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Stressor−Response Models: A Practical Application for the Development of Lake Nutrient Criteria in China Shouliang Huo, Beidou Xi,* Chunzi Ma, and Hongliang Liu State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China criteria that represent the toxic effects of chemical pollutants using simple laboratory studies have limited applicability to LNC development.3 Excess nutrients stimulate the deleterious proliferation of planktonic algal, which leads to oxygen depletion, reduced light transparency, the loss of biodiversity, and the production of algal toxins, eventually disrupting aquatic life, recreation, and drinking water supplies. Thus, stressor− response models (SRMs) representing the most important known relationships between N and P concentrations and primary productivity have been developed based on analyses of observational data collected in the field.4 SRMs are suitable for deriving the nutrient criteria of lakes affected by anthropogenic activities based on a given algal biomass criterion to protect the designated water uses in China. Moreover, the chlorophyll a concentration (Chl a), which is strongly related to the algal biomass, can serve as an important variable that is linked to nutrient concentrations when developing LNC for designated water uses. For example, LNC in support of drinking water supplies are affected by increased levels of algal toxins and organic carbon associated with algal blooms. Therefore, a target value (or criterion) for the response to Chl a must be established before N and P criteria for drinking water supplies hina has numerous lakes with significant regional diversity can be derived using SRMs.4 that have been threatened by extensive eutrophication. The US EPA has adopted the use of SRMs to derive numeric The current water quality standards (WQS) for lake protection N and P criteria to develop designated water uses based on Chl and eutrophication control were promulgated in 2002.1 a. To date, SRMs have not been extensively applied to the However, the WQS are not supported by corresponding development of LNC in China. Therefore, it is necessary for numeric nutrient criteria and do not consider regional Chinese researchers to begin to apply the currently available differences. Therefore, regional lake nutrient criteria (LNC) SRMs for nutrients to Chinese lakes and to conduct research must be developed to better reflect the regional econecessary for the development of regional LNC, especially for environment and current lake management needs in China. lake ecoregions with severe anthropogenic activities that reflect China has implemented the Regional Nutrient Criteria the basin characteristics of Chinese lakes. Research Plan since 2008 to formulate nutrient ecoregions and The adoption of SRMs to determine the ecoregional LNC in recommend regional LNC. Because there was no systematic China will be challenging for several reasons. (1) Determining or obtaining the relationship between Chl a and the key research to support the development of LNC in China, the plan indicators reflecting the designated water uses is the first issue was mainly developed as a case study to explore the feasibility that should be resolved. To derive a nutrient criterion using of the lake population distribution, reference lake, trisection, SRMs, the criterion value for Chl a should be initially and model extrapolation methods recommended by the U.S. established for diverse designated water uses in different lake Environmental Protection Agency (EPA).2 However, these ecoregions. Moreover, when defining Chl a criteria for lakes methods are not applicable to LNC establishment in China that have a designated water use, the aforementioned causal because of the widespread contamination of aquatic ecosystems chain that ultimately affects the attainment of designated uses by industrialization, urbanization, and agriculture across various for lakes should be clarified. (2) The sensitivity of algal to lake ecoregions. Furthermore, these methods do not consider nutrients might display significant heterogeneity across various the attainment of designated water uses for determining LNC. lake types. The SRMs are susceptible to being confounded with Therefore, there is an urgent need to develop suitable methods environment factors such as species biogeography, lake depth, for establishing LNC in China. watershed area, salinity, and water color. Hence, these factors Nutrients found in lakes, such as nitrogen (N) and phosphorus (P), are not toxic to aquatic organisms and humans at low concentrations, and methods to derive numeric Published: October 7, 2013
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© 2013 American Chemical Society
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should be identified or included in future models. (3) The estimation of the nutrient response types (N or P response) of lakes is difficult. P is the limiting nutrient in many freshwater lake systems. However, research has demonstrated that N and colimitation by N and P can be important in certain lake systems. (4) Shallow lakes have high concentrations of suspended solids. Algal and nonalgal turbidity should be differentiated when developing SRMs. As one example, most lakes in the central and lower regions of the Yangtze River of China are shallow and have high concentrations of suspended solids because of human activities and external disturbances (e.g., wind). Thus, the SRM between nutrients and algal is greatly affected by nonalgal turbidity. Although SRMs have been successfully applied in the US, it remains unclear whether the relationship between N and P, concentrations and Chl a or the relationship between Chl a and the attainment of designated uses for US lakes will be applicable to Chinese lakes. The applicability of SRMs in China will be determined by developing parameters for N, P, and Chl a concentrations and the attainment of designated uses to calibrate the SRMs for different lakes types and ecoregions of China. The establishment of LNC for ecoregions is critical for the development of scientifically defensible WQS. The Chinese government has recognized the importance of developing numerical nutrient criteria to protect the designated uses of lakes from nutrient enrichment. Therefore, nutrient criteria that are appropriate for all geographical and climatological areas of the country are being developed by considering ecoregional variations to improve and protect water quality. SRMs will provide a technically defensible and appropriate scientific basis for determining LNC in China. Moreover, complex environmental factors that might influence the sensitivity of Chl a to nutrients should be considered to improve the accuracy of the estimated SRMs.
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AUTHOR INFORMATION
Corresponding Author
*Corresponding Author E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This study was supported by the Mega-projects of Science Research for Water Environment Improvement in China (Program Nos. 2009ZX07106-001 and 2012ZX07101-002).
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REFERENCES
(1) Ministry of Environmental Protection PRC. Environmental Quality Standard for Surface Water (GB3838−2002); Standards Press: Beijing, China, 2002; pp 1−8. (2) Gibson, G.; Carlson, R.; Simpson, J.; Smeltzer, E. Nutrient criteria technical guidance manual: lakes and reservoirs (EPA-822-B00−001). United States Environment Protection Agency: Washington, DC, 2000. (3) Lamon, E. C.; Qian, S. S. Regional scale stressor−response models in aquatic ecosystems. J. Am. Water Resour. Assoc. 2008, 44, 771−781. (4) U.S. EPA. Using Stressor−response Relationships to Derive Numeric Nutrient Criteria, EPA-820-S-10-001; U.S. Environmental Protection Agency, Office of Water: Washington, DC, 2010.
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