Abstract
The increase of water temperature, due to thermal discharges from two nuclear power stations, was one of the most significant environmental changes since 1982 in the Daya Bay, located in the north of the South China Sea. This study investigates the long-term (1982-2012) environmental changes in Daya Bay in response to the increase of water temperature, via comprehensively interpreting and analyzing both satellite and in situ observations along with previous data. The results show that: 1) salinity, dissolved oxygen (DO), chemical oxygen demand (COD) and nutrients had been enhanced after the thermal discharges started in 1994; 2) the concentration of Chl-a increased while the net-phytoplankton abundance decreased; 3) diversity of the phytoplankton community had decreased; 4) fishery production had declined; and 5) frequency of Harmful Algal Bloom occurrence had increased. Satellite images show clearly that a thermal plume from the power stations extended toward the interior of Daya Bay, and that surface temperature of the seawater increased as one approached the power stations. The analysis suggests that the thermal water discharged from the two power stations was a driver of the ecosystem’s change in Daya Bay. Several factors, including nutrients, salinity, DO, and COD, varied according to the increase of water temperature. These factors affected the water quality, Chl-a, and phytoplankton in the short term and impaired aquatic organisms and the whole ecosystem in the long term.
Highlights
Water temperature is one of the most important factors to marine ecosystems; small changes of water temperature could have considerable environmental impacts on ecosystems [1] [2]
Many studies show that serious ecosystem degradations are related to aggressive human activities, such as nutrient enrichment caused by increasing discharge of daily-life and industrial sewage, as well as toxins discharged from the cage culture [3]-[5]
A comparative study of seawater temperature at twelve stations in Daya Bay before and after the start of operation of the Daya Bay Nuclear Power Station (DNPS) found that, since the operation of the DNPS, the annual mean Sea Surface Temperature (SST) has increased by 0.34 ̊C, and the greatest recorded change was of 2.30 ̊C in one summer [23]
Summary
Water temperature is one of the most important factors to marine ecosystems; small changes of water temperature could have considerable environmental impacts on ecosystems [1] [2]. Seawater warming can be caused by increasing mean global temperature or by local thermal discharge. It is critical to study and understand the impact of water temperature changes on marine ecosystems, caused by, for example, thermal discharge or global warming. Thermal pollution from power plants could elevate the seawater temperature and significantly impact the ecosystems of coastal bays [9]-[12]. The environmental impact on the ecosystem due to thermal water can be evaluated via analyzing the change in the amount, type, and distribution of the phytoplankton in the vicinity of the power stations in the bay. Understanding the impact of human activity on the bay ecosystem has high significance to safe and sustainable exploits in the coastal water
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