Integrated Ecological Economic Modeling and Valuation of Watersheds (NSF/EPA Partnership for Environmental Research)
Our project aims to integrate knowledge and develop new tools to enhance predictive understanding of watershed ecosystems (including processes and mechanisms that govern the interconnected dynamics of water, nutrients, toxins, and biotic components) and their linkage to human factors affecting water and watersheds. The goal is effective sustainable ecosystem management at the watershed scale.
Major research questions include:
(1) What are the quantitative, spatially explicit and dynamic linkages between land use and terrestrial and aquatic ecosystem structure and function;
(2) What are the quantitative effects of various combinations of natural and anthropogenic stressors on watershed ecosystems and how do these effects change with scale; and
(3) What are useful ways to measure changes in the total value of the landscape including both marketed and non-marketed (natural system) components and how effective are alternative mitigation approaches, management strategies, and policy options toward increasing this value.
The proposed research will achieve these goals by integrating ongoing and new scientific studies over a range of scales in the Patuxent River watershed in Maryland. Another version of the model is currently being implemented in the Everglades in Florida to examine the implications of management strategies on elements of the ecosystem such as water levels, nutrient dynamics, and plant successional patterns (Fitz et al. 1993). The Patuxent project is part of an ongoing modeling effort, currently funded by NSF/EPA Water and Watersheds Program for three years.
We have developed a General Ecosystem Model (GEM) that is designed to simulate a variety of ecosystem types using a process-based fixed model structure (Fitz et al. 1995). Driven largely by hydrologic algorithms for upland, wetland and shallow-water habitats, the model captures the response of macrophyte and algal communities to simulated levels of nutrients, water, and environmental inputs. It explicitly incorporates ecological processes that determine water levels, plant production, nutrient cycling associated with organic matter decomposition, consumer dynamics, and fire. To simulate an entire watershed, we replicate the GEM "unit" model and divide the watershed into homogenous grid-cell units and use GIS to link cells to the parameter set for its habitat type and location in the watershed.
We have developed an ecological landscape model (the Patuxent Landscape Model or PLM) that links together GEM unit models on the landscape, and we are in the process of linking an economic model which endogenizes economic components to produce an integrated ecological economic model. The PLM contains about 6,000 spatial cells each containing a GEM with 21 state variables. Calibration and testing of this model is being carried out using available data. We are working collaboratively with other researchers to find funds for further field data collection efforts. Data have been collected to initialize, calibrate or validate the model with land use from 1973, 1981, 1985, and 1991, stream flow, water quality and other data . The intent is to run scenarios to the year 2020.. Effort will then be devoted to simulating past behavior of the landscape.
The spatial resolution of the PLM (0.04 km2) allows evaluation of impacts from changes in land use type or practices for particular groups of cells in the watershed. The aim is to be able to estimate selected key indicator variables for the Patuxent River watershed. The model can estimate impacts of specific land use patterns on loads to the Patuxent River estuary. The ecosystem functions and the parameters of those functions that are simulated for any given cell in the landscape are dictated by the cell's land use or habitat designation at the beginning of any simulation time step. Then, conditioned on that land use and the stocks of the state variables at that point in time in the cell, the processes and fluxes are calculated. When these changes are programmed, the simulation can estimate impacts on runoff variables including nitrogen, phosphorus, organic matter and suspended inorganic sediments. The effects of vegetative buffers and retention ponds on urban and agriculture runoff can be simulated as plants retard erosion and take up nutrients. Evaluations of various mixes and ratios of land use can also be performed.
The ecological model calculates land use designation through a "habitat switching" model which determines when, through natural succession or weather-driven ecological catastrophe (e.g. flood, forest fire), the habitat shifts from one type to another. Recognizing that the ecological effects of human activity are driven by the specific uses humans choose to make of the stock of natural capital, one of the major contributions of the economics modeling effort is an understanding of how land use decisions are made by individuals and how they are related to both the ecological and economic features of the landscape. See description of land use change model for details. The second type of contribution being made by the economics extension of the PLM is in modeling conditional human interactions, in this case, farmer's choice of crops and best management practices adoption, as functions of ecological and economic forces are currently underway.