ALBERT

Beschreibung: Shanghai city has been suffering land subsidence caused by overly exploitation of ground water since 1921, which is a serious problem for this coastal city with altitude of 2.2–4.8 m above mean sea level. The largest cumulative land subsidence amounted to 2.6 m in the downtown area. Measures to decrease the ground water exploitation, change the pumping aquifers, and increase aquifer artificial recharge have been used to mitigate land subsidence since 1961. It is necessary to develop a proper numerical model to simulate and predict land subsidence. In this study, a decoupled three-dimensional (3-D) finite element land subsidence model including a 3-D ground water flow model and a 3-D geo-mechanical model was developed to simulate the 3-D deformation of the aquifer systems in the center area of Shanghai. The area of downtown Shanghai is 660 km2, with 10 million inhabitants, dense high buildings, and 11 metro lines. The simulation spans the period from 1979 to 1995. Two different assumptions have been tested on the side boundary, i.e., precluding the three components of the displacement, or assuming a free-displacement condition. The distribution of calculated land subsidence and horizontal displacements in different aquifers was analyzed. The computed vertical displacement fitted well with the available observations. It has been verified that the two different assumptions on the lateral boundaries in the geo-mechanical model caused different results just limited on nodes close to boundary. The developed 3-D land subsidence model is reasonable and can be used to simulate and predict 3-D movement of aquifer systems in the center area of Shanghai, which could provide scientific support to local government in controlling land subsidence and differential movements of the land surface.

Beschreibung: The aim of this study was to explore the effects of grazing on the formation of the spatial pattern of elm growth in a sparse woodland steppe. We used a point pattern method to analyze the elm trees within different diameter classes in both grazed and fenced plots, which were established in Horqin Sandy Land, northeastern, China. The results showed that, in the grazed plot, the distances where transformation between random and aggregated patterns occurred in class 1 (10 cm ≤ DBH ≤ 15 cm) and class 2 (15 cm ≤ DBH ≤ 20 cm) were 2.27 and 2.37 m, respectively. Meanwhile, in the fenced plot, the distances between random and aggregated patterns that occurred in class 1, class 2 and class 3 (DBH 〉 20 cm) were 3.13, 3.13 and 7.85 m, respectively. In the fenced plot, in distances larger than 67.72 m there were a negative association between class 1 and class 2, which was also the case between class 2 and class 3 and between class 1 and class 3 for distances greater than 104.09 and 128.54 m, respectively. Meanwhile, negative associations occurred only with distances larger than 29.38 m in the grazed plot. These findings suggest that grazing reduced the competition intensity between elm trees; and therefore, grazing management could be an effective strategy used to regulate the elm population in the degraded sandy land of Northern China.

Beschreibung: Heavy regional particulate matter (PM) pollution in China has resulted in an important and urgent need for joint control actions among cities. It's advisable to improve the understanding of regional background concentration of PM for the development of efficient and effective joint control policies. With the increase of vertical height the influence of source emission on local air quality is weakening, but the characteristics of regional pollution gradually become obvious. A method to estimate regional background PM concentration is proposed in this paper, based on the vertical variation periodic characteristics of the atmospheric boundary layer structure and particle mass concentration, as well as the vertical distribution of particle size, chemical composition and pollution source apportionment. According to the method, the averaged regional background PM2.5 concentration, being extracted from the original time series in Tianjin, was 40.0 ± 20.2, 63.6 ± 16.9 and 53.2 ± 11.1 μg m−3, respectively, in July, August and September.

Beschreibung: Tea fields emit large amounts of nitrous oxide (N2O) to the atmosphere. Obtaining accurate estimations of N2O emissions from tea-planted soils is challenging due to strong spatial variability. We examined the spatial variability in N2O emissions from a red-soil tea field in Hunan Province, China, on 22 April 2012 (in a wet season) using 147 static mini chambers approximately regular gridded in a 4.0 ha tea field. The N2O fluxes for a 30 min snapshot (10:00–10:30 a.m.) ranged from −1.73 to 1659.11 g N ha−1 d−1 and were positively skewed with an average flux of 102.24 g N ha−1 d−1. The N2O flux data were transformed to a normal distribution by using a logit function. The geostatistical analyses of our data indicated that the logit-transformed N2O fluxes (FLUX30t) exhibited strong spatial autocorrelation, which was characterized by an exponential semivariogram model with an effective range of 25.2 m. As observed in the wet season, the logit-transformed soil ammonium-N (NH4Nt), soil nitrate-N (NO3Nt), soil organic carbon (SOCt) and total soil nitrogen (TSNt) were all found to be significantly correlated with FLUX30t (r = 0.57–0.71, p 〈 0.001). Three spatial interpolation methods (ordinary kriging, regression kriging and cokriging) were applied to estimate the spatial distribution of N2O emissions over the study area. Cokriging with NH4Nt and NO3Nt as covariables (r = 0.74 and RMSE = 1.18) outperformed ordinary kriging (r = 0.18 and RMSE = 1.74), regression kriging with the sample position as a predictor (r = 0.49 and RMSE = 1.55) and cokriging with SOCt as a covariable (r = 0.58 and RMSE = 1.44). The predictions of the three kriging interpolation methods for the total N2O emissions of 4.0 ha tea field ranged from 148.2 to 208.1 g N d−1, based on the 30 min snapshots obtained during the wet season. Our findings suggested that to accurately estimate the total N2O emissions over a region, the environmental variables (e.g., soil properties) and the current land use pattern (e.g., tea row transects in the present study) must be included in spatial interpolation. Additionally, compared with other kriging approaches, the cokriging prediction approach showed great advantages in being easily deployed and, more importantly, providing accurate regional estimation of N2O emissions from tea-planted soils.

Beschreibung: The effects of naturally acidified seawater on shell traits were quantified through the comparison of dove snails (Family: Columbellidae) Anachis misera from vent environments with Euplica sp. from non-vent sites in northeastern Taiwan. Samples of A. misera were collected around a shallow vent (24.8341° N, 121.96191° E), which included the east, south, southwest, and northwest sites. An absence of Anachis snails was found in the most acidic north site (pH 7.19–7.25). Based on the similarities of protein expression profiles, the Anachis snails were classified into two groups, i.e., V-South (pH 7.78–7.82) and V-Rest (pH 7.31–7.83). Comparing their shell traits to the non-vent Euplica sp. from Da-xi (DX) and Geng-fang (GF) (pH 8.1–8.2), a difference in shell shape (shell width : shell length) was found, with the populations having more globular shells than the non-vent ones. The means of shell width were significantly different among sites (p 〈 0.01), with a descending order of GF 〉 DX 〉 V-South and V-Rest. The relationships of shell length to total weight were curvilinear for both Anachis and Euplica snails. The logarithmically transformed slopes differed significantly among sites, and the mean body weight of the GF population was greater than that of the others (p 〈 0.01). Positive correlations between shell length and shell thickness of body whorl (T1) and penultimate whorl (T2) were only observed in non-vent GF and DX populations. Anachis snails from vent sites were thinner in T1 and T2 compared to the Euplica snails from non-vent sites (p 〈 0.05). Within each vent group, shell thickness between T1 and T2 was insignificantly different. Between vent groups, T1 and T2 from V-Rest showed a decrease of 10.6 and 10.2%, respectively, compared to V-South ones. The decrease of T1 and T2 between vent Anachis snails and non-vent Euplica snails was as great as 55.6 and 29.0%, respectively. This was the first study to compare snail's morphological traits under varying shallow-vent stresses with populations previously classified by biochemical responses. Overall, the shallow-vent-based findings provide additional information from subtropics on the effects of acidified seawater on gastropod snails in natural environments.

Beschreibung: Changes in elemental stoichiometry, in most cases, attributed to land use alterations may cause vital impacts on the nutrient status and environmental quality of ecosystems. Here, we studied the stoichiometry and spatial distribution patterns of soil organic carbon (SOC), total soil nitrogen (TN), and total soil phosphorus (TP) in topsoil (0–20 cm; 1207 samples) ecosystems in a representative catchment of subtropical hilly region of China. Its main land uses are woodland, paddy fields, and tea farmlands. Data obtained show that the medians of SOC, TN, and TP were 16.97, 1.83, and 0.52 g kg−1, and medians of C : N, C : P, and N : P molar ratios were 10.0, 78.6 and 7.9, respectively. The best-fitting model were exponential models for SOC, TN, TP, C : N, and N : P, while for C : P was Gaussian model. The nugget values for SOC, TN, TP, C : N, C : P, and N : P were 1.0, 0.06, 0.01, 6.0, 56.0, and 1.0, respectively. And their ranges were 750, 1290, 570, 2970, 810, and 720, respectively. The nugget-to-sill ratio (NSR) for SOC, TN, TP, C : P, and N : P were 2.7 %, 14.3 %, 20.0 %, 4.0 %, and 10.0 %, respectively, and showed strong spatial autocorrelation. While C:N molar ratios had a moderate spatial correlation, with NSR of 49.95 %. Spatial analyses showed that agriculture derived land use changes alter largely the spatial distribution and stoichiometry of C, N, and P elements in individual landscapes and entire catchment. For woodland ecosystems, topography factors (elevation and slope) determined the elemental spatial distributions and stoichiometry (C : N, C : P, and N : P molar ratios). However, this status had been merged in agricultural ecosystems, due to the relative similarity in cropping and managing (N and P inputs through fertilization). Agriculture significantly increases N, and P contents but narrows C : N, C : P, and N : P molar ratios. Thus, our findings demonstrate that agricultural activities can affect carbon and nutrient stoichiometry at the catchment scale.

Beschreibung: Eddy covariance using infrared gas analyzes has been a useful tool for gas exchange measurements between soil, vegetation and the atmosphere. So far, comparisons between the open- and closed-path eddy covariance (CP) system have been extensively made on CO2 flux estimations, while lacking in the comparison of water vapor flux estimations. In this study, the specific performance of water vapor flux measurements of an open-path eddy covariance (OP) system was compared against a CP system over a tall temperate forest in northeastern China. The results show that the fluxes from the OP system (LEop) were generally greater than the LEcp though the two systems shared one sonic anemometer. The tube delay of closed-path analyzer depended on relative humidity, and the fixed median time lag contributed to a significant underestimation of LEcp between the forest and atmosphere, while slight systematic overestimation was also found for covariance maximization method with single broad time lag search window. After the optimized time lag compensation was made, the average difference between the 30 min LEop and LEcp was generally within 6.0 %. Integrated over the annual cycle, the CP system yielded a 5.1 % underestimation of forest evapotranspiration as compared to the OP system measurements (493 vs. 469 mm yr−1). This study indicates the importance to estimate the sampling tube delay accurately for water vapor flux calculations with closed-path analyzers, and it also suggests that some of the imbalance of the surface energy budget in flux sites is possibly caused by the systematic underestimation of water vapor fluxes measured with closed-path eddy covariance systems.

Beschreibung: To explore the intrinsic spatial patterns of N2O emissions in agricultural systems, not only should the spatial and temporal variability in N2O emissions be analyzed separately, but the joint spatio-temporal variability should also be explored by applying spatio-temporal semivariogram models and interpolation methods. In this study, we examined the spatio-temporal variability in N2O emissions from a tea-planted soil from 28 April 2014 to 27 May 2014 using 96 static mini chambers in an approximately regular grid on a 40 m2 tea field (sampling 30 times), and the results were compared with long-term observations of the N2O emissions recorded using large static chambers (sampling 5 times). The N2O fluxes observed by the mini chambers during a 30 min snapshot (10:00–10:30 a.m. China Standard Time) ranged from −2.99 to 487.0 mg N m−2 d−1 and were positively skewed with a median of 13.6 mg N m−2 d−1. The N2O flux data were then log-transformed for normality. After detrending the influences from the chamber placement positions (Position) and the precipitation accumulated over two days (Rain2), the log-transformed N2O fluxes (FLUX30t) exhibited strong spatial, temporal and joint spatio-temporal autocorrelations, which were used as three components of spatio-temporal semivariogram models and were characterized by models based on Stein's parameterized Matérn (Ste) function, exponential function and again the Ste function, respectively. The spatio-temporal experimental semivariogram of the N2O fluxes was fitted using four spatio-temporal semivariogram models (separable, product-sum, metric and sum-metric). The sum-metric model performed the best and provided meaningful effective ranges of spatial and temporal dependence, i.e., 0.41 m and 5.4 days, respectively. Four spatio-temporal regression-kriging interpolations were applied to estimate the spatio-temporal distribution of N2O emissions over the study area. The cross-validation results indicated that the four interpolations exhibited similar performances (r = 0.817–0.824, RMSE = 0.456–0.486, p 〈 0.001), and outperformed the multiple linear regression prediction (r = 0.735, RMSE = 0.560, p 〈 0.001). The predictions of the four kriging interpolations for the total N2O emissions from the 40 m2 tea field ranged from 18.3 to 18.5 g N; these values were approximately 25 % higher than the results predicted using the observations of large static chambers. Furthermore, compared with the other three models, the metric model exhibited weak sensitivity for peak prediction, although the cross-validation results indicated that they had same prediction capabilities. Our findings suggested: (i) that the size of large static chambers used for long-term observations of N2O fluxes should be no less than 0.4 m and the time interval for gas sampling should be constrained to approximately 5 days; and (ii) that more efficient testing methods should be adopted to replace the conventional cross-validation methods for evaluating the performance of spatio-temporal kriging.

Beschreibung: Heavy regional particulate matter (PM) pollution in China has resulted in an important and urgent need for joint control actions among cities. It is advisable to improve the understanding of the regional background concentration of PM for the development of efficient and effective joint control policies. With the increase of height the influence of source emission on local air quality decreases with altitude, but the characteristics of regional pollution gradually become obvious. A method to estimate regional background PM concentration is proposed in this paper, based on the vertical characteristics of periodic variation in the atmospheric boundary layer structure and particle mass concentration, as well as the vertical distribution of particle size, chemical composition and pollution source apportionment. According to the method, the averaged regional background PM2.5 concentration in July, August and September 2009, being extracted from the original time series in Tianjin, was 40 ± 20, 64 ± 17 and 53 ± 11 μg m−3, respectively.

Beschreibung: Ionospheric anomalies before earthquakes have become the subject of one of the most intensive studies in the area of ionospheric variation. The ionosphere has a large class of disturbances under quiet geomagnetic conditions, i.e., quiet time disturbances (Q disturbances). Hence, the characteristics of seismo-ionospheric anomalies obtained by statistical analysis should be compared with those of Q-disturbance events. Using the data of foF2 (F2-layer critical frequency) during the whole interval of 1978–2008 (~3 solar cycles), the local time (LT) variation in Q disturbances is investigated. The results showed that a well-pronounced nighttime peak took place for positive disturbances induced by Q-disturbance events, while positive disturbances related to earthquakes predominately occurred in the daytime, especially in the afternoon LT sector. This remarkable difference in local time variation in foF2 between the earthquake-triggered and Q-disturbance events is of great significance for the identification of ionospheric precursors.