Greater New Bedford Vocational Technical School, New Bedford, Massachusetts
Senior Botany Class of Greater New Bedford Regional Vocational Technical High School
The purpose of this study was to determine the impact that the autumn leaf drop associated with the changing seasons has on water quality. Students in the senior elective, Botany, participated in this study of the main outlet of Turner’s Pond in Dartmouth, Massachusetts. The students designated two test sites downstream from the dam that holds back Turner’s Pond. Testing was done October 6 and 7, 2005 and October 27 and 28, 2005. The first dates were prior to the leaf drop and the second dates occurred after leaf drop had started but not yet been completed. The macroinvertebrate sampling site was 100 feet downstream of the dam. The chemical and water quality sampling site was 200 feet downstream of the dam. Students used the sweep method to collect macroinvertebrate samples. The hydrolab was used to sample water quality and a grab sample was taken to measure the nutrient concentrations in the water. The flow and depth meter were used on October 7th to determine the stream bed depths and water flow to calculate loading. However, severe flooding made this procedure dangerous for the students and teachers on October 27 and 28th.
Students counted and identified the macroinvertebrates sampled at each date. The first sampling yielded a low count that students were able to complete without re-sampling the grid. The second sampling yielded a much higher count of macroinvertebrates that was divided by taking samples from four squares in the first box. The diversity of organisms in the second sampling was also much higher. However, when the major group biotic index was used at the family level the rating for October 7th was 3.9 – very good and for October 28th was 4.1 – very good.
The hydrolab data showed that oxygen levels in the water increased with the cooler temperatures. The pH data showed that the pH on the first sampling date ranged from 4.3 – 4.4 and that on the second sampling date the pH ranged from 4 – 4.1. The specific conductivity held consistently just below 0.17mS/cm on the first sampling date and just above 0.1mS/cm on the second sampling date. The grab sample data revealed that both the phosphate and nitrate concentrations were higher on the first sampling date. Loading was not calculated due to flooding on the second sampling date.
The students determined that the most dramatic difference between the two sampling dates was the drop in pH and the increase in the diversity and number of macroinvertebrates sampled on the second sampling date. These changes would appear to be directly related to leaf drop since the decomposing leaves would have added hydrogen ions to the water and provided more diverse and plentiful food sources for macroinvertebrates. Students realized that the macroinvertebrates could have been grouped by feeding strategy and hope to do this with the data in the future. They also realized that by not calculating loading they did not present a complete picture of the water chemistry. In the future they plan to have more numerous sampling dates throughout the leaf drop time period that will provide a more detailed picture of the changes caused by leaf drop.
Greater New Bedford Vocational Technical School, New Bedford, Massachusetts (2005). The Effect of Autumn Leaf Drop on Water Quality at Turner's Pond Outlet. In Watershed Access Lab Projects. Project 37.
Available at: http://vc.bridgew.edu/wal_projects/37
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