Environmental changes reflected by sedimentary geochemistry in recent hundred years of Jiaozhou Bay, North China

Environmental Pollution 145 (2007) 656e667 www.elsevier.com/locate/envpol

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Environmental changes reflected by sedimentary geochemistry in recent hundred years of Jiaozhou Bay, North China Jicui Dai a,b, Jinming Song a,*, Xuegang Li a, Huamao Yuan a, Ning Li a,b, Guoxia Zheng a,b a

Institute of Oceanology, Chinese Academy of Sciences, Qingdao, Shandong 266071, China b The Graduate School, Chinese Academy of Sciences, Beijing 100039, China

Received 21 February 2006; received in revised form 9 July 2006; accepted 4 October 2006

Identifying environmental changes by employing geochemical parameters combined with

210

Pb chronology.

Abstract Sediment geochemical technique was employed to assess how the sediment records reflect the environmental changes of Jiaozhou Bay, a semi-enclosed bay adjacent to Qingdao, China. In the past hundred years, Jiaozhou Bay has been greatly impacted by human interventions. A dated core sediment by 210Pb chronology was analyzed for trace metals including Li, Cd, Cr, Pb, Cu, Ni, Co, Zn together with C, N, P and BSi. Based on the research, the development of Jiaozhou Bay environment in the past hundred years can be divided into three stages: (1) before the 1980s characterized by relatively low sedimentation rate, weak heavy metal pollution and scarce eutrophication; (2) from the 1980s to 2000, accelerating in the 1990s, during which high sedimentation rates, polluted by heavy metals and the frequent occurrence of red tide; (3) after 2000, the period of the improvement of environment, the whole system has been meliorated including the heavy metal pollution and hypernutrification. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Geochemical records; Environmental changes; Biogenic elements; Trace metal; Jiaozhou Bay sediments

1. Introduction Marine sediments, including materials originating from the terrestrial inputs, as well as atmospheric deposition and autogenetic matter from ocean itself, preserve a continuous record of regional and even global environmental changes, which can be employed in reconstructing environmental evolution (Wan et al., 2003; Song, 2004). To some extent, sediment is the mirror of sedimentary environmental changes, which can reflect the biological, geodynamic and geochemical process of former conditions. On the other side, environmental changes are not only driven by natural forces, but also by anthropogenic effects (Kalis et al., 2003). Especially in recent years, the

* Corresponding author. Tel./fax: þ86 532 82898583. E-mail address: [email protected] (J. Song). 0269-7491/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2006.10.005

anthropogenic impacts on the environment have been leading to eutrophication in coastal zone and offshore and the interaction of the natural force and human activities have exerted great effects on the whole environmental system. During the past decades, the environmental change has gained increasing interests and has been substantially fueled by the concern about the trends of environmental changes. So it is essential to seek efficient proxies to indicate the sedimentary environmental changes and many indicators have been identified as powerful tools including grain size, pollen, organic carbon, biogenic opal, C/N atomic ratio and planktonic foraminifera are in the list constituting the multi-proxy studies of environmental changes (Song, 2004). Indicators are increasingly being developed and employed as efficient tools to address environmental issues. Coastal areas are sensitive to both climatic changes and human impacts, which make such areas ideal for studying

J. Dai et al. / Environmental Pollution 145 (2007) 656e667

environmental changes, and coastal sediment sequences have become attractive targets to document paleoenvironmental changes. Jiaozhou Bay is an excellent example for coastal sea with high terrestrial influences, which is a semi-enclosed bay, surrounded by industrial and densely populated areas. In recent years, impacts from human activities on Jiaozhou Bay have increased considerably and become a major concern even moved upwards on the political and scientific calendar. As the co-host city of the 2008 Beijing Olympic Games, during which the sailing events will be held there, Qingdao has deserved more attention than any time before. Therefore, the research on sedimentary environmental changes of Jiaozhou Bay is of major significance in the prediction of future trends. However, relatively few data on environmental changes are available about Jiaozhou Bay, information gained from sedimentary records may represent an especially valuable approach to compensate such a paucity of information. During the past decades, geochronology studies combined with the analysis of geochemical indicators in sediments have provided valuable information on contribution of ocean, terrestrial and anthropogenic inputs. Driven by a desire to gain information of environmental changes and gain insights into the development trends in Jiaozhou Bay, the paper presented here is based on the determination of chrono-geochemical records at first, and then extract useful environmental information from sedimentary sequences of known age. The ageedepth relationships in sediment can be estimated using the short-lived isotope 210Pb dating. On the basis of sedimentation dating, the study presented the biogenic elements including C, N, P, and BSi together with heavy metals. Here, through the interpretation of the information given by these geochemical records, we aim: (1) to determine the environmental changes in recent hundred years, including the eutrophication and heavy metals pollution history of Jiaozhou Bay; (2) to assess the impacts and proof of human activities on sedimentary environment; (3) to seek more efficient geochemical proxies indicating the sedimentary environmental changes. 2. Materials and methods 2.1. Site description The focus of the paper concentrates on Jiaozhou Bay. It is a semi-enclosed bay located on the south bank of Shandong Peninsula, China, linked with the Yellow Sea with a very narrow entrance about only 3.1 km (Fig. 1). It extends from 36 000 5300 N to 36 020 3600 N, from 120 160 4900 E to 120 170 3000 E. The average depth is 7 m, with the maximum of 64 m. It covers an area of 362 km2 of seawater with a population of 7.2 millions. Long-term range of annual rainfall is 340e1243 with an average of 775.6 mm, with 58% of that in summer and 23% in winter. More than 10 small seasonal streams empty into the bay with varying water and sediment loads, notably the Yanghe, Daguhe, Moshuihe, Baishahe and Licunhe River (Liu et al., 2005), and the largest one is Daguhe River, with an annual average runoff of 6.61  108 m3. Most of these rivers, however, have become canals of industrial and domestic waste discharge with the advance of economic activity and increased population in the region. According to Shen (2001), from 1962 to 1998, the population of Qingdao City increased from 4.6  106 to 7.0  106, and the gross value of industrial output increased 80 times. The discharge of industrial waste and sewage in urban district is 70.2  106 t/a and 14.4  106 t/a, respectively. In 1980, the total amount of waste water increased to 145.6  106 t/a and the use of fertilizers had

657

increased three times from 1980 to 1998. Overall, due to the rapid economical and social developments in this region, Jiaozhou Bay is greatly influenced by human activities, leading to increased amount of industrial, agricultural, and aquiculture input into Jiaozhou Bay (Fan, 1988). Red tide has become a frequent event, as the bay water is eutrophied. During the past 70 years, the water area of Jiaozhou Bay had decreased by one-third mainly because of the dumping of garbage from Qingdao City. The changes of water area in Jiaozhou Bay during the past hundred years are tabulated in Table 1.

2.2. Sampling The present study is based on B3 core sediments from inner of Jiaozhou Bay (Fig. 1) sampled on 6 September 2003. The core sediment was collected with a gravity corer onboard ‘‘Jinxing II’’. The core sediment was sectioned at 2 cm intervals and the pH, Eh and Es was determined in situ as soon as possible. Eh was measured at 2 cm depth intervals using a Pt electrode coupled with an Ag/AgCl reference electrode. Simultaneously, Es was determined with a multi-electrode, and pH was measured using a multi-electrode and a HANA pH meter. Eh and Es were corrected to the standard hydrogen electrode. Eh, Es, pH were measured in situ within 30 min after samples were acquired from the sea bottom (Li et al., 2005; 2006). The sediment cores were sealed with plastic caps and frozen for further analysis at the laboratory. The B3 (36 07.1130 N, 120 15.0610 E) column has a length of 94 cm with the depth of 16 m below water. For B3 core sediments, the upper layer 0e2 cm, it is yellowegrey gravelly mud (mainly mud, rare sand) and below 50 cm, especially below 70 cm, there are more shells. The sediment separated from the pore water was dried at 60  C in an oven for 72 h. Dried aliquots were ground using a mortar and pestle. The water content was determined using the difference in the weight of sediment before and after drying. Generally, water content in sediments increases from deeper to the upper layers and this change in sediment water content is a logical consequence of compaction due to sediment accumulation. Suitable amount of samples were sieved into three sizes (>63, 31e63 and <31 mm) through two different meshes sequentially using seawater, which was filtered by the membrane of 0.45 mm. Analyses were performed in every 2 cm of the first 18 cm of the cores, every 4 cm (18e30 cm), every 10 cm for depths greater than 38 cm. The basic physical parameters of the core are shown in Table 2.

2.3. Geochemical and radionuclide analysis The N and P abundances in sediments were determined using a PE2400 SERIES II CHNS element analyzer, and repeat measurements of standard samples have shown that analytical accuracy was 10% for N and P. Organic carbon (OC) concentration was determined according to Gaudette et al. (1974) and the BSi was analyzed employing the technique by Kamatani and Oku (2000). For BSi and OC analyses the variations within replicates were <10%. Inductively coupled Plasma-Mass Spectrometry (ICP-MS) was used to analyze for Zn, Cu, Co, Pb, Ni, Cd, Cr and Li in acid digestion with (HF þ HNO3 þ HClO4) performed according to Heinrichs and Herrmann (1990) in closed PTFE containers. The sediment should be grinded to minimize the effects of variable water content and grain size before analysis. Recoveries (%) varied according to the metal but they were all in the range of 90e95%, and the precision was nearly 10% under the confidence level of 95%. One of the most promising methods for estimation of sedimentation rate on a time scale of 100e150 years is by means of 210Pb, a naturally occurring radioisotope with a half-life of 22.3 years. Meanwhile, it is a common practice to use 137Cs as an independent tracer to verify 210Pb method (Lu and Matsumoto, 2005). However, for Jiaozhou Bay, the sedimentary environment is in relatively state in the past hundred years, so it is feasible to date only by 210Pb chronology in Jiaozhou Bay (Li et al., 2003). The 210Pb chronology and sedimentation rate were determined by measuring the 210Pb activity through its granddaughter product 210Po with 208Po added as an internal yield tracer in order to appraise possible losses incurred during application of the digestion protocol. The sediments in the paper were chemically pre-treated and then determined by alpha counting of 210Po deposited on Ag discs (Hamilton and Smith, 1986).

J. Dai et al. / Environmental Pollution 145 (2007) 656e667

658

Fig. 1. Geography of the study area and sampling site.

1 A0 t ¼ ln l Ai

3. Results and discussions 3.1.

210

ð1Þ

Pb chronology and sedimentation rate so

The core sediment was dated using 210Pb chronology from radioactive fallout. The 210Pb and excess 210Pb (210Pbxs) activities were plotted on a log scale versus the depth (Fig. 2). Ignoring compaction and assuming that: (1) the rate of deposition of 210Pbxs from the atmosphere is constant; (2) 210 Pbxs is quickly removed from solution onto particulate matter, so 210Pbxs activity in sediments is essential that due to overhead fallout from atmosphere; (3) the flux of 210Pbxs via the water column to the sediments is constant and (4) the 210 Pbxs, once incorporated in the sediments, does not diffuse via the pore water of the sediment (Schell and Nevissi, 1983; Ruiz-Ferna´ndez et al., 2004). Sedimentation rate was calculated from the slope of the least square fit of the plotted graphs. The age of each sliced layer was determined according to the Constant Initial Concentration (CIC) model (Robbins and Edgington, 1975; Goldberg, 1963) by using the equation,

Table 1 Area changes of Jiaozhou Bay during the past hundred years km2

Water area/

Water area below 0 m line

1863 1928 1935 1958 1963 1966 1977 1980 1985 1988 1992 2003

579 560 559 535 423 470 423 400 374 390 388 362

295 274 274 310 264 278 298 258 256 256 303

Intertidal area

Tidal current (108 m3)

285

21.6 12.667

159

10.665

142

9.626

85

9.593 w7

S¼

Xiþ1  Xi tiþ1  ti

ð2Þ

where A0 is unsupported 210Pb activity at surface sediments in dpm/g dried sediments, Ai is the unsupported 210Pb activity at depth i in dpm/g dried sediments, S (cm/a) is the sedimentation of definite layer, i ¼ ith depth interval, Xi ¼ depth of the top of the ith interval, ti ¼ age of the top of the ith interval. According to (1) and (2), the sedimentation rate of definite layers were calculated and tabulated in Table 3. Rapid increase of sedimentation rates was observed in sediment record of Jiaozhou Bay, which is also a common Table 2 Summary of chemical and geological characteristics for the core sediment Depth (cm)

pH

Es

Eh

F (%)

31 mm (%)

31e63 mm (%)

63 mm (%)

0 2 4 8 10 12 14 18 22 26 30 38 48 58 68 78 88 92

7.17 7.1 7.11 7.22 7.25 7.21 7.31 7.15 7.35 7.26 7.17 7.39 7.17 7.16 7.17 7.36 7.23 7.42

52 54 57 47 47 37 36 31 34 31 30 28 23 23 22 21 21 22

256 76 53 90 80 110 126 107 126 102 102 76 114 117 102 148 115 120

69 68.36 67.41 65.37 61.07 65.21 62.42 58.05 58.06 59.61 60.58 61.58 63.25 69.38 73.08 78.41 69.9 70.68

43.16 48.81 53.65 52.97 56.60 58.31 66.70 62.70 64.96 65.24 59.08 52.87 56.91 41.59 40.04 23.62 27.05 31.88

34.66 30.81 31.26 29.13 27.08 30.73 24.40 24.38 22.94 21.27 27.95 30.04 21.68 21.93 16.09 13.54 17.15 23.51

22.18 20.39 15.09 17.91 16.32 10.96 8.91 12.91 12.10 13.49 12.97 17.09 21.41 36.49 43.87 62.85 55.80 44.60

J. Dai et al. / Environmental Pollution 145 (2007) 656e667 210Pb

0.1

activity/(dpm/g) 1

10

0

Depth/cm

20

659

construction in the rivers entering the Bay can also affect the sediment inputs from rivers. For example, dams have been built since 1950s, which has reduced the sand inputs to the Bay in some degree. But the influence is rather weak compared with the sewage and wastewater discharge into the Bay, so the sedimentation rates of Jiaozhou Bay increased on the whole. 3.2. Heavy metals and their pollution tracers

40

60

80

100

Fig. 2. 210Pb activity in B3 core sediments of Jiaozhou Bay (:: the total 210 Pb; -: the excess 210Pb).

phenomenon in coastal areas especially in recent years. Intensification of land-use, rapid population growth deforestation and urbanization has resulted in significant increase in delivering of sediment to the Bay since the 1980s. Before the 1980s, the sedimentation rate of Jiaozhou Bay maintained relatively steady increase indicating a comparatively stable sedimentary environment and was only 0.30 cm/a. Climate changes such as large flood events were not observed in the past hundred years in Jiaozhou Bay, so the general accelerating trends in sedimentation rate in the 1980s would rather reflect the increasing effect of human impacts. With the rapid urbanization and economic growth after 1980s, increased effluent from industry and agriculture would induce the increase of sediment discharge, which may be related to the long-term increasing trends of sedimentation rate between 1980s and 2000. Since Qingdao was selected to be the co-host of 2008 Beijing Olympic Games, measurements have been adopted to manage the Jiaozhou Bay, such as the foundation of erosion control works (namely Licun, Haipohe and Tuandao wastewater treatment works distributed in the east bank of the Bay), improvement of effluent treatment, etc. may account for the decrease in sedimentation rate since the beginning of this century. Additionally, it is of major importance that deforestation and dam Table 3 Sedimentation rates for different years of B3 in Jiaozhou Bay Depth (cm)

Year

S (cm/a)

0 4 8 12 16 22 38

2003 1999 1992 1985 1972 1962 1910

0.64 1.60 0.60 0.60 0.48 0.31 0.30

Pollution is a negative outcome of rapid development and industrialization. Marine bays adjacent to metropolitan areas have been strongly polluted by domestic wastewater, factory disposal and other sources, and anthropogenic impacts have seriously influenced the whole marine ecosystem. Heavy metals are produced from a variety of natural and anthropogenic sources, for example, metal pollution can result from direct atmospheric deposition, geologic weathering or through the discharge of agricultural, municipal, residential or industrial waste products (Demirak et al., 2006). The distribution of metals in sediments adjacent to settlement areas can provide researchers with evidence of the anthropogenic impact on ecosystems and, therefore, aid in assessing the risks associated with discharged human waste (Demirak et al., 2006). Sediment trace metals data can be used to uncover the pollution history of aquatic system, because they are widely available and more reliable than dissolved metal concentrations in a water system (Valde´s et al., 2005). In the study, the Cr contents are from 37.1 to 82.6 mg/g with the average of 66.6 mg/g; the Cu concentrations are from 54.2 to 87.8 mg/g with the average of 66.5 mg/g; the Zn concentrations are in the range of 49.6e112 mg/g with an average of 87.23 mg/g; the Cd is from 0.48 to 1.79 mg/g with an average 0.76 mg/g; the Pb is from 18.2 to 36.3 mg/g with an average 28.85 mg/g; the Co is from 8.41 to 18.7 mg/g with an average 14.1 mg/g; the Ni concentrations are in the range of 18.9e42.7 mg/g and the Li concentrations are from 18.9 to 66.2 with an average of 46.7 mg/g. The vertical profiles of all heavy metals in Jiaozhou Bay sediments are presented in Fig. 3. It is showed that most of the metals increased from the bottom to the top of the cores, hence from past to present. Cadmium, copper and zinc showed fluctuating concentrations with increasing trend and the lowest concentrations at the bottom of the core with subsurface sediments having peak values, and only copper at the surface implying that the flux of the these metals have been progressively augmented with time, but a reduction of these metals during recent years. The correlation coefficients of the heavy metals with organic carbon and the grain size were calculated and tabulated in Table 4. The correlation between the metal concentration and the organic matter content in the sediments has been shown by various research teams (Duzzin et al., 1988; Martincic et al., 1990). Sedimentary organic matter may also influence metal concentrations in sediments suggesting that the accumulation of heavy metal is closely related to the accumulation of organic matter. Except Cd, the significantly positive correlations found between most metals and organic carbon

J. Dai et al. / Environmental Pollution 145 (2007) 656e667

660

Cr(µg/g) 100

0

0

50

0

100

Depth/cm

50

50

Co(µg/g) 0

0

20

20

40

Pb(µg/g) 150

50

0

0

0

1

0

0

50

100

40 60

Depth/cm

20

Depth/cm

Depth/cm

Depth/cm

40

Li(µg/g) 2

20

50

20

50

Cd(µg/g) 60

0

0

100

0

Ni(µg/g)

10

50

0

0

Depth/cm

Depth/cm

Zn(µg/g)

Cu(µg/g)

50

Depth/cm

0

50

80

40

60 80

100

100

100

Fig. 3. Vertical profiles of heavy metals in Jiaozhou Bay sediments.

(OC), suggest that they have a common origin and probably the metals have been introduced to the system attached to organic materials. And except Cd, the correlations between the heavy metals are positive indicating that the metals may originate from the same or similar sources. The metal content in marine sediments depends on the grain size distribution, since the increased specific surface of finer sediments favors adsorption processes (Cauwet, 1987). As shown inTable 4, except Cd, the significant positive correlation between the finest fractions and metals and negative correlation between the coarse fractions and metals observed validates the ‘‘Grain Size Control Effect’’ put forward by Zhao (1983), which says that the grain size is finer, the element concentration is more higher. To reduce the heavy metal variability caused by grain size and mineralogy of the sediments, and to identify anomalous metal contributions, geochemical normalization has been used with various degrees of success by employing conservaˆ ez-Osuna, 2001), of them, tive elements (Green-Ruiz and PaA

Al and Li are the most widely used elements. Al is often used as a conservative element because of the relative stability in sedimentation. However, Loring (1990) has shown that Li is superior to Al for the normalization of metal data from sediments derived mainly from the glacial erosion of crystalline rocks and is equal or superior to Al for those derived from non-crystalline rocks. A reference element must be strongly correlated to the fine fraction and not dependent on anthropogenic inputs (Mil-Homens et al., 2006). As shown in Table 4, the Li concentration has good correlationship with grain size which satisfied with demand. In order to gain information about the source, changes and influencing factors of heavy metals, the enrichment factor (EF) of heavy metal in the B3 core was calculated according to the following formula: EF ¼ ðM=Al or LiÞsample =ðM=Al or LiÞcrust

ð3Þ

In this paper, the baseline value adopted the element abundance in earth crust (Taylor, 1964; Szefer et al., 1998).

Table 4 Correlation coefficients of heavy metals with organic carbon and grain size

Cu Zn Cd Pb Co Ni OC Grain size

<31 mm 31e63 mm >63 mm

Cr

Cu

Zn

Cd

Pb

Co

Ni

Li

0.373 0.962 0.071 0.948 0.952 0.961 0.743 0.857 0.482 0.909

1 0.45 0.06 0.459 0.261 0.324 0.354 0.054 0.658 0.366

1 0.02 0.961 0.948 0.949 0.734 0.806 0.438 0.847

1 0.023 0.062 0.063 0.251 0.157 0.116 0.180

1 0.933 0.933 0.785 0.842 0.452 0.883

1 0.989 0.591 0.867 0.219 0.787

1 0.614 0.868 0.280 0.818

0.920 0.393 0.915

J. Dai et al. / Environmental Pollution 145 (2007) 656e667

According to Jiang and Li (2002) and Valde´s et al. (2005), if the EF is close to 1 it indicates a crust origin of metals, whereas EF over 10 denotes non-crustal source. Based on the research of Zhang and Liu (2002), if an EF value is between 0.5 and 1.5, it suggests that the trace metals may be entirely from crustal materials or natural weathering processes. If an EF is greater than 1.5, it suggests that a significant portion of trace metal is delivered from non-crustal or natural weathering processes, the trace metals are provided by other sources (Feng et al., 2004). The enrichment factor (EF) of the seven heavy metals in Jiaozhou Bay is presented in Table 5. It is seen that the EFs of these metals lied in the sequence, Cd > Pb > Cu > Zn > Cr > Co > Ni. Cd, Pb and Cu are therefore the most anthropogenic enriched elements in the sediment and Co and Ni appear to be the marginal for inclusion in this list. All the EF values were lower or close to 1 indicating that all these heavy metals were derived from crust. The relatively higher EFs of Cd and Pb than other heavy metals could be interpreted as the contamination in Jiaozhou Bay of Pb and Cd as both are the typical anthropogenic metals and affected by the human activities. On the whole, the pollution of heavy metals in Jiaozhou Bay is not serious based on the EF analysis. Streams are mainly carriers of anthropogenic as well as natural metals, increasing the human impacts on the whole aquatic system of Jiaozhou Bay especially in the recent two decades. On the other side, Qingdao has few heavy metal industries and therefore there is relatively a lack of these contaminated heavy metals in wastewater draining the Bay. As shown in Table 6, the area is not seriously polluted by heavy metals due to local human activities compared to other coastal areas in the world. Although from 1980s to 2000, the heavy metal pollution of the Bay is relatively serious, at the beginning of this century, the environmental quality of Jiaozhou Bay enhanced, as it is well known to all. 3.3. Biogenic elements and their eutrophication effects There are important interactions between the sediments and overlying water and sediments may play an essential role in regulating the phytoplankton production and the extent of bottom water hypoxia/anoxia (Jørgensen and Richardson, 1996). Table 5 The EF values of heavy metals in Jiaozhou Bay sediments Depth (cm)

Cr

Cu

Zn

Cd

Pb

Co

Ni

1 5 9 13 17 23 31 39 49 59 69 79 Average

0.33 0.24 0.29 0.29 0.25 0.28 0.28 0.28 0.28 0.29 0.33 0.39 0.29

0.79 0.51 0.52 0.44 0.46 0.43 0.39 0.45 0.40 0.57 0.72 1.13 0.57

0.63 0.47 0.50 0.49 0.48 0.54 0.49 0.56 0.54 0.53 0.61 0.75 0.55

1.52 0.95 4.09 1.64 0.97 1.59 0.86 1.63 0.99 1.43 2.41 3.29 1.78

1.15 0.94 1.01 0.87 0.88 0.89 0.91 0.94 0.99 1.07 1.26 1.54 1.04

0.25 0.21 0.23 0.23 0.24 0.25 0.25 0.25 0.25 0.26 0.30 0.37 0.26

0.19 0.15 0.16 0.17 0.17 0.19 0.19 0.17 0.18 0.18 0.20 0.27 0.18

661

So the eutrophication will certainly exert its influences on the composition of biogenic elements in sediments and the latter may act as the perfect proxies indicating the eutrophication and other environmental changes. In previous studies, many researchers have been devoted to establish sedimentary records to indicate the occurrence of major environmental changes (Cornwell et al., 1996; Zimmerman and Canuel, 2000; Bratton et al., 2003; Turner et al., 2004) including the eutrophication history. As for Jiaozhou Bay, based on the research of Shen (2001), from the 1960s to the 1990s, nutrient concentrations in overlying water have increased 1.4 times for PO4-P, 4.3 times for NO3-N, 4.1 times for NH4-N, but the SiO3-Si concentration has remained at a very low level from the 1980s to the 1990s and the SiO3-Si limiting has been increased. The nutrient structure of Jiaozhou Bay has changed and therefore should influence the structure and abundance of nutrients in the sediments. The eutrophication of coastal waters is a major problem affecting many regions of the world (Cloern, 2001). The increased loads of nutrients to seawater have caused eutrophication, a process that brings about an apparently positive rise in biological production and there are deleterious effects on the aquatic environment such as decreased water transparency, increased oxygen demand and even a threat to both human health and economy (Lysiak-Pastuszak et al., 2004). Since the 1980s, Jiaozhou Bay has experienced rapid population growth and agriculture and urban development, accompanied by substantial increase in nutrients loading and as a result, the water in Jiaozhou Bay has been in great hypernutrification. The hypernutrification is certain to induce the occurrence of red tide. The first red tide appeared in 1978 in Jiaozhou Bay. Till the beginning of 1990s, Jiaozhou Bay had been hypereutrophic and the frequency of red tide was continually increasing. Moreover, from 1980s, when the hypernutrification state of Jiaozhou Bay became serious and correspondingly, the sedimentation rates began to rise. It is obvious that eutrophication is tightly correlated to the development of industry and agriculture. Based on the analysis of vertical profiles of concentration and burial fluxes of biogenic elements, similar to heavy metal pollution history, the inputs history of biogenic elements in Jiaozhou Bay develops three periods e before 1980s, 1980e2000 and after 2000. Before 1980s, the biogenic elements concentrations and burial fluxes were in a relatively stable status. The sediment inputs of all biogenic elements began to increase over background at around 1980s, and generally consistent with the time of the rapid urbanization of Qingdao. Temporal shifts in nutrients concentrations and burial fluxes can be attributed to human activities. Evidences of history changes in eutrophication can be reflected in the vertical profiles of biogenic elements concentration, burial flux as well as the elemental ratios such as Cu/Zn, OC/OP, OC/TN, Si/N, Si/P, etc. in sediments. 3.3.1. Biogenic elements The vertical profiles of OC, TN, TP and BSi were aas shown in Fig. 4. In our study, most of the biogenic elements

J. Dai et al. / Environmental Pollution 145 (2007) 656e667

662

Table 6 Comparison of heavy metal contents between different regions

Jiaozhou Bay Pearl River Estuary, China Pearl River, China West Coast of Peninsular Malaysia Pacific of USA Southern Baltic Sea, Poland Southern Bay, Brazil Izmir, Turkey

Cd (mg/g)

Pb (mg/g)

Cu (mg/g)

Zn (mg/g)

Reference

0.76 e 0.83 0.89

28.85 59.5 57 21.87

66.5 40.9 55 17.29

87.23 115 303 70.9

This study Li et al. (2000) Chen et al. (2000) Yap et al. (2002)

2.1 0.81 0.07e0.11 0.22e0.42

47.9 31.5 42.0e43.5 32e62

81.6 12.6 22.7e28.1 32e70

160 60.1 94.2e114 99e260

Meador et al. (1998) Szefer et al. (1996) Rivail Da Silva et al. (1996) Atgin et al. (2000)

appear to follow the same vertical profiles, that is, all the concentrations increased upwards although there were some large fluctuations in some layers. The highest levels were almost at the top or subsurface of the core sediments. Upcore increases in the nutrients concentration of the core sediment profiles may reflect increasing nutrients loading through time. Organic matter (OM) accumulation rate in marine sediments are commonly used as a proxy for the past biological productivity (Miltner et al., 2005; Song et al., 2002). The OC abundance had an apparent trend of decreasing with the depth. There is a wide and obvious temporal variation in OC contents (0.07% and 0.45%; mean 0.38%) and OC contents progressively increase upward, leading to the highest values at the subsurface layers and decrease at the surface sediment, which indicates the reduction organic matter input. TN is the total quanta of nitrogen in sediments, which can be considered as the maximum nitrogen to take part in the nitrogen recycling (Lu¨ et al., 2005). Accordingly, the TN can be superior measurement for primary production. Vertical profile of TN in Jiaozhou Bay B3 core sediments was rather irregular and there were many fluctuations but the trend was increasing from bottom to top. The TN abundance was from 0.16 to 0.48 mg/g and the average concentration was 0.323 mg/g. Sediment phosphorus is not generally considered as a good indicator for eutrophication because much of the accumulated

phosphorus in marine systems is eventually remineralized from the sediment via sulfate reduction (Jensen et al., 1995; Song et al., 2003). Compared with TN, the changes of TP concentrations were slight and there were fewer fluctuations and in the range of 0.17e0.31 mg/g with the average of 0.22 mg/ g, but organic phosphorus showed generally increasing trends from bottom to top layers. The OP is quantitatively one of the most phosphate phases buried in the sediments and thus directly affects the availability levels of dissolved phosphorus for primary production (Edlund and Carman, 2001) and important organic phosphorus are formed primarily by biological processes and may be produced in situ or enter via sewage effluent containing body wastes and food residues. Sediment OP is a rough measure of organic production in the basin and decomposes slowly (Ruttenberg and Gon˜i, 1997a), it might be a better indicator of eutrophication than TP (Vaalgamaa, 2004). The OP abundance was with a wide range from 0.01 to 0.18 mg/g. Biogenic silica (BSi) accumulation in the sediments can reflect the general pattern of primary productivity in the overlying waters and can be used as a proxy for paleoproductivity studies (Berna´rdez et al., 2005; Masque´ et al., 2003; Song et al., 2003). Percent of BSi in Jiaozhou Bay were measured and the range was 1.11e2.17%. However, certain correlations between the eutrophication and Bsi were not found. Unlike TP and TN, BSi Concentration(mg/g)

Concentration/ 1

2

3

0

20

20

40

40

Depth/cm

Depth/cm

0

0

60

0

0.2

0.4

60

80

80

BSi/

TN TP

TOC/ 100

0.6

100

Fig. 4. The vertical profiles of OC, TN, TP and BSi in Jiaozhou Bay sediments.

OP

J. Dai et al. / Environmental Pollution 145 (2007) 656e667

abundance displayed an irregular profile and there were peaks at the layers of 4e6 cm, 22e24 cm, 68e70 cm and 92e94 cm, which may be related to the occurrence of algae bloom in the Bay, as the algae bloom occurs, the BSi abundance in sediments will increase, otherwise it will decrease and as a result, there were many fluctuations of BSi abundance.

BF ¼ Ci Srd ¼ Ci Sð1  Wc Þ=ðð1  Wc Þ=rs þ Wc =rw Þ

ð4Þ

where BF[mmol/(a$cm2)] as the burial flux of biogenic elements in sediments; Ci (mmol/g) the concentration of biogenic elements in sediments; S (cm/a) the sedimentation rate; rd (g/ cm3) the sediment dry bulk density; Wc (%) the water concentration in sediment; rs (g/cm3) the sediment grain density, BF is reported in units of mg/(a$cm2) and Ci in mg/g, respectively. Dry bulk density (DBD) of sediments was calculated by equation of Snoeckx and Rea (1995): rd ¼ ð1  Wc Þ=ðð1  Wc Þ=rs þ Wc =rw Þ

ð5Þ

where rd (g/cm3) the sediment dry bulk density; Wc (%) the water concentration in sediment; rs (g/cm3) the sediment grain density and assumed to be 2.56 g/cm3 (Chough and Lee, 1987) in this paper. In some sense, the burial flux can be an indicator of environmental change during definite time. Based on the formula (4) and (5), the burial fluxes of OC, TN, TP and BSi were descriptive in Fig. 5. As it showed, the burial fluxes of all biogenic elements began to increase in the 1980s with the peak at the end of last century. For example, the burial flux of OP was 0.464 mmol/(a$cm2) at the beginning of 1980s, but with a rapid augment of 1.569 mmol/(a$cm2) from 1998 to 2000. Fortunately, at the beginning of the century, with measurements adopted to manage pollution and eutrophication, the environmental quality has been improved greatly with the OP

OP TP

12

10

TN OC BSi

8

BF

3.3.2. Burial flux of biogenic elements Buried within the sediments is not only the ultimate but also the start of marine recycling of biogenic elements, that is, sediments act both as source and sink of biogenic elements. Therefore, the biogenic elements will exert its influences on the primary production and carbon cycle; moreover, biogenic elements buried by the sediments can be released to overlying water on appropriate conditions, so it is essential to well understand that how many biogenic elements were buried as well as the factors influencing the burial flux of biogenic elements. The burial flux of biogenic elements in marine sediments can be determined by the supply and preservation of biogenic elements into the sediments. The biogenic elements burial is dependent on some environmental factors, such as sedimentation rate, sediment porosity, microbial activity, bioturbation rates and bottom water oxygen conditions, etc. (Schenau et al., 2005). On the whole, three pieces of information are required to calculate the burial flux in marine sediments: the biogenic elements concentration of sediments accumulating below a defined horizon, the recent sedimentation rate and the dry bulk density. The burial flux (BF) can be expressed as (Ingall and Jahnke, 1994):

14

663

6

4

2

0 1900

1920

1940

1960

1980

2000

Year Fig. 5. The burial fluxes of nutrients in different periods in Jiaozhou Bay sediments.

burial flux dropped to 0.145 mmol/(a$cm2) even lower that at 1980s in which the rapid development of Qingdao incurred. Similar to OP, the burial flux of TN, TP, BSi and OC increased from the 1980s until 2000 or so. It suggests that burial flux of nutrient is a more effective proxy indicating eutrophication history of Jiaozhou Bay compared with the abundance of nutrients. It can be divided into three periods for eutrophication in Jiaozhou Bay in the recent hundred years according to the burial flux changes of nutrients. In details, the quantity and burial fluxes of nutrients have similar trends: (1) increasing steadily from 1900 to 1980, (2) increasing rapidly after 1980, (3) accelerating from 1900 to a peak in 2000, and (4) decreasing from 2000 to the present. Fertilizers applied in the catchment areas are a dominant source of eutrophication in coastal areas. The amounts of phosphorus and nitrogen fertilizers applied annually in the catchment area of Jiaozhou Bay increased by three times from 1980 to 1998 indicating that strong increase in fertilizer consumption that started in the early 1980s was followed by an increase of nutrients concentrations. All the burial fluxes of nutrients decreased from 2000 to present. This trend is attributed to source reduction associated with increased regulation of wastewater discharge, industrial production of nitrogen, phosphorus fertilizers, increased industrial waste recycling, and cleaner industrial processes. Much regulatory attention has also been given to sewage effluent and its detrimental environmental effects. Sewage treatment practices have been upgraded and monitored to reduce the concentrations of nutrients being introduced to the sediment record. 3.3.3. Biogenic element ratios and eco-environmental indicator Elemental ratios can be used as good indicators of sediment provenance and diagenetic changes. The organic matter to

J. Dai et al. / Environmental Pollution 145 (2007) 656e667

664

and OC/OP ratios incline to at about 8 cm depths, corresponding roughly to the 1980s, which is the rapid development of Qingdao. The vertical profiles of C/N and OC/OP ratios can also validate the fact that the land-derived inputs have become the dominant source of Jiaozhou Bay especially in recent years. Since 1950s, due to the rapid growth of Qingdao population and the accelerating development of industry and agriculture, the domestic, industrial, aquaculture sewage have exceeded the river input and become the main origin of Jiaozhou Bay sediments. Generally speaking, the Si/DIN and Si/P ratios can be used to identify the nutrient limiting factors for the growth of phytoplankton. As the Si/P < 16 or Si/DIN < 1 of overlying water in Jiaozhou Bay, the silica is the limiting factor for phytoplankton growth in Jiaozhou Bay (Yang et al., 2003). According to Shen (2001), the high ratio of DIN:PO4-P and low ratios of SiO3-Si:PO4-P (7.6  8.9) and SiO3-Si:DIN (0.19  0.15) in the water body showed that the nutrient structure of Jiaozhou Bay has changed from more balanced to unbalanced during the past 40 years. The reason may lie in that the phytoplankton consume the silica in overlying water and then transport downward by the biological pump, and finally deposit in the sediments, which is also embodied in the burial flux of BSi in the period and even reach up to 13.24 mmol/ (a$cm2). As Fig. 6 showed, the Si/TN and Si/16P ratios in the sediments are all more than 1, Si/N ratios are in the range of 12e83 and Si/P ratios are 37e124 indicating that the silica

marine sediments has two sources: terrestrial inputs and marine plants and have distinctive C:N:P ratios (Ruttenberg and Gon˜i, 1997b). Especially the OC/OP, OC/TN ratios have been widely applied to organic matter sources characterization (Tyson, 1995; Meyers, 1997). Marine phytoplankton has a mean molar OC/OP ratio of 106:1, and a mean molar OC/ TN ratio of 6.6:1 (Ruttenberg and Gon˜i, 1997b; Redfield et al., 1963). The C/N ratio values of organic matter have been widely used as a proxy to identify changes in the proportions of sedimentary organic matter originating from marine autogenic and terrestrial plants (St-Onge and Hillaire-Marcel, 2001). Algae have a C:N ratio between 4 and 10, whereas terrestrial organic matter has a C:N greater than 20 (Meyers, 1994). That is to say, increases in C:N ratio in sediment profiles can be interpreted to identify periods when sediments received a high proportion of terrestrial organic matter. Conversely, decreases in C:N ratios may be used to identify periods when sediments have received a high proportion of algal organic matter. Thereafter, the nutrients ratios (including OC/OP, OC/TN, Si/N and Si/P) can be employed to indicate the organic matter origin. In Jiaozhou Bay B3 core sediments, vertical profiles of OC/OP, OC/TN, Si/N and Si/P ratios were plotted as Fig. 6. As shown in Fig. 6, the C/N and OC/OP ratios of B3 core sediments are both higher than Redfield ratios, the former lies in the range of 34e357 and the latter was from 6 to 55 and generally decline with decreasing depth in the profiles. C/N

OC/TN 20

40

OC/OP 60

0

100

200

Si/N 300

400

0

Depth/cm

40 60

0

20

40

20

20

40

60

40

60

80 80

80

100

100

100

Cu/Zn

Si/TP 0

0

50

100

150

0

20

40

60

0

0.5

1

20

Depth/cm

Depth/cm

Depth/cm

20

0

Depth/cm

0

0

40

60

80 80 100 100

Fig. 6. Redox-indicator (Cu/Zn) and nutrient ratios of core B3.

1.5

60

80

100

J. Dai et al. / Environmental Pollution 145 (2007) 656e667

inclines to deposit in the sediments. The vertical profiles of Si/ N and Si/P ratios have similar trends with slight increasing downward. However, the Si/N and Si/P ratios in surface sediments are larger than that of subsurface sediments indicating that in the process of early diagenesis, the decomposition rates of nitrogen and phosphorus are larger than that of silica, and as a result, the silica accumulates gradually in the sediments and therefore silica is relatively scarce in overlying water. Also, it reveals that the accumulation rate of silica in sediments enhanced in recent two decades. The decrease of Si/TN and Si/P after 2000 may be due to improvement of environment quanlity, the silica limiting was no longer stronger as before. Similar to Fe and Mn, Cu/Zn ratio has been used to describe sediment redox-conditions (Hallberg, 1974; Tolonen and Merila¨inen, 1983; Vaalgamaa, 2004), so Cu and Zn are commonly used as indicators of anthropogenic influences. In Jiaozhou Bay sediments, the concentrations of Cu and Zn were close to each other and major changes of Cu/Zn can be seen at 50 cm and 15 cm or so below surface sediments indicating that during the periods there had been obvious sedimentary redox environment changes before 1900 and 1980s. The environmental changes before 1900 are beyond in the paper, and the environmental change at 1980s is the result of rapid urbanization of Qingdao City, increasing soil erosion, industrial effluent discharge and release of mostly untreated wastewaters into Jiaozhou Bay, which have exerted undesirable effects on environment and led to the change of the whole ecosystem and sedimentary redox environment.

4. Conclusions The study presented here has highlighted the importance of using multi-proxy geochemical indicators combined with the 210 Pb dating for interpretation of sedimentary environment changes of Jiaozhou Bay. There are two turning points in the past hundred years for the Jiaozhou Bay sedimentary environment, which can define three periods, before 1980s, from 1980s to 2000 and after 2000. The first period is characteristic of relatively low sedimentation rate, weak heavy metal pollution and the eutrophication is not serious. The second period is the time when Qingdao City developed quickly, during the time, Jiaozhou Bay has been subjected to various pollutant sources and led to the serious heavy metal pollution and hypernutrification; moreover, the peak years occurred at the 1990s. Correspondingly, the sedimentation rate has accelerated and the land-derived inputs have become the main source of sediment. The third period is the time when the sedimentary environment has been improved due to the measurements supported by the financial investment to mange the Jiaozhou Bay. From our investigation, it is obvious that potential driving forces for these alterations in Jiaozhou Bay sedimentary environment are almost certainly human induced and include the effects of deforestation, urbanization and industrialization, direct impacts on the marine environments such as large-scale coastal reclamation, sand and mud dredging and dumping, etc. And such information is vital for the effective

665

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