Study on the Track and Degree of Pb Content Transportation

: Heavy Pb pollution has been noted in many developed countries. This study examined Pb pollution in Jiaozhou Bay for human security. We used the survey data on the Jiaozhou Bay waters of May, September and October 1994, the results examines Pb content and its horizontal distribution in the surface water bodies, which showed that the in the waters of Jiaozhou Bay Pb content expresses the range of 0.12-2.48 μg/L, agreeing with the seawater standards of Class I and II. Moreover, it has been noted that by the view of Pb content, Pb content in May, September and October polluted the Jiaozhou Bay water bodies softly. In May, September and October, the Pb content in the waters of Jiaozhou Bay ranged from 0.12 to 0.47 μg/L, 0.84 to 1.34 μg/L, and 0.92 to 2.48 μg/L. These results show that Pb content in May did not pollute the Jiaozhou Bay water bodies. While Pb content during September and October slightly polluted. Three sources transported mainly Pb content into Jiaozhou bay. These sources are rivers, land surface runoff and offshore ocean currents. The rivers transported the Pb content 0.47-2.48 μg/L, the land surface runoff 1.25 μg/L and the offshore ocean currents 1.34 μg/L. It demonstrates that Pb slightly polluted rivers, land surface runoff and offshore ocean currents in the transportation of Pb. From May to October, rivers transported Pb content which varied significantly. In September, land surface runoff transported Pb content during the rainy season. In addition, the offshore currents also transported Pb content to the waters of Jiaozhou Bay. Human activities discharged Pb content to land and transported it to the ocean, relying on the land surface runoff and rivers. Thus, two channels were transporting Pb content on land to the ocean, increasing Pb content. Through ocean currents, Pb content was transported from the high-content water area to the low-content water area. Therefore, the Pb content transported by rivers and land surface runoff could raise concerns from humans.


Study development
Humans continually discharge Pb (Plumbum) content to land, resulting in mild contamination on the surface of land. So the amount of Pb is transported to the ocean by the land surface runoff and rivers [1][2][3][4][5][6][7][8][9][10][11][12][13]. So, the research hotspot fully and diligently probed Pb content's pollution degree, pollution sources, and the migration process,which hanppened in the coastal waters. Utilising the dataset in 1994, this study on the Jiaozhou Bay waters discusses the Pb content changing, horizontal distribution trend, and its original sources. It examined Pb content's water quality, sources' background, amount from sources, and migration paths and processes.

Materials and methods
The dataset on Pb content in Jiaozhou Bay in May, September and October 1994 used in this study is provided by the North Sea Monitoring Center of the State Oceanic Administration. At seven stations, H3101, H3102, H3103, H3104, H3105, H3106 and H3107 (Figure 1), we collected water samples at the surface and bottom layers if the depth was >10 m, and we got only the surface layer if the depth was <10 m. The Pb content dataset was obtained from the national standard method, found in the "Marine Monitoring Code" [14].

Pb content
The national seawater standards of Pb was divided into Class I (1.00 μg/L), Class II (5.00 μg/L), Class III (10.00 μg/L) and Class IV (50.00 μg/L). The Pb content in the waters of Jiaozhou Bay ranged in May, September and October, from 0.12 to 2.48 μg/L, meeting Class I and II in the seawater standards. In May, in the Jiaozhou Bay waters, the Pb content ranged from 0.12 to 0.47 μg/L ( Table 1). The highcontent area appeared in the estuary of the nearshore waters of Dagu River, H3102, here the Pb content was high (0.47 μg/L), meeting Class I. The low-content area was in the mouth waters of Jiaozhou Bay, H3101, and the Pb content very low (0.12 μg/L), far less than Class I. Moreover, relatively low of the Pb content appeared in the whole waters, further the Pb content showed the changing range of 0.12-0.47 μg/L, which meets Class I.
In September, in the Jiaozhou Bay waters, from 0.84 to 1.34 μg/L ranged the Pb content (Table 1). in the mouth of Jiaozhou Bay hanppened the high-content area, H3101, with 1.34 μg/L of the Pb content, satisfying Class II. The second high-content area hanppened in the northern and northeastern waters, H3103, H3105 and H3106. With relatively high, 1.18-1.25 μg/L,the Pb content satisfied Class II (5.00 μg/L). In the central waters of Jiaozhou Bay, a low-content area appeared in stations H3104, H3107 and H3102, with the relatively low Pb content, ranging from 0.84 to 0.98 μg/L, conforming to Class I. In September, in the whole waters it was relatively high, and its changing range was 0.84-1.34 μg/L, satisfying Class I and II.
In October, in the Jiaozhou Bay waters the Pb content it ranged from 0.92 to 2.48 μg/L ( Table 1). The high Pb content of 2.48 μg/L appeared in the estuary of Haibo River, H3104, meeting Class II. The low-content area in the northern waters of Jiaozhou Bay, H3103, had the relatively low Pb content (0.92 μg/L) and satisfied Class I. it was relatively high in other water areas of Jiaozhou Bay, exceeding Class I but lower than Class II. In October, in the whole Jiaozhou Bay waters Pb had relatively high content and its range of 0.92-2.48 μg/L, meeting Class I and II.
Therefore, in the Jiaozhou Bay waters the Pb content range showed 0.12-2.48 μg/L in May, September and October, meeting Class I and II. It illustrates that it mildly polluted the whole Jiaozhou Bay water body (Table 1).

Horizontal distribution trend
In May, Dagu River has the estuary, coastal waters,where appeared the highest Pb content (0.47 μg/L).Moreover, the coastal waters formed a high Pb content area and accordiong to different gradients a series of semi-circles appeared. Along the gradient it decreased from its high content (0.47 μg/L) in the center to the surroundings to 0.12 μg/L in the bay mouth waters ( Figure 2). In September, the Jiaozhou Bay mouth waters had the highest Pb content 1.34 μg/L. A high Pb content area centering on the bay mouth waters was formed, according to different gradients, its area was taking on a series of semi-circles. From a high content of 1.34 μg/L in the center, it along the gradient decreased to the surroundings to 0.84 μg/L in the southeastern waters ( Figure 3). In the northern waters, Pb had relatively high content (1.25 μg/L). So appeared the high Pb content area, centering on the northern waters, by different gradients its form took on a series of semi-circles. From a high content of 1.34 μg/L in the center it fell to the surroundings along the gradient to 0.84 μg/L in the southeastern waters ( Figure 3).
In October, the estuary, coastal waters of Haibo River appeared the highest Pb content 2.48 μg/L so that a high Pb content area centering on the estuary coastal waters was formed, and at the same time by different gradients, a series of semi-circles were taking on. Along the gradient, from its high content (2.48 μg/L) in the center it fell to the surroundings to 0.92 μg/L in the northern waters ( Figure 4).

Water quality
In May, September and October, in the bay waters Pb content arrived 0.12-2.48 μg/L, conforming to Class I and II. It indicates that it mildly polluted the whole water body in May, September and October.
In May, its range in the waters indicated 0.12-0.47 μg/L, expressing that Pb did not pollute the Jiaozhou Bay water body of. In the estuary of coastal waters of Dagu River, the Pb content was relatively high (0.47 μg/L), far less than the Class I. It illustrates that the water quality here arrived Class I resulting in the fact that Pb did not pollute the water. Therefore, Pb had the relatively low content in the whole waters, with the range of 0.12-0.47 μg/L, conforming to the Class I resulting that Pb did not pollutethe water.
In September, its change range was 0.84-1.34 μg/L, presenting that Pb mildly polluted the water body. In the mouth waters it was 1.34 μg/L, indicating that the water quality in this area arrived to Class II resulting in the fact that Pb mildly polluted the water. In the northeastern coastal waters, it ranged from 1.18 to 1.25 μg/L, displaying that ithe water quality reached Class II, so Pb mildly contaminated the water. In the central water areas, it had relatively low, with 0.84-0.98 μg/L, showing that the water quality reached Class I resulting in Pb not polluting the water.
In October, the changing range of Pb content took on 0.92-2.48 μg/L, showing that Pb mildly polluted the water body. In the estuary coastal waters of Haibo River, it was 2.48 μg/L, signifying that the water quality there reached the Class II inducing the fact that Pb mildly polluted the water. In the northern waters, it denoted 0.92 μg/L, so the water quality reached Class I, so the water could not be contaminated by Pb. In other water areas it took on relatively high content, exceeding the Class I but conforming to the Class II. Therefore, Pb slightly polluted the water.

Sources
In May, a high Pb content (0.47 μg/L) area was formed in the estuary of coastal waters of Dagu River due to the transportation of Dagu River. In September, a high Pb content (1.34 μg/L) area in the mouth of the Bay from the offshore ocean currents was noted. Also, a high Pb content (1.25 μg/L) in the northern waters due to the transportation of land surface runoff has been noted. In October, a high Pb content (2.48 μg/L) area in the estuary coastal waters of Haibo River was noted. The Pb content in the waters is mainly migrated from three sources: rivers, land surface runoff and offshore ocean currents. So it was 0.47-2.48 μg/L from rivers, 1.25 μg/L from land surface runoff, and 1.34 μg/L from offshore ocean current (Table 2).

Changes in the content in different sources
Three sources transported Pb content, i.e., rivers, land surface runoff, and offshore ocean currents, in May, September, and October. In May, the Pb content from the Dagu River was 0.47 μg/L.
In September, the Pb content from offshore ocean currents was 1.34 μg/L.
In September, the Pb content from land surface runoff was 1.25 μg/L.
In October, the Pb content from Haibo River was 2.48 μg/L.
In May, the Pb content transported by rivers was very low. However, it became very high in October, revealing that the rivers always transported Pb content from May to October, and the Pb content transported varied significantly. In September, the land surface runoff transported Pb content during the rainy season. In addition, the offshore ocean currents also transported Pb content to Jiaozhou Bay.

Pollution degree of sources
In May, the Pb content transported by Dagu River to Jiaozhou Bay was 0.47 μg/L, meeting the Class I. So, Pb did not pollut the Dagu River (Table 2). In September, it by the offshore ocean currents to Jiaozhou Bay was 1.34 μg/L, and by land surface runoff was 1.25 μg/L, meeting the Class II. The offshore ocean currents and land surface runoff were mildly polluted by it ( Table 2). In October, it by Haibo River to Jiaozhou Bay was 2.48 μg/L, meeting the Class II. The Haibo River was also mildly polluted by it (Table 2).
Thus, it from the Dagu River to Jiaozhou Bay meets the Class I, exhibiting that the Dagu River was not polluted by it. However, the Pb content of Haibo River, land surface runoff and offshore currents transported to Jiaozhou Bay exceeded the Class I but met the Class II.
This indicates that it slightly polluted the Haibo River, land surface runoff, and offshore ocean currents. So, the Pb source in the waters was a non-point one, mainly from the transportations of the Haibo River, of land surface runoff and of offshore ocean currents.

Pathways to transport Pb content
Three sources, transporting Pb content to the bay, were rivers, land surface runoff, and offshore ocean currents. Thus, it brought by human activities exhibits two pathways to transport it to the waters. Meanwhile, it accumulated by the ocean was transported to the water body through the offshore ocean currents, one pathway to transport it.
Human activities discharge Pb content to land and then transport it to ocean, relying on land surface runoff and rivers. Thus, two channels transport it on land to the ocean and increase it. Its transportation to the waters is in the following ways: (1) human activities directly discharge the Pb content to the land, and then the land surface runoff directly transports it to the waters through rainwater, by which it transported was 1.25 μg/L; (2) Human discharge it to the land, and it of 0.47-2.48 μg/L was then transported to the ocean through rivers. Its range transported by rivers was large. It transported by some rivers was significantly larger than that transported by land surface runoff, but by others was notably less than that by land surface runoff.
Rivers and land surface runoff continuously transported Pb content to the ocean day and night. With a change in time, the transported one accumulated and continuously increased in ocean. In this way, through ocean currents, it was transported from high-content waters to low-content waters. Therefore, it transported by the offshore ocean currents to the marine waters was 1.34 μg/L,which expressed three pathways to transport it to the ocean waters of Jiaozhou Bay ( Figure 5).

Pb content in different sources
Various sources transported different Pb contents to the water body. It transported by the same pathways was also different. It transported in the following order: Pb content transported by Haibo River > it by offshore ocean currents > it by land surface runoff > it by Dagu River. It of different rivers varied significantly, illustrating thatit of various rivers discharged by human activities differed. For example, it transported by the Haibo River was very high, reaching light pollution. In contrast, it by the Dagu River was very low without any pollution. This requires humans to carry out different measures according to the amount of Pb transported by different rivers.
The Pb content transported by land surface runoff was between it by rivers. This indicates that it discharged by humans on land was smaller than the amount of Pb discharged into the river because of the larger land area. it by surface runoff passed through the land surface and directly reached ocean, so it slightly polluted waters from the surface to the marine coastal waters. Human activities brought a large amount of it to land, continuously moving to the ocean through surface runoff and rivers. After years of transport, it continued to settle and accumulate in the ocean, increasing it in the ocean, which discloses that it by the offshore ocean currents was relatively high (1.34 μg/L) ( Figure 5), so it of the ocean water body took on also relatively high.

Transportation discharged by human activities
In May, September and October, it in the waters was 0.12-2.48 μg/L, conforming to Class I and II. Further, it mildly polluted the whole water body, in May, September and October. In May, its variation range in the waters was 0.12-0.47 μg/L, indicating that Pb did not pollute the water body. In the estuary of coastal waters of Dagu River,it was relatively high (0.47 μg/L), far less than the Class I, implying that the water quality in this area arrived to the Class I, and Pb did not pollute the water.
In September, its variation range in the waters was 0.84-1.34 μg/L, specifying that Pb content mildly polluted the water body. In the mouth and northeastern coastal waters, it was relatively high (1.18-1.34 μg/L), revealing that it mildly polluted the water. In the central water areas, it was relatively low, with 0.84-0.98 μg/L, signaling that it did not pollute the water. In October, its range in the waters 0.92-2.48 μg/L, denoting that Pb mildly polluted the water body. In the estuary coastal waters of Haibo River, it was relatively high (2.48 μg/L), showing that it mildly polluted the water. In the northern waters, it was relatively low (0.92 μg/L), conveying that it did not contaminate the water. In other water areas it was relatively high, and slightly polluted the water.
The Pb content in the waters is mainly transported from three sources, i.e., rivers, land surface runoff and offshore ocean currents. It from rivers was 0.47-2.48 μg/L, from land surface runoff 1.25 μg/L, and from offshore ocean currents 1.34 μg/L. In May, the Pb content transported by rivers was very low. Then it became very high in October, revealing that the rivers always transported it from May to October, and it transported varied significantly. In September, the land surface runoff transported it during the rainy season. In addition, the offshore ocean currents also transported it to Jiaozhou Bay. The Pb content of Haibo River, land surface runoff and offshore currents transported to Jiaozhou Bay exceeded Class I but met Class II. This presents that the transportation of the Haibo River, land surface runoff, and offshore ocean currents were all slightly polluted by Pb.
Human activities discharged Pb content to land and then transport it to ocean, relying on land surface runoff and rivers. Thus, two channels were transporting it on land to the ocean, increasing its amount. Its variation range transported by rivers was large. And it by some rivers was significantly larger than that by land surface runoff, but by others was notably less than that by land surface runoff. Rivers and land surface runoff continuously transported it to the ocean day and night, causing the ocean's Pb content to increase continuously. In this way, through ocean currents, it was transported from high-content waters to low-content ones. From land and ocean to Jiaozhou Bay water bodies, there exist three different migration paths for its transportation: 1) by surface runoff from land directly to the ocean 2) by rivers to the ocean 3) by the ocean currents from high content area to low one. Moreover, the study considered a model block diagram to present its amount transported by three pathways to the ocean.

Conclusion
The horizontal distribution is adopted to study the place, way and degree of Pb pollution source. Different sources transported Pb content to the water body with different contents. It was transported in the following order: Haibo River > offshore ocean currents > land surface runoff > Dagu River. It from different rivers varied considerably. it transported by land surface runoff was between these by rivers. So, it in the marine waters was relatively high, and mildly polluted the ocean. Overall, it transported by rivers and land surface runoff attracts human attention.
The studies showed clearly that the Human activities influenced the going process of Pb transporting from the land to the waters. In the future, we would further study the yearly changing process of Pb transporting in tempral and special variation.