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Nontidal Wetlands Assessment Methodologies

We assess wetlands for a variety of reasons: to report their general condition; to track changes in condition; to estimate their capacity to provide certain services; to evaluate human impacts; and to establish compensation requirements. 

The Virginia wetland condition assessment method is a multiple services model that involves three levels of data collection.  Here the Level 2 (Model Calibration) and Level 3 (Model Validation) sampling are intended to calibrate and validate the model that is applied at the Level 1 (model development) stage.  The data collections are not designed to operate independently.  In this method, the goal is to characterize the capacity of every mapped wetland to provide water quality and habitat services using remotely sensed data.  The model application produces a relative score for each wetland for each service. The purpose is to both describe current condition and trends at a planning scale, and to inform management decisions at a site-specific scale.

Model Development (Level 1)

The initial Model Development assessment uses remote sensing and GIS technology to characterize landuse patterns and features around wetlands such as surrounding landcover and density of roads as well as individual wetland characteristics such as wetland size and type to determine the wetlands overall condition as related to habitat and water quality functions. The water quality analysis determines the percentages of different landcovers and features within the contributing drainage area of the wetland.

Model Calibration (Level 2)

Model calibration is conducted on site by cataloging whether the wetland has been impacted by a suite of anthropogenic stressors such as ditching, filling, mowing, timbering, etc. and is designed to calibrate the assumptions in the Level 1 model about the relationship between landscape patterns and stressors that impact wetland services. For example, the Level 1 model assumes that increasing levels of agricultural landuse adjacent to wetlands will result in increasing levels of disturbance to hydrology, sediment transport, and plant communities. The Level 2 assessment is designed to document the statistical relationships between landuse patterns surrounding wetlands and the occurrence of those stressors. Findings from the Level 2 assessment are used to calibrate the relationships in the Level 1 model.

Model Validation (Level 3)

Model validation is the validation step for the Level 1 model. Here individual wetlands are intensively monitored to document the relationships between landscape parameters used in the Level 1 model, and the performance of actual habitat and water quality services. In the Level 3 assessment populations of animals using individual wetlands are documented and impacts on hydrologic processes in individual wetlands are measured (ecological service endpoints). The relationships that emerge from this sampling will confirm or refute the assumptions in the Level 1 model, and allow for refinement of that model to one supported by quantitative observations.

Wetlands Assessment Final Report - Phase I

Wetlands Assessment Final Report - Phase II (Coastal Plain and Piedmont Physiographic Provinces)