Driver: Human Activities in Proximity to Shoreline

The level of human activity in the Salish Sea region both partly springs from and leads to extensive use of nearshore ecosystems. Access to shipping, fishing and other commercial and recreational endeavors makes the region an attractive location for human settlement. Expanding settlement and human activities exerts growing pressures on the ecological system. In the Driver-Pressure-State-Impacts-Response (DPSIR) conceptual model, nearshore human activities are represented as “Drivers” (Figure 3). Because shoreline modification is a consequence of these driving activities, the threat is represented as a Pressure in our review.

In the sections below, we review the Pressures of shoreline modification, and the resultant State changes and system Impacts. To avoid repetition of an existing review of this topic, we rely heavily on reviews completed by the Puget Sound Nearshore Ecosystem Restoration Project (Simenstad et al. 2009; Schlenger et al., in review) but supliment this review with other information from the peer-reviewed literature. We recommend that readers consult Simenstad et al. 2009; Schlenger et al., in review for greater details, both with respect to specific shoreline modifications and the status of distinct geographic subunits in the region. Although Schlenger et al. is currently in review and therefore not part of the peer-reviewed literature, we rely heavily on this document because the authors have essentially completed the goals of this section – to review the peer-reviewed literature of the threats associated with shoreline modification.

Given the economic and recreational impetuses leading to shoreline modification, such activities clearly can have positive impacts on human socioeconomics and well-being. However, we only focus in the current draft on the ecological changes resulting from shoreline modification rather than the benefits to human health and well-being; additionally, negative impacts of ecological changes on human health and well-being, such as decreased resource availability, impaired water quality, and increasing expenditures for shoreline restoration, are currently omitted. Lastly, Chapter 4, Effectiveness of Strategies to Protect and Restore the System, addresses the human Response to the problems associated with such modifications, and will not be covered in the present section.

Placeholder – positive and negative impacts of residential, commercial and industrial development on human health, socioeconomics and overall well-being

 

Figure 3. Driver-Pressure-State-Impacts-Response conceptual model for shoreline modification in the Salish Sea ecosystem.

1. Pressure: Shoreline Modification

Modification of shoreline regions results in a wide range of state changes in nearshore ecosystems (Simenstad et al. 2009; Schlenger et al., in review; summarized in Table 3). These changes lead to impacts to the shoreline, to the adjacent upland and freshwater systems and to the Salish Sea estuary (Simenstad et al. 2009; Schlenger et al., in review; summarized in Table 4). Collectively, nearshore modification has resulted in shortening and simplification of shoreline over the past 150 years, from both direct (e.g., artificial structures) and indirect (e.g., disruption of shoreform sediment transport processes) modifications; the Sound has experienced a loss of over 1000 km of natural shoreline and the introduction of almost 400 km of artificial shoreline (Simenstad et al. 2009; Schlenger et al., in review). This loss of convoluted shoreline has resulted in an overall loss of nearshore area, leading to disruption or loss of important ecosystem functions such as sediment, detritus and nutrient transport, loss of habitat and changes in species composition.

Table 3. Extent, number and percent change in shoreline by modification type in Puget Sound, the Strait of Juan de Fuca, and southern Strait of Georgia1

Modification Type

Extent of Modification

Number Occurring

Percent of Modification

Armoring

1071 km

-

27%2

Tidal Barriers

263 km

-

7%2

Overwater Structures

9 km2

8972

-

Marinas

6 km2

171

-

Breakwaters & Jetties

37 km

136

-

Loss of Wetlands

273 km2

-

53% of historical extent3

Dams

13,000 km2 impounded

436

37% impounded4

Transportation Structures

383 km (312 km of roads, 71 km of railroads)

-

10%2

1Numbers derived from Simenstad et al. (2009) and Schlenger et al. (in review).
2Based on a total shoreline length of 3962 km.
3Based on historical extent of 514 km2.
4 Based on a total sub-basin drainage area of 34,710 km2.

 

Table 4. Summary of direct (D) and indirect (I) impacts to nearshore processes by shoreline modification type1

 

Modification Type

 

 

 

 

 

 

 

Nearshore Processes Impacted by Shoreline Modification

Armoring

Tidal Barriers

Native Vegetation Removal

Overwater Structures

Marinas

Breakwaters & Jetties

Dams

Transportation Structures

Sediment Input

D

 

I

I

I

I

D

D

Sediment Transport

D

D

 

I

D

D

D

I

Erosion/Accretion of Sediment

D

D

I

I

D

D

I

D

Tidal Flow

I

D

 

 

I

 

 

D

Tide Channel Formation and Maintenance

I

D

 

 

I

 

 

I

Distributary Channel Migration

D

D

I

 

 

I

D

I

Freshwater Input

I

 

I

 

I

 

D

I

Detritus Import and Export

D

D

D

I

I

I

I

D

Exchange of Aquatic Organisms

D

D

 

D

D

D

D

D

Physical Disturbance

D

I

 

I

D

D

I

D

Solar Incidence

I

 

D

D

D

I

 

I

1Partially reproduced from Schlenger et al. (in review), Table 4-19, pg. 123.

Many shoreline modifications are for residential, commercial and industrial purposes. Nearshore ecosystems are thus subject to the same pressures, state changes and impacts associated more generally with development-related LULC changes, such as altered material and water fluxes due to increased imperviousness (Schlenger et al., in review). However, specific modes of shoreline modification have distinct characteristics with respect to their impacts on nearshore environments. We review here many of these various state changes and their associated impacts.

State: Increased Armoring

Shoreline armoring refers to structures largely aimed at erosion control from coastal wave movement, and for retention of fill zones. Such armoring consists of walls or bulkheads, constructed of rock or concrete, erected parallel to shorelines. Covering over 1070 km of Puget Sound shorelines (Schlenger et al., in review), armoring is particularly prevalent in highly developed residential, urban or industrial centers, due to a combination of the need to protect developed structures (e.g., roads, buildings) and the increased potential for erosion due to the removal of vegetation for land development (Alberti 2008; Schlenger et al., in review). For instance, armoring frequently co-occurs with nearshore roads, railroad passages, and/or other transportation infrastructure (Simenstad et al. 2009; Schlenger et al., in review). Of the various shoreline modification forms, armoring is the most common, comprising 74 percent of all artificial shoreforms (Simenstad et al. 2009).

Impacts

Armoring significantly alters the movement of sediments and debris that provide physical structure to beaches and other nearshore zones (Simenstad et al. 2009; Schlenger et al., in review). By design, armoring structures block natural, more gradual upland erosion processes that deliver sediments and replenish shoreline materials carried away by waves and tides. In place of such processes, the abrupt physical barrier serves to intensify waterward erosion of waves, further altering beach structure.

These changes to movements of sediment and debris are one of the primary impacts leading to degradation of river deltas within the Salish Sea ecosystem. Approximately 44 percent of river delta extent (188 km2 of the 427 km2 historical area) has been lost due to impacts such as armoring (Schlenger et al., in review). Shoreline modifications such as armoring alter both the transport of sediments into river deltas and the distribution of sediments within the delta itself (Miles et al. 2001; Johannessen and MacLennan 2007). In turn, degradation of river deltas has significant ecosystem impacts, including loss of habitat and restriction of species ranges (e.g., salmon and other fish, shorebirds and the benthic invertebrates they depend on) (Griggs 2005; Buchanan 2006; Dethier 2006; Fresh 2006; Mumford 2007; Tonnes 2008). Resultant changes in sediment flows also increases estuarine turbidity.

Armoring results in the degradation of bluff-backed and barrier beaches (Canning and Shipman 1995; Johannessen and MacLennan 2007), particularly in South Central Puget Sound (Schlenger et al., in review). Bluff-backed beaches have declined by approximately 8 percent from their historical extent due to a range of factors including armoring (Simenstad et al. 2009; Schlenger et al., in review). Approximately 33 percent bluff beaches include some level of armoring, leading to disruption of the sediment and debris transport process that feeds these and nearby down-drift beaches. Coastal bluffs provide an estimated 90 percent of sediment to beaches along the Sound (Downing 1983), which in turn affects resilience of coastal embayments that depend on this input. Barrier beaches, which serve as protection for estuary lagoons and other coastal embayments, have also declined by 12 percent of their historical extent; of these, 27 percent include shoreline armoring (Simenstad et al. 2009; Schlenger et al., in review). Degradation and loss of bluff and barrier beaches result in loss of invertebrate habitats (Sobocinski 2003; Dugan and Hubbard 2006; see Schlenger et al., in review), which impacts fish, mammals and birds that feed on them. Armoring these systems also results in loss or impairment of spawning habitat of forage fish such as surf smelt and sand lance (Rice 2006; Penttila 2007) and herring, which may lead to declines in some species that feed upon these fish or their eggs (surf scoter populations, for instance Anderson et al. 2009).

Changes in sediment transport due to armoring have also contributed to loss or fragmentation of coastal embayments, such as inlets, barrier estuaries, barrier lagoons, closed lagoons and marshes (Schlenger et al., in review). Compared with historical occurrence, 53 of 173 open coastal inlets, 84 of 240 barrier estuaries, and 89 of 222 barrier lagoons have been lost. Closed forms of coastal embayments, such as lagoons and marshes that do not interface with open estuary, exhibit similar trends: comprising approximately 1.6 km of the Puget Sound shoreline (down from a historical extent of 2.6 km), only about 81 of 249 historic closed lagoons and marshes remain. As noted above, coastal sediment transport processes that create and maintain structure for barrier beaches form the boundaries for coastal embayments; disruption of such transport due to armoring in turns leads to the degradation of embayments (Schlenger et al., in review). Losses of embayments have been noted to have significant impact on juvenile Pacific salmon that use these habitats for feeding (Beamer et al. 2003; Fresh 2006). Other significant impacts include altered nutrient inputs and overall water quality, loss of or diminished primary productivity, and loss of biodiversity (Schlenger et al., in review).

Placeholder – discussion of riprap impacts on aggregating some fish species, and increasing velocity along river banks

State: Construction of Tidal Barriers

Tidal barriers consist of structures such as dikes, levees and tide gates that are used to restrict or divert tidal flows. They are often used to block tide waters (or in the case of tide gates, to drain water) from delta regions that have been converted to agricultural lands (Schlenger et al., in review). Tidal barriers are typically constructed of large rock and other heavy materials to prevent damage from flood waters. According to shoreform database estimates, approximately 418 km of tidal barriers exist within Puget Sound nearshore ecosystems (Simenstad et al. 2009; Schlenger et al., in review).

Impacts

Because of the nature of their construction and use, tidal barriers have particularly significant impacts on river deltas (Schlenger et al., in review). As with armoring, these barriers alter the transport and distribution of sediments to and within deltas, coastal marshes and tidal channels (Thom 1992; Barrett and Niering 1993; Brockmeyer et al. 1997; Bryant and Chabreck 1998; Hood 2004). These impacts in turn alter the formation and maintenance of tidal flow channels, and hence the overall structural integrity of river deltas. Changes in sedimentation also have potentially negative impacts on eelgrass and kelp survival (Mumford 2007; Schlenger et al., in review). As a consequence, shorebirds, fish and benthic invertebrates that rely on such river delta vegetation for foraging, spawning and refuge habitat experience declines in their abundance and distribution (Griggs 2005; Buchanan 2006; Dethier 2006; Fresh 2006; Mumford 2007; Tonnes 2008; cited in Schlenger et al., in review). Turbidity in the vicinity of river mouths also increases.

Placeholder – information on number of deltas with >75% coverage by tidal barriers, and the number being restored to remove tidal barriers

Open and closed coastal embayments are also significantly impacted by tidal barriers (Schlenger et al., in review). Barriers occur within the immediate vicinity of 16 percent of open coastal inlets and 21 percent barrier estuaries in the Sound (Simenstad et al. 2009). The structure of embayments, whose boundaries are dependent on persistent replenishment of sediments from both tidal and more upland flows, is frequently modified by the changes in sediment transport induced by tidal barriers (Schlenger et al., in review). Such shifts particularly alter or disrupt the morphology and vegetation composition of nearshore marshes (Barrett and Niering 1993; Bryant and Chabreck 1998; Hood 2004), and limit the availability of detrital nutrients used by aquatic organisms (Schlenger et al., in review).

State: Native Vegetation Removal

Changes in land cover, particularly removal and/or fragmentation of native vegetation, is frequently associated with artificial shoreline modifications (Schlenger et al., in review). Residential and industrial development, and the changes in land cover that it entails, is prevalent along Puget Sound shorelines, particularly in the central and southern Sound regions (Alberti et al. 2004; Simenstad et al. 2009) .

Impacts

As described above (see “State: Altered Biogeochemistry and Hydrology” under “Pressure: Land Use/Land Cover Change”), changes in land use and land cover modify the rates and volumes of upland water and material fluxes (Tague and Band 2001; Booth et al. 2002; Wickham et al. 2002; Brett et al. 2005; Kaye et al. 2006; Cuo et al. 2009), which in turn translate into altered transport into nearshore ecosystems.

Changes in sediment, water and nutrient fluxes due to upland vegetation conversion alter the geomorphic structure and ecosystem functioning of nearshore ecosystems (Schlenger et al., in review). Changes in upland transport of sediments interact with in-water fluxes to modify the structure and stability of shore banks, beaches and embayments. Degraded structural and biogeochemical changes to embayments and river deltas in turn alter, and often simplify, food webs and communities that depend on these shoreforms for shelter and foraging habitat (Griggs 2005; Buchanan 2006; Dethier 2006; Fresh 2006; Mumford 2007; Tonnes 2008; cited in Schlenger et al., in review).

State: Construction of Overwater Structures

Overwater structures comprise a general class of shoreline modification that includes fixed and floating docks, fixed piers, bridges, floating breakwaters, moored vessels, and support and stabilization piles. Approximately 6927 overwater structures can be found in the Puget Sound region, comprising a total area of approximately 6.5 km2 (Simenstad et al. 2009; Schlenger et al. in review). The severity of nearshore impacts of a given overwater structure depend on some of the following physical characteristics that determine its physical profile in and above the water (Nightengale and Simenstad 2001; Schlenger et al., in review): the structure’s size and shape; its height above the water and the depth of water below it; the number of support pilings it requires; its orientation to and location along the shore; and its proximity to other overwater structures.

Impacts

One of the key impacts of overwater structures is shading of nearshore habitats (Nightengale and Simenstad 2001; Schlenger et al., in review). Aside from the obvious implications for nearshore plants (Dennison 1987; Kenworthy and Haunert 1991), shading also impacts the distribution, behavior and survival of fish and other aquatic wildlife that occupy adjacent shoreline habitats. Sharp gradients of light and shadow, such as those that occur near overwater structures, affect feeding behavior and efficiency of visual foragers (e.g., salmon, Dungeness crab) as well as fish schooling and migratory movements (Nightengale and Simenstad 2001; Scheuerell and Schindler 2003; Thom et al. 2006; Schlenger et al., in review).

Placeholder – discussion of overwater structure impacts on fish aggregation vs. deterrence (e.g., does the shade help keep water temperatures cooler?)

As with other shoreline modifications that pose physical barriers, structural support pilings interfere with tidal flows and wave movements (Nightengale and Simenstad 2001; Schlenger et al., in review). Individual pilings may have negligible impacts on water movements and energy, depending on their size. However, because structures typically have multiple rows of pilings, these supports have cumulative impacts that attenuate wave energy, with consequent shifts in the deposition and distribution of adjacent and downdrift shoreline sediments.

Also associated with overwater structures, particularly those of older construction, is the potential introductions of contaminants into nearshore waters (Poston 2001; Schlenger et al., in review). Older, creosote- or copper-treated wood structures have been demonstrated to leach polycyclic aromatic hydrocarbons and copper arsenate compounds, respectively, into aquatic ecosystems (Valle et al. 2007).

Placeholder – discussion of short-term effects during construction with pile driving and sediment disturbance, particularly with respect to timing of construction relative to migrating animals

State: Construction of Marinas

Marinas are comprised of a diversity of in-water and/or overwater structures, as well as adjacent nearshore modifications such as parking lots and service buildings, that vary in impact depending on their specific physical characteristics (Schlenger et al., in review). Building structures of varying size, shape and orientation in conjunction with water vessel moorings alter both the geomorphic characteristics of shorelines and the flows of water and sediments; accompanying breakwaters and jetties (see below) further exacerbate impacts. Approximately 0.3 percent (around 6 km2) of Puget Sound shoreline is covered by over 170 marinas, with about one third occurring in the south Sound (Simenstad et al. 2009; Schlenger et al., in review).

Impacts

The impacts of marinas are significant on beach systems, river deltas and coastal embayments (Schlenger et al., in review). Physical in-water and overwater barriers associated with marinas alter or disrupt the transport of sediment, coarse debris and detritus, thereby degrading beach structure immediately adjacent to as well as downdrift from the marina. As noted above, shading from accompanying overwater structures also impacts plant productivity and aquatic wildlife foraging and movement behavior (Nightengale and Simenstad 2001; Schlenger et al., in review). Marinas constructed near river deltas or coastal embayments similarly alter both upland and in-water sediment transport processes that maintain the structure and water and material flows within these shoreforms. Upland armoring often accompanies marinas, degrading nearshore habitats for wildlife and further disrupting land-water interactions (Simenstad et al. 2009; see “State: Increased Armoring” above).

Marinas also introduce chemical contaminants into nearshore ecosystems (Poston 2001; Schlenger et al., in review). As with overwater structures, leaching of chemicals from treated wood structures is a potential risk. Perhaps more significant and prevalent, however, are risks of contaminants released into water and sediments from moored vessels and upland parking facilities. These petroleum-based and other forms of contaminants have significant impacts on plants, aquatic and nearshore wildlife and general nearshore food web structure (Schlenger et al., in review).

Placeholder – discussion of impacts from tin-based antifouling paints that are stored in the bottom sediments, from when these paints were legal in the USA

Placeholder – impacts of noise pollution from vessel traffic and industrial activity in and around marinas

Placeholder – potential impacts from stray electrical currents from marinas

Placeholder – positive vs. negative impacts on wintering populations of birds

State: Construction of Breakwaters and Jetties

Similar to tidal barriers (see “State: Construction of Tidal Barriers” above), breakwaters and jetties are structures designed to dissipate wave movement and energy, particularly near harbors, marinas and areas where vessels are moored (Schlenger et al., in review). Some breakwaters and jetties are composed of heavy rock or concrete armoring, while others are comprised of free-floating or anchored structures. There are 136 recorded breakwaters and jetties in the Salish Sea ecosystem, with about 65 percent occurring in the northern portion (Simenstad et al. 2009; Schlenger et al., in review). They range in length from as little as 5 m to as long as 5 km (Schlenger et al., in review).

Impacts

Impacts of breakwaters and jetties generally depend on their orientation to the shoreline (Schlenger et al., in review). Structures oriented parallel to the shore lead to deposition of sediment on the waveward side, resulting in accretion beaches and a deepening of shoreline channels on the opposite side of the structure. Breakwaters and jetties that are perpendicularly oriented disrupt shoreline sediment and detritus transport processes that maintain the geomorphology of downdrift beaches and coastal embayment boundaries. Breakwaters and jetties erected adjacent to river deltas and coastal embayments also serve to disconnect these aquatic ecosystems from the broader Sound and from one another. The resultant changes in shoreform morphology, connectivity and nutrient and water flows leads to degraded habitat quality for nearshore wildlife and plant communities (Schlenger et al., in review).

Placeholder – potentially positive impacts of breakwaters and jetties providing shelter for wintering bird populations in storms

State: Loss of Wetlands

Through a variety of forms of shoreline modification – particularly armoring and tidal barrier impacts on river deltas and coastal embayments as well as outright filling – significant loss of wetlands has occurred or is occurring along Puget Sound nearshore ecosystems (Simenstad et al. 2009; Schlenger et al., in review). Approximately 53 percent, or 273 km2 out of 514 km2, of historical wetland extent has been lost to these various stressors. Of particular concern are losses of tidal freshwater and oligohaline transitional wetlands: these two wetland classes have lost approximately 93% of the historical extent (Schlenger et al., in review).

Impacts

Losses of these important coastal ecosystems have significant implications. Ecosystem functions performed by wetlands, such as food and nutrient production, contaminant filtration, breeding and feeding habitat provision, become considerably impaired as wetland area diminishes (Schlenger et al., in review). Wetland losses particularly impact Chinook populations, since these shoreforms provide significant habitat during juvenile growth stages (Bottom et al. 2005; Fresh 2006).

Placeholder – expand discussion of impacts on Chinook

Placeholder – expand overall discussion of the ecological importance of the loss of wetlands

State: Construction of Dams

The number and distribution of dams in the Salish Sea ecosystem is of significant concern in terms of their impacts, which vary as a function of a given dam’s position in the watershed and the number of other dams up- and downstream of it (Neuman et al. 2009; Simenstad et al. 2009; Schlenger et al., in review). A total of 436 dams can be found in the Puget Sound basin, impounding approximately 13,000 km2, or 37 percent, of the total sub-basin drainage area (Simenstad et al. 2009; Schlenger et al., in review).

Impacts

By diverting or constraining the flow of water, sediments, nutrients and organic matter, dams prevent transport of materials necessary for the persistence of downstream nearshore ecosystems, particularly in river deltas and coastal embayments (Schlenger et al., in review). Along with upland sources, rivers and streams deliver sediments and organic matter that provide structural integrity to nearshore ecosystems, replenishing materials that are washed away via tides and waves. These materials, as well as nutrient and freshwater inputs, are important for the persistence of downstream plant (e.g., kelp, eelgrass) and animal (e.g., shellfish, juvenile salmon) populations and food web interactions (Schlenger et al., in review). Changes in water flow rates and levels result in water temperature regime changes both in upstream riverine and downstream nearshore ecosystems (Schlenger et al., in review). Significant disruption of native vegetation, soils and hydrologic regimes also occurs in reservoirs upstream of the dams, impacting upland biota and ecosystem functions in ways that then further impact downstream nearshore systems (Schlenger et al., in review).

Placeholder – expanded discussion of dam impacts; include specific discussion of the effects of dams on connectivity, stream temperature, migratory fish, and the timing and levels of flows

State: Construction of Transportation Structures

A number of different classes of transportation structures are found within close proximity to nearshore ecosystems, including railroads, nearshore roads, and stream crossings (Simenstad et al. 2009; Schlenger et al., in review). Roads and railroads occur along 312 and 71 km of Puget Sound shoreline, respectively, comprising almost 10 percent of its total length (Simenstad et al. 2009; Schlenger et al., in review).

Impacts

Impacts of these features are analogous to and compounded by the effects of upland impervious surfaces, particularly with respect to changes in hydrology and biogeochemistry and increased contaminant runoff (see “State: Increased Imperviousness” under “Pressure: Land Use/Land Cover Change”). Nearshore transportation corridors and structures contribute to disruptions in upland replenishment of sediment and detritus to beach and embayment shoreforms, particularly through interactive impacts with other shoreline modifications (e.g., armoring, vegetation removal, etc.). Fill material used to bolster transportation routes further alters the geomorphic structure of, and often eliminates, shoreline ecosystems (Schlenger et al., in review). Construction of transportation corridors frequently disrupts connectivity within and among shoreline ecosystems, particularly in the form of overpasses through or over river deltas and embayments. Lastly, increased contaminant loadings occur as a result of nearshore transportation structures, both directly deposited by automobiles and trains and indirectly mobilized via surface water runoff across impervious surfaces (Booth et al. 2002, 2004; Kaye et al. 2006; Krahn et al. 2007; Schlenger et al., in review).

States and Impacts: Cumulative Effects of Shoreline Modifications

As illustrated above, most of the various forms of shoreline modification have comparable impacts on nearshore ecosystems (Schlenger et al., in review): disruption of sediment and detrital transport rates, levels and mechanisms; altered and often simplified estuarine and freshwater flow pathways; increased contaminant levels; and general disruption of nearshore ecosystem functions and resultant habitat degradation. Exacerbating the effects of shoreline modification is the fact that often several of these modification forms co-occur within a given location. In change assessments for the Puget Sound, Strait of Juan de Fuca and Strait of Georgia Basins, 65 percent of drainage catchments include more than one type of modification (Simenstad et al. 2009; Schlenger et al., in review). For example, armoring commonly co-occurs with other stressor types, most frequently accompanying nearshore roads (in 46 percent of catchments). These findings suggest a significant risk of cumulative, synergistic impacts from multiple stressors.

Placeholder – expanded discussion of and citations for cumulative shoreline modification impacts

2. Uncertainties and Information Gaps

The uncertainties and knowledge gaps associated with shoreline modification in the Salish Sea ecosystem reflect questions in data availability and quality. In addition to extensively reviewing the forms of shoreline modification and their impacts, the PSNERP Strategic Needs Assessment Report (Schlenger et al., in review) also discuss such uncertainties in detail; we thus present only an overview of this topic.

One source of uncertainty lies in the quality of datasets available for analyzing shoreline modification extent and impacts. A comprehensive analysis covering the extent of shoreline in Salish Sea required compilation of data sets from a variety of sources, each of which includes its own level of accuracy and uncertainty. Inaccuracies are potentially most problematic for historical conditions, for which data are limited at best and require estimating of sedimentation rates and other key shoreline formation processes. Such inaccuracies can of course affect change detection and estimates, but are unavoidable and must therefore simply be taken into consideration as fully as possible.

In addition to those entailed in geographic measurements of the extent of shoreforms and their modification, uncertainties exist in the linkages between state changes and their systemic impacts. Assessment of impacts in Schlenger et al. (in review) and Simenstad et al. (2009) were based on review and synthesis of empirical investigations in peer-reviewed and gray literature. As reflected in our review above, such synthesis provides a qualitative understanding of potential impacts to Salish Sea biota and ecosystem processes; investigations targeted at specific cause-and-effect linkages are necessary to quantify the level of impacts. At the same time, applicability and generalizability of targeted studies to the broader system requires systematic review and evaluation. This requirement is particularly necessary when drawing conclusions from studies that examine causal linkages between shoreform modification and ecological impacts in systems comparable to, but not within, the Salish Sea region.

Lastly, specific scales of analysis may result in biases and uncertainties in estimated state changes and their impacts. PSNERP’s assessments of shoreline modification were aggregated at the catchment level as the finest scale of measurement (Simenstad et al. 2009; Schlenger et al., in review). Because such catchments vary in size throughout the region, measures of the extent of shoreline modification that are aggregated to this level can over- or underestimate absolute levels and intensity of modification within a given segment of the watershed. Schlenger et al. (in review) note that refined, more detailed site-level assessments can correct for these uncertainties. Additionally, some level of aggregation – preferably at fine enough scales to capture key biophysical processes such as sediment transport rates (as is true for catchments) – is all but necessary for broader-scale, relative trends that characterize segments of the Salish Sea ecosystem.

 

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