Definition
As defined in the US Army Corps of Engineers 2008 Mitigation Rule: Ecological Functions are defined as the physical, chemical, and/or biological processes that occur within and across ecosystems.
Representative Components
The three main functional groupings most typically characterized are bio-geochemistry, hydrology, and habitat support.
- Bio-geochemistry includes carbon fixation, nutrient cycling, denitrification, sediment filtration, and contaminant transformation.
- Hydrology would entail groundwater recharge, sediment transport, water source(s), hydro-dynamics, and water storage.
- Habitat support would consist of wildlife connectivity, biodiversity/species support, resistance to invasive species, and productivity.
Utility
Functions can be assigned or denoted as currency in a sense that can be used to evaluate the pace, extent, or nature of ongoing activities – productivity rates, seasonality, direction, and volumes of water flows, the cycling of constituents, measures of biodiversity, etc. Other functions like connectivity might be interpreted as a degree, such as that of gene flow for a species of interest or the number of species reliant on a corridor for movement across the landscape, including the extent the corridor may reach across the landscape.
Relevance
Functions are the processes as they exist in the ecosystem and whether biotic or abiotic, provide a common currency for relating and comparing across different systems. For example, nutrient cycling occurs in salt marsh as well as riparian wetlands and though the structures of these habitats take different forms, the ecological function offers a means for translating the relative contribution across them. Where in-kind mitigation options may not be available, establishing the relative contribution of each may afford a quantitative basis for guiding the proportion of out-of-kind mitigation necessary in order to adequately compensate for the loss of the impacted resource.
Research Needs & Hurdles
The main hurdle for assessing function is that we rarely observe or measure functions in the field, which would entail experimentation. Instead, we observe indicators or biotic or abiotic features or attributes that are correlated with underlying processes occurring at the site. Furthermore, the relationship between an indicator or set of indicators and an underlying function is often not well understood; in fact, in many cases, it is not linear. Also, in out-of-kind mitigation cases, the functions assessed at a mitigation site might be different in type and degree relative to functions at the impact site. For example, floodplain storage at an impact site with a low-order stream at the top of a watershed would typically be less than a mitigation site located in a high-order stream with well-developed floodplains closer to the outlet of the watershed. As another example, tidal attenuation occurring at a salt marsh impact site would not occur in open water habitat.
Example/Representative Metrics
Coming soon…
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