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Coastal rivers contributed the majority of anthropogenic nitrogen (N) loads to coastal waters, often resulting in eutrophication and hypoxia zones. Accurate N source identification is critical for optimizing coastal river N pollution control strategies. Based on a 2-year seasonal record of dual stable isotopes ( δ 15 N - NO 3 - and δ 18 O - NO 3 - ) and water quality parameters, this study combined the dual stable isotope-based MixSIAR model and the absolute principal component score-multiple linear regression (APCS-MLR) model to elucidate N dynamics and sources in two coastal rivers of Hangzhou Bay. Water quality/trophic level indices indicated light-to-moderate eutrophication status for the studied rivers. Spatio-temporal variability of water quality was associated with seasonal agricultural, aquaculture, and domestic activities, as well as the seasonal precipitation pattern. The APCS-MLR model identified soil + domestic wastewater (69.5%) and aquaculture tailwater (22.2%) as the major nitrogen pollution sources. The dual stable isotope-based MixSIAR model identified soil N, aquaculture tailwater, domestic wastewater, and atmospheric deposition N contributions of 35.3 ±21.1%, 29.7 ±17.2%, 27.9 ±14.5%, and 7.2 ±11.4% to riverine NO 3 - in the Cao'e River (CER) and 34.4 ±21.3%, 29.5 ±17.2%, 27.4 ±14.7%, and 8.7 ±12.8% in the Jiantang River (JTR), respectively. The APCS-MLR model and the dual stable isotope-based MixSIAR model showed consistent results for riverine N source identification. Combining these two methods for riverine N source identifications effectively distinguished the mix-source components from the APCS-MLR method and alleviated the high cost of stable isotope analysis, thereby providing reliable N source apportionment results with low requirements for water quality sampling and isotope analysis costs. This study highlights the importance of soil N management and aquaculture tailwater treatment in coastal river N pollution control. [ABSTRACT FROM AUTHOR]

This study was conducted to assess the compatibility of white shrimp Litopenaeus vannamei and giant freshwater prawn Macrobrachium rosenbergii in the polyculture system. Twelve 0.6 ha intertidal mudflat ponds of shrimp in the region around Hangzhou Bay, China, were divided into four culture systems based on the stocking densities of prawns. The groups were divided into the following: control (CON, no prawn), low stocking density (LSD, 75,000 ha−1), middle stocking density (MSD, 150,000 ha−1) and high stocking density (HSD, 225,000 ha−1) groups. Results showed that the survival (%), final weight, final length and condition factor of reared shrimp exhibited no significant difference among different culture systems. The profits of the polyculture systems significantly increased with prawn stocking density. The mean values of water quality parameters showed no significant difference (p > 0.05) between treatments. Phytoplankton abundance and biomass were significantly reduced in the polyculture groups. Desulforegula (9.39%), Citreicella (4.23%), Gemmobacter (3.66%) and Phycisphaera (2.93%) were the prevailing genera in the CON group. Aeromonas was the most abundant genus in the HSD group. However, most pathogenic bacteria in the pond water were undetected or observed at extremely low levels. The levels of Aeromonas and Pseudomonas sharply increased in the HSD group. These findings suggest that polyculture systems can increase profit without influencing water quality. However, high polyculture at 225,000 ind ha−1 may potentially cause pathogenic bacterial infection. Thus, the recommended model for this polyculture system is shrimp (900,000 ha−1) + prawn (150,000 ha−1). [ABSTRACT FROM AUTHOR]

This study was conducted to explore the feasibility of an integrated rotational farming system with shrimp Limpenaeus vannamei and three vegetable species (i.e., broccoli [ Brassica oleracea ], cole [ B. napus ], and potherb mustard [ B. juncea ]) in the tidal flat ponds of Hangzhou Bay, China. A six-month (November to May) vegetable planting experiment without the addition of fertilizer was conducted followed by a five-month (May to October) shrimp culture experiment. Results show that the concentrations of soil total nitrogen significantly decreased in the three vegetable rotational farming systems by the end of the experiment (P <.05), whereas a significant reduction in soil phosphorus was only observed in the broccoli and cole farming systems (P <.05). The straw fresh weight of broccoli, cole, and potherb mustard were 38.25 ± 1.29, 45.26 ± 3.03, and 30.75 ± 1.98 tons hm−2, respectively. The amount of removed nitrogen and phosphorus for the three vegetable rotational farming systems were 416.16 kg and 130.33 kg, 538.12 kg and 108.63 kg, and 17.70 kg and 19.68 kg per hectare, respectively. The nitrogen and phosphorus content in the pond water demonstrated significant variations (P <.05) in the three rotational systems at the 30th and 60th days of the experiment (P <.05). The phytoplankton species, abundance, and biomass in these rotational farming systems were significantly lower than those in the control group. The shrimp production in the rotational systems was also higher than that in control group. However, no statistical differences were observed among these groups (P >.05). The condition factor was higher in the rotational farming systems than in the monoculture group (P <.05). The shrimp costs in the rotational farming systems were similar to those in the monoculture group, whereas the shrimp returns in rotational farming systems (26,381.8 US$, 27,180.2 US$, and 26,880.6 US$ for broccoli, cole, and potherb mustard, respectively) were higher than those in the monoculture group (24,410.5 US$). The rotational farming systems of vegetables produced economic benefits for broccoli, cole, and potherb mustard (12,351.6 US$, 8699.6 US$, and 7092.7 US$, respectively). As expected, the profits of rotational farming systems were approximately 1.63 to 2.26 times higher than those of shrimp monoculture. The ecological and economic effects of different shrimp and vegetable combinations revealed that the rotational farming of shrimp and vegetables (i.e., broccoli, cole, and potherb mustard) is a feasible and sustainable development model that fits well with the conditions of shrimp ponds in the coastal tidal flats of Hangzhou Bay, China. The findings of this work have broad prospects in promoting the development of shrimp culture and in exploiting and utilizing coastal tidal flats. • Introduced a rotational farming system, with Limpenaeus vannamei and vegetables in the tidal flat pond. • Evaluated the ecological and economic effects of different shrimp-vegetable rotational farming systems. • Shrimp-vegetable rotational farming systems provide additional income from vegetable without reducing shrimp production. [ABSTRACT FROM AUTHOR]