Carbon storage in river and floodplain systems: A review of evidence to update and inform policy development for riverine nature based solutions

[Geoengineering News]

https://eprints.soton.ac.uk/479906/ Carbon storage in river and floodplain systems: A review of evidence to update and inform policy development for riverine nature based solutions Citation: Sear, David, Speck, Imogen and Pears, Benjamin (2023) Carbon storage in river and floodplain systems: A review of evidence to update and inform policy development for riverine nature based solutions University of Southampton 39pp. (doi:10.5258/SOTON/P1124). 02 August 2023 Record type: (Project Report) Abstract The threat of climate change is increasingly motivating goals that seek to achieve net zero emissions in the next few decades (Rutter and Sasse, 2022). In the UK, net zero is a statutory requirement that must be met by 2050 (Gregg et al., 2021). An important element of this strategy is determining how nature can contribute to achieving Net zero – largely via carbon sequestration and storage (Gregg et al., 2021). The degradation of many natural systems has impacted natural carbon stores and so the role of nature-based solutions is increasingly being implemented with the beneficial aims of both increasing biodiversity as well as supporting climate change mitigation (Gregg et al., 2021). Decomposition and combustion of organic material releases CO2 to the atmosphere, while accumulation of biomass and soil organic carbon (SOC) sequesters CO2 (Hoffmann 2021). Wetlands such as peatlands, swamps, marshes, estuaries and floodplains provide optimal conditions for the sequestration and long-term storage of carbon although the precise timing of storage will depend on erosional (turnover) time of the specific habitat/system. Low oxygen concentrations support anaerobic conditions that reduce decomposition, whilst overbank sedimentation buries organic matter protecting it from further decomposition. On floodplains, the high clay content of deposits provide sites for chemical bonding with organic matter further reducing loss of carbon through decomposition and gaseous emission (Hoffman 2021). Research to date all points towards a substantial role for rivers and floodplains in the global carbon cycle (Whol and Knox 2022, Hoffman, 2021). An increasingly expanding literature consistently demonstrates that riparian ecosystems and floodplains can store a significantly larger amount of carbon per area compared to surrounding land (Suftin et al., 2016; Whol and Knox 2022). Floodplains cover 0.5–1% of the global land area but have been suggested to account for a range of 0.5–8% of global SOC storage. River networks contain significant portions of terrestrial C with greatest retention occurring in floodplain riparian ecosystems D’Elia et al (2017). Although, there is a large range of estimated values of OC in watersheds (0.5 to 1.5 Pg (Aufdenkampe et al., 2011) and 0.9 Pg (Regnier et al., 2013)), some estimates in mountainous headwater streams in the USA, indicate that riparian areas including floodplains may store about 25% of the total OC while occupying less than 1% of watershed area (Wohl et al., 2012). Sutfin et al., (2016) reported 22% of carbon entering headwater streams is unaccounted for after quantifying delivery to oceans or losses to outgassing as carbon dioxide (CO2), suggesting there is a substantial reservoir of carbon in riparian systems derived from sediment deposition. The role of rivers in carbon sequestration has often been interpreted as a conduit between terrestrial and marine carbon stores (Gregg et al., 2021). Carbon can be stored in the floodplain in many forms including above ground vegetation (Dyabla et al., 2019), and soil (Wohl et al., 2017), as well as within the river channel as large, drowned wood and vegetation (Hinshaw & Wohl, 2021). Much of the evidence remains focussed on above ground biomass and the first metre of soil (D’Elia et al., 2017). However, it is argued in Young et al., (2019) that recent carbon accumulation rates in surface peat can be misinterpreted in relation to carbon storage. It suggests that surface/topsoil peat measurements do not account for the future ability to be decomposed/lost in comparison to deeper long-term stores. This suggests that although there may be peat/organic matter present in topsoil this may not necessarily translate into long term carbon sequestration. A need for deeper sediment cores and paleoenvironmental analysis to present the natural state of UK rivers is identified across the literature (D’Elia et al., 2017; Quine et al., 2022), however, is not yet widely implemented, although the current Natural England led project to develop a national peat map is aiming to rectify this omission. The quantification of carbon stored in floodplains and the potential for restoration to increase this remains poorly understood (Hinshaw & Wohl, 2021; Hofmann 2021). To be able to quantify carbon storage it requires understanding how much is buried (storage quantity), over what timescales (storage period), and what processes are associated with carbon burial and storage. These factors are addressed in this report to better understand carbon storage in UK floodplains and whether current restoration is effective at increasing this. Text Carbon in Floodplains Report 2023 - Version of Record Available under License Creative Commons Attribution Non-commercial. Download (2MB) Source: University of Southampton

[Michael Hayes]

[...] River restoration efforts include large wood addition to the river as well as replanting of trees in the 

riparian zone (Dybala et al., 2019; Lininger et al., 2021). This can act as an addition of another carbon 

store as well as influencing other processes such as overbank flooding increasing floodplain carbon 

storage and sedimentation rates (Lininger et al., 2021). Log jams can promote formation of multiple 

channels and complexity and smaller channel log jams can lead to abandonment of secondary 

channels and infilling of organic material (Sear er al., 2010; Lininger et al., 2021). Large wood can 

interact directly with particulate organic matter by creating depositional sites for particulate organic, 

which can also influence hydraulic influence the porosity of large wood (Lininger et al., 2021). Large 

wood can be added in channel by human activity as part of restoration process, but also transported 

from trees in the riparian zone particularly during flood events (Zischg et al., 2018; Lininger et al., 

2021). Floodplain large wood is likely to have a longer residence time particularly within areas that are 

highly productive but with reduced decay rates [...]

MH] The method of putting 'root ball trees', or logs that still have their root balls attached, into mountain streams has been used in the Mt Baker water shed area for around a decade, and the method has proven to be remarkable at improving a wide range of environmental systems within the broader riverine system.

I would recommend using Biochar in areas of accumulation in the streams and lakes as the downstream ecosystem will use any runnof of the Biochar. The MRV numbers at a full riparian scale would likely be soft as there are such a large spectrum of possible outcomes for the C, yet production of the biochar itself can supply rather firm MRV numbers to help economical support this form of C management within catchment areas.

Dumping Biochar into Hydroelectric dam intakes to start a heavy Biochar loading of a river system is interesting to think about, yet the dam owners would need to be convinced that the Biochar would do no damage to their turbines, Biochar likely will not. Furthermore, the lakes created by the dams can also likely use a thick layer of Biochar on their floor to help mitigate the CH4 generated by the artificial lakes.

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[Tom Goreau]

River floodplain sediments store enormous amounts of organic carbon.

 

We have been systematically destroying those resources everywhere.

 

Right here where I write these lines in Massachusetts, colonial americans dynamited the beaver dams to dry out land for farms, flushing ten thousand years of stored carbon down the Merrimack River to the Sea.

 

If we regenerate wetlands we will turn river valleys from global CO2 sources into sinks.

 

https://eprints.soton.ac.uk/479906/

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[Michael Hayes]

Tom, et al.,

Some riverine networks could use Biorock enhanced HDPE pipeline systems embedded in, under, or beside river courses as filters, hatcheries, and as renewable resources collection/management systems. 

Carbon, in the form of Biochar and a graphite coated sand¹, can filter most contaminates in the water. Biochar is rather good at collecting riverine nutrients. Growing biomass within the engineered riverine pipeline system can supply the needed C and meet CDR needs to some degree if scaled up. Scaling up, even installing scaled down riverine CDR prototypes along limited river runs, is more of a jurisdictional governance issue than a technical question.

However, getting roughly the same engineering done offshore, beyond national jurisdictions, would allow jurisdictions within any particular riverine system to rather quickly gain confidence that the tech package is worth supporting in their own jurisdictions. 

Biorock and Biochar can be key technologies as the use of each can be in both freshwater and saltwater. Biorock produced offshore in saltwater can be used within the upper riverine space as a replacement for the cement needed in such a complex engineering project. Freshwater use of Biorock ends the self repair aspect of Biorock in saltwater, yet it's still highly useful. Moreover, moving lots of Biorock upriver, at a CDR scale, would transport oceanic calcium upriver where it is needed in the riverine network as a pH buffer. 

1) https://pubs.aip.org/physicstoday/online/16037/Graphite-coated-sand-could-clean-up-dirty-drinking

Best regards

[Tom Goreau]

Fully agreed.

 

Biorock materials in freshwater environments become CO2 sinks by slow dissolution.

 

Biochar traps nutrients lost from land, and turns them into valuable fertilizer to recycle on land, instead of polluting the sea, causing eutrophication of coasts and spreading dead zones.

 

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[Dennis Amoroso]

Excellent point.

At Advanced Materials Processing Inc. we are currently working with the state governments of Nevada, Colorado, Kentucky, Ohio and partner companies in Florida and North Dakota.  They have all asked us to build production facilities to produce our NON chemical rock powder/biomass and biochar blend fertilizer for their agricultural industries.  In Dakota, Florida, California, and Colorado, the local investor community has come to us with proposals of capital funding.  This is primarily because we REMOVE the chemical farm runoff from the streams and water table as well as increase the yield in the crops and save a documented 30% of the water consumption of agriculture.  We also remove millions of tons of Methane, Nitrous Oxide, and CO2 because of the decomposition of the rock powder in the farmland.  Including our home state of California, we will be delivering to more than 100 million acres of farmland.

We stop the problem at its source: chemical farm runoff is destroying the ecosystems of our planet.

Dennis Amoroso President and Chairman

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[Michael Hayes]

A Biorock armored riverine raft of water flow filters, which use the Biochar/super sand filters, can possibly send lost ag nutrients in the river back to the local fields as an enhanced Biochar/fertilizer package. Adding oceanic calcium via Biorock to the mix, in total, would represent a high value input to local farmers. The 'Delivery at the dock' cost to the farmers can be rather low if the system gains C credits.

Working out the MRV numbers will be complex, yet both Biorock and Biochar communities can defend the CDR values of their respective fields in such a system of systems engineering valuation challange.

An important advantage of scaling down the first effort to a riverine scale is that the first prototypes can be toured up and down rivers as an educational aid to help build support for broader riverine and marine CDR work.

[Michael Hayes]

Dennis, et al.,

Very well said. My apologies for omitting rock dust to the riverine dock side delivery mix. Beneficial microbes can also be included into the mix.

As a side note on dock side deliveries, I recommend the dock be equipped with small plasma pyrolysis plants for:

1) Dewatering of biomass/Biochar production.

2) Reduction of trash to commercial gasses and an inert gravel that can take the place of sand for making graphite coated sand.

3) The 'super sand' collects many heavy metals and even pharmaceutical compounds. Once the super sand is fully bound up with such contaminates, running it through the dock side plasma pyrolysis unit will generate more substrate material for a fresh graphite surface.

The first Biorock enhanced hulls can be made along any coastal dock, the additional equipment assembled and installed in a rather simple way, there is no practical technical limiting factor for creating the first riverine CDR rafts. Getting jurisdictional permission to deploy a system is the primary limiting factor. 

Best regards