terrain there is at the bottom of it, for example large rocks or small rocks. I have researched these factors as they will help me determine the variables in my experiment.

Oxygenation levels of water are very important for the aquatic life within. Water becomes oxygenated in three main ways; the oxygen dissolves by diffusion from the surrounding air, aeration of water that has tumbled over falls and rapids and as a waste product of photosynthesis: (Carbon dioxide + Water —> Oxygen + Carbon-rich foods). So factors like velocity of water and amount of plant life in the water can effect how much dissolved oxygen is inside of it. [2]

Oxygenation levels must be over a certain concentration for aquatic life to survive, it must not reach too high, as that can be dangerous for the organisms living in the water. A scientific journal I have found during research states that: “Safe concentrations of dissolved oxygen for survival and adult emergence of larvae of nine species of aquatic insects, including mayflies, stoneflies and caddis flies ranged from 0.6 mg/litre for the midge Tanytarsus dissimilis to slightly less than saturation for the emergence of Ephemera simulans (18.5 C).

All species tested were less tolerant of low oxygen concentrations for 30 days than for 96 hours (90% of E. simulans survived 4 mg/litre for 96 hours, but no adults emerged successfully” this means that different oxygenation levels effect invertebrates in different ways, some have a resistance to low oxygenation levels and some cannot become fully developed flies if there is not enough oxygen in the water. This shows me that there should be a difference in the number of stonefly larvae depending on the oxygenation level of the water. [1]

My investigation is going to be centred on stonefly larvae. Stonefly larvae are weak swimmers and tend to crawl around and hide under the river or streams substrate. They prefer fast flowing water as their habitat as they are adapted to survival in it. Stonefly larvae can be herbivores that eat algae and decaying plant material, predators eating other smaller invertebrates or even both. The stonefly life cycle is quite large. After mating, the female deposits large masses of eggs.

The eggs hatch into larvae. Stonefly larvae have between 10 to 30 stages of development (called instars). They move from one stage to the next by shedding their exoskeleton (called ‘moulting’) over a period of 1-3 years. As the nymphs mature, wing pads appear and continue to become larger as development progresses. When the nymphs reach their last instar, they crawl out of the water and moult one last time, becoming adults. In most species, the adult stage feeds but dies shortly after mating.

Stonefly nymphs play an important role in freshwater systems, serving as a food source for various fish and invertebrate species. Stoneflies are often biological indicators of water quality because they require highly oxygenated water for respiration. As a result these macro invertebrates are labelled “Sensitive to Pollution” and their presence in a water system typically indicates good water quality. [3] and [4]

Stonefly larvae’s adaptations include a long and thin body so they are hydrodynamic in fast flowing streams. Hooked claws on there feet so they can cling to the substrate of their habitat even when the water is flowing really fast. Gills that give a large surface area for diffusion of oxygen into there bodies. [6]

Invertebrates like stonefly larvae need to filter oxygen from the water for use in aerobic respiration. Aerobic respiration may be represented by the general equation: C6H12O6 + 6O2 6CO2 + 6H2O. About 3000 kJ mol-1 of energy is released. Burning glucose in air would release this amount of energy in one go. However, it is not as simple as this in aerobic respiration. Aerobic respiration is a series of enzyme-controlled reactions that release the energy stored up in carbohydrates and make it available to living organisms. [5] Stonefly larvae are small enough so that they have a surface are to volume ratio which would allow them to diffuse oxygen into there bodies without the use of a specialised organ, however they live under water so they have specialised gills on there body which have a large surface area so when oxygenated water flows over them they absorb some of the oxygen that they can use for respiration.

Rationale

This experiment studies the affect of oxygen concentrations in water on aquatic life, mainly invertebrates. Therefore the results will help in understanding how pollution affects the growth and life cycles of aquatic animals. With increased research into this subject methods of preventing or treating polluted water can be found to increase biodiversity in rivers and streams. This will be beneficial to the fishing industries as the increase in aquatic life means an increase in fish.

Initial Planning

The independent variable I will be monitoring in my research is the amount of oxygen dissolved in the water. I will take readings in many different places as to get a wide range of oxygen readings. The dependant variable I will be measuring is the amount of stonefly larvae in an area, I will see if this number is affected by the independent variable. There are lots of control variables I need to think about. As this research is conducted in the field it is very hard to control some variable. I plan on taking as many measurements as I can but I need to think about where I will take them. I will take my measurements in places where there is little tree cover so that there is allot of light in the area.

I will also make sure the substrate is the same where I take measurements as it could affect my experiment allot, I will do this by picking places with the same sized rocks to take my measurements. Depth is another variable I will need to control, I will do this by measuring in places of roughly the same depth. Temperature and speed of the water are the hardest variables to control as they fluctuate in the different parts of the stream. I will measure these variables in my trial investigation to see what kind of affect they have on my dependent variable.

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