The Effects of Different Coastal Substrates on the Filtration of Surface Runoff into Bodies of Water

Aivan Durfee, Patrick LaCroix and Jack Lague, Narragansett High School, Narragansett, RI, United States
Surface runoff is the flow of water that occurs when excess stormwater, meltwater, or other sources flow over the Earth's surface. Past research has conveyed that surface runoff has destructive ramifications, as fertilizer, pesticides, and herbicides seep into local watersheds and oceans. This throws off the balance of local ecosystems, and impairs other biotic factors. This study’s purpose was to determine which coastal substrates best filtered agricultural runoff. The coastal substrates—gravel, beach-sand, and marshland—were used as independent variables in the study. These substrates were placed in three identical tanks of water, with a fourth tank acting as a control, without the presence of a substrate. Different surface runoff chemicals were released periodically into these tanks, where the concentration of the chemicals was measured in the water. Measurements used to test these chemicals included pH level and concentrations of nitrogen, phosphate, and algae. To make this study as lifelike as possible, research was done on what most large fertilizer companies use in their formula in order to see the effects of those chemicals on local ecosystems. The results of the study show a clear difference in the effectivity of different substrates’ filtration of agricultural runoff. While the marshland substrate efficiently absorbed the runoff, the other two substrates—gravel and beach-sand—were relatively poor as a natural filtration system. The filtration of these substrates led to different results in the water that was tested, as higher levels of nitrogen and phosphate were present in water located next to beach-sand and gravel as opposed to marshland. These results have serious implications, as the majority of coastlines are typically based around sandy and rocky environments, not marshlands. The results of this study, along with past research, indicate that surface runoff of harmful chemicals is a legitimate threat to coastal ecosystems on a global scale.