Contents 



Page 



Chapter Summary 87 



National Trends — Net Loss and Gain 87 



Factors Affecting Wetland Loss 88 



Trend Information 90 



Vegetated Wetland Trends 91 



Freshwater Wetlands 91 



Saltwater Wetlands 93 



Regional Trends 94 



Agricultural Conversions 108 



National Trends in Agricultural Land Use 112 



Chapter 5 References 113 



TABLES 



Table No. Page 



1 1 . Relationship Between Wetland Types Used for This Report 88 



12. Probable Causes of Freshwater Vegetated Wetland Changes 92 



13. Probable Causes of Saltwater Vegetated Wetland Changes 94 



14. Physiographic Regions Used for Regionad Analysis of 



National Wedand Trends Study Data 95 



15. Pattern of Wetland Loss by Physiographic Region 96 



16. Percentage of Vegetated Wetland Loss to Different Uses 



by Physiographic Region 97 



17. Wedand Case Study Sites 98 



18. Agricultural Conversions of Wetlands 100 



19. Conversions of Wetlands to Open- Water and Deep- Water Environments 102 



20. Wetland Losses From Urban Development 104 



21. Wetland Losses From Other Activities 106 



22. Surface and Subsurface Drainage of Farmland, 1900-1980 109 



FIGURES 



Figure No. Page 



6. Changes in Wedands Since the 1950's 88 



7. Freshwater Wetland Trends 92 



8. Saltwater Wetland Trends 93 



9. Physical Subdivisions 95 



