Phytoplankton biomass dynamics with diffuse terrestrial nutrients pollution discharge into bay

Diffuse terrestrial pollution in bay area has important ecological impacts on coastal ecosystems. This study investigated spatiotemporal changes in N, P, and chlorophyll a (Chla) in the Jiaozhou Bay (JZB) and phytoplankton biomass dynamics under terrestrial nutrients loading. The results from SWAT (Soil and Water Assessment Tool) model demonstrated that the annual average total N (TN) and total P (TP) loading from main rivers were 3626.3 t and 335.6 t, respectively, and were affected by land use type, precipitation, and temperature. Chla value interpreted by remote sensing showed a decrease from nearshore to the far shore. Changes in Chla concentration were usually "dual-cycle" in February and September, but explosive growth of Enteromorpha can cause multiple peaks. TN concentration in the bay was more susceptible to the impact of terrestrial input than TP. Phytoplankton biomass had a stronger correlation with P than with N in JZB. Enteromorpha contributing 4.05% of the phytoplankton biomass played a major role in phytoplankton biomass variability and responded most to nutrients loadings reduction. Under setting 5 m filter strip scenario, the Enteromorpha biomass removal efficiency could reach 35.25%. Furthermore, the findings of this study provide insights for sea-land integration and pollution prevention and control in urbanised bays.

Sources and spatiotemporal variations of nitrogen and phosphorus in Liaodong Bay, China

Excessive discharge of N and P pollutants results in deterioration of marine environment quality and reduction of sustainability and safety of marine ecology. Spatiotemporal variations characteristics and sources of N and P pollutants were determined based on the long-term monitoring data in Liaodong Bay. Results indicated that an evident spatiotemporal variation was investigated for nutrients. The highest concentrations of NH₃-N, NO₂-N, NO₃-N and PO₄-P were in spring (25.32 μg/L), summer (20.67 μg/L) and autumn (222.07 μg/L, 11.08 μg/L), respectively. The hot-spots of pollutants were mainly concentrated in estuarine and aquaculture areas. The hot spot of PO₄-P gradually extended to the middle of Liaodong Bay in autumn. In addition, pollution sources in each marine functional zone were different, the main pollution source was aquaculture wastewater, river input, domestic sewage. This study provided reasonable suggestions for effectively reducing N and P pollution in Liaodong Bay, and elsewhere.

Ecological risks posed by ammonia nitrogen (AN) and un-ionized ammonia (NH3) in seven major river systems of China

Previous studies showed that continuous exposure to ammonia nitrogen (AN) contributed to regional losses of benthic invertebrate diversity in China. Yet, the overall ecological risk of AN to aquatic organisms in major riverine systems of China has not been appropriately studied. Our research then investigated temporal (seasonally/yearly) and spatial distributions of AN and un-ionized ammonia (NH₃) in major Chinese river basins using historic data generated between 2007 and 2014, and developed risk assessment criteria. Our results showed that the highest average AN concentrations occurred during winter (0.82-2.76 mg/L) and the lowest during summer (0.36-0.78 mg/L). NH₃ exhibited the opposite trend with the highest average concentrations mostly observed during spring (15.13-92.84 μg/L) and the lowest concentrations mainly during winter (10.53-45.43 μg/L). Both AN and NH₃ concentrations steadily increased and reached maximum levels in 2008 (AN: 1.22 mg/L and NH₃: 50.65 μg/L), and then decreased. Temporal trends showed that the Yellow, Hai, and Huai river basins had the highest AN and NH₃ concentrations. Subsequently, conventional (hazard quotients) and probabilistic (joint probability curves) methods were applied to assess the hazards and risks posed by AN and NH₃. The results showed that the probability of exceeding the acute toxicity threshold for 5% of species (exposed to AN or NH₃) was less than 13.3% and gradually decreased over time. To protect aquatic organisms, an acute criterion of 51.4 μg NH₃/L and a chronic criterion of 1.14 mg AN/L at pH = 7.5, 20 °C were developed and are recommended for future risk assessment studies.