Elizabeth van Dijk10/23/13Bio 181-002IObservation of Aquatic Lake Life and the organisms at different water depthsAbstract:In this lab we went to Lake Wheeler in order to collect samples of living organisms and data on physical and chemical factors. To evaluate the data, we used a variety of instruments to collect our samples before completing further tests to develop our data upon return to the lab. In order to develop a complete picture of the community, we must take into account all the biological, physical, and chemical characteristics. The results showed the there were correlations between not only the biotic factors of the community, but also the abiotic factors. Thus, the abiotic characteristics influenced the distribution of the living samples, or the biotic characteristicsIntroduction:In this lab we studied and took samples from Lake Wheeler, which can otherwise be referred to as a lentic community, or an aquatic environment that is characterized by standing water (Department of Biology NCSU, 2013). The community is made up of abiotic factors and biotic factors that work together in order to live successfully as an ecosystem. The biotic factors consist of autotrophic, or photosynthetic organisms, and heterotrophic organisms that are herbivores or carnivores (Department of Biology NCSU, 2013). Both types of organisms live in different trophic levels and exchange among the levels in a food web. A similar study was done on the topic of lentic communities. Jason Hoverman and Pieter Johnson completed a descriptive essay on the topic aquatic ecosystems and the life within it. The article, "Ponds and Lakes: A Journey Through the Life Aquatic", consists of the analyzing and describing of different characteristics in a lentic community. The correlation between our study and theirs is that they have explained that characteristics of the community while we examined that correlation between the characteristics.A lentic community is separated into different zones based on depth of penetration of sunlight into the water. The zones of depth are the littoral and limnetic zone. The littoral zone is the shallow area near the shore and the limnetic zone is the open, offshore area of the lake. The limnetic zone is then divided into a trophogenic zone, tropholytic zone, and profundal zone (Hoverman 2012). The trophogenic zone is the upper level where photosynthesis and respiration occur and the tropholytic zone is below it allowing respiration only. The profundal zone encompasses the bottom sediments and has very low oxygen levels with high levels of carbon dioxide (Department of Biology NCSU, 2013).Time and sunlight are prime components in the factors of temperature, pH, and dissolved oxygen levels. During the day there is a large amount of sunlight which warms the surface of the water, lowering the density of the surface water and keeping it above the cooler, denser water. This layering effect is called thermal stratification and occurs during warmer seasons and thus continuing until the weather becomes cooler (Hoverman 2012). However, at night, the absorbed energy from the sun radiates out of the water back into the air making the upper levels cooler anddenser and makes the bottom layer warmer. This process is called convective mixing (Department Of Biology NCSU 2013). The dissolved oxygen and pH levels are also affected by sunlight and thus thermal stratification. As more sunlight strikes the surface, more photosynthesis occurs. This produces higher levels in dissolved oxygen and less carbon dioxide. Cellular respiration occurs during both the day and night and uses the dissolved oxygen to produce carbon dioxide. Because photosynthesis stops at night, this causes an increase in carbon dioxide, which then causes a dropin pH because of the increase of carbonic acid (Department Of Biology NCSU 2013). Thus,lentic communities are more acidic in the early morning before photosynthesis occurs and decreases acid levels. The sun is a huge factor in the way a lentic community cycles. The community is in a constant cycle as the biotic and abiotic factors influence each other; and are in direct correlation as the levels of chemicals and the rates of processes fluctuate. Methods: In this lab, we had to complete multiple tasks in order to collect the variety of samples. Specifically, we needed to find the lake's pH, compensation depth, plankton samples, sediment samples, dissolved oxygen, and temperature at different depths. We measured the pH by using a pH meter. This was completed by taking a sample of lake water into a jar and putting the pH meter into the water after we neutralized it with water of pH 7. This was completed three times and was then averaged. To determine light penetration at a certain depth, we used a Secchi disk to measure Secchi depth. We put the disk into the water and lowered it down until it could not be seen. The data collected was taken in two numbers, the measurement when the disk could not be seen and the measurement of the disk of when we could see it again. The numbers were then subtracted. This was completed three times and then averaged. To then calculate compensation depth, we took the average Secchi depth and multiplied by 2.5.Then, we determined dissolved oxygen concentration and temperature with a portable electronic dissolved oxygen meter. There is a submersible probe on the meter which was loweredby a cable into the water. This then measured the dissolved oxygen and the temperature of the water and was repeated and completed for depths of 0, 50, 100, 150, 200, and 250 cm.Samples of plankton were then collected at different depths. To obtain the samples we used a Schindler-Patalas trap. The trap is lowered into the water and hinged doors at the top and bottom of the trap open. As the trap is brought back up, the doors shut which traps a 12-liter sample of water from the depth to which the trap was lowered. When the trap is pulled out of the lake, the water inside flows out through a net which attaches a sample bucket to the trap. Organisms that were at the lowered depth are then retained in the sample bucket. Plankton samples were taken at levels of 0, 50, 100, 150, 200, and 250 cm. Two samples were taken from each depth and put into labeled jars. Three different sediment samples were then taken from the profundal, littoral, and shore zones. Each sample was taken using a Bottom Grab Sampler or the jar scoop. The shore samples were collected 1 meter above