Impact of Global Warming on Coastal Wetlands
Professor’s comment: Jane wrote this research paper for my Advanced Composition course. The assignment asks the students to read and understand six to ten articles within a research area of their choice, then synthesize the information so that a reader can quickly understand the present state of research in that area. Jane chose to look at how increased flooding and salinity might affect coastal wetland soils and species, and she organized the material clearly and effectively. What I liked particularly about this review was that it moved logically from the effects of flooding and salinity on wetland soils to the effects on the plants growing there to the overall effects on the wetland, both in terms of species composition and, more drastically, wetland survival. The tie-in with global climate change puts this local chain of cause and effect into a larger perspective.
Global climate change, rising sea levels and anthropogenic factors are creating increased flooding and salinity levels in coastal wetland areas. (Conner, 1994; Flynn et al., 1995; Webb et al., 1995; Conner and Askew, 1993; Allen et al., 1995; McCarron et al., 1998; Baldwin and Mendelssohn, 1998). Increased flooding and salinity levels can affect wetland soil parameters, and in turn, wetland associated plant species (Baldwin and Mendelssohn, 1998). Although some species are more tolerant to these conditions, most species demonstrate physiological responses and decreased survival at increased flooding and salinity levels. Therefore, changes in wetland species composition are expected unless intolerant species can adapt to heightened flooding and salinity levels imposed by changing environmental and global conditions (Allen et al., 1995).
Changes in Soil Parameters due to Increased Flooding and Salinity Levels
Because flooding creates anaerobic soil conditions, it decreases soil redox potential, Eh(Flynn et al., 1995; Webb, et al., 1995; Baldwin and Mendelssohn, 1998). Additionally, Ehhas been shown to decrease even further when soils are flooded with increased salinity levels (Baldwin and Mendelssohn, 1998; Flynn et al., 1995). Under these conditions, the soil medium becomes highly reducing and can affect wetland vegetation in two ways. First, and probably most significant, is the reduction of sulfate (present in seawater) to hydrogen sulfide, a known phytotoxin that has been shown to reduce wetland vegetation growth and/or survival at higher concentrations (Flynn et al., 1995). Secondly, highly reducing conditions can interfere with a plant’s ability to uptake nitrogen by altering its form and availability in the soil (Webb et al., 1995).
Other problems created by high salinity soil conditions include the change in water potential necessary for the plant to overcome the elevated salt concentration in the soil, and the possibility of toxicity due to uptake of Na+ and Cl– ions (Flynn et...