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MULTISCALE EXPERIMENTAL ECOSYSTEM RESEARCH CENTER |
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MULTISCALE EXPERIMENTAL ECOSYSTEM RESEARCH CENTER |
The Mission
Rapid population increases in coastal watersheds have led to increased contamination of coastal waters by industrial and agricultural chemicals and by excessive additions of nutrients from a variety of sources. These trends have been associated with losses of living resources and with degradation of aquatic habitats, including episodes of oxygen depletion and production of toxic algal blooms. Most research on the effects of environmental perturbations has focused on biological responses at scales that range from molecules to individual populations of organisms. Little is known about the responses at the levels of communities of organisms and of ecosystems. The ability to make predictions by extrapolating results from controlled laboratory experiments to natural ecosystems with known accuracy and precision is one of the most significant challenges facing the scientific community today.
To help address this challenge, in 1992 the U.S. Environmental Protection Agency established the Multiscale Experimental Ecosystem Research Center (MEERC) within the University System of Maryland's Center for Environmental Sciences. MEERC has its headquarters at the University's Horn Point Laboratory in Cambridge, Maryland and supports research at that Laboratory and its sister institutions, the Chesapeake Biological Laboratory and the Appalachian Laboratory.
A major goal of MEERC is to contribute to the fundamental understanding of the scale-dependent behavior of experimental and natural estuarine ecosystems, so that research information can be extrapolated systematically among experimental ecosystems and nature, and among natural ecosystems of different dimensions. An additional goal is to interpret this information so that managers can develop comprehensive strategies to mitigate human effects on the environment, especially with regard to contaminant material.
In pursuit of these goals, MEERC scientists seek to develop principles for scaling the structure, function, and dynamics of estuarine ecosystems as the basis for predicting responses of biological and chemical processes to anthropogenic perturbations. Scale is defined broadly to include space (e.g., area, depth, volume, and spatial heterogeneity of systems), time (e.g., duration and frequency of events, acclimation to conditions, and generation time), and ecological complexity (e.g., pathways of nutrient cycling, number of trophic levels and of species within trophic levels, habitat types, and connectivity between habitats).
Specific Objectives
To further these goals, MEERC has developed a series of objectives for its research:
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Research Hypotheses
Scientists within MEERC have developed a number of governing hypotheses, beginning with the concept that the scale-dependent behavior of ecological systems arises from two basic sources: 1) dimensional matching of critical time and length scales for biological-physical interactions and 2) spatial heterogeneity in distributions of key ecosystem properties and processes. We propose that these sources of scale-dependence produce discrepancies among controlled experiments and natural conditions, as well as differences in ecological dynamics in large and small habitats. We also propose that experiments can be designed to conserve essential dimensional features of the important scales of biological interaction (e.g., predator-prey interactions) or scales of physical-biological coupling (e.g., residence-time for biological processes). With respect to the importance of spatial heterogeneity, we postulate that many of the reported scale-dependent dynamics seen in aquatic ecosystems emerge from characteristic exchanges of material, energy, and motile organisms across space. Finally, we suggest that pulsed input to and physical coupling between experimental ecosystems can be used to reproduce and explore the dynamics of heterogeneous environments.
Integrated Research
These scaling hypotheses are explored through the integrated use of biological, physical, and mathematical models. To that end, we use experimental ecosystems, hydrodynamic experiments, and numerical and simulation models.
Experimental Ecosystems:
Research within MEERC uses experimental ecosystems (mesocosms) of various sizes, shapes,
and ecological complexity to evaluate scale-related hypotheses. The focal habitats of this
research are ecosystems at the land-sea interface (coupled pelagic-benthic systems,
seagrass beds, and marshes). The scale-dependent behavior of these living models is
assessed at a variety of hierarchical levels that range from primary producers to
carnivores, and from plankton physiology to primary productivity, respiration, and
biogeochemical cycling in whole ecosystems.
Hydrodynamic Experiments:
We recognize the critical role of physical transport and turbulent mixing in structuring
estuarine ecosystems. For this reason we make extensive use of physical models to aid in
the design of internal mixing and of exchange between coupled mesocosms.
Numerical Simulation Models:
Simulation models of individual habitat types form the base of our modeling program. The
development of models simulating biological, chemical, and physical processes is closely
coupled with the design and interpretation of experimental ecosystems. For instance, the
model validation process provides a useful mechanism for exploring the theoretical basis
of scale-dependent behavior observed in the experimental ecosystems.
Simulation modeling efforts are complemented by a variety of analytical modeling tools that include network analysis, dimensional analysis, and error and uncertainty analysis. Toxicological models are used extensively to explore the fate and effects of organic and inorganic compounds in experimental ecosystems.
Early MEERC Research
Research during the first phase of the project was divided into large multi-investigator 'core projects' that addressed broad scaling issues and into smaller, highly focused 'parallel projects', as described below. More detailed information and a list of publications can be found at this website.
Core projects:
This research focused on the design and construction of mesocosms and models of
pelagic-benthic, seagrass, and marsh systems. Initially we measured the effects of
mesocosm shape and size on the development of the pelagic-benthic ecosystems as well as
assessing the interactive effects of species complexity and nutrient loading on seagrass
and marsh ecosystems. In later experiments, we examined the effects on lower trophic
levels of introducing fish and nutrients in our pelagic-benthic mesocosms. Research on
contaminants focused on potential artifacts encountered when dosing mesocosms with
particle-reactive chemicals.
Parallel projects:
In most instances, these projects were central components of graduate student theses and
dissertations. They explored problems that influenced the design and interpretation of
ecosystem experiments in MEERC and provided information on specific processes or
populations in the mesocosms.
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Research Directions Since 1996
MEERC has been successful in establishing P/B, marsh, and SAV mesocosms that exhibit reproducible responses to perturbations over a range of scales and nutrient enrichment regimes. Since 1996, the Center focused on the use of experimental ecosystems and models to meet three major scientific goals:
• quantify and parameterize scale-dependent ecosystem responses to nutrient and contaminant inputs and changes in predation pressure by large consumers;
• construct predictive models of biological variability in ecosystems that interpolate across mesocosm scales and extrapolate to ecosystems in nature; and
• assess the pitfalls, errors and uncertainties of these approaches and evaluate the accuracy and reliability of results by comparing predictions with natural systems.
Research continued to consider dimensional scaling of physical-biological coupling, but a major focus was on the question of how spatial heterogeneity produces scale-dependent patterns and dynamics in nature that are not typically reproduced in mesocosms. Here we postulated that many of the reported scale-dependent dynamics seen in aquatic ecosystems emerge from characteristic exchanges of material, energy, and motile organisms across space. Effects of scaling exchanges of water, material, and organisms between adjacent habitats were examined, as were spatially-scaled top-down effects of movement and predation by large predators on processes at lower trophic levels. To that end, we linked mesocosms in multicosm arrays. We also examined how spatial patterns of marsh plant diversity and distribution (and temporal scaling of water-movement) affected ability of intertidal ecosystems to use and transform groundwater-delivered chemicals.
We also conducted a range of modeling experiments to test the dependence of model behaviors on their inherent time, space, and complexity scales. Modeling and synthesis included development of a 3-dimensional spatial simulation program that accommodates modeling of multiple habitats (marsh, SAV, plankton, benthos) with flexible spatial orientations and gridding densities. From the large spatial grid, a single ecosystem volume can be isolated and simulated apart from the surrounding spatial array. This isolated volume can be used to simulate dynamics of experimental mesocosms with limited (or regulated) exchanges. Simulated responses of such isolated-volume ecosystems ( the "simulated mesocosm") to treatments are being compared to those of the integrated spatial model. This will produce a suite of "simulated comparisons" of responses in "mesocosms" versus "nature." We believe that these kinds of modeling experiments will move us closer to a fundamental understanding of scaling relations for extrapolation from mesocosm experiment to estuarine ecosystem.
Contaminant studies examined how variations in trophic structure influence mobility and accumulation of toxic chemicals. This effort depended on analysis of spatial and temporal patterns in data from natural estuarine ecosystems. To further address the importance of mesocosm size, trophic status (oligotrophic/eutrophic) and food chain complexity in controlling the bioaccumulation of contaminants from sediments, we began a major new research direction, with the focus of research being at the Chesapeake Biological Laboratory. Mesocosms are being used to study the importance of resuspension and benthic-pelagic coupling in driving bioaccumulation of contaminants in both benthic and pelagic organisms. This work will provide important information on aspects of bioaccumulation and the importance of in-place sedimentary contaminants, an area of heightened concern for EPA, while at the same time exploring in depth the importance of mesocosm mixing in influencing bioaccumulation. Thus this work addresses another aspect of the problems associated with scaled experimental enclosures - the importance of the correct physical mixing environment.
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