Carleton James N, Park Richard A, Clough Jonathan S
U.S. Environmental Protection Agency, Washington, DC 20460, USA.
Environ Manage. 2009 Sep;44(3):485-92. doi: 10.1007/s00267-009-9344-2. Epub 2009 Jul 28.
Threshold concentrations for biological impairment by nutrients are difficult to quantify in lotic systems, yet States and Tribes in the United States are charged with developing water quality criteria to protect these ecosystems from excessive enrichment. The analysis described in this article explores the use of the ecosystem model AQUATOX to investigate impairment thresholds keyed to biological indexes that can be simulated. The indexes selected for this exercise include percentage cyanobacterial biomass of sestonic algae, and benthic chlorophyll a. The calibrated model was used to analyze responses of these indexes to concurrent reductions in phosphorus, nitrogen, and suspended sediment in an enriched upper Midwestern river. Results suggest that the indexes would respond strongly to changes in phosphorus and suspended sediment, and less strongly to changes in nitrogen concentration. Using simulated concurrent reductions in all three water quality constituents, a total phosphorus concentration of 0.1 mg/l was identified as a threshold concentration, and therefore a hypothetical water quality criterion, for prevention of both excessive periphyton growth and sestonic cyanobacterial blooms. This kind of analysis is suggested as a way to evaluate multiple contrasting impacts of hypothetical nutrient and sediment reductions and to define nutrient criteria or target concentrations that balance multiple management objectives concurrently.
营养物质对生物造成损害的阈值在流水系统中难以量化，但美国的各州和部落负责制定水质标准，以保护这些生态系统免受过度富集的影响。本文所述分析探讨了使用生态系统模型AQUATOX来研究与可模拟的生物指标相关的损害阈值。本次分析所选指标包括漂浮藻类中蓝藻生物量的百分比以及底栖叶绿素a。校准后的模型用于分析这些指标对中西部上游一条富营养化河流中磷、氮和悬浮沉积物同时减少的响应。结果表明，这些指标对磷和悬浮沉积物的变化反应强烈，对氮浓度变化的反应则较弱。通过模拟所有三种水质成分同时减少的情况，确定总磷浓度为0.1毫克/升是预防周丛生物过度生长和漂浮蓝藻水华的阈值浓度，因此也是一个假设的水质标准。建议采用这种分析方法来评估假设的营养物质和沉积物减少所产生的多种对比影响，并确定能同时平衡多个管理目标的营养标准或目标浓度。
