Urban Versus Natural Stream Resilience to Fertilizer Load and it’s Tendency to Become Eutrophic

HARBESON 30

Freshwater algae play a vital role in the health of an ecosystem and serve as indicators of environmental quality. Excessive nutrients from urban runoff lead to eutrophication, which disturbs the natural balance of algal ecology such as those found in Southern California along the Los Angeles River. For example, Echo Park Lake receives a nutrient load of about 209 lbs of nitrogen and 32.3 lbs of phosphorus per year (Los Angeles Area Lakes TMDLs March 2012 D-44). Benthic diatom populations are often used to assess anthropogenic impacts on water quality. A study of the diatoms in rivers has been completed by Descy and Coste (1990), who consider that their diatom indices provide excellent indicators of water quality, especially with increasing eutrophication (Round 130). To assess the response of diatom communities from urban vs. natural environments to nutrient runoff, five samples of algae were collected from an urban site, Marsh Park located in the middle of the city, and five from Switzer picnic area in the Angeles forest. They were treated with different doses of a generic, over the counter fertilizer. The fertilizer’s effect on the density and diversity of diatoms in these communities was monitored. The hypothesis was that the diatom community in the urban environment that has regular nutrient runoff is less susceptible to added fertilizer than those in the more natural setting which is higher up in the mountains and receives no fertilizer runoff.