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Water: Healthy Watersheds

Assessment Framework

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Healthy Watersheds Home Concept, Approach & Benefits Aquatic Biodiversity Aquatic Resource Surveys Biotic Condition Assessment Framework Examples of Assessments Habitat and Biodiversity Conservation Hydrology/Geomorphology Green Infrastructure Conservation Approaches & Tools Where You Live Integrated Assessments Landscape Condition Local Land Use Ordinances Publications Outreach Tools Natural Disturbance Regimes Nonpoint Source Pollution River Corridor Protection

chart describing the essential ecological attributes chemical/physical landscape condition ecological process natural disturbance biotic condition hydrology

chemical/physical landscape condition ecological process natural disturbance biotic condition hydrology

chemical/physical landscape condition ecological process natural disturbance biotic condition hydrology The Science Advisory Board (SAB) has developed a "Framework for Assessing and Reporting on Ecological Condition" (U.S. EPA, 2002). This framework was developed as an organizational tool for reporting on information about the health of ecosystems through an assessment of essential ecological attributes. The Healthy Watersheds concept views watersheds as integrated systems that can be understood through the dynamics of essential ecological attributes, as described below.

Landscape Condition: A mosaic of interacting ecosystems provides the green infrastructure necessary to maintain landscape condition in healthy watersheds. Green Infrastructure is "an interconnected network of natural areas and other open spaces that conserves natural ecosystem values and functions, sustains clean air and water, and provides a wide array of benefits to people and wildlife" (Benedict & McMahon, 2006). Large blocks of contiguous natural vegetative cover provide organic matter and nutrients to aquatic ecosystems (e.g., headwaters). Riparian vegetative zones also provide nutrients and organic material to streams. Vegetative cover maintains natural hydrology and functions as a buffer, filtering pollutants. Vegetative hubs and corridors connect terrestrial animals to sources of water and food, maintaining the food web. The extent, composition, and pattern of green infrastructure are critical components in a landscape condition assessment. (See Examples of Landscape Condition Assessments)

Biotic Condition: The biological condition of a waterbody is an indicator of watershed health. Aquatic organisms and communities reflect the cumulative conditions of watershed components. Healthy aquatic ecosystems reflect healthy watershed conditions. A biotic condition assessment for identifying healthy watersheds examines the presence, numbers, and condition of aquatic organisms and communities in a waterbody. State Natural Heritage Program biodiversity surveys are one important tool for assessing biotic condition. (See Examples of Biotic Condition Assessments)


Chemical/Physical Parameters: Environmental parameters such as nutrients, temperature, dissolved oxygen, organic matter, pH, etc. are important indicators of ecosystem health and a wealth of information is typically available for many of these components, as many monitoring programs routinely collect data on these parameters. (See Examples of Chemical/Physical Assessments)

Natural Disturbance Regimes: Most ecosystems are inherently resilient to natural patterns of disturbance and change. With disturbance comes opportunity. Floods, droughts, fires, insect infestations, etc. are responsible for much of the structural, functional, and biological diversity found in aquatic ecosystems. Maintenance of this diversity is critical for conservation and protection of healthy watersheds. (See Examples of Natural Disturbance Regime Assessments)

Hydrology/Geomorphology: Water flow, dynamic structural characteristics, and sediment transport are important determinants of aquatic ecosystem condition. These three components interact in the natural flow regime. Critical features of the natural flow regime that influence ecological integrity include magnitude, frequency, duration, timing, and rate of change of hydrologic conditions (Poff et al., 1997). River shape and form is maintained by water flow and sediment transport. Hydrologic connectivity is in turn largely influenced by channel morphology. Lateral (floodplain), longitudinal (stream network), and vertical (hyporheic zone) connectivity are important for maintenance and creation of aquatic habitat. Erosional and depositional processes create a dynamic equilibrium that provides for successional stages in riparian communities and floodplain vegetation, streambed spawning habitat for anadromous fish, and attachment sites for aquatic invertebrates. (See Examples of Hydrogeomorphic Assessments)

Ecological Processes: Ecological Processes, as defined in the SAB framework, include energy flow, elemental cycling, and the production, consumption and decomposition of organic matter. Important as these are, they are difficult to measure at broad (e.g., state) scales. Detailed, site-level data are typically required for assessments of ecological processes. Therefore, they are not explicitly assessed in the Healthy Watersheds framework. (See A Framework for Assessing and Reporting on Ecological Condition (PDF) (142 pp, 1.4MB, About PDF) for further discussion)

Integrated Framework for Assessing Healthy Watersheds: Integration of the essential ecological attributes is necessary for a holistic systems approach to identifying and assessing healthy watersheds or intact components of other watersheds. The Healthy Watersheds Framework addresses the complexity of watershed ecosystems through an integrated assessment of the landscape condition, biotic condition, chemical/physical parameters, and critical watershed functional attributes such as the natural disturbance regime and hydrology/geomorphology. Only through an understanding of these dynamic linkages can proactive management and protection of healthy watersheds be achieved. An integrated assessment framework can range from screening-level GIS assessments to sophisticated ecological modeling and statistical analyses of ecological attributes. (See Examples of Integrated Assessments)

EPA's Watershed Academy is a valuable resource for learning more about the ecological attributes of a watershed.

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