Effects of Depth and Sediment Concentration on the Penetration of Photosynthetically
IntroductionThe purpose of this study plan is to measure the effects of light on sedimentary particles in water. This study plan will include information pertaining to equipment, procedures, and analysis. This plan will also discuss problems that could arise during the sampling.
LiteratureEnergy is distributed throughout the world’s oceans in several usable forms. The heat transmitted during absorption is responsible for ocean waves, temperature and currents. Light penetration in water will measure in units of quanta. This measurement refers to the amount of sunlight that penetrates the water at various depths. The light energy is absorbed and scattered by suspended particles, dissolved substances, and the water itself (USGS). Other factors include attenuation coefficient: rate at which light decreases with depth. This means that each site studied may have a different attenuation coefficient. An example of a high coefficient would indicate a rapid decrease in light penetration, therefore, high sedimentation. Another factor to be aware of is the color of the water. Color can effect the light penetration and intensity. Also the turbidity which is a measure of water clarity and how much material is suspended in the water. Suspended material could include soil particles, algae, plankton, microbes, and other substances (EPA). The sources of the turbidity could include erosion, waste, runoff, and bottom feeders (EPA).
EquipmentThe instruments used to make photosynthetic measurements is called a Li-Cor Quantum/Radiometer/Photometer model #189. The sensory device is connected by a long cord and is used to measure at depth. It’s called an underwater PAR sensor; Li-Cor #1925. This sensing device or photocell can also be used to measure surface PAR. Other devices to be used during the data sampling include lowering frame Li-Cor #20095, various weights and cables. The cables and weights will used to hold the sensors in the water column at the proper depths. Another instrument could be used to calculate the amount of PAR that is received at the surface. This instrument is called a pryanometer. It is not a requirement to use two different instruments for surface PAR, but just a suggestion that might give more scientific validity to the data being collected.
ProcedureWhile conducting this experiment it is necessary to have at least two people present to take the measurements. One person will lower the sensor in the selected site locations. The other person will record the PAR measurements from the display and calculate range values. The measurements will be taken within a four-hour period, two hours on either side of the solar noon. Solar noon is half way between sunrise and sunset; not 12:00 noon. Solar noon is at 1:15 PM, Central Daylight Time. This is the time when light energy is at the maximum. Samples are taken between 11:15 AM and 3:15 PM and are taken every 30 minutes; and data recorded at 10 second intervals. Before the samples can be taken it is imperative that the Quantum Radiometer be clean and free of debris and calibrated. This calibration will correct errors that may occur. Also the collection of the control data must be present. This control must be free of errors and represent the selected site. Another measurement must be made of the surface PAR. This data will help determine the amount of light energy present at the surface. Next the determination of water columns is important. These sites must be chosen randomly and cover the entire site. Later others can concentrate studies in points of interest. These measurements are taken using the underwater sensor attached to the lowering frame. Each water column will be measured at every 10 cm. These recordings will continue until the photometer can no longer detect light energy. The underwater sensor must be perpendicular to the bottom surface so that light intensity will be scattered at a 90-degree angle. Each column will be tested twice so that representative data is present. These samplings should be recorded in a table format, and be divided into proper water column, and depth categories. The temperature of the outside environment should be determined and placed in the table format along with the descriptions of the sample sites and surface PAR data. The number of water columns is dependent on the sample site. Remember sample columns must be representative of area being tested.
AnalysisOther factors that may effect the data collected include not returning to the same sample site later to measure the same water column. This can be corrected by placing some type of marker on the shore if the sample column is near shore. Other marking devices are needed if the sample area is in the middle of the water where no references can be determined. These marking devices include floating buoys, and floating balls. These devices are necessary to make the data consistent and accurate. Another problem that can effect samples is shadows. It is important not to take the measurements when the area is being shaded. If there is abundant cloud cover out it is necessary to wait until clouds dissipate, or discontinue taking measurements for that period.
ConclusionA high sediment concentration in the water will increase water temperature because the material suspended absorbs more heat. Unfortunately this also leads to the decrease in light penetration because the particles block the light from reaching the bottom. Therefore reducing the amount of photosynthesis that will occur in the water. While conducting this study plan it could be said that light and depth are proportionate to each other. This means that the depth of the sensor effects the amount of light that can be measured through the sediment filled water.