Spatial Variations of N₂O Fluxes Across the Water‐Air Interface of Mariculture Ponds in a Subtropical Estuary in Southeast China

Abstract

While aquaculture ponds are potentially important sources of atmospheric N 2 O, the magnitude and variability of N 2 O concentrations and fluxes both within and across the ponds remain poorly understood. In this study, we examined the small-scale spatial variations of dissolved N 2 O concentrations in water and N 2 O fluxes across the water-air interface from three mariculture ponds in a subtropical estuary in southeast China. Our results showed that the dissolved concentrations and diffusive fluxes of N 2 O in the shrimp ponds ranged between 2.3-19.2 nM and 16.4-589.7 nmol m −2 hr −1 , respectively, over the culture period. Significant variations of N 2 O concentrations and fluxes were observed within the ponds, with higher values being observed in the aeration area that could be attributed to the high rates of nitrification in the water column, as well as sediment N 2 O production and diffusive flux into the overlying water. Also, N 2 O concentrations and fluxes varied significantly among the three ponds as a result of the difference in N-NO 3 − and N-NH 4 + concentrations in the water column. The large fine-scale spatial variations of N 2 O concentrations and fluxes observed in our aquaculture ponds suggested that management practices such as aeration and bait feeding could largely affect the extent that aquaculture activities have on N 2 O emissions and climate change through their influence on the physicochemical environment (e.g., oxygen and N-NH 4 + concentrations) of the ponds.

Foregone carbon sequestration loss dominates greenhouse gas budget in mariculture associated with coastal wetland conversion

“…Substantial N 2 O uxes were triggered by pond draining. This nding agreed well with previous studies that observed drainage episodes as the critical period for N 2 O emission from aquaculture ponds 21,22,58 . As discussed above, abundant soil NO 3 usually generates a higher ratio of…”

“…As for the N 2 O emission from aquaculture, the IPCC default emission factor and current estimates are also limited by modeling approaches using mathematic reckoning or known as indirect N 2 O data 21 . Large variations in N 2 O emission factors from aquaculture systems have been found due to the large variability in environmental conditions and yield performance of culturing species 21,22 . Previous studies reported that N 2 O production in extensively managed aquaculture ponds was limited by the high dissolved organic C (DOC) concentrations and anaerobic conditions, and the yield-scaled emission factor for N 2 O in these ponds was 7.85-time lower than the IPCC default value 17,23 .…”

Spatial and Seasonal Variability of Hydroxylamine Concentrations in a Human‐Impacted Estuary Off Southeast China

“…Air sampling at 1 m height above the water surface was conducted by means of a 50 mL gastight syringe (Bolige, Shanghai, China). The first gas sample was discarded and the second sample was stored in a 50 mL airbag (Delin, Dalian, China) (P. Yang et al., 2020). In addition, 500 mL water at 20 cm depth was collected with polyethylene bottle and used to measure NO 3 − , NO 2 − , NH 4 + , dissolved organic carbon (DOC), and total suspended particulate (TSP).…”

“…After 24 hr of oxidation, 20 mL water in serum bottle was replaced by same volume high‐purity helium to create headspace. These serum bottles were shaken at 200 rpm for 30 min to keep the balance between water and gas phases (P. Yang et al., 2020). N 2 O concentration in headspace gas was determined by gas chromatograph (GC‐2014, Shimadzu, Japan) coupled with electron capture detector (ECD).…”