Integration of ROV Sensor Data in the Study of Biological Responses in a Dynamic Buoyant River Plume, Hudson River Estuary, USA
Coastal waters extending from our estuaries to the continental shelf comprise roughly 10% of the our oceans, but the biological and chemical processes at work in these areas support over 90% of marine fisheries worldwide [2]. The bulk of this productivity is fueled by elements delivered by two main sources: upwelling and riverine inputs. In particular, major rivers deliver critical quantities of nutrients and other elements that support the growth at the most basic level of the food chain: phytoplankton. This growth in turn, supports higher trophic levels. However the interaction of people with these ecosystems is disturbing these habitats through, amongst many other activities, increasing inputs of nutrients and metals to rivers and coasts through suburban run-off. These increased loads interact with the rates and limits of biological processing and now pose several questions for researchers to answer. To begin with, "At what point do loads of nutrients and metals from large rivers, especially anthropogenic loads, compromise sustainability of coastal ecosystems?"
Figure 1: Satellite image of New York City and the Hudson River Estuary
(Image: NASA Public Domain)
To begin tackling these hard questions, Dr. Mark Moline of Cal Poly San Luis Obispo and a team of researchers from the University of Florida, Rutgers University, the University of Massachusetts, and the University of California Santa Cruz undertook a study of the buoyant river plumes that form at the mouth of the Hudson River.
Project Description
During a 13 day sampling campaign during April 2005, Dr. Moline and his team collected data on the levels of nutrients, metals, phytoplankton and zooplankton in the Hudson River estuary and a 120 km2 region along the New Jersey coastline. The data was collected utilizing station profiles and towed instrumentation from two research vessels, the R/V Cape Hatteras and the R/V Oceanus, which worked in tandem as to maximize their sampling efforts. Scientsts aboard the Cape Hatteras undertook the mapping of the local physical, biological and chemical oceanography and also characterized zooplankton biomass and size structure through the use of a laser optical plankton counter (LOPC). During the same time, the Oceanus also obtained optical measurements while collecting biomass samples to characterize phytoplankton productivity, zooplankton grazing, and to measure zooplankton trace metal concentrations. This data was supplemented with data collected by gliders, satellites and high frequency radar as part of the New Jersey Shelf Observing System [3].
Figure 2: Using Eonfusion, bathymetric data from the Hudson River Estuary is integrated with vertical profiles of water density (red) and surface chlorophyll-a concentrations (green) collected by the R/V Cape Hatteras and R/V Oceanus. Less-dense plume water (low salinity) is indicated by larger and darker red spheres, and increased chlorophyll-a concentrations are indicated by larger circles.
The Challenge
Integrating and visualizing complex data sets such as those previously described - particularly in the context of the local bathymetry - has traditionally been a laborious and time-consuming task. To circumvent this issue, researchers will often select a few key moments & locations in their time series data to focus their analyses. While this is acceptable in situations where the phenomena being studied are occurring at discrete locations or are relatively well understood, in cases where there a many factors interacting across a 4-dimensional space, this can lead to data omission, incomplete consideration of the data or missed opportunities for improved understanding.
The Result
Working in cooperation with Dr. Moline, the Myriax team used Eonfusion to integrate water density and chlorophyll-a (chl-a) concentrations with additional data collected by the R/V's and bathymetry data. The result was a 4-dimensional view of the buoyant river plume and adjacent areas.
Chl-a concentrations visible in the area of the plume indicated the accumulation of phytoplankton biomass which corresponded to high nutrient levels. Concentrations of chl-a was seen to drop off precipitously outside of the plume area and this was interpreted as confirmation that large phytoplankton which exited the plume rapidly sank to the sea floor.
Acknowledgement:
Myriax thanks Mark Moline of the California Polytechnic University, San Luis Obispo and the other members of his research team for their cooperation in the development of this case study. For more in-depth discussions of these and related topics, please refer to Dr. Moline's article in the Dec 2008 Journal of Oceanography and the following references.
References:
[1] Moline, M.A., et al. 2008. Biological Responses in a Dynamic River Plume. Journal of Oceanography, Vol 21, No. 4, pp 70-90.
[2] Agardy, T., et al. 2005. Chapter 19: Coastal systems. Pp. 515-549 in R. Hassan, R. Scholes, and N. Ash, eds, Ecosystems and Human Well-being: Current State and Trends: Findings of the Condition and Trends Working Group, Millennium Ecosystem Assessment (Program), Island Press, Washington, DC.
[3] Schofield, O., et al. 2002. The long-term ecosystem observatory: An integrated coastal observatory. Journal of Oceanic Engineering 27:146-154.
