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Zhang D.,Fujian Normal University | Chen X.,Fujian Normal University | Chen X.,Cultivation Base of State Key Laboratory of Humid Subtropical Mountain Ecology | Yao H.,Environment Canada | James A.,Nipissing University
Environmental Modelling and Software | Year: 2016

With enhanced availability of high spatial resolution data, hydrologic models such as the Soil and Water Assessment Tool (SWAT) are increasingly used to investigate effects of management activities and climate change on water availability and quality. The advantages come at a price of greater computational demand and run time. This becomes challenging to model calibration and uncertainty analysis as these routines involve a large number of model runs. For efficient modelling, a cloud-based Calibration and Uncertainty analysis Tool for SWAT (CUT-SWAT) was implemented using Hadoop, an open source cloud platform, and the Generalized Likelihood Uncertainty Estimation method. Test results on an enterprise cloud showed that CUT-SWAT can significantly speedup the calibration and uncertainty analysis processes with a speedup of 21.7–26.6 depending on model complexity and provides a flexible and fault-tolerant model execution environment (it can gracefully and automatically handle partial failure), thus would be an ideal method to solve computational demand problems in hydrological modelling. © 2016 Elsevier Ltd


Zhang D.,Fujian Normal University | Chen X.,Fujian Normal University | Chen X.,Cultivation Base of State Key Laboratory of Humid Subtropical Mountain Ecology | Yao H.,Environment Canada
Science of the Total Environment | Year: 2016

Nonpoint source modeling using hydrological models has been extensively studied at agriculture and urban watersheds; however, this has not been well addressed in forested ones where agricultural sources are comparatively minimal and nitrogen deposition exerts remarkable impacts on the nutrient cycles of a catchment. Thus it is critically important for hydrological models to incorporate the dynamics of nitrogen deposition and its transport processes, for reasonable nitrogen modeling. This is especially so for the Canadian Shield, which is characterized by a cold climate and special physiographic features. A revision of Soil and Water Assessment Tool for Canadian Shield (SWAT-CS) was proposed by Fu et al. (2014) to better characterize the hydrological features. In this study, more revisions were added to better simulate processes of nitrate by: 1) incorporating the dynamics of nitrogen deposition; and 2) allowing the deposition to distribute along with rapid-moving macropore flows. The newly revised model, SWAT-CSenm (SWAT-CS with an Enhanced Nitrate Module), and SWAT-CS were calibrated and tested with data of a subbasin of Harp Lake in south-central Ontario for 1990 to 2007. Modeling performance of nitrate flux rate in the stream for SWAT-CSenm was nearly acceptable with maximum daily Nash-Sutcliffe efficiencies (ENSs) for calibration and validation periods of 0.66 and 0.43, respectively; whereas the result of SWAT-CS was generally unsatisfied with maximum daily ENSs of 0.16 and 0.07, respectively. An uncertainty analysis using GLUE (generalized likelihood uncertainty estimation) showed a modest performance as about 50% of observations can be incorporated by the 95% prediction range deriving from the behavioral solutions (ENS ≥ 0.5) for both daily and monthly simulations. It is concluded that the enhanced nitrate module improved the model performance of SWAT-CS on nitrate modeling, since the previous SWAT-CS failed to consider the effect of dynamics of nitrogen deposition and its sequential processes at the investigated site. © 2016 Elsevier B.V..


Chen X.,Fujian Normal University | Chen X.,Cultivation Base of State Key Laboratory of Humid Subtropical Mountain Ecology | Lin B.,Fujian Normal University | Lin M.,Fujian Normal University
Advances in Science and Technology of Water Resources | Year: 2013

In order to investigate the impact of sample size for open channel vertical velocity distribution measurement on the log-law fitting, 110 measuring points were arranged within a 0.2 times water depth in flume experiments. The vertical velocities were collected with a laser Doppler anemometer (LDA). Based on the relative equidistance principle, 11 sets of velocity of different sample sizes generated from the 110 velocity measurements were used to conduct statistical analysis. The results show that the vertical velocity distributions agree well with the log-law formula. The fitted friction velocity, integral constant, statistical variables and variation coefficient obtained from log-law fitting vary with the size of the samples. With the sample size increase, these parameters tend to be stable which is consistent with the statistical law of large numbers. It can be concluded that a certain sample size is needed at its measuring point to accurately reveal the vertical velocity distribution. According to the present test, a sample size of about 50 is necessary for a reasonable fitting result within 0.2 times water depth when the measurements are uniform distributed with same interval in the vertical direction.


Zhang D.,Fujian Normal University | Chen X.,Fujian Normal University | Chen X.,Cultivation Base of State Key Laboratory of Humid Subtropical Mountain Ecology | Yao H.,Environment Canada | Lin B.,Fujian Normal University
Ecological Modelling | Year: 2015

Simulation of low flow process is critical to water quality, water supply, and aquatic habitat. However, the poor performance of Soil and Water Assessment Tool (SWAT) in dry seasons has impeded its application to watersheds characterized largely by low-flows. Aiming at overcoming this shortage, a seasonal calibration scheme was proposed, in which SWAT was calibrated separately for the dry and wet periods and the "optimal" simulation results of these two periods were combined into a complete runoff series. An extended SWAT model incorporating with the proposed seasonal calibration scheme, named SWAT-SC was constructed and compared with the original SWAT to simulate daily runoff in the Jinjiang watershed dominated by a typical subtropical monsoon climate in southeastern China. The study reveals that when Nash-Sutcliffe efficiency (ENS) of the original SWAT model indicated a satisfied model performance in a wet season or a whole year, it may not guaranty acceptable performance for the dry period. A significant improvement was achieved by using SWAT-SC for simulating runoffs in the dry period, and although not as notably as the dry period, improvements for runoff simulation of the wet and overall periods were observed as well. © 2015 The Authors.


Lin B.,Fujian Normal University | Chen X.,Fujian Normal University | Chen X.,Cultivation Base of State Key Laboratory of Humid Subtropical Mountain Ecology | Chen X.,Center for Monitoring Research | And 4 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2014

The effects of landscape pattern change on hydrological processes have become one of the major ecological concerns in the world. Some researches have been working on the yearly and monthly runoff response to the landscape pattern change based on distributed hydrological model. How the daily runoff, such as flood and low flow, responds to landscape pattern change has not been well studied. The study area of Jinjiang watershed, which is situated at southeastern China, is one of the regions where the economy grow fast and the landscape pattern change dramatically. It is worth to reveal how the change in landscape pattern influences the flood and low flow for the regional ecological security and economic development. In this paper, an integrated approach of distributed hydrological modeling and Pearson correlation analysis was applied to quantify the contributions of the changes of landscape indices on the variation in flood and low flow. Daily stream flow under the meteorological condition from 2002 to 2010 was simulated with the landscape pattern maps in two periods (1985 and 2006) using the Soil and Water Assessment Tool (SWAT), respectively. The changes of annual maximum 1- day, 5-day, and minimum 1-day, 7-day stream-flow between two simulations were calculated. Finally, the changes of stream-flow were related to the changes of landscape indices in Pearson correlation to quantify the impacts of changes in landscape on that of flood and low flow. The results show as following: (1) All Ens and R2 are above 0.75, and Ers are in the range of ±10% in the calibration and validation period for three gauge stations, suggesting SWAT model is well performance. (2) Compared with the landscape in 1985, the annual mean maximum 1-day and 5-day stream flow from 2002 to 2010, which was simulated by SWAT model with the landscape in 2006, increases by 5.46% and 4.97% in the Jinjiang watershed, while the annual mean minimum 1-day and 7-day stream flow decreases by 3.79% and 2.55%, respectively. (3) There are significant correlations between the variation of flood flow and landscape indices. The forestland area is negatively related with annual maximum 1- day and 5-day stream flow with the correlation coefficients of -0.764 and -0.721. The glass area is positively related with annual minimum 1-day and 7-day stream flow with the correlation coefficients of 0.461 and 0.478, respectively. It demonstrates that the increase of forest area can reduce the discharge of flood, while the increase of glass area can increase the discharge of low flow. Furthermore, the relationships between landscape metrics and flood are also revealed. SHDI and SHEI are significantly positively related with maximum 1-day flow with the correlation coefficients of 0.721 and 0.736, respectively. On the other hand, LPI and CONTAG show negative relationships with maximum 1-day flow with the coefficients of -0.61 and -0.596, respectively. The relationships between landscape metrics and flood reveal that equilibrium distribution of landscape classes and low connectivity reduces hydrologic cycle of the basin and eventually leads to the increase of flood flow. (4) Landscape metrics are not significantly related with low flow indicate that the impact of the change in landscape on that of the low flow is not so important.


PubMed | Cultivation Base of State Key Laboratory of Humid Subtropical Mountain Ecology
Type: Journal Article | Journal: Ying yong sheng tai xue bao = The journal of applied ecology | Year: 2013

Laboratory incubation test was conducted to study the effects of temperature on the CH4 emission from the leaves of subtropical common tree species Castanopsis carlesii, Schima superb, Cinnamomum chekiangense, Castsanopsis fabri, Cunninghamia lanceolata, and Citrus reticulata. Among the six tree species, only S. superb, C. reticulate, and C. fabri emitted CH4 at 10 degrees C. At above 20 degrees C, all the six species emitted CH4, and the average CH4 emission rate at above 30 degrees C (1.010 ng CH4 x g(-1) DM x h(-1)) was 2.96 times higher than that at 10-30 degrees C (0.255 ng CH4 x g(-1) DM x h(-1)). Moreover, increasing temperature had much more effects on the CH4 emission rate of C. reticulata and C. lanceolata than on that of the other four tree species. Incubation time affected the CH4 emission rate of all test tree species significantly, suggesting that the effects of temperature stress on the CH4 emission could be controlled by plant activity. Dry leaves could not emit CH4 no matter the temperature was very high or low. It was suggested that high temperature stress had important effects on the CH4 emission from subtropical tree leaves, and global warming could increase the CH4 emission from plants.


PubMed | Cultivation Base of State Key Laboratory of Humid Subtropical Mountain Ecology
Type: Journal Article | Journal: Ying yong sheng tai xue bao = The journal of applied ecology | Year: 2013

Negative air ion (NAI) concentration is an important indicator comprehensively reflecting air quality, and has significance to human beings living environment. This paper summarized the spatiotemporal distribution features of urban NAI concentration, and discussed the causes of these features based on the characteristics of the environmental factors in urban area and their effects on the physical and chemical processes of NAI. The temporal distribution of NAI concentration is mainly controlled by the periodic variation of solar radiation, while the spatial distribution of NAI concentration along the urban-rural gradient is mainly affected by the urban aerosol distribution, underlying surface characters, and urban heat island effect. The high NAI concentration in urban green area is related to the vegetation life activities and soil radiation, while the higher NAI concentration near the water environment is attributed to the water molecules that participate in the generation of NAI through a variety of ways. The other environmental factors can also affect the generation, life span, component, translocation, and distribution of NAI to some extent. To increase the urban green space and atmospheric humidity and to maintain the soil natural attributes of underlying surface could be the effective ways to increase the urban NAI concentration and improve the urban air quality.


PubMed | Cultivation Base of State Key Laboratory of Humid Subtropical Mountain Ecology
Type: Journal Article | Journal: Ying yong sheng tai xue bao = The journal of applied ecology | Year: 2011

By using Li-Cor 8100 open soil carbon flux system, the dynamic changes of soil respiration rate in Phyllostachys edulis forest in Wanmulin Natural Reserve in Fujian Province of China were measured from January 2009 to December 2009, with the relationships between the dynamic changes and related affecting factors analyzed. The monthly variation of soil respiration rate in the forest presented a double peak curve, with the peaks appeared in June 2009 (6. 83 micromol x m(-2) x s(-1)) and September 2009 (5.59 micromol x m(-2) x s(-1)), and the seasonal variation of the soil respiration rate was significant, with the maximum in summer and the minimum in winter. The soil respiration rate had significant correlation with the soil temperature at depth 5 cm (P < 0.05), but no significant correlation with soil moisture (P > 0.05). The monthly variation of litter fall mass in the forest was in single peak shape, and there was a significantly positive correlation between the monthly litter fall mass and soil respiration rate (P < 0.05). Two-factor model of soil temperature and litter fall mass could explain 93.2% variation of the soil respiration rate.


PubMed | Cultivation Base of State Key Laboratory of Humid Subtropical Mountain Ecology
Type: Journal Article | Journal: Ying yong sheng tai xue bao = The journal of applied ecology | Year: 2012

A monthly measurement of soil CH4 uptake rate (V(CH4)) in a natural Castanopsis carlesii forest in Wanmulin Natural Reserve of Fujian Province, East China was conducted from March 2010 to February 2011. The VCH4 showed a pronounced seasonal fluctuation, being higher in summer-autumn than in winter-spring, with the maximum value (95.13 microg x m(-2) x h(-1)) in September and the minimum value (9.13 microg x m(-2) x h(-1)) in March. With the increase of soil temperature and moisture, the V(CH4) showed an increasing and a decreasing trend, respectively, but the correlations of the V(CH4) with soil temperature and moisture were not significant. The annual soil CH4 flux of the forest (3.93 kg x hm(-2) x a(-1)) was higher than the average value of global natural forests (2.4 kg x hm(-2) x a(-1)) and of Asian tropical natural forests (2.07 kg x hm(-2) x a(-1)), but lower than that of Asian temperate natural forests (8.12 kg x hm(-2) x a(-1)).


PubMed | Cultivation Base of State Key Laboratory of Humid Subtropical Mountain Ecology
Type: Comparative Study | Journal: Ying yong sheng tai xue bao = The journal of applied ecology | Year: 2012

From January 2009 to December 2009, the soil respiration in the Citrus reticulata and Castanea henryi orchards in Wanmulin Nature Reserve was measured with Li-8100, aimed to characterize the dynamic changes of the soil respiration and its relationships with soil temperature and moisture in the two orchards. The monthly variation of the soil respiration in the orchards was single-peaked, with the peak appeared in July (3.76 micromol x m(-2) x s(-1)) ) and August (2.69 micromol x m(-2) x s(-1)). Soil temperature was the main factor affecting the soil respiration, and explained 73%-86% of the monthly variation of soil respiration. The average annual soil respiration rate was significantly higher in Citrus reticulata orchard than in Castanea henryi orchard, with the mean value being 2.68 and 1.55 micromol x m(-2) x s(-1), respectively. There was a significant positive correlation between the soil respiration rate and soil moisture content in Castanea henryi orchard, but less correlation in Citrus reticulata orchard. The Q10 value of the soil respiration in Citrus reticulata and Castanea henryi orchards was 1.58 and 1.75, and the annual CO2 flux was 10.01 and 5.77 t C x hm(-2) x a(-1), respectively.

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