Pollution and Degradation Environmental impact 12 Sustainability 11 Natural Resource Economics, (New March 2000) 10 Water Resources 10 Forests and Forest Trees (Biology and Ecology) 8 Land Resources 8 Meteorology and Climate 8 Forests 7 Agricultural Economics 6 Agriculture 6 Air pollution 6 Case studies 6 Industrial Wastes and Effluents 6 Phosphorus 6 Plants 6 Policy and Planning 6 Social Psychology and Social Anthropology, (New March 2000) 6 Soil Chemistry and Mineralogy 6 Water pollution 6 Water quality 6 Animal Wastes 5 Aquatic Biology and Ecology 5 Erosion 5 Erosion: Soil and Water Conservation 5 Nitrogen 5 Plant Production 5 Pollution 5 Socioeconomics 5 Soil Fertility 5