Yongtao Zhang

Spatial distribution and environmental determinants of denitrification enzyme activity in reed-dominated raised fields

Denitrification is an important process of nitrogen removal in lake ecosystems. However, the importance of denitrification across the entire soil-depth gradients including subsurface layers remains poorly understood. This study aims to determine the spatial pattern of soil denitrification enzyme activity (DEA) and its environmental determinants across the entire soil depth gradients in the raised fields in Baiyang Lake, North China. In two different zones of the raised fields (i.e., water boundary vs. main body of the raised fields), the soil samples from −1.0 m to 1.1 m depth were collected, and the DEA and following environmental determinants were quantified: soil moisture, pH, total nitrogen (TN), ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), total organic carbon (TOC), and rhizome biomass of Phragmites australis. The results showed that the soil DEA and environmental factors had a striking zonal distribution across the entire soil depth gradients. The soil DEA reached two peak values in the upper and middle soil layers, indicating that denitrification are important in both topsoil and subsurface of the raised fields. The correlation analysis showed that the DEA is negatively correlated with the soil depth (p < 0.05). However, this phenomenon did not occur in the distance to the water edge, except in the upper layers (from 0.2 m to 0.7 m) of the boundary zone of the raised fields. In the main body of the raised fields, the DEA level remained high; however, it showed no significant relationship with the distance to the water edge. The linear regression analysis showed significant positive correlation of the DEA with the soil TN, NO3−-N, NH4+-N, and TOC; whereas it showed negative correlation with soil pH. No significant correlations with soil moisture and temperature were observed. A positive correlation was also found between the DEA and rhizome biomass of P. australis.

Decomposition of Phragmites australis rhizomes in artificial land-water transitional zones (ALWTZs) and management implications

Rhizomes are essential organs for growth and expansion of Phragmites australis. They function as an important source of organic matter and as a nutrient source, especially in the artificial land-water transitional zones (ALWTZs) of shallow lakes. In this study, decomposition experiments on 1- to 6-year-old P. australis rhizomes were conducted in the ALWTZ of Lake Baiyangdian to evaluate the contribution of the rhizomes to organic matter accumulation and nutrient release. Mass loss and changes in nutrient content were measured after 3, 7, 15, 30, 60, 90, 120, and 180 days. The decomposition process was modeled with a composite exponential model. The Pearson correlation analysis was used to analyze the relationships between mass loss and litter quality factors. A multiple stepwise regression model was utilized to determine the dominant factors that affect mass loss. Results showed that the decomposition rates in water were significantly higher than those in soil for 1- to 6-year-old rhizomes. However, the sequence of decomposition rates was identical in both water and soil. Significant relationships between mass loss and litter quality factors were observed at a later stage, and P-related factors proved to have a more significant impact than N-related factors on mass loss. According to multiple stepwise models, the C/P ratio was found to be the dominant factor affecting the mass loss in water, and the C/N and C/P ratios were the main factors affecting the mass loss in soil. The combined effects of harvesting, ditch broadening, and control of water depth should be considered for lake administrators.

Profile Distribution Characteristics of Total Nitrogen and Soil Organic Matter in Different Types of Land Use in Baiyangdian Lake

Baiyangdian Lake is one of the biggest freshwater wetland in North China. However, in recent years, Baiyangdian Lake was disturbed and utilized intensively, resulting in its land-use types changed greatly, which might change the characteristics of the nutrient element distribution. So profile distribution characteristics of soil organic matter (SOM) and total nitrogen (TN) were measured in four different land-use types in Baiyangdian Lake. Profile maps were constructed to describe the spatial distribution of SOM and TN. Results showed that spatial distributions of both SOM and TN were very similar in soil profiles(0-100cm) of the soils of woodland, farmland, and grassland, decreasing gradually with depth, while in the reed-bed soils, the spatial distribution characteristics in soil profiles was the opposite, increasing gradually with depth. Correlation analysis showed that the distribution of SOM and TN were influenced by pH values more strongly than influenced by TP contents.