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Explore the effects of rainfall-induced runoff on Chlamydomonas reinhardtii population growth, assessing water quality and algal productivity. Experiment conducted using spectrophotometer analysis over 14 days. Results show increased growth in runoff-laden creek water.
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Effects of Rainfall on Aquatic Productivity Jacob Cebulak Pittsburgh Central Catholic HS Grade 11
Runoff • Part of the water cycle and describes the water that flows over a land surface. • Surface runoff occurs on land, typically creating a ‘watershed.’ • Artificial materials that are transported in surface runoff: fertilizers, petroleum, pesticides, herbicides, and salt. • Potential effects are assessed by chemical indicators and indicator species. • Rainfall can exacerbate this problem
Eutrophication • Caused by an overabundance of nutrients in an ecosystem • No limiting factor on algae populations • Uncontrollable growth takes up resources necessary for other organisms-oxygen. • Limits biodiversity • Can occur naturally • Typically occurs today by fertilizer run off
Chlamydomonas reinhardtii • Used as a bio-indicator • Genus of green algae • Has an Eyespot to orient itself to light • Two flagella, swims with a breaststroke-like motion • 10 μm in diameter • Large, crescent-shaped chloroplasts • Found in freshwater, soil, oceans, and snow
Purpose • To determine whether or not rainfall-induced runoff has a significant effect on algal population growth.
Hypotheses • Alternative: Runoff-laden creek water will significantly increase Chlamydomonas reinhardtii population growth. • Null: Runoff-laden creek water will have no significant effect on Chlamydomonas reinhardtii population growth.
Materials • Chlamydomonas reinhardtii (Carolina) • Plum Creek water prior to rainfall and after rainfall • Spring Water • Soil Water • Spectrophotometer • Micropipettes • 13x100 borosilicate culture tubes • Tube rack • Vortex • Lamp (21cm from the tubes) • 12 watt light bulb • Wax Paper
Procedure • 1. Water was collected from Plum Creek before rainfall occurred. • 2. Water was collected from Plum Creek 1 hour following heavy rainfall. (Note: The depth where the sample was collected rose by 2cm from when the first sample was collected.) • 3. The tubes were then filled with the following concentrations. Each concentration had 8 replicates.
Procedure (continued) • 4. Tubes were inverted and the absorbances, at 430 nanometers, were recorded with a Carolina spectrophotometer. Spring water was used as a blank. • 5. Placed tubes 21 cm below a 12 watt light bulb at 20 degrees Celsius. • 6. Recorded absorbance of each tube every other day for 14 days.
Results Day 14 P-Value: 5.06E-13 Day 14 P-value comparing before and after rainfall: 0.00013
Was there significant variation between Chlamydomonas r. grown in before-rain creek water and after-rain creek water? • Alpha: 0.05 • Day 6 p-value: 2.68E-08 • Day14 p-value: 0.00013 • There appeared to be a significant positive effect on Chlamydomonas reinhardtii population growth when grown in after-rain creek water.
Conclusions • Both samples of creek water seemed to promote Chlamydomonas growth. • The null hypothesis was rejected for both before and after rainfall due to the extremely low p-values. Increased rainfall seemed to significantly increase algal growth-promoting properties of creek water.
Limitations • Only one model was tested. • The chemical composition of the creek was not tested nor was pH. • Absorbance variation of culture tubes. • There were only 8 replicates. • Only one water source was tested. • Overall growth was very low. (Optimal health?)
Extensions • Use more than one model. • Use chemical indicators to determine the composition of the creek. • Test more than one water source. • Use more replicates. • Count the cells in the tubes for more precision. • Use different wattage bulbs. • Test different wavelengths of light. • Test optimal growth conditions.
References Nenninger, Katie. “Chlamydomonas Reinhardtii.” Chlamydomonas Reinhardtii, Missouri Science and Technology, web.mst.edu/~microbio/BIO221_2009/C_reinhardtii.html. US Department of Commerce, National Oceanic and Atmospheric Administration. “NOAA's National Ocean Service Education: Estuaries.” NOAA's National Ocean Service, 19 Dec. 2004, oceanservice.noaa.gov/education/kits/estuaries/media/supp_estuar09b_eutro.html. “The Most Important Organism on the Planet.” Ecology Global Network, 27 Apr. 2012, www.ecology.com/2011/09/02/the-most-important-organism-on-the-planet/. Perlman, USGS Howard. “Runoff (Surface Water Runoff).” Runoff (Surface Water Runoff), USGS Water Science School, 2 Dec. 2016, water.usgs.gov/edu/runoff.html.
