The Development of Lake Erie Ecosystem Forecasting System by Using the Finite Volume Coastal Ocean Model

Primary Investigator:

Meng Xia - NOAA/GLERL

Co-Investigators:

Dave Schwab - NOAA/GLERL
Dmitry Beletsky - NOAA/GLERL
Eric Anderson - NRC
Hongyan Zhang - University of Michigan - CILER*

Executive Summary of Rationale

This project is designed to develop and fully implement a three-dimensional finite volume coastal ocean model (FVCOM) that could simulate and predict the nutrient distribution, Dissolved Oxygen (Hypoxia) distribution as well as the lake circulation in the Lake Erie. The project will calibrate the model with the help of observational data. The project will help the Physical oceanographer and Biological Oceanographer understand the ecological processes in Lake Erie. Ultimately, we hope to gain insight regarding 1) the physical processes of Lake Erie and 2) the ecological processes of Lake Erie and their interaction.

Proposed Work

Implement FVCOM to Lake Erie to simulate the physical processes.
Application of FVCOM ecological model to simulate the nutrient distribution and potential dissolved oxygen dynamics.
Demonstrate the possibility of real-time application of the hydrodynamic-biological on Lake Erie.

Scientific Rationale

Lake Erie has historically experienced low-oxygen, particularly in its central basin hypolimnion (Delorme 1982). The extent of this “dead zone” increased during the mid-1900s, due to excessive phosphorus (P) inputs (Rosa and Burns 1987, Bertram 1993). Lake Erie hypoxia increased during the mid-1900s due to excessive phosphorus (P) inputs, and may have contributed to the decline of several commercially important fishes by the 1960s. In part due to P load reduction and enhanced oxygen levels, several of these species had begun to recover by the mid 1990s. More recently, large-scale low-oxygen conditions have returned to levels comparable to those during the height of eutrophication. It is not clear why this has happened.

Lake Erie hypoxia is driven primarily by the interaction of non-point sources of nutrients and climate variation as well as the lake physical circulation. This project will create, test, and apply models to forecast how anthropogenic (nutrient loading) and natural (climatic variability) stresses influence hypoxia formation and ecology. The task of year 2009 will firstly be to calibrate for the year 2005 and then more sensitivity experiments will be performed for the nutrient loading and natural stress. This will be done through a linked set of models to forecast changes in nutrient loads, responses of central basin hypoxia to those changes, and potential ecological responses to changes in hypoxia.

In the past, only two dimensional models (Zhang et al, 2008) have been applied to Lake Erie as well as a simple three dimensional phosphorous transport model with low resolution (Schwab et al, 2008). Thus, a high resolution three-dimensional is needed for Lake Erie. In response to these needs, we have constructed a three-dimensional mathematical ecological model of Lake Erie, FVCOM, which includes physical, chemical and biological components (Fig. 1). The FVCOM Model (Chen et al, 2003) serves as the base and main model for this system.

High-resolution unstructured FVCOM grid of Lake Erie for coupled physical-ecological modeling with resolved complex geometry of rivers, islands, and shorelines.

Fig. 1: High-resolution unstructured FVCOM grid of Lake Erie for coupled physical-ecological modeling with resolved complex geometry of rivers, islands, and shorelines.

There are several reasons to use the FVCOM for Lake Erie: 1)This is a test step for the future Great Lakes application by using the Finite Volume Coastal Ocean Model (FVCOM). 2.) The high-resolution grid is very important for the ecological modeling especially for the area of interest. Without resolving the 3D slope of steep bottom topography, numerical model could overestimate the on-bank residual current and thus generate different spatial structures of nutrients and phytoplankton.(Tian and Chen, 2007). 3.) The high resolution model could resolve the eddy distribution and unravel the potential influence to the local ecological process. (i.e. in the paper of Tian and Chen (2007), FVCOM predicted a pair of anticyclonic and cyclonic residual eddies by accurately resolving the coastlines). 4) The ecological interaction between the open lake and adjoining rivers could be well resolved in the high-resolution model as the grid could extend into the river mouths.

Over the past 5 years, the FVCOM model has been adapted for use in the estuary and coastal region in both the hydrodynamics and ecosystem modeling (Chen et al, 2008a; Chen et al, 2008b; Chen et al, 2008c, Ji et al,2006, Ji et al ,2007, Tian and Chen, 2006). The model is based on the three-dimensional, nonlinear Navier-Stokes equations. It employs a terrain-following vertical coordinate (sigma coordinate) to provide high vertical resolution even in shallow areas. Variables include the three-dimensional velocity field, the three-dimensional temperature field, the water level distribution and resuspension, transport, and deposition of bottom sediments. Simulations are made on a high-resolution horizontal unstructured grid with about 20 vertical slices comprising the vertical grid. More extensive evaluations have occurred in hind cast comparisons with field experiment data, including the ADCP real time current observation.

Our overall objective is to create and apply models to forecast how anthropogenic (nutrient loading) and natural (climatic variability) stresses influence hypoxia formation and the ecology of the system. Thus, our model can be used for investigating ecosystem processes regarding the importance of internal phosphorus loading relative to external phosphorus loading. The physical environment in Lake Erie will be driven dynamically by daily meteorological data. Vertically, Lake Erie has seasonal and diel thermostratification. In addition, gyres, river plumes traveling along the southern shore, or concentration gradients of nutrients and plankton will be resolved.

In the long term, this project could help the Great Lakes Forecasting System (GLFS, Bedford and Schwab, 1994; Schwab and Bedford, 1994) which has been developed to provide short-range operational (regularly scheduled) predictions of such conditions for the open waters of the Great Lakes.

Overall, our main tasks solve the following problems:

Could high resolution model resolve the Lake Eric eddy circulation?
Is hypoxia related to phosphorus loading or climate change?
Is there any difference by using structure and unstructured grid for Lake Erie ecological modeling?

Governmental/Societal Relevance

Lake Erie high-resolution hydrodynamics-eutrophication modeling system will be useful to all users of the Great Lakes coastal waters who require the information of temperatures, currents, water levels, and Dissolved Oxygen, particularly planners and managers responsible for any part of the Great Lakes ecosystem that is affected by nearshore circulation. The high-resolution numerical model is expected to provide the ecologist with a significant source of new information which should lead to considerable improvements both in the accuracy and efficiency of ecological marine forecasts for the Great Lakes.

The high-resolution numerical models could serve the Great Lakes connecting waterways, including emergency responses with DO dynamics. Also, FVCOM has a ecological sub model as well as a dye transport model. While each of these uses may require slight additions or modifications to the model, certain basic model properties or outputs are common to many or most uses. The model framework will be designed to allow linkages of hydrodynamic processes to water-quality, biological productivity, and sediment-transport models. The models will be based on open source codes and held in the public domain to facilitate their long-term distribution, use, and expansion.

Relevance to Ecosystem Forecasting

This project should contribute to the development of experiment forecasts of nutrient/contaminant distribution and DO dynamics. Very few studies have tested the ecological dynamics by using the FVCOM or finite volume model. This project could serve as a pilot study for the Great Lakes, and even the world. Within the frame of this project, the ecological models will be applied to Lake Erie in the first step. Although we will only calibrate the ecological process in FY2009, the model will be continue to improve to the future forecasting in the Lake Erie and the whole Great Lakes. While we will not focus on developing predictive capabilities for ecological process in FY2009 plan, we are confident that implementation of our model will improve forecasting in the future.

Cited References

Bedford, K.W, Schwab, D.J. (1994) The Great Lakes Forecasting System: An Overview Rumer (eds), Hydraulic Engineering ’94, Proceedings of the Conference, ASCE

Bertram, P.E., 1993. Total phosphorus and dissolved oxygen trends in the central basin of Lake Erie, 1970–1991. J. Great Lakes Res. 19, 224–236.

Chen, C., H. Liu, and R. Beardsley (2003), An unstructured grid, finite-volume, three-dimensional, primitive equations ocean model: Application to coastal ocean and estuaries, J. Atmos. Oceanic Technol., 20(1), 159 – 186.

Chen, C., P. Xue, P. Ding, R.C. Beardsley, Q. Xu, X. Mao, G. Gao, J. Qi, C. Li, H. Lin, G. Cowles, and M. Shi, (2008a), Physical mechanisms for the offshore detachment of the Changjiang diluted water in the East China Sea, J. Geophy. Res., 113, C02002, doi:10.1029/2006JC003994.

Chen, C., Q. Xu, R. Houghton and R. C. Beardsley, (2008b). “A model-dye comparison experiment in the tidal mixing front zone on the southern flank of Georges Bank”. J. Geophys. Res., 113, C02005, doi; 10.1029/2007jc004106

Chen, C, J. Qi, C. Li, R. C. Beardsley, H. Lin, R. Walker and K. Gates, (2008c). “Complexity of the flooding/drying process in an estuarine tidal-creek salt-marsh system: an application of FVCOM (DRAFT)”. J. Geophys. Res. doi: 10.1029/2007jc004328, in press.

Delorme, L.D. (1982) Lake Erie oxygen: the prehistoric record. Can. J. Fish. Aquat. Sci. 39: 1021-1029.

Ji, R. C. Chen, P. J. S. Franks, D. W. Townsend, E. G. Durbin, R. C. Beardsley, R. G. Lough, R.W. Houghton, (2006) “The Impact of Scotian Shelf Water “cross-over” on the plankton dynamics on Georges Bank: A 3-D experiment for the 1999 spring bloom”. Deep-Sea Res. II, 53, 2684-2707.

Ji. R., C. Davis, C. Chen, D. W. Townsend , D. G. Mountain and R. C. Beardsley, (2007) “Influence of ocean freshening on shelf phytoplantkon dynamics”. Geophys. Res. Lett. L24607, doi: 10.1029/2007GL032010

Rosa, F, and N. M. Bums. (1987) Lake Erie central basin oxygen depletion changes from 1929-1980. Journal of Great Lakes Research 13:684-696

Schwab, D.J. and K.W. Bedford, (1994). Initial implementation of the Great Lakes Forecasting System: a real-time system for predicting lake circulation and thermal structure. Water Poll. Res. J. Can., 29(2&3), 203-220.

Tian, R. and C. Chen, (2006) “Influence of model geometrical fitting and turbulence parameterization on phytoplankton simulation in the Gulf of Maine”, Deep-Sea Res. II, 53, 2808-2832.

Zhang,H.Y, Culver, D.A, Boegman, L. (2008) A two-dimensional ecological model of Lake Erie: Application to estimate dreissenid impacts on large lake plankton populations, ecological modeling, 2 1 4 , 219–241

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