Carbon And Nitrogen Transport In The Tail River And Estuaries Of The Yellow River And Their Effects On Carbon Release

Carbon and nitrogen cycles is the central part of material and energy flows in the riverway and estuary region. In this paper, with multiple voyage continuous sampling observation system, we studied the distribution characteristic, migration and transformation rule before and after flood season, and input flux of different forms of carbon and nitrogen in the Weilv riverway and estuary of the Yellow River. Moreover, we analyzed the effect of terrestrial carbon input on the CO2 emissions in the Yellow River estuary by the technology of stable carbon and nitrogen isotopes. The results are as follows:(1) Mainly influenced by water volume and mixing process between salt and fresh water, in the Weilv riverway of the Yellow River, the concentration of POC in the suspended solids after flood season is higher than pre-flood, while it’s just the opposite in the Yellow River estuary. Furthermore, the distribution characteristic of PN in the suspended solids is that, with respect to pre-flood, the concentration gradient is larger, and the distribution is uneven among the sampling points; however, the distribution is more even after flood season, and a large proportion of PN is organic nitrogen and the concentration of inorganic nitrogen content is very low.(2) The distribution characteristic of DIC in the Weilv riverway and estuary of the Yellow River is similar to that of POC, which is mainly because the increased water volume of the Yellow River in flood season exacerbates the dissolution of upstream carbonate, and the effect of water dilution is the main control factor after flood season. Besides, compared with pre-flood, the distribution characteristic of DOC in the whole study area is lower after flood season, which is mainly influenced by the photosynthesis. Generally, DIC and DOC showed the phenomenon of loss, and the main reason is calcium carbonate deposition and microbial consumption, respectively. Moreover, the main factors affecting the distribution of DIC concentration are temperature, salinity, chlorophyll-a, and suspended solids, whose accumulative contribution rate account for about 90.32 %. Accordingly, for the distribution of DOC, the main influencing factors are temperature, suspended solids, and DIC concentration, with the cumulative contribution rate of 91.69 %.(3) In 2013, the input flux of DIC in the Yellow River estuary was 698.24 tonnes and 1856.21 tonnes per day before and after flood season. Correspondingly, it was 167.09 tonnes and 167.77 tonnes, 61.07 tonnes and 79.47 tonnes, 13 tonnes and 20.81 tonnes for the input flux of DOC, POC, and PN, respectively. Moreover, NO3--N shares the majority of dissolved inorganic nitrogen, whose input flux was 77.21 tonnes and 159.87 tonnes per day before and after flood season.(4) The organic matter δ13C in the suspended solids shows the characteristics of aquatic plant, which mainly comes from the algae in the river water and seawater. In addition, the surface sediments are mainly the deposit of algae and terrestrial plants of the river water and seawater. Its δ13C shows the characteristics of aquatic and C4 plants, which is from algae and emergent plants, and the algae occupies the dominant status. Moreover, the source of TN in the suspended solids is single, while it’s mixed source for the organic matter in the surface sediments. Furthermore, organic nitrogen occupies the majority of TN, and the content of inorganic nitrogen is less; the content of TN in the surface sediments have been affected by human behavior, and may have involved the input of organic chemical fertilizers and pesticides.(5) The p CO2 in the Yellow River estuary would show the phenomenon of loss when the salinity less than 7.5‰, tending to be stable when the salinity is higher than 7.5‰. The main reason is that the settlement of carbonate would occur in the low salinity area, while the effect of seawater dilution is obvious in the high salinity area. The distribution of p CO2 is mainly affected by the temperature, salinity, chlorophyll-a and DIC, whose cumulative contribution rate reaches about 89.37%. Moreover, in the Yellow River estuary, it’s CO2 source in the spring and winter, while for the autumn and winter, it’s CO2 sink. Besides, the exchange of water-gas interface flux of CO2 was 0.34, 0.17, 0.3 and 0.43 per day in the spring, summer, autumn, and winter, respectively. The annual total amount of CO2 emissions into the atmosphere in the Yellow River estuary is about 10.95 billion mol.