Coastal Wetlands in the U.S. and Their Loss to Anthropogenic Causes

Background

 Wetlands can be a wide variety of ecosystems occurring at the transition between terrestrial and aquatic systems water (Coastal Wetlands 2018). Because of the large diversity within the umbrella term wetland, they have several definitions and categorizations created by organizations for accuracy and practicality. For example, the US Army Corps of Engineers Wetland Delineation Manual (1987) defines wetlands as:

“those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions.  Wetlands generally include swamps, marshes, bogs and similar areas.”

The Minnesota Wetland Conservation Act (WCA) defines a wetland as:

“lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water…and must

 (1) have a predominance of hydric soils,

 (2) be inundated or saturated by surface water or groundwater at a frequency and duration sufficient to support a prevalence of hydrophytic vegetation typically adapted for life in saturated soil conditions, and

 (3) under normal circumstances, support a prevalence of hydrophytic vegetation”

 The United States possesses a wide variety of wetlands including tropical rainforests, permafrost underlain wetlands, and riparian wetlands. They occur in every state in the US. In recent years, people have come to understand that wetlands are important for maintaining groundwater, water quality, providing fish and wildlife habitats, protecting shorelines from erosion, modifying climate, trapping sediments and pollutants, and storing water (Coastal Wetlands 2018). Wetlands provide recreational opportunities such as canoeing, wildlife watching, photography, kayaking, fishing, and hunting and certain kinds of wetland ecosystems function as carbon sinks, meaning that they store large amounts of carbon as plants grow rapidly and decompose slowly. However, during colonial times, people did not understand these valuable functions. Since the colonization of the US, wetlands have been regarded as wastelands hindering productive land use, thus people drained them to convert the land to something useful to them (Keizer 2018). Today wetlands in the U.S. are still being lost at twice the rate as they are being restored (Coastal Wetlands 2018).

Wetlands that reside in coastal watersheds, or coastal wetlands in the US warrant special attention as they are at projected risk of irreversible damage. They are experiencing disproportionate losses compared to inland wetlands because of the uneven pattern of human settlement in America among other factors. Nearly forty percent of wetland area in the United States is coastal. That amounts to about 40 million acres (Coastal Wetlands 2018). Humans also tend to live in coastal watersheds; over half of the U.S. population lives in these areas, which represent only 13 percent of acres in the US. The density of human population in coastal counties intensifies the stress on coastal wetlands because of the tendency to develop and expand and the pollution from lawn maintenance, industrial activities, and automobiles (Beach 2002).

Figure 1. Changes in population density in the contiguous United States in coastal and non-coastal counties from 1970 to 2010. Data adapted from NOAA (2012).

 But population growth is not the main problem; the culprit is the way that population develops the land around them. Coastal populations are consuming more and more land each year and building “dysfunctional suburban development patterns.” “Some large coastal metropolitan areas are consuming land ten times as fast as they are adding new residents” (Beach 2002). Additionally, driving has increased across the country disproportionately to the increase in population, leading to the development of more roads and more ecological damage and pollution. In 2000, land consumption occurred as 2.5 times the rate of population growth in the same area. These ideas are important to bear in mind when developing management strategies.

 Coastal wetlands are important to protect because they “are part of a diverse and complex set of ecosystems that are vital to the Nation’s economy”, they protect upland areas from flooding from storms or sea level rise, prevent coastline erosion by stabilizing soil with their root systems, and provide habitat for federally threatened and endangered species (Coastal Wetlands 2018). Alongside the natural animal communities, over 50 percent of southeastern US commercial fish and shellfish rely on coastal wetlands, which are among the most productive in the world. Coastal wetlands also provide food, shelter, nurseries, and breading grounds for a wide variety of terrestrial and aquatic animals as well as 5 percent of the U.S.’s waterfowl and migratory birds (Lellis-Dibble et al. 2008). In fact, in a 1995 report, the USFWS considered nearly 45 percent of endangered and threatened species in the U.S. to be depend on wetland habitats (Coastal Wetlands 2018).

Wetland Loss

 Wetland loss is a result of both natural processes and human activity. Human activities which can lead to loss are silviculture, agriculture, and urban and rural development. These land uses fragment wetlands on a larger scale, introduce pollutions, and change the hydrology of the area, affecting how much water the wetland receives and at what rate. These activities most often affect freshwater wetlands. Some natural processes that affect these wetlands are sea level changes and storms, which lead to erosion and inundation (Coastal Wetlands 2018).

 However, it is clear that human activity has had the most effect on wetlands in the last 200 years. It is estimated that 53 percent of wetland acres in the contiguous US have been lost from the pre-European colonial quantity. On average, that translates to a loss of over 60 acres of wetland every hour from 1780 to 1980. California has lost the most of their original wetlands with 91 percent lost. The mid-western farm belt accounts for over 36 million acres of loss from 1780 to 1980, that’s one third of all wetlands lost in the 200 years (Dahl 1990).

 a. b.

Figure 2. a. Saltwater losses and gains between 2004 and 2009 and the resulting changes in land cover. 94,999 acres of saltwater wetlands were studied (Stedman and Dahl 2008). b. Freshwater wetland losses and gains between 2004 and 2009 and the resulting changes in land cover. 265,723 acres of freshwater wetlands were sampled (Stedman and Dahl 2008).

Between 2004 and 2009, the annual rate of change was 25 percent higher than the rate of change from 1998 to 2004. This increase is statistically significant with a p-value of 0.007. During this time, different regions experienced differing amounts of land cover change, and in fact, reestablishment projects, mostly from agricultural lands, led to some coastal wetland gains. Nonetheless, Stedman and Dahl and others stand by this warning; “continuing losses of wetlands in coastal watersheds have direct costs for people and longer-term resource implications for fish, wildlife and other natural resources” (2008). Researchers are in agreement that the loss of these coastal habitats has diminished the health of their ecosystems and reduced their ability to provide environmental and socioeconomic services (Mazda and Wolanski 2009). There is also general recognition that once wetlands are lost through development, the loss of their functions and values is often irreversible (Mitsch and Gosselink 2000).

 Human activity that is not explicitly developing land can also have effects. The development of land and subsequent population increases lead to the demand for water in that area. For example, tapping a nearby water source for a growing city can potentially reduce the water level in a local wetland and have detrimental effects. One study found that reduced water levels in forested swamps and herbaceous-vegetation marshes led to a sharp decline in the wetlands’ abilities to store atmospheric carbon and nitrogen. “Wetlands with shorter hydroperiods had 50-60% less [wetland soil organic matter], C, and N per kg soil” (Lewis and Feit 2014).

 Development of land in a watershed and conversion of wetland to developed area both leads to damage to remaining wetland systems and impaired or lost ecosystem services from remaining or lost wetlands.

 Coastal development often contributes to land use changes that increases impervious surface area, affecting water quality or disturbing natural habitats through loss or fragmentation (Crawford et al. 2007). This is delicate because the way that water enters a wetland, hydrology, is considered the most important factor in some wetlands. Hydrology strongly affects the wetland’s production and turnover of the organic matter, which is critical to the development and self-maintenance of wetlands (Crawford et al. 2007). Abundant research confirms that when more than 10 percent of a watershed is covered by impervious surfaces (roads, Parking lots, buildings), rivers, creeks, and estuaries in that watershed become biologically degraded (Beach 2002). These surfaces allow rainwater to reach open water systems as runoff instead of percolating down into the water table, and thus carry more sediment, nutrients, and pollutants. The increased rate of runoff changes stream flow patterns and stream channel shape and stability (Booth 1991, Schueler and Holland 2000). The water temperature also increases with increasing impervious surface. As some aquatic creatures are very sensitive to oxygen levels and temperature, the temperature of the water is significant both directly and indirectly because water has a lower affinity to hold oxygen with increasing temperature

 Urban runoff transports pollutants like nitrogen, phosphorous, organic carbon, copper, zinc, lead, petroleum hydrocarbons, and pesticides into water systems (Schueler and Holland 2000). Additional nitrogen in wetland systems can cause algal blooms, the decay of which leads to reduced dissolved oxygen, which can kill fish and invertebrates in that system. Submergent plants can also be disadvantaged by reduced water clarity from overfertilization and dissolved minerals entering the system. Developed watersheds add to a wetland system’s natural input of nitrogen through lawns, golf courses, automobile tailpipes, and municipal wastewater treatment plants (Boesch et al. 2001).

Cars and trucks provide the largest source of metals in runoff, including cadmium, zinc, copper, and lead. Higher traffic has generally been found to correlate with higher levels of stormwater pollution. Even in watersheds with little industrial activity, metals have been found to accumulate in sediments at levels that are toxic to aquatic life. These metals were traced from roads, lawns, and automobiles (Hartwell et al. 2000).

Future Management

 Although the US has made improvements in the rate of wetland loss, some types of wetlands are still experiencing conversion and degradation. Losses have been more recently decreased and reestablishment programs implemented through the Clean Water Act and federal and state protective laws (Dahl 2011). Movements like New Urbanism and Smart Growth and scientific studies offer solutions for coastal management, some of which are at work in cities today, but need large-scale public support to be more widely implemented.

 The technology necessary for metropolitan regions to inventory their watersheds and decide on how to manage them is available through mapping systems and satellite imagery. Regions can analyze development potential and adopt informed land-use policies to protect ecosystems in their area (Beach et al. 2001).

 In his article, Coastal Sprawl, Beach poses this question: which development patterns can sustain aquatic ecosystems? The preservation of wetland ecosystems depends on successfully reforming the development patterns at site, neighborhood, and regional levels. The study concludes that “the central principle of a protection strategy must be to identify those watersheds that are less than 10 percent impervious and attempt to maintain most of them in an undeveloped state. The companion principle is that watersheds with imperviousness of more than 10 percent should absorb the majority of coastal growth over the coming decades.” With regards to meeting environmental aims in developed watersheds, reforms such as reduced car dependency, new paving techniques, and on-site stormwater management can decrease negative effects on surrounding ecosystems (2001).

 Specific forms of development spread management that are in place today are agricultural zoning and urban growth boundaries. These allow for growth within a set boundary designed for 20 years of expansion. If carried out well, these laws can allow for adequate growth within their boundaries without having a significant negative effect on local economy (Beach et al. 2001).

  Beach concludes that “management practices such as nutrient management, rotational grazing, integrated pest management, and buffer strips can substantially reduce the pollutant load from agricultural land uses. These types of practices are essential to healthy aquatic systems. Even though some human practices have caused enormous environmental damage in some coastal areas, such as confined animal feeding operations, “even at its most intense, the problems presented by agriculture [in rural watersheds] can be reversed, if the political will exists to do so”. However, the development in urban settings requires immediate action as “the mistakes made in the next few decades will persist—as will the ecological damage they cause” (Beach et al. 2001).

References:

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