Search

Hudson Canyon is the largest shelf-sourced canyon system off the east coast of the United States, and hosts a productive ecosystem that supports key fisheries. Here we report the results of a multi-year interdisciplinary study of the geological, geochemical, and physical oceanographic features and processes in the canyon that underpin that ecosystem. High-resolution multi-beam bathymetric and backscatter data show that the contrasting morphology of the two perpendicularly oriented branches at the head of the Hudson Canyon is indicative of different states of geomorphological activity and sediment transport. Tightly spaced ridges and gullies extend perpendicularly towards the canyon axis from the canyon walls. Numerous depressions are found at the base of the canyon walls or along the canyon axis at depths from 300 m to 600 m. Elevated concentrations of dissolved methane in the water column, where the highest density of depressions occur, suggests that methane is actively venting there. The topography and reflective floors of circular depressions in canyon walls and their association with methane maxima suggest that these represent active methane gas release-collapse pockmarks with carbonate floors. Patterns of irregular, low-relief, reflective depressions on the canyon floor may also represent methane release points, either as gas release or cold-seep features. The presence of methane maxima in a region of strong advective currents suggests continuous and substantial methane supply. Hydrographic observations in the canyon show that multiple layers of distinct inter-leaved shelf (cold, fresh) and slope (warm, salty) water masses occupy the head of the canyon during the summer. Their interactions with the canyon and with each other produce shifting fronts, internal waves, and strong currents that are influenced by canyon topography. Strong tidal currents with along-canyon-axis flow shear help to drive the advection, dispersion and mixing of dissolved materials in the water column that likely help support the rich canyon ecosystem.

With the increasing appreciation that sea grass habitats are in global decline, there is a great need to be able to efficiently and effectively assess and characterize the status and trends of sea grass in our coastal ecosystems. This paper examines the utility of remotely sensed vs. in situ plot-based monitoring using the Barnegat Bay-Little Egg Harbor (BB-LEH), New Jersey, USA estuarine system as a case study. Eelgrass (Zostera marina) is the dominant species, while widgeon grass (Ruppia maritima) is also common in lower salinity regions of the BB-LEH. Aerial imagery collected during the months of July and August 2009 was interpreted and mapped using object based image analysis techniques, similar to techniques used in the 2003 mapping survey of this system. Boat-based in situ monitoring data were collected concurrently with the aerial photography to assist the image interpretation and for an independent accuracy assessment. We compared the remotely-sensed mapping of sea grass cover change (in 2003 vs. 2009) vs. in situ plot-based monitoring conducted from 2004 through 2009. Comparison of the remotely-sensed vs. the in situ plot-change analysis suggests that the two methodologies had broadly similarly results, with the percent area showing declines in sea grass cover greater than those that exhibited increases. In conclusion, the two studies provide corroborating evidence that sea grass has declined in percent cover in the BB-LEH system during the decade of the 2000’s. While remotely-sensed surveys provide synoptic information for a “big picture” view on sea grass distribution, site specific in situ sampling is required to determine other aspects of sea grass status, e.g. above vs. below-ground biomass, blade length, shoot density, epiphytic loading, etc. Either method alone gives an incomplete picture. As demonstrated in this study, to fully characterize the spatial extent, health, and density of sea grass meadows across the entire estuary, combining remote sensing surveys concomitantly with comprehensive in situ assessment provides the most robust approach.

A data model to store and retrieve surface watershed boundaries using graph theoretic approaches is proposed. This data model integrates output from a standard digital elevation models (DEM) derived stream catchment boundaries, and vector representation of stream centerlines then applies them to three novel algorithms. The first is called Modified Nested Set (MNS), which is a depth first graph traversal algorithm that searches across stream reaches (vertices) and stream junctions (edges) labeling vertices by their discovery time, finish time, and distance from the root. The second is called Log Reduced Graphs (LRG), which creates a set S of logarithmically reduced graphs from the original data, to store the watershed boundaries. The final algorithm is called Stitching Watershed, which provides a technique to merge watershed boundaries across the set of graphs created in the LRG algorithm. This technique was applied to the ~ 30,600 km2 Delaware River Watershed and compared to hypothetical data storage models in terms of prep-processing, data storage, and query complexity costs. Results show that the proposed technique provides significant benefits vs. the hypothetical methods with a 99-98% reduction in prepossessing, 96-80% reduction in query complexity and a 76% reduction in storage costs. The increasing availability of high resolution elevation data within the United States and the internationally provides an opportunity to extend these results to other watersheds through the world.

A benthic habitat assessment study conducted in the Barnegat Bay-Little Egg Harbor Estuary from June to November 2006 reveals that boat-based videographic imaging is comparable to in situ diver observations for determining the occurrence and percent cover of seagrasses in actively growing beds. A Seaviewer Sea Drop camera and recorder unit deployed along 12 transects in the estuary generated 331 images of seagrass habitat during the study period. A comparison of video still images with data derived from diver observations indicates consistent results in terms of the presence/absence and percent cover of seagrass on the estuarine floor throughout the seagrass growing season. Plots of the percent cover of seagrass recorded by the camera system vs. in situ diver observations reveal a high correlation for the June–July, August–September, and October–November sampling periods (R2 = 0.936, 0823, and 0.894, respectively) as well as for the entire June–November sampling period (R2 = 0.888). A kappa stati...

A detailed submerged aquatic vegetation (SAV) study was conducted in Little Egg Harbor (39°35′N, 74°14′W), New Jersey, a lagoonal estuary located within the boundaries of the Jacques Cousteau National Estuarine Reserve, to assess the demographic characteristics and spatial habitat changes of Zostera marina beds over an annual growing period and to determine the species composition, relative abundance, and potential impacts of benthic macroalgae on seagrass habitat in the system. Two disjunct seagrass beds in Little Egg Harbor, covering an area of ∼1700 ha, were sampled at 10 equally spaced points along six, east–west-trending transects in spring, summer, and fall (June–November) of 2004. During this period, 180 seagrass samples were collected at 60 transect sites, together with an array of water quality measurements. Results of this investigation indicate that both aboveground and belowground biomass of seagrass peaked during June–July and declined significantly into the fall months. Mean abovegr...

A 3 year study (2000–2002) in Barnegat Bay-Little Egg Harbor (BB/LEH), New Jersey (USA), was conducted by the New Jersey Department of Environmental Protection, Division of Science Research and Technology (DSRT) in cooperation with several partners to assess brown tide blooms in coastal waters in NJ. Water samples were collected by boat and helicopter at coastal stations from 2000 to 2002 along with field measurements. Aureococcus anophagefferens were enumerated and associated environmental factors were analyzed. A. anophagefferens abundances were classified using the Brown Tide Bloom Index and mapped, along with salinity and temperature parameters, to their geo-referenced location using the ArcView GIS. The highest A. anophagefferens abundances (>106 cells ml−1), including category 3 blooms (≥200,000 cells ml−1) and category 2 blooms (≥35,000 to ≤200,000 cells ml−1), recurred during each of the 3 years of sampling and covered significant geographic areas of the estuary, especially in Little Egg Harbor. While category 3 blooms were generally associated with warmer water temperatures (>16 °C) and higher salinity (>25–26 ppt), these factors were not sufficient alone to explain the timing or distribution of A. anophagefferens blooms. There was no significant relationship between brown tide abundances and dissolved organic nitrogen measured in 2002 but this was consistent with other studies. Extended drought conditions, with corresponding low freshwater inputs and elevated bay water salinities, occurring during this time were conducive to blooms. A. anophagefferens abundances were well above the reported levels that have been reported to cause negative impacts on shellfish. It was shown that over 50% of the submerged aquatic vegetation (SAV) habitat located in Barnegat Bay/Little Egg Harbor was categorized as having a high frequency of category 2 or 3 blooms for all 3 years.

The benthic macrofaunal community of the Mullica River–Great Bay estuary in the Jacques Cousteau National Estuarine Research Reserve is characterized by both small-scale and large-scale distribution patterns that can be correlated to gradients in physicochemical parameters. Sediment composition is a major factor regulating the local distribution of benthic assemblages in the estuary, with the amount of silt-clay being particularly important. For example, one suite of benthic fauna (i.e., Ampelisca verrilli, Ensis directus, Haustorius arenarius, Pygospio elegans, and Oxyurostylis smithi) reported in the estuary has been found only in sediments with less than 20% silt-clay, whereas another (i.e., Acteocina canaliculata, Lumbrineris tenuis, Maldinopsis elongata, Tellina agilis, Turbonilla sp., and Unciola irrorata) has been observed only in sediments with more than 38% silt-clay. Other physicochemical factors (e.g., organic carbon content of the sediments, dissolved oxygen levels, bottom currents, a...

Side-scan sonar imaging conducted in Great Bay, New Jersey, during August 2003 reveals local variations in acoustic backscatter from the seabed that can be related to small-, medium-, and large-scale bedforms. Analysis of 600-kilohertz side-scan sonar data collected at a System-Wide Monitoring Program (SWMP) survey site of the Jacques Cousteau National Estuarine Research Reserve shows a relationship between backscatter intensity, bathymetry, and changing seabed morphology. Side-scan sonar records obtained at the survey site in Great Bay via deployment of an autonomous underwater vehicle (Remote Environmental Monitoring UnitS) provide in-depth characterization of an array of complex and multiscaled bedforms and associated benthic habitats. Bedforms documented within the swath map region by side-scan sonar imaging include constructive transverse forms, notably ripples, dunes, and sand waves. These bedforms are valuable for assessing potentially important habitats for benthic invertebrate and demers...