[Diffusive CO2 Flux Across the Water-air Interface of Reclaimed Shrimp Ponds in the Minjiang River Estuary Based on the TBL Model]

Freshwater aquatic ecosystems are important sources of greenhouse gases, such as CO₂. However, few studies have presented data on the greenhouse gas flux from coastal aquaculture ponds. Diffusion models are important tools for estimating the CO₂ exchange flux across the water-air interface of aquatic ecosystems. Several different parameterized means were selected to estimate the CO₂ gas exchange rate (k_x) and CO₂ diffusive flux across the water-air interface of shrimp ponds in the Minjiang River Estuary. The results indicated that:① the CO₂ gas exchange rate and diffusive flux over the culture period all presented significant temporal variation. This variation showed a dynamic trend:October > September > November > July > August and November > July > August > September > October. ② Wind speed, k_x, CO₂ concentration, pH, DOC concentration, and Chl-a concentration were important factors affecting the temporal variation of CO₂ diffusive flux. ③ There were differences in the estimated value of CO₂ diffusive flux across the water-air interface of the culture ponds in the Minjiang River Estuary among different parameterized approaches (P<0.01). This indicates that the model method has some uncertainties in estimating the CO₂ diffusive flux in culture ponds. Our results suggest that the models RC01 and CW03 are more suitable methods for estimating the CO₂ diffusive flux at the water-air interface of estuarine reclaimed aquaculture ponds in the Minjiang River Estuary, after comprehensive analysis of the water environment and the different estimation results.

[Parallel Factor Analysis of Fluorescence Excitation Emission Matrix Spectroscopy of CDOM from the Mid-culture Period of Shrimp Ponds in a Subtropical Estuary]

Components of chromophoric dissolved organic matter (CDOM) from eight coastal land-based shrimp ponds in the Minjiang, Mulan, and Jiulong rivers of subtropical southeastern China were determined by fluorescence excitation emission matrix spectroscopy combined with parallel factor analysis (EEMs-PARAFAC). Four separate fluorescence components, including two protein-like components (C1, C4) and two humic-like components (C2, C3), were identified as the dominant components of the CDOM in these shrimp ponds. The fluorescence indices (FI, BIX, and HIX) suggest that the CDOM of shrimp ponds shows low humification and is mainly derived from spontaneous sources. The protein-like and humic-like components have similar sources and exhibit a similar geochemical behavior. The salinity is negatively correlated with all CDOM fractions, whereas the DOC concentrations show only a positive correlation with the humic fractions of the CDOM. This study provides a scientific basis for the photochemical properties of CDOM in shrimp ponds.