Isotopic evidence for the shift of nitrate sources and active biological transformation on the western coast of Guangdong Province, South China

Assessing Seasonal Nitrate Contamination by Nitrate Dual Isotopes in a Monsoon-Controlled Bay with Intensive Human Activities in South China

“…where an average of λ jk and standard deviation of τ jk ; and ε jk represents the residual error of the additional unquantified variation between individual samples, which is normally distributed with an average of 0 and standard deviation of σ j . This model was successfully used in previous studies [4,11,17,24].…”

“…During the winter, the high Chl a levels were detected from Z6-Z20 (in the mid-bay and the bay mouth), and, while comparing the lower nutrient concentration in those areas, we considered that the low nutrient concentration may be due to the consumption by the phytoplankton. Along with this phytoplankton proliferation, a pronounced consumption of NH [4,5,31,35]. Irrigation, biological perturbation, and other physical perturbation can significantly occur in surface sediments, particularly during the winter monsoon period when wind-induced mixing and tidal pumping are strong [5,35].…”

“…Thus, the highest NO 3 − concentration in winter may have been influenced by local activities. However, NF, which was mostly in its reduced form, such as urea (71%), NH 4 HCO 3 , and NH 3 Cl (27%), is heavily applied in the catchment agriculture of Guangdong Province [4,5,31] and would be transported to the bay by river discharge and direct discharge from coastal mariculture ponds and wetlands with the heavy rainfall during the wet season. In addition, the heavy rainfall and river discharge could dilute the NO 3 − from manure, and thus, the NO 3 − from manure in winter was found to be significantly higher than that found in summer.…”

“…Eutrophication in coastal aquatic ecosystems has prompted wide public concern owing to significantly increased nutrient inputs to coastal waters [1][2][3]. N loads to the coastal environment have been increasing as a result of intensive industrial activity, agricultural activity, and rapid urbanization in coastal areas [4][5][6][7]. Heavy nitrate (NO 3 − ) pollution has risen above acceptable levels in many areas, which greatly alters the N cycle in aquatic ecosystems, thereby endangering coastal ecosystems and biogeochemical cycles [8][9][10].…”

“…Zhanjiang Bay is a closed bay with intensive human activities in South China. Recently, high loads of inorganic N and phosphate (PO 4 3− ) were found in the seawater of Zhanjiang Bay, owing to the rapid economic growth and urban development in the surrounding area [18]. Clear spatial and seasonal variations in the degree of eutrophication were previously reported in Zhanjiang Bay [19].…”