Substrate consolidation

Substrates can be either hard (consolidated), consist of fragmented material (unconsolidated) or intermediate (for example coffee rock and beach rock). Consolidated substrates break down into unconsolidated sediments and over geological time are reconstituted into consolidated substrates again – see the Rock Cycle[3]. Substrate grain size, Substrate composition and Geology/lithology are important factors in describing substrate consolidation.

Consolidation is independent of terrain but shapes terrain morphology. Being more enduring, consolidated areas are usually the more resistant peaks and ridges while more mobile unconsolidated material is transported by currents, carried through channels and settles into depressions (deposition). Terrain roughness is influenced by consolidated substrates, their geology, and factors influencing the roughness of unconsolidated substrates include geomorphological processes (e.g. waves, transport and deposition etc.) and substrate grain size.

While consolidation is independent from substrate composition, there is variation in substrate consolidation that is influenced by its composition, including:

• Voids - gaps between particles of unconsolidated substrates or splits in consolidated substrate - detailed further in substrate grain size
• Layering – detailed further in substrate grain size
• Colour – detailed further in substrate composition
• Compaction – the accumulated weight of unconsolidated sediments on the sediments below. The spacing between sediment particles due to compaction reduces so that particles repack into tighter arrangements. Moisture content may also influence compaction. Subsurface sediment compaction is important for infauna taxa which burrow to different depths within the substrate depending on its moisture and compaction[5].
• Naturalness – Urbanisation, transport networks, infrastructure and agricultural practices include activities that alter substrate consolidation. All these changes have an impact on the biota – for example house blocks, concrete paths, roads, carparks and boat ramps increase water runoff and decrease infiltration into the groundwater – changing the freshwater flow regime.

Rocky headlands, coral reefs and rocky reefs are all examples of highly valued consolidated substrates. Consolidated reef substrates are hotspots of marine biodiversity and important fish habitats[6].

Consolidation influences basic physical, chemical and biological wetland function at all scales, for example:

• Consolidation shapes hydrodynamics (how water moves, current flows, eddies etc.), by providing a resistant surface with friction that water particles must overcome to flow around, reflect against or refract. Consolidated substrates form a barrier to water infiltration (aquitards).
• Consolidated substrates provide an anchoring point for animals and plants, and refugia for hiding. Reefs are consolidated substrates that provide diverse habitat for animals (e.g. fish) and plants, however the type of reef is defined by its substrate composition (e.g. a coral reef is composed of carbonate, while a rocky reef is terrigenous i.e. from the land).
• Unconsolidated sediments are subject to water infiltration, flow and chemical soil-forming processes, regulating/slowing down water flow and are critical for maintaining groundwater reservoirs and groundwater processes (see groundwater dependent ecosystems).
• Unconsolidated substrates support important wetland food webs and nursery habitats by providing a burrowing space for animals, and a secure substrate for plant roots to source nutrients and water. For example, shorebirds and fish feed on macroinvertebrates in unconsolidated substrates and dugong and turtles graze on seagrass meadows found on unconsolidated substrates.

Natural patterns of consolidated and unconsolidated substrates support natural wetland hydrology and biota, however, human activities have modified many of these natural patterns and processes and the services they deliver. Characterising the substrate and surrounding habitats is best practice prior to designing interventions that aim to rehabilitate habitats[1]. Water modellers use areas of consolidation to model water flows and runoff models needed for water-sensitive urban design. Opportunities to modify consolidation in wetland catchments include water-sensitive urban design features such as ‘re-wilding’ urban waterways, changing concrete drains back to natural vegetated stream banks, encouraging wetland biota to return[2].

Artificial reefs are consolidated substrates established as fish aggregation devices that are prohibited in the Great Barrier Reef Marine Park. Previously oysters grew on a variety of consolidated and unconsolidated substrates, were over-harvested and died from disease. Shellfish reef restoration projects aim to create artificial shell structures for the potential settlement of oyster larvae[4].

Links

Substrate consolidation (Intertial and Subtidal)

References

1. ^ Gillies, CL, McLeod, IM, Alleway, HK, Cook, P, Crawford, C, Creighton, C, Diggles, B, Ford, J, Hamer, P, Heller-Wagner, G, Lebrault, E, Le Port, A, Russell, K, Sheaves, M & Warnock, B (14 February 2018), 'Australian shellfish ecosystems: Past distribution, current status and future direction', PLOS ONE. [online], vol. 13, no. 2, p. e0190914, ed. L D Coen. Available at: https://dx.plos.org/10.1371/journal.pone.0190914 [Accessed 25 March 2019].
2. ^ Government of Netherlands (14 February 2023), 'Going with the flow - Why rewilding waterways is the way ahead', Valuing Water Initiative. [online] Available at: https://valuingwaterinitiative.org/going-with-the-flow-why-rewilding-waterways-is-the-way-ahead/ [Accessed 19 September 2023].
3. ^ a b Nichols, G (2009), Sedimentology and stratigraphy, John Wiley & Sons.
4. ^ (28 August 2023). 'Ozfish Projects'. [online] Available at: https://ozfish.org.au/projects/moreton-bay-shellfish-reef-restoration/ [Accessed 19 September 2023].
5. ^ Shinoda, A, Fujiwara, S, Niiya, H & Katsuragi, H (2019), 'Physical constraints on sand crab burrows: Mechanical properties of wet sand explain the size and spatial distributions of burrows on beaches', PLOS ONE. [online], vol. 14, no. 5, p. e0215743, ed. G J Vermeij. Available at: https://dx.plos.org/10.1371/journal.pone.0215743 [Accessed 16 September 2021].
6. ^ Stuart-Smith, RD, Edgar, GJ, Barrett, NS, Bates, AE, Baker, SC, Bax, NJ, Becerro, MA, Berkhout, J, Blanchard, JL, Brock, DJ, Clark, GF, Cooper, AT, Davis, TR, Day, PB, Duffy, JE, Holmes, TH, Howe, SA, Jordan, A, Kininmonth, S, Knott, NA, Lefcheck, JS, Ling, SD, Parr, A, Strain, E, Sweatman, H & Thomson, R (February 2017), 'Assessing National Biodiversity Trends for Rocky and Coral Reefs through the Integration of Citizen Science and Scientific Monitoring Programs', BioScience. [online], vol. 67, no. 2, pp. 134-146. Available at: https://academic.oup.com/bioscience/article-lookup/doi/10.1093/biosci/biw180 [Accessed 19 September 2023].

Last updated: 10 May 2023