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ABSTRACT Ryu, J.; Bianchette, T.A.; Liu, K.-B.; Yao, Q., and Maiti, K.D., 2018. Palynological and Geochemical Records of Environmental Changes in a Taxodium Swamp near Lake Pontchartrain in Southern Louisiana (USA) during the Last 150 Years. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 381–385. Coconut Creek (Florida), ISSN 0749-0208. The hydrological and environmental histories of estuarine wetlands in southern Louisiana are not well-documented. To better understand their local developmental processes, a 59 cm sediment core (WMA-1) was extracted from a bald cypress (Taxodium distichum) swamp located approximately 800 m west of Lake Pontchartrain. This area has been heavily influenced by human activities, and is susceptible to inundation from storm surges from Lake Pontchartrain as well as fluvial and lacustrine processes. 210Pb analysis indicates that WMA-1 has a sedimentation rate of 0.39 cm/year, consistent with the detection of a 137Cs peak at 18 cm depth. Sedimentological and geochemical analyses reveal two distinct sedimentological facies: an organic-rich dark brown peat unit from 0 to 29 cm containing low concentrations of terrestrial elements (e.g., Ti, and Fe), and a clay unit from 29 to 59 cm with elevated concentrations of most elements (e.g., Sr, Cl, Ti, Mn, and Fe). The pollen assemblage in the clay section is dominated by TCT (mainly Taxodium), but it is replaced by Salix and wetland herbaceous taxa in the overlying peat. The Taxodium swamp was present at the site at least 150 years ago, and was replaced by Salix and other bottomland hardwood trees and wetland herbs due to a decrease in water level around AD 1940. While climate may have played a role, this hydrological change was most likely caused by the significant regional human activities during the last 100 years. Two thin clay layers (at 3–5 cm, 14–19 cm) embedded in the upper peat section were likely deposited from hurricanes Isaac (2012) and Betsy (1969): two events responsible for heavy rain and significant storm-surge flooding. Our findings suggest that human activities are capable of altering local wetland hydrology and ecology, while the clay layers represent hurricane-induced floods at the site during the past century. [ABSTRACT FROM AUTHOR]

Ryu, J.; Bianchette, T.A.; Liu, K.-B.; Yao, Q., and Maiti, K.D., 2018. Palynological and Geochemical Records of Environmental Changes in a Taxodium Swamp near Lake Pontchartrain in Southern Louisiana (USA) during the Last 150 Years. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 381–385. Coconut Creek (Florida), ISSN 0749-0208. The hydrological and environmental histories of estuarine wetlands in southern Louisiana are not well-documented. To better understand their local developmental processes, a 59 cm sediment core (WMA-1) was extracted from a bald cypress (Taxodium distichum) swamp located approximately 800 m west of Lake Pontchartrain. This area has been heavily influenced by human activities, and is susceptible to inundation from storm surges from Lake Pontchartrain as well as fluvial and lacustrine processes. 210Pb analysis indicates that WMA-1 has a sedimentation rate of 0.39 cm/year, consistent with the detection of a 137Cs peak at 18 cm depth. Sedimentological and geochemical analyses reveal two distinct sedimentological facies: an organic-rich dark brown peat unit from 0 to 29 cm containing low concentrations of terrestrial elements (e.g., Ti, and Fe), and a clay unit from 29 to 59 cm with elevated concentrations of most elements (e.g., Sr, Cl, Ti, Mn, and Fe). The pollen assemblage in the clay section is dominated by TCT (mainly Taxodium), but it is replaced by Salix and wetland herbaceous taxa in the overlying peat. The Taxodium swamp was present at the site at least 150 years ago, and was replaced by Salix and other bottomland hardwood trees and wetland herbs due to a decrease in water level around AD 1940. While climate may have played a role, this hydrological change was most likely caused by the significant regional human activities during the last 100 years. Two thin clay layers (at 3–5 cm, 14–19 cm) embedded in the upper peat section were likely deposited from hurricanes Isaac (2012) and Betsy (1969): two events responsible for heavy rain and significant storm-surge flooding. Our findings suggest that human activities are capable of altering local wetland hydrology and ecology, while the clay layers represent hurricane-induced floods at the site during the past century. [ABSTRACT FROM AUTHOR]

Despite the large number of tsunamis that impact Mexico’s Pacific coast, stratigraphic studies focusing on geological impacts are scanty, making it difficult to assess the long-term risks for this vulnerable region. Surface samples and six cores were taken from Laguna Mitla near Acapulco to examine sedimentological and geochemical evidence for marine incursion events. Sediment cores collected from behind the beach barrier are dominated by intercalated layers of peat and inorganic sediments, mostly silt and clay, with little or no sand. Sand- and shell-rich clastic layers with high levels of sulfur, calcium, and strontium only occur adjacent to the relict beach ridge remnants near the center of the lagoon. With the exception of one thin fine sand layer, the absence of sand in the near-shore cores and the predominance of the terrigenous element titanium in the inorganic layers, evidently eroded from the surrounding hillslopes, suggests that these large-grained intervals do not represent episodic marine incursions, but rather were likely formed by the erosion and redeposition of older marine deposits derived from the beach ridge remnants when water levels were high. These results do not support the occurrence of a large tsunami event at Laguna Mitla during the Late Holocene. [ABSTRACT FROM AUTHOR]

Wang, L.; Bianchette, T.A., and Liu, K.-b., 2019. Diatom evidence of a paleohurricane-induced coastal flooding event in Weeks Bay, Alabama, USA. Journal of Coastal Research, 35(3), 499–508. Coconut Creek (Florida), ISSN 0749-0208. Sand layers deposited in coastal backbarrier lakes and marshes have been taken as indicators of overwash processes generated by hurricane landfalls, but sand layers discovered in sediments from non-backbarrier estuarine settings have not been as thoroughly investigated. Sedimentological and diatom analyses of a 44-cm core (WB 08-04) taken from a seep forest on the north shore of Weeks Bay in southern Alabama contains an 8-cm-thick sand layer embedded in dark gray peat. As an aid to determining the provenance of the sand layer, diatoms were also analyzed from eight surface samples taken from five nearby environments representing different salinity conditions. The diatom assemblage in the sand layer is dominated by acidophilous (Eunotia spp., Frustulia krammeri) and freshwater (Pinnularia neomajor, Pinnularia latevittata) species, suggesting that they were transported by fluvial processes from the acidic and freshwater bogs above the banks of Fish River. The sand layer also contains small percentages of brackish and marine diatoms (Tryblionella marginulata, Planothidium delicatulum), suggesting that incursion of seawater and brackish water from Weeks Bay and Mobile Bay also played a role in its deposition. It is inferred that the sand layer was deposited by a hurricane that brought both intense precipitation to coastal Alabama and a storm surge into Weeks Bay. Heavy rainfall caused overbank flooding of Fish River, which transported sand from the river banks and diatoms from nearby bogs to the coring site. Concurrently, storm surge waters also deposited marine and brackish diatoms at the site. Historical records suggest that the Bernard Romans' Gulf Coast Hurricane in AD 1772 may have been responsible for the flooding that resulted in the deposition of the sand layer. [ABSTRACT FROM AUTHOR]

Hurricanes play an important role in shaping the coast of Louisiana. Although the sedimentary signatures of hurricane deposits have been documented in several different coastal environments along the northern Gulf coast, no studies have as yet documented the signatures in wetlands adjacent to large, inland brackish water bodies. In this paper we present results of a case study documenting the distribution and characteristics of storm surge deposits related to Hurricane Isaac (2012) in a wetland on the western shore of Lake Pontchartrain, Louisiana. Hurricane Isaac, a category1 storm, made landfall near the mouth of the Mississippi River on August 28, 2012. Due to its large size and slow movement, Isaac generated strong easterly winds across Lake Pontchartrain, producing a large storm surge along the west shore of the lake and unprecedented flooding in the surrounding lowlands. Loss-on-ignition, XRF, radioisotopic, and grain-size analyses conducted on sediment cores and surface samples from the area identify two distinct sedimentary signatures for the Hurricane Isaac deposits. Near the lake shore the signature is characterized by a laminated silty sand with a geochemical profile closely resembling that of lake bed material. Storm deposits located in a brackish swamp ~ 1km inland consist of a dark, low-organic mud with low concentrations of terrestrial metals and elevated concentrations of Br, S, and Cl. Differences in the storm signal are explained by the differing effect of topographical features on the depositional and transportation processes occurring at the two sites. Utilizing the geochemical/compositional signatures as a hurricane-generated storm surge proxy indicates the possible occurrence of a similar event predating the historical record. [ABSTRACT FROM AUTHOR]

Liu, K.., McCloskey, T.A., Bianchette, T.A., Keller, G., Lam, N.S.N., Cable, J.E., Arriola, J. 2014. Hurricane Isaac Storm Surge Deposition in a Coastal Wetland along Lake Pontchartrain, Southern Louisiana. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 266-271, ISSN 0749-0208. Hurricanes play an important role in shaping the coast of Louisiana. Although the sedimentary signatures of hurricane deposits have been documented in several different coastal environments along the northern Gulf coast, no studies have as yet documented the signatures in wetlands adjacent to large, inland brackish water bodies. In this paper we present results of a case study documenting the distribution and characteristics of storm surge deposits related to Hurricane Isaac (2012) in a wetland on the western shore of Lake Pontchartrain, Louisiana. Hurricane Isaac, a category1 storm, made landfall near the mouth of the Mississippi River on August 28, 2012. Due to its large size and slow movement, Isaac generated strong easterly winds across Lake Pontchartrain, producing a large storm surge along the west shore of the lake and unprecedented flooding in the surrounding lowlands. Loss-on-ignition, XRF, radioisotopic, and grain-size analyses conducted on sediment cores and surface samples from the area identify two distinct sedimentary signatures for the Hurricane Isaac deposits. Near the lake shore the signature is characterized by a laminated silty sand with a geochemical profile closely resembling that of lake bed material. Storm deposits located in a brackish swamp ~ 1km inland consist of a dark, low-organic mud with low concentrations of terrestrial metals and elevated concentrations of Br, S, and Cl. Differences in the storm signal are explained by the differing effect of topographical features on the depositional and transportation processes occurring at the two sites. Utilizing the geochemical/compositional signatures as a hurricane-generated storm surge proxy indicates the possible occurrence of a similar event predating the historical record. [ABSTRACT FROM AUTHOR]

The northern Gulf of Mexico shoreline is rapidly retreating, and coastal features of the abandoned Mississippi River delta complexes are eroding and subsiding. Bay Champagne is located in the Caminada-Moreau headland, a region located west of the currently active delta that has one of the highest rates of retreat and land loss globally. As a result, the shoreline at Bay Champagne has retreated more than two kilometers in the past 130 years, causing a gradual transition from a stable, circular freshwater lake to a frequently disturbed, semi-circular backbarrier lagoon. Analyses of clastic layers in a series of sediment cores collected at this site over the past decade indicate the lake was less perturbed in the past and has become increasingly more sensitive to marine incursion events caused by tropical cyclones as the shoreline retreated. Geochemical and pollen analyses of the cores also reveal profound changes in environmental and chemical conditions at Bay Champagne over the past century. Through relating stratigraphy to spatial changes observed from satellite imagery, this study establishes a timeline of the transition of Bay Champagne from an inland lake to a backbarrier environment, and demonstrated that these changes have not occurred at a constant rate. These results provide a case-study of changing local environmental conditions in response to rapid shoreline retreat, and therefore serve as a model for future coastal changes for Louisiana and other Gulf coastal areas. [Display omitted] • The shoreline at Bay Champagne (LA) retreated >2 km over the last century. • Maps and imagery detail a transition from freshwater lake to brackish lagoon. • Geochemical results from sediment cores also show a lake to lagoon transition. • Linking shore retreat with stratigraphy serves as a model for future changes. [ABSTRACT FROM AUTHOR]

To understand the geological processes induced by tropical cyclones, geochemical and sedimentological analyses were performed on a 3 m sediment core (basal 14C date of 940 +/- 50 years BP) extracted from a marsh adjacent to a backbarrier lake along Louisiana's Gulf of Mexico coast (USA). This study was conducted in order to identify the geologic changes within a subsiding coastal region in the light of coastal recession and past hurricane activity. Previous studies show that Bay Champagne, a semi-circular lake near Port Fourchon, Louisiana, is subjected to subsidence rates between 1.0 and 1.2 cm year-1, the highest rate of retreat within the entire northern Gulf of Mexico. Loss-on-ignition (LOI) and X-ray fluorescence (XRF) analyses, employed to generate lithological and geochemical core profiles, identified three distinct sand layers measuring up to 50 cm in thickness deposited by recent hurricanes. LOI shows large decreases in water, organic, and carbonate contents, indicating the occurrence of marine inundation. Within each marine incursion layer terrestrial elemental concentrations as determined by XRF display large depletions. Grain size analysis of a portion of the core (30-86 cm) indicates the presence of two series of sequential high-energy storm deposits followed by intense fluvial flooding within Bay Champagne. These events are attributed to Hurricanes Katrina/Rita in 2005 and Gustav/Ike in 2008. [ABSTRACT FROM AUTHOR]

Naquin, J.D., Liu, K.B., McCloskey, T.A., Bianchette, T.A., 2014. Storm Deposition Induced by Hurricanes in a Subsiding Coastal Zone. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium(Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 308-313, ISSN 0749-0208. To understand the geological processes induced by tropical cyclones, geochemical and sedimentological analyses were performed on a 3 m sediment core (basal 14C date of 940 +/− 50 years BP) extracted from a marsh adjacent to a backbarrier lake along Louisiana's Gulf of Mexico coast (USA). This study was conducted in order to identify the geologic changes within a subsiding coastal region in the light of coastal recession and past hurricane activity. Previous studies show that Bay Champagne, a semi-circular lake near Port Fourchon, Louisiana, is subjected to subsidence rates between 1.0 and 1.2 cm year−1, the highest rate of retreat within the entire northern Gulf of Mexico. Loss-on-ignition (LOI) and X-ray fluorescence (XRF) analyses, employed to generate lithological and geochemical core profiles, identified three distinct sand layers measuring up to 50 cm in thickness deposited by recent hurricanes. LOI shows large decreases in water, organic, and carbonate contents, indicating the occurrence of marine inundation. Within each marine incursion layer terrestrial elemental concentrations as determined by XRF display large depletions. Grain size analysis of a portion of the core (30-86 cm) indicates the presence of two series of sequential high-energy storm deposits followed by intense fluvial flooding within Bay Champagne. These events are attributed to Hurricanes Katrina/Rita in 2005 and Gustav/Ike in 2008 [ABSTRACT FROM AUTHOR]