Zhi Zeng

Utilizing data from the four survey voyages in the Beibu Gulf from 2021 to 2022, this study investigates the variations in water temperature and salinity at different survey periods across its central and eastern regions, analyzing their horizontal and vertical distribution patterns. The research further explores the relationship between these distributions and the gulf’s circulation dynamics, elucidating their underlying formation mechanisms. The results indicate that the variations of water temperature and salinity are obviously different in different periods. Horizontally, spring and summer survey voyages exhibit a transition from high-temperature (max 31.90 °C), low-salinity (min 29.54 PSU) waters in the north to low-temperature (min 21.10 °C), high-salinity (max 34.19 PSU) waters in the south, while autumn and winter survey voyages show low-temperature (min 18.57 °C), low-salinity (min 29.54 PSU) waters in the north shifting to medium-to-low-temperature (21.52–28.20 °C), high-salinity (max 34.19 PSU) waters in the south. Vertically, the spring survey period displays distinct stratification with multiple thermoclines and haloclines in different regions. The summer survey period exhibits the strongest thermohaline gradients, with intensified thermoclines and haloclines accompanied by regional up- and downwelling. In the autumn survey period, vertical mixing homogenizes temperature and salinity, while the winter survey period shows near-complete mixing, effectively eliminating stratification. These patterns are driven by a combination of oceanic dynamics and regional climatic factors, including monsoon forcing, solar radiation, coastal runoff, horizontal circulation, and up-/downwelling processes.

Rapid and accurate dynamic monitoring and quantitative analysis of red tide disasters are of significant practical importance to national economic development. Remote sensing technology is an effective means for monitoring red tides. This paper utilizes GOCI satellite data and employs a quasi-analytical algorithm (QAA) to retrieve the spectral curves of phytoplankton absorption coefficients. On the basis of a detailed analysis of the differences in the spectral curves of the phytoplankton absorption coefficients between red tide and non-red tide waters, we establish a red tide identification algorithm for the East China Sea on the basis of phytoplankton absorption coefficients. The algorithm is applied to multiple red tide events in the East China Sea. The results indicate that this algorithm can effectively determine the occurrence locations of red tides and extract relevant information about them.

The diffusion characteristics of thermal discharge from coastal power plants were studied by analyzing the Ningde Nuclear Power Plant and Kemen Power Plant, which are located in different geographical regions in China. The former is in the open sea, and the latter is in a well-sheltered bay. In the vicinity of the outfall areas of the two power plants, large-area surface temperature observations and tidal current observations were conducted. The results indicate that the thermal discharge diffusion characteristics of coastal power plants located in different geographical environments are significantly different. In the well-sheltered sea area of the Kemen Power Plant, the water temperature diffuses faster along the coast, in line with the direction of tidal movement, and slower in the offshore direction under the influence of rectilinear tidal currents within the bay, resulting in a significantly greater longitudinal diffusion distance of thermal discharge along the shore than the transverse diffusion distance offshore. In the area surrounding the Ningde Nuclear Power Plant, rotational currents diffuse the thermal discharge in various directions, causing the range of temperature rise to expand toward the outer sea. Dominant tidal currents within the tidal cycle in the sea area can influence the distribution of high-temperature rise zones near outfalls. The distribution of high-temperature rise zones predominantly occurs on the side with the higher average tidal velocity, either the ebb tide side if its velocity is greater than that of the flood tide or the flood tide side otherwise.

This study analyzed the horizontal and vertical distribution characteristics of temperature and salinity in the central and eastern regions of the Beibu Gulf, based on conductivity measurements in summer 2022, temperature, and depth (CTD) measurement data from the Sino–Vietnamese cooperative project “Demonstration Study on Ecological Protection and Management in Typical Bays: Seasonal Survey of the Beibu Gulf”. Furthermore, the study utilized the computational results from the numerical Finite-Volume Coastal Ocean Model (FVCOM) to elucidate the intrinsic patterns that formed the temperature and salinity distribution characteristics in August 2022 from both thermodynamic and dynamic perspectives. The circulation in the Beibu Gulf drives external seawater to move northward from the bay mouth. During this movement, numerous upwelling areas are created by lateral Ekman transport. The formation of different scales of cyclonic and anticyclonic vortices and current convergence zones is influenced by topography, runoff, and the water flux from the Qiongzhou Strait, which are key factors in the formation of upwelling and downwelling. The surface circulation in August 2022 significantly differed from the 20-year average surface circulation, with an influx of 1.15 × 10⁴ m³/s more water entering the Beibu Gulf compared to the multi-year average. The water flux from the Qiongzhou Strait is a critical factor affecting the circulation patterns in the Beibu Gulf. The northeastern waters of the Beibu Gulf are characterized by current convergence zones, where extensive upwelling occurs. The rich nutrient salts in these areas promote the reproduction and growth of phytoplankton and zooplankton, making this the most favorable ecological environment in the Beibu Gulf and serving as a natural reserve for fisheries, coral reefs, dugongs, and Bryde’s whales.

The runoff of the Jiulong River (JLR) is a key parameter that affects the estimation of pollutant flux into Xiamen Bay (XMB). The precise runoff estimation of the JLR can be used to determine the accuracy of the pollutant flux estimation flowing into XMB. In this study, to analyze the hydrological dynamic characteristics and identify the correlation between fixed-site real-time ocean current observations and cross-sectional navigation flow observations, we conducted six navigation observations on two cross-sections of the JLR estuary during the spring tide and neap tide in the normal season, wet season, and dry season in 2020. Simultaneously, we measured hydrological observation data by a fixed-site buoy located in the JLR estuary and collected runoff data that were measured upstream of the JLR. The results showed that the average correlation coefficient between the average velocity of the fixed-point buoy and average velocity of the section was more than 0.90, higher than expected, the minimum average deviation was 4%, and the minimum sample standard error was 5.7%, which was a good result. In this study, we constructed a model for estimating the runoff of the JLR into the sea. The findings demonstrated that Acoustic Doppler Current Profiler (ADCP) online monitoring data were useful to estimate runoff of the JLR with high accuracy, could promote the accuracy of estimated pollutant flux of the JLR’s discharge into XMB, and could provide more scientific and reliable basic data for future load flux estimation research.

Zeng, Z.; Luo, Y.; Chen, Z.J.; Tang, J.J.; Wang, Y.H., and Chen, C.H., 2020. Impact assessment of thermal discharge from the Kemen power plant based on field observation and numerical simulation. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 351–361. Coconut Creek (Florida), ISSN 0749-0208.The impact of the Kemen Power Plant thermal discharge on temperature rise in the ambient waters in the Luoyuan Bay was studied using field observation and numerical simulation. The scope of influence, indicated by the maximum temperature rise envelope curves during the observation period, was determined through field measurements of water temperature in the study area. The measurements revealed that the surface water with temperature rise diffused along the shoreline to the upstream and downstream of the power plant after the thermal discharge entered the sea. The longitudinal diffusion distance along the direction parallel to the shoreline was significantly longer than the transverse diffusion distance along the direction perpendicular to the shoreline. The area with the maximum temperature rise was near the outfall. Under the field conditions given in this paper, the surface seawater temperature rise varied from a maximum of 10 °C near the outfall to 0.5 °C at a distance of 600 m from the shore. Temperature rise was mainly observed in the surface water, and the scope of influence rapidly diminished vertically with minimal temperature rise in the waters 3 m below the surface. Meanwhile, a 2-D tide field mathematical model and a thermal discharge diffusion model were developed to simulate the diffusion process of the power plant thermal discharge in the sea area. A comparison of the simulated results obtained under the same conditions as the field measurements showed that the established numerical model can effectively reflect the temperature diffusion of the thermal discharge, as well as the scope of full-tide maximum temperature rise at typical tide phases. Therefore, the numerical model of thermal discharge described in this paper can serve as a powerful tool to predict the impact of thermal discharge from power plants.