This Dynamic Earth
This USGS website discusses the history, theory, science, and impacts of plate tectonics on people.
http://pubs.usgs.gov/publications/text/dynamic.html

The Rock Cycle
Featuring a clickable map, this site provides a general explanation of the rock cycle with more detail provided as needed.
http://www.science.ubc.ca/~geol202/rock_cycle/rockcycle.html

NASA's Observatorium - The Hydrologic Cycle
This NASA website features animations of the different phases of the hydrologic cycle. Other earth related phenomena are also described at this site.
http://observe.arc.nasa.gov/nasa/earth/hydrocycle/hydro1.html

Issues in Ecology
Human alteration of the global nitrogen cycle: Causes and consequences. This article authored by well known environmental scientists discusses the nitrogen cycle and its disruption by human activity.
http://www.sdsc.edu/ESA/tilman.htm

Goddard Institute for Space Studies
This NASA website addresses the issue of increased atmospheric carbon dioxide and rising global temperatures resulting from human activities.
http://www.giss.nasa.gov

National Water Quality Assessment Program
This site is the homepage of NAWQA which is a USGS program that deals with water quality problems in 50 major rivers and aquifers throughout the U.S. Emphasis is on the development of long-term data that are comparable across basins and through time.
http://water.usgs.gov/nawqa

Gulf of Mexico Program
This EPA program is designed to protect water and habitat quality in the Gulf of Mexico.
http://www.epa.gov/gmpo

Department of Earth Sciences and Geology, Stockholm University
Research and courses focus on element cycling and environmental processes. Fields of special interest are the biogeochemistry of the Baltic Sea, origin of life, and the rise of oxygen in the atmosphere. Special interest is also given to environmental issues associated with bacterial activity, e.g., acid mine drainage and bioremediation of soils. Web site has on-line publications on these topics.
http://www.geo.su.se/ehome.html

Environmental Sciences Division at Oak Ridge National Laboratory (ESD ORNL)
The Microbial Biogeochemistry and Biotechnology Group focuses on basic microbial ecology and bioremediation. The web site provides access to publications about these areas of research.
http://www.esd.ornl.gov/research/mbb.html

National Center for Atmospheric Research (NCAR)
NCAR conducts atmospheric and related research programs, including biogeochemistry. NCAR is sponsored by the National Science Foundation. The web site provides access to NCAR sponsored research papers.
http://www.ncar.ucar.edu

Oak Ridge National Laboratory (ORNL)
ORNL is a multiprogram science and technology laboratory managed for the U.S. Department of Energy by UT-Battelle, LLC. Scientists and engineers at ORNL conduct basic and applied research and development. The web site provides access to publications and journals.
http://www.ornl.gov