1.3.4 Summary |
Landscape ecology and geomorphic context were critical tools for applying the conceptual framework to Bainbridge Island shorelines. The assessment was conducted on a “reach-by-reach” scale, fairly small definable landscapes, which were determined by homogeneous stretches of shoreline as defined principally by the WDNR ShoreZone database (WDNR 2001). The advantage of this approach was that most information was preexistent, detailed, relatively current, and widely available. When used in concert with aerial photographs (WDOE 1977, 1992, 2000) and local knowledge, geomorphic context allowed us to refine predictive relationships between shoreline modifications and nearshore functions. Fine-scale, georeferenced data recently collected by COBI (COBI 2002, Best 2003) were used as the basis for quantifying nearshore habitat modifications and habitat structural attributes. This dataset provided detailed information (e.g., extent and number of modifications, encroachment into the intertidal zone, marine riparian vegetation cover and type, stormwater outfalls) that assisted in quantifying impacts to controlling factors within a particular reach of shoreline. Aerial imagery and historic photographs provided additional information for verifying assumptions and completing the picture of nearshore conditions.
Table 2. Conceptual Model Applied to Geomorphic Classes by Each Controlling Factor Metric.
Geomorphic Class |
Habitat Structure |
Habitat Processes |
Ecological Function |
Wave Energy |
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| Rocky | Generally not an issue, but may affect structure of attached macroalgae community. | Only as it affects macroalgal productivity. | May affect biodiversity maintenance. |
| Marsh/Lagoon | Generally not an issue in these wave protected habitats, though habitat structure of marsh plant community could be affected. | Loss of primary production and altered sediment flux. | |
| Spit/Barrier/ Backshore | At critical tidal elevations or areas exposed to waves, turbulence may displace rooted aquatic vegetation (e.g., eelgrass), suspend and coarsen fine sediment, reduce LWD retention | Loss of primary production. Increased sediment and carbon flux. Landscape fragmentation. | Loss of associated habitat functions, including salmon prey production and refuge. Loss of eelgrass affects herring spawn; altered sediment composition may affect forage-fish spawning substrate. |
| Low Bank | |||
| High Bluff | |||
Loss of Natural Shade |
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| Rocky | Light increase generally not an issue (little riparian vegetation) | N/A | N/A |
| Marsh/Lagoon | Loss of riparian vegetation affects habitat complexity. Increased light levels reaching marsh/mudflats increases desiccation and temperature regimes. | Loss of primary productivity from riparian litterfall. Carbon flux alteration and landscape fragmentation. | Loss of biodiversity, prey production (terrestrial insects), and refuge. Increased water temperatures in lagoons may affect herring embryo development. |
| Spit/Barrier/ Backshore | Same as Rocky (low growing dune vegetation). | N/A | N/A |
| Low Bank | Same as Marsh/Lagoon. | Same as Marsh/Lagoon. | Same as Marsh/Lagoon. Increased temperatures and desiccation affects beach spawning forage-fish embryos. |
| High Bluff | |||
Artificial Shade |
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| Rocky | Total light loss would impact attached macroalgae communities, including patch size, density, and shape. | Loss of primary productivity from macroalgae. Landscape fragmentation. | Loss of associated biodiversity, prey production, and refuge. Darkness may inhibit salmon migration. |
| Marsh/Lagoon | Total light loss would impact vascular marsh plant, macroalgae, and eelgrass communities, including patch size, density, and shape. | Loss of primary production. Carbon flux alteration. Landscape fragmentation | |
| Spit/Barrier/ Backshore | Total light loss would impact eelgrass and marine vegetation, including patch size, density, and shape. | ||
| Low Bank | |||
| High Bluff | |||
Sediment Supply |
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| Rocky | Generally not an issue, though blockage of alongshore transport may change some substrate characteristics. | Only as it affects sediment flux, if present. | May affect biodiversity. |
| Marsh/Lagoon | Excessive supply from fluvial sources likely to be issue. May affect beach slope and smother eelgrass beds and marsh vegetation. | Altered sediment flux. Loss of eelgrass and riparian primary production, carbon flux, and landscape connectivity. | Loss of eelgrass associated salmon refuge and prey production. Excessive sediments may smother benthos, reducing biodiversity . |
| Spit/Barrier/ Backshore | Impoundment of backshore sediments may cause beach erosion, coarsening of sediments, and loss of rooted vegetation. | Loss of eelgrass associated salmon refuge and prey production. Substrate coarsening affects biodiversity. . |
|
| Low Bank | Impoundment of backshore sediments may cause foreshore and alongshore beach erosion (due to loss of sediment source), bank steepening, and sediment coarsening. Loss or change of rooted vegetation. | ||
| High Bluff | Major issue. Same as Low Bank, but may be more significant along high bluffs, which are often important feeder bluffs. | ||
Substrate Type |
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| Rocky | Generally not an issue; modifications are often rock cobble or concrete. | N/A. | N/A |
| Marsh/Lagoon | Change from soft sediments to novel hard substrates (e.g. rock, concrete, steel, wood) associated with structures. Attached macroalgae and biota (e.g., mussels and barnacles) subsume soft sediment-associated vegetation and animals. |
Reduction in sediment flux and alteration of landscape connectivity. Also affects source of primary production and carbon flux. | Alters local biodiversity (especially vegetation and invertebrate communities) in favor of those attaching to hard structures. Also, potential loss of beach spawning habitat for forage fish. |
| Spit/Barrier/ Backshore | |||
| Low Bank | |||
| High Bluff | |||
Depth - Slope |
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| Rocky | May alter distribution of attached macroalgae and biotic (e.g., mussels, barnacles) communities depending upon encroachment. May also simplify habitat complexity. | May reduce landscape connectivity. | May alter biodiversity maintenance and salmon migratory corridors. |
| Marsh/Lagoon | Change in distribution of eelgrass, salt marsh vegetation, and mudflat channels. Impacts to associated landscape metrics. | Same as above, as well as modification of sediment flux and reduction of primary production. | Same as above, as well as alteration of salmon prey production. |
| Spit/Barrier/ Backshore | Encroachment and slope increase narrows distribution of eelgrass and other vegetation, simplifying or reducing habitat structure. | ||
| Low Bank | |||
| High Bluff | |||
Pollutants/ Nutrients |
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| Rocky | Nutrients may initiate nuisance algal blooms and epiphyte growth. Herbicides, contaminants, or water quality impacts may affect kelp vegetation, cause disease outbreaks, and affect growth. | May fragment landscape, affect sediment nutrient, and carbon flux, and reduce habitat connectivity and primary productivity.. | Direct toxicity to organisms, especially relevant to herring spawn, juvenile salmon, and their prey. Loss of vegetation causes reduction in salmon prey production and refuge. Affects biodiversity maintenance both in subtidal and riparian settings. |
| Marsh/Lagoon | Especially relevant in these settings with low flushing rates. Same impacts as noted above, especially as related to eelgrass, marsh, and marine riparian vegetation. | ||
| Spit/Barrier/ Backshore | Same impacts as noted above, especially as related to eelgrass and dune vegetation. | ||
| Low Bank | Same impacts as noted above, especially as related to eelgrass and riparian vegetation. | ||
| High Bluff | |||
Hydrology |
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| Rocky | Generally not an issue. | N/A | N/A |
| Marsh/Lagoon | Constrictions may impact tidal influence and flushing rates, affecting the distribution and diversity of riparian, eelgrass, and marsh vegetation. | Affects primary production, carbon, nutrient, and sediment flux, landscape connectivity | Affects associated plant and animal biodiversity and disturbance regulation. Vegetation change alters migration corridors for birds, mammals, and fishes. |
| Spit/Barrier/ Backshore | Encroachment into intertidal zone may alter tidal hydrology and displace dune vegetation | Same as Marsh/Lagoon. As well, altered hydrology may affect spawning success of forage fish (both via modifications to groundwater seeps and surface flow scour). |
|
| Low Bank | Alteration of groundwater and surface flows may impact riparian vegetation distribution and slope stability, whereas tidal encroachment by structures and location of outfalls may displace or scour intertidal salt marsh vegetation and eelgrass. | ||
| High Bluff | Same as Low Bank, though likely greater impacts to slope stability. | ||
Physical Disturbance |
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| Rocky | Benthic disturbances alter patch size, shape, and density of attached macroalgae and invertebrates (e.g. barnacles, mussels). | May fragment landscape and affect primary production associated with eelgrass or marsh communities. Altered carbon, nutrient, and sediment flux. | Biodiversity maintenance and natural disturbance regime. |
| Marsh/Lagoon | Unnatural or frequent disturbance of benthic habitats affects the distribution, size, shape, and density of eelgrass beds, macroalgae, and benthic communities. | Bottom disturbances affect benthic community biodiversity, salmon prey production and refuge, as well as disturbance regulation. May also affect spawn of forage fish. Human noise, activity, and sound may impact nesting and migration corridors of mammals and birds. | |
| Spit/Barrier/ Backshore | |||
| Low Bank | Same as above. Also, vegetation removal affects structure and complexity of riparian cover. |
Same as above. Also, reduced contribution of riparian primary production. |
|
| High Bluff | |||
| << 1.3.3 Geomorphology and the Conceptual Model |