H. Rodger Harvey

Black carbon in estuarine and coastal ocean dissolved organic matter

We measured black carbon (BC) in ultrafiltered, high‐molecular weight dissolved organic matter (UDOM) in surface waters of Delaware Bay, Chesapeake Bay, and the adjacent Atlantic Ocean (U.S.A.) to investigate the importance of riverine and estuarine dissolved organic matter (DOM) as a source of BC to the ocean. BC was 5‐ 72% of UDOM-C (27 6 17%), which corresponds to 8.9 6 6.5% of dissolved organic carbon (DOC), with higher values in the heavily urbanized midbay region of the Delaware Estuary and lower yields in the river and coastal ocean. The spatial and seasonal distributions of BC along the salinity gradient of Delaware Bay suggest that the elevated levels of BC in surface water UDOM originate from localized sources, possibly from atmospheric deposition or release from resuspended sediments. BC in UDOM made up 4‐7% of the DOC in the coastal Atlantic Ocean, revealing that river‐estuary systems are important exporters of colloidal BC to the ocean. The annual flux of BC from Delaware Bay UDOM to the Atlantic Ocean was estimated at 2.4 3 10 10 gB C yr 21

Kinetics of phytoplankton decay during simulated sedimentation: changes in lipids under oxic and anoxic conditions

A series of oxic and anoxic incubations examined lipid degradation in two marine phytoplankton, the diatom Thalassiosira weissflogii and the coccoid cyanobacterium Synechococcus sp., using flow-through systems without macrozooplankton grazers. Total extractable lipids and individual compounds (fatty acids, sterols and hydrocarbons) were quantified over time. Oxic decay constants of total lipid and POC showed good agreement between the two phytoplanktors, suggesting that changes in composition at the molecular level during degradation would be similar. Detailed analysis of individual lipids, however, revealed significant differences, with unsaturated moieties being degraded more rapidly than their saturated counterparts. Calculated turnover times for individual lipids ranged from 8.8 days for unsaturated alkenes of diatoms under oxic conditions to over 142 days for phytol under anoxia, with the absence of oxygen decreasing the decay rate for all lipids. Diatom sterols showed the largest reduction in degradative rate when oxygen was absent (almost 13-fold). Contrary to expectations, individual lipids common to both phytoplankton did not always show similar patterns of decay, suggesting that factors other than chemical structure may control degradative rate. Carbon isotopic analysis of the total lipid pool over the time course of all incubations revealed that the residual lipid pool shifted to lighter values, opposite of that typically observed for POC. The observed isotopic and molecular changes during degradation suggest that the residual lipid pool, which is preserved yet difficult to characterize, is similar to the fraction which is preserved in sediments.

LIPID COMPOSITION IN PARTICULATE AND DISSOLVED ORGANIC MATTER IN THE DELAWARE ESTUARY : SOURCES AND DIAGENETIC PATTERNS

Abstract Dissolved organic matter (DOM) was isolated from surface waters of Delaware Bay along a transect from freshwater to the coastal ocean and fractionated by tangential flow ultrafiltration into high (1–30 kDa; HDOM) and very high (30 kDa–0.2 μm; VHDOM) nominal molecular mass fractions. Carbon content, stable carbon isotopes, and lipid composition were measured for each DOM fraction, and particles collected in parallel. Lipids, excluding hydrocarbons, comprised up to 0.33% of HDOM organic carbon, 1.6% of VHDOM carbon, and 10% of POC, the majority of which were fatty acids. Although lipids comprised a small fraction of HDOM, fatty acids and sterols provided valuable information on the origins of DOM. Molecular composition of particulate and dissolved lipids and bulk stable carbon isotopes demonstrated differences in organic sources along the estuarine gradient with distinct terrestrial signals in the river and turbid middle estuary and an algal signal in the lower estuary and coastal ocean. Both particulate organic matter and VHDOM samples were enriched in lipids on a carbon basis compared to the HDOM fraction, which suggests that the HDOM fraction was less labile than particulate organic matter or VHDOM. Selective degradation of labile lipids by the microbial community can account for the depletions of unsaturated fatty acids, sterols, and phytol within HDOM relative to particles.

Novel lineages of Prochlorococcus and Synechococcus in the global oceans

Picocyanobacteria represented by Prochlorococcus and Synechococcus have an important role in oceanic carbon fixation and nutrient cycling. In this study, we compared the community composition of picocyanobacteria from diverse marine ecosystems ranging from estuary to open oceans, tropical to polar oceans and surface to deep water, based on the sequences of 16S-23S rRNA internal transcribed spacer (ITS). A total of 1339 ITS sequences recovered from 20 samples unveiled diverse and several previously unknown clades of Prochlorococcus and Synechococcus. Six high-light (HL)-adapted Prochlorococcus clades were identified, among which clade HLVI had not been described previously. Prochlorococcus clades HLIII, HLIV and HLV, detected in the Equatorial Pacific samples, could be related to the HNLC clades recently found in the high-nutrient, low-chlorophyll (HNLC), iron-depleted tropical oceans. At least four novel Synechococcus clades (out of six clades in total) in subcluster 5.3 were found in subtropical open oceans and the South China Sea. A niche partitioning with depth was observed in the Synechococcus subcluster 5.3. Members of Synechococcus subcluster 5.2 were dominant in the high-latitude waters (northern Bering Sea and Chukchi Sea), suggesting a possible cold-adaptation of some marine Synechococcus in this subcluster. A distinct shift of the picocyanobacterial community was observed from the Bering Sea to the Chukchi Sea, which reflected the change of water temperature. Our study demonstrates that oceanic systems contain a large pool of diverse picocyanobacteria, and further suggest that new genotypes or ecotypes of picocyanobacteria will continue to emerge, as microbial consortia are explored with advanced sequencing technology.

Terrigenous dissolved organic matter along an estuarine gradient and its flux to the coastal ocean

The contribution of terrigenous organic matter (TOM) to high molecular weight dissolved and particulate organic matter (POM) was examined along the salinity gradient of the Delaware Estuary. Dissolved organic matter (DOM) was fractionated by ultrafiltration into 1‐30 kDa (HDOM) and 30 kDa‐0.2 mm (VHDOM) nominal molecular weight fractions. Thermochemolysis with tetramethylammonium hydroxide (TMAH) was used to release and quantify lipids and lignin phenols. Stable carbon isotopes, fatty acids and lignin content indicated shifts in sources with terrigenous material in the river and turbid region and a predominantly algal/planktonic signal in the lower estuary and coastal ocean. Thermochemolysis with TMAH released significant amounts of short chain fatty acids (C9‐C13), not seen by traditional alkaline hydrolysis, which appear to be associated with the macromolecular matrix. Lignin phenol distributions in HDOM, VHDOM and particles followed predicted sources with higher concentrations in the river and turbid region of the estuary and lower concentrations in the coastal ocean. TOM comprised 12% of HDOM within the coastal ocean and up to 73% of HDOM within the turbid region of the estuary. In the coastal ocean, TOM from high molecular weight DOM comprised 4% of total DOC. The annual flux of TOM from the Delaware Estuary to the coastal ocean was estimated at 2.010 10 g OC year ˇ1 and suggests that temperate estuaries such as Delaware Bay can be significant sources of TOM on a regional scale. # 2000 Elsevier Science Ltd. All rights reserved.

Catalysts or contributors? Tracking bacterial mediation of early diagenesis in the marine water column

A series of oxic and anoxic incubations examined the changes in bacterial biomass and diagnostic fatty acids during degradation of two marine phytoplankton, the diatom Thalassiosira weissflogii and the coccoid cyanobacterium Synechococcus sp. Flow-through systems were used to simulate sedimentation, while macrozooplankton grazers were excluded. Bacterial abundance was strongly coupled to the decay sequence for algal carbon under both oxic and anoxic conditions, with loss of particular organic carbon (POC) accompanied by a rapid increase in bacterial biomass. Bacterial carbon increased over 3.7-fold during the period when maximal loss of diatom derived POC was observed. In the oxic cyanobacterial decay experiment bacterial biomass showed a different pattern, with a rapid increase prior to the time period of particulate carbon loss and decrease thereafter. The total concentration of “bacterial” fatty acids for all incubations increased from time zero, with highest concentrations (164 μg l−1) in oxic incubations and coinciding with periods of highest bacterial carbon. Bacterial carbon accounted for up to 32.6% of total POC during the early stages of anoxic diatom decay, with lower maximum amounts (21.4%) in parallel incubations under oxic conditions. Carbon isotopic signatures of individual fatty acids representing algal, bacterial and mixed sources were determined during oxic diatom decay, and showed a small enrichment (average of +1.6‰) in 13C after the period of major POC loss. A comparison of total fatty acids attributed to bacteria and bacterial carbon calculated from measured bacterial cells showed no strong relationship, suggesting that fatty acids considered diagnostic of bacteria remain a qualitative tool for the estimation of bacterial contributions to sediments.

Protein and amino acid cycling during phytoplankton decomposition in oxic and anoxic waters

Abstract The fates of proteins and amino acids were followed during the oxic and anoxic decay of three marine phytoplankton (diatom Thalassiosira weissflogii , cyanobacterium Synechococcus sp., and dinoflagellate Prorocentrum minimum ) during simulated sedimentation. In the stationary phase of phytoplankton growth, 36–100% of total hydrolyzable amino acids were comprised of amino acids associated with a ≥2000 Da molecular weight fraction. After cell death, proteins degraded at similar rates, independent of which phytoplankton species they originated from, but dependent on oxygen. Protein degradation was rapid under oxic conditions, with 2–8% of the initial ≥2000 Da protein amino acid fraction remaining at the end of the incubations. Under anoxic conditions, 17–46% of the ≥2000 Da protein amino acid fraction remained. Throughout oxic and anoxic incubations, amino acids normalized to particulate nitrogen paralleled carbon normalized values. 51–82% of the particulate nitrogen could be attributed to proteins, polypeptides and/or bound amino acid monomers, suggesting that these nitrogen-rich compounds can be refractory. A comparison of the changes in concentrations of constituent amino acids of the total amino acid and ≥2000 Da protein amino acid fractions suggests that all amino acids are lost at comparable rates during the degradation sequence. For the dinoflagellate decay, two non-protein amino acids, β-alanine and γ-aminobutyric acid, exhibited rate constants similar to those observed for total hydrolyzable amino acids; relative abundances of β-alanine and γ-aminobutyric acid in degraded material did not significantly differ from that in fresh material. At the conclusion of oxic and anoxic diatom decay and oxic cyanobacterial decay, the slight increase in these two non-protein amino acids suggests sorption to the remaining organic matrix.

Preservation of protein in marine systems: Hydrophobic and other noncovalent associations as major stabilizing forces

—The fate of proteins during early diagenesis was investigated in environments with low mineral content to assess preservation mechanisms other than mineral sorption. Preservation was examined in anoxic, organic-rich sediments of Mangrove Lake, a marine environment located in Bermuda, and for particulate material generated during oxic decay of diatoms.N-phenacylthiazolium bromide (PTB) treatment tested the hypothesis that proteins may undergo modification reactions with glucose to form advanced-glycation end products (AGEs). A small but significant release (additional 14%) of proteins was observed after PTB treatment in surficial sediments, indicating that some aggregations can proceed through an α-dicarbonyl intermediate of the AGE pathway. Size-exclusion high-pressure liquid chromatography with protein fluorescence, absorbance, and evaporative light-scattering detector measurements under native (phosphate or bicarbonate buffers) and denaturing (guanidine · HCl, urea, or acetonitrile) conditions point to the importance of hydrophobic and other noncovalent interactions in the stabilization of proteinaceous material in the environment. Soluble aggregates of substantial, relative molecular mass (Mr ≳ 106) appear to be formed early in the diagenetic sequence. The preferential preservation of very highMr, multisubunit phytoplankton proteins in sediments suggests that such aggregations confer resistance to degradation. Alternatively, some of the proteinaceous material may represent that fraction of organic matter that is highly prone to aggregations. Extended incubations (18 h; 37°C) with trypsin and proteinase-K showed that much of the aggregates that could be extracted are receptive to proteolytic cleavage. Buffer-, surfactant-, and NaOH-extractable aggregates comprised most of the acid-hydrolyzable proteinaceous material in detritus and surficial sediments but <35% in 9.7-m-deep sediments, suggesting additional mechanisms for preservation might be in operation. The results are direct evidence for the preservation of peptide linkages in sediments as old as 4000 yr and for noncovalent associations (hydrophobic interaction, hydrogen bonding) of protein as important mechanisms in long-term preservation.

Preservation of proteinaceous material during the degradation of the green alga Botryococcus braunii: A solid-state 2D 15N 13C NMR spectroscopy study

Using solid-state cross-polarization-magic-angle-spinning (CPMAS) 13C and 15N nuclear magnetic resonance (NMR) and 2-D double cross polarization (DCP) MAS 15N 13C NMR techniques, microbially degraded Botryococcus braunii was analyzed to study the chemical nature of organic nitrogen in the algal residue. The amide linkage, as found in protein, was observed as the major nitrogen component in 201-day-old degraded algae. No significant amount of heterocyclic nitrogen, or evidence for melanoidin products, was found. The results strongly suggest that proteinaceous material can survive early diagenesis and be preserved via its encapsulation by refractory, macromolecular, organic matter.

Preservation of algaenan and proteinaceous material during the oxic decay of Botryococcus braunii as revealed by pyrolysis-gas chromatography/mass spectrometry and 13C NMR spectroscopy

Botryococcus braunii cells were grown until the late-stationary phase of growth and subsequently decomposed under oxic conditions for 201 days using a microbial consortium obtained from a freshwater lake.Degradation exhibited multi-G model kinetics, with a ‘labile’ fraction lost at a rate two to three times slower than those observed for the degradation of other previously studied phytoplankton, and a ‘refractory’ fraction lost even more slowly.Scanning electron microscopy of the 201-day detritus, as previously seen for the kerogen, indicates the preservation of cell wall material with loss of intracellular contents.Detrital samples analyzed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and solid-state ramp-CPMAS 13 C NMR, however, indicates the preservation of highly aliphatic material, algaenan, as well as ‘intrinsically labile’ proteinaceous components.These results further support the encapsulation hypothesis that proteins may be sterically protected from enzymatic attack via intimate associations with refractory, macromolecular organic matter. # 2003 Elsevier Science Ltd.All rights reserved.