Biological assessment
potential EFFECTS OF PROPOSED ACTION
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- DIRECT IMPACTS
potential EFFECTS OF PROPOSED ACTIONConstruction of this project has the potential to impact the Appalachian elktoe and its Designated Critical Habitat in a variety of ways, both during construction and once the road is in use. It should be noted that potential impacts to the Appalachian elktoe are not limited to the areas immediately adjacent to the water bodies because the eastern portion of the project in Yancey and Mitchell Counties eventually drains to either the Cane River or South Toe River, and adverse impacts can occur considerable distances downstream. Potential project-related impacts to the Appalachian elktoe and its Designated Critical Habitat are considered here. Direct, indirect, and cumulative impacts as defined in 50 CFR 402.02 are analyzed. DIRECT IMPACTSDirect impacts refer to consequences that can be directly attributed to the project. Direct impacts associated with road construction include, but are not limited to, land clearing, loss of habitat, stream re-channelization, hydrologic modification, and erosion. Potential direct impacts to aquatic species, especially freshwater mussels, associated with transportation projects include: siltation, substrate disturbance, alteration of flows, and introduction of toxic compounds. The highest potential for direct impacts to the Appalachian elktoe occurs at the Cane River and South Toe River crossings, which are occupied by the species. Direct impacts to the species and its Designated Critical Habitat may also occur from construction activities at the individual crossings of the tributaries to the Cane River, South Toe River, and North Toe River. The severity of potential impacts at these crossings decreases with increasing distance from the receiving water body (Cane, South Toe, or North Toe rivers), and decreasing size (length) of impacted area. Conversely, multiple impact sites on the same water body increases the potential for downstream impacts. This is especially true for the Cane River and South Toe River, as there are a total of 10 and 8 stream impact sites respectively that are less than 0.5 miles upstream of occupied habitat (Table 9, 10). The potential for stream crossing impacts to affect occupied habitat in the North Toe River is less, as the closest stream impact site to the North Toe River is 1.76 miles (Table 11). The respective distance of all tributary crossings to the Cane River, South Toe River and North Toe River are shown in Tables 9-11. Table 9. Distances from permitted sites to Cane River.
Table 10. Distances from permitted sites to South Toe River.
* R-2519B is in the preliminary design phase; therefore, there are no assigned impact site numbers and structure sizes and types are subject to change.. Table 11. Distances from permitted sites to North Toe River (R-2519B)
* All sites are associated with R-2519B, which is in the preliminary design phase; therefore, there are no assigned impact site numbers and impacts are subject to change. ** NA denotes information not available at this time Stream Fill (Substrate (Habitat) Disturbance/Loss) Highway construction within and around water bodies often results in the placement of fill into streams and adjacent floodplains. Two types of fill may occur, permanent and temporary. Permanent fills consist of bridge piers and abutments, culvert and pipe construction or extensions, and roadway fill slopes. Construction causeways and work bridges used for equipment access are examples of temporary fill. Permanent fill in the Cane River and South Toe River stream-bottom substrate will result in a permanent loss of potential mussel habitat. The tributary streams do not provide habitat for the Appalachian elktoe; however, fills to stream substrates may cause downstream impacts to the species by impacting stream stability and thus resulting in sedimentation/erosion, which could then impact occupied habitat. Temporary fill in the Cane and South Toe Rivers may also result in the permanent loss of habitat, as the impacts may be long-lived, or essentially permanent. Erosion/Sedimentation From Construction The detrimental effects of siltation on freshwater mussels have been discussed earlier. Excessive suspended solids in the water column, sedimentation and turbidity result in reduced biodiversity as well as a decline in productivity at all trophic levels (Gilbert 1989). Because of the topography and the erodible nature of the soils in the project area, activities such as highway construction have the potential to result in sedimentation into receiving waters. Sedimentation coming from the project area within the Nolichucky River Basin (FBR Subbasin 04-03-06 and FBR Subbasin 04-03-07), particularly at the South Toe River and Cane River crossings, has the potential to adversely impact habitat occupied by the Appalachian elktoe. Alteration of Flows/Channel Stability Geomorphically stable stream channels and banks are a primary constituent element essential for the survival and conservation of the Appalachian elktoe. Stream channel instability can result directly from bridge construction and culvert/pipe crossings. Natural stream stability is achieved when the stream exhibits a stable dimension, pattern, and profile such that over time, the channel features are maintained, and the channel neither aggrades, nor degrades. Channel instability occurs when scour results in degradation, or when sediment deposition leads to aggradation (Rosgen 1996). The placement of fill, such as bridge piers, culverts, pipes, and causeways, into streams can alter the normal flow pattern of a water body by reducing flow velocities upstream, increasing sedimentation and flow velocities downstream, and resulting in scour and erosion. Roadway Runoff Numerous pollutants have been identified in highway runoff, including various metals (lead, zinc, iron, etc.), sediment, pesticides, deicing salts, nutrients (nitrogen, phosphorus), and petroleum hydrocarbons (Yousef et al. 1985; Gupta et al. 1981). The sources of these runoff constituents range from construction and maintenance activities to daily vehicular use. Hoffman et al. (1984) concluded that highway runoff can contribute up to 80% of the total pollutant loadings to receiving water bodies. Petroleum hydrocarbons, polycyclic aromatic hydrocarbons, lead, and zinc were some of the pollutants identified in this study. The toxicity of highway runoff to aquatic ecosystems is poorly understood. A major reason for this poor understanding is a lack of studies focusing solely on highway runoff. Potential impacts of highway runoff have often been inferred from studies conducted on urban runoff; however, the relative loadings of pollutants are often much greater in urban runoff, because of a larger drainage area and lower receiving water dilution ratios (Dupuis et al. 1985). The negative effects of urban runoff inputs on benthic macroinvertebrate communities have been well documented (Garie and McIntosh. 1986; Jones and Clark 1987; Field and Pitt 1990). Lieb (1998) found the macroinvertebrate community of a headwater stream in Pennsylvania to be highly degraded by urban runoff via a detention pond. Improvements were observed at continual distances downstream from the discharge point; however, all sites examined were still impaired compared to a reference community. The few studies that examined actual highway runoff show that some species demonstrate little sensitivity to highway runoff exposure, while others are much more sensitive (Dupuis et al. 1985). Maltby et al. (1995) found elevated levels of hydrocarbons and metals in both stream sediments and the water column below a heavily traveled British motorway. They demonstrated that the benthic amphipod (Gammarus pulex) experienced a decrease in survival when exposed to sediments contaminated with roadway runoff. However, this species showed no increase in mortality when exposed to water contaminated with roadway runoff. Unfortunately, most of these studies only measured acute toxicity to runoff and did not examine long-term impacts. The effects of highway runoff on freshwater bivalves have not been studied extensively. Augspurger (1992) compared sediment samples and soft tissues of the common eastern elliptio (Elliptio complanata) upstream and downstream of the I-95 crossing of Swift Creek in Nash County, North Carolina. The sediment samples as well as the mussels (n = 3) exhibited higher levels of aliphatic hydrocarbons, arsenic, lead, zinc, and other heavy metal contaminants in the downstream samples. Because of the small sample size, the effect on the health of these mussels was not studied. NCDOT funded a two-year study that investigated the impacts of highway runoff on the health of freshwater mussels. Contaminant analysis of stream sediments showed an increase of polycyclic aromatic hydrocarbons and some metals downstream of road crossings, although there was no direct correlation found between increasing contaminant levels and decreasing mussel abundance at these crossings (Levine et al. 2005). The eastern elliptio was the only mussel species that was found in large enough numbers for statistically valid comparisons. The eastern elliptio is generally considered more tolerant of water quality degradation than many other mussel species, such as members of the genus Alasmidonta. Further research is needed before the effects of highway runoff on sensitive mussel species such as the Appalachian elktoe can be determined. INDIRECT IMPACTS Indirect impacts are those effects that are caused by or will result from the proposed action and are later in time, but are still reasonably certain to occur [50 CFR 402.02]. These types of impacts can include natural responses to the proposed action’s direct impacts, or can include human induced impacts associated with the proposed action. Disruption of Fish Host Migration In addition to the direct impacts of bridge and causeway construction and culvert/pipe crossings that were discussed above, another concern with construction of these structures is the potential for creating barriers to fish migration. Disruption of fish migrations can indirectly affect freshwater mussels if the fish that are disturbed serve as fish hosts for the mussel species and are infested with glochidia (juvenile mussels) at the time when their migration patterns are disrupted. Temporary causeways placed in flowing waters can disrupt migration patterns of fish species by creating a physical obstruction in the streambed or by creating increased velocities from channel constriction that are too high for fish to swim up. Potential of Toxic Spills Roadway construction can also indirectly effect the aquatic environment by increasing the potential for toxic spills once the facility is in operation. As evidenced from the Clinch River in Virginia (addressed earlier), toxic spills resulting from traffic accidents can be devastating to mussel populations. Indirect Effects on Land Use Project-induced changes in land use are also considered part of the indirect impacts of a proposed action. These types of land use changes are not direct consequences of the road construction, but result from modifications in access to parcels of land and from modifications in travel time between various areas (Mulligan and Horowitz 1986). They are defined as those impacts that are “caused by an action and are later in time or farther removed in distance but are still reasonably foreseeable” (40CFR 1508.8). Indirect land use impacts of highway projects include residential, commercial, and industrial developments and linear urban sprawl along a highway corridor. The purpose and need of this project are adding capacity to the existing facility to provide system linkage and increased safety. One unintended consequence of roadway improvements can be, depending upon local land development regulations, development demand, water/sewer availability, and other factors, encouragement of additional development and sprawl. Improvements to levels of service, better accommodation of merging and exiting traffic, and reductions in travel times can have land development impacts outside of the direct project area. Any induced growth and development within this area has the potential to degrade water quality, scenic values, and recreational opportunities unless proper planning and development regulations are utilized. This potential increases when it occurs in an area with minimal or no planning programs and virtually non-existent development controls. Local development controls along this corridor should be encouraged.
Impervious Surface Area The correlation of increasing development within a watershed and decreasing water quality is well documented (Lieb 1998, Crawford and Lenat 1989, Garie and McIntosh 1986, Lenat et al. 1979) and is often a result of increases in impervious surface area. Although the increase in amount of impervious surface area is a direct consequence associated with project construction, it will not directly impact the adjacent water bodies, or the Appalachian elktoe. However, the increases in impervious surface area can indirectly impact water quality in a variety of ways, particularly with regards to stormwater impacts. Peak Discharge Peak discharge is the maximum rate of stormwater flow expected from a storm event, measured in cubic feet per second. Peak discharge is often one metric used in analyzing impacts from development. Peak discharge affects channel stability (or instability) which is one of the identified action area threats (Section 4.3.1). Increases in peak discharge equates to higher velocity, which in turn increases the scouring effect (erosion) of the runoff. Accordingly, sedimentation will increase as erosion rates increase. In a recent study of the Goose Creek Subbasin, which is occupied another endangered mussel species, the Carolina heelsplitter (Lasmigona decorata), and is undergoing urbanization throughout the watershed, Allan (2005) documented dramatic increases in sediment and nutrient concentrations during high flow events. Increases of peak discharge rates coupled with deforestation, has been shown to result in stream narrowing and incision and subsequent loss of ecosystem function (Sweeney et al. 2004). If peak discharge velocities are high enough, mussels can become dislodged resulting in mortality if the mussels are deposited in unsuitable habitat or in the floodplain. As discussed in Section 3.2.3, the Appalachian elktoe was susceptible to being dislodged during the flood events of 2004. Detention ponds and similar stormwater devices, as well as buffer restrictions should be encouraged to be implemented with future development activities in the area to minimize the potential for increases in peak discharge. Runoff Volume Runoff volume is the amount of stormwater expected from a storm event, measured in acre-feet. Like peak discharge, runoff volume is another metric often used in determining impacts of development, especially on the aquatic environment. For example, increases in the amount of runoff normally equates to increased sediment. While the two indicators are related, both are useful when assessing impacts to aquatic systems. In a stable system, an increase in the velocity may have little impact if volume does not change, provided that measures to slow the increased velocity have been implemented. However, the increased runoff volume may have enough sediment to cause detrimental impacts. Regardless, it is important to consider both the rate (peak discharge) and the amount (runoff volume) when assessing impacts to aquatic systems. Again, stormwater control with future development activities in the watershed is essential for conservation of the Appalachian elktoe. Decreased Base Flow Increases of impervious surface lead to decreases in infiltration and base flow within adjacent streams. This can result in the following: During periods of reduced base flow, there is more stream bottom surface area with less water to cover it. Widened streams (less tree cover) are exposed to more sunlight resulting in increased water evaporation and heating, especially in areas with shallower water. If base flow is reduced, yet WWTP discharge remains constant or increases, it takes longer for the stream to dilute the nutrients and toxins in the effluent, thereby extending the WWTP “plume” further downstream. During dry or drought conditions is the most critical time for agricultural operations and golf courses; as such this is when water is pumped out of the streams, exacerbating the already low flow conditions. Stream Temperature Changes Concerns over impacts of thermal pollution from urban runoff on aquatic systems have increased in recent years. Elevation of stream temperature can raise Biological Oxygen Demand (BOD), lower dissolved oxygen (DO) and can alter faunal composition (Roa-Espinosa et al.2003, Poole et al. 2001). Stormwater runoff from the site will increase in temperature due to the removal of the existing vegetation and the proposed impervious areas. Typically, runoff from a developed impervious area will have a temperature similar to the temperature of the impervious area. During the hot summer months, this could potentially make the stormwater runoff reach temperatures up to and above 90°F, which could be detrimental to the aquatic life downstream of the site. Various stormwater BMPs have been shown to be effective in ameliorating temperature effects (NC State Cooperative Extension 2006a). Bioretention devices were shown to reduce runoff temperature by 5-10 °F in Greensboro, NC (NC State Cooperative Extension 2006b). In addition to stream temperature increases associated with runoff from heated impervious areas, the loss of riparian buffer that may be associated with future development, as well as peak discharge-related channel widening, can also contribute to stream temperature increases. CUMULATIVE IMPACTS Cumulative Impacts are those effects of future state or private activities, not involving federal activities, which are reasonably certain to occur within the action area of the proposed federal action. As discussed above, the Nolichucky River Basin has experienced water quality degradation from past mining and agricultural practices. This degradation undoubtedly adversely impacted the aquatic fauna of the watershed, including the Appalachian elktoe. Given the dynamic nature of riverine habitats and the large amount of land area encompassed in a watershed, it is virtually impossible to eliminate all potential impacts to the aquatic species in these habitats. However, aquatic species can be conserved with environmentally sound land use in the respective watershed. As a result of general improvements in land use practices in recent years, overall water quality has improved in the Nolichucky River Basin. Due in part to the improving water quality, the Appalachian elktoe population in the Nolichucky River Basin appears to be viable and expanding. The recent (summer-fall 2004) catastrophic flooding in this region may have adversely impacted the Appalachian elktoe population in the basin; however, given the expansive range and apparent health of the population prior to these events, it is unlikely that the flooding will affect the population’s future viability. In addition to highway improvements, other infrastructure projects such as water and sewer service have the potential to stimulate land development and directly or indirectly result in impacts to the Appalachian elktoe and it’s Designated Critical Habitat. 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