Date of Award


Document Type



Environmental Science

Thesis Advisor

Mark Teece


Nitrogen, Phytoplankton


To study a site of eutrophication, mesocosms with pore water additions, connections to the substrate (seeps) and controls were designed to test the response of phytoplankton to differences in nitrogen sources. We analyzed concentrations of nitrate, ammonium, phosphate, and chlorophyll a, along with the 815N and 8180 values of nitrate in mesocosms with various treatments in Guinea Creek, DE. Nutrient concentrations in the groundwater (delivered to the seeps) and in the pore water (delivered to the pore water mesocosms) differed markedly; the average nitrate concentration for the pore water (295 ± 3.55 μmol/L) was significantly higher than the groundwater (83 ± 33.80 μmol/L); while the average ammonium concentration for the pore water (4 ± 0.18 μmol/L) was significantly less than the groundwater (48 ± 5.59 μmol/L). Elevated levels of nitrate which ranged from 30 to 50 μM were found in the pore water mesocosms while the other two treatments ranged from 1 to 13 μM. The phytoplankton biomass increased over time for the seeps, from about 8 μg/L to 11 μg/L, and in the pore water mesocosms, from about 4.5 μg/L to 6.5 μg/L. The 815N and the 0180 values of nitrate ranged from +5.1 %0 to +12.5%0 and +2%o to +13.6%0 respectively. The nitrate isotope values reflected the presence of fertilizer and manure in the groundwater as the source of nitrate to the estuary. These data are useful tools to engage further research at this study site and begin to guide management plans in order to remediate water quality issues in this area.