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Current CHRP Research Projects

Modeling Hypoxia and Ecological Responses to Climate and Nutrients

(2007-2012)

Michael Kemp (lead PI), Ming Li, Elizabeth North

University of Maryland, Center for Environmental Science, Horn Point Laboratory

 

Walter Boynton, David Secor

University of Maryland, Center for Environmental Science, Cambridge Biological Laboratory

 

Domenic DiToro

 

University of Delaware

 

Katja Fennel

 

Dalhousie University

Coastal eutrophication and associated bottom water hypoxia are problems of growing proportions worldwide. Although in many estuaries water quality monitoring and modeling programs have been developed to assess and forecast ecological responses to nutrient loading, site-specific approaches and ineffective researcher-manager communications have limited their success. This project will produce robust science-based predictive tools readily implemented for any coastal system to simulate ecological responses to climate and nutrient input management.

The project combines:

(1) retrospective analysis of existing data on climate, nutrients, and hypoxia, with

(2) diagnostic assessment of mechanisms underlying observed ecological dynamics,

(3) simulation studies that develop numerical models to forecast and analyze water quality responses to climate and nutrient management, and

(4) habitat evaluation of the associated variations in size and quality of living space for selected fish and invertebrate populations.

Because of the existing rich data bases and active collaborations between researchers and managers, the partially-stratified Chesapeake Bay (CB) and the shallow well-mixed Delaware Inland Bays (DIB) offer ideal but contrasting study sites.

Information on variations in river flow, water temperature, and wind velocity will be used in conjunction with water quality monitoring data to produce statistical models (CART, GAM, ARMA) for quantitative interpretation of spatial-temporal patterns of water quality in relation to climate and nutrient loading variations at relatively coarse scales. A coupled model of physical circulation (ROMS) and biogeochemistry (RCA) will be used to analyze these data further and to improve quantitative understanding of mechanisms underlying observed hypoxia responses to climate variations at finer scales.

Adjoint data assimilation methods will be used for parameter optimization in the biogeochemical model, as implemented for a well-studied nutrient enrichment experiment (MERL). Simulation performance of the coupled ROMS-RCA model will be tested quantitatively by comparing model and data both for series of specific observations and for statistically derived functional relationships among key processes and properties. The coupled circulation-biogeochemical model, which is designed with open source-codes and flexible structures, will be readily transferable for implementation by other users in diverse coastal systems. Ensemble simulations, with alternative parameter sets and forcing climatologies, will provide confidence-limits to help scientists and managers interpret scenarios and forecasts.

Model simulations will include routine seasonal forecasts of hypoxia distribution and intensity in upcoming summer seasons based on spring climatic and ecological conditions and on average summer climatology. Annual and decadal scale simulations will also examine ecological responses to nutrient management scenarios under different climatic conditions. In addition, output from the coupled ROMS-RCA model will be combined with habitat suitability and bioenergetic algorithms for key fish and invertebrates to compute habitat quantity and quality as well as potential fish production. This project will be conducted by a team of ecologists, oceanographers and modelers working in direct collaboration with technical staff of resource management agencies (EPA, NOAA, DNR, DNREC), thereby facilitating transfer of results to CB and DIB managers. We will use teacher internships to engage K-12 educators and students into our research, developing friendly interactive websites for classroom applications.

Linking Hypoxia-Induced Habitat Degradation to Fishery Outcomes: A Bioeconomic Approach Based on Brown Shrimp (2005-2008)

Kevin Craig - Duke University

Larry Crowder - Duke University

Martin Smith - Duke University

Abstract: Estuaries are important ecosystems supporting the production of commercial fisheries but are also subject to a variety of anthropogenic influences that potentially undermine this function. The biological and physical processes that make estuaries valuable nursery habitats for a variety of fish and crustacean species can also lead to hypoxia (i.e., low dissolved oxygen) as a result of anthropogenic eutrophication.

Understanding the ecological and economic effects of hypoxia is critical to evaluating consequences for marine resources and fisheries, as well as the efficacy of environmental

policies. This proposal addresses the ecological and economic effects of hypoxia on brown shrimp (Farfantepenaeus aztecus) and the shrimp fishery in the Albemarle-Pamlico estuarine system that result from the impairment of estuarine nursery habitats providing the environmental basis for shrimp production. An approach is proposed to develop a fully integrated empirical bioeconomic model linking hypoxia effects on shrimp population dynamics to fisheries behavior, catch, and profits.

The primary objectives are to:

  1. Quantify spatial and temporal variation in indicators of brown shrimp production (i.e., abundance, size structure) and relationships to indices of the severity of hypoxia,
  2. Assess the relative importance of alternative mechanisms underlying oxygen effects on shrimp condition and growth,
  3. Develop and extend a spatially-explicit individual-based population model to assess the consequences of annual variation in the severity of hypoxia on shrimp production,
  4. Evaluate the responsiveness of commercial fishing effort to spatial and temporal variation in shrimp production and potential consequences of hypoxia on shrimper revenues, and
  5. Develop a bioeconomic model to trace the ecological effects of hypoxia through to spatial and temporal patterns in fishing behavior and associated economic outcomes.

The approach proposed to address these objectives includes: (1) analysis of existing, long-term fishery independent shrimp and oxygen monitoring surveys (Objective 1), factorial experiments and targetted field studies to address the effects of hypoxia on shrimp energetics and growth (Objective 2), extension and further development of a spatially-explicit individual-based population model to quantify the effects of hypoxia on shrimp abundance and size structure (Objective 3), econometric analysis of commercial fishery data (Objective 4), and development of a process-oriented bioeconomic model that incorporates both the spatial and temporal dynamics of brown shrimp and the fishery (Objective 5).

While estuarine nursery habitats are generally thought to provide a variety of ecosystem services, approaches to valuing these services are not well developed. The proposed modeling and empirical approach will provide the basis for coupling the natural system with human activities (i.e., fishing) in a way that incorporates the dynamic nature of both. As such, the model can be used as a tool for policy-makers to evaluate the costs and benefits of hypoxia and associated remediation policies on the ecosystem services supporting an economically important commercial fishery.

Watershed—Estuary—Species Nutrient Susceptibility (2005-2010)

Donald Scavia - University of Michigan

Gloria Helfand - University of Michigan

Robert Howarth - Cornell University

Richard Alexander - US Geological Survey

Denise Breitburg - Smithsonian Environmental Research Center

Abstract: Increased nutrient inputs to coastal waters have led to substantial changes to coastal ecosystems in the United States and around the world with an estimated degradation of 2/3 of U.S. coastal systems. Predicting the sensitivity of coastal systems to degradation and the likely consequences of human activities, are critical to protect restore, and manage our Nation's waterways. Three interconnected processes determine the likelihood that an estuary will suffer consequences of nutrient over enrichment:

  1. Physical and economic characteristics of watersheds that affect the delivery of nutrients,
  2. Physical and biological characteristics of estuaries that regulate the expression of symptoms; and
  3. Physical and biological characteristics of estuaries that determine the effect of those symptoms on living resources. Improved models of these processes and their interactions, can improve prioritizing systems for protection and remediation.

Our overall objective is to integrate existing data and models within a framework to allow the flow of information, forecasts, and scenarios from watershed and climate change, through hydrologically-modulated estuarine susceptibility, to potential impacts on upper trophic levels.

Objective 1: Refine and compare 3 models of environmental and economic effects of changes in land-use, nutrient management, and climate on nutrients flux to estuaries. The watershed team will build more detailed databases and use them to refine, compare, and apply the models for Atlantic and Gulf watersheds at temporal resolution needed to assess the effects of climate change and land-use/land cover on nutrient delivery to estuaries. An economic analysis of the impacts of policy actions will relate potential load targets to their costs.

Objective 2: Develop a set of models to classify estuaries according to their susceptibility and test them against an expanded NOAA data set. The estuary team will enhance the existing NOAA eutrophication data set, use relatively simple models to produce eutrophication response surfaces as a function of key driving variables (e.g., nutrient load, flushing), and test the resulting classification surfaces with the enhanced data set.

Objective 3: Develop biological, physical, and morphological indicators of the effects of eutrophication on upper trophic levels and explain its variation among estuaries. The living resource team will integrate data and information from the primary and secondary literature with statistical and mechanistic models to develop indicators that explain variations in upper trophic level response to eutrophication.

This work is intended to lead to a better predictive understanding of the potential causes and consequences of nutrient pollution on estuarine ecosystems and how estuarine hydrology and morphology modulate estuarine and upper trophic level responses.  

For more information visit the project website at: http://sitemaker.umich.edu/chrpwe/home

Historical Trends of Hypoxia in Three Basins of Puget Sound (2005-2008)

Eric Crecelius - Battelle Memorial Institute

Abstract: Puget Sound has had seasonal hypoxia for at least 50 years; however, only in the last few years have hypoxic events caused unprecedented fish closures and fish kills with associated severe environmental and economic impacts. In Puget Sound , the primary cause of hypoxic events is not yet well understood. Both physical (stratification caused by freshwater runoff) and biological (enhanced organic matter caused by nutrient input) factors may have contributed to greater intensity of hypoxia. Until the cause of the problem is clarified, an appropriate management strategy to mitigate impacts cannot be developed or implemented.

To address this issue, Battelle is proposing to reconstruct the history of hypoxia in three basins of Puget Sound by examining the chemical and biological record of past hypoxic events recorded in age-dated sediment cores. Previous studies conducted by Battelle for NOAA have demonstrated that a detailed history of chemical contamination is recorded in the sediment of Puget Sound . Battelle has assembled a team of experts that use sediment to understand past environmental conditions in estuaries. Parameters that will be quantified include diatom shells (an indicator of eutrophication in the water column), foraminifera (an indication of oxygen concentration in the bottom water), pollen (an indicator of land clearing in the watershed), stable isotopes of carbon and nitrogen (indicators of the sources of organic matter and nutrients), biomarkers for terrestrial and marine carbon, and metals that are enriched in anoxic sediment.

Sediment cores will be collected in Hood Canal, central Puget Sound, and southern Puget Sound. These three basins have different physical oceanography conditions and different mixes of land used, river flow, and urbanization. Both Hood Canal and Budd Inlet in southern Puget Sound have histories of hypoxia, whereas the central basin has most of the urban contamination but apparently no hypoxia. The Puget Sound Action Team, which is funding studies of nutrient sources in Hood Canal, is enthusiastic about this proposal that will be the first historical examination of water and sediment quality. Questions that will be answered will include the following: Has hypoxia only occurred following European settlement? Is land clearing or dam building correlated with changes in sedimentation rate and terrestrial carbon content of sediment? How has nutrient loading contributed to the increase in eutrophication? And do changes in diversity of diatoms and foraminifera correlate with the history of nutrient loading?

The goals of this project are twofold:

  1. To describe the history of hypoxia and correlate changes that provide evidence of the causes of hypoxia, and
  2. To provide coastal resource managers with tools in the form of either biomarkers or chemical parameters that will indicate the status of a basin in terms of the stage of becoming hypoxic. These tools will allow a predictive capability for given current conditions and potential natural or anthropogenic scenarios, including management alternatives, such as nutrient removal and river flow control.

The strength of this project is that we combine the expertise of nationally known specialists to interpret organic geochemical analyses, which will be verified against paleoecological and inorganic indicators, to better understand changes in community diversity in the water column and redox conditions in the sediment and deep waters. This information will be used to better determine what combination of factors is triggering increased eutrophication in Puget Sound waters and subsequent appropriate action.

Linking Water Quality Models with Individual-Based Models to Investigate Impacts of Diel-Cycling Hypoxia on Nursery Habitat Quality for Estuarine Dependent Fishes (2005-2008)

Timothy E. Targett - University of Delaware

Dominic M. Di Toro - University of Delaware

Robert J. Diaz - Virginia Institute of Marine Science, College of William and Mary

Abstract: Eutrophication and resulting hypoxia are well studied phenomena in deep water estuaries such as the Gulf of Mexico and the Chesapeake Bay. However, the impact of eutrophication on shallow estuaries, such as coastal lagoons which make up 13% of the global coastline habitat, remains poorly understood. Shallow systems with restricted exchange with the ocean are particularly vulnerable to diel-cycling hypoxia. This study proposes to connect the growing spatial extent of diel-cycling hypoxia to estuarine dependent fish (weakfish and summer flounder) that use these vital areas as nursery habitat. In order to establish this link, the proposed work will take a synthesized laboratory, field and modeling approach. An existing water quality model (WQM) and continuous water quality monitoring will characterize the nature of diel-cycling hypoxia observed in this case study of Delaware Coastal Bays. Fish tracking and video mounted benthic sleds will characterize the response of fish and benthos to low dissolved oxygen (DO). Trawling for fishes will determine distribution and spatial/temporal differences in feeding, relative to diel cycling hypoxia and prey resource abundance. Finally, water quality model output and direct field measured organism response will be input into an individual-based model that also incorporates laboratory growth and behavioral data for these two species. The proposed project that includes data collection, model integration and calibration as necessary, is a unique opportunity to utilize a comprehensive WQM and IBM to address one of the ultimate concerns of water quality modelers: namely the impact of water quality variations on fish production and health. If this is successful, it will begin a new era in living resources management, where a direct link is made between the nutrient and other constituents discharged to a water body, through the computed water quality variables, to the affected living resources. This has been a goal of water quality based management for many years. This project offers the opportunity to test its feasibility in a setting where the necessary components are essentially available at the start of the project.

Oxygen Dynamics Models Applied in Narragansett Bay (2005-2010)

Candace Oviatt - Graduate School of Oceanography, University of Rhode Island

Deanna Bergondo - Graduate School of Oceanography, University of Rhode Island

Daniel Codiga - Graduate School of Oceanography, University of Rhode Island

Chris Kincaid - Graduate School of Oceanography, University of Rhode Island

Scott Nixon - Graduate School of Oceanography, University of Rhode Island

David Ullman - Graduate School of Oceanography, University of Rhode Island

Warren Prell - Brown University

James Kremer - University of Connecticut Avery Point

Mark Brush - Virginia Institute of Marine Science

Abstract: Time series observations initiated in 1999 by Dana Kester of water quality parameters in upper Narragansett Bay have indicated hypoxic/anoxic events in the summer months associated with the neap tide period (Bergondo et al. In Press). A network of monitoring stations and surveys have been improved and developed since that time to document the spatial and temporal distribution of low oxygen by the Rhode Island Department of Environmental Management, the Narragansett Bay Estuarine Research Reserve, the Narragansett Bay Estuary program, the Narragansett Bay Commission, the NOAA National Marine Fisheries Service and the Graduate School of Oceanography making available a large and growing data set for the development and verification of predictive simulation models. In 2003 an anoxic event during the neap tide occurred in Greenwich Bay resulting in a large fish kill (RIDEM 2003). In response, a state law was championed and passed by both the state legislature and the Governor to impose nitrogen limits on the largest wastewater treatment facilities (WWTFs) discharging to or just upstream of the Bay. Despite previous modeling efforts, no predictive system presently exists to adequately evaluate the response of Narragansett Bay to these planned nutrient loading reductions. Our hypotheses have expanded from an original prediction of stratification induced hypoxia during neap tides to include system metabolism, river runoff, winds, residence time, vertical mixing features, nutrients and advection. We propose a hybrid model based on a simplified ecosystem model (Kremer-Brush) linked to a 3D hydrodynamic model (ROMS), providing a likelihood of predictions of low oxygen events and the response of the Bay to reduced nitrogen inputs closely tied to real-world process rates. Our objectives are:

  1. Develop a new simplified ecological model to predict low oxygen.
  2. Collect new data to calibrate and verify the ecological model.
  3. Adapt the ROMS hydrodynamic model to Narragansett Bay using the current network of data collection for calibration and verification and link to the ecological model.
  4. Collect new data on vertical mixing rates and vertical current structure.
  5. Collect new data on the spatial extent of hypoxia and synthesize data on oxygen dynamics.
  6. Examine historical oxygen conditions through use of sediment cores.
  7. Provide regulators with the tools to assess decisions to reduce nutrients.

Our work plan is to make predictions about the oxygen dynamics by applying the hybrid model to a suite of scenarios involving various physical conditions and varied nutrient loads. For the ecosystem model we will need to calibrate and verify the model in each spatial element. For this model we will make new measures of primary production, water column and benthic respiration and construct a new mass balance for nitrogen. We will collect data to improve the parameterization and verify the hydrodynamic model. The focus of field measurements for the hydrodynamic model will be in a large area of uncertainty for these models, vertical mixing at key boundary areas. We will also measure the spatial/temporal extent of hypoxia in intensive surveys. These efforts will help decision-makers better predict ecosystem responses related to hypoxia generation for present nutrient conditions and future nutrient controls.