VI. D. 3. Impacts - Physical Processes and Biological Considerations |
The introduction of chemicals, such as polychlorinated biphenyls (PCBs) and creosote, into nearshore areas has documented effects on sediment contamination and subsequently on organisms that utilize benthic habitats. Bottom-dwelling flatfish, such as the English sole (Pleuronectes vetulus), have shown an increase in liver abnormalities linked to contaminants that collect in marine sediment within Puget Sound (Puget Sound Water Quality Action Team 2002). Over time, those toxins settle to the bottom sediment. When resuspended, for example during dredging activities, they are once again released into the water column (Newton et al. 1998).
The discharge of raw sewage into nearshore environment can elevate levels of contaminants, such as fecal coliform bacteria, disease-causing bacteria and viruses, dissolved material, solid matter, and heavy metals. Impacts to the nearshore community arise from scouring, organic enrichment, and physiological effects of the chemicals themselves (National Oceanic and Atmospheric Administration 2000; Williams et al. 2001). Contaminants released into the water column will adhere to other particles and sink, which subsequently results in low levels of pollutants in the water column and bioaccumulation in organisms as evidenced by tumors on flatfish (Newton et al. 1995). As a result, organics and metals are generally observed in higher concentrations in local sediment than in the water column.
Organic enrichment is caused by the presence of excess amounts of organic carbon, which acts as a food source for invertebrate communities. If a benthic community is inundated with a large amount of organic carbon, it may be directly smothered or undergo organic enrichment. The effects of organic enrichment have been studied for 50 years, and much is known about how enrichment affects benthic communities (Word 1990; Williams et al. 2001). If the nearshore habitat consists of sand, there will be a shift in community structure from a suspension or surface detrital feeding community to one dominated by surface or subsurface deposit feeding organisms. Sensitive species (amphipods, echinoderms) will decrease in abundance, while tolerant species will increase. If the nearshore habitat consists of fine silts and clays, the community may undergo a shift to tolerant species (e.g., capitellid and spionid polychaetes) that thrive in habitats with high organic carbon content.
Changes in nearshore communities caused by chemical contamination are more difficult to document (Williams et al. 2001). These effects can be masked by the presence of organic carbon, which can have a stimulatory effect on the nearshore community. Catastrophic input of chemicals into the nearshore environment will have an immediate, acute impact on the community resulting in the immediate loss of all but the most tolerant individuals. Little is known about the chronic input of low levels of chemicals to this habitat. Evidence suggests that sensitive species will decrease in richness and abundance (as described above), whereas there may be no change in the condition of tolerant species (Word et al. 1981). However, this inference was based on an examination of the deep subtidal benthic community in the erosional environment off the West Point outfall, rather than a true nearshore community.
Non-point pollution affects nearshore ecosystems in several ways. Pollutants contained in untreated runoff enter nearshore marine waters and degrade water quality. Leaking septic tanks and other NPS sewage contaminate shellfish beds. Almost 33% of Washington’s shellfish beds have been impacted by fecal pollution, with failing septic systems, animal waste, stormwater runoff, and boat discharge identified as the primary sources (Puget Sound Water Quality Action Team 2002; Kitsap County Health District 2002). Commercial or residential development involves clearing land of vegetation and increasing the area of impervious surfaces, exacerbating stormwater runoff into nearshore waters. Increases in stormwater runoff can elevate erosion, with subsequent sediment inputs and increased organic nutrient loads, causing eutrophic effects on receiving water bodies (Puget Sound Water Quality Action Team 2002). Local eutrophication can intensify algal blooms, increase turbidity, and reduce dissolved oxygen levels, especially in estuaries. Increased growth of macroalgae species such as Ulva may degrade nearshore habitat by limiting eelgrass (Zostera spp.) distribution through competition (Puget Sound Water Quality Action Team 2000a).
Exhaust, maintenance waste, and spills associated with boating activities also pollute waters directly. Commercial marinas affect nearshore habitat by increasing boat traffic and decreasing water quality. Boaters noticeably affect water quality in several ways. Small amounts of leaking oil can contaminate many gallons of water, and paint scrapings and many boat solvents are toxic to nearshore fish and wildlife (Puget Sound Water Quality Action Team 2000b). Untreated sewage that is pumped overboard introduces bacteria and viruses to the nearshore and may contaminate shellfish. Together, these additional forms of NPS pollution can have large negative impacts on the nearshore ecosystem.
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