Metals in Sediment Cores from Nine Coastal Lagoons in Central Vietnam

Problem statement: After being dramatically hit by war events, Vietnam is presently experiencing a huge economical and social development. However, very few data, relative to pollution levels and trends, are available for the correct management of critical areas such as coastal lagoons, where many economical activities are linked to high value environmental features. Approach: A set of sediment cores from nine coastal lagoons of central Vietnam (Lang Co, Truong Giang, An Khe, Nuoc Man, Nuoc Ngot, Thi Nai, O Loan, Thuy Trieu and Dam Nai) were sampled in 2008 and analyzed to assess metal and (Al, Cd, Cr, Cu, Fe, Hg, Li, Mn, Ni, Pb, V, U and Zn) and As levels and historical trends. Results: Concentrations are generally low, with the exception of As, which often exceeds ERL guidelines and Ni that does the same at O Loan. In some cases, concentrations-depth profiles account for recent increasing trends but surficial values are still low when compared to both international guidelines and polluted sediments all around the world. Sediment grain size seems to affect the depth distribution of a number of metals and when normalized to the content of silt and clay, values are particularly high at Dam Nai and Thi Nai, due to the very coarse composition of surficial sediments. Conclusion: Metal concentrations in lagoon sediments derive from the composition of rocks and soils in the watersheds. However, recent increasing trends need for further monitoring

KẾT QUẢ BƯỚC ĐẦU NGHIÊN CỨU TỐC ĐỘ LẮNG ĐỌNG, NGUỒN TRẦM TÍCH ĐÁY VỊNH HẠ LONG: DẤU HIỆU TỪ KHOÁNG VẬT SÉT, ĐỒNG VỊ 210Pb VÀ 137Cs

Ha Long bay is the World Natural Heritage, which annaually attracts a lot of foreign and domestic tourists. Nevertheless, in recent years, the landscape of Ha Long bay is devastated by many negative impacts-the shallowing of the bottom of bay is one of the great negative impacts. How is the shallowing of the bottom of Ha Long bay? What are reasons for the negative impacts? Based on the approach “source-to-sink” combined with results of clay mineral contents, results of 210Pb and 137Cs radionuclides, this study will contribute to clarifying the shallowing of the bottom of Ha Long bay. Results of smectite, illite and smectite/(illite+chlorite) ratios indicated that the sediment in Ha Long bay not only derives from the surrounding region of Ha Long bay but also derives from Red river system. Results of 210Pbex and 137Csex revealed the sedimentation rates in the Ha Long bay have varied between 0.47 - 0.75 cm/year over the last 100 years. It can be divided into four periods: period I (1920 - 1930); period II (1930 - 1960); period III (1960 - 1990); and period IV (1990 - 2011) with the average rate of 0.45 cm/year; 0.66 cm/year; 0.50 cm/year; and 0.85 cm/year respectively. The shallowing of the bottom of Ha Long bay was impacted by human activities such as building reservoirs, mining, urbanization or aquaculture etc.Vịnh Hạ Long là một trong những di sản thiên nhiên thế giới, hàng năm, vịnh thu hút nhiều du khách trong và ngoài nước. Tuy nhiên, trong những năm gần đây, cảnh quan vịnh bị tác động bởi hàng loạt các tác động tiêu cực - bồi lắng đáy vịnh là một trong những tác động tiêu cực lớn. Đáy vịnh Hạ Long bồi cạn ra sao? nguyên nhân nào gây ra? Theo cách tiếp cận từ nguồn cung cấp đến bồn lắng đọng trầm tích “source-to-sink” và phối hợp với kết quả thành phần khoáng vật sét và đồng vị phóng xạ 210Pb và 137Cs, nghiên cứu này sẽ góp phần là sáng tỏ vấn đề trên. Kết quả hàm lượng smectite, illite và chỉ số smectite/( illite+chlorite) chỉ thị: trầm tích chuyển vào vịnh Hạ Long không chỉ nhận từ vùng xung quanh vịnh mà nó còn nhận từ hệ thống sông Hồng. Kết quả 210Pb và 137Cs cho thấy: tốc độ lắng đọng trầm tích tại vịnh Hạ Long trong vòng 100 năm qua, dao động trong khoảng 0,47 - 0,75 cm/năm, và có thể chia làm 4 giai đoạn: giai đoạn I (từ năm 1920 - 1930), giai đoạn II (từ năm 1930 - 1960); giai đoạn III (1960 - 1990) và giai đoạn IV (từ năm 1990 - 2011) với tốc độ lắng đọng trung bình lần lượt là 0,45 cm/năm; 0,66 cm/năm; 0,50 cm/năm; và 0,85 cm/năm tương ứng. Các hoạt động của con người như: xây hồ chứa, khai thác mỏ, đô thị hóa, nuôi trồng thủy sản ... là nguyên nhân gây bồi cạn đáy vịnh

Late Pleistocene-Holocene sequence stratigraphy of the subaqueous Red River delta and the adjacent shelf

The model of Late Pleistocene-Holocene sequence stratigraphy of the subaqueous Red River delta and the adjacent shelf is proposed by interpretation of high-resolution seismic documents and comparison with previous research results on Holocene sedimentary evolution on the delta plain. Four units (U1, U2, U3, and U4) and four sequence stratigraphic surfaces (SB1, TS, TRS and MFS) were determined. The formation of these units and surfaces is related to the global sea-level change in Late Pleistocene-Holocene. SB1, defined as the sequence boundary, was generated by subaerial processes during the Late Pleistocene regression and could be remolded partially or significantly by transgressive ravinement processes subsequently. The basal unit U1 (fluvial formations) within incised valleys is arranged into the lowstand systems tract (LST) formed in the early slow sea-level rise ~19-14.5 cal.kyr BP, the U2 unit is arranged into the early transgressive systems tract (E-TST) deposited mainly within incised-valleys under the tide-influenced river to estuarine conditions in the rapid sea-level rise ~14.5-9 cal.kyr BP, the U3 unit is arranged into the late transgressive systems tract (L-TST) deposited widely on the continental shelf in the fully marine condition during the late sea-level rise ~9-7 cal.kyr BP, and the U4 unit represents for the highstand systems tract (HST) with clinoform structure surrounding the modern delta coast, extending to the water depth of 25-30 m, developed by sediments from the Red River system in ~3-0 cal.kyr BP.ReferencesBadley M.E., 1985. Practical Seismic Interpretation. International Human Resources Development Corporation, Boston, 266p.Bergh  G.D. V.D., Van Weering T.C.E., Boels J.F., Duc D.M, Nhuan M.T, 2007. Acoustical facies analysis at the Ba Lat delta front (Red River delta, North Vietnam. Journal of Asian Earth Science, 29, 532-544.Boyd R., Dalrymple R., Zaitlin B.A., 1992. Classification of Elastic Coastal Depositional Environments. Sedimentary Geology, 80, 139-150.Catuneanu O., 2002. Sequence stratigraphy of clastic systems: concepts, merits, and pitfalls. Journal of African Earth Sciences, 35, 1-43.Catuneanu O., 2006. Principles of Sequence Stratigraphy. Elsevier, Amsterdam, 375p.Catuneanu O., Abreu V., Bhattacharya J.P., Blum M.D., Dalrymple R.W., Eriksson P.G., Fielding C.R., Fisher W.L., Galloway W.E., Gibling M.R., Giles K.A., Holbrook J.M., Jordan R., Kendall C.G. St. C., Macurda B., Martinsen O.J., Miall A.D., Neal J.E., Nummedal D., Pomar L., Posamentier H.W., Pratt B.R., Sarg J.F., Shanley K.W., Steel R. J., Strasser A., Tucker M.E., Winker C., 2009. Towards the standardization of sequence stratigraphy. Earth-Science Reviews, 92, 1-33.Catuneanu O., Galloway W.E., Kendall C.G. St C., Miall A.D., Posamentier H.W., Strasser A. and Tucker M.. E., 2011. Sequence Stratigraphy: Methodology and Nomenclature. Newsletters on Stratigraphy, 44(3), 173-245.Coleman J.M and Wright L.D., 1975. Modern river deltas: variability of processes and sand bodies. In: Broussard M.L (Ed), Deltas: Models for exploration. Houston Geological Society, Houston, 99-149.Doan Dinh Lam, 2003. History of Holocene sedimentary evolution of the Red River delta. PhD thesis in Vietnam, 129p (in Vietnamese).Duc D.M., Nhuan M.T, Ngoi C.V., Nghi T., Tien D.M., Weering J.C.E., Bergh G.D., 2007. Sediment distribution and transport at the nearshore zone of the Red River delta, Northern Vietnam. Journal of Asian Earth Sciences, 29, 558-565.Dung B.V., Stattegger K., Unverricht D., Phach P.V., Nguyen T.T., 2013. Late Pleistocene-Holocene seismic stratigraphy of the Southeast Vietnam Shelf. Global and Planetary Change, 110, 156-169.Embry A.F and Johannessen E.P., 1992. T-R sequence stratigraphy, facies analysis and reservoir distribution in the uppermost Triassic-Lower Jurassic succession, western Sverdrup Basin, Arctic Canada. In: Vorren T.O., Bergsager E., Dahl-Stamnes O.A., Holter E., Johansen B., Lie E., Lund T.B. (Eds.), Arctic Geology and Petroleum Potential. Special Publication. Norwegian Petroleum Society (NPF), 2, 121-146.Funabiki A., Haruyama S.,  Quy N.V., Hai P.V., Thai D.H., 2007. Holocene delta plain development in the Song Hong (Red River) delta, Vietnam. Journal of Asian Earth Sciences, 30, 518-529.General Department of Land Administration., 1996. Vietnam National Atlas. General Department of Land Administration, Hanoi, 163p.Hanebuth T.J.J. and Stattegger K., 2004. Depositional sequences on a late Pleistocene-Holocene tropical siliciclastic shelf (Sunda shelf, Southeast Asia). Journal of Asian Earth Sciences, 23, 113-126.Hanebuth T.J.J., Voris H.K.., Yokoyama Y., Saito Y., Okuno J., 2011. Formation and fate of sedimentary depocenteres on Southeast Asia’s Sunda Shelf over the past sea-level cycle and biogeographic implications. Eath-Science Reviews, 104, 92-110.Hanebuth T., Stattegger K and Grootes P. M., 2000. Rapid flooding of the Sunda Shelf: a late-glacial sea-level record. Science, 288, 1033-1035.Helland-Hansen W and Gjelberg, J.G., 1994. Conceptual basis and variability in sequence stratigraphy: a different perspective. Sedimentary Geology, 92, 31-52.Hori K., Tanabe S., Saito Y., Haruyama S., Nguyen V., Kitamura., 2004. Delta initiation and Holocene sea-level change: example from the Song Hong (Red River) delta, Vietnam. Sedimentary Geology, 164, 237-249.Hunt D. and Tucker M.E., 1992. Stranded parasequences and the forced regressive wedge systems tract: deposition during base-level fall. Sedimentology Geology, 81, 1-9.Hunt D. and Tucker M.E., 1995. Stranded parasequences and the forced regressive wedge systems tract: deposition during base-level fall-reply. Sedimentary Geology, 95, 147-160.Lam D.D. and Boyd W.E., 2000. Holocene coastal stratigraphy and model for the sedimentary development of the Hai Phong area in the Red River delta, north Vietnam. Journal of Geology (Series B), 15-16, 18-28.Lieu N.T.H., 2006. Holocene evolution of the Central Red River Delta, Northern Vietnam. PhD thesis of lithological and mineralogical in Germany, 130p.Luu T.N.M., Garnier J., Billen G., Orange D., Némery J., Le T.P.Q., Tran H.T., Le L.A., 2010. Hydrological regime and water budget of the Red River Delta (Northern Vietnam). Journal of Asian Earth Sciences, 37, 219-228.Mather S.J., Davies J., Mc Donal A., Zalasiewicz J.A., and Marsh S., 1996. The Red River Delta of Vietnam. British Geological Survey Technical Report WC/96/02, 41p.Mathers S.J. and Zalasiewicz J.A.,1999. Holocene sedimentary architecture of the Red River delta, Vietnam. Journal of Coastal Research, 15, 314-325.Milliman J.D. and Mead R.H., 1983. Worldwide delivery of river sediment to the oceans. Journal of Geology, 91, 1-21.Milliman J.D and Syvitski J.P.M., 1992. Geomorphic/tectonic control of sediment discharge to the Ocean: the importance of small mountainous rivers. Journal of Geology, 100, 525-544.Mitchum Jr. R.M., Vail P.R., 1977. Seismic stratigraphy and global changes of sea-level. Part 7: stratigraphic interpretation of seismic reflection patterns in depositional sequences. In: Payton C.E. (Ed.), Seismic Stratigraphy-Applications to Hydrocarbon Exploration, A.A.P.G. Memoir, 26, 135-144.Nguyen T.T., 2017. Late Pleistocene-Holocene sedimentary evolution of the South East Vietnam Shelf, PhD thesis (in Vietnamese), Hanoi University of Science, Vietnam, 169p.Nummedal D., Riley G.W., Templet P.T., 1993. High-resolution sequence architecture: a chronostratigraphic model based on equilibrium profile studies. In: Posamentier H.W., Summerhayes C.P., Haq B.U., Allen G.P. (Eds.), Sequence stratigraphy and Facies Associations. International Association of Sedimentologists Special Publication, 18, 55-58.Posamentier H.W. and Allen G.P., 1999. Siliciclastic sequence stratigraphy: concepts and applications. SEPM Concepts in Sedimentology and Paleontology, 7, 210p.Posamentier H.W., Jervey M.T. and Vail P.R., 1988. Eustatic controls on clastic deposition I-Conceptual framework. Sea-level changes-An Integrated Approach, The Society of Economic Paleontologists and Mineralogist. SEPM Special Publication, 42, 109-124.Reineck H.E., Singh I.B., 1980. Depositional sedimentary environments with reference to terrigenous clastics. Springer-Verlag Berlin Heidelberg New York, 551p. Ross K., 2011. Fate of Red River Sediment in the Gulf of Tonkin, Vietnam. Master Thesis. North Carolina State University, 91p.Saito Y., Katayama H., Ikehara K., Kato Y., Matsumoto E., Oguri K., Oda M., Yumoto M. 1998. Transgressive and highstand systems tracts and post-glacial transgression, the East China Sea. Sedimentary Geology, 122, 217-232.Stattegger K., Tjallingii R., Saito Y., Michelli M., Nguyen T.T., Wetzel A., 2013. Mid to late Holocene sea-level reconstruction of Southeast Vietnam using beachrock and beach-ridge deposits. Global and Planetary Change, 110, 214-222.Tanabe S., Hori K., Saito Y., Haruyama S., Doanh L.Q., Sato Y., Hiraide S., 2003a. Sedimentary facies and radiocarbon dates of the Nam Dinh-1 core from the Song Hong (Red River) delta, Vietnam. Journal of Asian Earth Sciences, 21, 503-513.Tanabe S., Hori K., Saito Y., Haruyama S., Phai V.V., Kitamura A., 2003b. Song Hong (Red River) delta evolution related to millennium-scale Holocene sea-level changes. Quaternary Science Reviews, 22(21-22), 2345-2361.Tanabe S., Saito Y., Lan V.Q., Hanebuth T.J.J., Lan N.Q., Kitamura A., 2006. Holocene evolution of the Song  Hong  (Red  River) delta system,  northern Vietnam. Sedimentary Geology, 187, 29-61.Thanh T.D. and Huy D.V., 2000. Coastal development of the modern Red River Delta. Bulletin of the Geological Survey of Japan, 5, 276.Tjallingii R., Stattegger K., Wetzel A., Phung VP., 2010. Infilling and flooding of the Mekong River incised valley during deglacial sea-level rise. Quaternary Science Reviews, 29, 1432-1444.Vail P.R., 1987. Seismic stratigraphy interpretation procedure. In: Bally, A.W. (Ed), Atlats of Seismic Stratigraphy. American Association of Petroleum Geologist Studies in Geology, 27, 1-10.Van Wagoner J.C., Posamentier H.W., Mitchum R.M., Vail P.R., Sarg P.R., Louit J.F., Hardenbol J., 1988. An overview of the fundamental of sequence stratigraphy and key definitions. An Integrated Approach, SEPM Special Publication, 42, 39-45.Veeken P.C.H., 2006. Seismic stratigraphy Basin Analysis and Reservoir Characterization. Handbook of geophysical exploration, Elsevier, Oxford, 37509p.Yoo D.G., Kim S.P., Chang T.S., Kong G.S., Kang N.K., Kwon Y.K., Nam S.L., Park S.C., 2014. Late Quaternary inner shelf deposits in response to late Pleistocene-Holocene sea-level changes: Nakdong River, SE Korea. Quaternary International, 344, 156-169.  

PCDD/Fs in sediments of Central Vietnam coastal lagoons: In search of TCDD

Samples from nine Central Vietnam coastal lagoons, together with three soils and sediments collected in 24 two freshwater reservoirs of the Thua Thien-Hué province, were analysed for polychlorinated dibenzo-p- 25 dioxins and dibenzofurans (PCDD/Fs). Total concentrations are low, from 192 to 2912 pg g1 and depth 26 profiles in Tam Giang-Cau Hai (TG-CH) sediment cores show only minor changes over time in PCDD/F 27 input and composition. Octachloro dibenzo-p-dioxin (OCDD) is the prevailing congener (approximately 28 90%), indicating combustion as the main PCDD/F source to these coastal systems, whereas natural forma- 29 tion might be partly responsible for the presence at depth. 2,3,7,8-Tetrachloro dibenzo-p-dioxin (TCDD), 30 largely sprayed together with Agent Orange over the study areas during the war (1961–1971), is absent 31 or very low. This result supports the hypothesis of strong degradation soon after spraying. Multivariate 32 statistical analyses account for the presence of local, short-range sources as observed in the northern part 33 of the TG-CH lagoon

Changes in soil characteristics and C dynamics after mangrove clearing (Vietnam)

International audienc

Distribution and density of Lutraria rhynchaena Jonas, 1844 relate to sediment while reproduction shows multiple peaks per year in Cat Ba-Ha Long Bay, Vietnam

Lutraria rhynchaena Jonas, 1844 is of great commercial interest, but its reserves have dramatically declined over recent decades. Therefore, there is an urgent need of scientific basis to propose effective fishery management measures and improve artificial aquaculture of the clam. In this study, we investigated the distribution and density of L. rhynchaena, sediment characteristics, and established the clam’s reproductive cycle through monthly observations from August 2017 to July 2018. The study results showed that distribution and density of clams are related to sediment types, and the sediment type of medium sand is likely the best benthic substrate for the clams. The spawning of clams occurred throughout the year with three spawning peaks in January, April and September. For the sustainable management of the clam resource in Cat Ba-Ha Long Bay, the fishery authorities can issue a ban on harvest of the clam in spawning peak months in January, April and September