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387 Great progress has been made since the mid-1960s to control direct human impacts to coastal wetlands in the United States; and more recently, similar efforts by certain Canadian provinces have helped reduce salt marsh destruction from human activities . Various levels of government in the United States and Canada have enacted laws or policies to protect tidal wetlands to some degree, and the quality of many tidal wetlands has increased through restoration efforts by government agencies and private organizations. While these types of programs and policies have greatly improved the status of coastal wetlands over what they were prior to the 1960s, it must be recognized that laws can be changed by legislative bodies and the effectiveness of regulations at protecting wetlands can be weakened by the courts or by lack of enforcement. Nonetheless, even with existing regulations and policies in effect, serious threats to coastal wetlands remain. Population pressure on coastal resources continues as 53 percent of the U.S. population live in the nation’s coastal counties (Crossett et al. 2004). This represents a 28 percent increase since 1980. Marsh degradation, loss of vegetative buffers, and estuarine enrichment (eutrophication) continue despite regulations that attempt to protect the physical integrity of tidal wetlands. Wetland wildlife is also suffering from these actions as habitat quality is diminished for fish and aquatic invertebrates with negative ­ consequences felt by other organisms through the estuarine food web. Development in coastal watersheds adversely impacts wetland­ animals as well as terrestrial wildlife. It was disheartening to learn the conclusions of a recent study: when coastal watersheds in the Chesapeake Bay region experienced as little as 3.5 percent urban development, there was a significant negative impact on estuarine waterbirds—gulls, waders, raptors, kingfishers , and waterfowl (DeLuca et al. 2008). An earlier study by these researchers found that when 14 percent of the land within 1,640 feet (500 m) of a tidal marsh was developed and 25 percent of the land was developed within 3,280 feet (1,000 m), estuarine marsh bird communities were adversely impacted (DeLuca et al. 2004). If these statistics hold true for other estuaries, the future looks bleak for marsh birds and waterbirds as human population will continue to expand and convert upland forests to residential and commercial development in the coastal zone. Marsh view properties are high-valued real estate. To say that coastal resource planners have significant challenges before them is an understatement. Habitat destruction and degradation by human actions are continuing problems for tidal wetlands, especially in the tropics. While laws and regulations have significantly reduced wetland losses in the United States, pollution (e.g., estuarine eutrophication ) remains an issue for resource managers . The other main threat to tidal wetlands 12 The Future of Tidal Wetlands 388  Chapter 12 worldwide is not a point source that can be stopped by adopting a national wetland conservation policy or by enacting wetland or water quality laws, regulations, or other land use restrictions. Instead, it is a global force brought about by climate change. Increasing concentrations of carbon dioxide (CO2 ), methane, chlorofluorocarbons, and other gases from the burning of fossil fuels, deforestation, and cement manufacture have released sufficient quantities of CO2 to significantly raise the level of this gas in the atmosphere and contribute to global warming . Atmospheric CO2 levels have increased 40 percent from pre-industrial levels (~280 ppm) to current levels (~388 ppm) ( ­ Langley et al. 2009). Annual emissions of CO2 have increased by 80 percent from 1970 to 2004 (Intergovernmental Panel on Climate Change 2007). The International Panel on Climate Change (IPCC) predicts an increase of 2.0° to 11.5°F (1.1°–6.4°C) with a best estimate of 3.2° to 7.2°F (1.8°–4.0°C) by 2100 (IPCC 2007). The effect of global warming on sea level has enormous consequences for coastal wetlands. When water is heated it expands (thermal expansion) and since the Earth is 75 percent water, this process in combination with accelerated melting polar and glacial ice (which adds more water to the oceans) cause a rise in sea level referred to as “eustatic sea-level rise.” Local and regional conditions (e.g., subsidence and tectonic activity) may affect the position of the land relative to sea level. The combined effects of eustatic sea-level rise and local land elevation changes produce what is called “relative sea-level rise” (Figure 12.1). Relative sea-level rise is greater than eustatic sea-level rise where land...

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