Evaluation of the potential impacts of the proposed Mobile Harbor navigation channel expansion on the aquatic resources of Mobile Bay, Alabama

Abstract

This report assesses potential impacts to aquatic resources resulting from proposed navigation channel expansion activities within Mobile Bay, Alabama. This work was conducted for the U.S. Army Corps of Engineers (USACE) Mobile District, to support development of a supplemental Environmental Impact Statement. Changes in water quality and hydrodynamics were evaluated for potential impacts to benthic macroinvertebrates, wetlands, submerged aquatic vegetation, oysters, and fish. The assessment includes extensive characterization of baseline conditions, evaluation of estimated post-project conditions related to aquatic resource habitat (e.g., changes in salinity, dissolved oxygen). An analysis of potential impacts related to a 0.5-m sea level rise (SLR) scenario were also evaluated. Results suggest that no substantial impacts in aquatic resources within the study area are anticipated due to project implementation, as the area of greatest potential changes to environmental conditions are already adapted to natural shifts in salinity (and other factors), and to conditions resulting from the existing navigation channel. Although SLR has the potential to alter aquatic resource habitats with Mobile Bay, additional impacts related to project implementation remain negligible under the 0.5-m SLR scenario. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.

Gulf Sturgeon (Acipenser oxyrinchus desotoi) in the Mobile Bay Estuary, Alabama: Documentation of Use Outside of Designated Critical Habitat

“…Subadult and adult GS exclusively feed in marine environments, because they must consume sufficient prey items to regain weight loss during riverine fasting, maintain positive growth, and have sufficient energy for spawning (Fox, Hightower, and Parauka, 2002;Gu et al, 2001;USFWS and NOAA, 2003). The Mobile Bay Estuary has sediment characteristics similar to previously identified foraging habitats in the Mississippi Sound that have been found to be used by both western and eastern river system GS (Berkowitz et al, 2020;Ross et al, 2009;Wilber, Peterson, and Slack, 2019). In addition, sediment and benthic macroinvertebrate sampling in the Mobile Bay Estuary identified GS prey items within this system (Berkowitz et al, 2020).…”

“…The Mobile Bay Estuary has sediment characteristics similar to previously identified foraging habitats in the Mississippi Sound that have been found to be used by both western and eastern river system GS (Berkowitz et al, 2020;Ross et al, 2009;Wilber, Peterson, and Slack, 2019). In addition, sediment and benthic macroinvertebrate sampling in the Mobile Bay Estuary identified GS prey items within this system (Berkowitz et al, 2020). Therefore, the nonanomalous occurrence of up to 47.7% of tagged GS detected in the Mobile Bay Estuary (Figure 4) indicates this system is used by GS as foraging habitat.…”

“…Previous studies have identified known GS prey items (i.e. polychaetes and amphipods) within the Mississippi Sound from Dauphin Island to Gulf Shores, Alabama, and in the mouths of the Tensaw, Mobile, and Alabama Rivers (Berkowitz et al, 2020;Wilber, Peterson, and Slack, 2019). Furthermore, the Mobile Bay Estuary was noted as a potential overwinter feeding habitat for juvenile GS (Sulak et al, 2016), andParauka, Duncan, andLang (2011) tracked 43 tagged adult GS to the mouth of Mobile Bay proper.…”

Connecting coastal wetland microbial community characteristics with soil physicochemical properties across an estuarine salinity and vegetation gradient in Mobile Bay, AL, USA

“…Each collection day ran ~1000-1400 to align with lowest possible water levels (<30 cm) and to keep daily tidal inundation between sites as consistent as possible. Sample locations were identified using wetland plant community maps described in Berkowitz et al (2020), targeting the commonly encountered wetland types in the Bay while representing the wide gradient of vegetation salinity tolerances observed in the region (tolerance values derived from USDA, 2000). The elevation distribution of wetland plant communities was determined based on digital elevation mapping (Berkowitz et al, 2020).…”

“…Sample locations were identified using wetland plant community maps described in Berkowitz et al (2020), targeting the commonly encountered wetland types in the Bay while representing the wide gradient of vegetation salinity tolerances observed in the region (tolerance values derived from USDA, 2000). The elevation distribution of wetland plant communities was determined based on digital elevation mapping (Berkowitz et al, 2020). Samples were all collected within <50 km proximity of each other (Figure 1).…”