Elizabeth A. Canuel

A geochemical record of eutrophication and anoxia in Chesapeake Bay sediments: anthropogenic influence on organic matter composition

Abstract Organic and inorganic geochemical indicators were examined in a 3-m core collected from the mesohaline region of Chesapeake Bay (CB) to determine how sources of organic matter (OM) have changed during the preceding three centuries of increasing anthropogenic influence in this region. This study also establishes the history of eutrophication and anoxia/hypoxia and relates these processes to changes in OM deposition and preservation and to historical events within the Bays watershed. The sediment record shows that a marked increase in organic carbon (35%–50%), biogenic silica (18%) and total sulfur (42%) occurs between 1934 and 1948. This transition is likely due to increasing anoxic/hypoxic bottom water conditions as indicated by an abrupt change in sulfur speciation. Lipid biomarker distributions indicate that a substantial change in the sources of OM deposited since 1934 has also occurred. Biomarker compounds derived from phytoplankton and microbial sources show a 2- to 4-fold increase in their abundance relative to total organic carbon (TOC) between 1948 and 1975. Using both diagenetic models and information on lipid reactivity, an effort is made to distinguish compositional changes due to changes in OM delivery (both quantity and quality) from changes that may be due to OM degradation. It appears that enhanced OM production in the mesohaline region of CB has contributed to the observed changes in quantity and character of OM preserved in sediments from this site. Increased inorganic fertilizer application and human population growth in the watershed are coincident with the onset of eutrophic and hypoxic conditions in CB, suggesting that anthropogenic activities within estuarine watersheds may exert a substantial influence on carbon cycling processes in estuaries and potentially the coastal ocean.

Polycyclic aromatic hydrocarbon (PAH) distributions and associations with organic matter in surface waters of the York River, VA Estuary

Abstract Surface water samples were collected along the salinity gradient of the York River, VA Estuary, between June 1998 and April 1999, to examine spatial and temporal variability in particulate polycyclic aromatic hydrocarbon (PAH) concentrations and their interactions with suspended particulate organic matter (POM). Specifically, relationships with source-specific lipid biomarker compounds (sterols and fatty acids) were examined to assess PAH associations with POM and to help elucidate PAH sources and modes of entry into the estuary. Principal component analysis (PCA) revealed that PAHs in the estuary can be classified into three groups: volatile, soot-associated and perylene. The three PAH groups differed in their relationships with particulate organic carbon (POC) as well as with source-specific lipid biomarkers reflecting processes controlling their delivery to the estuary. The more volatile PAHs showed a strong positive correlation with biomarkers for autochthonous (i.e. plankton-derived) POM, but only weak correlations with total POC in spring/early summer. In contrast, all PAHs except perylene were correlated with sterols of vascular plant/freshwater microalgal origin (i.e. allochthonous) during fall/winter. Perylene concentrations decreased from the head to the mouth of the estuary and were correlated with terrestrial biomarkers, suggesting that the freshwater end-member is the dominant source of perylene to this system. The varying relationships between distinct groups of PAHs and lipid biomarkers indicate that very specific pools of POM play an important role in the fate and transport of hydrophobic organic contaminants.

Chemical Biomarkers in Aquatic Ecosystems

Preface xi Acknowledgments xix Chapter 1. Metabolic Synthesis 1 Chapter 2. Chemical Biomarker Applications to Ecology and Paleoecology 19 Chapter 3. Stable Isotopes and Radiocarbon 30 Chapter 4. Analytical Chemical Methods and Instrumentation 49 Chapter 5. Carbohydrates: Neutral and Minor Sugars 79 Chapter 6. Proteins: Amino Acids and Amines 98 Chapter 7. Nucleic Acids and Molecular Tools 127 Chapter 8. Lipids: Fatty Acids 144 Chapter 9. Isoprenoid Lipids: Steroids, Hopanoids, and Triterpenoids 169 Chapter 10. Lipids: Hydrocarbons 185 Chapter 11. Lipids: Alkenones, Polar Lipids, and Ether Lipids 207 Chapter 12. Photosynthetic Pigments: Chlorophylls, Carotenoids, and Phycobilins 221 Chapter 13. Lignins, Cutins, and Suberins 248 Chapter 14. Anthropogenic Markers 267 Appendix I. Atomic Weights of Elements 287 Appendix II. Useful SI Units and Conversion Factors 291 Appendix III. Physical and Chemical Constants 293 Glossary 295 Bibliography 309 Index 385

Relations between river flow, primary production and fatty acid composition of particulate organic matter in San Francisco and Chesapeake Bays: a multivariate approach

Estuarine environments influence particulate organic matter (POM) composition in the coastal zone as regions of high primary production and through their roles in the modification and exchange of organic materials. In this study, fatty acids (FA) associated with surface water particulate organic matter (POM) were collected seasonally and used to identify spatial and temporal variations in organic matter sources within two important estuaries in the USA–San Francisco Bay and Chesapeake Bay. Factor analysis was used to identify the dominant source signatures and the environmental processes important in controlling FA distributions within each estuary. In the San Francisco Bay dataset, Factor 1 explained 29% of the variance and had positive loadings for odd–numbered branched FA (C13, C15, C17 and C19), 16:1ω7 and long-chain FA (LCFA). Factor 1 was also negatively correlated with salinity and temperature,` suggesting that concentrations of these FA were controlled by seasonal fluctuations in freshwater inflow and the delivery of allochthonous materials. In contrast, loadings on Factor 2 (16% variance) in SFB were most positive for 16:0 and 18:0 and most negative for 20:5ω3, 14:0, 16:1ω7 and C16 polyunsaturated FA. These compounds are generally attributed to plankton sources. Factor 2 was inversely correlated with chlorophyll concentrations suggesting it was useful in resolving between FA derived from the spring (diatom) vs. non-spring plankton community. In Chesapeake Bay, Factor 1 explained 24% of the variance and was characterized by high positive loadings for 12:0 and C22 polyunsaturated FA and negative loadings for 16:1ω7 and n- and branched C13, C15 and C17 acids. Factor 1 was significantly correlated with salinity, suggesting it was useful for identifying regional differences in FA composition. Factor 2 (18% of the variance) was weighted positively for 18:1ω9 and negatively for 14:0 and 16:1ω7. This factor was inversely related to samples collected under bloom conditions (chl a>10 μg l−1) and chl a concentrations (r2=0.543; P <0.0001), indicating its usefulness for identifying temporal and regional differences in phytoplankton production and species composition. POM quality was, on average, higher in Chesapeake Bay vs. San Francisco Bay. Concentrations of total FA and polyunsaturated FA were higher in Chesapeake Bay, suggesting that POM is generally more labile and potentially more useful to heterotrophic organisms than in San Francisco Bay. Moreover, POM quality increased along the Chesapeake Bay salinity gradient. Overall, this study demonstrates that biomarker methods can provide insights useful in unraveling the complex factors that control the quality of POM in estuaries, particularly when coupled with environmental data (salinity, temperature and phytoplankton distributions) and multivariate statistical methods.

Influence of natural and novel organic carbon sources on denitrification in forest, degraded urban, and restored streams

Organic carbon is important in regulating ecosystem function, and its source and abundance may be altered by urbanization. We investigated shifts in organic carbon quantity and quality associated with urbanization and ecosystem restoration, and its potential effects on denitrification at the riparian–stream interface. Field measurements of streamwater chemistry, organic carbon characterization, and laboratory-based denitrification experiments were completed at two forested, two restored, and two unrestored urban streams at the Baltimore Long-Term Ecological Research site, Maryland, USA. Dissolved organic carbon (DOC) and nitrate loads increased with runoff according to a power-law function that varied across sites. Stable isotopes and molar C:N ratios suggested that stream particulate organic matter (POM) was a mixture of periphyton, leaves, and grass that varied across site types. Stable-isotope signatures and lipid biomarker analyses of sediments showed that terrestrial organic carbon sources in streams...

Composition of particulate organic matter in the southern Chesapeake Bay: Sources and Reactivity

The distribution of two classes of lipid biomarker compounds (fatty acids and sterols) was used in conjunction with several bulk parameters (total suspended solids, chlorophyll a, and particulate carbon and nitrogen concentrations) to examine spatial and temporal variability in the sources of particulate organic matter (POM) important to southern Chesapeake Bay. Based on these geochemical parameters, we found that suspended and sedimentary organic matter in the southern Chesapeake Bay is derived from autochthonous sources including a mixture of fresh and detrital phytoplankton, zooplankton, and bacteria. The dominant factor contributing to temporal variability during our study was phytoplankton productivity. Enrichments in particulate organic carbon, chlorophyll a, total fatty acids, total sterols, and a number of biomarkers specific to phytoplankton sources were found in particles collected from surface (1 m) and deep (1 m above the bottom) portions of the water column at several sites during the spring bloom in March 1996 and during a localized bloom in July 1995. Comparison of sites at the mouths of two tributaries (York and Rappahannock rivers) to southern Chesapeake Bay with two sites located in the bay mainsterm indicates spatial variation in the composition of POM was not significant in this region of the bay. The energetic nature of this region of the Chesapeake Bay most likely contributes to the observed homogeneity. Comparison with biomarker studies conducted in other estuaries suggests the high levels of productivity characteristic of the Chesapeake Bay contribute to high background levels of POM.

A Pb isotope record of mid-Atlantic US atmospheric Pb emissions in Chesapeake Bay sediments

We have analyzed sediments from three sites in the mesohaline portion of Chesapeake Bay (CB) for Pb isotopes. The well-preserved and well-dated sediments provide an excellent opportunity to compare the anthropogenic Pb isotope record in CB to other Pb isotope records of US industrial atmospheric emissions. Over the past century, there is excellent temporal agreement between anthropogenic CB 206Pb/207Pb isotope ratios and those determined in a dated coral from Bermuda [Earth and Planetary Science Letters, 82 (1987) 289] almost 2000 km away. We use this correlation to argue that CB sediments contain a regional, industrial atmospheric Pb isotope signal that is representative of the mid-Atlantic region of the US. Anthropogenic Pb is found in sediments deposited as early as approximately 1800. From about 1800 to 1930, the Pb signal in the CB sediments is probably derived from the burning of coal. After this period, and up until about the 1980s, the signal is overwhelmed by the Pb derived from the combustion of gasoline.

Effluent organic nitrogen (EON): bioavailability and photochemical and salinity-mediated release.

The goal of this study was to investigate three potential ways that the soluble organic nitrogen (N) fraction of wastewater treatment plant (WWTP) effluents, termed effluent organic N (EON), could contribute to coastal eutrophication--direct biological removal, photochemical release of labile compounds, and salinity-mediated release of ammonium (NH4+). Effluents from two WWTPs were used in the experiments. For the bioassays, EON was added to water from four salinities (approximately 0 to 30) collected from the James River (VA) in August 2008, and then concentrations of N and phosphorus compounds were measured periodically over 48 h. Bioassay results, based on changes in DON concentrations, indicate that some fraction of the EON was removed and that the degree of EON removal varied between effluents and with salinity. Further, we caution that bioassay results should be interpreted within a broad context of detailed information on chemical characterization. EON from both WWTPs was also photoreactive, with labile NH4+ and dissolved primary amines released during exposure to sunlight. We also present the first data that demonstrate that when EON is exposed to higher salinities, increasing amounts of NH4+ are released, further facilitating EON use as effluent transits from freshwater through estuaries to the coast.

Rapid export of organic matter to the Mississippi Canyon

Coastal margins, where rivers serve as the dominant control on productivity and delivery of dissolved and particulate materials, have been understudied.The potential importance of certain river-dominated margins (RiOMars), such as those of the Mississippi River plume, to the global carbon budget is garnering increased attention because of their disproportionate role in transporting terrigenous materials to the ocean [Dagg et al., 2004; McKee et al., 2004]. This study concludes that labile (readily open to chemical, physical, or biological change) sedimentary organic matter, produced by in situ diatom production in the Mississippi River plume, is rapidly transported to the Mississippi Canyon. Despite the notion that canyon sediments are typically unstable and lack adequate food resources to support significant macrobenthic communities, this study suggests that productive RiOMars are important conduits for transporting fixed carbon from highly productive plume waters on the shelf to deeper benthic communities.

Nutrient Enrichment and Food Web Composition Affect Ecosystem Metabolism in an Experimental Seagrass Habitat

Background Food web composition and resource levels can influence ecosystem properties such as productivity and elemental cycles. In particular, herbivores occupy a central place in food webs as the species richness and composition of this trophic level may simultaneously influence the transmission of resource and predator effects to higher and lower trophic levels, respectively. Yet, these interactions are poorly understood. Methodology/Principal Findings Using an experimental seagrass mesocosm system, we factorially manipulated water column nutrient concentrations, food chain length, and diversity of crustacean grazers to address two questions: (1) Does food web composition modulate the effects of nutrient enrichment on plant and grazer biomasses and stoichiometry? (2) Do ecosystem fluxes of dissolved oxygen and nutrients more closely reflect above-ground biomass and community structure or sediment processes? Nutrient enrichment and grazer presence generally had strong effects on biomass accumulation, stoichiometry, and ecosystem fluxes, whereas predator effects were weaker or absent. Nutrient enrichment had little effect on producer biomass or net ecosystem production but strongly increased seagrass nutrient content, ecosystem flux rates, and grazer secondary production, suggesting that enhanced production was efficiently transferred from producers to herbivores. Gross ecosystem production (oxygen evolution) correlated positively with above-ground plant biomass, whereas inorganic nutrient fluxes were unrelated to plant or grazer biomasses, suggesting dominance by sediment microbial processes. Finally, grazer richness significantly stabilized ecosystem processes, as predators decreased ecosystem production and respiration only in the zero- and one- species grazer treatments. Conclusions/Significance Overall, our results indicate that consumer presence and species composition strongly influence ecosystem responses to nutrient enrichment, and that increasing herbivore diversity can stabilize ecosystem flux rates in the face of perturbations.