Identification of Hydrologic Controls on Coastal Spartina patens Marshes and Optimal Hydrological Conditions for Sustainable Mottled Duck Habitat

Science Center Objects

Mottled ducks rely on the coastal marshes of the Texas Chenier Plain, which are considered among the most critically endangered habitats in the United States. USGS scientists are evaluating what might be contributing to the degradation of high-quality mottled duck habitat to better understand the causes of habitat loss and subsequently mitigate those losses.

Mottled duck habitat

In hydrologically stressed Spartina patens marshes, plants begin to grow in hummocks, or areas of higher elevation. Over time, the hollows, or the low-lying unvegetated areas between the hummocks, continue to expand until the area is dominated by open water and the mottled duck habitat is lost.

(Public domain.)

The Science Issue and Relevance: Although the Texas Chenier Plain coastal marshes were historically characterized as high-quality habitats for mottled ducks (Anas fulvigula), this critical habitat has been impacted by natural and anthropogenic changes that have resulted in declines. Because of the cumulative and synergistic effects of hydrologic alterations, urbanization, and invasive species encroachment, now this habitat is considered among the most critically endangered habitats in the United States. Specifically, in the McFaddin National Wildlife Refuge (Texas), Spartina patens brackish marshes are rapidly deteriorating, resulting in low quality habitat for mottled ducks and, in some cases, complete habitat loss. Thus, to effectively mitigate the losses of mottled duck habitat, the optimal conditions for vegetation growth need to be clearly identified.

 

Methodology for Addressing the Issue:  Environmental conditions in three healthy and three degraded S. patens brackish marshes will be compared to identify factors contributing to the degradation of mottled duck habitat in McFaddin NWR. Determining these factors is critical to understanding the causes of habitat loss and subsequently mitigating those losses.

 

Future Steps: To further ensure the sustainability of this critical habitat, it is also necessary to understand what conditions contribute to optimal habitat function. The study will quantify the relationship between elevation, salinity, and plant community composition across elevation and salinity gradients across three marsh types (fresh, brackish, and salt marshes) within the Texas Point NWR. This data will help establish a baseline of hydrologic conditions that will allow managers to optimize plant vegetation growth and mottled duck habitat.