West Back Bay in Biloxi, Mississippi is an oligohaline estuary. Salt-tolerant submerged aquatic vegetation (SAV) and saltmarsh grasses are found ubiquitously throughout this estuary with Vallisneria americana and Juncus roemerianus being the dominant SAV and saltmarsh vegetation. No studies have directly evaluated the role of these vegetation species in the food web. Carbon and sulfur stable isotope analyses were used to identify primary source contributions to fishes Menidia beryllina, Fundulus grandis, and Lepomis macrochirus. Isotopic niche overlap was compared between fishes and basal carbon sources bimonthly from May 2021 through May 2022. Fishes had greater than 50% isotopic niche overlap with SAV compared to fringing saltmarsh. Overlap was less than 23% for Juncus roemerianus and negligible for other saltmarsh species. These results suggest that Vallisneria americana in Back Bay is a primary driver of these fishes’ diets and should be a focus of habitat conservation efforts in oligohaline ecosystems.

Biogenic isoprene plays an important role in tropospheric chemistry. We use HCHO column measurements by the Global Ozone Monitoring Experiment (GOME) to constrain isoprene emissions. Using the global Goddrad Earth Observing SystemChemistry (GEOS-Chem) as the forward model, a Bayesian inversion of GOME HCHO observations from September 1996 to August 1997 is conducted. Column contributions to HCHO from 12 sources including 10 terrestrial ecosystem groups, biomass burning, and industry are considered and inverted for 8 geographical regions globally. The a posteriori solution reduces the model biases for all regions, and estimates the annual global isoprene emissions of 566 Tg C yr-1, ~50% larger than the a priori estimate. Compared to the Global Emissions Inventory Activity (GEIA) inventory (~500 Tg C yr-1), the a posteriori isoprene emissions are generally higher at mid latitudes and lower in the tropics. This increase of global isoprene emissions significantly affects tropospheric chemistry, decreasing the global mean OH concentration by 10.8% to 0.95106 molecules/cm3. The atmospheric lifetime of CH3CCl3 increases from 5.2 to 5.7 years. Positive matrix factorization (PMF), an advanced method for source apportionment, is applied to TRAnsport of Chemical Evolution over the Pacific (TRACE-P) measurements and it is found that cyanogenesis in plants over Asia is likely an important emission process for CH3COCH3 and HCN. This approach also is applied to estimate source contributions to the tropospheric ozone (O3) with Tropospheric Ozone Production about the Spring Equinox (TOPSE) and TRACE-P measurements. The corresponding GEOS-Chem simulations are applied to the same factor-projected space in order to evaluate the model simulations. Intercontinental transport of pollutants is most responsible for increasing trend of springtime O3, while stratospheric influence is the largest contributions to troposperic O3 variability at northern middle and high latitudes. On the other hand, the overall tropospheric contributions to O3 variability are more important at northern low latitudes by long-range transport, biomass burning, and industry/urban emissions. In general, the simulated O3 variabilities are comparable with those of observations. However, the model underestimates the trends of and the contributions to O3 variability by long-range transport of O3 and its precursors at northern middle and high latitudes.