Landscape Ecology

Assessing the Spatial and Temporal Variation in the Estuarine Vegetation Communities at Aransas National Wildlife Refuge (ANWR), TX

Rachel E. Butzler and Stephen E. Davis, III

Understanding the implications of a proposed freshwater diversion from the Guadalupe Estuary is needed because the estuarine wetlands in this system support the endangered Whooping Crane (Grus americana). Our aquatic plant research and monitoring efforts in this estuary target the salt marshes at ANWR utilized by the cranes each winter. Past research indicates that Carolina Wolfberry (Lycium carolinianum) contributes to 21-52% of crane energy intake early in the wintering period. Changes in freshwater inflow patterns to the estuary in addition to other factors such as sea-level rise may affect estuarine salinity and marsh inundation patterns, which can play an important role in determining estuarine marsh vegetation community structure and productivity. We sampled multiple transects and repeatedly sampled macrophyte plots at 3 sites to understand natural spatial and temporal variability in these communities. Overall, the marsh supports a mixed community dominated by species characteristic of high marsh zones. Six of the 15 species were frequently encountered at all 3 sites. The lowest salinity site (Boat Ramp) seems to support the highest diversity, along with the greatest Wolfberry abundance and frequency. Continued sampling and greenhouse experiments will further clarify the role of salinity and inundation in governing marsh community dynamics at ANWR.

Hydrologic Connectivity of Saltwater Ponds Adjacent to Sundown Bay, Aransas National Wildlife Refuge, TX

Carrie J. Miller, Daniel L. Roelke, and Stephen E. Davis III

In many seemingly isolated systems, temporal hydrologic connectivity is important to nutrient renewal and maintaining species richness. Typically seen as isolated, saltwater ponds in the marsh adjacent to Sundown Bay in Aransas National Wildlife Refuge (ANWR) become hydrologically connected during periods of high water, presumably via tidal creeks that bring water from Sundown Bay deeper into the marsh. Understanding the connectivity of these ponds is important for several reasons, including their perceived importance in whooping crane habitat. In order to quantify the extent of hydrologic connectivity among the ponds, a topographical survey of the ponds and the surrounding marsh will be coupled with water level data from tidal creeks and ponds at three locations along Sundown Bay. To examine the effect of hydrologic connectivity on temporal and spatial variability, benthic chlorophyll-a and ash-free dry weight, as well as several other parameters are being measured in five ponds at three sites along Sundown Bay, with the intent of comparing spatial heterogeneity within ponds, between ponds, and between sites.