7 Environmental Systems and Ecosystem Ecology Part A PowerPoint® Slides prepared by Jay Withgott and Kristy Manning Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

This lecture will help you understand: The nature of systems Ecosystem-level ecology Nutrient cycles: C, P, N The hydrologic cycle Plate tectonics and the rock cycle

Central Case: The Gulf of Mexico’s “Dead Zone” Major fisheries off Louisiana were devastated by die-offs. Scientists found large regions of low oxygen in the Gulf. The recurring “dead zone” resulted from nitrogen pollution traveling down the Mississippi River.

Earth’s environmental systems Our planet consists of many complex, large-scale, interacting systems. System = a network of relationships among a group of parts, elements, or components that interact with and influence one another through the exchange of energy, matter, and/or information

Feedback loops: Negative feedback Feedback loop = a circular process whereby a system’s output serves as input to that same system In a negative feedback loop, output acts as input that moves the system in the opposite direction. This compensation stabilizes the system

Feedback loops: Positive feedback In a positive feedback loop, output acts as input that moves the system further in the same direction. This magnification of effects destabilizes the system.

Dynamic equilibrium, homeostasis Dynamic equilibrium = when processes in a system move in opposite directions at equivalent rates so their effects balance out This can contribute to Homeostasis = tendency of a system to maintain constant or stable internal conditions Earth’s climate and an animal’s body are examples of homeostatic systems in dynamic equilibrium.

Emergent properties Properties of a whole system not evident in the system’s components “The whole is more than the sum of its parts.” A tree is an element of a forest, a sink for CO2, and habitat for birds.

Closed and open systems Closed system = isolated and self-contained Open system = exchanges energy, matter, and information with other systems It is useful to think of Earth as a closed system. But any system is open if we examine it closely enough or long enough.

An environmental system Mississippi River as a system: Emergent properties Input of water, fish, pollution, etc. Output to Gulf of Mexico

Two systems or one? The Mississippi River system and the system of the Gulf of Mexico interact. Understanding the dead zone requires viewing the Mississippi River and the Gulf of Mexico as a single system. This holistic kind of view is necessary for comprehending many environmental issues and processes.

Increasing nitrogen inputs Amount of nitrogen fertilizer used rose greatly, 1950–80 Nitrate concentrations in Midwestern rivers in 1980–98 were much more than in 1905–07.

Eutrophication Key to the dead zone = Eutrophication: excess nutrient enrichment in water, which increases production of organic matter... … which when decomposed by oxygen-using microbes can deplete water of oxygen.

Creation of the hypoxic dead zone Nitrogen input boosts phytoplankton… …which die and are decomposed by microbes that suck oxygen from water, killing fish and shrimp.

Earth’s structural spheres Lithosphere = rock, sediment, soil below Earth’s surface Atmosphere = air surrounding the planet Hydrosphere = all water—salt and fresh, liquid, ice, and vapor Biosphere = all the planet’s living things, and the abiotic parts of the environment with which they interact