Moist Soil Management

INTRODUCTION

Waterfowl Management Objectives

Waterfowl management aims to fulfill the seasonal life history and habitat needs of waterfowl using moist-soil management techniques. Moist-soil management is the practice of mimicking the seasonal cycles of natural wetlands to promote the growth of seed-producing native wetland plants (Williams et al. 2002). Therefore, waterfowl management is tied to wetland management. The importance of wetlands must be recognized in waterfowl management. Waterfowl management should provide the necessary resources upon arrival and through the winter. Management should ensure that waterfowl are healthy and strong before the birds migrate north to lay an excellent hard egg, providing the return of healthy waterfowl populations (TWRA 2023). 

TYPES OF WETLANDS

To mimic or manage natural wetlands, a land manager must understand the various types of wetlands and the unique behavior and complexities of each type. According to Brinson, there are a variety of wetlands (1993). Types of wetlands include marshes, swamps, bogs, and fens. Marshes and swamps are most often associated with waterfowl, although they also use bogs for survival (EPA 2024). A collection of one or more of these types in an area forms a wetland complex. 

Marsh Types

A marsh is a wetland dominated by herbaceous plants such as grasses, rushes, or sedges. As the marsh transitions to drier land, small shrubs often grow along the perimeter. Marshes usually form along the shallow edges of lakes and rivers. Marshes are frequently or continually flooded with water and contain vegetation adapted to saturated soil conditions. Marshes receive most of their water from surface water; some are fed by groundwater. Nutrients are plentiful, and the pH is usually neutral, producing abundant plant and animal life (EPA 2024). 

Marshes play a vital hydrological role. Marshes recharge groundwater supplies and moderate streamflow. The presence of marshes in watersheds helps to reduce flood damage by slowing and storing flood water. As water moves slowly, sediment and other pollutants settle into the substrate, making marshes essential to clean water. Marsh vegetation and microorganisms can also use excess nutrients that would otherwise pollute surface water, such as nitrogen and phosphorus from fertilizer (EPA 2024).

Non-tidal marshes are the most common wetlands in North America. They are primarily freshwater marshes, although some are brackish or alkaline. They occur along streams, in poorly drained depressions, and shallow water along the boundaries of lakes, ponds, and rivers. Water levels in these wetlands vary from a few inches to two or three feet, and some marshes, like prairie potholes, dry out seasonally (EPA 2024).

Freshwater marshes are highly productive ecosystems due to their high levels of nutrients. They contain highly organic, mineral-rich soils of sand, silt, and clay. They often contain a diverse array of plant communities that support a wide variety of wildlife disproportionate to their size. Prairie potholes, playa lakes, vernal pools, and wet meadows are examples of non-tidal marshes (EPA 2024). 

Tidal marshes can be found along coastlines and fringes of bays and sounds (Hindman and Stotts 1989). Some are freshwater marshes, others are brackish, and others are saline. Tidal marshes are split into two distinct zones: the lower or intertidal marsh and the upper or high marsh (EPA 2024). The lower marsh extends from sea level to high water level. The tide floods and exposes the lower marsh twice daily. It is predominantly covered by smooth cordgrass. The upper marsh occurs above high water levels and is irregularly flooded. The upper marsh is sporadically covered by water and grows mainly saltgrass, black needle rush, glassworts, sea lavender, and marsh-hay cordgrass (Gordon et al. 1989). Saline marshes support highly specialized organisms adapted for saline conditions (EPA 2024).

Tidal marshes serve many important functions. They buffer stormy seas, slow shoreline erosion, and absorb excess nutrients before they reach oceans and estuaries. They also provide vital habitat for clams, crabs, and juvenile fish and offer cover for migratory waterfowl (EPA 2024).

Hindman and Stotts further offer the following classification of wetlands that fringe the bays and sounds of North Carolina based on salinity, tidal fluctuations, water depth, and dominant vegetation (1989): Estuarine river marshes are wetlands that extend inland along valley floors. There are two types: freshwater estuarine river marshes and brackish estuarine river marshes. The diversity of emergent plants varies by water depth in the freshwater estuarine river marsh, while Cordgrass dominates in the brackish estuarine river marsh (Hindman and Stotts 1989).

Freshwater estuarine bay marshes occur on broad, shallow estuarine flats flooded by fresh or slightly brackish water. These marshes attract fewer waterfowl than riverine marshes. Olney bulrush dominates most of these wetlands (Hindman and Stotts 1989). 

Salt estuarine bay marshes have high salinity. These wetlands often include large offshore islands as well as the fringes of the bayshore. Black Ducks widely use this wetland type throughout the year (Hindman and Stots 1989).  

Freshwater estuarine bay habitats have declined in importance to coastal waterfowl of North Carolina due to water quality issues and a decline in submerged aquatic vegetation. However, Canada Geese, Mallard, and Black Duck use these wetlands extensively in areas where these wetlands adjoin upland agricultural land (Hindman and Stotts 1989).

Slightly brackish estuarine bays occur between fresh and brackish estuarine bays. This is a highly productive area that supports diverse submerged aquatic vegetation. Various pondweed species and common widgeon weed are prevalent. Canvasback, American Wigeon, Lesser Scaup, Ruddy Duck, and Redhead are the primary species in this habitat (Hindman and Stotts 1989).

Brackish estuarine bay habitats are the most important waterfowl habitats in North Carolina sounds. Submerged aquatic vegetation biomass is most significant in this habitat, with widgeon weed and pondgrasses dominating. These wetlands provide food, cover, and refuge from hunting or ice (Hindman and Stotts 1989).

Salt estuarine bay habitats contain open water and are dominated by eelgrass, widgeon weed, and sea lettuce. Waterfowl use these habitats mostly when forced out of other habitats icing over (Hindman and Stotts 1989). 

Emergent marshes are 6 inches to 3 feet deep and contain vegetation that emerges above the surface while rooted in soil. Emergent plants include sedges, spikerush, bulrush, and cattail. These marshes serve as valuable feeding, nesting, and roosting habitat. When the marsh reaches 50 percent vegetation cover it is called a hemi-marsh. A marsh will transition from emergent to hemi-marsh and be dominated by emergent cover. Succession should be managed with bush hogging and heavy disking when woody plants are 2-3 inches in diameter. This can return the succession to the grass stage (Nelms 2007). 

Swamp Types

A swamp is a wetland dominated by woody plants. Swamps have saturated soils during the growing season and standing water during certain times of the year. Highly organic soils create a thick, often black, nutrient-rich environment for water-tolerant trees. Swamps can be divided into two groups based on the type of vegetation: forested and scrub/shrub (EPA 2024). 

Forested swamps are found throughout the United States and are often flooded by nearby rivers and streams. Their presence is critical to the survival of dependent species like Wood Ducks, which are cavity nesters and need flooded hardwood bottom habitat. This habitat is used by migrating waterfowl yearly and varies based on the abundance of mast available (Hindman and Stotts 1989). Bottomland hardwood swamp is a name commonly given to forested swamps in the south-central United States. 

When water control measures are used on a bottomland hardwood site, it is called a greentree reservoir (Nelms 2007).  Such flooding makes mast, benthic organisms, wild millet, and smartweed available, providing cover for nesting and roosting (Payne 1998). In the Atlantic flyway, Mallards, Wood Ducks, and American Black Ducks are most common in greentree reservoirs (Payne 1998). These should only be flooded during dormancy as early fall flooding can cause damage. Swollen or cracked trunks, dead branches, yellowish leaves, and a failed acorn crop are signs of improper flooding. Flooding and draining times should fluctuate yearly, and the area should be left dry for 1 in 4 years (Nelms 2007). When selecting tree species for planting, consider flood tolerance. 

Shrub swamps are similar to forested swamps except that shrubby vegetation is most prevalent. Buttonbush, willow, dogwood, and swamp rose are common in shrub swamps. Forested and shrub swamps often grow adjacent to one another. These swamps usually contain 6 to 24 inches of water during the growing season. They are transitional between emergent wetlands and forested wetlands. The primary value of shrub/scrub is thermal roosting cover as the low, thick vegetation retains heat (Nelms 2007). 

Identifying the type of wetland or types of wetlands that comprise the complex is the first crucial step to waterfowl management using moist-soil techniques. The type(s) of wetland(s) present will affect available habitats. This habitat availability will determine the species that can utilize the wetland. 

HABITAT PREFERENCES

After identifying the type of wetland present, a land manager must inventory the food, cover, water, and space resources the wetland or wetland complex offers targeted waterfowl and other wildlife. This will allow the land manager to identify which species are likely to use the wetland or wetland complex, how the birds will likely use these resources, when those resources need to be available, and how to tailor management practices to maximize benefits.  

Dabbling Ducks

This group of ducks generally utilizes shallow water. Dabbling ducks are herbivorous. They feed on the surface of the water or pull vegetation from beneath them. Many of the dabbling ducks filter feed using lamellae on their bills. During the breeding season, many dabbling ducks consume large quantities of insects and aquatic invertebrates (Winkler et al. 2020). 

The difference in habitat preferences between species in this group is apparent when comparing the following dabbling ducks. For example, Mallard nest in a wide variety of situations with dense cover, including grasslands, marshes, bogs, riverine floodplains, dikes, roadside ditches, pastures, cropland, shrubland, fencelines, rock piles, forests, and fragments of cover around farmsteads (Drilling et al. 2020). American Black Ducks are mainly freshwater breeders, but winters are primarily spent in salt water (Longcore et al. 2020). Wood Ducks prefer riparian habitats, wooded swamps, and freshwater marshes. Females nest in tree cavities or nest boxes. (Hepp and Bellrose 2020). 

Diving Ducks

This group is much more diverse than dabbing ducks and includes notable genera such as Aythya, Melanitta, Mergus, Lophodytes, Bucephala, and Oxyura (Sibley 2017). Waterfowl managers should consider the targeted species’ dietary needs to ensure the most effective management. These ducks are omnivorous. Their diet varies geographically, seasonally, by age, and by reproductive status, and they eat a broad range of plant and animal foods. Diving ducks eat seeds and other parts of aquatic plants, fish, insects, mollusks, crustaceans, and other invertebrates. They dive underwater to obtain much of their food (Winkler et al. 2020). The following examples demonstrate the diversity of this group. 

Redheads' diets during breeding consist of plants and invertebrates, most commonly chironomid larvae and pupae. Their wintering diets include rhizomes of shoal grass, submerged aquatic plants, and available seeds (Wooden and Michot 2020). 

Mollusks were important for diving ducks on the Keokuk pool of the Mississippi River. The ducks ingest larger benthic organisms until large items become unavailable. These ducks ate 25 percent of the benthic standing crop during the fall. These findings suggest that waterfowl land managers must ensure that food resources are available appropriately (Thompson 1973). 

To further highlight the diversity within this group, Hooded Merganser diet analysis showed they ate 44% fish, 22% crayfish, 13% aquatic insects, 10% other crustaceans, 6% amphibians, 4% vegetation, and <1% mollusks (Duggar et al. 2020).

Generally, diving ducks use deeper, open water (Winkler et al. 2020). According to Bergan and Smith, habitat needs and use will vary between species within this group (1989). Ring-necked Ducks and Buffleheads used shallower habitats, while Lesser Scaup and Ruddy Duck preferred submergent vegetation and open water sites. Within species, females used shallow and vegetated sites more than males. Diving ducks increase their use of shallow and vegetated sites as winter progresses (Bergan and Smith 1989). These findings highlight the waterfowl's complexity and land managers' challenges in providing the needed vegetation. 

Cover needs within this group are equally varied as diets. For example, Greater Scaup needs marine habitats during overwintering, usually extensive, shallow, salt-water bays and brackish river inlets with protection from cold winds. Their nesting cover is the previous year's growth of grass or sedge close to emergent aquatic vegetation, providing critical escape cover (Kessel et al. 2020). 

Contrast this with the cover needs of Surf Scoter. They breed in or near spruce, covering slightly upland from wetland areas. Brood-rearing sites are on small to medium wetlands. (Anderson et al. 2020). 

Again, the Hooded Merganser can highlight the contrasts between diving ducks. As cavity nesters, they use live or dead trees for nesting cover (Duggar et al. 2020). This is in sharp contrast to the Redhead, which creates overwater nests in tall, dense emergent vegetation of deeper semipermanent and permanent marshes (Wooden and Michot 2020). 

Geese

Geese are herbivorous, and most geese graze to feed. Canada Geese depend primarily on grasses, sedges, and other green monocots in spring and summer. Post-fledging, during fall and winter, they rely on foods higher in carbohydrates, such as berries, seeds, and agricultural grains (Mowbray et al. 2020).

For Snow Geese, the main foods during winter and migration are seeds, stems, leaves, rhizomes, stolons, tubers, and roots of grasses, sedges, rushes, and other aquatic plants; grains and young leafy stems of various crops; stems of horsetails; and a variety of berries. During the breeding season, snow geese rely on leafy parts of grasses, sedges, rushes, willows, and other aquatic plants; rhizomes, tubers, and roots of grasses, rushes, sedges, forbs, and tundra shrubs. Brooding goslings may also feed on fruits and flowers, shoots of horsetails, and chironomid larvae (Mowbray et al. 2020).

Snow Geese spend the winter in the southeastern US in coastal areas, estuarine marshes, marine inlets, bays, shallow tidal waters, and coastal freshwater and brackish marshes. Further inland, they inhabit wet grasslands, freshwater marshes, coastal prairies, and cultivated fields (Mowbray et al. 2020). 

NON-GAME/NON-AVIAN BENEFITS

Other Wildlife Benefits

Moist-soil management practices contribute to wetland ecosystems' overall ecological health, balance, and diversity. Therefore, moist-soil and waterfowl management will benefit many other species. Wood frogs and spotted salamanders thrive in the temporary wetlands formed through moist-soil management, using them for breeding and providing essential habitat for tadpole development. Snakes, such as water snakes and garter snakes, may find favorable conditions for foraging and refuge in the diverse microhabitats within moist-soil areas, contributing to the reptile diversity (Williams et al. 2002).

A diverse array of insects inhabit moist-soil areas (Nelms 2007). Early season shallow water flooding creates an invertebrate bloom (TWRA 2023).

Voles, mice, and other small mammals are attracted to the rich vegetation of moist-soil areas. These mammals serve as prey for owls, hawks, and snakes, contributing to the overall trophic dynamics in the ecosystem. The periphery of moist-soil areas may provide foraging opportunities for larger herbivores like white-tailed deer (TWRA 2023).

Short-eared Owls, Barn Owls, and various hawk species find ample prey in the form of small mammals inhabiting moist-soil areas. Larger wetland areas connected to moist-soil sites attract eagles and falcons, expanding the range of hunting grounds for these birds of prey. Bald and Golden Eagles, for instance, may target waterfowl or fish in these ecosystems (Williams et al. 2002).

MANAGEMENT PRACTICES:

Management Practices Overview

The management practices needed will be determined by wetland type, water source, year's season, game management strategies, and flora and fauna species present. Land managers would be wise to let the type of soil and hydrology of the property dictate what is planted and how it is managed, but a general framework is presented below (TWRA 2023).

As waterfowl arrive, they must find the resources to recharge immediately after migrating. Summer and early fall management practices should emphasize producing the food that waterfowl arriving in autumn will need to recover and prepare for winter. After hunting season, using refuges and WMAs is very important to waterfowl as their needs are high. During this time, they pair and molt. Management practices during this season should prioritize the cover needed to molt, and the food resources waterfowl will need to prepare to migrate north. After the waterfowl have left, land managers prioritize growing the necessary fall crop through the late spring and summer (TWRA 2023). 

Several basic steps to manage moist-soil wetlands for waterfowl and other wildlife are as follows. First, decide when to start drawing water off wetlands. Generally, later drawdowns are preferred. Long, slow drawdowns are usually better than short, fast ones (Seek 2024).

Next, monitor the plant response. Seed-bearing annual plants such as smartweed, millet, and panic grasses can quickly replace less desirable perennials like bulrush, cattails, or woody shrubs. If needed, set back plant succession. Most moist soil managers prefer to maintain 50 to 70 percent of wetlands in the early annual plant stage of succession by disking, burning, mowing, spraying, or limited cropping (Seek 2024). Burning is the most desirable option as it affects plant succession and promotes the growth of good seed producers. It creates open water by breaking up vegetation stands, releasing seeds, enhancing germination, and eliminating green vegetation that would otherwise decompose after flooding (Gordon et al. 1989). Marsh burning can increase food plant production, prevent the invasion of woody plants, and reduce perennial plants. Marsh fires are classified as cover, root, or peat. Cover burns reduce vegetation density, leaving roots unharmed. Root burns during periods of low soil moisture set back succession. Peat burns help create open-water ponds (Gordon et al. 1989). 

Finally, flood the moist soil habitat in the fall. Gradual flooding will boost seed production in water-loving plants such as smartweeds and millet and create shallow mudflats. Making food available through gradual flooding creates a diversity of resources. Increase the water level throughout the fall migration. Water depths ranging from less than one inch to 18 inches will support the greatest diversity of waterfowl and other wildlife (Seek 2024). 

In summary, draw water off slowly in the spring, create disturbance in the summer to set back plant succession, and slowly put it back on again in the fall.

Acquiring and managing properties as complexes connecting areas along a flyway have benefited migratory waterfowl. Connecting areas of flyway complexes offer refuge points as waterfowl migrate. Providing diverse habitats allows for managing multiple species within a refuge area or WMA. The most beneficial benefit occurs if each of the wetlands in the complex is in several different stages of succession, as this increases the diversity of resources (Nelms 2007).

A diversified diet of natural foods and invertebrates provides waterfowl with the needed proteins, carbohydrates, fats, and minerals (Gordon et al. 1989). Invertebrate populations are essential to many species yearly (Nelms 2007). Rice cutgrass and marsh smartweed provide a habitat for invertebrates, which increases waterfowl's food availability. 

Waterfowl needs are best met through variety. Offering scrub/shrub, moist soils, greentree reservoirs, native hardwood river bottoms, and supplemental agricultural grains such as corn, rice, or millet creates diversity that meets the needs of various waterfowl. Corn is best for cold temperatures and roosting cover. It must be levee-protected or planted just above the floodplain to avoid losing crops. A disadvantage of corn is the tendency for ducks to be more active nocturnally. Corn does not provide a complete diet for waterfowl (TWRA 2023). Also, large mono-crop properties are vulnerable to agricultural pests and do not offer diversity, as aquatic invertebrates are rare in agricultural areas (Nelms 2007). Often, naturally occurring seeds have higher overall nutrition than many cereal grains (Nelms 2007). 

Desirable seed production declines each year, and an area is managed for moist soil, which is undisturbed. Disking or prescribed burns are necessary every 2 to 3 years. This also controls the encroachment of woody plants (Nelms 2007).  

Water sources

A variety of sources can feed wetlands. The three general water sources are surface water only, mainly groundwater, and about an equal mix of both. Surface water comes from precipitation, tides, streams, lakes, or reservoirs. Groundwater mainly benefits furbearers, not waterfowl, as it tends to be cold and nutrient-deficient with reduced plant growth (Payne 1998). 

Wetlands generally form where water lies at or near the land surface, either above or below, and where surface and groundwater accumulate within depressions. Seepage wetlands occur where groundwater discharges on slopes or near the shores of streams, lakes, and oceans. Fringe wetlands form along shorelines due to periodic flooding by adjacent bodies of water. Perched wetlands form above low-permeability substrates where infiltration is restricted, such as above rock, clay, or permafrost. (US EPA 2008). Brinson’s wetland classification methodologies consider wetland water sources (1993). 

Wetlands are usually found in low-energy environments, where water is flowing with slow velocity. Three variables categorize wetland water behavior:  water level, hydropattern, and residence time. Water level relative to the soil surface can be used as an indicator of likely vegetation. The timing, duration, and distribution of water levels are the hydropattern. The hydropattern of some wetlands, such as tidal marshes, fluctuates over short periods, while other wetlands, such as seasonally flooded bottomland hardwood, fluctuate slowly over time. Some wetland systems are more static and may not vary. Residence refers to the water’s travel time through the wetland (US EPA 2008). 

Water Control Structures

Dams, dikes, levees, ditches, channels, pumps, siphons, and various piping configurations control water. Dikes, separate impoundments, and levees are used to prevent flooding. Both are low forms of dams. All contain some type of control structure. Dams may contain a whistle tube or drop inlet control structure (Payne 1998). Levees or dikes may use a pipe with a control valve to connect the two sides. The whistle tube control structure is the most common for inland marshes. It uses stoplogs in the riser for water level management. When inserted into the riser, the stoplogs form a wall, forcing the water to rise. The impoundment can drain if all the stop logs are removed (Payne 1998). Flapgate structures are used in tidal areas to prevent the flood tide from flowing out and draining impoundment. A trunk is a water control structure in the South Atlantic coastal zone. It was designed for water manipulations in tidal wetlands. Trunks should be installed and well-sealed into dikes. The bottom of the structure at/or 10 to 15 cm below the low water mark will allow for complete drainage (Gordon et al. 1989). 

Ditches can move water between and around impoundments. Main ditches bring in water, while spreader ditches disperse it (Payne 1998). 

Pumping is necessary to drain low impoundments, supplement gravity, tidal drainage, and flooding, and sometimes, groundwater can be pumped to provide needed water. Pumps include turbine pumps, propeller pumps for low-head, high-volume operations, centrifugal pumps for high-head and high pressure, and mixed flow pumps for moderately high head (Payne 1998). 

Siphons with appropriate elevation differences and suitably sized tubes can drain or flood impoundments. Freshwater can be added to a tidal wetland by connecting a siphon to the river and the wetland (Payne 1998). Not all wetlands need water control, and in certain situations, it isn’t feasible (Payne 1998). 

Flood/Drain Information

The timing of the annual drawdown is the most important factor when managing moist soil areas. Early season drawdown prioritizes seed production, while later drawdowns favor desirable grasses, diversity, and higher stem density (Payne 1998). Early drawdowns provide longer growing seasons, which increases survival and density. Late summer drawdowns produce moist-soil plants for geese. Early fall drawdown exposes minnows and invertebrates to migrant ducks. Winter drawdowns after freeze-up can improve germination and recovery of submerged aquatic vegetation and solidify and aerate the bottom (Payne 1998).

The length of the drawdown also affects vegetation. Slow drawdowns will favor diversity and can be achieved by removing one board from the water control structure every 4 to 10 days. Fast drawdowns usually produce stands of similar vegetation and are created by pulling all the boards simultaneously. Complexes with multiple areas being managed will benefit from different dates and drawdown rates as this increases habitat diversity (Nelms 2007). Managing groups in different states of drawdown or rotations is influential as it provides diversity to the wetland complex (Payne 1998). 

A complete drain is not necessary. Partial draining, ¼ to ½ of boards, will provide moist-soil benefits and retain late spring and summer habitat for wildlife. The remaining water may evaporate and provide conditions for germination. Complete drawdown is used when complete rejuvenation is needed. Partial drawdowns are preferred as some water will be left for broods, invertebrates will not be lost, volunteer millet and smartweed will establish better in higher water tables, muskrats will survive better, and the plant-to-open water ratio is improved (Payne 1998). 

Flooding is also essential. A few boards need to be replaced to achieve 25 percent flooding in the early season. Later in the season, a board should be replaced every 7 to 10 days to allow new food and habitat to become available slowly (Nelms 2007).

Land managers should allow plants to grow 4 to 6 inches before flooding. Barnyardgrass, smartweeds, and sedges respond well to shallow flooding of 1 to 2 inches. Complete submergence can be allowed for 2 to 3 days, but if submerged plants do not reach the surface in 2 to 3 days, water levels need to be lowered. Ideally, Water levels should equal ⅓ of the height of newly established moist-soil plants. (Nelms 2007).

Flood timing can be used to manage undesirable herbaceous and woody growth. Certain possibly undesired species, such as cockleburs, die when root systems and bases are submerged. Water levels can be adjusted to hinder undesired growth while maximizing desired plant species (Nelms 2007). 

Typical Management Scenarios by Wetland Type

The following management scenarios are meant to target specific plant species based on the type of wetland. These target plant species are listed by wetland type in Table 1 (Williams et al. 2002). Table 2 breaks down typical improvement and management scenarios for each type of wetland (Williams et al. 2002).

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