NUMERICAL: cell counting:
Probably the oldest method is cell counting and it requires the most common of lab equipment--a microscope. This method has been used since the invention of the microscope and discovery of the microscopic world by Antony van Leeuwenhoek in the late 1600s. (Leeuwenhoek wasn't even trained as a scientist, but was instead a businessman and inventor.)
Counting is usually used when scientists want to know WHICH algae are present as well as how many. It is done using counting chambers that hold a known amount of water and counting and identifying each cell. It requires a microscope and some knowledge of the taxonomy of algae. It is simple because all you have to do is count. It gets more complicated without any knowledge of algae identification.
The most common modern method of measuring the amount of algae (biomass) in water is the measurement of chlorophyll-a. Only photosynthetic organisms contain chlorophyll-a, so this removes any confusion over same-sized organisms that are not photosynthetic. This measurement requires either a fluorometer or a spectrophotometer. It is VERY simple if one of those pieces of equipment is available. Details of how to do this analysis are available in any standard method of water analysis.
GRAVIMETRIC: an almost no-equipment method:
Gravimetric methods are rarely used nowadays by scientists studying algae or aquatic systems since chlorophyll-a measurement has become the standard method, but it may be just what you need. Take your sample and try to screen out any large organisms, like zooplankton, insect larvae etc.. Zooplankton are the tiny animals in the water that eat algae. Most (but not all) can be removed by screening with a mesh of approximately 150 micrometers. This size may remove some large algae, too. A very simple method is to allow the sample to settle in a graduated cylinder and measure the volume. This is faster if the cells are killed with alcohol, formalin or an iodine solution called Lugol's iodine — all are toxic to humans. Samples can be concentrated using a centrifuge, if that is available. The most efficient method is to filter the sample onto a pre-weighed filter then reweigh--the difference is the wet weight. To measure dry weight, filter onto a pre-weighed filter and dry the sample overnight in a low temperature oven (about 60 degrees C) then reweigh to get dry weight by difference.
For our experiment, as we are unable to obtain either a fluorometer or a spectrophotometer, we will instead be using a turbidity sensor, and measuring the Formazin Turbidity Unit (FTU) of the set-ups.
2.1 Equipment List
Usage/Where to Obtain
To measure the amount of FTU
To store the water, algae and
Finely Ground Fertiliser
Contains NPK needed for the experiment
To measure the amount of fertilizer before being exposed to algae
Measuring Cylinder (500 ml)
To measure the amount of water for each cup
To pour the water
Water for the algae to be in
1 Litre Plastic Jug
Labquest 2 Datalogger
To store the ice/water
To clean the equipments
2.2 Diagrams of experimental setup
1. Collect 5L of water from a pond using the jugs.
2. Using the Logbook, record the appearance and your observations of the water.
We will be doing 6 different concentrations (2.5g to 15g, in 2.5g increments). Each concentration will be repeated 3 times so as to make the results more reliable. The control will also be repeated 3 times. (you will require 21 cups)
3. Pick out 18 plastic cups, group them into 6 groups and label the groups as follows: (Group Number)(Group Letter A-F)(Amount of Fertiliser).
4. Pick out another 3 plastic cups and label them as follows: (Group number)(Control 1-3)
5. Filter out the pondweed using the plastic spoon into a bowl and put a teaspoonful of pondweed into every cup.
6. Pour in 200ml of pond water into all of the 21 cups by measuring with the measuring cylinder. Stir the pondweed and the water with the plastic spoon (stir the cups 5 times each and ensure that it is mixed by the same person) and measure the turbidity of every set-up and tabulate the data in a table.
Each individual group will then be subjected to different scenarios.
7. Measure the mass of the fertilizer using an electronic balance and add it into the cups according to their groups. Stir the solution to dissolve the NPK. Ensure that all cups are mixed equally and by the same person (stir the cups 5 times each).
8. The cups will then be covered by a cling wrap to minimise evaporation loss.
9. Measure the turbidity of every cup including the controls on the first, second and fifth day of the experiment. Before measuring the turbidity of each set-up, mix the set-ups 5 times each and ensure that it is mixed by the same person. After which, turbulate the data into the table.
Figure 4.1, mass of fertiliser for each set-up.
Mass of fertiliser / g
Volume of pond water / ml
2.4 Risk Assessment and Management
Spilled water (When setting up experiment) may be a slipping hazard and can cause us to be seriously injured and delay the setup time. (to a certain extent)
Be careful when setting up experiment, ensure that other group members are around before starting with the experiment so as to look out for each other and assist each other when the risk occurs (wipe up the water)
Possible risk of infection from the pondweed due to open wounds.
Wear gloves and goggles when conducting any tests or when handling samples. Wash our hands before and after the experiment. Do not handle the pondweed when have open wounds.
As the experiment involves glassware, there is a risk of breakage (when we are moving the glasswares around or when using the glasswares), and cutting of the hands.
Wear gloves when carrying out the experiment. In case of breakage, the cut to the hands will be minimized. Be careful when moving/using the glasswares during our experiment.
The fertilizers we use for our experiments might be toxic to humans when inhaled.
Wear masks when grinding the fertilizer into fine powder.
Unlikely and not severe harm
Likely but not severe OR Unlikely but severe
Likely and Severe harm
2.5 Data Analysis
1. Tabulate the data and calculate the amount increase in concentration of pondweed in water to the mass of NPK (nitrogen, phosphorus, and potassium).
2. Plot a graph which would show the mass of NPK (nitrogen, phosphorus, and potassium) of all the set-ups and use the results to conclude how the mass of NPK affects the concentration of pondweed in water.
3. From the graph, determine the gradient, and conclude how the concentration of pondweed in water is affected by the mass of NPK (nitrogen, phosphorus, and potassium), and hence find out the effects NPK has on pondweed growth with the goal to control the growth of algae.