Isotopic N Exchange at Critical Landscape Interfaces
TERRECO Cluster H-01
From 10/2012 to 03/2018Principal Investigator: Gerhard Gebauer, Stefan Peiffer, Egbert Matzner, Ji-Hyung Park
Staff: Silvia Parra Suárez
Abstract 2013: Streams, rivers and lakes are recipients of nitrate from terrestrial ecosystems via leaching to surface waters and groundwater. The nitrate contamination sources are difficult to determine, but identifying them is an essential step to control nitrate inputs to aquatic systems, and to make management decisions aimed at protecting water quality. Stable isotopes are a useful tool to quantify and determinate the origin of nitrate inputs into the Soyang Lake, and in the end to contribute to a better management of nitrate sources in the watershed. In this study we will use a dual isotope approach. The δ15N values of nitrate from different sources often show overlapping ranges, but the additional measurement of the δ18O values allows a more precise classification. Different nitrate sources have distinct isotopic signatures: nitrate isotopic composition (δ15N δ18O) is useful in fingerprinting these sources.
The δ18O values of NO3- are especially useful for discriminating between NO3- deposited from the atmosphere and NO3- formed by microbial nitrification. The formation of NO3- in the atmosphere involves exchange of oxygen atoms with ozone which has a high δ18O value. In contrast, NO3- formed by microbial nitrification derives most of its oxygen from water which has a lower δ18O value. According to this principle, the nitrates derived from sewage or manure or fertilizer are isotopically distinct from one another and from the other sources. To know how the biogeochemical and hydrological processes are driving the nitrate inputs to the Soyang Lake, we must identify how much of nitrate is contributed from each watershed into the whole water system. We will address the question how much nitrate enters the rivers of the Soyang Lake Watershed, how much enters the lake, and how much is found at the end of the system, flowing out from the lake; and even more important, what are the nitrate sources. The biogeochemical and hydrological processes in the Soyang Lake are influenced by land use and seasonality. To know how land use influences these processes we will compare the amount of nitrate exported from agricultural areas from forested (broadleaf and coniferous) areas. To know how seasonality influences these processes, we will compare the nitrate inputs during the pre-monsoon season, monsoon season and after the monsoon season. In the end, to answer our main question we want to follow N from the land surface through the river system and into the Soyang Lake, but also the transformation and fate of N within the lake.
Keywords: Biogeochemistry, sub-catchments, fertilizer, nitrate, surface water, ground water, stable isotopes
