Estuaries occur where freshwater rivers meet the oceanic salty waters, are influenced by tidal flooding, and experience frequent periodic changes in salinity, water levels, sunlight, and oxygen.
Limiting Factors and Recommended Approaches
Limiting Factor: Increasing Development, Land Use Conversion, and Altered or Blocked Tidal Flow
Estuary habitat has been lost to a variety of causes, including: diking, ditching, and drainage; tide gates; inadequate flow through culverts under roads and railroads; industrial and residential development; log storage areas, pilings, docks, or bridge structures; and aquaculture practices that reduce eelgrass beds and disturb winter waterfowl. Estuarine development closer to the ocean can impact habitats as well. For example, building and maintaining jetties, piers, breakwaters, marinas, and navigation channels, including disposal of dredge materials, can alter the habitat and impact nearshore Strategy Species.
Continue to provide incentives to protect, conserve, and restore estuaries. Where appropriate, work to restore hydrology to tidal wetlands by removing dikes, filling ditches, and replacing undersized culverts. Continue successful education programs focused on the function and services provided by estuaries. Work with agency partners to support and implement existing land use regulations that preserve and restore habitats. For example, refer to seasonal in water work window for estuaries designed to minimize impacts to out-migrating salmon. Continue to develop and refine “best management practices” for aquaculture. Maintain and restore eelgrass beds as a habitat feature. (KCI: Land Use Changes)
Limiting Factor: Alteration of Freshwater Inputs Into the Estuary
In addition to the restoration of tidal flow discussed above, the amount and timing of freshwater inputs into estuaries are critical in maintaining the hydrological regime that supports the delicate estuarine balance. When either the amount or timing of freshwater input is altered, several results are possible: inundation of floodplains, increased sedimentation, decreased residence time of water (which reduces the filtering benefits of estuaries), altered fish community dynamics, and/or increased stress on juvenile fish, nekton, or other animals. Changes in hydrological regimes can make estuaries prone to invasive species, which compound the problem.
Evaluate the potential impacts of water diversions from the estuary (e.g., for agriculture, residential, or industrial purposes) on floodplain dynamics and other functions of estuaries. Prioritize basins for the acquisition of sufficient instream flows.
Limiting Factor: Degraded Water Quality
Water quality in estuaries is degraded by both point and non-point sources of pollution both within the estuary and from its contributing watershed. Runoff from residential, agricultural, and forest land, failing septic systems, animal waste, and storm events can affect water quality. Water temperature can be affected by dredging or sedimentation and stormwater runoff. Oil discharge and spills also affect water quality. Other discharges, such as runoff from boat and ship yards and fish processing operations, can also be a factor. Among other issues, estuaries are susceptible to increased bacterial loads. Low dissolved oxygen levels are often an additional concern. Estuaries are also affected by acidification effects from terrestrial input, which combined with ocean water acidification, can decrease water quality for some marine organisms in estuaries.
Continue current efforts to consider impacts on estuarine water quality in land use planning. Support efforts of the Oregon Department of Environmental Quality (DEQ) to assess water quality and develop Total Maximum Daily Loads and water quality management plans where necessary to address issues. Continue coordination to ensure that plans and goals consider impacts to water quality sufficient to protect fish and wildlife in addition to other goals (i.e., recreation). (KCI: Water Quality and Quantity)
Limiting Factor: Invasive Species
Non-native invasive plants and animals can easily disrupt the estuary environment. Invasive plants can alter water circulation and sediment patterns. For example, common cordgrass poses a great threat to Oregon’s estuaries. Common cordgrass has been documented in two Oregon estuaries and is well-established in Washington and California. Where it occurs, it reduces mud flat habitats, disrupts nutrient flows, displaces native plants and animals, alters water circulation, and traps sediments at a greater rate than native plants, thus altering the elevation and the resulting habitats. Three other cordgrass species have invaded the Pacific coast and threaten Oregon’s estuaries. Invasive plants can alter ecological community dynamics, such as competition, predation, or even parasitic relationships with native species. Estuaries are one of the most vulnerable habitats for invasive species due to ship traffic and release of ballast water. Ballast water can also carry invasive animals, algae, protists, and potentially, bacteria. Invasive species can also be introduced into estuaries through aquaculture, recreational or commercial boating, or the aquarium trade. Examples of non-native invasive animals found in Oregon estuaries include: the parasitic Griffen’s isopod which has been linked to declines of native blue mud shrimp populations, the Japanese oysterdrill, the New Zealand mudsnail, the purple varnish clam, and a colonial tunicate.
Emphasize prevention, risk assessment, early detection, and quick control to prevent new invasive species from becoming fully established. Control key invasive plants using site-appropriate tools, such as hand-pulling, covering with geotextile cloth, repeated mowing, flooding, and/or herbicides focusing on spot treatment. Monitor estuaries for potential invasive species, and use site-appropriate methods to control newly-established species for which management can be most effective. Work with partners to implement existing ballast water regulations. Develop methods to treat ballast water. Work with partners to limit the spread of invasive species that are established. Allow increased harvest of species suitable for human consumption such as purple varnish clams. (KCI: Invasive Species)
Limiting Factor: Coordination of Management
Many jurisdictions and agencies have management authority and interest in estuaries, which can make management more complex and difficult. In Oregon, 22 cities, 7 counties, 13 port districts, many state agencies (e.g., Department of State Lands, Oregon Water Resources Department, Oregon Department of Land Conservation and Development, DEQ, Oregon Department of Agriculture (ODA), ODFW, Oregon Parks and Recreation Department) have planning and management responsibilities for estuaries as does the federal government. Many organizations have interests in estuaries.
Coordination among agencies is a high priority. Because estuarine issues are complex, clear identification and communication of conservation opportunities, goals, and threats should precede management actions, ensuring that all interests are considered and coordinated.
Limiting Factor: Loss of Habitat Complexity
Habitat complexity provides refugia for estuarine fish and wildlife. Complex habitat supports diverse ecological communities, contributing to resiliency to climate change impacts. Removal or loss of large downed trees reduces habitat complexity, insect production, and food and cover for juvenile salmonids. Disconnection from the floodplain interrupts the natural transition zones between the aquatic, intertidal, and upland ecosystems. Dredging, ditching, channelization, and filling in estuaries alters marine and freshwater inputs and reduces habitat function. In-water (e.g., pilings, jetties, seawalls) or overwater (e.g., mooring buoys, floating docks) structures can reduce habitat complexity, as can bayside development that extends into intertidal areas. Natural factors can also reduce habitat complexity, such as damage or movement caused by seasonal runoff or significant storm events, especially where the estuary has already been compromised and floodplains have been lost.
Assure that permit application reviews consider alternative sites and practices to reduce and minimize impacts, and provide full mitigation. Encourage and participate in cooperative efforts and incentives to promote habitat complexity in estuaries. Prioritize conservation and restoration efforts to restore floodplain connectivity, tidal marshes, and swamps and to conserve eelgrass. Increase outreach and education about the importance of habitat complexity.
Limiting Factor: Climate Change
Climate change may impact estuaries in several major ways: loss of wetlands due to sea level rise, alteration of hydrology, increases in erosion and salinity, changes in storm patterns, and ocean acidification. The effects of sea level rise are being modeled in Oregon’s estuaries, incorporating tectonic uplift, different levels of predicted sea level changes, and information on sediment inflow. The goal is to identify which estuarine areas are the most susceptible and where future marshes are likely to be to help restoration specialists and planners define desired future conditions and actions. Additional information is needed to understand the effects of climate change (including storm surge impacts and sediment movement patterns) on species with a variety of life stages in estuaries. Ocean acidification and the impact of anoxic (hypoxia) conditions in estuarine and nearshore areas are also of concern. Additional information is needed to determine what adaptation measures can be taken.
Use emerging models of future sea level rise and changing salinity regimes to inform conservation actions in estuaries. Work with property owners, land use planners, and restoration practitioners to focus attention on vulnerable areas. Support efforts to restore natural processes of tidal exchange and sediment deposition, which will enable tidal wetlands to maintain their elevation relative to rising sea levels. Support efforts to re-connect floodplains to adjacent uplands by removing barriers, placement of large woody debris, and planting of riparian areas. Conserve areas that will become new marshes with sea level rise. Inform communities about climate change impacts and support community preparedness. (KCI: Climate Change, Climate Change and Oregon's Nearshore Open Water Habitat)
Limiting Factor: Oil Spills
Oil (and other hazardous waste) spills are of concern in estuaries. If a spill occurs, oil accumulation can have lasting impacts in estuaries.
Review and update oil spill contingency plans based on new estuary maps and climate change considerations. Work with Oregon Department of Geology and Mineral Industries, DEQ, and local emergency officials to identify hazardous material use and storage sites in high risk areas and seek ways to minimize these risks.