Influence of Human Activity on Hg Transportation

: Hg pollutes the environment, living organisms, and humans; hence, studying Hg content is essential for human health security. Using the dataset in May, September, and October, the Hg content, horizontal distribution, sources and transportation paths in the waters of Jiaozhou Bay were easily determined. These results indicate that the Hg content changing range in the waters in May, September and October was 0.015-0.150 μg/L, corresponding to the national seawater quality standards of Class I and Class II. The Hg content in the water body mainly arises from two sources, the transportation of rivers and offshore ocean currents. It from rivers' offshore ocean currents was 0.019-0.150 μg/L and 0.020 μg/L, respectively. Among them, the transportation of rivers includes the transportation of Haibo River, Licun River and Loushan River. So, a model block diagram has been built to unveil Hg contents and its different paths during the transportation to Jiaozhou Bay. Thus, it becomes easy to quantitively determine the migration process of Hg content through human activities to the ocean and rivers. Hg's different paths and contents reveal four rules for entering Jiaozhou Bay. In May, the offshore ocean currents and Haibo River did not affect by Hg pollution. In September, the Laoshan River was not polluted by it. In October, the Licun River was not, while the Haibo River exhibited light Hg pollution. When the Hg content transported by rivers was relatively low, it by offshore ocean currents became visible. From May to October, three rivers were transporting Hg content. Hg mildly polluted only one river in October, depicting that human activity is a key concern for environmental protection. It discharged by humans to land was relatively low, meanwhile only once was river transportation slightly polluted by it.


INTRODUCTION
With the increase of Hg discharged by industries to the environment, Hg content appears in the land, atmosphere and ocean. Hg content sources and its pollution degree in the coastal waters have attracted people's attention [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. According to the data from 1993, this study examines the Hg content level, horizontal distribution and sources in the waters, which show the water quality, background sources, and Hg quantity in Jiaozhou Bay, determining the matter water theory for maintaining sustainable ecological development.

Study environment
Jiaozhou Bay is a marine bay, between 120°04′-120°23′E and 35°58′-36°18′N near Qingdao City. There are islands, such as Tuan Island and Xuejia Island, and connected to the Yellow Sea. It has an area of about 446 km 2 and an average water depth of about 7 m. There are many rivers enter Jiaozhou Bay. Around the bay, appear Haibo River, Licun River and Loushan River and so on [12][13].

Methods
In this study, the dataset on Hg content in Jiaozhou Bay in May, September and October 1994 was obtained from the North Sea Monitoring Center of the State Oceanic Administration. Water samples were taken from seven stations: H3101, H3102, H3103, H3104, H3105, H3106 and H3107 (Figure 1), and were taken at the surface and bottom layers if the depth was >10 m, and only the surface layer if the depth was <10 m. The Hg content dataset was obtained with the national standard method and originated from the National Marine Monitoring Code [15].

3.1Content change
Hg contenthas the national seawater quality standards of Class I (0.05 μg/L), Class II (0.20 μg/L), and Class IV (0.50 μg/L) China. In May, September and October, its range was 0.015-0.150 μg/L, conforming to the Class I and Class II. In May, its variation range in the water body was 0.016-0.024 μg/L ( Figure 1). The first high-content area happened in the estuary of coastal waters of Haibo River, H3104, where it was relatively high at 0.024 μg/L, corresponding to the Class. The second high-content area appeared in the mouth waters, H3101, where it was relatively high at 0.020 μg/L, satisfying to the Class I. without the estuary of coastal waters of Haibo River and the waters of the bay mouth, in the other water areas, such as the northeastern and northern part, it was lower than 0.019 μg/L, indicating that the water quality in the northeastern and northern parts of the Bay was very good, and it reached the Class I.
In September, it in the waters ranged 0.015-0.019 μg/L ( Table 1). The high-content area happened in the estuary of coastal waters of Loushan River, H3105, where it was relatively low at 0.019 μg/L, meeting the Class I. But the estuary of the coastal waters of the Loushan River, in other water areas of Jiaozhou Bay, such as the eastern and southeastern part, it was lower than 0.016 μg/L, conforming to the Class I. For Hg content, the water was very clean and met the Class I.
In October, its changing range in the water body was 0.015-0.150 μg/L ( Table 1). The first high-content area took on in the estuary of coastal waters of Haibo River, H3104, where it was relatively high at 0.150 μg/L, exceeding the Class I and conforming to the Class II. The second high-content area appeared in the estuary of coastal waters of Licun River, H3106, where it became relatively high at 0.035 μg/L, conforming to the Class I. Without the estuary of coastal waters of Haibo River and Licun River, in the other water areas, such as the western and northern parts, it took on lower than 0.021 μg/L, conforming to the Class I. For Hg content, the water took on clean with good quality and arrived to the Class I.
So, it in the water body ranged 0.015-0.150 μg/L in May, September and October, conforming to the Class I and Class II. It unveils that, in May, September and October, the water quality for Hg content in the whole waters reached the Class I and Class II. Thus, the water was not polluted by Hg or slightly (Table 1).

Horizontal distribution
In May, in the estuary of coastal waters of Haibo River, H3104, it took on relatively high at 0.024 μg/L. There was a high-content Hg area with the estuary of coastal waters of Haibo River as the center, becoming a series of semicircles according to different gradients. From the high content of 0.024 μg/L in the center to the inner side of the Bay mouth, it fell along the gradient to 0.018 μg/L in the northeastern part and 0.016 μg/L in the northern part ( Figure 2). In the bay mouth, H3101, itt was relatively high at 0.020 μg/L. With the bay mouth as the center, a high-content Hg area appeared, forming a series of parallels according to different gradients. From the high content of 0.020 μg/L in the center to the bay inner side, it fell along the gradient to 0.018 μg/L in the northeastern part and 0.016 μg/L in the northern part ( Figure 2).
In September, in the estuary of the Loushan River coastal waters, H3105, it was relatively high at 0.019 μg/L. A high-content Hg area appears with the estuary of coastal waters of the Loushan River as the center, forming a series of parallels with different gradients. it decreased from 0.019 μg/L in the high content area in the center to surroundings by the gradients to 0.015 μg/L in the mouth waters ( Figure 3).
In October, in the estuary of coastal waters of Haibo River, H3104, it took on relatively high at 0.150 μg/L. A high-content Hg area happened with the estuary of coastal waters of Haibo River as the center, taking on a series of semicircles according to different gradients. From the high content of 0.150 μg/L in the center, it fell to the bay inner side through the gradient to 0.018 μg/L in the northeastern waters and 0.015 μg/L in the western waters ( Figure 4). In addition, a high-content Hg area appeared with the estuary of coastal waters of Licun River as the center, forming a series of semicircles according to different gradients. From the high content of 0.0351 μg/L in the center, it fell to the surroundings by the gradient to 0.018 μg/L in the northeastern waters and 0.015 μg/L in the western waters ( Figure 4).

Water quality
In May, September and October, it in the waters took on 0.015-0.150 μg/L, satisfying the Class I and Class II. It indicates that for Hg, in the whole waters in May, September and October, Hg pollution did not affected some water areas, while it mildly did.
In May, it in the waters ranged 0.016-0.024 μg/L, indicating that Hg did not contaminate the waters. In the estuary of the coastal waters of Haibo River, it arrived to a relatively high value, 0.024 μg/L and 0.020 μg/L in the mouth waters, implying that the water quality got the Class I and then the water was not contaminated by Hg. But for the waters in the estuary of the coastal waters of Haibo River and in the bay mouth, it became relatively low in other parts, far less than Class I. The water was clean and was no contamination of Hg.
In September, it changing range in the waters was 0.015-0.019 μg/L, expressing that Hg did not contaminate the waters. In the estuary of coastal water of Loushan River, it arrived to a very low level, 0.019 μg/L, specifying that the water quality got Class I and the absence of Hg contamination. But for the estuary of coastal waters of Loushan River, it became much lower, far less than the Class I. The water showed up clean. So no Hg contamination was observed.
In October, its range in the waters took on 0.015-0.150 μg/L, signifying that Hg mildly contaminated the waters.It in the estuary of coastal waters of Haibo River arrived to a relatively high level, 0.150 μg/L, expressing that the water quality got Class II and had a mild Hg contamination. In the estuary of coastal waters of Licun River, it looked relatively high at 0.035 μg/L, indicating that the water quality conformed to Class I and further there was no Hg pollution. But for the estuary of coastal waters of Haibo River and Licun River, in the other water areas, it took on relatively low, far less than Class I. The water showed up clean without Hg pollution.

Sources
In May, a high-content Hg area appeared in the estuary of coastal waters of Haibo River, denoting that it originated from the transportation of Haibo River with a relatively low content of 0.024 μg/L. In the mouth waters, a high-content Hg area was noted, indicating that it originated from offshore ocean currents with a very low content of 0.020 μg/L. In September, it happened a high-content Hg area in the estuary of coastal waters of the Loushan River, indicating that it originated from the Loushan River with a relatively low content of 0.019 μg/L. In October, it happened a high-content Hg area in the estuary of coastal waters of Haibo River, signifying that it originated from Haibo River with a relatively high content of 0.150 μg/L. Further, a high-content Hg area was formed in the estuary of coastal waters of the Licun River, indicating that its source was from the Licun River transportation, where it transported with relatively high at 0.035 μg/L.
Two sources for it exist: the transportations of rivers and of offshore ocean currents. It transported by rivers was 0.019-0.150 μg/L, and by offshore ocean currents 0.020 μg/L ( Table 2).

Migration rules of transportation
Two sources transported it in May, September, and October, i.e., rivers and offshore ocean currents. In the transportation, rivers includes Haibo River, Licun River and Loushan River. This study set up a model block diagram, which quantitatively elucidated its different paths and contents through the migration process ( Figure  5). So, it quantitatively explained its migration by its discharge of human activities to land and the ocean. In May, the Hg contents transported by the Haibo River and offshore ocean currents were 0.024 μg/L and 0.020 μg/L, respectively. In September, it by the Loushan River was 0.19 μg/L. In October, it by the Haibo River and Licun River were 0.150 μg/L and 0.035 μg/L, respectively.
In the transportation to Jiaozhou Bay, four rules have been unveiled by different paths and content levels in the migration of Hg content: 1) From May to October, rivers transport Hg content all the time, and the Hg content transported varies significantly. 2) From May to October, various rivers transport Hg content, such as the Haibo River, Licun River and Loushan River, located at the eastern coastal waters of Jiaozhou Bay. 3) The Hg content transported by rivers varies largely from May to October. In May, the Hg content transported by rivers was very low, while very high in October. For example, the Hg content transported by the Haibo River increased from 0.024 μg/L in May to 0.150 μg/L in October. The Hg content by rivers increased six times from May to October. 4) In May, the Hg content transported by rivers was very low, 0.024 μg/L. At this time, there was the transportation of Hg content by offshore ocean currents at 0.020 μg/L. Moreover, the transportation of offshore ocean currents did not appear in the latter several months.

Pollution degree of sources
In May, the Hg content transported by the Haibo River was 0.024 μg/L, unveiling that it transported to Jiaozhou Bay was very low, and did not pollute the Haibo River.
In May, it by offshore ocean currents was 0.020 μg/L, presenting that it transported to Jiaozhou Bay was very low, and did not pollute offshore ocean currents.
In September, it by the Loushan River was 0.019 μg/L, showing that it transported to Jiaozhou Bay was very low, and did not pollute the Loushan River.
In October, it by Haibo River was 0.150 μg/L, explaining that it transported to Jiaozhou Bay was relatively low, and mildly polluted Haibo River.
In October, it by the Licun River was 0.035 μg/L, expressing that it transported to Jiaozhou Bay was very low, and did not pollute the Licun River. Therefore, in May, it by the offshore ocean currents to Jiaozhou Bay was 0.020 μg/L, corresponding to Class I, indicating that Hg did not pollute the offshore ocean currents.
It by Haibo River in May, Loushan River in September and Licun River in October was within 0.019-0.035 μg/L, corresponding to Class I. It confirms that Hg content did not pollute Haibo River in May, Loushan River in September, and Licun River in October.
In October, it by Haibo River to Jiaozhou Bay was 0.150 μg/L, satisfying Class II, denoting that it mildly polluted Haibo River.

Transportation of human activities
In May, it transported by offshore ocean currents to Jiaozhou Bay was 0.020 μg/L, and Hg did not contaminate the ocean currents. This reveals that humans' Hg input into the ocean after a long period results in its increasing. Although it did not pollute, it was relatively high in the ocean body. When it by rivers was relatively low, the transportation of Hg content by offshore ocean currents appeared.
Except for it by the offshore ocean currents, there was only the transportation of rivers. It unveiled that at first humans discharged Hg to the land, then it moved by the force of various rivers to the coastal waters of ocean. From May to October, three rivers transported Hg, and only one river in October was mildly polluted by Hg content. This presents much attention paid to environmental protection by humans, and it from the humans discharge to the land was relatively low.

CONCLUSION
The horizontal distribution is adopted to study the place, way and degree of the source of Hg pollution. The main conclusions from this study can be summarized as follows: In May, September and October, Hg content ranged 0.015-0.150 μg/L, conforming to Class I and Class II, indicating that in the whole waters in May and September, it did not pollute the water, while in October, it mildly polluted some water areas. In May, its range in the waters was 0.016-0.024 μg/L, showing that Hg did not contaminate the waters. In the estuary of Haibo River, it arrived to a relatively high value, 0.024 μg/L, and 0.020 μg/L in the mouth waters of the Bay. In other water areas, it took on relatively low.
In September, it in the waters ranged 0.015-0.019 μg/L, indicating that Hg did not contaminate the waters. In the estuary of the Loushan River, it arrived to a relatively high level of 0.019 μg/L. In other water areas, it became much lower. In October, it in the waters ranged 0.015-0.150 μg/L, expressing that Hg mildly contaminated the waters. It in the estuary of Haibo River arrived to a relatively high level of 0.150 μg/L, presenting a mild Hg contamination. In the estuary of the Licun River, it took on relatively high at 0.035 μg/L, indicating that Hg did not pollute the water. In other water areas, it looked relatively low.
It in the water body chiefly arises from two sources, the transportation of rivers and offshore ocean currents. It from rivers was 0.019-0.150 μg/L and 0.020 μg/L from offshore ocean currents. In its transportation, there are rivers, including Haibo River, Licun River and Loushan River. Further, a model block diagram was set up to elucidate Hg content trend and its different paths in the transportation to Jiaozhou Bay. So, it is easy to quantitatively unveil its migration process because of human activities for Hg content to ocean and rivers. It and its different paths unveiled four rules for entering Jiaozhou Bay.
In May, it by the offshore ocean currents to Jiaozhou Bay was 0.020 μg/L, satisfying Class I. It indicates that Hg did not pollute the offshore ocean currents. It by Haibo River in May, Loushan River in September and Licun River in October was within 0.019-0.035 μg/L, satisfying Class I. It showed that it did not pollute the Haibo River in May, Loushan River in September, and Licun River in October.
In October, it by Haibo River to Jiaozhou Bay was 0.150 μg/L, satisfying Class II. It implied that it mildly polluted the Haibo River. It by offshore ocean currents explained that Hg input into the ocean by humans after a long time and increased in ocean. Although it did not pollute, it was relatively high in the ocean body. When it by rivers was relatively low, its transportation by offshore ocean currents appeared.
It by rivers unveiled that at first humans discharged it to land, and then various rivers transported it to the coastal waters of the ocean. From May to October, three rivers transported Hg, and only one river in October was mildly polluted by it. This denotes that humans pay much attention to environmental protection, and the Hg content of humans' discharge to land became relatively low.