In addition to those contained in 23 U.S.C. 101(a), the following definitions shall apply as used in this part:

Biogeochemical transformations means those changes in chemical compounds and substances which naturally occur in ecosystems. Examples are the carbon, nitrogen, and phosphorus cycles in nature, in which these elements are incorporated from inorganic substances into organic matter and recycled on a continuing basis.

Compensatory mitigation means restoration, enhancement, creation, and under exceptional circumstances, preservation, of wetlands, wetland buffer areas, and other natural habitats, carried out to replace or compensate for the loss of wetlands or natural habitat area or functional capacity resulting from Federal-aid projects funded pursuant to provisions of title 23, U.S. Code. Compensatory mitigation usually occurs in advance of or concurrent with the impacts to be mitigated, but may occur after such impacts in special circumstances.

Mitigation bank means a site where wetlands and/or other aquatic resources or natural habitats are restored, created, enhanced, or in exceptional circumstances, preserved, expressly for the purpose of providing compensatory mitigation in advance of authorized impacts to similar resources. For purposes of the Clean Water Act, Section 404 (33 U.S.C. 1344), use of a mitigation bank can only be authorized when impacts are unavoidable.

Natural habitat means a complex of natural, primarily native or indigenous vegetation, not currently subject to cultivation or artificial landscaping, a primary purpose of which is to provide habitat for wildlife, either terrestrial or aquatic. For purposes of this part, habitat has the same meaning as natural habitat. This definition excludes rights-of-way that are acquired with Federal transportation funds specifically for highway purposes.

Net gain of wetlands means a wetland resource conservation and management principle under which, over the long term, unavoidable losses of wetlands area or functional capacity due to highway projects are offset by gains at a ratio greater than 1:1, through restoration, enhancement, preservation, or creation of wetlands or associated areas critical to the protection or conservation of wetland functions. This definition specifically excludes natural habitat, as defined in this section, other than wetlands.

On-site, in-kind mitigation means compensatory mitigation which replaces wetlands or natural habitat area or functions lost as a result of a highway project with the same or like wetland or habitat type and functions adjacent or contiguous to the site of the impact.

Practicable means available and capable of being done after taking into consideration cost, existing technology, and logistics, in light of overall project purposes.

Service area of a mitigation bank means that the service area of a wetland or natural habitat mitigation bank shall be consistent with that in the Federal Guidance for the Establishment, Use and Operation of Mitigation Banks (60 FR 58605, November 28, 1995), i.e., the designated area (e.g., watershed, county) wherein a bank can be expected to provide appropriate compensation for impacts to wetlands and/or other aquatic or natural habitat resources.

Wetland or habitat enhancement means activities conducted in existing wetlands or other natural habitat to achieve specific management objectives or provide conditions which previously did not exist, and which increase one or more ecosystem functions. Enhancement may involve tradeoffs between the resource structure, function, and values; a positive change in one may result in negative effects to other functions. Examples of activities which may be carried out to enhance wetlands or natural habitats include, but are not limited to, alteration of hydrologic regime, vegetation management, erosion control, fencing, integrated pest management and control, and fertilization.

Wetland or habitat establishment period means a period of time agreed to by the FHWA, State DOT, and U.S. Army Corps of Engineers, as necessary to establish wetland or natural habitat functional capacity in a compensatory mitigation project sufficient to compensate wetlands or habitat losses due to impacts of Federal-aid highway projects. The establishment period may vary depending on the specific wetland or habitat type being developed.

Wetland or habitat functional capacity means the ability of a wetland or natural habitat to perform natural functions, such as provide wildlife habitat, support biodiversity, store surface water, or perform biogeochemical transformations, as determined by scientific functional assessment. Natural functions of wetlands include, but are not limited to, those listed by the U.S. Army Corps of Engineers at 33 CFR 320.4(b)(2)(i) through (viii).

Wetland or habitat preservation means the protection of ecologically important wetlands, other aquatic resources, or other natural habitats in perpetuity through the implementation of appropriate legal and physical mechanisms. Preservation of wetlands for compensatory mitigation purposes may include protection of upland areas adjacent to wetlands as necessary to ensure protection and/or enhancement of the aquatic ecosystem.

Wetland or habitat restoration means the reestablishment of wetlands or natural habitats on a site where they formerly existed or exist in a substantially degraded state.

Wetland or wetlands means those areas that are inundated or saturated by surface or ground water at a frequency and duration to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

Wetlands or habitat mitigation credit means a unit of wetlands or habitat mitigation, defined either by area or a measure of functional capacity through application of scientific functional assessment. With respect to mitigation banks, this definition means the same as that in the Federal Guidance for the Establishment, Use, and Operation of Mitigation Banks.