(CRAM) For Wetlands User's Manual Version 5.0.2

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California Rapid Assessment Method for Wetlands v. 5.0.2 – Chapter 4 Table 4.7: Rating for Average Buffer Width (based worksheet 4.3). Rating Alternative States A Average buffer width is 190 – 250 m. B Average buffer width 130 – 189 m. C Average buffer width is 65 – 129 m. D Average buffer width is 0 – 64 m. 4.1.4 Buffer Condition A. Definition: The condition of a buffer is assessed according to the extent and quality of its vegetation cover and the overall condition of its substrate. Evidence of direct impacts by people are excluded from this metric and included in the Stressor Checklist. Buffer conditions are assessed only for the portion of the wetland border that has already been identified or defined as buffer, based on Section 4.1.2 above. B. Rationale: The condition or composition of the buffer, in addition to its width and extent around a wetland, determines the overall capacity of the buffer to perform its critical functions. C. Seasonality: This metric is not sensitive to seasonality. D. Office and Field Indicators: Buffer condition must be assessed in the field. The method is the same across all wetland types. Prevalence of native vegetation, absence of exotic vegetation, absence of recent substrate disturbance, and absence of trash or debris are assumed to indicate good buffer conditions. For the purpose of assessing substrate condition in the buffer, no evidence of problems more than 3 years old should be considered. Narratives for Buffer Condition ratings are provided in Table 4.8. If there is no buffer, assign a score of D. Table 4.8: Rating for Buffer Condition. Rating Alternative States A B C D Buffer for AA is dominated by native vegetation, has undisturbed soils, and is apparently subject to little or no human visitation. Buffer is characterized by an intermediate mix of native and non-native vegetation, but mostly undisturbed soils and is apparently subject to little or no human visitation. Buffer is characterized by substantial amounts of non-native vegetation AND there is at least a moderate degree of soil disturbance/compaction, and/or there is evidence of at least moderate intensity of human visitation. Buffer is characterized by barren ground and/or highly compacted or otherwise disturbed soils, and/or there is evidence of very intense human visitation. 52
4.2 Attribute 2: Hydrology California Rapid Assessment Method for Wetlands v. 5.0.2 – Chapter 4 Hydrology includes the sources, quantities, and movements of water, plus the quantities, transport, and fates of water-borne materials, particularly sediment as bed load and suspended load. Hydrology is the most important direct determinant of wetland functions (Mitch and Gosselink 1993). The physical structure of a wetland is largely determined by the magnitude, duration, and intensity of water movement. For example, substrate grain size, depth of wetland sediments, and total organic carbon in sediments tend to be inversely correlated to duration of inundation in a lacustrine wetland. The hydrology of a wetland directly affects many physical processes, including nutrient cycling, sediment entrapment, and pollution filtration. For example, Odum and Heywood (1978) found that leaves in freshwater depressional wetlands decomposed more rapidly when submerged. The hydrology of a wetland constitutes a dynamic habitat template for wetland plants and animals. For example, Richards et al. 2002 concluded that meandering and braiding in riverine systems control habitat patch dynamics and ecosystem turnover. The spatial distribution of plants and animals in a tidal marsh closely correspond to patterns of tidal inundation or exposure (Sanderson et al. 2000). 4.2.1 Water Source A. Definition: Water Sources directly affect the extent, duration, and frequency of saturated or ponded conditions within an Assessment Area. Water Sources include inputs of water into the AA as well as any diversions of water from the AA. Diversions are considered a water source because they affect the ability of the AA to function as a source of water for other habitats while also directly affecting the hydrology of the AA. Inputs of water affecting conditions during the dry season are especially important because they strongly influence the structure and composition of wetland plant and animal communities. The Water Source metric therefore focuses on conditions that affect dry season hydrology. Natural water sources include precipitation, ground water discharge, and flooding of the AA due to high tides or naturally high riverine flows. Examples of unnatural sources include stormdrains that empty into the AA or into an immediately adjacent area. For seeps and springs that occur at the toes of earthen dams, the reservoirs behind the dams are water sources. Large reservoirs and lakes that do not drain directly into the AA should not be considered water sources, although they can have systemic, ubiquitous, effects on the condition of the AA. For example, although the salinity regimes of some estuarine wetlands in San Francisco Bay are indirectly affected by dams in the Sierra Nevada, others are directly affected by nearby discharges from sewage treatment facilities. This metric focuses on the more direct water sources. Engineered hydrological controls, such as pumps, weirs, and tide gates can serve to demarcate the boundary of an AA (see Section 3.5), but they are not considered water sources. B. Rationale: Wetlands depend on constant or recurrent, shallow inundation or saturation at or near the surface of the substrate (National Research Council 2001). Consistent, natural inflows of water to a wetland are important to their ability to perform and maintain most of their intrinsic ecological, hydrological, and societal functions and services. The flow of water into a wetland also affects its sedimentary processes, geo-chemistry, and basic physical structure. Sudol and Ambrose (2002) found that one of the greatest causes of failed wetland mitigation or restoration projects is inadequate or inappropriate hydrology. 53
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