Abstract
Isotope measurements were performed on dissolved nitrate (NO3−) and ammonium (NH4+) in the coastal waters of the northeastern Beibu Gulf, China, to investigate the seasonal nitrate sources and their biogeochemical processes, which are due to the rapid development of local industrialisation and urbanisation. The high N/P ratio observed in the coastal bay during both fall and spring suggests that P is a limiting nutrient, which in turn indicates that increasing P causes conditions favourable for algal blooms. Higher nutrient concentrations and δ15N-NO3− and δ15N-NH4+ values were found in the nearshore area in the fall, suggesting that nutrients originated mainly from land-based pollution. A Bayesian isotope mixing model was used to calculate the contribution of potential NO3− sources and the results showed that in the nearshore area, NO3− originated mainly from manure and sewage (58%). In the spring, however, in addition to the impact of urban sewage effluents, the exchange of sediment and water was another important factor causing higher nutrient concentrations and positive NO3− isotopes in the nearshore area. There were lower concentrations of nutrients and an increase in δ15N-NO3− and δ15N-NH4+ values in the offshore area in the fall, and the NO3− loss in the surface water was mainly caused by the process of assimilation. However, the exchange of sediment and water was the dominant factor causing higher nutrient concentrations (except for NO3−) and positive dual nitrate isotopes but lower NO3− concentration in the offshore area during the spring. Overall, isotope analysis of NO3− and NH4+ helps to illustrate the major sources of the former and their biological transformation in the northeastern Beibu Gulf.
Highlights
To provide a comprehensive overview of nitrate sources and cycles in the northeastern Beibu Gulf, we investigated the concentrations of the nutrients NO3 −, NO2 −, NH4 +, and
The Beibu Gulf is a semi-enclosed gulf with an area of approximately 130 × 103 km2 and is located in the tropical and sub-tropical areas of southern China. It is influenced by the East Asian monsoon, which in turn is influenced by cold air from mainland China during the winter-spring season, with wind rising from the tropical ocean during the
A high N/P ratio was recorded in the coastal bay during both fall and spring, suggesting that P was a limiting nutrient and indicating that increasing P would be favourable for algal blooms
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. To provide a comprehensive overview of nitrate sources and cycles in the northeastern Beibu Gulf, we investigated the concentrations of the nutrients NO3 − , NO2 − , NH4 + , and PO4 3− and the isotopes δ15 N-NO3 − , δ18 O-NO3 − , and δ15 N-NH4 + in the seawater during different seasons (fall and spring). These data enable us to qualitatively characterise the main N sources in the coastal area and understand the factors controlling the distribution of the nutrients studied
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
