Put the Land Back on the Land: A National Imperative

Abstract

The Rivers and Harbors Act of 1899 (RHA1899), the Soil Conservation Act of 1935 (SCA1935), and the Clean Water Act (CWA1972) were pivotal in managing United States (US) waters. RHA1899 provided the Army Corps of Engineers authority to regulate dredge and fill operations. SCA1935 authorized the US Department of Agriculture to combat soil erosion. CWA1972 empowered the US Environmental Protection Agency to regulate point-source pollution. The implementation of the European Soil Charter of 1972 and the 2000 European Water Framework Directive empowered Europe to address similar soil erosion and water quality problems. By 2022, improvements in erosion losses were obtained with soil conservation programs, but continued losses of organic topsoil threatened soil health, human welfare, and water ecosystems. Worldwide losses, estimated at 24 billion tonnes per year, include US and European losses of ~3 billion and 970 million tonnes per year, respectively. Approximately 60% of eroded materials are delivered to rivers and lakes threatening waters. Dredged freshwater sediments, however, have beneficial uses including restoring health of agricultural and forestry lands and water resources. National initiatives involving defense, agriculture, and environmental governmental units are proposed for recycling organic, nutrient-rich aquatic sediments in world-wide Put the Land Back on the Land programs.

1. Introduction

The world’s land and water resources are constantly changing due to natural and anthropogenic forces. Causative agents for these changes are numerous, but a commonality among many identified agents is the influence of erosion. Knowledge of sediment generation, downgradient transport, and deposition have been well described [1, 2] and advances in our understanding of these processes continue as outlined in this book.

Soil erosion and its effects on water quality at catchment scales have become a recent focus for many investigations because of the importance of nonpoint source inputs of nitrogen, phosphorus, and organic carbon to waterways which contribute to the eutrophication of many global waters [3]. Worldwide losses of fertile topsoil have been estimated at 24 billion tonnes per year [4] with United States (US) and European Union (EU) having losses of ~3 billion [5] and 970 million tonnes per year, respectively [6]. By the beginning of the twenty-first century, it was also recognized that 90% of US croplands, due to soil erosion, were losing fertile soil faster than it could be replaced by natural regenerative processes [7, 8]. These erosional losses, besides delivering nutrients and organic carbon to waterways and impacting agricultural production, have reduced reservoir and lake water storage capacity. Deposition of these eroded soils has restricted navigation, made lands adjacent to waterways prone to flooding, and delivered various contaminants (e.g., pesticides and heavy metals) to aquatic systems throughout the world. Approximately 60% of the eroded soil is deposited rivers and lakes [5]. Pimentel [5] concluded that “soil erosion is second only to population growth as the biggest environmental problem the world faces.”

The total costs of land degradation to any country alone are difficult to accurately estimate because of the many uncertainties associated with calculating cost estimates [9], but annual global damage from soil erosion has been estimated at $400 billion (USD) with US agricultural losses alone reaching ~$37 billion per year [5]. Removing ~135 million m³ of sediment annually from EU and United Kingdom (UK) waters [10] is estimated to cost 2.3 billion euros (€) per year (~$2.6 billion USD). In fiscal year 2022, the US Congress allocated $3.44 billion specifically for navigation maintenance and improvements of harbors and inland, coastal, and intracoastal waterways [11].

Removing sediments from waterways is expensive. But to reduce the total costs associated with soil erosion to societies, here we present an approach that we call Put the Land Back on the Land. This approach focuses on waterways that are not included in traditional coastal navigation, harbors, and inland and intracoastal waterways. Our proposed approach will assist in mitigating many land and water problems due to soil erosion. We proffer the approach will lead to improved cost/benefit ratios to societies by reincorporating sediments deposited in aquatic systems back onto the watershed landscape.

If soil erosion is the second biggest worldwide environment problem due to its threat to food security [5], our Put the Land Back on the Land addresses not only a national imperative of many nations, but an important national security issue for those nations. To understand our contention that now is the time to implement Put the Land Back on the Land programs across the world, we discuss four themes:

• Historical Development of the Erosion Problem and Its Management

• Key Steps for Implementing a Put the Land Back on the Land Program

• Risk Considerations

• Research for Successful Sediment Recycling

We also identify some of the major socio-political influences on the management of eroded sediments deposited in aquatic systems (Sections 2.1, 2.2). We especially note influences before and after the rise of the environmental movement on the development of regulations imposed by the US and the EU for dredged sediments. Next, we discuss problems with using and interpreting sediment quality guidelines (SQGs) developed for aquatic systems when applied to soils and experiences with sediment reuse in agriculture (Sections 2.3, 2.4). We then discuss key steps needed for implementation of a successful national sediment recycling program (Sections 3.1, 3.2, 3.3, 3.4). Finally, we highlight some risk considerations (Section 4.0), identify research needed for successful sediment recycling (Section 5.0). and conclude that recycling aquatic sediments is inevitable to maintain sustainable productivity of agricultural lands. Given the possible future risks posed by projected climate change and other environmental changes, the loss of vital topsoil, and diminishing agricultural/forestry lands to population growth, now is the time to begin to Put the Land Back on the Land!

2. Historical development of the erosion problem and its management

The poet Maya Angelou reportedly stated that you cannot really know where you are going until you know where you have been. The written history on dredging, soil erosion, and their environmental impacts (e.g., eutrophication) are dominated by authors from Europe and the US [12]. This is also true for the beneficial use of dredged material [13]. To understand actions taken by different world governments during specific times, actions must be placed in the context of socio-political norms [14].

2.1 Why soil erosion is a concern?

Humankind through the ages have used water systems for the transportation of people and goods. Waterborne transportation, however, was often hindered by the movement of bottom sediments and the sedimentation of eroded material from upstream watersheds. Humans responded first by removing bottom materials by hand, then by animal power, and finally by use of machines. The breakthrough in sediment removal technology [15, 16] was the development of the suction dredge in the eighteenth century by American Nathaniel Lebby (1857) and French engineer Henri-Émile Bazin (1867). Suction dredging facilitated the creation of channels and harbors of sufficient depth for larger and larger ships and became over time one of the commonly used methods in modern dredging [17].

The severity of soil erosion in upstream watersheds depends on geomorphic processes [18]; thus, humankind’s responses to soil erosion vary. However, erosion at many worldwide sites became, and still is, a major constraint to agriculture, affecting crop yields and jeopardizing the sustainability of agriculture activities [19, 20]. Land degradation is therefore considered one of the planet’s greatest environmental issues [21].

Soil erosion, however, is known to have beneficial agricultural effects downstream from the original fields. Deposition of eroded sediments created the fertile floodplain soils (e.g., the Mississippi River and Nile River basins) and created land (e.g., deltas) that benefited wildlife and humans [22]. But regular flooding was required to maintain land fertility and flooding over time was deemed undesirable by humans living alongside flowing waters. Most societies, therefore, established flood control projects (e.g., 1928 Flood Control Act, 70th US Congress, Sess. 1. Ch. 569, enacted May 15, 1928) to prevent damage to infrastructure and provide water storage. Soil erosion mitigation or Keep the Land on the Land became the dominant approach to maintain agricultural vitality and there was little consideration of using dredged sediments to maintain soil fertility [23]. Dredged materials were viewed as a waste to be disposed of quickly and cheaply.

Although significant improvements in erosion losses have been obtained in many countries, losses of organic topsoil remain at levels threatening soil health and national welfare [24], raising the question as to why dredged sediments are not routinely recycled back onto agricultural lands. There are of course many reasons put forth, but the toxicity of chemicals in the dredged material became a major concern for the environmental movement in the 1970s [25]. Implementing dredging programs then became problematic because of the necessity to comply with new laws and regulations designed to provide protection for the environment and human health. Besides the scientific and legal issues, there were also social and cultural issues. The number of stakeholders involved increased and each group had varying opinions on what to do. There was angst among stakeholders because there were uncertainties about the impact of a proposed project on other community problems. Most importantly, the economic burden of any dredging project became a confrontational issue. Implementing projects, therefore, became the proverbial Gordian Knot and numerous desired dredging projects in the US and Europe reached a standstill.

The United States Environmental Protection Agency (USEPA) and the United States Army Corps of Engineers (USACE) recognized that due to efforts implemented under the Clean Water Act (CWA1972: 3 U.S.C. §1251 et seq. 1972) that both sediment and water quality have improved to a point where toxicity criteria are often achieved. Dredged materials from many US water bodies were now deemed “clean enough” to be recommended for beneficial uses [26, 27]. For example, one identified use after appropriate evaluations (physical, chemical, and biological) was applying dredged material to agricultural and forestry lands to reclaim and conserve topsoil. Similar conclusions were also reached in Europe [28].

2.2 Past efforts and challenges

Waterways have served as transportation routes throughout history. People also dug channels to irrigate crops. Maintaining waterways for commercial and national defense became a priority for many nations in the nineteenth century as ships of war became larger and more goods and people were transported by larger ships. In the case of the US, the USACE was assigned the mission of constructing and maintaining reliable, navigation systems. USACE and military organizations in Europe were the only organizations in the nineteenth century that had the engineers needed to improve and develop new dredging technology as well as the ability to address the economic and national security imperatives of their country.

Until the 1970s, dredged materials were viewed as beneficial in Europe and the US. They were used to fill coastal and inland marshlands, to create land for building sites, roads, and rails to cross lowlands, as well as for agriculture. For many countries, wetlands were considered an obstacle to development. This belief was best illustrated in the US when Congress passed the Swamps Land Act of 1850 (Thirty-First Congress, Chapter 84) that provided the mechanism for transferring title of federally owned wetlands to states that would drain the land for productive agricultural uses. The nutrient-rich soil under wetlands was especially attractive as agricultural land once drained.

In the twentieth century, the 1930s Dust Bowl in the US focused attention on soil erosion (Public Law 74-76, Statute 163). The Dust Bowl was viewed as a national disaster because the uprooting of topsoil posed a national security threat [29]. Soil erosion, however, was treated as a natural resource management issue, not a national defense issue. The US Congress established the Soil Conservation Service (SCS) to combat soil erosion and “to preserve natural resources, control floods, prevent impairment of reservoirs, and maintain the navigability of rivers and harbors, protect public health, public lands and relieve unemployment.” Consequently, SCS initiated a program for building water bodies across the US to trap sediments eroding from the land and increase water storage for agricultural and forestry operations.

The problem of soil erosion became severe enough in Europe to be part of the environmental agenda of the EU due to its impacts on food production, drinking water quality, eutrophication, and ecosystem services [6]. Small reservoirs became the preferred infrastructure for use against intensive runoff processes [30]. As in the US, European small reservoirs increased in number to provide greater water storage and trapping of sediments [31].

By the 1970s, Earth Day and the rising environmental movement established a new “Environmental Paradigm” [32, 33]. Concurrently, a new social movement emphasizing the importance of “Deep Ecology” emerged, a phrase originated in 1972 by Norwegian philosopher Arne Naess [34, 35]. This social change led to the promulgation of many new laws, regulations, and policies in both Europe and the US as well as worldwide [36, 37], with the two pieces of iconic legislation being the CWA1972 and the 2000 European Water Framework Directive (Directive 2000/60/EC).

The CWA1972 was passed in response to the discharge of hazardous substances into rivers, the loss of wetlands by dredging and in-filling, and nutrient enrichment, which were becoming national environmental concerns. The 1977 CWA [Section 404(f)], however, exempted discharges associated with normal agricultural and forestry activities. By 1987, many of the discharges of toxic materials from point sources had been removed or plans to remove them established. Parties interested in eutrophication issues expanded the focus from point source controls to include nonpoint sources of pollution (Section 319 of CWA). Although agriculture was recognized as a major source of nonpoint source nutrients, exemptions for agriculture remained in place for the US. The agricultural exemptions recognized that American agriculture fulfilled the public need for supplying abundant and affordable food and fiber. Other nations also had similar exemptions for agriculture.

By the 1970s, many world scientists also began to focus on the eutrophication of lakes [38]. The Clean Lakes Program (CWA Section 314) directed the USEPA to develop better methods for removing silt, aquatic growth, and other obstructions in lakes. USEPA was also directed to create silt traps and devices to prevent sediment deposits in lakes and demonstrate the benefits of using dredged material for land reclamation. Subsequently, many international conventions (London Convention of 1972, Barcelona Convention of 1976, Helsinki Convention of 1992, and OSPAR Convention of 1992) encouraged the exploration of alternative uses for dredged materials. Such efforts, however, were stymied due to a lack of funding and concerns about using contaminated sediments. USEPA came to view dredging and other palliative approaches (e.g., aquatic weed control) as “short-term” solutions for eutrophication problems and used regulation 40 CFR Part 35.1650-2 to disallow funding for many desired dredging projects and other lake management palliative methods.

Accepting that dredged materials could have beneficial uses was also hindered because agronomic units of government were focused on Keep the Land on the Land programs, that is, erosion control. Environmental governmental units, which often blamed agriculture and dredging for the loss of wetlands [39], began to focus on sediment contamination issues. This concern about contaminants in sediments, coupled with limited data in the early stages, fostered the belief that dredged sediments should always be treated as a waste!

The management approach for dredged material, therefore, became to place sediments into confined disposal facilities (CDF) or dispose materials in the open water of large lakes (e.g., the US and Canadian Great Lakes) or the oceans. Despite the holding capacity of CDFs becoming limited and the dumping of materials in open waters being restricted in the twenty-first century, legislative limitations developed in the late twentieth century hindered the recycling of dredged sediments, especially in the EU [40].

2.3 Sediment contamination

Research on contaminated underwater sediments evolved slowly in the latter part of the twentieth century. One of the most important regulatory tools for aquatic sediment management has been the development of sediment quality guidelines (SQGs). Guidelines were based on the hypothesis that a chemical concentration level could be identified in sediments below which aquatic life would not be harmed. The Threshold Effect Limit (TEL) hypothesis was first proposed by the USEPA and USACE in the early 1970s to assess the disposal of dredged material at sea [41, 42]. The contaminated sediments issue, however, was not specifically addressed in the laws of the US until the Water Resources Development Act of 1992 (WRDA).

Since the 1980s, numerous SQGs have been established by different organizations and countries with each SQG incorporating different criteria to account for the varied conditions in which sediment contamination occurs. Consequently, identifying the concentration threshold for chemicals below which aquatic life was not harmed remained problematic [43] and only guidelines, not numerical legal standards, exist for most nations.

The development of SQGs led to the use of both the TEL and Probable Effect Limit (PEL). As noted previously, the TEL is the sediment contamination concentration at which a toxic response was first observed for benthic test organisms. The PEL was the concentration at which a great percentage of the benthic population showed a toxic response. Concentrations above the PEL were deemed problematic. When a chemical concentration was between the TEL and PEL, professional judgment was to be used to assess the consequences of sediment contamination.

Because of the uncertainty factors (UF, generally not reported) inherent in different SQG approaches, nations are still developing SQGs in the twenty-first century. In South America, SQGs that are meaningful for the unique biological conditions of tropical and high-altitude environments are being developed [44]. However, the more significant issue to consider for agricultural interests is that SQGs have been developed for aquatic systems, not agricultural lands. If the sediment is not going to be re-used in a wet system (e.g., wetland restoration), SQGs are of limited value for dry land application. Consequently, various guidelines for agricultural soil health have been developed, and there is an ongoing need to define contaminant risk levels for agricultural soils. Most agricultural TELs are greater than aquatic TELs (Table 1).

Substance	Sediment			Soil3		Compost4
	TEL1	Lowest effect Level 2	Severe effect level2	TEL	Lower guideline value	Agricultural use
Metals
Arsenic (As)	5.9	6	33	5	50	23
Cadmium (Cd)	0.6	0.6	9	1	10	1
Cobalt (Co)				20	100
Chromium (Cr)	37.3	26	110	100	200	70
Copper (Cu)	35.7	16	110	100	150	150
Iron (Fe)
Manganese (Mn)
Nickel (Ni)	18	16	50	50	100	60
Lead (Pb)	35	31	110	60	200	120
Antimony (Sb)		2	25	2	10
Vanadium (V)				100	150
Zinc (Zn)	123	120	270	200	250	500
Mercury (Hg)	0.17			0.5	2	0.7
PAHs and PCBs
Anthracene	50	85.3	1100	1000	5000
2-Methylnaphthalene		70	670
Acenaphthene	10	16	500
Acenaphthylene	10	44	640
Benzo(a)anthracene	70	261	1600	1000	5000
Benzo(a)pyrene	90	430	1600	200	2000
benzo(b)fluoranthene	70			1000	5000
benzo(ghi)perylene
benzo(k)fluoranthene	60
Chrysene	110	384	2800
Dibenz(a,h)anthracene		63,4	260
Fluoranthene	110	600	5100	1000	5000
Fluorene	20	19	540
Henanthrene
Naphthalene	30	160	2100	1000	5000
Indeno(1,2,3-cd)pyrene
Phenanthrene	90	240	1500	1000	5000
Pyrene	150	665	2600
Total PAH	870	4022	44,792	15,000	30,000	10,000
Total PCBs	34	22.7	180	100	500	100

Table 1.

Screening criteria for metals (mg kg⁻1), polycyclic aromatic hydrocarbon (PAHs; μg kg⁻1 dry weight), and total polychlorinated biphenyls (PCBs; μg kg⁻1 dry weight) in sediment, soil, and compost.

¹

TEL, threshold effect level; Represents the concentration below which adverse effects on sediment-dwelling organisms are unlikely to be observed regarding metals [45] and organic contaminants [46].

²

Screening criteria for sediments in New York State. The Lowest Effect Level indicates a level of sediment contamination that can be tolerated by the majority of benthic organisms, but still causes toxicity to a few species. The Severe Effect Level indicates the concentration at which pronounced disturbance of the sediment dwelling community can be expected. A sediment is considered contaminated if either criterion is exceeded. If both criteria are exceeded, the sediment is considered to be severely impacted. If only the Lowest Effect Level criterion is exceeded, the impact is considered moderate [47, 48].

³

The Finnish legislation sets concentration levels by each hazardous element to identify soil contamination and remediation needs. Threshold value is equally applicable for all sites, and it indicates the need for further assessment of the area. In areas where background concentration is higher than the threshold value, background concentration is regarded as the assessment threshold. The second concentration level is the so-called “guideline value.” If this is exceeded, the area has a contamination level which presents ecological or health risks. Different guideline values are set for industrial and transport areas (higher guideline value) and for all other land uses (lower guideline value) [49].

⁴

Maximum limit values of heavy metal concentration in compost “class. A” which is suitable for agriculture in Europe [50].

In the case of heavy metals, the background concentrations at a particular geographic location need to be considered. In highly mineralized soils, existing aquatic SQGs might be exceeded, resulting in unnecessary restrictions on the recycling of dredged sediments. Spreading dried dredged material in thin layers across a large agricultural landscape links to the historical practice “Dilution is the Solution to Pollution.” Dredged sediments and the agricultural lands proposed for deposition should, therefore, be tested for contaminants. Each nation has established toxicity levels for various contaminants that are likely to elicit toxic effects. If the spreading process is done so that the final contaminant concentration is below the toxicity levels known to cause toxic effects in organisms, there should be no environmental impact. The United States Department of Agriculture (USDA) developed simple equations to identify the maximum amount of material that can be applied to a given amount of land [51].

Land application experience with materials previously considered waste has been gained by spraying or spreading biosolids (sewage sludge) onto the land surface. Both the EU and US emphasize the beneficial effect of recycling nutrient rich biosolids, while seeking to reduce risks from pathogens and other contaminants [52, 53]. Injecting of biosolids beneath the land surface or incorporating the biosolids into the soil by discing the soil can serve to either condition the soil or fertilize crops and vegetation grown in the soil. Landfarming is also a “Dilution is the Solution to Pollution” biotreatment technology that uses available agricultural methods to enhance biodegradation of organic contaminants. The Dilution is A solution to pollution approach should not be summarily discounted because it has been branded with a bad connotation in the past. Sediments, once spread in thin layers and mixed into the underlying soil, permit natural attenuation processes to degrade and immobilize many contaminants [54].

While the presence of chemical contaminants has occupied the attention of many scientists during the latter part of the twentieth century, one of the other issues that was a major concern was the eutrophication of aquatic systems from point source and nonpoint source nutrient inputs [38, 55].

2.4 Sustainability (eutrophication, the circular economy, soil health, and plant growth)

Concerns regarding eutrophication and the approaches to use to mitigate adverse effects of nutrient enrichment dominated world-wide research efforts in the late twentieth century [55]. Once Vollenweider [56] introduced the concept of nutrient loading to the scientific community, governmental environmental agencies began to focus on limiting point source nutrient inputs, especially phosphorus, to waterways with many successes [57]. However, it was realized that lakes were very complex and often responded differently to point source and nonpoint source nutrient control strategies [58]. This was especially true for shallow (<3 m), productive lakes where the internal supply of nutrients was great [59, 60, 61]. In many systems, internal nutrients, especially phosphorus, were mobilized (released) into the water column as sediments became anoxic [62, 63] or wind mixing brought nutrient-rich sediments into the water preventing improvements in water quality [61, 64].

Conversion of natural landscapes to agricultural and urban uses occurred throughout the world with population growth and changing climate. Human activities, however, often increased erosion, sediment transport, and sedimentation in aquatic systems. Erosion rates can be 100 to 1000 times greater than the geological erosion rate [65]. The implications for eutrophication are considered well known [66, 67]. Changes in agricultural operations [68] and the construction of wetlands [39, 69, 70, 71] have been some of the measures employed to try to control nonpoint source nutrient inputs. Best management practices (BMPs) have proven to be largely inadequate for restoring eutrophic lakes; thus, additional measures will be needed to reduce internal nutrient supplies [61, 72].

Explanations for the inadequate BMP responses have centered on legacy P [73, 74] and N [75] inputs from the waterbody’s watershed stymying management programs [76, 77, 78]. Soil phosphorus buildup due to past management practices (Legacy P) is often considered a root cause for eutrophication. Legacy nutrients also exist in lake and river sediments [64, 79]. Missimer et al. [64] concluded that despite extensive efforts to control external nutrient loads into Florida’s Lake Okeechobee, the frequency of algal blooms will continue until the sediments containing legacy nutrients are removed [61, 63].

Khare et al. concluded that the most cost-effective approach for achieving an average flow-weighted total phosphorus (TP) concentration of 40 μg/L at Lake Okeechobee’s inflows would require an estimated $4.26 billion [70]. This approach involves the implementing of nutrient management BMPs, Dispersed Water Management programs, as well as the construction of ~200 km² of Wetland Restoration and Stormwater Treatment Areas (STAs). The total costs and the need for such a large wetland area may be daunting for all but the most affluent nations and those with the capacity to convert a great quantity of agricultural/forestry lands to wetlands. Whether or not wetlands could reduce nonpoint source nutrient inputs sufficiently to lower Lake Okeechobee’s TP remains speculative and does not address the Legacy P problem.

Federal and state scientists estimated that fully dredging Lake Okeechobee would cost at least $1 billion, but <$4.26 billion for the establishment of BMPs, and restored wetlands and the construction of STAs [80]. Dredging would remove decades of Legacy P helping reduce in-lake TP and algal bloom frequencies [61, 64]. Deepening Okeechobee would increase water storage and provide water needed for agriculture and the growing population of south Florida [14]. Reducing the need to raise lake levels would also decrease detrimental ecological damage to Okeechobee’s marshes [14, 81]. Past efforts to reduce nonpoint nutrient inputs to Lake Okeechobee have failed to meet legally established goals [61, 64], but dredging will provide benefits even if nutrient inputs are not decreased [82].

Many lake restoration experts, however, now support removing bottom sediments to promote the concept of sustainable lake restoration [83]. Sustainable lake restoration can improve water quality, while delivering numerable socio-economic benefits. It also melds well with the Circular Economy concept developed in Europe [84, 85]. The Circular Economy Action Plan (CEAP) was accepted by the European Commission in March 2020. The concept, however, has not been readily adopted in other nations because of limited documentation of any successes. There are also cultural barriers, a lack of consumer interest and awareness, as well as a hesitant company culture and concerns by policy makers [86]. Removal of nutrients from lake ecosystems for their recovery and re-use (i.e., circular economy) should be prioritized [63].

Because the concept of reusing sediment aligned with circular economy principles and coincided with growing interests in global sustainability, research on the impact of reused sediment on soil and plant growth increased in the early twenty-first century. Studies demonstrated that there were significant benefits for applying aquatic sediments to agricultural lands [40, 87, 88, 89, 90]. Benefits included improved topsoil organic matter content, a greater amount of available water and nutrients for plants, and improved crop yields [40, 87, 88, 89, 90, 91]. As a soil amendment, some recycled sediments also improved soil cation exchange capacity [87, 92], elevated soil pH [93, 94], and decreased soil bulk density [87, 95].

Application of recycled lake sediment has been tested on vegetables and fruits [87, 93, 96], field crops like cereals and grasses [96, 97, 98, 99, 100], and ornamentals [101, 102] with positive effects on yield response. In general, studies where the recycled sediments were tested against control soils that were adequately fertilized similar growth resulted. As an example, Woodard [95] reported that forage crops (alfalfa and big bluestem) grown in a South Dakota lake’s sediment had similar or slightly higher shoot dry matters and higher relative N and P uptakes compared with those plants grown in silty clay loam soil. Ebbs et al. [93] also suggested that reclaimed slightly alkaline silty loam sediment from Lake Peoria (Illinois) could be utilized for vegetable production.

Crop yield benefits have been most notable in nutrient-deficient soils [87, 92, 95, 97]. A recent promising example of sediment recycling for soil fertilization comes from Lake Mustijärv (Estonia), where sediment removal and recycling led to increased growth and nutrient uptake of grass mixture, demonstrating the potential of sediment as a valuable resource in both short and longer terms [98, 99, 103]. Similar approaches have also been developed at Lake Ormstrup (Denmark) to reduce internal phosphorus loading and establish links to circular economy principles [104]. These efforts highlighted the growing interest in sediment recycling as a sustainable agricultural practice for closing the human-related nutrient cycle.

However, not all sediment recycling experiments have yielded positive results. Reduction in crop yields, due to soil compaction of loamy sand soil, occurred when sediment from Besko Reservoir (Poland) was added [105]. Chechlo Reservoir (Poland) sediment with a 2.7-fold lower carbon content and poor P and K fertility also reduced crop yields [106]. Also, sediment from constructed Finland wetlands had very low P availability for plants [107, 108], probably because of great amounts of P-binding compounds in sediments. Sediment originating from diverse sources (e.g., agriculture, industry, or urban areas) will have varying soil properties and may contain pollutants such as heavy metals and organic pollutants [40]. Given these variations in sediments quality and the associated ecological risks, it is essential to conduct appropriate evaluations of the sediments and to characterize their compositions to appropriately apply amendments and treatments when warranted before utilizing them in agricultural lands.

3. Key steps for implementing a Put the Land back on the Land Program

In the twenty-first century, “Sustainability” emerged as a scientific goal to find ways to use natural resources in a manner to guarantee their continuity and the continuity of humanity itself [109]. Put the Land Back on the Land is an approach to sustainability for each nation’s agricultural and forestry lands. However, education will be an important component if the approach is to be successful for dredged materials that have been viewed as a waste (often a hazardous waste) since the 1970s. Also, the number of stakeholders involved has increased and each has varying opinions on what to do. Conflict resolution will become important to avoid the proverbial Gordian Knot.

3.1 Prioritizations

Every nation has issues that must be prioritized, with national defense being a top priority for all nations. A key component of all national defense strategies is food security [110, 111, 112]. Global population increases generally lead to a reduction of farmland due to increasing urbanization. Urbanization further limits global food production capacity [113, 114]. Losses of organic topsoil also threaten soil health and national welfare [24, 29]. Consequently, the USDA established a soil health division in 2015. Feeding more people with less farmland or less productive farmland, therefore, requires technological changes and the development of appropriate public policies to ensure vital food security within the global security system.

Regenerative farming has garnered increased attention in the twenty-first century as a technological change that offers promise to resolve some issues related to agricultural lands [115, 116]. This approach, however, maintains the same soil management philosophy of Keep the Land on the Land. While retaining the Keep the Land on the Land approach is still valid, it is not sufficient alone to address erosion and loss of topsoil. To address the many intertwining issues associated with erosion (e.g., the shallowing of waterways and eutrophication), a holistic Put the Land Back on the Land freshwater sediment recycling program and needed infrastructure enhancements must be developed in addition to the current Keep the Land on the Land approach to enhance and maintain the productivity of agricultural and forestry lands through the remainder of the twenty-first century.

3.2 Funding

Limited local governmental budgets, as well as limited local sponsor budgets, discourage the removal of sediments from waterbodies and the use of more costly beneficial use alternatives, even if those alternatives are more environmentally sustainable [117]. Alternatively, many port dredging projects are funded at the national level. The Food & Global Security Network (NETWORK) convened a meeting of 22 experts (military minds, NGO leaders, scientists, and practical farmers) to discuss the critical importance of soil health [118]. The NETWORK called on national governments to formally recognize healthy soil as a strategic asset and critical for maintaining national security.

Approximately 877 billion dollars (USD) were spent on US national defense in 2022 and 17 billion dollars (USD) were spent on Army Civil Works studies and projects (Public Law 117-58), to maintain existing infrastructure, repair damage, and dredge channels in response to floods and coastal storms. NETWORK experts urged each nation’s defense departments to work with their agricultural and environmental counterparts to jointly oversee delivery of increased food sovereignty as well as the regeneration of soil function. Each agency can no longer work just within their own legislatively mandated silo if environmental sustainability is to be achieved. This philosophical shift emphasizes that holistic management can be a more efficient approach for managing soil erosion problems and restoring the vitality of agricultural lands.

In the US, a 2% annual increase in the nation’s defense budget would provide adequate funding (~17 billion annually) to support the operation of a national Put the Land Back on the Land program for freshwater systems and develop the infrastructure needed to support such a program. With adequate funding, Put the Land Back on the Land initiatives can aid in closing an important environmental loop that would limit nutrient loss from agricultural lands. Each nation can adjust funding to meet their national need.

3.3 Contacting potential stakeholders

First, the Put the Land Back on the Land approach is workable only if supported by landowners willing to accept reclaimed sediments. These landowners will include agricultural/forestry landowners, or other landowners desiring organic sediments for soil augmentation. Due to past erosion control programs, many if not most agricultural landowners have small water bodies on their land to trap sediments. Initial efforts should focus on these waters as the landowners recognize the trapped sediments came from their land. Governmental agricultural organizations should test these sediments for soil quality to demonstrate how testing will also be done on sediments from other water bodies. This knowledge should help to alleviate contamination concerns by not only the agricultural landowner but other stakeholders agreeing to accept reclaimed sediments.

Involving landowners directly is key to helping with an understanding of the benefits of putting the material back on their land. Some landowners with waterbodies on their properties, however, may not initially want governmental employees or contractors on their land. If the “Do It Myself” attitude becomes the limiting factor, equipment such as agitator pumps and soaker hoses can be provided to those landowners for delivery of sediments to the surrounding lands. When placing large amounts of water on the land would interfere with intended agricultural/forestry operations or contribute to new soil erosion, parabolic wedge-wire filters or a vertical geotube dewatering tower (Figure 1) could be utilized. These devices offer a simple economical approach for both small and large landowners needing to remove sediments from their waterbodies. The parabolic wedgewire or the vertical dewatering systems not only permit a return of the water to the water body but provide a form of sediment that can be spread on the land using available (owned or rented) farm equipment.

Figure 1.

Parabolic rundown screen (a) and vertical geotube tower (b) removing dredge material at farm sites. MuckVac™ sediment processing unit (c) and application tractor (d) used by AGUACULTURE of Clearwater, FL.

For landowners not wanting to work on their waters, but receiving truckable sediments from distant waters, centralized processing facilities can be developed and scaled to the size of the waterbody having sediments removed. From these facilities, dry material of appropriate quantity can be delivered, per agreement with the landowner, to the agricultural lands without disrupting normal agricultural operations.

One encouraging example of the ways to engage landowners is a decision-making tool for Brazilian farmers who commonly use sediments from close-by lakes and ponds that dry out regularly, making the dredging more feasible. The app (https://resed-cientista-chefe-v1.streamlit.app/, App Developer- Brennda Bezerra Braga Ph.D) facilitates farmers to calculate the economically feasible distance for transportation of the sediments based on the properties of soils and sediments and the costs of alternative, mineral fertilizer.

The advantage of first working directly with landowners is that it will build their support for accepting beneficial material from other water sources. A list of willing landowners will facilitate determination of the available acreage for receiving aquatic sediment enhancements. Successful sediment removal will, by removing decades of legacy nutrients deposited in the water bodies, reestablishes the sediment trapping ability of waterways, thus reducing the delivery of erodible material downstream. The cooperative work efforts will open the opportunity for conservation staff to ensure effective erosion management strategies (e.g., filter strips and sediment retention ponds) are in place. More importantly, the landowners, especially the agricultural/forestry owners, may then become part of the solution for mitigating ongoing eutrophication by receiving potentially more nutrients that are released by their lands.

Many freshwater water bodies located downstream of agricultural/forestry lands have accumulated sediments that restrict intended uses of the water bodies. Each nation’s environmental organization should work with non-landowning stakeholders to prioritize waters for refurbishment and the establishment of sustainable lake restoration programs [83]. These stakeholders need to be informed the Put the Land Back on the Land program is not a program to drain wetlands or remove base materials from a water body to increase water storage. The approach for sediment removal is analogous to vacuuming the nutrient-rich organic matter off the bottom to provide material to replenish lost topsoil.

The non-landowning stakeholders will be informed removed sediments will be tested for contaminants and results reported to them and the soil recipients to ensure soil health on lands proposed for disposal. In Florida, the Florida Department of Environmental Protection (FDEP) discourages agricultural landowners from placing material on their land if nutrients can re-enter waterways to contribute to nonpoint source nutrient loads. All stakeholders and regulatory agencies must acknowledge that multiple decades of legacy nutrients will be removed from these waterways. Even though there is the possibility of future inputs of some of these nutrients coming back into these waterways, the net reduction of nutrients should outweigh what re-enters from the reclaimed sediments.

Another concern of landowners and non-landowners is the loss of water during sediment removal operations. When there is sufficient water, where loss of water does not become a major stakeholder concern, and nearby agricultural or forest lands are reachable (~1.6 km), a vacuum system (MuckVac™) that ensures only the free-floating, unconsolidated muck is extracted from the lakebed has been used in South Florida. The extracted sedimentary material is conveyed via a diesel pump and reinforced lay-flat hoses, to a specialized Application Unit. If needed, removed material can be stored in mobile frac tanks until applied to the land. The Application Unit is an agricultural-grade tractor that pulls the lay-flat hose through the application field (Figure 1). The discharge of the material is meticulously calibrated to agronomic rates. To reach a distant site (>1.6 km), additional pumps are used (AGUACULTURE, www.agcutech.com, Clearwater, FL).

For many waters, the stakeholders do not want water removed from their water body and regulatory agencies often apply water quality standards to the returning dredge water. In 2000, there was another breakthrough in dredging technology, the Genesis Rapid Dewatering System™ (RDS) by Genesis Water (Figure 2). The RDS system permitted rapid dewatering of dredged sediments. Separation of solids and water from the dredged materials helped mitigate the size of needed disposal areas and thus reduce the overall project footprint [119]. Because the RDS system is scalable, waters in urbanized areas could be dredged. Dredged materials were also repurposed after physical, chemical, and biological characterization [119]. Less contaminated or uncontaminated sediments generally are suitable for commercial or beneficial reuse without treatment [120]. The RDS system also treats the return water to meet local water quality standards. Returning water to the dredged system has a tremendous economic impact for project developers.

Figure 2.

A 15 m³/min Genesis Rapid Dewatering System™ (a), clear return water (b), and truckable dry material (c) as operated by Revive Water Technologies of Bloomington, Illinois.

Since the introduction of RDS, improvements in the system have been made by Revive Water Technologies of Bloomington, Illinois. The system now provides a continuous 1:1 operating ratio of dredging to dewatering, timely production of stackable and truckable solids, immediate release of clear water discharge, and mobility with minimal energy and maintenance. Besides removing legacy nutrients from the return water, the system also greatly reduces the concentrations of various water quality contaminants from these same return waters (Table 2).

Parameters	Influent concentration	Revive RDS concentration	Reduction percentage
Arsenic	160 μg/L	3.3 μg/L	97.9%
Copper	790 μg/L	2.3 μg/L	99.7%
Iron	290,000 μg/L	170 μg/L	99.9%
Lead	9100 μg/L	8.2 μg/L	99.9%
Nickel	250 μg/L	2.3 μg/L	99.1%
Mercury	4.0 μg/L	0.062 μg/L	98.5%
Total nitrate	16.7 mg/L	11.35 mg/L	31.9%
Phosphorous	4500 μg/L	48 ppb	98.9%
Total suspended solids	150,000 mg/L	15 mg/L	99.9%

Table 2.

Sawgrass Lake—demonstration of rapid dewatering technology. U.S. Lake Dredging Project: RDS Contaminant Reduction (modified table re-produced with permission from Author) [121].

Having the dewatered sediments truckable is a great advantage as uncontaminated material can be delivered to more distant recipient lands. As dry sediments, large amounts of material could be transported by rail to distant agricultural lands. Transportation by rail would also permit contaminated sediments to be shipped to remote decontamination centers where treatments could be applied to make material suitable for agricultural uses.

3.4 Legislative laws, regulations, policies, and potential bottlenecks

Each nation has a myriad of laws, regulations, and policies governing dredging and disposal of removed materials. Typically, there is little meshing because the laws, regulations, and policies were developed for each regulatory agency staying within its narrowly defined legislative mission. Sometimes agency missions overlap but there is a tendency for each agency to only cite the laws, regulations, and policies used by their agency. When broad-based program like Put the Land Back on the Land is advanced, confusion often follows. For example, Finland and the Czech Republic permit direct reuse of sediments dredged from inner water bodies on agricultural soils if contaminant concentrations meet their national legislation thresholds [40]. Other European nations do not, and current EU actions place limitations on the application of sediments in agriculture [40].

Dredged sediments, recognized as natural resources, pose challenges in terms of management and disposal, contingent on factors like sediment type, pollution levels, and proximity to disposal facilities near dredging areas [40]. The diverseness of these environmental factors has made it difficult to formulate universal sediment management regulations. Consequently, the EU has indirectly addressed dredged material management by applying existing directives like the EU Water Framework Directive, EU Waste Directive, and EU Directive on protected areas, rather than a dedicated framework directive [40]. The EU Water Framework Directive checks water quality, but contamination limits for sediments vary by member state. The Waste Directive classifies sediments as either hazardous or non-hazardous waste, potentially allowing reuse (receiving codes in the European Waste Catalogue 170,505 (hazardous waste) or 170,506 (non-hazardous waste)). The Groundwater Directive oversees dredging activities, with a focus on groundwater quality and flood control. The European Landfill Directive does not cover using dredged sludge for fertilization or depositing non-hazardous sludges near water bodies, and the Habitat and Birds Directives safeguards biodiversity and controls dredging near nature protection sites.

The lack of specificity in existing European legislative guidance causes uncertainty about the legality of the Put Land Back on the Land approaches and may hinder or stop its implementation. The use of recycled sediments on agricultural lands as well as their use as fertilizers therefore needs greater legislative clarity. The laws, regulations, and policies also need to be reviewed to facilitate greater agency cooperation for achieving each nation’s goal to achieve environmental sustainability. In the US, USACE and USEPA have worked closely on sediment removal and beneficial use efforts since the end of the twentieth century and bringing closer cooperation/joint efforts with the USDA-National Resource Conservation Service will greatly enhance future management efforts.

4. Risk considerations

Each society will have to confront issues where there are pros and cons to be considered. For policy makers, decisions are often influenced by uncertainty. Here, a distinction must be made between generic uncertainty as a human (i.e., not knowing or understanding risk to oneself or family if there is any presence of a contaminant at all) and the use of scientific uncertainty factors in the law and toxicology. When a water quality standard is placed in legislative law, the published number is associated with an uncertainty factor of 10, 100, or 1000 depending on the quality and type of toxicological study conducted [122].

When extrapolating from valid experimental results, a 10-fold factor is applied [123]. This is done in studies involving prolonged exposure to average, healthy humans. This factor is intended to account for the variation in sensitivity among the members of the human population. An additional 10-fold factor is used when extrapolating from valid results of long-term studies on experimental animals (the results of studies of human exposure are not available or are inadequate). This factor is intended to account for the uncertainty involved in extrapolating from animal data to humans. Finally, an additional 10-fold factor is used when extrapolating from less than chronic results on experimental animals and there are no useful long-term human data [124].

When dealing with recycled sediments or soil health, and in the absence of specific data sufficient to support the setting of legislatively authorized standards, regulatory agencies use guidelines when setting regulations and policies. Their use is generally based on professional judgment. The Society of Environmental Toxicology and Chemistry (SETAC, offices in North America and Europe) recommended aquatic sediment management decisions should be based on site-specific information generated to evaluate the predictive ability of SQGs at a site of interest [43]. Sediment assessment frameworks for aquatic systems as for soil assessment frameworks, therefore, must be flexible for different management purposes. Policy makers must use their judgment to determine the greater good when dealing with recycled sediments because guidelines may not adequately account for the combined impact of various contaminants when they are present together, as opposed to situations involving only one type of contaminant [125]. While it is well recognized that the operational approach to environmental risk management strategies for sediments is to reduce the potential risk of contaminants, as total elimination of environmental risk from contaminants is typically not feasible or achievable, the lack of total risk elimination of contaminants from recovered sediments should not necessarily preclude the reuse and reincorporation of these sediments back on the landscape. Evaluations of potential risks from multiple contaminants can be evaluated, and potential concentration level limits can be developed to provide the desired level of protection that would allow these sediments to be safely reincorporated onto the landscape for beneficial uses.

As a matter of practicality, when only a TEL for an aquatic system is available, multiplying that number by an uncertainty factor of 10 will most likely approach a guideline derived for soil. If that number is associated with another uncertainty factor of 10, there is still a good safety factor for soil. While this approach would be technically sound for sediments from many waters, there will be a limited number of waters where the sediments might have to be classified as non-usable to avoid risks. However, the understanding of risk continues to evolve and numbers between a TEL and PEL are in a gray zone. Professional judgments will still be needed to interpret risk factors until better toxicological data are derived [122, 123, 124]. Whenever soil-based screening level guidances are available, they should be examined for use when considering land-based applications of dredged sediments. In the absence of such soil-based screening level guidances, then use the above stated TEL with uncertainty factor approach.

5. Research for successful sediment recycling

The implementation of sediment recycling programs such as Put the Land Back on the Land necessitates a continued comprehensive and multidisciplinary approach. To address the intricate challenges associated with sediment management, it is imperative to merge insights from diverse fields including environmental science, agriculture, engineering, and law. Such an approach will be needed to continue developing scalable, cost-effective, sediment removal technologies that can adapt to individual environmental systems.

Past research initiatives have focused on understanding the impact of sediment recycling on both soil environmental conditions and waterbody ecosystem, in addition to assessing potential benefits for plant production. The sediment excavation and reuse initiatives in Lake Mustijärv and the ongoing efforts in Lake Ormstrup emphasize the importance of merging limnology, agriculture, and engineering expertise [98, 99, 103, 104]. In addition, engineering research has contributed innovations such as the MuckVac™ system and the Genesis Rapid Dewatering System™ (RDS), streamlining the extraction and reuse processes. These technologies showcase the collaborative efforts of engineers and environmental scientists in creating efficient and sustainable sediment management tools. Moreover, efforts need to be made to address economic impacts. The economic loss due to the decline of land productivity (on-site effects) caused by water erosion is estimated at about 1.25 billion € per year in the EU [126]. Considering economic principles, agricultural advancements, and techniques for sediment removal provides a holistic perspective on Put the Land Back on the Land.

6. Conclusions

There are certain inevitabilities that all societies on earth will have to deal with regularly. Sediment erosion will continue and there will be a loss of organic topsoil and nutrients. Sedimentation will result in the shallowing of waterways, and eutrophication of aquatic systems will continue. Throughout the twentieth century, knowledge regarding how to mitigate these problems advanced considerably and improvements have been made. Techniques for removing sediments from waterways to support commercial and/or recreational uses advanced to the point where removed sediments can now be rapidly dewatered and the water returned to the targeted waterway safely. Beneficial uses for dredged material have also been identified, but continued education will become paramount for success [109].

Agriculture fulfills the vitally important public need for all nations in supplying abundant and affordable food and fiber. The loss of organic topsoil and the diminishing productivity of agricultural lands will, therefore, become the premier concern for many nations in the remainder of twenty-first century as food security IS national security.

American President Dwight D. Eisenhower [127] during his 1961 farewell speech spoke about the military-industrial complex and discussed the people’s expectation that political leaders must find essential agreement on issues of great moment, the wise resolution of which will better shape the future of a Nation. He also noted that all proposals must be weighed in the light of a broader consideration: the need to maintain balance in and among national programs—balance between the private and the public economy, balance between cost and hoped for advantage—balance between the clearly necessary and the comfortably desirable; balance between essential requirements as a nation and the duties imposed by the nation upon the individual; and balance between actions of the moment and the national welfare of the future. Good judgment seeks balance and progress; lack of it eventually finds imbalance and frustration. We submit the holistic Put the Land Back on the Land program meets these criteria and avoids the impulse to live only for today [128] without considering environmental sustainability for future generations.

Sufficient knowledge regarding the recycling of dredged materials now exists and in the words of American President Franklin Delano Roosevelt “We have nothing to fear but fear itself” [129]. The management goal for all dredged materials should, therefore, be to use removed material beneficially unless chemically unsuited to remain in the environment. The soil management philosophy of Keep the Land on the Land (i.e., soil conservation) has made important contributions to the worldwide conservation effort and needs to continue in the future. The Keep the Land on the Land management approach, however, failed to close an important environmental loop for nutrients, ultimately threatening environmental sustainability. Recycling aquatic sediments to agricultural lands is inevitable. The time is now that Nations should adopt and implement the Put the Land Back on the Land approach to foster sustainability and resiliency of both the aquatic and terrestrial resources that are imperatives to not only their individual national interests, but more broadly the collective Global Planetary interests that benefit all peoples.

Acknowledgments

We thank our past and present scientific and lake management colleagues for obtaining the vast amount of information needed to finally help us see the many linkages between the different scientific disciplines and environmental problems. We especially appreciate the multiple conversations regarding the issues discussed in this paper that led to the recognition Put the Land Back on the Land programs are a national imperative for all nations.

We thank Brian Dyson and Ken Forshay of the USEPA Office of Research and Development (ORD) and James Grundy of the USEPA Office of Land and Emergency Management (OLEM) for their critical review comments which helped improve this chapter. We also thank editor Andrew J. Manning for his editorial comments. Olga Tammeorg was supported by Maa- ja Vesitekniikan tuki ry (project nr 4644) and Estonian Research Council (grant PRG 1167).

Conflict of interest

The authors declare no conflict of interest. The views expressed in this chapter are those of the author(s) and do not necessarily represent the views or the policies of the USEPA. Any mention of trade names, manufacturers, or products does not imply an endorsement by the United States Government or the USEPA.