Soil respiration (Rs) is a major source of carbon emission in terrestrial ecosystems. Despite the fact that the influence of land use practice on Rs has been widely studied, the patterns and drivers ...on Rs of Citrus reticulata cultivation, a worldwide land use practice are unclear. In this current study, we investigated the influence of long-term cultivation of Citrus reticulata (CO) and of CO intercropped with soybean (CB) on soil nutrients, water availability, and Rs in southern China. Results indicated that after 21 years of cultivation, CO and CB significantly increased total soil carbon (TC), total soil nitrogen (TN), and soil organic matter (OM) at 0-20 cm and 20-40 cm, both at upslope and downslope compared with bare soil (CK). However, soil moisture (SM), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) decreased under CB. In addition, no significant variation was found in soil pH between CK, CO, and CB. Across incubation time (56 days), Rs decreased exponentially with incubation time and CB showed the highest Rs rate irrespective of soil depth or topography. Linear regression further showed TC and TN as the two major factors influencing Rs upslope, while DOC was the dominant factor in regulating Rs downslope. These findings demonstrated that long-term cultivation of citrus significantly changed soil nutrients, water availability, and Rs rate.
The distributions and fluxes of the climatically-active gases dimethylsulfide (DMS), isoprene, methyl bromide (CH3Br), and methyl iodide (CH3I) were measured in the surface waters of the central ...basin (CB) of the South China Sea (SCS) in July 2014; the possible production pathways of the gases are discussed to evaluate their biological sources and relative contribution to the global climate. The mean concentrations of DMS, isoprene, CH3Br, and CH3I were 1.76 ± 1.35 nmol L−1, 6.92 ± 2.68 pmol L−1, 0.82 ± 0.23 pmol L−1, and 2.72 ± 0.72 pmol L−1, respectively. The vertical profiles of the trace gases were similar to that of chlorophyll-a (Chl-a). The maxima appeared in the euphotic zone and approximately agreed with the Chl-a maximum layer, whereas the concentrations were below the detection limits beneath the euphotic zone. A significant positive correlation (R = 0.590, p < 0.005, n = 19) was found between isoprene and Chl-a while no correlations occurred between the other gases and Chl-a. The seawater temperature was also an important factor affecting the isoprene and CH3I distributions in the study area. The sea-to-air fluxes of DMS, isoprene, and CH3I were estimated at 4.36 ± 3.94 μmol m−2d−1, 12.38 ± 6.80 nmol m−2d−1, and 8.70 ± 4.79 nmol m−2d−1, respectively, suggesting that the CB of the SCS was a substantial source of these trace gases to the atmosphere. In contrast, the study area was a net sink of CH3Br and its air-to-sea flux was estimated at 1.97 ± 1.44 nmol m−2d−1.
•Isoprene, CH3Br and CH3I were determined for the first time in SCS.•Nutrients and phytoplankton impacted greatly on the biogenic gases concentrations.•The SCS was an important source for atmospheric DMS, isoprene and CH3I, and a sink for CH3Br during summer.
We use the U.S. Navy's Master Oceanographic Observation Data Set (MOODS) for the Yellow Sea/East China Sea (YES) to investigate the climatological water mass features and the seasonal and ...non-seasonal variabilities of the thermohaline structure, and use the Comprehensive Ocean-Atmosphere Data Set (COADS) from 1945 to 1989 to investigate the linkage between the fluxes (momentum, heat, and moisture) across the air-ocean interface and the formation of the water mass features. After examining the major current systems and considering the local bathymetry and water mass properties, we divide YES into five regions: East China Sea (ECS) shelf, Yellow Sea (YS) Basin, Cheju bifurcation (CB) zone,Taiwan Warm Current (TWC) region, Kuroshio Current (KC) region. The long term mean surface heat balance corresponds to a heat loss of 30 W m^-2 in the ESC and CB regions, a heat loss of 65 W m^-2 in the KC and TWC regions, and a heat gain of 15 W m^-2 in the YS region. The surface freshwater balance is defined by precipitation minus evaporation. The annual water loss from the surface for the five subarea sranges from 1.8 to 4 cm month^-1. The fresh water loss from the surface should be compensated for from the river run-off. The entire water column of the shelf region (ECS, YS, and CB) undergoes an evident seasonal thermal cycle with maximum values of temperature during summer and maximum mixed layer depths during winter. However, only the surface waters of the TWC and KC regions exhibit a seasonal thermal cycle. We also found two different relations between surface salinity and the Yangtze River run-off,namely, out-of-phase in the East China Sea shelf and in-phase in the Yellow Sea. This may confirm an earlier study that the summer fresh water discharge from the Yangtze River forms a relatively shallow, low salinity plume-like structure extending offshore on average towards the northeast.
Eleven chlorobenzenes (CBs) in surface water and sediments of Tonghui River, a main urban drainage river of Beijing in China, were determined in October 2003, January 2004, and April 2006. CBs were ...widely detected and the summation operatorCB concentrations in water ranged from 89.9 to 6638.0 ng/L, with average values of 1902.8 ng/L in 2003, 2084.0 ng/L in 2004, and 1281.2 ng/L in 2006, respectively. The summation operatorCB concentrations in surficial sediments varied from 18.2 to 1827.7 ng/g dry weight (dw), with average values of 897.4 ng/g dw in 2003, 653.4 ng/g dw in 2004, and 562.6 ng/g dw in 2006, respectively. Nonparametric statistical analysis (Mann-Whitney U test) showed that there were no statistically significant changes in summation operatorCB concentrations in either surface water or sediments over the period 2003-2006. The distribution pattern of CBs in the Tonghui River indicates that further effort is warranted in reducing local sources of contaminants. Additionally, the summation operatorCB levels in sediment samples were found to be dependent on total organic carbon contents.
Soil respiration (Rs) is a major source of carbon emission in terrestrial ecosystems. Despite the fact that the influence of land use practice on Rs has been widely studied, the patterns and drivers ...on Rs of Citrus reticulata cultivation, a worldwide land use practice are unclear. In this current study, we investigated the influence of long-term cultivation of Citrus reticulata (CO) and of CO intercropped with soybean (CB) on soil nutrients, water availability, and Rs in southern China. Results indicated that after 21 years of cultivation, CO and CB significantly increased total soil carbon (TC), total soil nitrogen (TN), and soil organic matter (OM) at 0-20 cm and 20-40 cm, both at upslope and downslope compared with bare soil (CK). However, soil moisture (SM), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) decreased under CB. In addition, no significant variation was found in soil pH between CK, CO, and CB. Across incubation time (56 days), Rs decreased exponentially with incubation time and CB showed the highest Rs rate irrespective of soil depth or topography. Linear regression further showed TC and TN as the two major factors influencing Rs upslope, while DOC was the dominant factor in regulating Rs downslope. These findings demonstrated that long-term cultivation of citrus significantly changed soil nutrients, water availability, and Rs rate.
This paper discusses natural attenuation of chlorobenzene (CB) elimination in a deep confined aquifer in a certain test site in China during a groundwater artificial recharge process. Pilot-scale ...experiments were conducted in laboratory, including adsorption and biodegradation experiments. The results from the adsorption experiments indicated that the adsorption rate increased within the temperature range 0–20 °C. Processes were fitted to the pseudo-first-order and pseudo-second-order kinetic equations, Freundlich and Langmuir models. Maximal amounts of adsorption were 20.747, 21.505 and 23.364 µg/g at 0, 10 and 20 °C, respectively. The adsorption of CB was an endothermic process. The results from the biodegradation experiments indicated that the processes were well fitted by the Monod and first-order decay kinetics equations at different temperatures. It showed that the Monod
μ
max
changed from 0.0314 to 0.0387 h
−1
, and the half-life (
t
1/2
) decreased from 3.02 to 1.46 d with an increase in temperature from 0 to 20 °C. The influence of temperature on the biodegradation rate was expressed by the Arrhenius equation. This study provides information on the mechanisms of natural attenuation of CB in the subsurface environment, whilst also providing the necessary technical information for the security of artificial recharge implementation.
S2; Serious soil erosion is one of the major issues threatening sustainable land use in semiarid areas, especially in the Loess Plateau of China. Understanding the effects of land use on soil and ...water loss is important for sustainable land use strategy. Two sub-catchments: catchment A (CA) and catchment B (CB) with distinct land uses were selected to measure soil moisture, runoff and soil nutrient loss in Da Nangou catchment of the Loess Plateau of China. The effects of land use patterns on runoff and nutrient losses were analyzed based on soil moisture pattern by kriging and soil nutrients using multiple regression model. The results indicated that there were significant differences in runoff yield and soil nutrient losses between the two sub-catchments. With similar land uses, the CA produced an average sediment yield of 49 kg ha-1 and 22.27 kg ha-1 during two storm events.Meanwhile, there was almost no runoff in the CB with dissimilar land uses during the same events.Buffer zones should be established to
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