Atmospheric nitrogen deposition and its impact to Lake Sihwa in South Korea from January 2004 to September 2005

Abstract

Atmospheric wet and dry deposition samples collected from three sites (Hwasung, Ansan and Daeboo) around Lake Sihwa, South Korea were used to calculate the atmospheric deposition of nitrogen to the lake and to evaluate its effects on primary production. The analytical parameters included pH, conductivity, and cation (Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺) and anion (Cl^-, NO₃^-, SO₄^2-) concentrations. The monthly volume-weighted mean pH of the rainwater ranged from 3.9 to 5.1, with a mean of 4.5, thus showing moderate to strong acidification. Factor analysis indicated that the possible sources for the major ions in the precipitation were anthropogenic/crustal, marine and biomass burning products. Wet deposition varied with season; the highest flux of inorganic nitrogen (NO₃^--N + NH₄⁺-N) occurred in the summer and averaged 160 mg/m²/month. Less nitrogen was delivered by dry deposition which was highest in spring 2004 (March-May, 23 and 50 mg/m²/month for NO₃^--N and NH₄⁺-N, respectively). The total annual atmospheric deposition of NH₄⁺-N (1100 mg/m²/yr) was about twice that of NO₃^--N (560 mg/m²/yr). The combined direct deposition to the lake proper was 7.1 × 10⁷ g-N/yr while the estimated annual flux to the entire Lake Sihwa basin was 7.9 × 10⁸ g-N/yr. Of the total atmospheric inorganic N entering Lake Sihwa (2.7 × 10⁸ g-N/yr), 26% was from direct deposition and 74% from indirect deposition. To estimate the potential impact of atmospheric nitrogen on primary production in the lake, chlorophyll-a equivalents were calculated assuming Redfield stoichiometry; this was estimated to be about 8% of the total chlorophyll-a produced in 2004.