Rongrong Wan

Inferring land use and land cover impact on stream water quality using a Bayesian hierarchical modeling approach in the Xitiaoxi River Watershed, China.

Lake eutrophication has become a very serious environmental problem in China. If water pollution is to be controlled and ultimately eliminated, it is essential to understand how human activities affect surface water quality. A recently developed technique using the Bayesian hierarchical linear regression model revealed the effects of land use and land cover (LULC) on stream water quality at a watershed scale. Six LULC categories combined with watershed characteristics, including size, slope, and permeability were the variables that were studied. The pollutants of concern were nutrient concentrations of total nitrogen (TN) and total phosphorus (TP), common pollutants found in eutrophication. The monthly monitoring data at 41 sites in the Xitiaoxi Watershed, China during 2009-2010 were used for model demonstration. The results showed that the relationships between LULC and stream water quality are so complicated that the effects are varied over large areas. The models suggested that urban and agricultural land are important sources of TN and TP concentrations, while rural residential land is one of the major sources of TN. Certain agricultural practices (excessive fertilizer application) result in greater concentrations of nutrients in paddy fields, artificial grasslands, and artificial woodlands. This study suggests that Bayesian hierarchical modeling is a powerful tool for examining the complicated relationships between land use and water quality on different scales, and for developing land use and water management policies.

Non-stationary water-level fluctuation in China’s Poyang Lake and its interactions with Yangtze River

Seasonal water-level fluctuations (WLF) play a dominate role in lacustrine ecosystems. River-lake interaction is a direct factor in changes of seasonal lake WLF, especially for those lakes naturally connected to upstream and downstream rivers. During the past decade, the modification of WLF in the Poyang Lake (the largest freshwater lake in China) has caused intensified flood and irrigation crises, reduced water availability, compromised water quality and extensive degradation of the lake ecosystem. There has been a conjecture as to whether the modification was caused by its interactions with Yangtze River. In this study, we investigated the variations of seasonal WLF in China’s Poyang Lake by comparing the water levels during the four distinct seasons (the dry season, the rising season, the flood season, and the retreating season) before and after 2003 when the Three Gorge Dam operated. The Water Surface Slope (WSS) was used as a representative parameter to measure the changes in river-lake interaction and its impacts on seasonal WLF. The results showed that the magnitude of seasonal WLF has changed considerably since 2003; the seasonal WLF of the Poyang Lake have been significantly altered by the fact that the water levels both rise and retreat earlier in the season and lowered water levels in general. The fluctuations of river-lake interactions, in particular the changes during the retreating season, are mainly responsible for these variations in magnitude of seasonal WLF. This study demonstrates that WSS is a representative parameter to denote river-lake interactions, and the results indicate that more emphasis should be placed on the decrease of the Poyang Lake caused by the lowered water levels of the Yangtze River, especially in the retreating season.

Ecological risk assessment of ecosystem services in the Taihu Lake Basin of China from 1985 to 2020

There are tremendous theoretical, methodological and policy challenges in evaluating the impact of land-use change on the degradation of ecosystem services (ES) at the regional scale. This study addresses these challenges by developing an interdisciplinary methodology based on the Procedure for Ecological Tiered Assessment of Risk (PETAR). This novel methodology integrates ecological models with a land-use change model. This study quantifies the multi-dimensional degradation risks of ES in the Taihu Lake Basin (TLB) of China from 1985 to 2020. Four key ES related to water purification, water quantity adjustment, carbon sequestration and grain production are selected. The study employs models of Denitrification-Decomposition (DNDC), Soil-Water-Atmosphere-Plant (SWAP), Biome-BGC and Agro-ecological Zoning (AEZ) for assimilations. Land-use changes by 2020 were projected using a geographically weighted multinomial logit-cellular automata (GWML-CA) model. The results show that rapid land-use change has posed a great degradation risk of ES in the region in 1985-2020. Slightly less than two-thirds of the basin experienced degradation of ES over the 1985-2010 period, and about 12% of the basin will continue to experience degradation until 2020. Hot spots with severe deterioration in 2010-2020 are projected to be centered around some small and less developed cities in the region. Regulating accelerated urban sprawl and population growth, reinforcing current environmental programs, and establishing monitoring systems for observing dynamics of regional ES are suggested as practical counter-measures.

Using fuzzy theory and variable weights for water quality evaluation in Poyang Lake, China

Achieving water purity in Poyang Lake has become a major concern in recent years, thus appropriate evaluation of spatial and temporal water quality variations has become essential. Variations in 11 water quality parameters from 15 sampling sites in Poyang Lake were investigated from 2009 to 2012. An integrative fuzzy variable evaluation (IFVE) model based on fuzzy theory and variable weights was developed to measure variations in water quality. Results showed that: 1) only chlorophyll-a concentration and Secchi depth differed significantly among the 15 sampling sites (P < 0.01), whereas the 11 water quality parameters under investigation differed significantly throughout the seasons (P < 0.01). The annual variations of all water quality variables except for temperature, electrical conductivity, suspended solids and total phosphorus were considerable (P < 0.05). 2) The IFVE model was reasonable and flexible in evaluating water quality status and any possible ′bucket effect′. The model fully considered the influences of extremely poor indices on overall water quality. 3) A spatial analysis indicated that anthropogenic activities (particularly industrial sewage and dredging) and lake bed topography might directly affect water quality in Poyang Lake. Meanwhile, hydrological status and sewage discharged into the lake might be responsible for seasonal water quality variations.

Comprehensive Performance Evaluation for Hydrological and Nutrients Simulation Using the Hydrological Simulation Program–Fortran in a Mesoscale Monsoon Watershed, China

The Hydrological Simulation Program–Fortran (HSPF) is a hydrological and water quality computer model that was developed by the United States Environmental Protection Agency. Comprehensive performance evaluations were carried out for hydrological and nutrient simulation using the HSPF model in the Xitiaoxi watershed in China. Streamflow simulation was calibrated from 1 January 2002 to 31 December 2007 and then validated from 1 January 2008 to 31 December 2010 using daily observed data, and nutrient simulation was calibrated and validated using monthly observed data during the period from July 2009 to July 2010. These results of model performance evaluation showed that the streamflows were well simulated over the study period. The determination coefficient (R2) was 0.87, 0.77 and 0.63, and the Nash-Sutcliffe coefficient of efficiency (Ens) was 0.82, 0.76 and 0.65 for the streamflow simulation in annual, monthly and daily time-steps, respectively. Although limited to monthly observed data, satisfactory performance was still achieved during the quantitative evaluation for nutrients. The R2 was 0.73, 0.82 and 0.92, and the Ens was 0.67, 0.74 and 0.86 for nitrate, ammonium and orthophosphate simulation, respectively. Some issues may affect the application of HSPF were also discussed, such as input data quality, parameter values, etc. Overall, the HSPF model can be successfully used to describe streamflow and nutrients transport in the mesoscale watershed located in the East Asian monsoon climate area. This study is expected to serve as a comprehensive and systematic documentation of understanding the HSPF model for wide application and avoiding possible misuses.

Satellite data application for the assessment of water balance in the Taihu watershed, China

Abstract With the development of population and economy, the problems of deficit in water resources and degradation in water environment are increasingly serious in the Taihu watershed of China. The information on spatial and temporal availabilities of water will be helpful for the optimum utilization of water resources. In this study, we apply precipitation (P) from the Tropical Rainfall Measuring Mission (TRMM) products, evapotranspiration (ET) derived from MODIS data, and ground-observed runoff. Then annual water budgets in the Taihu watershed from 2005 to 2007 and the variation of water budget components in spatial and temporal (monthly and annually) scales were evaluated. The results indicated that ET was the most notable component of water consumption in the watershed. The annual mean ratio of the ET to the precipitation was 0.73 to 0.89 in the watershed and 1.1 to 1.3 in Lake Taihu area from 2005 to 2007. The analysis of water balance in the watershed indicated that the amount of water input and output were approximately equal for the watershed and the lake areas with imbalance percentages of 1.4% to 4.4% and 0.1% to 4.0%, respectively.

Simulating the Impacts of Land Use/Cover Change on Storm-Runoff for a Mesoscale Watershed in East China

This study aims to explore the impacts of Land use/cover change (LUCC) on storm-runoff by simulating two typical flood events for five land cover scenarios in a mesoscale watershed in east China by distributed hydrologic modeling system HEC-HMS. It was concluded from the modeled hydrographs that built-up land will reduce the basin’s ability of smoothing flood wave by changing flood peak remarkably, while forestation will mitigate and postpone flood peak. The statistic analysis of the key flood parameters, runoff coefficient and peak discharge, produced by five different land covers exhibited highly quantitative relationships, from which we may estimate the runoff changes due to land use/cover changes under 5-year return period typhoon rain or Plum rain. The study provides some information on the influences of LUCC on storm-runoff by modeling approach and it will contribute to flood control and management in Tai Lake Basin in east China.

Water quality control plan with BATHTUB model for lake inflow rivers – A case study of total phosphorus in Northwest Lake Taihu, China

Total phosphorus (TP) standards for lakes differ from those for rivers in GB3838-2002. This disjunction may lead to the failure of lake-water quality improvement plans that control nutrient inputs from inflow rivers. With monthly monitoring data for the period 2009-2015, Northwest Lake Taihu was regarded as a case study and the BATHTUB model was utilised to simulate the correspondence between concentrations of TP in the lake and in its inflow rivers. A control plan for TP in Northwest Lake Taihus inflow rivers is proposed. To guarantee the fulfillment of the control goals of TP in the lake, concentration of TP in the inflow rivers of North Zone, Zhushan Bay, Meiliang Bay and Gonghu Bay should be reduced by 50%, 58%, 18% and 11%, respectively, and TP flux loads should be maintained under 227.35, 173.39, 113.69 and 90.62 ta-1, respectively. Meanwhile, total TP influxes from Northwest Lake Taihu should be maintained under 604.63 ta-1. A control plan that is more restrictive than GB3838-2002 should be proposed to address the TP pollution of the lake. This research provides the foundation for quantifying reduction of the nutrient loading from the catchment and for maintaining Lake Taihu and other typical eutrophic lakes.

The effect of the Changjiang River on water regimes of its tributary Lake East Dongting

The blocking or reversing effect of the downstream trunk river on its tributary lakes is an essential aspect of river-lake hydraulics. To measure how and the extent to which a trunk river can influence its tributary lakes, we made a case study in Changjiang River and one of its tributary lakes, Lake East Dongting (Lake ED) during a 35-year study period (1980–2014). Specifically, we investigated Lake ED’s discharge ability into Changjiang River using stage-discharge relationship curves, and hence the changes of the lake discharge ability under different hydrologic conditions of the Changjiang River. The results show that (1) the Changjiang River does exert a huge impact on the water regimes of Lake ED. And this impact varies seasonally. A variation of 3000 m3/s in Changjiang River’s runoff would change the lake water level by about 1.1 m in dry seasons, by 0.4 m in wet seasons, and by 0.6 m during severe summer floods. (2) Changes in the Changjiang River runoff triggered by the Three Gorges Dam since 2003 have led to dramatic water regime variations in Lake ED. Other factors, including reduction of lake inflow and the lake bed erosion, also exacerbated the water regime variations in Lake ED.

Water Security-based Hydrological Regime Assessment Method for Lakes with Extreme Seasonal Water Level Fluctuations: A Case Study of Poyang Lake, China

Extreme seasonal water level fluctuations characterize natural floodplain lakes in monsoon regions, which are crucial for ensuring lake water security, including flood prevention water supply and health of aquatic ecosystem. In order to achieve this goal, we established a hydrological regime assessment method based on a set of hydrological indicators for lakes with heavy seasonal water level fluctuations. The results suggest that time-sensitive hydrological indicators and specific time scales for various water security aspects must be considered. We discovered that it is more practical and meaningful to combine the water level classification derived from statistical analyses with characteristic hydrological values linked to water security. The case study of Poyang Lake results show that there are no discernable trends of Poyang Lake water regime status over the last 35 years, and the two periods of poor status are in accordance with climate variation in the lake basin area. Scholars and policy makers should focus on both floods and droughts, which are the main water security problems for Poyang Lake. It is hoped that this multi-scale and multi-element hydrological regime assessment method will provide new guidelines and methods for other international scholars of river and lake water assessment.