The relationship between biodiversity and wetland cover varies across regions of the conterminous United States
Jeremy S. Dertien, Stella Self, Beth E. Ross, Kyle Barrett, and Robert F. Baldwin
Summarized by Habiba Rabiu, a student of environmental geosciences at Fort Hays State University. Habiba is interested in all aspects of environmental science and conservation & sustainability. She would like to work in educating others about those topics. In her free time, she likes to read, write, and bake.
What data were used? Using data from the National Wetlands Inventory and the National Land Cover Database, the researchers modeled wetland cover for the conterminous (continental 48) United States and collected estimates for how much wetland existed in the continental U.S. in 2001 and 2011. From various other sources they compiled more information essential to understanding wetland habitats: which animal species live in the areas and their distribution/ranges, the average temperatures and precipitation levels of the wetlands, and the elevation or altitude.
Methods: The maps showing the ranges of the endemic (native) birds, mammals, reptiles, and amphibians were accumulated into one endemics raster (a grid where each cell represents a piece of data) for analysis. Each cell represented a 10×10 km area, so the estimated amount of wetland cover (in hectares) per every 100 km² was the focus. Wetlands smaller than 0.01 hectares and large bodies of water were removed from the data to prevent flawed or biased results.
To calculate wetland change, the researchers subtracted the wetland cover estimates of 2011 from the 2001 coverage to calculate the 10-year change. To calculate per-cell percentage change of wetland cover they divided the 2001 wetland cover per cell by the estimate of 10-year wetland change.
Results: The proportional wetland cover varied from 0.0 to 5841.0 ha/100 km² across all 48 states considered. The area with the most wetland cover was the southeastern U.S. including portions of Alabama, Georgia, Florida, and North and South Carolina. The three areas with significant percentages of wetland cover were Florida, particularly in the northern part of the state and in the Everglades National Park, the floodplain of the Mississippi Valley, and parts of northern Minnesota and Wisconsin. The western U.S. had the least wetland cover with areas of less than 100 ha/100 km² in the Mojave and Sonoran Deserts. Between 2001 and 2011, wetland coverage decreased by approximately 481,500 ha. The highest percentage of loss was in the Great Plains region.
The models for the four animal groups showed regional hotspots where proportional wetland cover was positively or negatively correlated with species diversity. There was no consistent relationship between wetland cover and species variety across the entire 48 states, but on a regional scale there were correlations. Birds, reptiles, and endemic species groups all showed large areas of positively significant correlation with wetland cover while mammals and reptiles showed relatively larger negatively significant correlations.
Why is this study important? While wetlands all over the United States should be protected, certain areas are in a more delicate balance than others simply due to how many organisms rely on them. Knowing which regions have the most wetland cover and biodiversity can indicate where efforts of conservation and restoration should be particularly focused to have the most valuable impact.
The big picture: Wetlands are important habitats and migratory stops for wildlife and provide essential services to the environment including carbon sequestration, water filtration, nutrient retention, and flood mitigation. The loss of wetlands in the U.S. to human activity and urban development has already been significant. The prevention of further damage has to begin with providing clear and concise information about the wetlands and the resources they provide.
Citation: Dertien JS, Self S, Ross BE, Barrett K, Baldwin RF (2020) The relationship between biodiversity and wetland cover varies across regions of the conterminous United States. PLoS ONE 15(5): e0232052. https://doi.org/10.1371/journal.pone.0232052