Polycyclic aromatic hydrocarbon (PAH) contaminated sediments from Piles Creek (PC) and Newtown Creek (NC) in the NY/NJ Harbor estuary were separated into size fractions and further separated into low (<1.7 g cm(-3)) and high (>1.7 g cm(-3)) density fractions. The fractionated sediments were characterized for carbon content pore structure, surface area, and PAH concentration. Most PAHs (50-80%) in both sediments were associated with the low-density fraction, which represents only 3-15% of total sediment mass, at levels greater than expected based on equilibrium partitioning. PC low-density sediment had 10 times greater organic carbon-normalized equilibrium partitioning coefficients (Koc) than the other size fractions and whole sediment. Characterization of the sediment organic matter suggested that the preferential sequestration observed in PC sediment was not correlated with soot carbon but was likely due to the presence of detrital plant debris, an important food source for benthic animals. Fractional PAH desorption from whole PC sediment was significantly higher than from NC sediment after 3 months. For both sediments, a smaller percentage of the total PAHs was desorbed from the low-density fraction. However, because PAH concentrations were greatly elevated in these fractions, more PAH mass was desorbed than from the corresponding bulk and high-density fractions. These results demonstrate that PAHs are preferentially sequestered in a separable, low-density fraction at levels not predictable by equilibrium partitioning theory. Further, the low-density fraction apparently controls whole-sediment PAH release. Although plant debris appears to be an important sorbent for PAHs, this material may readily release PAHs into the aqueous phase.

This study considers desorption kinetics for 12 field-aged polycyclic aromatic hydrocarbons (PAHs) desorbing from size- and density-fractionated sediments collected from two locations in the New York/New Jersey Harbor Estuary. Desorption kinetics for PAHs with a log octanol-water partition coefficient greater than 6 were well-described by a one-domain diffusion model that assumes that PAHs are initially uniformly distributed throughout spherical sediment aggregates. PAH hydrophobicity and sediment specific surface area were the parameters most strongly correlated with the magnitude of the observed diffusivity for the one-domain model. For less hydrophobic PAHs, a two-domain desorption model was used also, and the results suggest that a substantial fraction of these field-aged PAHs desorb via a relatively fast macro-mesopore diffusion mechanism. The model-predicted fraction of PAHs in the fast-diffusion regime by compound and sediment was highly correlated with the measured percent PAH desorption in 24 h. The fast-domain diffusivity was 100 times greater than the slow-domain diffusivity, was correlated with both PAH properties and sediment physical and chemical properties, and could be estimated by readily obtainable physical and chemical parameters. In contrast, the slow-domain diffusivity was not significantly correlated with PAH properties. Our results suggest that macro-mesopore diffusion may control mass transport of less-hydrophobic PAHs in estuarine sediments.

Feeding experiments were conducted on marine, deposit-feeding benthic invertebrates to test the predictions of an optimal foraging model. Food item selection based on sediment particle size and presence or absence of an organic coating on particles was investigated. Animals displaying a wide range of feeding mechanisms were studied in particle size-selection experiments using artificial sediment of closely controlled size composition. Nine of 10 species from 4 phyla ingested smaller particles in greater proportions than the particles were present in the sediment. In experiments where animals fed on a mixture of two particle types, one with and one without a surface protein coating, 6 of 7 species from 3 phyla ingested preferentially the protein-coated beads. While these trends of selection of smaller particles and protein-coated particles follow qualitatively the predictions of the optimal foraging model, the animals did not ingest exclusively the preferred particle types. Mechanics of particle handling rather than behavioral responses to particle characteristics appear to offer the better explanation for the observed selection patterns. In particular, the results support strongly the recently proposed role of mucous adhesion in particle selection by deposit feeders.These and other results from studies of deposit feeders suggest that factors in addition to food item selection must be considered when testing the assumptions and predictions of optimal foraging theory. Specifically, feeding energetics are also affected by postfood-selection processes such as variation of ingestion rate. Furthermore, the effects of abiotic environmental factors on foraging behavior cannot be overlooked in evaluating the optimality of foraging behavior; variable water velocity affected differently the particle size selectivity of 3 sympatric polychaete species in these studies.

The feeding behavior of three species of spionid polychaetes varied with water velocity. At moderate flows the worms ceased deposit feeding, formed their feeding tentacles into helices, and lifted them into the water column to capture material in suspension. This behavior was apparently a response to increased flux of suspended matter at high flows rather than to flow velocity alone. Organisms capable of switching their feeding behavior may be common in dynamically variable benthic environments.

No abstract

We studied the effects of a bacterium (Pseudomonas chlororaphis) and a bactivorous protozoan (Uronema sp.) on transformations of labile dissolved organic carbon (DOC). In 36-day time series experiments, bacteria were grown on glucose both with and without protozoa. We measured bulk organic carbon pools and used electrospray ionization mass spectrometry to characterize dissolved organic matter on a molecular level. Bacteria rapidly utilized glucose, depleting it to nondetectable levels and producing new DOC compounds of higher molecular weight within 2 days. Some of these new compounds, representing 3 to 5% of the initial glucose-C, were refractory and persisted for over a month. Other new compounds were produced and subsequently used by bacteria during the lag and exponential growth phases, pointing to a dynamic cycling of organic compounds. Grazers caused a temporary spike in the DOC concentration consisting of labile compounds subsequently utilized by the bacteria. Grazing did not increase the complexity of the DOC pool already established by the bacteria but did continually decrease the particulate organic carbon pool and expedited the conversion of glucose-C to CO 2 . After 36 days, 29% of initial glucose-C remained in pure bacteria cultures, while only 6% remained in cultures where a grazer was present. In this study the bacteria were the primary shapers of the complex DOC continuum, suggesting higher trophic levels possibly have less of an impact on the qualitative composition of DOC than previously assumed.Dissolved organic matter (DOM) comprises the largest, yet least-characterized reservoir of reduced organic carbon in aquatic systems, estimated at 700 ϫ 10 15 g C (11). DOM is important in the carbon and nitrogen cycles, the scavenging and solubilization of trace contaminants, and biogeochemical cycles of other elements (3,14). Heterotrophic bacteria process and reprocess some of this DOM (2), channeling about one-half of oceanic primary production through the microbial loop (8).The role of bacteria in the rate and extent of DOM mineralization and their production of (semi)refractory DOM have received less attention. Some studies indicate that bacteria produce refractory DOM that is resistant to further utilization (5,12,37,39). Ogawa et al. (26) showed that a natural inoculum of marine bacteria (and undoubtedly nanoflagellates and viruses) growing on labile compounds (glucose and glutamate) produce new DOM compounds that appear to be refractory for at least a year. It was not known if a single strain of bacteria could produce similar refractory material. Bacterioplankton can also be a source of photoreactive C-DOM that is refractory to a natural bacteria assemblage following photochemical alteration (18). What kinds and how many different compounds make up the refractory DOM pool are largely unknown.In aquatic ecosystems, bacteria are consumed by protozoa and other zooplankton, which in turn release DOM as colloidal matter (17, 40) and macromolecular organic complexes (24). A substantial portion (Ͼ50%...

A feeding model for a generalized, benthic deposit feeder is derived from a filter-feeding model and used to predict how such a deposit feeder would adjust its feeding to maximize its net energy gain. Under the assumption that deposit feeders are utilizing the bacterial fraction of the sediment or other surface organic coatings as food, the model predicts that the smallest particles should always be ingested, while the selection of larger particles depends on several parameters, including gut passage time and assimilation efficiency of the deposit feeder. The model also predicts relationships among particle size selection, assimilation efficiency, gut passage time, gut volume, and particle rejection costs.

Spatiotemporal variation and metabolic activity of the microbial community were studied in coarse-grained Middle Atlantic Bight shelf sediments in relation to pools of dissolved and particulate carbon. Algal cells were present 8->70 mum) fraction of the sediment held the major share (61-98%) of benthic bacteria. Bacterial and algal cell abundances, exoenzymatic activity, and [DOC] generally showed higher values in May/July 2001 than in August/December 2000. Carbohydrates and proteins were hydrolyzed at potential rates of 1-12 nmol cm(-3) h(-1) (beta-glucosidase) and 3-70 nmol cm(-3) h(-1) (aminopeptidase), respectively. Fluorescence in situ hybridization analyses of the benthic microbes assigned 45-56% of DAPI-stained cells to Eubacteria and less than 2% to Eukarya. The prokaryotic community was dominated by planctomycetes and members of the Cytophaga/Flavobacterium cluster. Near the sediment surface, iodonitrotetrazolium violet reducing cells, that are considered actively respiring, amounted to 15-29% of total bacteria. Despite a low organic content (particulate organic carbon <0.03%) and relatively low bacterial abundances (<10(9) cm(-3)), the Middle Atlantic Bight shelf sediments showed organic matter turnover rates that are comparable to those found in organic-rich finer-grained deposits. Our findings suggest a high biocatalytic filtration activity in these coarse permeable sediments.