Sampling Techniques
The data for the study is going to be collected along a number of sites along the river channel, in total there will be 10 sites. Choosing the sites to collect the data can be chosen in several ways:
Random Sampling
This is where sites are chosen using completely random methods, such as random numbers from a calculator. These numbers will relate to points along the river and this is where data collection will take place.
Systematic Sampling
This sampling technique is less biased as the sites are chosen by deciding that data is to be collected a fixed distance along the river each time, such as every 10 meters along the river.
Stratified Sampling
This method of sampling requires you to think of where pollution would affect the river the most along its course and chose prime areas along the river that will provide above average data.
I decided to choose systematic sampling as this would provide the most unbiased results as I would collect data at regular intervals. This created a slight problem as some of the sites I chose were unreachable as they were on private land or part of a sewage system. this meant that I had to carry on as close to the original site I chose, but was not the exact point.
Methodology
In order to collect the results I first needed to create a site map. On this map I systematically plotted the sites I was going to visit, approximately 2cm apart on the map. This then provided me with a guide to where I should collect all of my data and also made sure that they were collected fairly.
In order to test my hypothesis I needed to collect a variety of data. Some results were found on site, these included, temperature, velocity, pH, Nitrates and the biotic index, while others had to be found in the classroom using samples of water collected on the day, such as oxygen levels, phosphate levels and the amount of ammonia in the water.
Temperature
To collect the temperature I needed to hold a thermometer in the river for 10 seconds. This would enable the temperature of the water to take full effect on the thermometer.
Velocity
The velocity of the river is how fast the water travels downstream. I collected this data using a flow meter. I had to place the rod with the fan on it in the river and record how fast the propeller took to move down the rod. The propeller needed to be faced upstream as to have the full effect of the river flowing downstream.
pH
Measuring the pH levels tell me how alkaline or acidic the river is. The optimum level for the river would be if it had a pH of 7, this means that the river is neither alkaline nor acidic and so is neutral. I measured the pH level using a pH strip. This strip was dipped into the river for one second. The strip then changed colour and a colour chart was used to distinguish how acidic or alkaline the river is.
Nitrates
Nitrates are chemicals that enter the river either through farming practices or traffic along the roads in urban areas. To test the water for Nitrates, I needed to take a nitrate stick and place it in the water for one second. I then let this dry off for a minute or two. The end of the nitrate stick should have changed colour from white to a purpler colour. The shade of the purple determines the concentration of nitrates in the water and can be measured using the colour chart provided with the nitrate sticks.
Biotic Index
The biotic index required me to collect a sample of invertebrate at each site. I collected this data by performing a kick test. Firstly a net had to be placed in the channel so that anything travelling downstream will get caught in the net. I then proceeded to kick the river bed, dislodging any material or species from the bed and into the net. This had to be carried out for 3 minutes to get the full effect. The contents of the net were then poured onto a white tray filled with 2 centimetres of water to cater for the invertebrates the type and amount of each individual species then needed to be counted. The invertebrates are then checked against a chart and a result is recorded.
Water Sampling
Due to the complicatedness of the oxygen, phosphate and ammonia tests, these needed to be tested back in the classroom. In order for the results to be fair, a water sample from each site needed to be collected so that the results all coincided. To collect the water sample an empty bottle of water no smaller than 500ml was emptied, rinsed out and water from the river was then collected in this bottle. A water sample from each site visited was collected as each site needed these last three tests top be carried out.
Results
To ensure that all the results coincide with each other and have been fairly collected, all data was collected on the same day. This ensured that the results were not affected by weather or varying rates of pollution on different days.
Table 1
Biotic Index Score
Spearman Rank
The spearman rank test it used to find if there is any significance of two sets of results. This enables us to discover if two sets of data collected are linked in to the health of the river. In this test I will be finding the significance between the level of oxygen in the river and the temperature of the river.
Null Hypothesis
As the oxygen levels increase the biotic index score will decrease.
Table 2
R = 1 – 6xΣd²
n³-n
r = 1 – 6x216
1000-10
r = 1 – 1296
990
r = 1 – 1.3
r = -0.3
The way the rank spearman result is interpreted, is if the end value comes out as -1, this means that there is a strong negative relationship between the two sets of data and if the result is +1, there is a strong relationship. My end result was -0.3, this shows that there is a weak negative correlation. This means that it is not statistically significant that as oxygen is lower the biotic index is lower.
Analysis of Photos
The source - Priory Gardens
This was my first site and was at the source of the River Cray. As you can see from the photo, there is very little pollution and the presence of wildlife also indicates this as they would feed on the other life in the water. There is only one piece of pollution in the picture and that was caused by humans. Priory Gardens is a small park area and is available for use by the public at all times so has the potential to become polluted, but careful management prevents this.
Site 2 -
