The sedimentary processes on tidal flats

THE SEDIMENTARY PROCESSES ON TIDAL FLATS IN THE NORTH OF VIETNAM: INITIAL RESULTS AND IMPLICATION FUTURE Dang Hoai Nhon1, Tran Duc Thanh1, Dinh Van Huy1, Nguyen Thi Kim Anh1, Nguyen Mai Luu1, Nguyen Dinh Khang1, Phan Son Hai2, Nguyen Manh Ha3, Pham Tien Duc3, Lai Thi Bich Thuy4 Institute of Marine Environment and Resources, Vietnam Academy of Science and Technology (VAST) Nuclear Research Institute, Nguyen Tu Luc Str., Da Lat City, Lam Dong province Faculty of Chemistry, Hanoi University of Sciences, 19 Le Thanh Tong Str., Ha Noi Centre for Geological Analysis Laboratory, Thanh Xuan, Ha Noi SUMMARY Tidal flats in North Vietnam extending from Mong Cai (Quang Ninh province) to Kim Son (Ninh Binh province) are affected by human activities and land – ocean interaction processes It can be shown in erosion, accretion, accumulation of pollutants with time For understanding sedimentary processes on tidal flats, samples from 11 collected sediment cores were in analysis of 210Pb, 226Ra, grain size, metals and minerals The sediment parameters on tidal flats are divided in three sedimentary environment types, including Deltaic tidal flat sedimentary environment from southwest Do Son Peninsula to Kim Son and dominated by accretion processes, estuarine tidal flat sedimentary environment from northeast of Do Son Peninsula to southwest of Cat Ba Islands, and embayment tidal flat sedimentary environment from Cat Ba Islands to Mong Cai and characterised with slow accretion and small rate of sedimentation Keywords: tidal flat, sedimentary process, North Vietnam, 210Pb, heavy metals INTRODUCTION Tidal flat which is a kind of coastal wetlands plays an important role for human life by providing space for socio-economic development and being in high biodiversity [20] Because the tidal sediments record many of information on the impacts from nature and human activities, it is a key factor to understand sedimentary processes Tracking environmental changes using many indicators of biology and geochemistry [12] can help us to get information on environment conditions in the past and at present The coastal provinces of North Vietnam extend from Quang Ninh to Ninh Binh where the rivers discharge to sea through their mouths of Ka Long, Tien Yen, Ba Che, Troi, Bach Dang, Cam, Lach Tray, Van Uc, Thai Binh, Ba Lat, Ninh Co and Day (Fig.1) The channels which bring water from mainland to sea are changing coastal environment conditions The coastal environments record human impacts, nature events in sediments, but they are reflected changing with time As part of the coastal region of North Vietnam, intertidal zones interest many scientists, indicating with the number of articles on environmental sediment These studies can help us understand environmental conditions as sedimentation and erosion rates [11, 15, 19, 21], geological structure of tidal flats in Holocene [7, 18], sediment compositions [9, 16] and sediment geochemistry [1, 2, 6, 14, 19] These publications have shown that nature and human activities are influenced on the tidal environment Our research questions are in the past and at present what the human and the nature have affected on the tidal environment By analysis of sediment cores in the tidal flats in grain size, 210Pb, 226Ra, metals and minerals, sedimentary processes on tidal flats will be clearer understood 3 MATERIALS AND METHODS 3.1 Materials During 2009 – 2012, three campaigns were carried out to collect samples of sediment cores MC (0-40cm) and MC (0-63cm) in April 2009, MC (0-40cm) and MC 11(0-50cm) in October 2010, and MC 1(0-90cm), MC (0-70cm), MC (0-70cm), MC (0-90cm), MC (0-90cm), MC (0-90cm) and MC 10 (0-90cm) in March 2012 (fig.1) 108º01' Đồ ng Ru i Cẩ m P đảo ẩm C lạ ch VịN H H i Lim N hà êêênn yyyuuu HH cchhh llạạcm ssôông n ng ng gN Nin inh hC Cơ bả n o tr Ch én ng đả 20 MC bá n đ ảo 10 Đồ Sơn Đ Long Châu 20 LEGEND cưa cưaL© L© L© n n Core positions MC  30 50 s g n a m 50 20 10 cưa l¹c h MC 10 Tô Cô m ũi Đồ Sơn 25 Giang ssôôn ng gĐĐ áy áy MC 11 Q.Đ Đ Quan Lạn tt LLạạ BBaa aa ccửử Ninh Bình cử cửa aĐĐ áy áy 19 55' 10 Đ ảo Cá t Bà MC cửa cửaLa La Lan n Hạ Hạ cửa cửaĐĐ èèii vơng vơng Quan Quan L¹ L¹ n n na cửa cửaDiê Diêm mĐĐ iề iền n sông sôngDiêm Diê Diêm mHộ Hộ n a m địn h 31 29 Đ Vân Đ ồn MC m m Êm C ÊÊ aaaCC ccưưư m m ccÊÊ gg ss««nn h Đố H Núi C ơng ả u ''''''' ịn h n q cư cưa aT Trµ rµL Ly y đ i 27 10 Đ C ao Lô Cá Đ L O n g cư cư cưa a aTT hiƯ h iệuu cử cử cửaaĐĐ Mô M ônn ôn ôn «ng gM M Ma a a MC o¸¸ Ho gH ng ss««n ss«« nngg HH åånn gg 20 10 nngg aaaÔÔÔ ccửửử ii rrớớ TT nngg ssôô o đả Bạc ôn ssôn g gĐĐ áá Bạc ông ông ộộộ aaaĐĐĐĐĐĐộộộ gggĐĐĐĐĐĐaaa ôn ôn ônggg s s ôn ss sôn sôn Thái Bì nh ằằnn gg MC h hááii B Bì ì n nh h H n g n Bé 10 G a i cccưưư aaLLL¹ ¹¹ccch hTTT rraay yy Hả i Phò ng ssôô ccử aV nng ửa Văă vv nU Ucc ccửửaa ăănnúú n TTh h cc ssôôônn ggTT hháái iiB B Bì ì nnh h h v Bắ c BầU V ụngQ uỳt MC 10 V ịn h ch lạ ĐảO C¸I P H L·o Väng ơcc LLơ cư cư cưaa 10 hhẽẽ aaCC BB nngg ssôô 20 Đ G Đ Thoi Xanh ccửửử aaBB ôô V Và ànn gg cửa cửa cửaMô Mô Mô đ ảo Quay ccửử aaBB ạạcc hh ĐĐ T rà hực nh T ĩ Đ V Ĩuu iiĨ aaTTT ccưưư 10 10 i b· 21º 34' 20 iên Ch Đ C Cổ ạạạiii aaĐĐ ccửửửa nn YYêê êênn TTii nngg ssôô sssôsôssôn ôônn ôn nng gg gg gĐĐĐ ĐĐĐầm ầầm ầm ầ ầm m m HH HH Hààà H ààà MC Quảng Ninh quảng ninh M Ma aH Hà MC1 sô ssô s«n «n n ng gK Ka aL Lo on ng g viƯt Nam µ µm mC CCaai Co on ng i LLa g am mC Coon ngg H Hµµ oo 106 00' 21 34' V ịn h B ắc B é 106º 00' 19º 55' 108º01' Fig Position of sediment cores on the tidal flats of North Vietnam 3.2 Methods We had cut 2.0 cm per samples from the top to the end of cores, and kept them at 0C in field before storing in laboratory In the laboratory, all sediments are dried in air-condition at 160C Grain sizes of sediment were analyzed by sieves for coarse grain (> 0.063mm) and particle size analyzers CILAS 990 for fine grain (< 0.063mm) after removing salts and organic matters by distilled water and hydrogen peroxide (10% H2O2) Sediment classification is according to Lisitzin [13] The 210Pb analysis in sediments was calculated indirectly by 210Po in sediments, the sediments were extracted by HNO and HF concentrated Then we used 0.1 % diethylammonium diethyldithiocarbamate and chloroform in 5M HCl to absorb 210Po by silver dish and measured on alpha spectrometry We used 209Po as initial standard assess recovery of extraction [8] The 226Ra in sediments as background were measured directly by gamma spectrometry The constant rate supply (CRS) model is used to calculate chronology of sediment layers (1) This model was suggested by Krishnaswami [10], later have been modified [3, 4, 17] Nowadays, this CRS model is used very common in calculating sedimentation rate in coastal and estuaries A(0) t  ln( ) (1)  A( x ) Where t: year; λ constant = 0.031; A(0) is total of 210Pbexcess in sediment core (210Pbexcess=210Pbactivity – 226Ra); A(x) is 210Pbexcess in sediment core at depth x For metals analysis: Weighed 0.5g dry sediments, then were extracted by 10 ml 8N HNO3 and 3ml 30 % H2O2 under reflux column at 950C in 15 minutes After that samples were cooled and added about 5ml 16N HNO3, then kept at 950C in hours (Method 3050b), cooled and filtered by 0.45 μm papers (Whatman) Finally, samples were diluted to 100 ml and measured by using ICP-MS method (Elan 9000 Perkin Elmer) All chemicals are in grade analysis For control QA/QC of analysis processes, the certified reference material samples (PACS2, MESS-3) were used Minerals in sediments were analyzed by two methods, which were analysis by thermo gravimetric on STA-PT 1600 instrument for clay minerals with relative error ± 5%; other minerals were analysis by X-ray diffraction analysis on D8-Advance Bruker instrument with in ± % relative error RESULTS AND DISCUSSION 4.1 Distribution of grain size in tidal flats From Mong Cai to Kim Son, sediments on tidal flats were composed of coarse sand (Md = 0.50-1.00mm), medium sand (Md = 0.25 - 0.50mm), fine sand (Md = 0.10 - 0.25mm), coarse aleurites (Md = 0.05 - 0.10mm), fine-aleurites muds (Md = 0.01- 0.05mm) and alerutic-pelitic muds (Md < 0.05mm) Coarse, medium and fine sands were only in the north of the study area (MC 1, MC3) and most of them were medium and well in sorting Fine-grain sediments dominated the south of the area and most of them were poor to medium in sorting In fig 2, the diameters of sediments in the cores changed in depths, reflecting the change of sedimentary environmental conditions with time Based on the diameters, sediments can be divided into two sedimentary processes of erosion and accretion on the tidal flats Erosion processes are seen at MC 11 in depth of 27-50 cm At MC 10 erosion and accretion were alternative from 22 to 90 cm, at MC in depth of 33 – 40 cm, at MC in depth of 20 – 66 cm and on MC at 15 - 90 cm, where the diameters were from coarse aleurites to coarse sands Accretion processes are seen in all cores, at MC 11 in depth of 0-27 cm, at MC 10 from 0-22 cm, at MC in depth of 0-27cm, at MC 7, MC and MC in all of depth in cores, on MC and MC in depth of 0-20cm Based on mean diameters (Md) of sediments, three areas were divided, including Deltaic tidal flat sedimentary environment (MC 11, MC 10, MC 9, MC 8, MC 7) with most sediments of coarse aleurites to fine-aleurites muds; Estuarine tidal flat sedimentary environment dominated by fine-aleurites muds (MC 4, MC 5); and Embayment tidal flat sedimentary environment dominated by fine to coarse sands (MC 1, MC 3) Table Sediment parameters on the tidal flats Cores MC MC MC MC MC MC Min 0.052 0.080 0.008 0.008 0.022 0.019 Md (mm) Max Aver 0.725 0.224 0.181 0.130 0.057 0.024 0.034 0.015 0.063 0.048 0.116 0.040 S0 SD 0.119 0.021 0.015 0.007 0.012 0.029 Min 1.297 1.531 2.284 1.601 1.740 1.803 Max 6.381 4.047 3.988 2.986 3.557 3.060 Aver 2.280 1.887 3.262 2.686 2.991 2.565 SD 1.497 0.654 0.380 0.324 0.408 0.255 MC MC 10 MC 11 0.054 0.051 0.037 0.102 0.084 0.068 0.065 0.066 0.057 0.008 0.007 0.008 1.255 1.233 1.366 3.635 3.588 2.696 2.119 2.108 2.151 0.810 0.848 0.410 Min = minimum; Max = maximum; Aver = average; SD = Standard deviation Sediment parameters (Md, S0) Sediment parameters (Md, S 0) 0.0 0.1 0.1 0.2 0.21.0 2.0 Sediment parameters (Md, S 0) 3.0 10 5.0 0.00 0.05 MC 20 60 Md (mm) S0 70 Depth (cm) Depth (cm) MC 50 3.00 4.00 5.00 MC 20 Md (mm) S0 30 40 0.102.00 10 10 20 Depth (cm) 4.0 0 30 40 Md (mm) S0 30 40 50 50 60 60 70 80 70 90 80 Sediment parameters (Md, S 0) Sediment parameters (Md, S0) 0.00 0.02 0.04 2.00 3.00 4.00 0.00 5.00 0.08 2.00 Sedimentary parameters (Md, S 0) 3.00 4.00 5.00 0.00 10 10 30 35 40 45 40 50 60 50 55 2.00 3.00 4.00 5.00 MC 10 Md (mm) S0 30 Depth (cm) Depth (cm) Md (mm) S0 25 0.10 MC 20 20 0.05 MC 15 Depth (cm) 0.04 Md (mm) S0 15 20 25 30 70 35 60 80 65 40 Sediment parameters (Md, S0) 0.00 10 0.05 0.10 2.00 3.00 4.00 5.00 0.00 10 MC 0.05 0.10 2.00 3.00 4.00 0.00 5.00 Md (mm) S0 40 50 50 60 70 70 80 80 90 90 2.00 3.00 4.00 5.00 Md (mm) S0 40 60 0.10 10 Md (mm) S0 30 Depth (cm) 30 0.05 MC 11 MC 10 20 Depth (cm) 20 Depth (cm) Sediment parameters (Md, S0) Sediment parameter (Md, S0) 20 30 40 50 Fig Distribution of sediment parameters on tidal flats 4.2 Distribution of 210Pb and 226Ra and sedimentation rate on tidal flats The 210Pb and 226Ra in sediments can help us tracking change of environments; they are indicators for erosion or accretion processes When the content of 226Ra in sediment layer is higher than that of 210Pb, there is no deposition of sediment On the other hand, if the content of 210Pb in sediment is higher than that of 226Ra, it will show the deposition of sediment On the tidal flats of North Vietnam, there are consisted of two above cases In the sediment cores MC 2, MC 4, MC 5, MC 6, MC on the tidal flats, the content of 210 Pbactivity is higher than that of 226Ra in all layers, indicating the accretion in these areas for the whole time (Fig 3) In the sediment cores MC 3, MC 8, MC 9, MC 10, MC 11 in the tidal flats, there are in these sediment cores two phases, including the first phase with content of 210 Pbactivity in sediment higher than that of 226Ra and the later second phase with content of 226Ra in sediment higher than that of 210Pbactivity (Fig 3) 20 40 Pbactivity and 226Ra (Bq/kg) 60 80 100 210 120 140 160 MC 210 226 Depth (cm) 30 40 Pbactivity and 226Ra (Bq/kg) 60 80 100 210 120 140 160 10 Ra MC 30 210Pb activity 226Ra 40 30 40 50 60 50 70 60 40 Pbactivity and 60 226 80 Ra (Bq/kg) 100 120 140 MC 20 20 40 50 20 10 Pbactivity Depth (cm) 10 20 20 Depth (cm) 210 0 60 80 70 90 210Pb activity 226Ra 160 210 Pbactivity and 226Ra (Bq/kg) 20 40 60 80 100 210 210 Pbactivity and 226Ra (Bq/kg) 120 140 160 20 40 60 80 100 120 140 30 210 35 226 Depth (cm) MC 25 Pbactivity Ra 40 45 50 55 210 Pbactivity 20 226 Ra 25 40 60 80 Pbactivity and 120 160 20 40 60 80 140 160 210Pb activity 226Ra 40 50 80 100 120 MC 10 210 Pbactivity 40 226 Ra 50 60 60 30 70 70 35 80 80 90 90 40 60 30 Depth (cm) Depth (cm) 25 Pbactivity and 226Ra (Bq/kg) 20 MC 30 Ra 40 10 20 226 20 210 20 160 Pbactivity 226 210 120 MC 15 140 210 Ra 100 P b activity 160 MC 226 10 10 Depth (cm) 140 140 80 210 100 120 50 70 Pbactivity and 226Ra (Bq/kg) 20 100 Ra 60 40 80 40 35 210 60 30 30 60 65 Pbactivity and 226Ra (Bq/kg) 20 15 Depth (cm) 20 40 10 MC 10 15 20 10 Depth (cm) 160 210 Pbactivity and 226Ra (Bq/kg) 20 40 60 80 100 120 140 160 MC 11 10 210 Pbactivity Depth (cm) 15 226 Ra 20 25 30 35 40 45 50 Fig Distribution of 210 Pb and 226Ra in sediments on tidal flats Sedimentation rates on tidal flats were timely changed in different areas They were low in MC and MC 10 (fig 4), high in MC 2, MC 4, MC 5, MC7, MC 9, MC 11 (table and fig 4) On tidal flats, there were not only accretions, but also erosion that was indicated at MC 11, MC10, MC 9, and MC The sedimentation rate is closely related to the diameter of sediment The high sedimentation rate, the much more fine sediment is In three sedimentary environments mentioned above, high sedimentation rate was recorded in estuarine tidal flat sedimentary environment and deltaic tidal flat sedimentary environment Table Sedimentation rates (cm/year) on tidal flats MC 0.11 1.31 0.82 0.37 Min Max Aver SD MC 0.04 0.34 0.14 0.11 MC 0.19 2.35 1.40 0.65 MC 0.26 15.00 2.94 4.01 MC 0.13 1.18 0.50 0.31 MC 0.17 14.42 2.08 3.105 MC 0.07 3.24 0.77 0.83 MC MC 10 MC 11 0.06 0.14 0.09 15.83 0.64 14.84 3.04 0.34 1.71 5.27 0.15 4.15 Min = minimum; Max = maximum; Aver = average; SD = Standard deviation In table 2, at MC 5, MC 7, MC and M C11 standard deviation of sedimentation rates are high, because in these cores sedimentation rates are change very fast and suddenly (fig 4), they show that effect from sedimentary environment, we are also seeing same trend changes by concentration of metals and clay minerals and quartz in these sediment cores Sedimentation rate (cm/year) Sedimentation rate (cm/year) MC 10 12 14 16 2012 2006 1995 1979 1957 1932 1887 15 17 19 22 26 30 34 38 42 46 50 54 61 65 10 Sedimentation rates (cm/year) 12 14 16 MC Years Years - depth (cm) Years 2012 2010 2009 2007 2005 2003 2001 1999 1997 1996 1993 1988 1984 1979 1973 1964 1954 1942 1923 2012 2011 2010 2009 2008 2007 2006 2005 2004 2003 2002 1998 1996 1993 1990 1986 1982 1977 1973 1965 1953 1930 MC 10 12 14 16 10 Sedimentation rates (cm/year) Sedimentation rate (cm/year) 12 14 16 10 12 14 16 Years 2012 2011 2010 2008 2007 2005 2004 2003 2001 1998 1995 1991 1986 1980 1970 1960 1931 1912 1877 2012 2009 2001 1992 1987 1979 1974 1970 1963 1949 22 26 30 34 38 42 46 50 55 61 67 73 79 85 2008 2007 2005 2003 2001 MC MC 1998 1995 Years Years Years-depth (cm) Sedimentation rate (cm/year) 2008 2006 2002 1999 1997 1993 1989 1988 1985 1984 1983 1982 1980 1977 1971 1964 1959 1944 1935 1991 1986 1981 1976 1970 1959 1952 1935 1917 1894 Sedimentation rate (cm/year) 10 14 16 2007 2006 Years-depth (cm) Years -depth (cm) MC 1998 1996 1994 1989 1984 1979 1970 1957 1926 1915 34.5 2012 2010 2009 2008 2004 2003 1995 1972 1939 22 26 30 34 38 42 46 50 55 61 67 73 79 85 89 10 10 12 14 16 12 14 16 MC Sedimentation rate (cm/year) 12 2009 2001 Sedimentation rate (cm/year) 12 14 16 MC 10 MC 10 Sedimentation rate (cm/year) Years-depth (cm) 2009 2008 2006 2003 2000 1993 1986 1975 1968 1964 1958 1936 28.5 31.5 34.5 37.5 40.5 43.5 46.5 49.5 14 16 MC 11 Fig Sedimentation rates on tidal flats 4.3 Distribution of metals on tidal flats Heavy metals in sediment cores were analyzed including Cu, Pb, Zn, As, Ni, Cr High concentrations of elements are As, Cu, Pb and Zn in MC 5, MC 6, M C7, MC and MC 10 In comparison with MC 1, MC and MC in the north of the study area, the concentrations of metals in the south of the study area is higher Metals in sediment cores increased in recent years, clearly in MC 5, MC and MC (table 3) Copper (Cu) in sediments were in the range from low to high concentration, the highest concentration at MC and MC Most of them are higher than ISQG levels of Canadian standard The lower concentration compared with ISQG is in MC MC and MC (table 3) The concentration of lead (Pb) in sediment had a trend similar to the one of Cu It was high in sediment cores MC 5, MC 6, MC 7, MC and MC 10, only at MC 1, MC and MC but lower than ISQG level The highest concentration was at MC Table Value of metals (mg/kg) in core sediments on tidal flats MC MC (n=20 (n= ) ) Min 2.17 10.06 Max 7.37 18.84 Aver 5.12 14.80 SD 1.83 2.20 ISQG Min 5.78 18.37 Max 26.06 31.12 Aver 19.59 23.71 SD 6.98 2.93 ISQG Metal Levels Cu Pb MC (n=21 ) 0.69 12.14 3.85 2.80 5.99 22.99 12.69 4.00 MC MC MC MC MC 10 MC 11 (n= (n= (n=19) (n=17) (n=4) (n=18 ) 24) 23) 47.66 53.25 60.31 19.93 33.68 11.42 70.88 89.01 94.76 85.59 74.55 36.12 57.58 80.05 72.93 56.03 50.41 23.72 8.03 8.46 7.78 21.51 17.54 6.77 18.70 59.61 55.36 70.96 22.32 60.59 12.67 90.20 82.25 120.32 96.28 103.01 111.63 76.16 72.25 95.02 61.27 79.41 28.61 6.88 8.72 12.24 22.48 18.76 21.43 30.20 Min Max Aver SD ISQG Min Max Aver SD ISQG Min Max Aver SD ISQG Min Max Aver ISQG TEL Zn As Ni Cr 3.95 45.66 30.69 14.39 13.26 492.01 81.62 111.89 19.63 62.64 35.89 11.37 0.61 6.69 4.22 2.18 3.15 9.69 6.10 2.21 0.26 8.41 4.01 2.18 10.88 23.86 16.38 4.18 9.93 41.44 18.12 8.43 2.60 24.97 16.09 6.62 5.35 22.17 16.44 5.74 17.07 54.46 24.11 8.30 5.98 17.65 11.47 2.75 87.46 94.25 137.68 132.99 111.66 123.05 18.26 8.72 124.00 23.43 20.24 53.93 42.94 38.29 27.53 12.86 5.27 7.20 30.96 23.16 44.80 36.83 38.10 31.92 4.34 3.85 34.40 28.71 49.80 47.83 41.98 41.41 5.11 4.39 52.30 72.21 62.19 88.60 26.67 143.68 151.79 152.08 152.16 98.89 106.22 113.80 65.97 17.71 27.20 30.93 29.88 25.78 38.62 32.80 4.00 7.13 42.16 26.68 11.38 13.27 30.81 21.66 7.96 376 12.09 7.31 2.22 34.66 74.11 44.18 9.82 8.74 63.67 32.41 12.01 34.88 55.97 44.49 8.75 2.05 323.32 45.89 83.66 32.35 53.33 42.60 5.00 12.70 50.83 33.19 12.75 30.67 44.40 36.55 5.79 8.86 22.71 15.78 3.53 Min = minimum; Max = maximum; Aver = average; SD = Standard deviation; n= number of sample Zinc (Zn) has high concentration in sediment in MC 5, MC and MC 10 Although average concentration of Zn was lower than ISQG level, some layers in cores were higher than ISQG level At some positions on the tidal flats, the concentration recently (MC 8, MC 11, MC and MC 2) increased The lowest concentration was in MC and MC (Fig 5, table 3) Concentration of metals (mg/kg dry weight) 20 40 60 80 100 120 Concentration of metals (mg/kg dry weight) 140 160 0 20 40 60 80 300 Concentration of metals (mg/kg dry weight) 400 500 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 10 MC 10 10 20 50 60 30 Depth (cm) Cu Pb Zn 40 Cu Pb Zn 20 Depth (cm) 30 Depth (cm) 20 MC MC Cu Pb Zn 40 30 40 50 70 50 60 80 90 60 70 Concentration of metals (mg/kg dry weight) 20 40 60 80 100 120 Concentration of metals (mg/kg dry weight) 140 160 0 20 40 60 80 100 120 Concentration of metals (mg/kg dry weight) 140 160 0 40 60 80 100 120 140 160 140 160 10 10 10 MC 40 Cu Pb Zn 20 Depth (cm) Cu Pb Zn 30 30 50 Cu Pb Zn 20 MC Depth (cm) 20 Depth (cm) 20 30 MC 40 50 60 70 60 40 80 Concentration of metals (mg/kg dry weight) 20 40 60 80 100 120 Concentration of metals (mg/kg dry weight) Concentration of metals (mg/kg dry weight) 140 160 0 20 40 60 80 100 120 140 160 0 MC 10 Cu Pb Zn MC 11 Cu Pb Zn 20 60 80 100 120 30 20 30 Depth (cm) 20 40 10 Depth (cm) Depth (cm) 10 20 40 MC 10 50 60 30 40 70 80 40 50 90 Fig Distribution of Cu, Pb and Zn in sediments on tidal flats Cu Pb Zn Arsenic (As) in sediments was quite high in concentration, up to five times higher ISQL levels Arsenic at MC 1, MC and MC had concentrations lower than ISQG levels Niken (Ni) in sediment got its high concentration at MC 7, MC10 and MC 11, but low concentration at MC 1, MC and MC The increasing in concentration of Ni was shown at MC 1, MC 2, MC and MC (Fig 6) Concentration of metals (mg/kg dry weight) 10 20 30 40 50 60 Concentration of metals (mg/kg dry weight) 70 80 0 10 20 30 40 50 60 Concentration of metals (mg/kg dry weight) 70 80 0 10 MC 60 Depth (cm) 50 30 40 50 60 70 80 20 MC 20 As Ni Cr 40 Depth (cm) Depth (cm) 30 20 10 10 20 10 As Ni Cr 30 MC 30 As Ni Cr 40 40 50 70 50 60 80 90 60 70 Concentration off metals (mg/kg dry weight) 10 20 30 40 50 60 Concentration of metals (mg/kg dry weight) 70 80 0 10 20 30 40 50 60 Concentration of metals (mg/kg dry weight) 70 80 0 MC 10 30 40 20 30 50 30 40 50 60 70 80 70 80 MC 20 As Ni Cr Depth (cm) Depth (cm) Depth (cm) 20 20 10 MC 10 As Ni Cr 10 As Ni Cr 30 40 50 60 70 60 40 80 Concentration of metals (mg/kg dry weight) 10 20 30 40 50 60 Concentration of metals (mg/kg dry weight) Concentration of metals (mg/kg dry weight) 70 80 0 50 100 150 200 250 300 350 10 As Ni Cr 20 20 30 40 50 60 MC 10 20 MC 11 30 As Ni Cr Depth (cm) 20 10 MC Depth (cm) Depth (cm) 10 10 0 30 As Ni Cr 40 50 60 30 70 40 80 40 50 90 Fig Distribution of As, Ni and Cr in sediments on tidal flats Chromium (Cr) in sediment on all tidal flats had its concentration lower than ISQG level, changing in a sediment core but not clear among the cores The highest concentration of Cr was recorded at MC 5, MC and MC Along tidal flats of the North Vietnam, heavy metals are high concentration of Cu, Pb, As and Zn, most of them is higher than ISQG levels High concentrations of metals are focus on Hai Phong to Ninh Binh coastal area, where mean diameters of sediment are smaller and clay minerals content are higher than Cua Luc to Mong Cai 4.4 Distribution of minerals on tidal flats Minerals in sediments on tidal flats are monmoriolite, kaolinite, illite, chlorite, fenspate, quartz and goethite Clay minerals which are common in sediment cores are kaolinite, illite; monmoriolite and chlorite had low concentrations (fig.7) Quartz was high in concentration in all the cores while other minerals (fenspate and goethite) were low in concentration in tidal sediment (fig 8) Monmoliolite was not common in tidal sediments of North Vietnam, its concentration was highest in MC and MC There was no change or less than limit detection of equipment at MC 2, MC Table Value of minerals (%) in core sediments on tidal flats Mineral Levels Min MC (n= 20 ) 3.00 MC (n=21 ) 3.00 MC (n=16 ) 3.00 MC (n= 14) 3.00 MC (n=23) 3.00 MC (n= 16) 3.00 MC 11 (n=20) 3.00 Kaolinite Monmoriolite Illite Chlorite Fenspate Quartz Goethite Max Aver SD 3.00 3.00 3.00 3.00 6.00 4.44 6.00 4.43 5.00 3.22 4.00 3.19 5.00 3.45 0.00 0.00 1.26 1.40 0.60 0.40 0.61 Min Max Aver SD Min Max Aver SD Min Max Aver SD Min Max Aver SD Min Max Aver SD Min Max Aver SD 11.00 18.00 15.45 1.70 10.00 19.00 15.90 1.77 5.00 6.00 5.20 0.41 3.00 5.00 4.40 1.42 39.00 63.00 46.15 4.92 6.00 8.00 7.35 0.75 4.00 15.00 7.67 3.06 7.00 19.00 12.76 3.94 3.00 7.00 4.68 1.65 3.00 4.00 3.14 0.91 48.00 83.00 64.76 8.89 3.00 6.00 4.33 1.56 14.00 23.00 19.13 3.12 21.00 27.00 24.00 2.16 8.00 11.00 8.94 1.00 5.00 7.00 5.88 0.96 20.00 39.00 27.56 4.07 5.00 9.00 6.56 1.26 15.00 23.00 19.79 2.58 16.00 29.00 24.00 3.11 6.00 10.00 8.43 1.59 4.00 6.00 5.29 0.73 22.00 47.00 29.43 5.96 5.00 8.00 6.57 0.76 8.00 16.00 12.26 2.20 19.00 27.00 22.65 2.55 5.00 7.00 6.65 0.57 4.00 15.00 6.74 2.77 31.00 47.00 39.30 4.58 4.00 7.00 5.65 0.83 7.00 13.00 10.31 1.89 17.00 29.00 23.56 3.60 7.00 10.00 8.13 1.09 5.00 13.00 6.69 2.70 32.00 52.00 39.31 6.11 4.00 7.00 5.88 0.89 6.00 14.00 9.10 2.15 15.00 25.00 19.70 3.10 6.00 9.00 6.95 0.83 4.00 14.00 7.20 2.82 38.00 59.50 46.30 4.79 3.00 7.00 5.10 0.79 Min = minimum; Max = maximum; Aver = average; SD = Standard deviation; n= number of sample Kaolinite had a high concentration after those of illite and quartz The highest content was at MC 2, MC and MC 6; the lowest content was at MC and MC 11 Taking kaolinite as an indicator for accretion, it shows accretion in all depth of the cores MC 2, MC 5, MC and MC Illite had the highest concentration in clay minerals of tidal sediments and been observed of changing as of kaolinite It is a good indicator for understanding environmental conditions; at position of cores have high sedimentation rate which are positive linear with content of illite Chlorite concentration was only higher than that of monmoriolite in clay minerals The concentration was higher at MC 5, MC and lower in other cores Comparison with other clay minerals in tidal sediments, the concentration of chlorite was changed in depths but not so clear Content of minerals (%) 10 15 20 30 35 10 MC 20 Monmoliolite Kaolinite Illite Clorite 30 10 15 20 0 10 10 20 Depth (cm) Depth (cm) Content of minerals (%) Content of minerals (%) 25 10 15 20 25 30 35 25 30 35 20 Depth (cm) 0 Monmoriolite Kaolinite Illite Clorite 30 40 MC 30 Monmoliolite Kaolinite Illite Clorite 40 40 50 50 50 60 60 60 70 Content of minerals (%) 10 15 20 Content of minerals (%) 25 30 35 0 10 10 20 15 30 MC 20 Monmoliolite Kaolinite Illite Clorite 25 10 15 20 Content of minerals (%) 25 30 35 MC 50 60 35 70 40 80 10 15 10 Monmoriolite Kaolinite Illite Clorite 40 30 20 Depth (cm) Depth (cm) Depth (cm) 0 MC Monmoriolite Kaolinite Illite Clorite 20 30 40 Content of minerals (%) 10 15 20 25 30 35 Depth (cm) 10 20 30 MC 11 40 Monmoriolite Kaolinite Ilite Clorite 50 Fig Distribution of monmoriolite, kaolinite, illite and chlorite in sediments on tidal flats Fenspate in sediments was high in concentration at MC and MC 11 at depth from 30cm to the end of cores The lowest concentration of fenspate was at MC and MC 3, but not clearly changing in the cores Content of minerals (%) 10 30 40 Content of minerals (%) Content of minerals (%) 50 60 70 80 90 0 10 10 40 60 80 0 10 10 10 20 30 40 50 60 70 80 90 MC 20 30 40 20 MC 30 Depth (cm) Fenspate Quartz Goethite Depth (cm) Depth (cm) 20 Fenspate Quarzt Goethite 40 50 MC 30 Fenspate Quartz Goethite 40 50 50 60 60 60 70 Content of minerals (%) 10 20 30 40 Content of minerals (%) 50 60 70 80 90 0 10 30 50 Content of minerals (%) 60 70 80 90 Fenspate Quartz Goethite 30 15 30 40 10 Fenspate Quartz Goethite 30 40 50 60 Depth (cm) MC 20 10 MC 20 Depth (cm) 10 10 Depth (cm) 40 MC 20 Fenspate Quartz Goethite 30 70 40 80 40 Content of minerals (%) 10 15 30 40 50 60 70 80 90 Depth (cm) 10 20 MC 11 Fenspate Quartz Goethite 30 40 50 Fig Distribution of fenspate, quartz and goethite in sediments on tidal flats 10 50 60 70 80 90 Quartz in tidal sediments was quite high in concentration at all cores In table standard deviation of mineral is high with quartz, this mineral are most abundant in tidal sediment, if concentration of quartz changes that mean sedimentary environment are changed, these event are shown in MC (at 20-70 cm in depth), MC (at 30 - 40cm in depth), MC (27-40 cm in depth) and MC 11 (27-50 cm in depth) (fig 8) Goethite had the highest concentration at MC 2, followed by those at MC 5, MC In the other cores, the change in concentration was not so high As the results, it is difficult to indicate for dynamic conditions, but it may be an indicator for physical – chemical of sediment Generally, in three environments mentioned above, common clay minerals in sediment cores are kaolinite and illite The highest content in these clay minerals are in the order: MC > MC > MC > MC > MC 11 > MC Quartz was concentrated at MC Taking the concentrations of clay minerals and quartz as indicators for sedimentary processes, the accretion takes place where high clay minerals are concentrated and the erosion with low sedimentation rates is at the areas with high quartz concentration Finally connection all data in sediment cores shows that used 210Pb and 226Ra in monitoring sedimentation rates only true for the accretion environment, but environmental erosion did not specify the exact age This problem is seeing in sediment cores at MC 3, MC 8, MC 9, and MC 11, other sediment parameters are complementary to each other reflect sedimentary processes at tidal flats As difference of 210Pb and 226Ra at layers are causes of during time, mean diameters, clay minerals and condition environment All of them show clearly two sedimentary processes which are erosion and accretion in the North of Vietnam CONCLUSIONS Based on study results on the sedimentary characteristics of grain size, sedimentation rate, metals and minerals, three sedimentary environments are classified, including deltaic tidal flat sedimentary environment from Kim Son to southwest Do Son Peninsula, estuarine tidal flat sedimentary environment from northeast Do Don Peninsula to southwest Cat Ba Island and embayment tidal flat sedimentary environment from Cat Ba to Mong Cai In deltaic tidal flat sedimentary environment, two sedimentary processes of accretion that is dominant and erosion that appears at 30cm in depth of MC 8, MC 9, MC 10 and MC 11 are with common fine sediments and high sedimentation rate, accumulation of metals in sediment, high clay minerals concentration Estuarine tidal flat sedimentary environment is characterised by accretion process, dominating fine sediment, high sedimentation rate, highest accumulation of metals and high clay minerals Embayment tidal flat sedimentary environment is with low sedimentation rate, 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