Ligang Xu

Nitrate-Nitrogen Leaching and Modeling in Intensive Agriculture Farmland in China

Protecting water resources from nitrate-nitrogen (NO3-N) contamination is an important public health concern and a major national environmental issue in China. Loss of NO3-N in soils due to leaching is not only one of the most important problems in agriculture farming, but is also the main factor causing nitrogen pollution in aquatic environments. Three typical intensive agriculture farmlands in Jiangyin City in China are selected as a case study for NO3-N leaching and modeling in the soil profile. In this study, the transport and fate of NO3-N within the soil profile and nitrate leaching to drains were analyzed by comparing field data with the simulation results of the LEACHM model. Comparisons between measured and simulated data indicated that the NO3-N concentrations in the soil and nitrate leaching to drains are controlled by the fertilizer practice, the initial conditions and the rainfall depth and distribution. Moreover, the study reveals that the LEACHM model gives a fair description of the NO3-N dynamics in the soil and subsurface drainage at the field scale. It can also be concluded that the model after calibration is a useful tool to optimize as a function of the combination “climate-crop-soil-bottom boundary condition” the nitrogen application strategy resulting for the environment in an acceptable level of nitrate leaching. The findings in this paper help to demonstrate the distribution and migration of nitrogen in intensive agriculture farmlands, as well as to explore the mechanism of groundwater contamination resulting from agricultural activities.

Analysis of Water Balance in Poyang Lake Basin and Subsequent Response to Climate Change

ABSTRACT Xu, L.G.; Zhu, M.L.; He, B.; Wang, X.L.; Zhang Q.; Jiang J.H., and Razahindrabe B.H.N., 2014. Analysis of water balance in Poyang Lake basin and subsequent response to climate change. The runoff in Poyang Lake Basin has a reversal decreasing phenomenon in 1997. Moreover, recent drought-prone pattern and low-flow events have been a serious threat to the water resource and water security in Poyang Lake in China. The water resource change is affected by regional climate change, human activities and water conservancy projects within the basin. The Poyang Lake and its watershed are selected as study sites to investigate the influence of key driving factors such as precipitation, temperature and water usage. The runoff and water level change of Poyang Lake were explored and analyzed based on the System Dynamic (SD) method. Monthly flow and water depth in lake was simulated and compared with observed values for both calibration periods from 1978 to 1997 and validation periods from1998 to 2007.The results demonstrated that SD method can acquire an ideal performance on basin runoff yielding and water resource exchanging between rivers and lake. Furthermore, 10% decrement and increment of precipitation, temperature and water usage scenario for climate change analysis showed that the proportion of impact from water use, temperature and precipitation is about 1:3:10. The changing trends of water balance in the Poyang Lake Basin are basically consistent with the effect of temperature and precipitation, but due to the function of outflow and smaller impact from the inflow during July to September, the changing trends of water level are different before and after July. Findings of this paper provide an important scientific basis for the development of integrated watershed management measures for water security in Poyang Lake.

Nitrate attenuation in low-permeability sediments based on isotopic and microbial analyses

This study investigated nitrate attenuation in low-permeability sediments (LPS) in a multi-layer aquifer by integrating hydrochemical, isotopic and microbiological molecular techniques in a field site. In the meantime, the overlying high-permeability sediment (HPS) was also examined on the nitrate attenuation for the sake of comparison. Additionally, laboratory flow-through experiments were conducted to assess the overall nitrate reduction rate in the two types of sediment. The δ15N-NO3- and δ34S-SO42- values were more enriched by approximately 37‰ and 15‰ in the LPS than the overlying HPS associated with substantial reductions of the NO3- and SO42- concentration, indicating the occurrence of strong bio-reductions in nitrate and sulfate. The microbial community diversity analyses showed a higher diversity of the denitrifiers encoding nirS- (Shannon Index SI=6.3) and nrf-type gene (SI=2.7), and the sulfate reduction bacteria (SRB) encoding the dsr gene (SI=6.4) in the LPS than in the HPS. The bacterial community structure was influenced by the groundwater hydrochemistry and the redox conditions. Due to the presence of anoxic groundwater with low levels of nutrients, the LPS featured higher abundances of nitrate reducers belonging to Alphaproteobacteria and SRB belonging to the strictly anaerobic class Clostridia relative to the HPS. Notably, chemolithotrophs were abundant in the LPS and likely coupled the reduction of nitrate with the oxidation of iron. Furthermore, the LPS was demonstrated to attenuate nitrate at a rate two times of the HPS in flow-through experiments, and denitrification accounted for approximately 93% of the nitrate reduction. The high nitrate reduction rate of the LPS was likely attributable to its high functional genes diversity. This study confirmed the occurrence of strong nitrate attenuation in the LPS. The LPS was found to play a significant role in protecting aquifers from anthropogenic contamination.

Effects of Prescribed Fire on Plant Traits and Community Characteristics of Triarrhena Lutarioriparia in Poyang Lake, China

As an important wetland with international significance in biodiversity conservation, Poyang Lake is under severe pressure from increasing human activities, such as prescribed fire. In this study, a fire-prone plant community (Triarrhena lutarioriparia L. Liou) was selected in Poyang lake, and a 5-year study on annual prescribed fire and corresponding monitoring were conducted in this representative plant community. Results showed that sprout density, plant height and biomass of burn samples were significantly higher than those of the control. However, burn samples presented significantly lower values of species richness and community biodiversity in the later period. Furthermore, periodical fire significantly promoted the availability of nitrogen and phosphorous in surface soil, which were closely and positively related to height, dominance and biomass of T. lutarioriparia.. Considering the positive influences on the plant traits and species composition, prescribed fire could potentially be used as an effective means to maintain the ecological health of Poyang Lake.

Relationship Between Vegetation Community Distribution Patterns and Environmental Factors in Typical Wetlands of Poyang Lake, China

Poyang lake is the largest freshwater lake in China, possessing global ecological functions. Impact of soil characteristics on vegetation distribution is potentially important but is poorly understood in this typical vast water-passing lake wetland. To explore the relationships between soil properties and vegetation distribution, soil moisture, soil nutrients, species construction, diversity and biomass were measured monthly in two dominant vegetation communities, namely, the Artemisia selengensis community and the Carex cinerascens community. Canonical correspondence analysis (CCA) and spearmen correlation were performed to evaluate the relationships between vegetation characteristics and edaphic variables. Results showed great heterogeneity in the ecological characteristics of plants. There are positive relationships between soil nutrients and ecological characteristics of plants, especially the biomass and the maximum height of the dominant species. Cynodon dactylon and Artemisia selengensis were mainly distributed in the upland with lower nutrient concentration and moisture content, whereas Cardamine lyrate, Triarrhena Lutarioriparia and Carex cinerascens were mainly found near the lake shore where the moisture and nutrients accumulated, demonstrating a legible zonal distribution along the edaphic gradient. The findings have provided an extension to the existing literatures, improving the understanding of the potentially crucial edaphic effects on vegetation in Poyang lake wetlands.

Removal of pollutants during storm and non-storm events by two wetlands

AbstractThis research investigated the pollutant removal efficiency by two constructed wetlands located on the north shore of the Fuxian Lake, Yunnan Province, China. We conducted continuous monitoring for a storm to examine residence time variations in pollutants (nitrogen and phosphorus) under local hydrologic conditions. During storm events, water samples with an interval of a few hours from the beginning of the rain at the inlet and outlet of the wetland were collected and analyzed for nitrogen (total nitrogen, ammonium, nitrate, and nitrite) and phosphorus (total phosphorus (TP)). The results have implications for stormwater management. While concentrations of nitrogen species are variable, they are not strongly related to flow conditions, so treatment systems must be designed to cope with stochastic inflow concentrations at all times. Principal components analysis of water quality parameters using data collected during non-storm periods at the Yaonigou wetland (Phase I) and the Yaonigou wetland (Pha...

Comparison of semi-natural and constructed wetlands for agricultural wastewater treatment

AbstractAn experiment was carried out to assess the effectiveness of two different wetland systems in the treatment of agricultural wastewater. East River wetland is a semi-natural riparian wetland system, with three functional units, grit chamber, organic oxidation pond, and surface flow wetland unit. The functional units were planted with umbrella plant (Cyperus alternifolius L.), canna（Canna indica L.), calamus (Acrorus calamus L.), etc. Yaonigou wetland is a kind of constructed wetland, with different wetland plants. The wetland removed the significant amount and the degree of total suspended solids and biochemical oxygen demand (BOD), respectively, from agricultural wastewater. The results demonstrated that the effluent concentration of ammonia, nitrite, nitrate, and total nitrogen of East River riparian wetland increased in spring and summer, decreased in autumn and winter. On average removal rates for nitrogen compounds ranged from 70.45 to 97.59% for ammonia, 7.87 to 96.25% for nitrite, and 12.5 t...

Ecological remediation of waste resources by comprehensive afforestation utilization in mudflat ecosystem

AbstractThe ecological rehabilitation engineering out of the coastal mudflat ecosystem was accomplished principally by virescence. However, the lack of proper soil resources for reformation of the coastal mudflat was the primary difficulty. Artificial soil mounds composed of three solid wastes (dredged sediments, caustic sludge, and coal ash) were constructed and afforested. The waste properties and the effects of the unnatural soil on tree growth, desalination, pH value, biomass, microbial community, and toxic metals were investigated in the next couple of years. After four growing seasons, salt content was reduced to the threshold for salt-sensitive plants and the pH value remained stable (below 8.30). The total biomass of the tree–shrub–herb community, which was composed of Fraxinus pennsylvanica Marsh, Populus tomentosa Carr, Robinia pseudoacacia Linn, Loniccra macckii. Maxim, Tamarix chinensis Lour, and Medicago sativa L, was above 31.92 t hm−2. The survival, tree height, diameter, and biomass of the...