Petermann, E., Knöller, K., Rocha, C., Scholten, Jan, Stollberg, R., Weiß, H. and Schubert, M. (2018) Coupling End-Member Mixing Analysis and Isotope Mass Balancing (222-Rn) for Differentiation of Fresh and Recirculated Submarine Groundwater Discharge Into Knysna Estuary, South Africa. Journal of Geophysical Research: Oceans, 123 (2). pp. 952-970. DOI 10.1002/2017JC013008.

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Abstract

Quantification of submarine groundwater discharge (SGD) is essential for evaluating the vulnerability of coastal water bodies to groundwater pollution and for understanding water body material cycles response due to potential discharge of nutrients, organic compounds, or heavy metals. Here we present an environmental tracer‐based methodology for quantifying SGD into Knysna Estuary, South Africa. Both components of SGD, (1) fresh, terrestrial (FSGD) and (2) saline, recirculated (RSGD), were differentiated. We conducted an end‐member mixing analysis for radon (222Rn) and salinity time series of estuary water over two tidal cycles to determine fractions of seawater, riverwater, FSGD, and RSGD. The mixing analysis was treated as a constrained optimization problem for finding the end‐member mixing ratio that is producing the best fit to observations at every time step. Results revealed highest FSGD and RSGD fractions in the estuary during peak low tide. Over a 24 h time series, the portions of FSGD and RSGD in the estuary water were 0.2% and 0.8% near the estuary mouth and the FSGD/RSGD ratio was 1:3.3. We determined a median FSGD of 41,000 m³ d−1 (1.4 m³ d−1 per m shoreline) and a median RSGD of 135,000 m³ d−1 (4.5 m³ d−1 per m shoreline) which suggests that SGD exceeds river discharge by a factor of 1.0–2.1. By comparison to other sources, this implies that SGD is responsible for 28–73% of total DIN fluxes into Knysna Estuary.

Document Type:	Article
Keywords:	submarine groundwater discharge, end‐member mixing Analysis, Radon, isotopes, Knysna, water balance
Research affiliation:	Kiel University > Kiel Marine Science OceanRep > The Future Ocean - Cluster of Excellence Kiel University
Refereed:	Yes
Open Access Journal?:	No
Publisher:	American Medical Association
Projects:	Future Ocean
Date Deposited:	29 Mar 2018 11:00
Last Modified:	08 Feb 2021 07:37
URI:	https://oceanrep.geomar.de/id/eprint/42539

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