Investigating Aquatic Dead Zones.

We are increasingly aware of our changing coastal oceans and how they impact our lives--from rapidly eroding shorelines to harmful algae blooms, expanding dead zones, and declining fisheries. Although we read about these and other trends in news articles, their causes and consequences are poorly understood by the general public. Scientific research has produced logical explanations for many of these trends, but clear understanding of the science behind these dynamic processes does not always translate to the broader community. [ILLUSTRATION OMITTED] This article features two engaging high school activities that include current scientific information, data, and authentic case studies. The activities address the physical, biological, and chemical processes in aquatic systems that are associated with oxygen-depleted areas, or "dead zones," in aquatic systems. Students can explore these dead zones through both hands-on investigations and interdisciplinary, critical-thinking exercises. These activities were designed by a research scientist, graduate students, a teacher, and an undergraduate student as part of the Center for Ocean Sciences Education Excellence (COSEE) Coastal Trends Scientist-Educator Partnerships (see "On the web") and were tested in both middle and high school classrooms. Understanding dead zones Dead zones are regions in fresh and marine aquatic environments in which dissolved oxygen concentrations drop to extremely low levels. This condition of oxygen deficiency, known as hypoxia, results from a combination of biological, chemical, and physical conditions. In the absence of sufficient oxygen, most nonmicrobial organisms (e.g., fish, worms, and plants) must migrate to more oxygenated areas, or they will suffer physiological stress or even death (Diaz and Rosenberg 1995). Many bacteria, however, can thrive in this region, or "dead zone," by feeding on the abundant food produced in the overlying waters; a few invertebrate species can temporarily withstand the negative effects of low oxygen. Dead zones currently occur, or have occurred, in many aquatic ecosystems around the world, including Lake Erie, the Northern Gulf of Mexico, the Chesapeake Bay, the Black Sea, and Tokyo Bay (Diaz and Rosenberg 2008; Kemp et al. 2009). Although dead zones develop naturally in many ecosystems, some have expanded and new ones have formed over the last 50 years. This expansion is usually a result of increased land-water loads of key pollutants (e.g., organic matter and inorganic nutrients) derived from human activities such as population growth and associated sewage discharges, expanded use of fertilizers, and increased release of nutrients into the atmosphere from the burning of fossil fuels and animal agriculture. Because dead zones can negatively affect aquatic ecosystems in broad (many organisms suffer) and pronounced (many are killed) ways, efforts to remediate these zones have increased in recent years (Kemp et al. 2009)--many of which have focused on changing human activities on land and in the water. Scientific efforts to understand dead zones require the cooperation and collaboration of experts from many different disciplines. As a result, this topic is well suited for a range of science classes, including biology, physics, chemistry, ecology, and environmental science. In this article, we present a series of small-group activities and investigations that use readily available materials to explore the various causes of dead zones. All of the activities require some degree of teacher supervision and are best performed in the suggested sequence. From these activities, students gain both scientific training and a greater appreciation for an important socioeconomic problem. Biology and dead zones Phytoplankton are free-living, microscopic plants that inhabit all water bodies--they are responsible for the green color of most lakes, ponds, and coastal waters. …