Recent sedimentation rates in Garaet El Ichkeul La

Authors: Yasser Trabelsi Foued Gharbi Abdessalem El Ghali Mansour Oueslati Mohammad Samaali Wahid Abdelli Souad Baccouche Malik Ben Tekaya Moncef Benmansour Lionel Mabit Nabiha Ben M’Barek Nafaa Reguigui Jose M Abril

Publish Date: 2012/03/16

Volume: 12, Issue: 5, Pages: 784-796

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Abstract

Ichkeul National Park NW Tunisia is a UNESCO Biosphere Reserve Garaet El Ichkeul Lake is known for its seasonal variability in water level and salinity In recent decades the waterbody has been affected by the construction of new hydraulic structures To reduce the impacts of dams and to maintain the sustainability of the ecosystem a sluice was built at the outlet of the lake and it operated for the first time in 1996 This paper describes an investigation of recent sedimentation dynamics in Ichkeul Lake determined by radiometric dating of sediment coresA sediment core was collected with a UWITEC gravity corer at the deepest central part of the lake in August 2009 Specific activities of unsupported lead210 210Pb and caesium137 137Cs were measured in the core enabling calculation of recent sediment accumulation rates SAR Published radiometric data from nearby sediment cores collected in 1997 and 1982 provide a comparisonThe measured excess 210Pb inventory was 5300 ± 500 Bq m−2 leading to an estimation of constant flux of 165 ± 16 Bq m−2 yr−1 a value higher than the best estimate for local atmospheric fluxes 123 ± 12 Bq m−2 yr−1 and the flux estimated from the core collected in 1982 48 Bq m−2 yr−1 The 137Cs inventory was 3550 ± 120 Bq m−2 two times higher than the historical 137Cs atmospheric deposition in the area The 137Cs profile displayed a distinct peak but the 137Cs depthdistribution did not follow the pattern expected from atmospheric deposition Application of the constant rate of supply CRS model with the reference point method produced a chronology and SAR values comparable to those found in previous work The whole 137Cs profile was quantitatively reconstructed from the historical records of atmospheric deposition using the systemtimeaveraged STA modelThe CRS and STA models provide consistent sediment accumulation results for the whole data set considering the time resolution of the chronology ~6 years and analytical uncertainties Results from cores sampled in 1982 1997 and 2009 reveal an increasing SAR trend from ~025 g cm−2 yr−1 in the early 1940s to ~067 g cm−2 yr−1 at present In the 13 years since installation of sluice gates at Tinja SAR in the central Ichkeul Lake has not declined Thus if siltation continues at the present rate shallowing of the lake will seriously affect the hydromorphology and ecology of this important lakeThe authors gratefully acknowledge the support provided by the International Atomic Energy Agency The work reported in this paper was undertaken as part of the IAEA Technical Cooperation Programme Project RAF7/008 The authors would like as well to thank the editors and reviewers for their comments which substantially improved the initial submitted manuscript

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