| Bohai Bay is a typical semi-enclosed area, which is located in the west of the Bohai Sea in northern China. Due to the poor water exchange, many kinds of pollutants were unable to transport and diffuse, as a result they cumulated in the bay easily. In particular, during the recent decades, with the rapid development of industrialization and urbanization, the seashore area of Bohai Bay was reclaimed for port, industry and aquiculture. so a large amount of wastewater was discharged into the bay. Consequently, there are numerous environmental problems appeared, such as seawater quality deterioration, eutrophication, and red tide. To understand the influence of ecosystem it is important to announce the variation of environment. However, little information is available in Bohai Bay since 2000. In this study, the long-term (2000-2012) variation of environmental chemical factors, phytoplankton, and macroinvertebrate were surveyed, the changing process of Bohai Bay ecosystem was revealed. This work provided the basis for environmental management and ecosystem protection, and it is of great significance for the harmonious development of economy and environment and for the comprehensive pollution control of Bohai Bay.Seawater was collected from 2000 to 2012 were analyzed for nutrients (DIN and DIP), total petroleum hydrocarbons (TPH), and six heavy metals (As, Cu, Zn, Pb, Cd and Hg). These pollutants showed remarkable spatial and temporal distribution characteristics:high concentrations were found in the wet season and the concentrations of them decreased from the shoreline to offshore sites gradually. There were different year-to-year variations for different environmental chemical factors. In general, the DIN increased from 2000 to 2012. On the contrary, DIP and TPH decreased. However, no significant trend could be found for the concentration of heavy metals. When comparing with the Sea Water Quality Standard of China, the pollution statuses of the selected pollutants showed that DIN exceeded the grade-Ⅲ level in most years (10/13), while, DIP, TPH and most heavy metals (except of Pb and Zn) met the grade-Ⅱ level. This result indicates that DIN has been the main pollutant in the Bohai Bay.In order to understand the changing process of the main environmental chemical factors in sediment, surface sediments of Bohai Bay were collected, and TPH and five heavy metals were analyzed. Two environmental chemical factors showed different temporal-spatial variations. TPH concentrations generally decreased from 2001 to 2007 and increased afterwards. However, the concentrations of heavy metals increased from 2001 to 2005 and then decreased. Spatial variation of TPH and heavy metals (except Cd) was that their concentrations gradually decreased from the shoreline to offshore sites. This indicated that terrestrial inputs were the main important source of TPH and heavy metals. Concentrations of TPH and heavy metals met the highest level of Marine Sediment Quality Standards of China, indicating that the sediment was fairly clean. However, when assessed the risk based on the effects range-median (ERM) quotient method, the calculated values for all of the sampling sites were greater than 0.10, which suggested that there was a potential adverse biological risk in Bohai Bay. According to the calculated results, the biological risk decreased from 2001 to 2007 and increased afterwards. High-risk sites were mainly distributed along the coast.Phytoplankton was surveyed in Bohai Bay since 2000. The results showed that a total of approximately 100 taxa of phytoplankton were identified. Over 80% of the taxa were diatoms and dinoflagellate with an average abundance 118×104 cells/m3.In general, the abundance of phytoplankton gradually reduced from the shoreline to offshore sites, and it increased from 2000 to 2002 and then there were no regular variations. Generally speaking, the abundance of phytoplankton decreased from 2000 to 2012. However, they were significantly higher that the data of the corresponding period before 2000. There was an obvious variation in the dominant phytoplankton species and the biodiversity of phytoplankton increased from 2000 to 2005 while decreased from 2005 to 2009, and increased afterwards. If take the data of 2007 as an example to describe the effect of the environmental chemical factors on phytoplankton distribution in Bohai Bay based on the multivariate analysis techniques, the results of redundancy analysis (RDA) indicated that (NO3-N), nitrite(NO2-N), and dissolved inorganic phosphorus (DIP) were the most important environmental factors influencing phytoplankton assemblages in spring, while ammonium (NH4-N) and water temperature (WT) played key roles in summer.The sediment samples were collected by a Van Veen benthic grab facility and the macrobenthos were examined. A total of 136 taxa of macrobenthos were identified in Bohai Bay since 2000. Most of them were mollusca, annelida, and arthroplda and the average abundance was 149 ind./m2. The high abundance of macroinvertebrate was found along the coast, especially estuaries. The amount of the macroinvertebrate decreased from 2000 to 2005 and increased afterwards. There were 8 dominant maroinvertebrate were found during the survey years (13 yr) with a degree of dominance between 0.02-0.22. And the biological diversity index of macroinvertebrate was between 1.54 and 2.87, with an average value of 2.23. The data in 2008 were taken as an example to describe the effect of the environmental chemical factors on macroinvertebrate using the canonical correspondence analysis (CCA). The results showed that the maroinvertebrate were influenced by not only sediment but also water environmental factors. TOC was the main control factor among the sediment environmental factors, while water depth, temperature, inorganic nitrogen (DIN) and salinity played important roles in water environmental factors. |
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