Synergistic effect of drought and rainfall events of different patterns on watershed systems.

The increase in extreme climate events such as flooding and droughts predicted by the general circulation models (GCMs) is expected to significantly affect hydrological processes, erosive dynamics, and their associated nonpoint source (NPS) pollution, resulting in a major challenge to water availability for human life and ecosystems. Using the Hydrological Simulation Program-Fortran model, we evaluated the synergistic effects of droughts and rainfall events on hydrology and water quality in an upstream catchment of the Miyun Reservoir based on the outputs of five GCMs. It showed substantial increases in air temperature, precipitation intensity, frequency of heavy rains and rainstorms, and drought duration, as well as sediment and nutrient loads in the RCP 8.5 scenario. Sustained droughts followed by intense precipitation could cause complex interactions and mobilize accumulated sediment, nutrients and other pollutants into surface water that pose substantial risks to the drinking water security, with the comprehensive effects of soil water content, antecedent drought duration, precipitation amount and intensity, and other climate characteristics, although the effects varied greatly under different rainfall patterns. The Methods and findings of this study evidence the synergistic impacts of droughts and heavy rainfall on watershed system and the significant effects of initial soil moisture conditions on water quantity and quality, and help to guide a robust adaptive management system for future drinking water supply.

Factors affecting microbial and physico-chemical pollutants in stormwater in a typical Chinese urban catchment.

An understanding of microbial pollution characteristics is needed for stormwater reuse and development of microorganism simulations in urban stormwater. This study investigated the discharge characteristics of faecal indicator bacteria (faecal coliforms) in urban runoff by field sampling both the underlying surfaces and the stormwater pipe outlet. Faecal coliform contamination in urban runoff was found to be frequent, and the highest instantaneous concentration reached 2.42 × 106 MPN/100 ml. Faecal coliforms did not show a consistent first flush effect amongst the different surfaces sampled, and this was exacerbated under rainfall events with high intensity. PROMETHEE (Preference Ranking Organization Method for Enrichment Evaluation) and GAIA (Geometrical Analysis for Interactive Aid) analyses were further applied to explore the ranking of pollutants, the relationship among the pollutants, and the factors affecting the contamination in cases of multiple underlying surfaces, multiple pollutants and rainfall events. For the pollutants of suspended solids (SS), total phosphorus (TP) and chemical oxygen demand (COD), the road sample contamination was significantly higher than on the roof surfaces. No such trend in ranking of faecal coliforms was observed. Rainfall depth and intensity were found to have a significant influence on stormwater contamination by physico-chemical pollutants, while having a somewhat smaller influence on faecal coliform contamination. Faecal coliform contamination is closely associated with the index related to the antecedent dry period. The average temperature and average relative humidity also showed a positive relationship with faecal coliform contamination. The effects of antecedent dry period duration on contamination of physico-chemical pollutants and faecal coliform are completely opposite. Antecedent dry period duration was positively related to the contamination of physico-chemical pollutants, but negatively related to faecal coliform contamination. Therefore, three variables, i.e., antecedent dry period duration, average temperature and average relative humidity, might be used to model the survival/die-off of faecal coliform during the antecedent dry period.

A systematic assessment of watershed-scale nonpoint source pollution during rainfall-runoff events in the Miyun Reservoir watershed.

The assessment of peak flow rate, total runoff volume, and pollutant loads during rainfall process are very important for the watershed management and the ecological restoration of aquatic environment. Real-time measurements of rainfall-runoff and pollutant loads are always the most reliable approach but are difficult to carry out at all desired location in the watersheds considering the large consumption of material and financial resources. An integrated environmental modeling approach for the estimation of flash streamflow that combines the various hydrological and quality processes during rainstorms within the agricultural watersheds is essential to develop targeted management strategies for the endangered drinking water. This study applied the Hydrological Simulation Program-Fortran (HSPF) to simulate the spatial and temporal variation in hydrological processes and pollutant transport processes during rainstorm events in the Miyun Reservoir watershed, a drinking water resource area in Beijing. The model performance indicators ensured the acceptable applicability of the HSPF model to simulate flow and pollutant loads in the studied watershed and to establish a relationship between land use and the parameter values. The proportion of soil and land use was then identified as the influencing factors of the pollution intensities. The results indicated that the flush concentrations were much higher than those observed during normal flow periods and considerably exceeded the limits of Class III Environmental Quality Standards for Surface Water (GB3838-2002) for the secondary protection zones of the drinking water resource in China. Agricultural land and leached cinnamon soils were identified as the key sources of sediment, nutrients, and fecal coliforms. Precipitation volume was identified as a driving factor that determined the amount of runoff and pollutant loads during rainfall processes. These results are useful to improve the streamflow predictions, provide useful information for the identification of highly polluted areas, and aid the development of integrated watershed management system in the drinking water resource area.

An auto-adaptive optimization approach for targeting nonpoint source pollution control practices.

To solve computationally intensive and technically complex control of nonpoint source pollution, the traditional genetic algorithm was modified into an auto-adaptive pattern, and a new framework was proposed by integrating this new algorithm with a watershed model and an economic module. Although conceptually simple and comprehensive, the proposed algorithm would search automatically for those Pareto-optimality solutions without a complex calibration of optimization parameters. The model was applied in a case study in a typical watershed of the Three Gorges Reservoir area, China. The results indicated that the evolutionary process of optimization was improved due to the incorporation of auto-adaptive parameters. In addition, the proposed algorithm outperformed the state-of-the-art existing algorithms in terms of convergence ability and computational efficiency. At the same cost level, solutions with greater pollutant reductions could be identified. From a scientific viewpoint, the proposed algorithm could be extended to other watersheds to provide cost-effective configurations of BMPs.

Targeting priority management areas for multiple pollutants from non-point sources.

The control of multiple pollutants from non-point sources is very difficult because their loss potentials are not consistent on the same spatial distributions. In this research, an innovative approach was established for multiple-pollutant priority management areas (MP-PMAs). In the new framework, the MP-PMA approach focused on the sensitive areas that contributed a variety of pollutants instead of a specific targeted pollutant by integrating a watershed model and a Pareto-based multi-criteria evaluation approach. Based on the results, multiple levels of MP-PMAs were established with respect to the corresponding requirements of clean water statutes. Compared to traditional separate strategies, the MP-PMA approach would lead to more cost-effective watershed management because those moderate-level PMAs for specific targeted pollutant might be the high-level MP-PMAs. With respect to spatial distribution, the MP-PMA approach provided more accurate target results for the high-level PMAs, especially among the headwater areas. From a scientific view, the MP-PMA approach provides an integrated suggestion for the placement and removal potentials of best management practices at the watershed scale.

[Impact of environmental changes on Oncomelania snail distribution in Dongting Lake beach].

OBJECTIVE: To study the impact of environmental changes on the distribution and the growth and decline of Oncomelania snails in Dongting Lake beaches after the implementation of Three Gorges Project. METHODS: T-embankment of Junshan District where there was a greater human factor related to the snail spread and a lake beach named Dongkou of Junshan District where there was a less human factor related to the snail spread were selected as study areas. The various ground elevations were measured and the high points were marked with GPS. The height of vegetation was surveyed regularly, soil moisture content and micro-environment temperature and humidity at different elevations in the lake beaches were detected, and the snail distribution was investigated. Both the longitudinal and retrospective studies were conducted. RESULTS: In 1993, the soil was taken from the lake beach at the elevation of 25 m to build an isolated canal, and this made snail density decline year by year, and no snails have been found since 1998. The elevation of the vegetation in the T-embankment was significantly lower than that in Dongkou, and there was no high rod plant growth. The snails were found in the elevation from 23.5 to 26.5 m where the vegetation was mainly Cyperus spp. The growth of the vegetation was 16.0 to 54.0 cm 30 days after flood withdrew, and the vegetation reached the highest density 60 days after flood withdrew. The snail density was highest at the elevation from 24.5 to 25.5 m, and the elevation of snails and their eggs was lower than that in 1980s. In the dry season, the water content of the soil in Dongkou was from 46.80% to 52.20%, which was more than that in T-embankment, while at the elevation over 26.0 m, the water content was from 21.36% to 29.77%, which was equal to that in T-embankment. CONCLUSION: Three Gorges Project plays an important role in the control of water level of Dongting Lake, but there is no impact on the snail reproduction and density.