Temporal patterns of Deepwater Horizon impacts on the benthic infauna of the northern Gulf of Mexico continental slope.

The Deepwater Horizon oil spill occurred in spring and summer 2010 in the northern Gulf of Mexico. Research cruises in 2010 (approximately 2-3 months after the well had been capped), 2011, and 2014 were conducted to determine the initial and subsequent effects of the oil spill on deep-sea soft-bottom infauna. A total of 34 stations were sampled from two zones: 20 stations in the "impact" zone versus 14 stations in the "non-impact" zone. Chemical contaminants were significantly different between the two zones. Polycyclic aromatic hydrocarbons averaged 218 ppb in the impact zone compared to 14 ppb in the non-impact zone. Total petroleum hydrocarbons averaged 1166 ppm in the impact zone compared to 102 ppm in the non-impact zone. While there was no difference between zones for meiofauna and macrofauna abundance, community diversity was significantly lower in the impact zone. Meiofauna taxa richness over the three sampling periods averaged 8 taxa/sample in the impact zone, compared to 10 taxa/sample in the non-impact zone; and macrofauna richness averaged 25 taxa/sample in the impact zone compared to 30 taxa/sample in the non-impact zone. Oil originating from the Deepwater Horizon oil spill reached the seafloor and had a persistent negative impact on diversity of soft-bottom, deep-sea benthic communities. While there are signs of recovery for some benthic community variables, full recovery has not yet occurred four years after the spill.

Sediment quality benchmarks for assessing oil-related impacts to the deep-sea benthos.

Paired sediment contaminant and benthic infaunal data from prior studies following the 2010 Deepwater Horizon (DWH) oil spill in the Gulf of Mexico were analyzed using logistic regression models (LRMs) to derive sediment quality benchmarks for assessing risks of oil-related impacts to the deep-sea benthos. Sediment total polycyclic aromatic hydrocarbon (PAH) and total petroleum hydrocarbon (TPH) concentrations were used as measures of oil exposure. Taxonomic richness (average number of taxa/sample) was selected as the primary benthic response variable. Data are from 37 stations (1300-1700 m water depth) in fine-grained sediments (92%-99% silt-clay) sampled within 200 km of the DWH wellhead (most within 40 km) in 2010 and 32 stations sampled in 2011 (29 of which were common to both years). Results suggest the likelihood of impacts to benthic macrofauna and meiofauna communities is low (<20%) at TPH concentrations of less than 606 mg kg-1 (ppm dry weight) and 700 mg kg-1 respectively, high (>80%) at concentrations greater than 2144 mg kg-1 and 2359 mg kg-1 respectively, and intermediate at concentrations in between. For total PAHs, the probability of impacts is low (<20%) at concentrations of less than 4.0 mg kg-1 (ppm) for both macrofauna and meiofauna, high (>80%) at concentrations greater than 24 mg kg-1 and 25 mg kg-1 for macrofauna and meiofauna, respectively, and intermediate at concentrations in between. Although numerical sediment quality guidelines (SQGs) are available for total PAHs and other chemical contaminants based on bioeffect data for shallower estuarine, marine, and freshwater biota, to our knowledge, none have been developed for measures of total oil (e.g., TPH) or specifically for deep-sea benthic applications. The benchmarks presented herein provide valuable screening tools for evaluating the biological significance of observed oil concentrations in similar deep-sea sediments following future spills and as potential restoration targets to aid in managing recovery. Integr Environ Assess Manag 2017;13:840-851. Published 2017. This article is a US Government work and is in the public domain in the USA.

Persistent impacts to the deep soft-bottom benthos one year after the Deepwater Horizon event.

In fall 2010, several months after the Deepwater Horizon blowout was capped, zones of moderate and severe impacts to deep-sea, soft-bottom benthos were identified that together extended over an area of 172 km2 . A subset of stations sampled in 2010 was resampled in May and June 2011, 10 to 11 months after the event, to determine whether the identified adverse effects were persisting. The design compared 20 stations from the combined moderate and severe impact zone to 12 stations in the reference zone that were sampled in both years. There were no statistically significant differences in contaminant concentrations between the impact and nonimpact zones from 2010 to 2011, which indicates contaminants persisted after 1 y. Whereas there were some signs of recovery in 2011 (particularly for the meiofauna abundance and diversity), there was evidence of persistent, statistically significant impacts to both macrofauna and meiofauna community structure. Macrofaunal taxa richness and diversity in 2011 were still 22.8% and 35.9% less, respectively, in the entire impact zone than in the surrounding nonimpact area, and meiofaunal richness was 28.5% less in the entire impact zone than in the surrounding area. The persistence of significant biodiversity losses and community structure change nearly 1 y after the wellhead was capped indicates that full recovery had yet to have occurred in 2011. Integr Environ Assess Manag 2017;13:342-351. © 2016 SETAC.

An integrated assessment of habitat quality of national estuarine research reserves in the southeastern United States.

Multiple indicators of water quality, sediment quality, and biological condition were used to assess the status of ecological condition of National Estuarine Research Reserve System (NERRS) sites in North Carolina, South Carolina, and Georgia relative to a suite of corresponding scoring criteria. All measurements were made in subtidal aquatic habitats. Calculated scores were integrated into an overall index of habitat quality and used to make comparisons among the various NERR and nonNERR estuaries throughout the region. Sediment quality scores varied considerably among NERR sites, but in most cases were similar between individual NERR and non-NERR sites in corresponding states. Water quality and biological condition indicators scored consistently higher for NERRs versus non-NERR sites. Overall habitat quality scores also were consistently higher for NERRS sites, suggesting that these areas are on par with if not in slightly better condition ecologically than neighboring nonNERR estuaries. Portions of individual NERR sites rated as poor with respect to overall habitat quality were limited to relatively small areas (<13% of a reserve's total sampling area).

Deep-sea benthic footprint of the deepwater horizon blowout.

The Deepwater Horizon (DWH) accident in the northern Gulf of Mexico occurred on April 20, 2010 at a water depth of 1525 meters, and a deep-sea plume was detected within one month. Oil contacted and persisted in parts of the bottom of the deep-sea in the Gulf of Mexico. As part of the response to the accident, monitoring cruises were deployed in fall 2010 to measure potential impacts on the two main soft-bottom benthic invertebrate groups: macrofauna and meiofauna. Sediment was collected using a multicorer so that samples for chemical, physical and biological analyses could be taken simultaneously and analyzed using multivariate methods. The footprint of the oil spill was identified by creating a new variable with principal components analysis where the first factor was indicative of the oil spill impacts and this new variable mapped in a geographic information system to identify the area of the oil spill footprint. The most severe relative reduction of faunal abundance and diversity extended to 3 km from the wellhead in all directions covering an area about 24 km(2). Moderate impacts were observed up to 17 km towards the southwest and 8.5 km towards the northeast of the wellhead, covering an area 148 km(2). Benthic effects were correlated to total petroleum hydrocarbon, polycyclic aromatic hydrocarbons and barium concentrations, and distance to the wellhead; but not distance to hydrocarbon seeps. Thus, benthic effects are more likely due to the oil spill, and not natural hydrocarbon seepage. Recovery rates in the deep sea are likely to be slow, on the order of decades or longer.

Habitat-related benthic macrofaunal assemblages of bays and estuaries of the western United States.

Data from 7 coastwide and regional benthic surveys were combined and used to assess the number and distribution of estuarine benthic macrofaunal assemblages of the western United States. Q-mode cluster analysis was applied to 714 samples and site groupings were tested for differences in 4 habitat factors (latitude, salinity, sediment grain size, and depth). Eight macrofaunal assemblages, structured primarily by latitude, salinity, and sediment grain size, were identified: (A) Puget Sound fine sediment, (B) Puget Sound coarse sediment, (C) southern California marine bays, (D) polyhaline central San Francisco Bay, (E) shallow estuaries and wetlands, (F) saline very coarse sediment, (G) mesohaline San Francisco Bay, and (H) limnetic and oligohaline. The Puget Sound, southern California, and San Francisco Bay assemblages were geographically distinct, while Assemblages E, F and H were distributed widely along the entire coast. A second Q-mode cluster analysis was conducted after adding replicate samples that were available from some of the sites and temporal replicates that were available for sites that were sampled in successive years. Variabilities due to small spatial scale habitat heterogeneity and temporal change were both low in Puget Sound, but temporal variability was high in the San Francisco estuary where large fluctuations in freshwater inputs and salinity among years leads to spatial relocation of the assemblages.

Effects of Hurricane Katrina on benthic macroinvertebrate communities along the northern Gulf of Mexico coast.

The effects of Hurricane Katrina on benthic fauna and habitat quality in coastal waters of Louisiana, Mississippi, and Alabama, USA, were assessed in October, 2005, 2 months after the hurricane made landfall between New Orleans, LA and Biloxi, MS. Benthic macrofaunal samples, sediment chemical concentrations, and water quality measurements from 60 sites in Lake Pontchartrain and Mississippi Sound were compared with pre-hurricane conditions from 2000-2004. Post-hurricane benthic communities had significant reductions in numbers of taxa, H(') diversity, and abundance as well as shifts in composition and ranking of dominant taxa. These effects were not associated with changes in chemical contamination, organic enrichment of sediments, or hypoxia and were likely due to hurricane-related scouring and changes in salinity.

Ecosystem responses to extreme natural events: impacts of three sequential hurricanes in fall 1999 on sediment quality and condition of benthic fauna in the Neuse River Estuary, North Carolina.

A study was conducted in November 1999 to assess sediment quality and condition of benthic fauna in the Neuse River Estuary (NRE), North Carolina, USA, following the passage of three Atlantic hurricanes during the two months prior. Samples for analysis of macroinfauna (>0.5 mm sieve size), chemical contamination of sediments, and other abiotic environmental variables (salinity, dissolved oxygen, pH, depth, sediment granulometry) were collected at 20 sites from the mouth of the Neuse River at Pamlico Sound to approximately 90 km upstream. Results were compared to those obtained from the same area in July 1998 using similar protocols. Depressed salinity, caused by extreme rainfall and associated high freshwater flow, persisted throughout much of the estuary, which had experienced periods of water-column stratification and hypoxia of underlying waters. Fifteen of the 20 sites, representing 299 km2 (76% of the survey area), also showed signs of benthic stress based on a multi-metric benthic index of biotic integrity (B-IBI). Benthic impacts included reductions in the abundance, diversity, and numbers of species and shifts in taxonomic composition, with a notable increase in dominance of the opportunistic polychaete Mediomastus ambiseta as other former dominant species declined. There was no significant increase in the extent of chemical contamination compared to pre-hurricane conditions. Storm-related reductions in dissolved oxygen and salinity were the more likely causes of the observed benthic impacts, though it was not possible, based on these results, to separate storm effects from seasonal changes in the benthos and annual episodes of summer anoxia and hypoxia.

Incidence of stress in benthic communities along the U.S. Atlantic and Gulf of Mexico coasts within different ranges of sediment contamination from chemical mixtures.

Synoptic data on concentrations of sediment-associated chemical contaminants and benthic macroinfaunal community structure were collected from 1,389 stations in estuaries along the U.S. Atlantic and Gulf of Mexico coasts as part of the nationwide Environmental Monitoring and Assessment Program (EMAP). These data were used to develop an empirical framework for evaluating risks of benthic community-level effects within different ranges of sediment contamination from mixtures of multiple chemicals present at varying concentrations. Sediment contamination was expressed as the mean ratio of individual chemical concentrations relative to corresponding sediment quality guidelines (SQGs), including Effects Range-Median (ERM) and Probable Effects Level (PEL) values. Benthic condition was assessed using diagnostic, multi-metric indices developed for each of three EMAP provinces (Virginian, Carolinian, and Louisianian). Cumulative percentages of stations with a degraded benthic community were plotted against ascending values of the mean ERM and PEL quotients. Based on the observed relationships, mean SQG quotients were divided into four ranges corresponding to either a low, moderate, high, or very high incidence of degraded benthic condition. Results showed that condition of the ambient benthic community provides a reliable and sensitive indicator for evaluating the biological significance of sediment-associated stressors. Mean SQG quotients marking the beginning of the contaminant range associated with the highest incidence of benthic impacts (73-100% of samples, depending on the province and type of SQG) were well below those linked to high risks of sediment toxicity as determined by short-term toxicity tests with single species. Measures of the ambient benthic community reflect the sensitivities of multiple species and life stages to persistent exposures under actual field conditions. Similar results were obtained with preliminary data from the west coast (Puget Sound).