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Yan Hui Life in a Vernal Pool
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On October 9, the opportunity to answer all my questions came. It rained heavily in the vicinity of Kinkaid's backyard. The next day, October 10, I went to the school backyard to find out whether a vernal pool had formed. The vernal pool area was flooded with water.  The flooded Kinkaid vernal pool.  Graph 1 (Click to enlarge) The duration of this flooded vernal pool was 10 days. It formed on October 10 and was completely dry by October 19. During this time, the air temperature ranged from 65 degrees F. to 84 degrees F., the water temperature was between 67 degrees F. and 77 degrees F., and the humidity range was from 58 percent to 75 percent. There was no additional rain during this period of time. The pool was 19 inches deep on the first day, and the depth increased by one inch on the second day as water was still draining into the pool from the surrounding area. However, the depth of the pool started to decline almost linearly after that, until it dried up. The atmospheric conditions do not seem to have affected the rate of water loss due to evaporation and seepage. The vernal pool swelled to a maximum size of approximately 65 feet long by 25 feet wide, or 1,625 square feet total, and then shrank slowly until it was dried up on the 10th day (Graph 1).  Graph 2(Click to enlarge) I analyzed water samples taken from two locations in the pool, Location A and Location B (see Map), for water quality. I found that the water quality did not fluctuate very much for the duration of the pool until the day before the pool dried up (Graph 2). The water had a pH of 6, total alkalinity was 0 ppm (parts per million), total hardness was 50 ppm, the iron content was 0 ppm, copper was 0.5 ppm, free chlorine and total chlorine were both 0.1 ppm, nitrate was 0.5 ppm, and nitrogen was 0.15 ppm, in both locations. On the day before the water dried up, the water qualities changed slightly. The total hardness increased to 120 ppm, the total chlorine content increased to 0.2 ppm, and the concentrations of nitrate/nitrite nitrogen and nitrite nitrogen declined to 0 ppm. The changes in water quality on the last day may be due to the increased concentration of dissolved minerals in the water due to evaporation. I also tested distilled water and found that there were no dissolved minerals in it at all. Houston tap water had a total hardness of 120 ppm, and a free chlorine and total chlorine content of 1.0 ppm. Compared to the standards of the U.S. Environmental Protection Agency, the water quality of the vernal pool is within the EPA recommendations, and I deduced that it was suitable for organisms to live in. However, I did not observe any microorganisms under the microscope in the water samples taken from the pool. I only observed rotting tissues from vegetation. My observations showed that the rotting process was taking place in the water, and explained why I had seen gas bubbling from the pool. |
 Yan Hui collecting specimens and a water sample from the pool. Every afternoon I went to the pool to look for organisms. I waded in the pool and tried to collect specimens using a fish net. During the first few days, I looked for frogs, salamanders, toads, and their eggs, as these are some of the animals that spend one or more stages of their life cycles in vernal pools. None were found. However, I observed a lot of mosquitoes flying above the surface of the pool on the first day, and a few larvae were found on the second day. As the days progressed, fewer mosquitoes were found, but more and more mosquito larvae were seen. Later, the larvae metamorphosed to pupae. On the eighth and ninth day, mosquitoes were again seen flying above the surface of the pool.  Bugle Sprite, Micromenetus d. dilatatus, a species of freshwater snail found in the vernal pool. I realized that I had witnessed the complete life cycle of the mosquito. The adult mosquito has unique white bands on its legs and body. Based on Internet literature, I identified the mosquito as the Asian tiger mosquito, Aedes albopictus. Some skaters were found, too, but they may have originated from the nearby Buffalo Bayou. About seven disk-shaped snails were seen in the pool. These are presumably water snails of the species Micromenetus d. dilatatus, also called the bugle sprite. They were about 0.3 inches in diameter, 0.2 inches thick, and light yellowish-brown in color. They were found on submerged vegetation in the pool.
As the vernal pool was drying up, insects and spiders were seen crawling around in the receded area. The receded area was moist and muddy. When the vernal pool was almost dried up, a lot more organisms were found. Dot-sized organisms were darting in the water. Small insects were flying over the surface of the water, too. I caught a dark, flattish, rod-like organism with a pinlike tail in my net. It was one inch long and was quite abundant in the water and could be the larvae of the dobsonfly. A lot of guppies, approximately one inch in length, were seen swimming in the water. I observed them because they were concentrated in a shrinking pool of water. I had not seen any eggs in the pool for the past nine days. I wondered where these fish had come from, because according to the Internet, a vernal pool is not supposed to have fish in it. Then I noticed that there was a small dry depression leading to the vernal pool. I assumed that the fish were washed into the vernal pool when the nearby Buffalo Bayou overflowed its banks after the rain. The pool had a strong smell of decaying vegetation. |
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