Analysis of Missouri Floodplain Soils Along the Mississippi River and an Assessment of Ecosystem Services

Abstract

Floodplain ecosystems have been substantially altered because of land management decisions. Land management decisions have been made primarily for economic development, increased food demand, and reducing flood risks. Recently, increased attention has been devoted to restoring selected floodplain ecosystem services that have important benefits for habitat and wildlife, water purification, forest restoration, and carbon sequestration. Considering the Mississippi River floodplain as a portion of the state of Missouri, we summarize the key soil and soil features and elaborate on ecosystem site descriptions to support assessment of land management’s influence on ecosystem services. Given the significant government investment in detailed soil mapping and development of the ecosystem site descriptions, the fusion of these two advancements is critical for evaluating ecosystem service restoration.

1. Introduction

The Mississippi River is the world’s fourth largest river system, with the lower portion of the river supporting 10 million ha of floodplain forest wetlands. The establishment of 3500 km of levees has improved river navigation, barge transport, agriculture, and economic development. Although the economic savings from flood risk is substantial, a large portion of the floodplain (75–90%) is no longer influenced by flooding and its ecosystem services similarly altered [1].

Lewin reviewed floodplain evolution and geomorphology [2]. With an emphasis on the Mississippi River, Lewin noted the following typical characteristics: (i) the shallow floodplain gradient is approximately 0.1 m km⁻¹, (ii) the floodplain width varies between 40,000 and 200,000 m, (iii) the channel width is centered around 1000 m, and (iv) the channel width to floodplain width ratio varies from 0.025 to 0.005. Landform features include the presence of sandbars and an abundance of abandoned channels, levees, and scroll bars (scroll bars are a series of ridges formed from continuous lateral meander migration). Lewin further stressed that the average flow regime may be misleading when describing floodplain dynamics. Magilligan et al. [3] studied the historic flood of 1993 in the upper Mississippi River, documenting only minor overbank deposition and suggesting that substantial flow regimes may not result in significant soil disturbance. Because the soil maintained their textural and structural stability during the 1993 flood, the lack of significant soil disturbances reduced stream sediment transport.

Hupp et al. [4] documented changes in ecosystem services in North Carolina, western Tennessee, and Louisiana because of land management. Alterations to river dynamics because of dams, stream channelization, and levee and canal construction increase sediment transport and stream velocities. Mungai et al. [5] studied soil landforms in the Lake Victoria basin of east Africa. Soil analysis tended to show that ß-glucosidase activities, clay abundances, and phosphorus levels were more available or abundant in soils experiencing flood, whereas organic carbon and exchangeable potassium levels were more abundant or available in flood-protected soils.

Price and Berkowitz [1] investigated the Mississippi River flood of 2019, wherein there was more than 150 days of floodwater inundation. The study was concentrated along the states of Missouri, Arkansas, and Tennessee. The floodwater increased the abundance of woody debris and forest floor litter; however, many other hydrogeomorphic features were not significantly altered. The change in the abundances of woody debris and forest floor litter decreased the wetland’s ability to detain floodwater, retain precipitation, recycle nutrients, and export organic carbon.

Guo et al. [6] investigated soil organic and inorganic carbon contents in the upper Yellow River Delta in China. The typical soil organic carbon contents centered at 9.3 g kg⁻¹ for the surface horizons and 2.4 g kg⁻¹ at the 80–100 cm soil depth. Soil inorganic carbon varied from 10.5 to 12.7 g kg⁻¹. The authors concluded that soil organic carbon increases influenced soil inorganic carbon accumulation. Along the Yellow River in China, Hou et al. [7] investigated reclamation efforts to improve soil organic carbon and soil inorganic carbon. Over the considerable timetable of this study, the authors documented that soil organic carbon increased by 2.7 Mg carbon ha⁻¹ yr.⁻¹. The increase of soil organic carbon was greater for the 0–20 cm soil layer than the 80–100 cm layer. The inorganic carbon content increase was more modest and showed that the soil profile accumulation distribution differed across regions.

Using the lower Missouri River floodplain, Moore et al. [8] developed a factorial experimental design involving soil columns collected from sites having: (i) long-term agroforestry, (ii) row crop, and (iii) riparian forests. Nitrogen treatments were incorporated into the experimental design. The objective of the study was to discern if the greenhouse gas emissions of CH₄, N₂O, and CO₂ were influenced by vegetation and nitrogen fertilization practices. The long-term agroforestry plots exhibited the smallest CO₂ and N₂O emissions. In a central European forest, Valtera et al. [9] investigated anthropogenic changes to water regimes, documenting that human-altered water regimes frequently threaten the stability and existence of floodplain forests. Soil organic carbon and microbial biomass deceased on transition from pristine natural floodplain forests to plantation forests.

For Central European floodplains, Hornung et al. [10] developed a matrix that considered linkages of management options with the preservation of identified ecosystem services. Of interest to this manuscript, specific management options included: (i) reduction of pollution because of agricultural practices, (ii) establishing buffer zones, (iii) limiting soil acidity attainment, (iv) restoration of the natural river flow regime, (v) floodplain vegetation and habitat restoration, (vi) restoration of longitudinal connectivity, (vii) prevention of adverse land drainage impacts, and (viii) limiting introduction and spread of invasive species. In Germany, Fischer et al. [11] developed a habitat provisional index to facilitate decision makers’ ability to sustain or improve floodplain biodiversity.

In humid climates, flooding regimes support elevated N₂O and CH₄ emissions. Limpert et al. [12] added water to a degraded semi-arid floodplain and observed reduced CH₄ and CO₂ emissions by 28 to 84%. The reduced carbon emissions were attributed to reduced mineralization of soil organic matter, greater CO₂ sequestration, and increased plant growth.

In the United Kingdom, Lawson et al. [13] extended the natural capital concept to define it as an accounting protocol for estimating the quantity of a resource (stocks) and the services provided (flows). Resources are partitioned as: (i) renewable if the benefits are exploited sustainably, and (ii) non-renewable or non-sustainable if the resource regeneration time interval is excessive. Lawson et al. [13] envisioned researchers assessing the resource serially as: (i) its extent, (ii) its condition, (iii) the physical and monetary ecosystem service flow, and (iv) providing the resource with a monetary value. Rajib et al. [14] proposed that long-term floodplain land use data may quantify floodplain services and provide sustainable land management options. Additionally, land area changes in the Mississippi floodplain show an expanding agriculture domain.

In Germany, Stammel et al. [15], in a compelling manuscript, provided an integrated river and floodplain management protocol, wherein ecosystem services and their respective indicators were modeled to reveal advantageous management options. In addition to the ecosystem services stipulated by Lawson [13], Stammel et al. [15] provided or prioritized nitrogen retention, phosphorus retention, drought risk mitigation, and mass flow and sediment mitigation. Employing ecosystem mapping of the floodplain’s area of interest, synergistic or antagonistic relationships among the ecosystem services are more evident.

2. Ecosystem services of floodplains

In the United States, the ecological site concept embodies principles and site data derived from physiographic features, climate assessments, hydrologic features, soil properties and their distribution, and existing and ancestral vegetation to create a framework for predicting ecological dynamics resulting from land management. Ecological sites provide a consistent framework for classifying and describing rangeland and forestland soils and vegetation, thereby delineating land units that share similar capabilities to respond to management activities or disturbance. Aide et al. [16] presented the status of ecosystem site descriptions development in Missouri, showing how landowners may anticipate land management impacts.

Talbot et al. [17] reviewed the impact of flooding on aquatic ecosystem services. They identified ten ecosystem services and associated processes: (i) net primary production influenced by nutrients or physical conditions; (ii) soil formation involving sediment transport and deposition; (iii) water regulation supporting anthropogenic use; (iv) water quality with an emphasis on nitrogen and phosphorus; (v) regulation of human disease; (vi) climate regulation involving CO₂ and methane emissions; (vii) drinking water and pollution; (viii) food supply as influenced by crops, fish, and livestock; (ix) esthetic values including housing values because of flood risk; and (x) recreation and tourism. Importantly, Talbot et al. [17] evaluated these ecosystem service gains and losses in response to frequently occurring and extreme flooding.

The United Nations Department of Economic and Social Affairs developed 17 Sustainable Development Goals [18]. These goals include ending poverty, zero hunger, good health and well-being, good education, climate education, and others. The sustainable development goals are partitioned into three domains: (i) environmental, (ii) social, and (iii) economic. Visser et al. [18] remarked that the three development goals are sufficiently linked such that the attainment of any one domain is dependent on attainment of the other two domains. They further discussed the role of the soil-water system on the achievement of the 17 sustainable achievement goals. Keesstra et al. [19] supported “nature-based solutions” as a cost-effective and long-term solution in coastal or fluvial land management in order to enhance ecosystem services. Soil-based solutions attempt to support soil health and restore or maintain soil processes that provide environmental stewardship for water quality and availability, soil fertility, and multi-use landscapes.

Lawson et al. [13] and Petsch et al. [20] provided listings of ecosystem services associated with floodplains (Table 1). Similarly, Jose [21] provided a listing of ecosystems associated with agroforestry, some of which may also be important for floodplain environments. In addition to the ecosystem service listing provided by Larson [13], Jose [21] provided two additional ecosystem services: (i) a mosaic of net primary production sites across the floodplain forest and (ii) clean air. Birkhofer et al. [22] presented a substantial literature base with narratives discussing the current challenges and opportunities for evaluating ecosystem services. Noting that assessment of ecosystem services requires a spanning set of indicators to indicate the extent and intensity of the ecosystem services and their provisioning services, Birkhofer and his colleagues [22] provided four sequential challenges when evaluating ecosystem services: (i) understanding anthropogenically modified systems, (ii) assessing ecosystem services, (iii) analyzing relationships between ecosystem services, and (iv) considering appropriate spatial and temporal scales. Evaluating these four challenges provides a multifaceted understanding of human-ecosystem interaction to support resource sustainability.

Ecosystem Service	Examples of Environmental or Social Attributes
Food	Crop and livestock production
Fiber	Timber, reed production
Mitigation climate change	Carbon sequestration and storage
Pollination	Habitats for pollinating insects
Biocontrol	Nesting habitats for birds, bats, and others
Water quality	Sediment trapping
Flood risk alleviation	Flood water storage
Conservation genetic resources	High diversity and species rich habitats
Pollution abatement	Nutrient management
Maintenance of soil fertility	Soil development
Cultural history	Historical context, heritage, and sense of place
Esthetics	Enhancement of landscape appeal
Recreation and health	Access to nature

Table 1.

Ecosystem services of Mississippi river floodplains.

Source: Lawson et al. [13] and Petsch et al. [20].

Jose [21] conducted a review and synthesis of recent investigations involving agroforestry and their provision of ecosystem services and environmental benefits. Jose classified ecosystem services in agroforestry into four categories: (i) carbon sequestration, (ii) soil enrichment, (iii) biodiversity conservation, and (iv) air-water quality. Many of the items in these categories are apropos to floodplain ecosystems. The quantity of carbon sequestered is a complex function of vegetation composition, stand age, location, environmental and climatic factors, and land management. Jose reported that 630 million ha of unproductive croplands and grasslands when converted to agroforestry would likely result in soil carbon increases of 586,000 Mg C yr.⁻¹. Soil enrichment could be attributed to forest species having biological nitrogen fixation capacity, incorporation of canopy and soil organic carbon, nutrient recycling, soil water infiltration and storage improvement, increased aggregate stability of soil structures, and more robust microbial activities. Biodiversity conservation was manifested as (i) habitat provisions, (ii) preservation of germplasm, (iii) habitat connectivity, and (iv) erosion control and water recharge. Air and water quality improvements include: (i) tree barriers and shelterbelts to reduce odor movement, (ii) reduced nitrate and phosphate transport, and (iii) enhanced nutrient and other element biocycling.

The objectives of this manuscript are: (i) to provide general soil descriptions of typical Mississippi River floodplain soils in Missouri; (ii) to provide an introduction to floodplain ecological site descriptions to focus on key ecosystem services, including carbon sequestration and forest productivity; and (iii) to estimate future research needs to better evaluate floodplain soils and their influence on ecosystem services. We also desire to support the development of ecological site descriptions and the important role they play in allowing landowners to understand the consequences of land management decisions.

3. Climate, physiography, and geology of the Mississippi River in East Central Missouri

The ecological site concept correlates principles and site data derived from physiographic features, climate assessments, hydrologic features, soil properties and distribution, and existing and ancestral vegetation to create a framework for predicting ecological dynamics resulting from land management [16]. Ecological sites provide a consistent framework for classifying and describing rangeland and forestland soils and vegetation, thereby delineating land units that share similar capabilities to respond to management activities or natural disturbances. The study area is within the Major Land Resource Area 115X-Central Mississippi Valley Wooded Slopes. The selected ecological site descriptions include: (i) F115XB015MO (sandy/loamy floodplain forest) [23], (ii) F115XB041MO (clayey floodplain forest) [24], and (iii) F115XB042MO (ponded floodplain prairie) [25]. These sites are in the riverine wetlands class of the hydrogeomorphic classification system [26].

The sandy and loamy floodplain forest ecological sites possess soils that are very deep and exhibit sandy to loamy soil textures and have evolved under eastern cottonwood (Populus deltoides) and black willow (Salix nigra) forest [23]. These soils are located where comparatively swift flood currents preferentially deposit sandy to silty sediments. Over time, these soils accumulated a more diverse vegetation and subsequently deposited fine-textured alluvium. Forest vegetation altered in response to landscape elevation with a greater presence of shade-tolerant forest species, such as American elm (Ulmus americana), ash (Fraxinus pennsylvanica), and hackberry (Celtis occidentalis). Catastrophic flooding may reestablish a willow and eastern cottonwood-dominated forest. Typical soils include Blake, Haynie, Caruthersville, and Commerce.

The clayey floodplain ecological sites are not usually adjacent to perennial rivers and streams; rather these sites reside in lower landscape positions. Given the clayey floodplain soils are positioned in low-lying and depressional areas, they are thoroughly influenced by a seasonal high-water table and often show typical backswamp features such as a fine texture, slickensides, and gleization. The clayey floodplain forest is generally supported by a silver maple (Acer saccharinum), American elm (U. americana), and eastern cottonwood (P. deltoides) forest [24]. The ponded floodplain prairie is in the floodplains of perennial streams and backswamp environments that are not adjacent to the Mississippi River channel. Typical soils include Alligator, Bowdre, Darwin, Nameoki, Parkville, Sharkey, and Waldron. The ponded floodplain prairie possesses a high-water table and soils exhibiting fine textures and enriched soil organic matter contents that have evolved under herbaceous wetland vegetation, including graminoids, sedges, and wetland forbs [25].

Forest species associated with the Mississippi River floodplain include northern red oak (Quercus rubra), eastern cottonwood (P. deltoides), American elm (U. americana), white oak (Quercus alba), black walnut (Juglans nigra), silver maple (A. saccharinum), yellow poplar (Liriodendron tulipifera), pin oak (Quercus palustris), American sycamore (Platanus occidentalis), green ash (F. pennsylvanica), sweetgum (Liquidambar styraciflua), black willow (S. nigra), red maple (Acer rubrum), nuttall oak (Quercus texana), water oak (Quercus nigra), pecan (Carya illinoinensis), common hackberry (C. occidentalis), river birch (Betula nigra), boxelder (Acer negundo), and bald cypress (Taxodium distichum).

Most Mississippi River floodplain soils are from Holocene age and include the soil orders Entisol, Inceptisol, Mollisol, and Vertisol [27]. The reference plant community is forested with black willow, eastern cottonwood, hackberry, river birch, sycamore, silver maple, and American elm. In the absence of levees, occasional to frequent flooding is generally very brief (less than 48 hours) to brief (2 to 7 days). During flood events, water is accumulated by overland flow and baseflow from the channel to shallow unconfined aquifers.

4. The study area section of the Mississippi River in Missouri

The study area resides in Mississippi River floodplains in the Missouri counties of Ste. Genevieve County, Perry County, Cape Girardeau County, Mississippi County, and New Madrid County. In Cape Girardeau County, the January average temperature is 1.6°C (35°F), whereas the July average temperature is 26°C (79°F) [28]. The total annual precipitation ranges from less than 0.97 meters (38 inches) to more than 1.42 meters (56 inches), with an average of 1.19 meters (47 inches). Rainfall varies seasonally, with spring having typically greater rainfall totals and autumn having typically smaller rainfall totals. Where levees are not present, flooding ranges from short (a few days) to medium (several weeks) durations, with spring flooding corresponding to more northern snow melt conditions; however, flooding may occur at any time during the year, and long-term flood events have occurred. The surrounding geologic setting generally has Ordovician dolomites and sandstones overlain with thick loess deposits. Bottomland expanses have massive alluvium, with textures ranging from sand to fine clay [28, 29, 30].

5. Laboratory protocols

Soil pH in water, exchangeable cations, total neutralizable acidity, and organic matter content by loss on ignition are routine procedures [31]. The clay, silt, and sand fractions were separated by Na-saturation of the exchange complex, washing with water–methanol mixtures, dispersion in Na₂CO₃ (pH 9.2), followed by centrifuge fractionation and wet sieving [31]. Two M acetic acid extractable SO₄-S were determined by the soil testing laboratory at the University of Missouri-Columbia Delta Center (Portageville, MO).

An aqua-regia digestion was performed to estimate elemental concentrations associated with whole soil soluble, exchangeable, organically complexed, and adsorbed/co-precipitated with oxyhydroxide environments and the partial degradation of phyllosilicates. In this procedure, 0.25 g of finely ground fine earth fraction was digested in 0.01 liter of aqua regia (1 HCl:3HNO₃) for 1 hour, followed by 0.45 μm filtering with an aliquot analyzed using inductively coupled plasma – atomic emission spectrometry (ICP-AES) [32].

6. Soil descriptions across the study area

We selected 22 soil series that occur in the Mississippi River floodplain or in levee-protected land areas. The parent materials are (i) Mississippi River alluvium with soil textures ranging from coarse to fine and (ii) stream alluvium transporting silty materials from the surrounding loess mantled uplands. The Alligator, Commerce, Caruthersville, Sharkey, and Steele are examples of soils whose parent materials mostly are derived from the Mississippi River, whereas the soils Falaya, Haymond, Mhoon, Wakeland, and Wilbur have parent materials derived from loess that were stream transported onto the floodplains. In the study area, the soils and their taxonomic classification are listed in Table 2, and the appropriate soil horizons and diagnostic horizons for each soil are listed in Table 3.

Soil Name	Taxonomy Description
Alligator	Very-fine, smectitic, thermic Chromic Dystraquerts
Beaucoup	Fine-silty, mixed, superactive, mesic Fluvaquentic Endoaquolls
Bowdre	Clayey over loamy, smectitic, thermic Fluvaquentic Hapludolls
Commerce	Fine-silty, mixed, superactive, nonacid, thermic Fluvaquentic Endoaquepts
Caruthersville	Coarse-silty, mixed, superactive, calcareous, thermic Typic Udifluvents
Darwin	Fine, smectitic, mesic Fluvaquentic Vertic Endoaquolls
Dupo	Coarse-silty over clayey, mixed over smectitic, superactive, nonacid, mesic Aquic Udifluvents
Elsah	Loamy-skeletal, mixed, superactive, nonacid, mesic Typic Udifluvents
Falaya	Coarse-silty, mixed, active, acid, thermic Aeric Fluvaquents
Haynie	Coarse-silty, mixed, superactive, calcareous, mesic Mollic Udifluvents
Jackport	Fine, smectitic, thermic Chromic Epiaquerts
Haymond	Coarse-silty, mixed, superactive, mesic Dystric Fluventic Eutrudepts
Leta	Clayey over loamy, smectitic, mesic Fluvaquentic Hapludolls
Mhoon	Fine-silty, mixed, superactive, nonacid, thermic Fluvaquentic Endoaquepts
Nameoki	Fine, smectitic, mesic Aquertic Hapludolls
Parkville	Clayey over loamy, smectitic, mesic Fluvaquentic Hapludolls
Sharkey	Very-fine, smectitic, thermic Chromic Epiaquerts
Steele	Sandy over clayey, mixed, superactive, nonacid, thermic Aquic Udifluvents
Wakeland	Coarse-silty, mixed, superactive, nonacid, mesic Aeric Fluvaquents
Walbash	Fine, smectitic, mesic Cumulic Vertic Endoaquolls
Waldron	Fine, smectitic, calcareous, mesic Aeric Fluvaquents
Wilbur	Coarse-silty, mixed, superactive, mesic Fluvaquentic Eutrudepts

Table 2.

Taxonomic classification of selected Mississippi river floodplain soils.

Soil Name	Horizon Sequence	Diagnostic Horizons
Alligator	A-Bg-Bssg-Bssycg-Cg	Ochric, cambic
Beaucoup	A-Bg-Cg	Mollic
Bowdre	A-Bw-2C	Mollic
Commerce	A-Bw-Bg-Bssg	Ochric, cambic
Caruthersville	A-C-Cg	Ochric
Darwin	A-Bg-Cg	Mollic, cambic
Dupo	A-Bg-2Ab-2Bgb-Cg	Ochric
Elsah	A-C	Ochric
Falaya	A-Bw-Cg	Ochric, cambic
Haynie	A-C	Ochric
Jackport	A-Bg-Bssg	Ochric, cambic with slickensides
Haymond	A-Bw-C	Ochric, cambic
Leta	A-Bg-2Cg	Mollic, cambic
Mhoon	A-Bg-Cg	Ochric, cambic
Nameoki	A-Bw-2Btg-Cg	Mollic, cambic
Parkville	A-2Cg	Mollic
Sharkey	A-Bssg-Bssyg	Ochric, cambic with slickensides
Steele	A-C2g-2Abg-2Cg	Ochric
Wakeland	A-Cg	Ochric
Walbash	A-A1-Bg	Mollic, cambic
Waldron	A-C-Cg	Ochric
Wilbur	A-Bw-Cg	Ochric, cambic

Table 3.

Soil horizon sequences and diagnostic horizons.

In soil taxonomy, soil diagnostic horizons are soil horizons having characteristics that indicate pedogenic development and are discerned in the field without additional laboratory data [33]. With considerable generalization, mollic epipedons are surface horizons that are not acidic, have high-base saturations, and possess significant soil organic matter abundances [34]. Mollic epipedons are presumed to have had prairie vegetations; however, all mollic epipedons in this study have significant smectite clay contents that limit microbial soil organic matter decomposition. Ochric epipedons are like mollic epipedons but lack significant soil organic matter contents. The cambic horizons are subsurface soil horizons that show some pedogenic development but not to the extent of other subsurface diagnostic horizons (Table 3).

7. Soil properties across the study area

Table 4 provides value ranges for the selected soils by soil depth and includes typical soil profile permeabilities, volumetric available water contents (AWC), soil textures, soil pH levels, and soil organic matter (SOM) contents. The values are provided by the soil surveys for the study area [28, 29, 30]. Permeability (Perm) on an hourly basis is vs. for very slow (<0.15 cm), s for slow (0.15 to 0.51 cm), ms for moderately slow ((0.51 to 1.5 cm), and m for moderate ((1.5 to 5 cm). mr is moderately rapid (5 to 15 cm), r is rapid (16 to 50 cm), and vr is very rapid (>50 cm).

	Depth		Perm		AWC
	cm	cm/hr	cm/cm	Texture	pH	SOM
Alligator	15	ms	0.19	sicl	4.5–6.0	1 to 3
	117	vs	0.16	clay	4.5–5.5
	152	vs	0.16	clay	6.5–7.3
Beaucoup	48	ms	0.22	sicl	5.6–7.8	5 to 6
	112	ms	0.19	sicl	5.6–7.8
	152	ms	0.2	sicl	5.6–7.9
Bowdre	15	s	0.17	sicl	5.6–7.3	1 to 3
	113	ms	0.21	sil	6.1–8.4
	137	m	0.18	sandy loam	6.1–8.4
	152	mr	0.1	loamy sand	6.1–8.4
Commerce	30	ms	0.21	sicl	5.6–7.8	0.5 to 2
	58	ms	0.21	sicl to sil	6.1–8.4
	152	ms	0.21	sl to sic	6.6–8.4
Caruthersville	71	m	0.2	sandy loam	6.6–7.8	1 to 2
	152	m	0.17	sand-sil	6.6–8.4
Darwin	38	vs	0.13	sic	6.1–7.8	4 to 5
	152	vs	0.13	sic	6.1–7.8
Dupo	18	m	0.23	sil	5.6–7.3	1 to 2
	71	m	0.21	sil	5.6–8.4
	152	s	0.14	sicl to sic	6.6–7.8
Elsah	30	m	0.21	loam	5.6–7.3	1 to 3
	132	mr	0.11	cherty loam	5.6–7.3
	152	m	0.03	cherty sand	5.6–7.3
Falaya	15	m	0.21	sil	4.5–6.5	0.5–3
	152	s	0.18	sil to sic	4.5–5.5
Haynie	23	m	0.21	sil to sic	7.8–8.4	1 to 3
	152	m	0.2	sil to sic	7.8–8.4
Jackport	13	ms	0.2	sicl	4.5–7.3	1 to 3
	147	vs	0.15	clay	4.5–5.5
	160	s	0.19	sic to sil	6.1–7.8
Haymond	23	m	0.23	sil	5.6–7.3	1 to 3
	150	m	0.21	sil	5.6–7.3
	183	m	0.21	sil	5.6–7.3
Leta	38	s	0.13	sic	6.6–7.8	2 to 4
	69	s	0.15	sicl	6.6–7.8
	152	m	0.18	sil	6.6–8.4
Mhoon	10	m	0.22	sil	6.1–7.8	0.5 to 2
	152	s	0.2	sil to sic	6.1–8.4
Nameoki	38	vs	0.16	sicl	6.1–7.3	2 to 4
	76	vs	0.13	sicl	5.1–7.3
	132	m	0.16	sil	5.1–7.8
	178	m	0.1	sl to sil	5.6–7.8
Parkville	43	vs	0.12	sic	6.6–8.4	1 to 3
	104	m	0.2	sil	7.4–8.4
	152	mr	0.13	sandy loam	7.4–8.4
Sharkey	18	vs	0.19	sicl	5.1–8.4	0.5 to 2
	137	vs	0.19	clay	5.6–8.4
	183	s	0.2	clay	6.6–8.4
Steele	20	r	0.08	sand	5.6–7.3	0.5–1
	56	r	0.11	loamy sand	5.6–7.3
	66	r	0.11	loamy sand	5.6–7.3
	152	s	0.18	sicl	5.6–7.3
Wakeland	30	m	0.23	sil	5.6–7.3	1 to 3
	152	m	0.21	sil	5.6–7.3
Walbash	15	vs	0.13	sic	5.6–7.3	2 to 4
	185	vs	0.09	sic	5.6–7.3
Waldron	20	vs	0.13	sic	6.6–7.8	2 to 4
	152	s	0.17	sicl	7.4–8.4
Wilbur	23	m	0.23	sil	5.6 to 7.3	1 to 3
	152	m	0.21	sil	5.6 to 7.3

Table 4.

Representitive soil depth, permeability, available water content (AWC), texture, pH, and soil organic matter (SOM) content.

Perm is permeability: vs. is very slow, s is slow, ms is moderately slow. m is moderate, mr is moderate rapid, r is rapid. Texture: sil is silt loam, sicl is silty clay loam, sic is silty clay.

The Alligator, Darwin, Sharkey, and Walbash soils have moderately slow to very slow permeabilities and silty clay to clayey textures. To some extent, the soils Jackport, Leta, Nameoki, and Waldron share these attributes. Conversely, the soils Caruthersville, Elsah, and Steele have coarse-textured surface horizons and moderate to moderately rapid permeabilities. In general, soils having very slow to slow permeabilities have very high to high shrink-swell capacities, whereas soils with rapid to very rapid permeabilities have low shrink-swell capacities.

The volumetric available water contents (AWC) when adjusted for a 1.83 m (6 ft) soil profile depth show a moderate available water content for the Walbash soil, high available water contents for the Darwin and Waldron soils, and very high available water contents for the Haymond and Wilbur soils. Virtually all soils in the floodplain support high to very high volumetric available water provision. Soil pH levels range from very strongly acidic to slightly alkaline.

Floodplain ecosystem evolution because of land management is an area of active research. The soil profile values by soil depth for permeability, available water contents, textures, pH, and soil organic matter contents (Table 4) will almost certainly be leading indicators for documenting soil changes because of land management. These indicators permit an estimation of forest species suitability and growth potential. Other indicators will likely be required, and their values will be experimentally determined. Soil indicators and the ecosystem site descriptions collectively are integral to assessing soil health potential and evaluating ecosystem service functions.

The Sharkey soil series belongs to the Vertisol order and is representative of soils in the clayey floodplain forested ecological site. The pedon has an Ap – Ap2 – Bssg horizon sequence where the ss represents slickensides caused by repeated soil expansion attributed to the large content of smectite (montmorillonite) clay, and g represents gleization (Table 5). The pedon shows a clay loam – silty clay loam transitioning to a clay texture, resulting in the very high shrink-swell capacities and the large cation exchange capacity. The phosphorus and sulfate concentrations are considered low. The effective rooting depth was less than 1 meter because of the shrink-swell capacity, clay contents, and the lack of soil structure. The pH is slightly alkaline. Aqua-regia digestion of this pedon for Fe, Mn, Cr, Co, Ni, Cu, Zn, Pb, and Cd reveals that all elements have typical abundances [35] and does not indicate significant heavy metal impact (Table 6).

Horizon	Depth	Texture	pH	SOM	P	CEC	SO4-S
		cm	water	%	ppm	cmol kg^−1	ppm
Ap	15	clay loam	7.9	2.1	22	24.2	6.6
Ap2	30	silty clay loam	7.8	1.8	31	23.6	5.6
Bssg1	46	silty clay loam	7.9	2.6	15	26.0	4.5
Bssg2	61	clay	7.6	2.3	7	29.4	6.7
Bssg3	91	clay	7.8	1.5	4	27.9	6.7
Bssg4	122	clay	7.3	1.7	3	28.0	6.2
Bssg5	153	clay	7.9	1.4	10	28.2	8.3

Table 5.

Routine characterization of the Sharkey pedon.

SOM is soil organic matter and CEC is the cation exchange capacity.

Horizon	Fe	Mn	Cr	Co	Ni	Cu	Zn	Pb	Cd
	-------------------------------------------mg kg^−1---------------------------------------------------
Ap	18,300	258	28	4.8	16.3	11.4	64	17.3	0.15
Ap2	18,300	350	29	5.5	17.2	13.7	69	22.9	0.19
Bssg1	22,600	308	33	5.7	18.2	12.3	73	16.4	0.07
Bssg2	23,800	447	22	6.8	17.7	11.3	69	14.7	0.07
Bssg3	29,600	1160	36	9.7	25.2	10.2	83	15.3	0.13
Bssg4	24,400	417	34	6.5	20.7	12.5	75	15.2	0.08
Bssg5	23,200	252	36	5.6	22.2	11.5	76	15.7	0.09
Typical values for the selected transition elements in soil (Source: Kabata-Pendias)
Soil	35,000	488	60	8	29	39	70	27	0.3

Table 6.

Aqua regia digestion for selected transition metals for the Sharkey pedon.

The Commerce soil series belongs to the Inceptisol order and is representative of soils in the sandy and loamy forested floodplain ecological site. The pedon has an Ap – Bw-Cg horizon sequence where the w represents a slightly altered subsoil parent material, and g represents gleization (Table 7). The pedon shows a silt loam profile, with the cambic horizon having a silty clay loam texture. The phosphorus and SO₄-S concentrations are considered low. The effective rooting depth was more than 2 meter. The Ap and Bw horizon pH activities are neutral, whereas the Cg horizon sequence is acidic. Aqua-regia digestion values for Fe, Mn, Cr, Co, Ni, Cu, Zn, Pb, and Cd reveal that all elements have typical abundances and do not indicate significant heavy metal impact [35] (Table 8).

Horizon	Depth	Texture	pH	SOM	P	CEC	SO4-S
	cm	water	%	ppm	cmol kg^−1	ppm
Ap	15	silt loam	7.0	4.6	28	22.0	4.6
Bw1	30	silty clay loam	7.1	1.9	8	19.9	2.8
Bw2	45	silty clay loam	6.1	0.9	14	14.3	8.8
Cg1	60	silt loam	5.7	0.6	16	10.9	20.7
Cg2	90	silt loam	5.5	0.6	7	9.7	29.7
Cg3	120	silt loam	5.5	0.5	8	10.1	55.3
Cg4	150	silt loam	5.4	0.5	8	10.9	68.3

Table 7.

Routine characterization of the Commerce pedon.

Horizon	Fe	Mn	Cr	Co	Ni	Cu	Zn	Pb	Cd
	------------------mg kg^−1--------------------
Ap	24,200	560	32	10.5	26.9	20.7	90	23.2	0.30
Bw1	23,300	615	32	8.9	26.1	19.2	89	30.1	0.31
Bw2	17,700	277	25	6.5	13.8	13.7	44	11.8	0.04
Cg1	15,300	567	21	8.8	14.1	14.4	35	9.3	0.03
Cg2	15,500	636	21	8.3	15.7	12.0	39	10.9	0.04
Cg3	16,700	626	23	8.0	19.2	17.1	38	10.2	0.08
Cg4	14,600	567	20	7.7	16.8	12.7	40	9.6	0.08
Typical values for the selected transition elements in soil (Source: Kabata-Pendias)
Soil	35,000	488	60	8	29	39	70	27	0.3

Table 8.

Aqua regia digestion for selected transition metals for the Commerce pedon.

The Wilbur and Haymond soils are Inceptisols whose parent materials are derived from loess-mantled upland erosion and subsequently deposited in the floodplains. The Wakeland soil is an Entisol and shares an evolutional history like that of the Wilbur and Haymond. All soils have uniform silt loam textures (Table 9). Wilbur, Haymond, and Wakeland are somewhat poorly drained, moderately well-drained, and poorly drained pedons, respectively. The upper portion of the Wilbur and Wakeland pedons are slightly acidic, whereas the deeper horizons are very strongly acidic. The cation exchange capacity is generally medium, and the soil organic matter contents show a decreasing abundance on progression through the soil profiles. The Wilbur pedon shows typical transition metal contents and do not indicate any heavy metal impact [35] (Table 10). The Haymond and Wakeland heavy metal soil profile concentrations are similar to that of the Wilbur pedon.

Horizon	Depth	pH	Acidity	SOM	CEC	BS
	cm	cmol kg^−1	%	cm kg^−1	%
	Wilbur
Ap	13	6.4	5.7	2.0	17.2	80
A	25	6.4	3.6	1.2	16.6	83
Bw1	41	6.1	3.8	1.0	14.1	79
Bw2	56	5.4	5.3	0.8	13.3	65
Bw3	74	4.7	5.2	0.4	11.0	53
Cg1	89	4.2	4.1	0.2	5.7	44
Cg2	104	4.3	4.6	0.2	8.8	55
Cg3	152	4.9	3.1	0.2	10.8	78
Cg4	183	5.1	3.0	0.2	10.4	78
Cg5	203	5.2	3.0	0.2	10.5	78
	Haymond
Ap	15	4.9	5.2	1.5	12.9	64
A	28	5.2	4.6	0.8	13.2	69
Bw1	41	5.0	4.4	0.7	11.4	73
Bw2	74	4.4	3.6	0.3	6.9	65
C	97	3.9	5.4	0.2	6.6	41
C2	124	4.1	4.0	0.2	6.7	55
C3	145	4.5	3.1	0.2	7.8	72
C4	170	5.3	2.5	0.2	7.5	78
	Wakeland
Ap1	8	6.0	1.4	1.5	7.9	90
Ap2	20	6.0	1.4	0.5	7.9	90
Cg1	43	6.0	2.5	0.7	9.5	83
Cg2	66	6.1	2.7	0.7	8.7	88
Cg3	91	6.2	2.8	0.5	8.6	81
Cg4	122	5.8	4.9	1.2	15.5	76
Cg5	145	4.8	5.3	0.5	9.2	60

Table 9.

Routine characterization of three soils along drainageways to the Mississippi River floodplain.

All soil profiles have a uniform silt loam texture. SOM is soil organic matter, CEC is cation exchange capacity, BS is percent base saturation. Acidity is the total acidity attributed to titratable H and Al

Horizon	Fe	Mn	Cr	Co	Ni	Cu	Zn	Pb	Cd
	-----------------------------------------mg kg^−1--------------------------------------------
Wilbur Soil #1
Mean	16,940	832	21.8	7.2	17.2	15.4	43	12.3	0.14
Coeff. Var.	23	79	13	56	29	24	33	37	62
Wilbur Soil #2
Mean	17,720	906	22.0	8.4	17.5	13.5	45	12.1	0.10
Coeff. Var.	15	55	7	42	23	14	25	27	81

Table 10.

Aqua regia digestion for selected transition metals for the Wilbur pedon.

Coeff. Var. is the percent coefficient of variation.

8. Employing soil data and the ecosystem site descriptions to advance sustainable land management

Ecological site descriptions are intended for conservation planning and implementation of sophisticated land management. Within the ecological site description, a “State” is largely the dominant vegetation status, whereas the transition involves a natural event (flooding, fire) or land management that fosters vegetational changes. The sandy/loamy floodplain forest provides a State and transition model, wherein the reference States include: (i) eastern cottonwood and hackberry/willow and (ii) sycamore and eastern cottonwood/willow. The transition from the eastern cottonwood and hackberry/willow State to the sycamore and eastern cottonwood/willow State involves flood disturbance. The reverse transition involves no flooding disturbance or sedimentation. Non-reference States include: (i) cropland and (ii) cool season grasslands, with appropriate events or activities promoting the respective transitions. The clayey floodplain forest provides a State and transition model, wherein the reference states include: (i) Hackberry American Elm, and (ii) Hackberry-American Elm/Pin Oak. The transition from Hackberry American Elm to Hackberry-American Elm/Pin Oak involves an absence of disturbance events. The reverse transition involves natural disturbances every 2 to 5 years. Other States include: (i) low disturbance/logged woodland, (ii) cool season grassland, and (iii) cropland, with each transition between the states specified.

Effectively evaluating the ecosystem services for these floodplain soils require: (i) select the ecosystem services to be evaluated, (ii) determine the indicators that will be used to infer the effectiveness of the ecosystem service, and (iii) given the reference and non-reference States for each ecological site provide field work that infers the benchmark rating and variance for the selected indicators. Specifically, provision for each ecosystem service for each reference State needs to be clarified. Suppose carbon sequestration is selected as a vital ecosystem service, then the following needs elucidation: (i) the initial and long-term carbon sequestration potential for each soil, (ii) determination of the intensity of the transitions to improve or degrade the desired outcomes, (iii) determination of any synergistic or antagonistic correlations. Thus, future research needs to determine which ecosystem services are deemed to have the greatest need to support using land management.

Conflicts of interest

The authors have no conflicts of interest.