US Estuaries Research Articles

Evaluation of 224Ra as a tracer for submarine groundwater discharge in Long Island Sound (NY)

The approach to quantify submarine groundwater discharge using Ra isotopes generally involves developing a Ra mass balance in an estuary, bay or lagoon. In this work we present a 224Ra mass balance used to evaluate the importance of the submarine groundwater discharge (SGD) in Long Island Sound (NY, US), the third most important estuary in US, located between Long Island and Connecticut that is usually affected by summertime hypoxia in the western basin. Three surveys were conducted between April 2009 and August 2010 where 25 water stations were sampled for Ra isotopes, oxygen and Mn. Stations were oriented along 4 transects: one axial extending from the western to the eastern Sound and three longitudinal transects in the western, central and eastern Sound. The inventory of 224Ra in the water column in summer was circa 2 times greater than in winter, suggesting an increased 224Ra flux to the Sound in summer. A mass balance for 224Ra was constructed considering tidal exchange, inputs from rivers, desorption from resuspended particles, diffusive fluxes (including bioirrigation) from bottom sediments and radioactive decay in the water column. Fluxes of 224Ra from bottom sediments were measured by incubating cores under oxic conditions in a continuous flow mode such that the overlying water was circulated through a Mn-oxide fiber to maintain a constant activity of 224Ra. Fluxes from muddy sediments (comprising ∼67% of the Sound bottom) ranged from 127 to 312dpmm−2d−1 and were ∼60dpmm−2d−1 in sandy sediments (33% of the Sound). Incubations under hypoxic conditions showed variable fluxes depending on reduction and mobilization of Mn. The 224Ra mass balance shows a net input of Ra to the Sound of 106±50×1012dpmy−1 in spring and 244±112×1012dpmy−1 in the summer that is attributed to SGD. Elevated 224Ra values were observed near shore and in the pore fluids of the coarse beach sands along the Long Island and Connecticut coasts, suggesting that SGD driven by tidal recirculation through the beach face is a major source of 224Ra to the Sound. Seasonal variation in this source seems unlikely, and the calculated 224Ra SGD fluxes for spring and summer overlap within the uncertainties. Nevertheless we conclude that variations in the 224Ra water column inventories could be produced by seasonal changes in bioirrigation and/or redox cycling of Mn as well as sediment resuspension and desorption of 224Ra from resuspended particles, and that our mass balance underestimates these terms, particularly in the summer. 224Ra fluxes from sediments in estuaries, especially those with significant areas of muddy sediments and seasonal hypoxia, are important and should be well constrained in future uses of this isotope as a tracer for SGD.

From Headwaters to Coast: Influence of Human Activities on Water Quality of the Potomac River Estuary

The natural aging process of Chesapeake Bay and its tributary estuaries has been accelerated by human activities around the shoreline and within the watershed, increasing sediment and nutrient loads delivered to the bay. Riverine nutrients cause algal growth in the bay leading to reductions in light penetration with consequent declines in sea grass growth, smothering of bottom-dwelling organisms, and decreases in bottom-water dissolved oxygen as algal blooms decay. Historically, bay waters were filtered by oysters, but declines in oyster populations from overfishing and disease have led to higher concentrations of fine-sediment particles and phytoplankton in the water column. Assessments of water and biological resource quality in Chesapeake Bay and tributaries, such as the Potomac River, show a continual degraded state. In this paper, we pay tribute to Owen Bricker’s comprehensive, holistic scientific perspective using an approach that examines the connection between watershed and estuary. We evaluated nitrogen inputs from Potomac River headwaters, nutrient-related conditions within the estuary, and considered the use of shellfish aquaculture as an in-the-water nutrient management measure. Data from headwaters, nontidal, and estuarine portions of the Potomac River watershed and estuary were analyzed to examine the contribution from different parts of the watershed to total nitrogen loads to the estuary. An eutrophication model was applied to these data to evaluate eutrophication status and changes since the early 1990s and for comparison to regional and national conditions. A farm-scale aquaculture model was applied and results scaled to the estuary to determine the potential for shellfish (oyster) aquaculture to mediate eutrophication impacts. Results showed that (1) the contribution to nitrogen loads from headwater streams is small (about 2 %) of total inputs to the Potomac River Estuary; (2) eutrophic conditions in the Potomac River Estuary have improved in the upper estuary since the early 1990s, but have worsened in the lower estuary. The overall system-wide eutrophication impact is high, despite a decrease in nitrogen loads from the upper basin and declining surface water nitrate nitrogen concentrations over that period; (3) eutrophic conditions in the Potomac River Estuary are representative of Chesapeake Bay region and other US estuaries; moderate to high levels of nutrient-related degradation occur in about 65 % of US estuaries, particularly river-dominated low-flow systems such as the Potomac River Estuary; and (4) shellfish (oyster) aquaculture could remove eutrophication impacts directly from the estuary through harvest but should be considered a complement—not a substitute—for land-based measures. The total nitrogen load could be removed if 40 % of the Potomac River Estuary bottom was in shellfish cultivation; a combination of aquaculture and restoration of oyster reefs may provide larger benefits.

Factors influencing expanded use of urban marine habitats by foraging wading birds

Urban marine habitats are often utilized by wildlife for foraging and other activities despite surrounding anthropogenic impact or disturbance. However little is known of the ecological factors that determine habitat value of these and other remnant natural habitats. We examined the preferential use of urban marine habitats in a northeast US estuary to try to elucidate the factors driving enhanced foraging activity at these sites. Using a bioenergetic model, we compared energy intake to energy expenditure and examined differences in behavior and foraging success of great egrets Ardea alba at three urban and three rural salt marshes in Narragansett Bay, Rhode Island USA. Mean per site available nekton energy averaged 4.44 ± 0.97 GJ site−1 and was significantly higher at urban than at rural sites. While energy expenditure by birds was similar across all sites, mean strike and prey capture rate were significantly greater at urban sites, and 70.1 ± 12.2 % of strikes by egrets at urban sites were successful. Egrets foraging at urban sites consumed significantly more energy (23.2 ± 6.62 W bird−1) than those at rural sites. Model results indicated a net energy gain by egrets foraging at urban sites, versus a net energy loss at rural sites. Our results may help explain previously observed increases in the numbers of egrets foraging at urban marine habitats, and help provide input into decisions about the extent to which these areas should be considered for restoration or protection.

Quantifying the Loss of a Marine Ecosystem Service: Filtration by the Eastern Oyster in US Estuaries

The oyster habitat in the USA is a valuable resource that has suffered significant declines over the past century. While this loss of habitat is well documented, the loss of associated ecosystem services remains poorly quantified. Meanwhile, ecosystem service recovery has become a major impetus for restoration. Here we propose a model for estimating the volume of water filtered by oyster populations under field conditions and make estimates of the contribution of past (c. 1880–1910) and present (c. 2000–2010) oyster populations to improving water quality in 13 US estuaries. We find that filtration capacity of oysters has declined almost universally (12 of the 13 estuaries examined) by a median of 85 %. Whereas historically, oyster populations achieved full estuary filtration (filtering a volume equivalent or larger than the entire estuary volume within the residence time of the water) in six of the eight estuaries in the Gulf of Mexico during summer months, this is now the case for only one estuary: Apalachicola Bay, Florida. By contrast, while all five estuaries on the North Atlantic coast showed large decreases in filtration capacity, none were achieving full estuary filtration at the time of our c. 1900 historic baseline. This apparent difference from the Gulf of Mexico is explained at least in part by our North Atlantic baseline representing a shifted baseline, as surveyed populations were already much reduced by exploitation in this region.

Impacts of an abundant introduced ecosystem engineer within mudflats of the southeastern US coast

Invasive ecosystem engineers can have far-reaching effects on systems, especially if they provide structure where none was before. The non-native seaweed Gracilaria vermiculophylla has proliferated on estuarine mudflats throughout the southeastern US, including areas (South Carolina and Georgia) that historically were extremely low in seaweed biomass. Quantitative field surveys across 150 km of high salinity estuaries revealed that the density of the native onuphid polychaete Diopatra cuprea and the aboveground height of its biogenic tubes, which Diopatra decorates with drifting debris and seaweed, positively influenced Gracilaria biomass. The abundance of Gracilaria epifauna, composed primarily of amphipods and small snails, increased with Gracilaria biomass at many locations in our field surveys. To examine whether epifauna were facilitated by Gracilaria we experimentally manipulated Gracilaria biomass in two locations. Consistent with the field surveys, we found that increasing Gracilaria biomass facilitated epifauna, particularly amphipods and snails. Epifaunal densities on Gracilaria were higher than on a biologically-inert structural mimic of Gracilaria (plastic aquarium alga), indicating that epifauna colonize Gracilaria because Gracilaria provisions both physical structure and a biological resource. We also quantified the seaweed’s net rate of productivity and decomposition. Primary production of Gracilaria was variable, but massive in some areas (up to 200 % net biomass increase in 8 weeks). The seaweed rapidly degraded upon burial in silty sediments (79 % loss in mass within 10 days) and thus may represent an important new addition to detrital foodwebs. As a copious, novel source of primary production, detritus, and desirable habitat for epifauna, Gracilaria has the potential to transform southeastern US estuaries.

Toxicity of sediment pore water in Puget Sound (Washington, USA): a review of spatial status and temporal trends

Data from toxicity tests of the pore water extracted from Puget Sound sediments were compiled from surveys conducted from 1997 to 2009. Tests were performed on 664 samples collected throughout all of the eight monitoring regions in the Sound, an area encompassing 2,294.1 km(2). Tests were performed with the gametes of the Pacific purple sea urchin, Strongylocentrotus purpuratus, to measure percent fertilization success as an indicator of relative sediment quality. Data were evaluated to determine the incidence, degree of response, geographic patterns, spatial extent, and temporal changes in toxicity. This is the first survey of this kind and magnitude in Puget Sound. In the initial round of surveys of the eight regions, 40 of 381 samples were toxic for an incidence of 10.5 %. Stations classified as toxic represented an estimated total of 107.1 km(2), equivalent to 4.7 % of the total area. Percent sea urchin fertilization ranged from >100 % of the nontoxic, negative controls to 0 %. Toxicity was most prevalent and pervasive in the industrialized harbors and lowest in the deep basins. Conditions were intermediate in deep-water passages, urban bays, and rural bays. A second round of testing in four regions and three selected urban bays was completed 5-10 years following the first round. The incidence and spatial extent of toxicity decreased in two of the regions and two of the bays and increased in the other two regions and the third bay; however, only the latter change was statistically significant. Both the incidence and spatial extent of toxicity were lower in the Sound than in most other US estuaries and marine bays.

Lineage distribution and barriers to gene flow among populations of the globally invasive marine mussel Musculista senhousia

Introduced species seem to rapidly adapt to non-native conditions although founder events may decrease genetic variance and impede adaptation. Cryptic introductions of an invader from different parts of its native range may allow colonization of habitat patches with compatible conditions, or admixture may restore genetic diversity lost during invasion bottlenecks. We present the first genetic study of global invasion pathways for the Asian date mussel, Musculista senhousia, comparing three putative source populations from Asia with six US estuaries and one invaded site in New Zealand and the Mediterranean Sea, totaling 117 individuals. Distribution of mitochondrial DNA and alleles of a nuclear intron revealed two genetically divergent populations in the native range. A warm-water lineage from Tokyo Bay and southwestern South Korea predominated in southern California and New Zealand, while a cold-water haplotype group sampled in northeastern Korea was more abundant at invaded sites in the northwestern US and Mediterranean Sea. The duration of high summer water temperatures accounted for substantial variance in the worldwide distribution of common haplotype groups, suggesting thermal pre-adaptation may influence invasion success for differentiated source populations. There was no gene flow across central California, but on either side of this phylogeographic barrier there was high exchange among estuaries within the northern and the southern US regional populations. Gradients in water temperature may therefore constrain post-introduction spread by limiting dispersion along a coast.

Relationships between Nutrient Enrichment and Benthic Function: Local Effects and Spatial Patterns

Eutrophication-induced changes to benthic faunal activities are problems of significant ecological impact, affecting global nutrient budgets as well as local trophic connections. We address the question of how nitrogen loads to estuarine embayments alter the bioturbation activities of benthic fauna. Specifically, we related local benthic activities to calculated local nitrogen concentrations for 22 northeastern US estuaries. These local nitrogen concentrations were derived from the calculated nitrogen loading for the embayment together with the spatial distribution of the local flushing time. Our results showed a maximum bioturbation rate at intermediate nitrogen concentrations or a “hump-shaped” pattern of response. This behavior was evident in all embayments that had a range of concentrations including low, intermediate, and high values. Embayments where sampling did not include this full range did not show this behavior. This work provides methods and guidance to help managers make decisions concerning the effects of nitrogen loading on the activities and well-being of benthic fauna in coastal embayments. The novelty of this approach lies in identifying the response of bioturbation to nitrogen loading in many systems, without costly and time-consuming speciation of benthic fauna, and also in rapidly identifying embayments and aquatic areas with vulnerable fauna. These results are ecologically significant in supporting the hypothesis that benthic organism abundance and activity will peak at mid-levels of nitrogen due to the interplay of food availability and oxygen levels, noting that the critical levels of these factors differ among water bodies.

Changes in molecular genetic variation at AFLP loci associated with naturalization and domestication of the Pacific oyster (Crassostrea gigas)

The Pacific oyster (Crassostrea gigas) is an important commercial species in the US Pacific Northwest with a history of production initially based on wild-caught seed imported directly from the Miyagi region of northern Japan (1920s–1970s) followed by an extended period of seed collection from a small number of naturalized, self-recruiting populations in US estuaries (early 1970s-present) and more recently through large-scale hatchery production of seed oysters (mid 1970s-present). I studied the genetic level consequences of each of these major transformations of the oyster industry by examining the patterns of private alleles (bands unique to one sample), the number of polymorphic loci, expected heterozygosity, genetic distance between populations and genetic divergence between individuals within and among three native Pacific oyster populations in Japan (Hiroshima, Miyagi, Midori River), five naturalized populations in North America (Pipestem Inlet BC, Nootka Inlet BC, Dabob Bay WA, Willapa Bay, WA, and Tillamook Bay, OR), two in New Zealand (Chance Bay and Kaipara Harbor), and seven domesticated and selectively bred cohorts from an ongoing genetic improvement program on the West Coast of the United States using amplified fragment length polymorphism (AFLP) markers. All but one of the naturalized populations in both the USA and New Zealand are genetically more similar to native populations from the Ariake Sea (Midori River) than to the Miyagi region of their origin, but all domesticated stocks more closely resemble the wild Miyagi population. According to local oyster producers, the one exceptional naturalized population (Tillamook) is a very recent colonization derived from farmed oysters. Such consistency is unexpected under random genetic drift, and I speculate that both natural and artificial selection may have altered AFLP allele frequencies in this species in the course of naturalization and domestication.

Local-scale characteristics of high-marsh communities next to developed and undeveloped shorelines in an ocean-dominated estuary, Murrells Inlet, SC

Anthropogenic alteration of terrestrial shorelines can have pronounced effects on marine environments at the upland-marsh boundary. Possible terrestrial development effects on several physical and biological variables of high-marsh habitats were examined along developed and undeveloped shorelines in an ocean-dominated, southeastern US estuary. Analyses of sediment characteristics suggested development of the upland boundary affected physical conditions within the high-marsh. For example, pore water salinities were greater along undeveloped shorelines during a non-drought period even after rain events. Significant floral and faunal differences also existed between shoreline treatments. Black needle rush stems were significantly taller and marsh periwinkle densities significantly greater, but eastern coffee bean snail densities were significantly reduced along developed shorelines. Benthic infaunal community abundance and composition also were significantly different between shoreline treatments with sand fly larvae, human pest precursors, either only present or present in greater densities along developed shorelines. Sediment respirometry experiments indicated significant differences in heterotrophic and autotrophic processes occurring between shoreline treatments. Greater sediment surface temperatures along developed shorelines provided one possible mechanism driving high-marsh responses to boundary alteration. The history and extent of shoreline development along with a tendency in ocean-dominated southeastern marshes to resist change likely influenced current ecological conditions within our high-marsh study areas. A greater understanding of the driving mechanisms producing localized effects on salt marshes and recognizing regional differences in marsh resistance to change will facilitate predictions of shoreline development consequences and help in proposing effective management strategies for coastal boundaries.

User-based skill assessment techniques for operational hydrodynamic forecast systems

NOAA’s National Ocean Service (NOS) applies hydrodynamic models for the development, transition and implementation of operational forecast systems in US estuaries, ports, lakes and the coastal ocean. These models and systems have applications in the support of safe and efficient marine navigation and emergency response, as well as marine geospatial and ecological applications. As part of the forecast system development, skill assessment is required to evaluate each model system. A forecast model has to be ensured that it has been developed and implemented in a scientifically sound and operationally robust way, and its performance should meet or exceed target benchmarks before its products are approved for release to the public.This paper discusses a new approach for the development of standards and procedures for skill assessment of operational forecast systems, which are designed primarily to support marine transportation and emergency response. Accordingly, this skill assessment focuses on variables, statistics and targets that are of the most use to these communities. The components of skill assessment include: data analysis techniques, definition of model run scenarios and statistical variables, and NOS target values and acceptance criteria. In addition, a large suite of skill assessment software has been developed to compute the new skill assessment scores using data files containing modelled variables and observed data. This software ingests model forecasts and observational data, fills in gaps, creates time series, extracts skill-specific parameters, and computes the skill scores. The software has been tested and applied to all NOS operational forecast systems.

Dermestid Beetles Inhabiting Wading-Bird Nests in Northeastern US Estuaries

Abstract Ectoparasitism of nesting birds is known to impact reproduction for many species including cavity-nesting swallows and ground-nesting colonial seabirds. Little information is available from wading birds (e.g., herons, egrets, ibises). We documented skin-eating dermestid beetle abundance in 261 wading-bird nests in seven heronries located in northeastern US estuaries during 1991–2000. Beetles were collected after fledglings were no longer using the nest. We examined all twigs and debris for larval and adult beetles, and excavated holes in twigs to count pupating insects. In addition, nest size was evaluated. Dermestes nidum (dermestid beetle) larvae were prominent members of nest faunal communities in all estuaries. We detected no evidence that beetle abundance correlated with wading-bird species, nest reuse, nest substrate species, or nest-collection date. Regression analysis and partial correlation analysis identified nest size, colony, and year as factors showing a significant relationship with...

Characterization of the toxicity of Cochlodinium polykrikoides isolates from Northeast US estuaries to finfish and shellfish

Harmful algal blooms caused by Cochlodinium polykrikoides are annual occurrences in coastal systems around the world. In New York (NY), USA, estuaries, bloom densities range from 103 to 105mL−1 with higher densities (≥104cellsmL−1) being acutely toxic to multiple fish and shellfish species. Here, we report on the toxicity of C. polykrikoides strains recently isolated from New York and Massachusetts (USA) estuaries to juvenile fish (Cyprinodon variegates) and bay scallops (Argopecten irradians), as well as on potential mechanisms of toxicity. Cultures of C. polykrikoides exhibited dramatically more potent ichthyotoxicity than raw bloom water with 100% fish mortality occurring within ∼1h at densities as low as 3.3×102cellsmL−1. More potent toxicity in culture was also observed in bioassays using juvenile bay scallops, which experienced 100% mortality during 3 days exposure to cultures at cell densities an order of magnitude lower than raw bloom water (∼3×103cellsmL−1). The toxic activity per C. polykrikoides cell was dependent on the growth stages of cultures with early exponential growth cultures being more potent than cultures in late-exponential or stationary phases. The ichthyotoxicity of cultures was also dependent on both cell density and fish size, as a hyperbolic relationship between the death time of fish and the ratio of algal cell density to length of fish was found (∼103cellsmL−1cm−1 yielded 100% fish mortality in 24h). Simultaneous exposure of fish to C. polykrikoides and a second algal species (Rhodomonas salina or Prorocentrum minimum) increased survival time of fish, and decreased the fish mortality suggesting additional cellular biomass mitigated the ichthyotoxicity. Frozen and thawed-, sonicated-, or heat-killed-, C. polykrikoides cultures did not cause fish mortality. In contrast, cell-free culture medium connected to an active culture through a 5μm nylon membrane caused complete mortality in fish, although the time required to kill fish was significantly longer than direct exposure to the whole culture. These results indicate that ichthyotoxicity of C. polykrikoides isolates is dependent on viability of cells and that direct physical contact between fish and cells is not required to cause mortality. The ability of the enzymes peroxidase and catalase to significantly reduce the toxicity of live cultures and the inability of hydrogen peroxide to mimic the ichthyotoxicity of C. polykrikoides isolates suggests that the toxicity could be caused by non-hydrogen peroxide, highly reactive, labile toxins such as ROS-like chemicals.

Effects of nutrient enrichment in the nation's estuaries: A decade of change

An updated assessment of nutrient related impacts in US estuaries was completed in 2007. This assessment evaluates three components for each estuary: the influencing factors (e.g. land use, nutrient loads), the overall eutrophic condition (e.g. chlorophyll a, presence of nuisance/toxic algae and macroalgae, extent of dissolved oxygen problems, loss of submerged aquatic vegetation), and future outlook. Eutrophication is a widespread problem with 65% of assessed systems showing moderate to high level problems. The most impacted region was the mid-Atlantic. The majority of estuaries assessed, with the exception of North Atlantic systems (Cape Cod north to Maine), are highly influenced by human related activities that contribute to land-based nutrient loads. Conditions were predicted to worsen in 65% and to improve in 19% of the assessed estuaries in the future. Analysis of the extent of change from the early 1990s to the early 2000s, for those systems for which sufficient data were available, shows that conditions mostly remained the same (32 of 58 systems) though changes were observed in several smaller systems; 13 systems improved and 13 systems worsened. Chlorophyll a and HAB impacts have increased in the mid-Atlantic region, the only region with data adequate for comparison. These symptoms are more prevalent in systems with longer residence times, such as coastal lagoons. The successful restoration of seagrass in Tampa Bay is encouraging though future management to sustain the recovery will be difficult given expected population increases. This national assessment illustrates the need for coordinated and integrated action that balances management action, efficient monitoring to assess the effectiveness of the management, focused research, and a communication campaign aimed at engaging the broader community.

Contaminant concentrations in whole-body fish and shellfish from US estuaries

Persistent bioaccumulative and toxic (PBT) pollutants are chemical contaminants that pose risks to ecosystems and human health. For these reasons, available tissue contaminant data from the US EPA Environmental Monitoring and Assessment Program's National Coastal Assessment were examined to estimate to what areal extent PBTs are found in US estuarine resources. The data document composite, whole-body tissue chemical concentrations for 736 sampling sites across Northeast, Southeast, Gulf of Mexico, and West Coast estuaries. Tissue chemical concentrations were compared to US EPA non-cancer risk guidelines for recreational fishers, because of a lack of ecological guidelines for these chemical concentrations. Samples were analyzed for 23 PAH compounds, 21 PCB congeners, 6 DDT derivatives and metabolites, 14 chlorinated pesticides (other than DDT) and 13 metals, including mercury. Total PCBs were found to exceed recreational fisher guidelines most frequently (31% of samples evaluated), followed by mercury (29%), total PAHs (21%), and DDT and its metabolites, DDD and DDE (11%). Toxaphene, cadmium and dieldrin were found but in fewer than 1% of the samples.

Fluxes and behavior of radium isotopes, barium, and uranium in seven Southeastern US rivers and estuaries

This paper demonstrates the importance of advective transport of water through permeable estuarine and salt marsh sediments. This transport delivers significant quantities of radium and barium to the coastal ocean; and, in some cases may remove significant quantities of uranium. These conclusions are based on repeated analyses of seven river–estuarine systems from North Carolina to Florida. Fluxes of radium and barium from these river systems are shown to be inadequate to balance the dissolved inventories of these elements in the South Atlantic Bight. The strong interactions that occur between surface and subsurface waters as these rivers encounter coastal marshes lead us to consider these river mouths as marsh-dominated in terms of their chemical fluxes to the ocean. Such interactions between the river and coastal marsh must be considered when estimating fluxes of material between the land and ocean.

Untapped Bounty: Sampling the Seas to Survey Microbial Biodiversity

Untapped Bounty: Sampling the Seas to Survey Microbial Biodiversity

The Ecological Condition of Veracruz, Mexico Estuaries

During June and July, 2002, forty-seven stations were sampled within estuaries along the gulf coast of the state of Veracruz, MX, using a probabilistic survey design and a common set of response indicators. The objective of the study was to collect information to assess the condition of estuarine waters within the state of Veracruz, and to provide data that would strengthen future assessments of Gulf of Mexico estuaries. Samples for water quality, sediment contaminants, sediment toxicity, and benthic populations were collected in a manner consistent with EPA's National Coastal Assessment (NCA). Data were evaluated by comparing indicator measurements to tropical waters threshold values cited in US EPA's National Coastal Condition Report II, 2004, for tropical waters. In Veracruz, 75% of the area sampled rated poor for water quality, attributed primarily to high concentrations reported for chlorophyll a, and dissolved nutrients. One percent of the area exhibited poor sediment quality, based on PAH and metals concentrations. Compared to US estuaries of the Gulf of Mexico, water quality observed in Veracruz estuaries was more affected by nutrient over-enrichment. The probabilitistic nature of the survey design allowed for the comparison of the condition of Veracruz and the US GOM estuaries.

Variability in radiocarbon ages of biochemical compound classes of high molecular weight dissolved organic matter in estuaries

High molecular weight dissolved organic matter (HMW-DOM, >1000 Da) represents a major fraction (>30%) of dissolved organic carbon (DOC) in the ocean and thus plays an important role in the global biogeochemical cycling of carbon and many other elements. Its organic sources and formation mechanisms, however, are still not well understood especially in estuarine and coastal regions where multiple natural and anthropogenic sources contribute to total HMW-DOM. In this paper we report our measurements of natural radiocarbon ( 14C) abundances and stable carbon isotope ( 13C) compositions of the major biochemical compound classes: amino acids, carbohydrates and lipids separated from eight HMW-DOM samples collected from five US estuaries as part of our on-going study of sources, distribution and transport of chromophoric dissolved organic matter (CDOM) in estuarine and coastal waters. Distinct differences in both 14C and 13C values were found among the bulk HMW-DOM samples as well as the individual compound classes. Radiocarbon ages of the major compound classes varied by as much as 27,000 years in a single sample. The calculated average radiocarbon ages of the compound fractions of HMW-DOM indicate that the total lipid fraction is very “old”, while the acid-insoluble fraction is slightly younger. Total amino acid and carbohydrate fractions, however, have relatively modern apparent 14C ages. The significant variability in 14C ages among the compound classes indicates not only multiple organic carbon sources but also different formation and turnover pathways controlling the cycling of different biochemical components of HMW-DOM in estuarine and coastal waters.

Estuarine habitat evaluation measured by growth of juvenile summer flounder Paralichthys dentatus in a North Carolina estuary

Habitat quality and fish success, in terms of growth and mortality, are presumably correlated, and abiotic conditions are likely to be a major component in determining habitat quality. We assessed habitat quality in terms of fish growth and mortality using basic abiotic factors as the major variables. Juvenile summer flounder Paralichthys dentatus (42 to 59 mm total length) were caged at 5 sites in and around Masonboro Island, North Carolina, USA, during June and July 1999. Temperature, dissolved oxygen, salinity and pH were recorded every 30 min at each enclosure site during the experiment. Potential predators were excluded by cages and known quantities of food were provided to reduce potential impacts of food availability. Fish were individually tagged, and growth rates calculated for surviving fish. Abiotic conditions varied significantly among sites, although no differences in growth rates were detected among sites. Variability in growth rates both within and among sites was high, with 1 site experiencing total mortality. Results suggest that basic abiotic conditions, at the levels and durations that occur within a southeastern US estuary during summer, have little impact on juvenile summer flounder growth, but may influence survival.