The degradation of water quality in lakes and its negative effects on freshwater ecosystems have become a serious problem worldwide. Exploring the dynamics in the associated factors is essential for water pollution management and control. GIS interpolation, principal component analysis (PCA) and multivariate statistical techniques were used to identify the main pollution sources in different areas of Honghu Lake. The results indicate that the spatial distribution of the concentrations of total nitrogen (TN), total phosphate (TP), ammonia nitrogen (NH₄⁺–N), and permanganate index (COD_Mn) have similar characteristics and that their values gradually increased from south to north during the three seasons in Honghu Lake. The major influencing factors of water quality varied across the different areas and seasons. The relatively high concentrations of TN and TP, which might limit the growth of submerged aquatic plants, were mainly caused by anthropogenic factors. Our work suggests that spatial analyses combined with PCA are useful for investigating the factors that influence water quality and submerged aquatic plant biomass in different areas of a lake. These findings provide sound information for the future water quality management of the lake or even the entire lake basin.

Paddy soils developed from various parent materials are widely distributed in the subtropical region in China and have a non-negligible but unclear potential to consume nitrous oxide (N₂O) due to long-term flooding. This study selected three of the most common paddy soils in subtropical China, developing from quaternary red soil (R), lake sediment sand (S), and alluvial soil (C), to study their total N₂O consumption and total nitrogen (N₂) production using N₂-free microcosm experiments. These paddy soils were treated with N₂O addition (N₂O treatment) or helium (He) addition (CK treatment) and incubated under flooding and anoxic conditions. The results showed that three alluvial soils (C1, C2, and C3) consumed over 99.93% of the N₂O accumulated in the soil profile, significantly higher than R and S soils (p < 0.05). And the N₂ production in three C soils was also significantly higher than other soils, accounting for 81.61% of the total N₂O consumption. The main soil factors affecting N₂O consumption in C, S, and R soils were soil clay content (p < 0.05), soil sand content (R² = 0.95, p < 0.001), and soil available potassium (AK) (p < 0.01), respectively. These results indicate flooding paddy soils, no matter the parent materials developed, could consume extremely large amount of N₂O produced in soil profiles.