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Potential Effects of Non-chemical Methods on Listed Species and Critical Habitats Associated with CRB Water Bodies

Intense Ultraviolet-B and Ultraviolet-C Radiation | Drawdowns and Dewatering

Intense Ultraviolet-B and Ultraviolet-C Radiation

Increases in ambient levels of UV-B radiation have significantly contributed to amphibian population declines (Blaustein and Wake 1995). Researchers have found that UV-B radiation can kill amphibians directly, cause sublethal effects, such as slowed growth rates and immune dysfunction, and work synergistically with contaminants, pathogens, and climate change (Kiesecker and Blaustein 1995, Long et al. 1995, Anzalone et al. 1998, Blaustein et al. 1998, Belden and Blaustein 2002, Blaustein et al. 2003).

Drawdowns and Dewatering

Winter drawdowns can decrease taxonomic richness of macrophytes and benthic invertebrates and shift assemblage composition to favor taxa with r-selected life history strategies and with functional traits resistant to direct and indirect drawdown effects (Carmignani and Roy 2017). Fish assemblages, though less directly affected by winter drawdowns (except where there is critically low dissolved oxygen), can be indirectly negatively affected via decreased food resources and changes in spawning habitat (Carmignani and Roy 2017).


Drawdowns modify abiotic conditions, cause sediment dessication and freezing, place stress on vegetative root structures (Siver et al. 1986), displace plants as a result of erosion of frozen sediment during spring refills (Beard 1973, Mattson et al. 2004), and stifle species growth by increasing acidity and cations to toxic concentrations (Peverly and Kopka 1991). Annual winter drawdowns can, through time, coarsen sediment texture and remove nutrients in the exposure zone, making these sites unsuitable for macrophyte colonization and growth, particularly in steep-sided basins (Hellsten 1997).

Other adverse impacts of drawdowns (New Hampshire Department of Environmental Services 2019) may include:

  • Large amounts of aquatic plants and organisms that succumb to the drawdown begin to decay shortly after drawdown, but nutrient release to the water body may not occur until full-pond level is achieved. Nutrients released from decayed material will quickly be used by algae and cyanobacteria, leading to increased cell production. Shallow lakes have shown shifts from clear, plant-dominated conditions to turbid, algal dominated systems.

  • Algal or cyanobacteria blooms may follow.

  • Aquatic food web changes may result in shifts in plant and animal structure.

  • Oxygen concentrations throughout the water column may be impacted.

  • Changes in the bottom sediment may also occur. Softer sediments may become compacted, or frozen segments that are lighter than water could loosen and float around in large masses, or as floating islands in the water body, only to settle once again in a new location.

Impacts to aquatic animal species can be significant. These impacts range from stranding animals to food chain modifications, or stressors associated with the drawdown. Fish, frogs, salamanders, turtles, aquatic insect larvae, mussels, and others can be affected by a drawdown. Agile and faster moving organisms may be able to move upstream or downstream to other unimpacted habitats, however, these fish may be confined to smaller, shallower areas where they become easy prey to consumers, or suffer from oxygen deprivation. Slower moving, more sedentary organisms have a greater risk to negative impacts. Freshwater mussels, snails, insects, and crayfish may not be able to find suitable habitat, and may succumb to the drawdown.

Manual and Mechanical Dreissenid Removal

Physical harvesting of dreissenids can reduce the diversity and abundance of soft-sediment benthic community taxa (Wittman et al. 2012). Following best management practices for manual removal minimizes any effects on non-target organisms (Culver et al. 2013). Steps involved in manual removal (Culver et al. 2013) include: organize divers, train divers, conduct pre-implementation surveys, prepare target site, manually remove mussels using hand-held tools, collect removed mussels, dispose of removed mussels, decontaminate persons and gear, and evaluate efficacy of effort.

Effort to remove mussels manually can be minimized by using a suction pump made from PVC and a SCUBA tank to vacuum the mussels into collection bags, however, use of this technique can significantly disrupt benthic macroinvertebrate community structure (Wittman et al. 2012).

Suction harvesting side effects can include high turbidity, reduced clarity, and algae blooms from nutrient release caused by disturbance of bottom sediment, which can reduce oxygen conditions and ultimately affect ecosystem communities (New York State Department of Environmental Conservation 2005). Suction harvesting also has the potential to release sediment-bound heavy metals into the water column, which can affect the food chain in the water body (New York State Department of Environmental Conservation 2005).

Oxygen Deprivation

Bottom/benthic barriers or mats can be installed on portions of lake bottoms and weighted, resulting in oxygen deprivation. This tactic is used for low to moderate mussel infestations in difficult to access locations, and can be enhanced by combining it with tactics that target larval stages (Culver et al. 2013). This method is not as effective in locations with large infestations.

Steps involved in oxygen deprivation (Culver et al. 2013) include: organize divers and boat operators, locate needed supplies, review the need for area closures, determine mussel distribution, conduct pre-implementation survey, conduct a pilot study, install tarps, add chemicals/biocides if needed, monitor during installation, remove tarp, decontaminate persons and gear, and evaluate efficacy of effort.

Benthic barriers interfere with respiration in fish and macroinvertebrates. Benthic barriers comprised of anchored textile/plastic are generally placed over vegetation to prevent the growth and establishment of plants whereas benthic barriers can be created by depositing silt to smother bottom-dwelling organisms (US Army Corps of Engineers 2012). Response to silt barriers can include feeding inhibition, reduced metabolism, avoidance, or mortality (Collins et al. 2011).

Although studies have shown that benthic barriers may impact non-target organisms, especially benthic dwellers, and will affect chemistry at the sediment-water interface, impacts are limited to the area of installation, and because only a small percentage of lake bottoms are typically exposed to benthic barriers, lake-wide impacts are not expected and have not been observed (Mattson et al. 2004).

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