Increasing intrusion of high salinity water alters the mariculture activities in Zhanjiang Bay during the past two decades identified by dual water isotopes

Using dual water isotopes to quantify the mixing of water masses in the Pearl River Estuary and the adjacent northern South China Sea

“…The seawater samples for d 18 O and dD were measured by using the equilibration method. The detailed process can be found in Lao et al, 2022a andLao et al, 2022b). In brief, samples were equilibrated with H 2 or CO 2 , and the equilibrated gas was measured by an elemental analysis isotope ratio mass spectrometer (Gasbench II-IRMS) (Gasbench II interfaced with a 253 plus mass spectrometer).…”

“…where X ij and S jk represent the d 18 O and dD of a mixed water sample and isotope signature values of water mass sources, respectively; S jk represents normal distribution with standard deviation w jk and mean deviation m jk ; P k represents the proportion of different water masses; c jk represents the fractionation factor for dD and d 18 O of different water masses, normally distributed, with mean l jk and standard deviation t jk ; ϵ jk represents the residual error of the addition of an unquantified change between samples, normally distributed, with mean 0 and standard deviation s j . Since the d 18 O and dD in seawater are less affected by biogeochemical processes (Fairbanks, 1982;Hattori, 1997;Lian et al, 2016;Wang et al, 2018), the Bayesian mixing model was successfully applied to quantify the mixing contribution of water masses (Lao et al, 2022a andWu et al, 2021;Lao et al, 2022b). The advantage of the Bayesian mixing model compared to other methods, such as the model MixSIR, is the residual error term in the form of standard deviation included in the model (Jackson et al, 2009).…”

“…However, such traditional method has some limitations to trace the mixing of water masses because the salinity and temperature are not the characteristic of water itself (Bigg and Rohling, 2000;Lao et al, 2022a). It is difficult to identify the mixing of water masses with the same salinity in the oceans, particularly in the coastal areas (Lao et al, 2022a andLao et al, 2022b). In coastal waters, water masses are mixed from different freshwater masses, and these water masses may have similar or even the same temperature and salinity, thus making it difficult to distinguish their contribution (Bigg & Rohling, 2000;Lao et al, 2022a andLao et al, 2022b).…”

“…It is difficult to identify the mixing of water masses with the same salinity in the oceans, particularly in the coastal areas (Lao et al, 2022a andLao et al, 2022b). In coastal waters, water masses are mixed from different freshwater masses, and these water masses may have similar or even the same temperature and salinity, thus making it difficult to distinguish their contribution (Bigg & Rohling, 2000;Lao et al, 2022a andLao et al, 2022b). By contrast, d 18 O and dD are properties of the water itself, and they are less influenced by biogeochemical processes (Lian et al, 2016;Jin et al, 2018;Chen et al, 2020b;Lao et al, 2022a).…”

“…For example, the water mass processes are quantitatively identified between the western Pacific Ocean and the South China Sea (SCS) (>3,700 m) by using the dual water isotopes combined with temperature-salinity profiles (Wu et al, 2021). In the coastal oceans, the mixing of different water sources and the intrusion of the high salinity to the coastal waters (Lian et al, 2016;Chen et al, 2020), and their impacts on the groundwater (Tran et al, 2019;Zhang et al, 2022) and coastal ecological environment, such as the distribution of nutrient and primary productivity (Lao et al, 2022a) and the mariculture activities (Lao et al, 2022b), were also identified by the dual water isotopes. Thus, the isotope tool has been successfully used to track the movement and mixing of water masses (Legrande and Schmidt, 2006;Deshpande et al, 2013;Sengupta et al, 2013;Lian et al, 2016;Benetti et al, 2017;Chen et al, 2020b).…”