Nitrogen cycling at Emerald Lake watershed, Sequoia National Park

Abstract

An annual nitrogen balance was used to develop a conceptual model of nitrogen cycling at the 120 ha Emerald Lake watershed. Atmospheric loadings of NO₃⁻ (7200 eq) and NH₄⁺ (6800 eq) from snow represent the largest external nitrogen sources. Approximately 75 percent of the annual nitrate mass flux is transported by the first 40 percent of the annual lake inflow. The sum of NO₃⁻ and NH₄⁺ deposited from the atmosphere (21,000 eq) and released by soil mineralization (40,000 eq) exceeds inflow mass flux (8,000 eq). Denitrification (10,000 - 20,000 eq) and plant uptake may account for this difference. NH₄⁺ deposition (10,000 eq) and mineralization release (26,500 eq) are large, but the NH₄⁺ inflow flux is near zero. This difference may be due to nitrification with subsequent denitrification, or plant uptake. Data gaps preclude calculation of an annual overall acidity affect. Nitrification is a potential seasonal source of acidity.