An integrated methodology for assessing ecosystem response to environmental stressors under changing climatic conditions in coastal wetlands.

Three cores were taken along the salinity gradient (n-s) in the coastal wetlands of Louisiana; an intermediate marsh, a brackish marsh, and a mangrove swamp. The cores display remarkable stratigraphic and chronologic correlations, representing six successive ecosystems and environments, namely: interdistributary bay, freshwater marsh/swamp, deltaic lake, freshwater marsh/swamp, intermediate marsh, and brackish/saline. Sedimentary, geochemical, and palynological data were used to reconstruct the paleoenvironments, including ambient environment and ecosystem types. Concentrations of Ba and Br, along with six elemental ratios (Ca/Rb, Zr/Rb, Ti/Rb, K/Ti, Mn/Rb, S/Rb), were employed to infer proxies for a range of environmental conditions (waterlogging, redox levels), depositional processes (fluvial vs marine or in situ), and sediment characteristics (grain size). Correlating the identification of environment types, inferred depositional processes, and the known history of the Mississippi delta cycle with the ecosystem reconstruction provides insight into ecosystem response to a variety of stresses, which information can be used to better understand and predict present and future responses to the ongoing stresses. Additionally, a simple elemental ratio (Zr/Rb) was used to produce a continuous (2 cm resolution) estimate of grain size along the length of the cores. The close correlation between the estimated grain size and measured samples shows that this ratio is a valid method for quickly assessing rough grain size, and is especially useful for identifying sedimentary inflection points.

The use of multivariate PCA dataset in identifying the underlying drivers of critical stressors, looking at global problems through a local lens.

Palynology-based multivariate datasets including geological, ecological, and geochemical data identified the relative importance of the underlying drivers of critical stressors to coastal wetlands by identifying and distinguishing between fluvial flooding, saline water intrusion, delta switching, and the landward migration of coastal plants. A sediment core was retrieved using a vibracorer from an intermediate marsh in Lake Salvador, Louisiana, USA. X-ray Fluorescence (XRF) quantified fluvial and marine elemental concentrations (Cl, Sr, Ca, Mn, K, Ti, Fe, Zn, Zr, Br). Palynology-based agglomerate hierarchical analysis of thirty-two pollen taxa was employed to define ecological clusters. The implementation of multivariate principal component analysis (PCA) to geochemical and ecological variables inferred the source of sedimentary material by correlating four taxonomic groups (floodplain trees, upland trees, tidal freshwater herbs, and inland herbs) to specific geochemical signatures and facilitated the testing of potential correlations between geo- and hydrological-conditions and the six ecosystems (interdistributary, delta-plain, deltaic lake, bottomland and swamp forests, freshwater marsh, and intermediate marsh) depicted in each PCA biplot. The PCA scores quantified the relative importance of multiple variables. The squared cosine function, which demonstrates the relative importance of a variable for a given observation, was used to estimate the representation of each variable on the principal component biplots. Multivariate statistical datasets can be valuable to any scientist working across the spectrum of environmental and planetary science fields as a means of identifying the relative importance of diverse background parameters in controlling ecological and environmental conditions. This methodology is applicable across both natural and social sciences as a means of distinguishing natural and anthropogenic impacts.

Re-Evaluating the Geological Evidence for Late Holocene Marine Incursion Events along the Guerrero Seismic Gap on the Pacific Coast of Mexico.

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.