Substrate (including geology and soils)

In wetland and aquatic ecology, substrate includes the sediment, soil, bedrock and other material, either biotic or abiotic, that comprises the floor or bed of the sea, a lake, river or wetland[4].

Substrate is important for animals, plants, ecosystems and people in many different ways. For animals and plants, the substrate is a secure living space for attachment and shelter, providing a refuge from predators, extremes of temperature, wind and water, a food source, and a source of nutrients and freshwater.

Substrates are important for many key ecosystem processes, providing a foundation for living ecosystems, regulating groundwater and surface water interactions, tidal pumping and chemical exchange between the land and the sea, soil formation and nutrient processing. Substrates also deliver services that people value, such as filtering water, buffering coastlines from weather and wave energy, providing building materials, providing sandy beaches and rocky headlands for recreation and aesthetic values, islands, beaches and tidal flats, and are an essential part of areas of spiritual and cultural significance.

Quick facts

Darker consolidated substrates

reach higher temperatures and retain heat longer than lighter coloured substrates.[2]

Physical characteristics of substrate

Characteristics of the substrate include:

• Geology /Lithology - the mineral composition and properties of substrates
• Substrate composition - the source characteristics and composition of the non-living substrate
• Consolidation - whether it is consolidated (rocky) or not – for biota living space
• Substrate grain size - the grain size of substrates that consist of fragments (unconsolidated) usually occurring in mixtures of different grain sizes termed 'sediment texture'

Substrates are subject to change or variability. Geological, geomorphological and physical processes (e.g. compaction) play an important role in substrate consolidation and substrate grain size, and chemical processes (e.g. certain geological or soil-forming processes) influence substrate composition and lithology. For more information about these processes, see the rock cycle and geology/lithology.

Some variable properties that apply to substrates include:

• Voids - the gaps or interstitial spaces between unconsolidated substrate particles, important for permeability and infiltration and providing a living space for interstitial animals and plants
• Layering (e.g. sand over clay, over rock etc.) - influences how water infiltrates into or flows through the substrate (see groundwater).
• Colour - reflects the chemical content of the substrate and influences how much heat is retained in the substrate and its wetness. Colour can be an indicator of a chemical process or mineral content of the substrate.
• Compaction - if substrate particles are tightly packed against each other animals find it difficult to burrow into the substrate.
• Naturalness - humans change the substrate, by removing, replacing or depositing substrates with different characteristics (e.g. consolidation, grain size, composition) from their natural state, or by installing artificial substrates (e.g. metal, concrete). This can result in changes in physical and chemical processes including water movement and hydrodynamics, sediment transport and deposition and soil forming processes. Properties of the substrate that provide suitable conditions for plant and animals are altered, affecting the services a substrate may provide, and the way people value the substrate.

Chemical characteristics of substrate

Nutrients and other chemical compounds such as carbon, nitrogen, phosphourus, oxygen, iron and potassium exist in substrate such as soils and sediment. Chemical compounds in substrates may change due to weathering, and some elements are insoluble. The presence of chemicals can affect the erositivity and productivity of the substrate. Mineral and chemical composition of substrate strongly influences the type of soil that can develop. Salinity can be natural in soils and can be linked to soil degradation, including soil erosion.

Chemical processes include dissolution, chemical precipitation/cementation, recrystallization, or formation of concretions or nodules. An example of a chemical process in sediments is induration, which involves dissolution and precipitation. Dissolved iron and aluminium oxides percolate through the soil layers and solidifies as an indurated layer during deep weathering processes such as laterisation. Cementation results when crystals grow within the pore spaces of sediments. Cementation of unconsolidated substrates can be irregular, such as nodules or concretions, or form regular bands of rock of intermediate consolidation such as beach rock or coffee rock.

Carbon

Substrates (particularly soils and sediments) can store, cycle and emit different forms of carbon as part of the carbon cycle. Soils store more carbon than the atmosphere and plants combined[5][1][3]. Wetland soils are characterised by having high levels of carbon, and can form peats in certain circumstances.

Organic carbon in soils is comprimsed of decaying plant matter, soil organisms and microbes. Inorganic carbon is mineral based (such as calcium carbonate). Carbon and organic matter in soil provides energy and nutrient storage. Soils are better able to hold water with more organic material and resist acidification[5], by increasing pH buffering capacity. Organic carbon supports soil structure by binding particles into aggregates, increases water infiltration and prevents losses of nutrients.

Soil cultivation and soil degradation can impact organic carbon levels, by disturbing the soil and removal of plant residue.

More information and links:

Carbon processes and cycle - WetlandInfo

Wetlands and the carbon cycle - WetlandInfo

Soil carbon - Queensland Government

Soil carbon sequestration - NSW Department of Primary Industries

Carbon cycle and budgets - State of the Environment

Soil Organic Matter- Department of Natural Resources and Environment Tasmania

Nitrogen

Nitrogen in sediment and soil is crucial for their health and productivity. Nitrogen can accumulate via sediment into wetlands, can be stored in organic matter (immobilisation) and undergo processes where it is transformed into other nitrogen compounds which plants and bacteria can use.

Storage of nitrogen is important as it contributes to soil health and productivity of plants (such as mangroves). Nitrous oxide (N₂O) is a greenhouse gas that is released from soils in repsonse to weather events, changes in soil (due to land use) or released through denitrification.

Comprehensive information on Nitrogen processes and forms is available here and in The Nitrogen Books.

Pages under this section

References

1. ^ Carbon | Australia state of the environment 2021. [online] Available at: https://soe.dcceew.gov.au/land/environment/carbon [Accessed 8 September 2023].
2. ^ Janetzki, N, Benkendorff, K & Fairweather, PG (26 January 2021), 'Rocks of different mineralogy show different temperature characteristics: implications for biodiversity on rocky seashores', PeerJ. [online], vol. 9, p. e10712. Available at: https://peerj.com/articles/10712 [Accessed 19 July 2021].
3. ^ NSW, , AGLSTERMSAA & corporateName=DPI (1 July 2021), Soil carbon sequestration. [online] Available at: https://www.dpi.nsw.gov.au/dpi/climate/Carbon-and-emissions/carbon-opportunities/soil-carbon-sequestration [Accessed 8 September 2023].
4. ^ Queensland Museum & Griffiths, M (2022), Wetlands of Queensland Book, p. 437, Queensland Museum, Brisbane, Queensland, eds. B Mitchell & R Ridgway.
5. ^ a b Queensland, , AU & o=The State of, Soil carbon | Soil properties. [online] Available at: https://www.qld.gov.au/environment/land/management/soil/soil-properties/carbon [Accessed 7 September 2023].

Last updated: 6 September 2023