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Chapter 8: Technical Considerations for Habitat Restoration

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Contents

Physical Considerations

Sea Level Rise

Sediment Supply

Sediment Deposition

Design and Management Considerations

Self-Maintaining Habitats

Managed Habitats

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This section describes some of the technical issues that will need to be considered as part of planning for wetlands restoration and enhancement. It is divided into two parts: physical considerations, and design and management considerations.

Physical Considerations

Restoring and enhancing the Bay's wetlands requires an understanding of the physical factors that control the distribution, quantity, and quality of the baylands and adjacent habitats. The dominant controlling factors are climate, topography, and land use. These are the dominant factors because they control the supplies of water and sediment that are essential to create and maintain the baylands and adjacent habitats. In general, topography and land use modify the influence of climate, but these three factors can interact. For example, weather is the result of interactions between climate and topography. Figure 8.1 shows how these and many other factors interact to form the baylands environment.

Climate controls sea level, wind, temperature, and rainfall, all of which affect the availability of sediment and water. Sediment is especially important for bays and tidal habitats where water is almost unlimited. And water is especially important in diked baylands and adjacent upland habitats where sediment is almost unlimited. During times of wind and rain, erosion in the uplands and waves in the Bay increase the availability of sediment. Rainfall and runoff affect the salinity of the tides and soil. Temperature affects the potential rate of evaporation.

Climatic conditions change slowly. The average annual values for rainfall and air temperature have not changed significantly for the Bay Area in hundreds of years, despite obvious seasonal and annual variations.

Topography controls the distribution of water and sediment supplies. The topography of tidal baylands, relative to sea level, determines the frequency and duration of tidal inundation and where the tides go. The topography of diked baylands and adjacent upland habitats controls where rainfall drains or stays above or below the ground. Slight variations in topography can have ecologically significant effects on the distribution of water on the ground surface. Like climate, topography changes slowly, except for the local effects of landslides, earthquakes, and people. The interactions among topography, sediment, and water, as controlled by climate, account for the natural forms and ecological functions of the baylands.

See Figure 8.1 Relation of Local and Regional Factors That Control Wetlands and Adjacent Habitats

Land use can directly affect the quality and quantity of the baylands and adjacent habitats. For example, altered topography and artificial control structures levees, tide gates, drainage ditches, and settling basins and chemical pollution from industry or even roadways can affect supplies of water and sediment. Land use can further affect habitat quality through fragmentation of habitats, introduction of invasive species, and the disturbance or over harvest of plants and wildlife.

Sea level rise and sediment supply and deposition are among the most important physical factors to consider in planning baylands restoration and enhancement.

Sea Level Rise

Sea level fluctuation plays an important role in forming many landscapes and it has influenced the estuary for millennia. At the end of the last glacial period, some 15,000 to 18,000 years ago, the seas began their most recent rise, and about 10,000 years ago, ocean waters began to flood the estuary basin. Initially, sea level rise within the basin was relatively rapid, but about 6,000 years ago it slowed to approximately the present rate of about 0.1 inch per year.

It is generally accepted that sea level will continue to rise in the future. This will have several effects on the baylands including the need for more shoreline protection, changes in the distribution of tidal marsh, and altered salinity patterns and associated changes in the vegetational make-up of tidal marshes.

At the current rate of sea level rise, the water surface of the Bay will rise eight or nine inches in the next 100 years. If global warming increases the rate of sea level rise, the effects on the estuary will become apparent sooner. Rising sea level will cause many changes in the estuary, one of the most obvious being the increased flood threats associated with high water. For example, it has been predicted that a one foot rise in sea level could double the average number of floods of Delta islands. Rising sea level will necessitate adding or improving bank stabilization and flood protection features throughout the estuary in rural and urban areas; levees will need to be raised, protected shorelines re-rocked, and other similar features strengthened.

On flatter lands around the estuary primarily in Suisun, North Bay, and South Bay rising sea level will make it possible for tidal marshes to move landward, provided there is an adequate supply of sediment to maintain the marsh plain and undeveloped space for the marshes to colonize.

Rising sea level also will change the estuary's salinity regime. As saline water moves further inland on incoming tides, salinity gradients will shift upstream. The salinity of Delta channels will become more like that of Suisun today, and the vegetation influenced by the tides will become more brackish. Likewise, as Suisun Marsh becomes more saline, its vegetation will become more like the vegetation that now exists in the North Bay.

It is not a simple matter to predict what the estuary's marshes will be like in one hundred years, considering the expected sea level rise. Many factors interact to complicate the picture. For example, one might predict that if sea level rise exceeds a certain rate, the limited sediment supply would prevent the marsh plain from building up, and marshes would be drowned. However, this could be offset by global warming which is expected to intensify rainfall events, increase erosion, and thus make more sediment available to raise the marsh plain.

Sediment Supply

Restoring large areas of the baylands to tidal marsh will require an adequate supply of sediment to raise the bottom elevation of subsided lands to an elevation appropriate for tidal marsh vegetation, about MHW to MHHW. Sediment also will be needed to maintain the elevations of the restored and existing marshes in the long term.

There are two main sources of sediment for the baylands tidal marshes: bottom material that is resuspended by currents and wind-driven waves, and material that is transported to the estuary from tributaries. As many as 286 million cubic yards of sediment are resuspended each year in the Bay. More than six million cubic yards of sediment enter the estuary each year, 86 percent of which comes from the rivers of the Central Valley, mostly the Sacramento River, and the remainder is supplied by local tributaries. Only a small proportion of the sediment from these sources is transported to the shoreline and is available for marshes; the remainder settles out on the Bay bottom (and may be resuspended) or is carried to the ocean.

A key question regarding large-scale tidal marsh restoration is whether there will be an adequate supply of sediment in the long-term to raise and maintain the baylands marsh plains. Although it is difficult to answer this question with a high degree of certainty, a couple of factors indicate that sediment availability will likely decline in the coming decades. First, as the large mass of material from Gold Rush hydraulic mining continues to pass through the Bay system, the volume of resuspended sediment will decline. Second, recent research indicates that the volume of sediment provided to the estuary by the Sacramento River has declined by about one-half since 1960, mostly as a result of dams. Assuming that existing and perhaps additional dams continue to trap sediments, it is reasonable to assume that there will be less material coming into the Bay from tributaries in the future. Although millions of cubic yards of sediment likely will continue to enter the Bay each year, given the expected trend of declining sediment supply, large-scale tidal marsh restoration will probably need to occur over a period of many decades, and the rate of restoration will need to be closely linked to sediment availability. As described in Chapter 10, the limited use of dredged material may be appropriate in certain circumstances to augment the natural sediment supply for purposes of restoring and enhancing habitats.

Sediment Deposition

In subsided areas of the Bay, tidal marsh restoration will proceed primarily by deposition of suspended sediment. Observations indicate that, while deposition rates vary around the Bay, deposition will continue until the marsh plain reaches an equilibrium elevation about equal to MHHW.

The rate of sediment deposition is affected by many parameters including suspended sediment concentration, water column depth, local wave conditions, salinity regime, and presence of vegetation. In some parts of the estuary, sediments have been found to accumulate very quickly, up to five feet per year at some sites.

Initial accretion rates of more than two feet per year are common in deeply subsided sites, but these rates decrease as the marsh plain rises. While the amount of sediment available for deposition decreases as the marsh plain rises, the establishment of vegetation accelerates the rate of rise towards equilibrium by reducing turbulence and adding organic matter.

Ongoing tidal marsh restoration at several sites in the Bay indicates that substantial sediment deposition and re-colonization by marsh vegetation can occur fairly quickly. These sites include Carl's Marsh adjacent to the Petaluma River, White Slough near the Napa River, Pond 2A in the Napa Marsh, Toy Marsh near Black Point, Whale's Tail Marsh near the Alameda Flood Control Channel, and outer Bair Island on the west side of the South Bay.

In the South Bay, it has been predicted that natural sedimentation would take about 10 to 15 years to raise the bottom of a moderately subsided (-3 feet Mean Sea Level) salt pond to an elevation where native vegetation would become established. In the most severely subsided areas, as at New Chicago Marsh near Alviso, where the bottom has subsided as much as 15 feet, it would take longer. In the North Bay, where diked lands have typically subsided less than in the South Bay, tidal marsh restoration using natural sedimentation processes could occur much faster.

Estimates of sediment deposition rates are based on historical and existing sediment concentrations. While these concentrations are not expected to change quickly, it is important to recognize, as noted above, that the Bay's long-term sediment budget likely will differ from present conditions. Therefore, it is difficult to predict how much sediment will be available for tidal marsh restoration. However, given the current expectations regarding future sediment availability and deposition rates, it would be prudent to plan to effect the restoration of tidal marsh at the scale envisioned in this report over a period of several decades.

Design and Management Considerations

The baylands ecosystem supports many species of fish and wildlife, some introduced and some native. In developing habitat goals, Project participants have attempted to account for and balance the needs of a large number of these organisms. This is critical if we are to integrate, balance, and phase large-scale restoration projects so that restoration of different wetland types occurs concomitantly on a subregional scale. The objective is to avoid short-term or long-term losses of one habitat type, such as seasonally ponded wetlands, in the process of creating another type of wetland, such as tidal marsh. This will be especially important as efforts move forward to recover endangered species that are associated with tidal habitats.

In formulating habitat goals we make recommendations to protect, maintain, restore, or enhance many kinds of habitats. These habitats fall into two broad categories: those that maintain themselves through natural processes, and those which must be actively managed. Self maintaining habitats are those which, left to natural processes and not subject to outside perturbation, will maintain themselves through time. In the bay or baylands these include deep and shallow bays and channels, tidal flats and eelgrass beds, tidal marsh, and lagoons. Adjacent to the baylands they include moist grasslands, grasslands with vernal pools, and riparian forest.

Managed habitats are those which require active intervention to maintain the desired attributes or functions. Attaining the desired habitat functions may be the direct result of management efforts, as at waterfowl management areas, or the indirect result of management for another purpose such as grazing, farming, or salt production. In the baylands these habitats include managed marsh, managed seasonal pond, and managed saline pond.

All of the habitats in and adjacent to the baylands are dynamic, and they are subject to natural and anthropogenic influences that affect how they are maintained and how they function to support the organisms that depend upon them. The design and management of these habitats must consider these influences.

The following sections describe, for many of the key habitats, attributes of "good" habitat and considerations for design and management. For purposes of presentation, the habitats are classified as self-maintaining or managed.

Self-Maintaining Habitats

Tidal Flat

As noted above, we have little control over the factors that determine the location and design of tidal flat; this habitat occurs at the water's edge wherever there is suitable topography, sediment supply, and currents. We do, however, have some control over how tidal flats are managed. Therefore, it is important to highlight the characteristics of high quality tidal flat and to identify several management considerations.

High quality tidal flat has:

• An absence of vascular vegetation.

• Geographic stability over the long term.

• A plentiful and diverse supply of diatoms.

• Diverse and abundant infauna and epifauna attractive to shorebirds at low tide and macroinvertebrates and fishes at high tide.

• No or few exotic or invasive species.

• A range of particle size from sandy to clay.

• Stable salinities that are not subject to rapid fluctuation.

• Well-oxygenated sediments and low contaminant concentrations.

• Nearly flat to very low slope.

• A wide area with little shoreline disturbance.

Design and management of tidal flat restoration projects should:

• Maximize distance from adjacent upland edge.

• Ensure sediments free from chemical conditions toxic to desired organisms.

• Ensure absence of post-pilings and other human structures and powerlines.

• Locate between subtidal and tidal marsh habitats.

• Minimize human disturbance.

• Regularly assess level of human access.

• Ensure presence of immediately adjacent, protected roosting areas.

Eelgrass

It is difficult to control the factors that determine the distribution of eelgrass beds in the estuary. Reducing turbidity is one of the most important factors that will allow an increase in the areal extent of this valuable habitat.

High quality eelgrass beds are:

• Free of vascular vegetation other than eelgrass.

• Free from chemical conditions toxic to desired organisms.

• Geographically stable over the long term.

• Located in non-erosive environments.

• Usually on very gently sloping substrate.

• Rooted in a substrate of medium to fine sediment.

Design and management of eelgrass restoration projects should:

• Recognize that the local wave energy environment will determine sustainability.

• Minimize anthropogenic turbidity to increase transplanting success.

• Enhance existing eelgrass beds by revegetating areas within bed margins.

• Limit restoration of beds only to those areas where key water quality features (e.g. low turbidity, well-oxygenated sediments) indicate a high likelihood of success.

• Locate transplants in areas with smaller tidal ranges.

• Locate transplants in areas that support deeper vertical distribution, as this may make beds less vulnerable to adverse conditions such as storm events or desiccation.

• Schedule planting when water is warmer.

Tidal Marsh

Tidal marsh is the tidal habitat type that we have the greatest ability to restore. By restoring tidal marsh, we can expect to directly affect the structure and processes which form and maintain deep and shallow bays and channels, and tidal flats. These effects, as noted in the previous section, would result from changes in tidal prism, sediment deposition and scour, and possible changes in salinity gradients. Through the process of developing goals, a description has emerged of what constitutes good tidal marsh.

Tidal marsh restoration designs can vary according to their specific ecological objectives. Different designs will emphasize different amounts of natural restoration and habitat components. The components to consider are the tidal channels large and small, natural and man-made levees, drainage divide ponds and transitional pannes, and the vegetated plain. All of these components will evolve in some form on their own in the suitable setting, but they can also be created or nurtured through restoration design. The relative abundance of these components can also be controlled, at least through the period of marsh maturation. For example, the amount of ponds and the amount of small channels are inversely proportional. The restoration of low marsh will encourage the formation of more small channels in complex drainage networks. The restoration of high marsh will encourage the formation of ponds between less complex drainage systems with fewer small channels. The more complex drainage systems with more small channels will favor fish support and pollution filtration. The less complex systems with more ponds will favor waterfowl and shorebird support. The best designs will follow directly from very specific project goals that are consistent with the regional goals.

Tidal marsh restoration designs can also vary with environmental setting. The setting dictates much about the restoration opportunities. For example, large brackish marshes tend to have less extensive drainage networks and fewer but larger drainage divide ponds than saline marshes. Narrow marshes along major channels or the bay tend to have simple drainage networks parallel to each other and normal to the shoreline, regardless of salinity. Along the upland ecotone, all marshes tend to be poorly drained and subject to freshwater influences from surface runoff and ground water discharge. This is the setting for transitional pannes. Natural restoration will proceed more quickly where there are large supplies of suspended sediment, such as along the tidal reaches of rivers and streams, or along the bayshore. To be brackish, tidal marshes must be near freshwater inputs during spring.

The science of tidal marsh restoration is growing, but much needs to be learned. Here are some important lessons from experiences in the Bay Area:

• Constructed marshland surfaces should be low enough to let natural sedimentation achieve the final design elevations, except where very high habitats such as ponds or high marsh plains are immediately required.

• If a large site must be restored in phases, restoration should proceed from upstream to downstream, with initial channel excavation from the tidal source sufficient for full tidal excursion into the upstream starting place. Otherwise, the upstream location may never receive sufficient tidal flows and suspended sediment for natural marsh restoration.

• The amount of downstream channel excavation will depend upon the tidal volume needed to restore the marsh upstream. An oversized channel is better than an undersized channel, since the channel dimensions will tend to naturally decrease faster than they can increase, as the channel adjusts to changes in the upstream volume of the tides.

• The relationship between tidal prism and channel size appears to vary with tidal salinity and marsh elevation. There is also a relationship between tidal prism, or tidal marsh size, and the ability of whole drainage networks within the tidal marsh to maintain themselves. Of course, if the shoreline erodes, then the marsh becomes narrower and the drainage network is foreshortened. If the shoreline expands outward, then the drainage network also moves outward with the marsh, but may fill in upstream, such that the overall amount of channel remains about the same. The process of self-maintenance is different for the broad, gently sloping marshes away from the shoreline. Here the process is affected more by salinity.

• For brackish-saline conditions, self-maintaining drainage networks have at least 5 miles of small channels. Such systems service about 200-300 acres of mature tidal marsh. If the amount of marsh is decreased, then some of the smaller channels will fill with sediment and vegetation, and the larger channels will tend to shoal and narrow. More tidal marsh is required to maintain small channels under freshwater conditions than under saline conditions.

Things will change through time and recently restored sites will evolve as physical and biological systems. The initial set of habitat components will not remain the same forever. For example, under natural conditions, low marsh matures into high marsh. During this maturation, the drainage network becomes less complex, remaining channels become deeper and narrower, the salinity gradients across the marsh plain become more variable and steeper in general, the amount of marsh plain that is not directly serviced by any channel increases, surface drainage decreases, and the amount of ponds increases. Tidal marsh restoration designs should consider the eventual set of habitat components that is likely to exist when the site matures.

High quality tidal marsh has:

• A well-developed system of tidal channels.

• Connections to natural uplands. The transition zone from tidal marsh to uplands is an area of high biotic diversity and is important in supporting the functions of the marsh. The upland area adjacent to the marsh also serves an important role in buffering the marsh from disturbance. Ideally, buffers of at least 100 yards should be provided between the upper end of the marsh/upland transition and neighboring areas of developed use.

• Tidal ponds in the marsh plain and transitional pannes along the marsh/upland transition.

• Other wetland types and mudflats nearby.

• A corridor of tidal marsh connecting one marsh to another.

• A dominance of appropriate species of native plants and animals.

• A minimum of uplands or structures intruding into or fragmenting the marsh. These features facilitate predator access and adversely affect endemic marsh species.

Design and management of tidal marsh restoration projects should:

• Assess the salinity regime and tidal range in the area where restoration will be implemented; there should be congruence between the physical parameters of the area (salinity, tidal range) and the expected habitat structure.

• Provide unrestricted tidal exchange, except when muted conditions are necessary (see Muted Tidal Marsh discussion). Where full tidal exchange is not possible, maximum tidal amplitude should be encouraged.

• Utilize remnant natural channels (if present) as the template for channel formation. Fill borrow ditches when possible to keep them from capturing tidal circulation.

• Grade levees to marsh elevations (at or slightly above MHHW) when restoring diked baylands.

• Where levees will be required as part of the restoration, design them to mimic naturally occurring transition zones, i.e., the slope should be as flat as possible.

• Give priority to restoring tidal marshes on sites that are contiguous with uplands and alluvial soils, seeps, and streams to facilitate establishment of natural transitions.

• Provide for ongoing control of undesirable species including invasive plants, undesirable predators, and mosquitos.

• Rely upon natural sedimentation and plant colonization processes for restoration to the maximum extent possible. Natural sedimentation is preferable if adequate sediment supply is available for timely restoration of desired habitat. Generally, natural colonization by plants should be relied upon, but there are some rare plant species that need to be reintroduced.

• Restore tidal marsh throughout the salinity gradient of the estuary and its sub-estuaries to promote species and habitat diversity.

• Consider the presence of artificial fresh water flows. Where tidal salt marsh is desired, restoration near large local wastewater discharges should be avoided. New discharges of wastewater in proximity to existing salt marshes or sites planned for such restoration should be discouraged.

• Provide topographic variation to mimic natural conditions within the marsh. Small supratidal islands at or slightly above MHW should be provided by leaving remnant levees or placing fill at appropriate elevations.

• Provide broad corridors (100 yards or more) to connect marshes except when they connect very small marshes.

• Restore diked sites of high existing wildlife value only after alternative habitat is developed or unless the habitat type to be displaced is, and will remain, abundant in the area.

• Undertake restoration only where the habitat value can be increased.

• Create naturalistic, unmanaged facsimiles of historic marsh ponds, transitional pannes, and salt ponds at appropriate locations within restored tidal marsh complexes. Marsh ponds equivalent to the smaller, mid-marsh depressions frequently flooded by spring tides ("drainage divide ponds") should be established artificially within some restored marshes to support near-marine salinity, to conserve viable populations of Ruppia maritima and to support diverse macroalgae beds. Such ponds would probably take many decades or more to form naturally.

• The development of transitional pannes or salt ponds would require constructing very low berms (less than one foot above MHHW) across shallow basin floors near MHW elevation to allow passive overtopping by spring tides. Subsequent evaporation would concentrate salts. Salt ponds could be constructed near the landward edge of restored tidal marsh on the eastern shore of the Bay in Alameda County. These may be derived by construction of internal levees within existing salt ponds that are restored to tidal action, or they may be established in part by engineered placement of suitable dredged material.

Muted Tidal Marsh

Muted tidal marsh is tidal salt marsh or tidal brackish marsh that has restricted tidal influence. Restrictions on tidal amplitude are required at marshes where tidal flow is desired, but must be limited to prevent inundation of the site.

Muting tidal flows can be a useful mechanism to encourage the development of specific tidal habitat features in subsided areas: salt marsh habitat can be developed or enhanced in subsided areas, tidal flat conditions can be maintained on sites that would normally be vegetated, and open water habitats that do not restrict fish movement can be maintained on sites that otherwise might become vegetated. Muting the tidal flow can also be used to desynchronize tidal inundation, providing tidal flats that are available for shorebird foraging and roosting during high tide.

High quality muted tidal marsh has:

• Open water areas that are subject to restricted tidal influence and which provide important habitat for diving ducks, terns, and pelicans.

• Areas maintained as tidal flat with desynchronized tidal flooding to provide important high tide foraging and roosting habitat.

Design and management of muted tidal marsh should:

• Determine desired habitat conditions and identify species to be accommodated.

• Assess site constraints. Muted tidal management should generally be considered for tidal marsh restoration only when full tidal influence cannot be achieved due to flood considerations or when full tidal influence cannot achieve wildlife or habitat objectives.

• Monitor hydrology and sedimentation to assure that the desired conditions for healthy marsh vegetation are maintained. The same considerations apply to areas being managed as tidal flats.

• Consider the possibility of elevating roads, rail lines, or transmission towers, especially when these structures are scheduled to be improved, in order to provide full tidal flows to a site.

• Consider developing muted tidal ponds or lagoons on subsided lands for waterfowl management. Such conditions would provide shallow water fish habitat without concerns for entrapment.

Riparian Forest and Willow Grove

Riparian habitats border each side of every river and stream. They comprise the ecotone between the river or stream and the rest of its watershed. Natural riparian habitats are characterized by steep and variable gradients of moisture and light, lush vegetation, and very high biological diversity. Of all the riparian habitats in the Bay Area, the riparian forests are the most complex and support the greatest total number of plant and animal species.

In the Bay Area, natural riparian ecotones tend to be long and narrow. Historically, this was because the natural rivers and streams were entrenched within their canyons and valleys, such that the active flood plains were below the valley floors. The downstream reaches of some of these rivers and streams have since filled with sediment, such that the valleys sometimes flood, but the lateral extent of the riparian habitat is usually constrained by adjacent land use or flood control levees. The riparian forests on either side of a river or stream are therefore typically less than a few trees wide. In urban settings, the riparian forest is unnaturally broken into a number of short segments, most of which are less than a block long. There are only a few remaining examples of riparian forests that extend from the upper reaches of local watersheds all the way to the Bay. The amount of riparian forest that can grow along the tidal reaches of streams depends upon the tidal salinity, with lower salinity supporting more riparian forest.

Much of the remaining riparian forest is threatened by bank erosion and proposed land development. Modern land uses tend to increase runoff that causes the channels to undercut their banks and riparian trees. Many of the trees along the middle and upstream reaches of our rivers and streams are poised to fall. Typical efforts to stop bank erosion involve the removal of riparian trees.

The species composition of the riparian forests differs among the regions. For the South Bay, the list of common native riparian trees includes sycamore and cottonwood. In the North Bay, the list includes ash and bay-laurel. Box elder is locally abundant. Some species of willows and oaks are common riparian trees throughout the region. Non-native trees, like acacia and eucalyptus, comprise much of the riparian forests in urban and suburban landscapes.

Willow groves are distinct from riparian forests. They are mostly associated with shallow groundwater away from any river or stream. In the Bay Area, willow groves were historically associated with springs and areas of ground water discharge along the margins of the bay.

High quality riparian (and, as applicable, willow grove) habitat should:

• Extend in a continuous corridor along a streamcourse.

• Extend laterally from the stream channel across an unimpeded floodplain.

• Form a natural transitional ecotone with the adjacent uplands.

• Be free of domesticated animals and human disturbance.

• Support a diversity of native understory and canopy plant species, and be free of invasive plants.

The design and management of riparian (and, as applicable, willow grove) restoration projects should:

• Incorporate setback levees into flood control planning to restore or maintain flood plain and riparian habitats.

• Allow natural stream processes to maintain channel form, provide flood flow passage, and maintain riparian vegetation.

• Control or remove non-native invasive species, e.g., giant reed, German ivy, and eucalyptus.

• Provide buffers of at least 100 feet in width from the top of stream bank.

• Minimize trails, grazing, and other disturbance within the riparian corridor.

• Utilize native plant species from the local area in restoration projects.

Managed Habitats

The Goals Project has identified several managed habitats that occur in diked portions of the baylands. These habitats include managed marsh, managed saline ponds, and managed seasonal ponds. The conditions of these habitats, and their ability to support certain plant, fish, and wildlife species, are directly or indirectly a result of past and present management actions.

Many of these managed habitats function as substitutes for natural habitat features which occurred historically in the Baylands (tidal ponds, transitional pannes, lagoons), or in the adjacent uplands (seasonal ponds and vernal pools), but have been lost as a result of reclamation and other alterations. The functions of these habitat types for various species vary widely and are largely determined by management objectives. For example, managed marsh and managed seasonal ponds that are best for waterfowl differ significantly from those that are best for shorebirds.

Designing a managed habitat requires clearly defining the type of habitat desired, assessing the suitability of the site for that habitat type, and considering the degree of management that will be necessary to maintain the habitat. To illustrate this point, we can use diked baylands that are seasonally ponded: Many Project participants have recommended that the goals emphasize seasonal ponds that occur in the diked farmed and grazed baylands, particularly because they provide substantial benefits to shorebirds. The management practices on these lands influence shorebird habitat quality and quantity by affecting vegetation type and height through ground water management, mowing, disking, or grazing. In the absence of this type of management, other types of habitat would develop, such as ruderal baylands, diked brackish marsh, or diked salt marsh, all of which are less suitable for shorebirds but that support other wildlife. Discontinuing the current land use of a site that supports desired species assemblages may not be appropriate if the site is not managed to assure the continuation of those existing functions. The reasons why the desired functions occur on a site must be determined if the management objective is to maintain those functions.

Following are some general considerations for the design of managed wetland habitats:

• Identify the type of managed wetland that is desired, the assemblage of species for which habitat is to be provided, and the species' habitat requirements.

• Determine if water salinities in the area are appropriate.

• Determine if the quantity and quality of available water is adequate.

• Assess whether the hydrology of the site is appropriate to develop and maintain the desired habitat functions without intensive management.

• Determine the need for levees. If required, levees should be wide enough to support maintenance equipment. Also, minimize the length of levees required.

• Minimize active management to the maximum extent feasible.

• Determine if there are analogs or reference sites upon which to base the intended management. Assess the hydrology of the reference site and try to duplicate it.

• Determine the intensity of management that will be required to maintain the desired habitat.

• Consider operations and maintenance issues such as operation and maintenance of water control structures, obligations to protect adjacent properties from flooding, the need for fish screens, and requirements for vegetation and invasive species control.

• Consult with the local mosquito abatement district to determine the requirements for mosquito control.

• Ensure absence of overhead powerlines, berms, or boardwalks that facilitate predation by raptors or small mammals.

Managed Marsh

Managed marsh has several components that may be modified to meet certain management objectives. For example, deeper water is beneficial for diving waterfowl, and shallow water benefits shorebirds. In many cases, it is possible to combine objectives to provide benefits for a wide variety of organisms with only minor modification of management practices.

A high quality managed marsh has:

• A diversity of habitat features to provide nesting, roosting, and foraging opportunities for the target and non-target species. These features should include a mosaic of marsh vegetation, open water of varying depth, fluctuation zones with minimal vegetation (mudflats) and areas of uplands within or adjacent to the marsh. Emergent vegetation provides cover for resting, nesting, and foraging habitat for a variety of marsh species including grebes, marsh wrens, waterfowl, egrets and pond turtles. Open water ponds or lagoons provide loafing and foraging areas primarily for waterfowl, but are also used for foraging by terns, grebes, and egrets. Water depth and duration are important in defining the types of wildlife that will utilize the marsh. A variety of water depths is desirable to maximize the utility of the habitat to the broadest range of species. Providing deeper areas allows for the maintenance of fish populations that diversify the prey base of the marsh and aid in controlling mosquitoes.

• Water level management to optimize wildlife utilization. The ability to vary water surface elevations aids in managing and controlling the types and amount of vegetative cover which, in turn, determines if the habitat will be available to shorebirds and or what types of waterfowl will utilize the marsh. Shallow water areas (< 4 inches) with exposed drawdown zones are extremely important to shorebirds, particularly in the spring.
• Provision for wetland habitat functions that are in short supply during certain seasons, years, and portions of the tidal cycles. These include non-tidal habitat for shorebirds and waterfowl during late summer and fall, and foraging and roosting habitat for shorebirds during high tide.

• A minimum impact on fisheries resulting from water diversions.

• Properly designed and maintained water controls (flood and drain capabilities) to manage the depth, duration, and timing of flooding. To operate most efficiently, it is desirable that these be able to bring water on and off the marsh by gravity flow.

• For brackish or freshwater marshes, the ability to prevent excessive soil salinity and the formation of acid sulfates in the soil. (The formation of acid sulfates is caused by soil oxidation associated with flooding/drying patterns, not by salinity.)

• Sufficient topographic variation to provide for a variety of water depths, wetland plant diversity, and high water refugia.

• Well-maintained levees, preferably with some outboard marsh for buffer.

• An absence of contamination that adversely affects biota.

The design and management of managed marsh should:

• Identify and evaluate the management objectives and determine if the desired habitat and functions can be developed.

• Consider pond bottom elevations when selecting a site. Is the site subsided and can water be drained without pumping? Should the site be contoured to increase topographic variation?

• Determine the availability of adequate water. If fresh or brackish marsh vegetation is the management objective, water of suitable salinity must be available.

• Determine if the desired hydrologic regime can be maintained on the site in a cost-effective manner. Can water be moved onto and off of the site at the appropriate times of year? Can the site be flooded and drained by gravity flow or will pumping be required?

• Maximize a diversity of habitat functions in conjunction with the primary management objectives for a particular species or group of species.

• Determine the type and amount of vegetation desired. When feasible and consistent with management objectives, establishment of native plant species should be emphasized.

• Install fish screens on water diversions where there is a potential to entrain endangered aquatic species.

Managed Seasonal Pond

Seasonal ponds occur in the baylands within several of the key habitat types including diked marsh; managed marsh; and farmed, grazed, and ruderal bayland. They also can occur in abandoned salt ponds and in areas adjacent to the baylands. Seasonal ponds within the baylands, other than those found in managed marshes, characteristically develop on poorly drained sites.

Direct rainfall is the primary water source for most seasonal ponds; in some areas, however, runoff from adjacent lands may also be an important source. Rainfall patterns and topography strongly influence the duration and areal extent of ponding in a given year.

Land management practices strongly influence the habitat quality of seasonal ponds. If management ceases or changes, most ponded areas will evolve to another habitat type such as emergent marsh, permanent open water, or upland. These habitat types generally are not as desirable for key baylands species such as shorebirds and waterfowl.

Farmers seek to minimize the extent and duration of seasonal ponding since it adversely affects crop production. They manage ponding by pumping groundwater, and this results in short periods of inundation in all but the wettest years.

Seasonal ponding in managed marsh can vary widely and is not dependent on precipitation or local runoff. The timing, duration, depth, and extent of ponding are generally determined by the management objective of the marsh. The ability of the marsh manager to meet ponding objectives is strongly influenced by the elevation of the site and the ability to bring water on and drain it off.

Seasonal ponding on grazed land can be better tolerated in comparison to farmed areas. Grazed land is pumped only enough to draw off surface water. Water is often allowed to remain in low or poorly drained spots, ditches, and remnant tidal channels.

Diked marsh, ruderal bayland, and inactive salt ponds are similar to grazed baylands in that they are dependent upon direct precipitation and local runoff as their source of water. These sites are generally poorly drained, unless actively drained to minimize wetland vegetation. Consequently, the timing, duration, and extent of ponding are generally dictated by precipitation patterns in any given year. Generally, these sites do not begin to pond until well into the migratory season.

The transitional pannes of high tidal marshes are subject to ponding as a result of precipitation, local runoff, and tidal flooding during high tide periods. These pannes are limited in extent in the Bay and little is known about their patterns of flooding.

Seasonal ponds can support an array of wildlife and plant species. They are most noted for providing foraging and roosting habitat for migratory shorebirds and waterfowl.

High quality managed seasonal ponds have:

• Shallow ponding with feathered edges and a minimum of emergent vegetation. Sites that usually receive the highest use, particularly by shorebirds, are managed to reduce vegetative cover. As indicated, birds such as waterfowl and shorebirds prefer sites with different habitat characteristics:

Waterfowl

• 12-18 inches water depth

• Some emergent vegetation

• Consistent and extended ponding

• Presence of food plants or seeds in the soil

• Presence of preferred invertebrates

Shorebirds

• Shallow water, generally less than 4 inches

• Extensive unvegetated edge with fluctuating water levels

• Presence of bare areas, and minimal emergent vegetation

• In close proximity to tidal mudflats

• Consistent and extended ponding Presence of preferred invertebrates

• Frequent or continuous inundation during the winter rainy season (November through April). To achieve maximum value for shorebirds, inundation should be long enough to discourage dense ruderal cover, but short enough to preclude establishment of emergent vegetation.

• Presence of ponds every year. Generally, seasonal ponds that show the highest bird use are those which are consistently present from one year to the next, pond earliest, and remain ponded into late spring.

• Limited nearby obstructions and disturbance.

Design and management of managed seasonal pond habitat should:

• Provide areas which consistently pond water when target species are present. For areas of seasonal ponding that are dependent solely on precipitation as a source of water, minimize drainage and encourage soil compaction to maximize ponding extent and duration. Ponding should occur as early in the season as possible. In marshes being managed as seasonal ponds, flooding should be initiated in late summer or early fall for migrating shorebirds and waterfowl.

• Select sites that do not have high ground water during the dry season to control the establishment of dense emergent vegetation.

• Provide water of suitable quality.

• Retain or enhance depressional topography on the site.

• Provide a diversity of habitats by designing small impoundments within larger ones to allow for varied water depths, salinities, and other management practices.

• Construct levees of suitable width and slope to support maintenance vehicles, maximize levee stability, minimize maintenance, and allow for transition of wetland to uplands vegetation. Arrange levees to minimize exposure to wave action.

• Limit drainage to maximize ponding during the rainy season.

• Select sites that have no or few power lines nearby.

• Control water depth unless the site has adequate topographic variation to maintain shallow areas with increasing water depth. Limit vegetative cover, particularly by emergent types, for shorebirds. Provisions for gradual draw down during the spring should be made. Ground water should be below the root zone during late spring and summer to discourage emergent vegetation.

• Control vegetation to maintain large areas of no or sparse low vegetation. Management techniques include grazing, mowing, disking, burning, and manipulating hydrology.

• Inspect structures, water levels, and vegetation frequently to ensure the system is meeting its design criteria.

• Inspect for and control undesirable species, i.e., invasive plants, unwanted predators, and mosquitos.

• Establish upland buffer at least 100 feet wide (preferably 300 feet wide) around pond complexes.

• Ensure the absence of boardwalks or berms that facilitate access for predators.

The majority of diked baylands that support seasonal ponds do not incorporate these design and management criteria. Improving seasonally ponded habitats will require changing land management practices. As long as farming continues in the North Bay, it will be important to find ways for private landowners to manage farmlands with dual objectives of providing seasonally ponded wildlife habitat while still producing crops.

Managed Saline Pond

This section describes the habitat attributes of managed saline ponds. The design and management recommendations presented here apply to salt pond complexes that have been taken out of commercial salt production.

High quality managed saline ponds have:

• A complex of ponds with salinities varying from low to mid-salinity (< 180 ppt), with few high-salinity ponds. Within the pond complex water depths are spatially variable providing a variety of water depths.
• Water depths from very shallow to shallow (< 3 feet). For shorebirds, water elevation should be less than 4 inches, with 2 inches ideal. Water deeper than three feet in lower salinity ponds provides habitat for diving ducks.
• Barren islands within the ponds and/or remote, undisturbed parts of dikes between ponds. These features provide important roosting and nesting sites for shorebirds and terns.

• Proximity to tidal flats to minimize loss of energy in shorebirds moving from tidal flats to peripheral foraging habitat.

• Limited nearby obstructions and disturbances.

Design and management of managed shallow ponds should:

• Provide optimal habitat for shorebirds, waterfowl, other water birds, invertebrates, and plant species that typically occur in salt ponds.

• Provide ponds as a complex with a series of ponds of various salinities (up to 180 parts per thousand) and water depths. Ponds should also have islets with little or no vegetation to provide roosting habitat for a variety of shorebirds and nesting habitat for terns, avocets, stilts, snowy plovers, and other birds.

• Ensure that the pond complex has access to tidal saltwater. The system should include the capability to bring in low salinity water to dilute the concentrated salt water before discharging it back to the Bay. In the absence of salt production it is necessary to be able to discharge brines to optimize habitat values.

• Prevent drainage or flooding of ponds when nests are present.

• Manage 1,000 - 2,000 acres of selected ponds to provide seasonally dry pond bottoms as nesting habitat for snowy plover. Draw down during early spring can optimize value to migrating shorebirds.

• Construct nesting islands from levee remnants or by placing fill. Islands should be barren (dry mud is fine) and just above MHHW.

• Manage ponds so that islands will not eventually cover with salt marsh vegetation. Vegetation removal or drowning islands for 3-6 months during non-nesting season may be required.

• Manage ponds to provide appropriate conditions for nesting. Some species (e.g., Forster's tern) prefer to nest in low-salinity ponds, while others will nest in low and mid-salinity ponds.

• Provide deeper water depths in some ponds during the winter for diving ducks.

• Protect from human disturbance in adjacent areas.

• Minimize maintenance requirements, and move towards natural systems where possible. Designs should be tested to develop ponds which mimic historically occurring salt ponds or pannes.

• Manage levees and other features to discourage use as predator corridors. Minimize the number and extent of levees when designing shallow ponds in order to minimize fragmentation and predator access. Provide for ongoing control of undesirable species including invasive plants and undesirable predators.