DISSERTATION RESEARCH: Pulsed and Pressed: the Interactive Effects of Disturbance Intensity and Complex Chemical Exposure on the Productivity of Urban Stream Ecosystems

Duke University, Durham NC

Investigators

Abstract

Streams in urban landscapes can be negatively impacted by increased flooding due to runoff from impervious surfaces and elevated exposures to both nutrients and pollutants that wash off of those surfaces and can be delivered from inadequate waste water treatment systems. Understanding the individual contributions of these different factors in limiting the productivity and health of urban streams is important for an understanding of the impacts of land use changes, but difficult to identify, because they can occur simultaneously. This project will make use of controlled experimental stream channels to separate how physical disturbances associated with high flows and increased contaminant exposure affect the productivity of stream ecosystems. In small streams, almost all of the productivity is associated with organisms living on the stream bed. Stream beds vary in their stability, or susceptibility to disturbance, largely due to the mixture of streambed materials including the sizes of sediments and rocks. The researchers will compare the rates of recovery and compositions of streambed communities in experimental channels following exposure to storm flows. The experimental treatments will involve different doses of common urban contaminants added to the stream water and adjusting the size of sediments within the streambed. The researchers will train a high school student from a rural community in New York in research, develop a lesson plan for high school environmental science students, and engage the public through a research website and professional meetings. The goal of this research is to experimentally measure the independent and interactive effects of physical (pulse) and chemical (press) disturbance on aquatic ecosystem productivity. The researchers will test the alternative hypotheses that: 1) more severe disturbances may exacerbate the effects of chemical stress by increasing the susceptibility of biofilms to contaminant exposure; or 2) less severe disturbance may exacerbate the effects of chemical stress by increasing the accumulation of contaminants in biofilms. Water chemistry, biofilm composition, and whole-stream metabolism will be measured throughout the recovery period following a physical disturbance in experimental stream channels with cobble beds and sand beds.