Clarity and colour

Water clarity (or transparency) is an indicator of how far light can penetrate through the water column[11] and is important for aquatic ecosystems, drinking water, aesthetics and recreational values. The ANZECC 2000 (Vol 1) identifies guideline values of water clarity for swimming or recreational use to provide confidence and safety and ensure obstructions and dangers can be seen. High levels of algae or sediment contribute to low clarity, reduce chlorine treatment effectiveness, increase pathogen risk and water treatment costs[7].

Water clarity can be assessed in a number of ways, including by Secchi depth, light attenuation, photosynthetically active radiation (PAR), euphotic depth (measured as depth at which 1% of surface PAR remains), and turbidity. Water clarity can impact water colour in numerous ways. Water colour is measured as either true colour or apparent colour[4].

As plants require light to grow and undertake photosynthesis, disruption to light availability can negatively impact aquatic plants, and the organisms that feed on them[3]. Water clarity determines the light available to benthic substrates, submerged plants and plankton.

Low nutrient, high water clarity conditions favour the dominance of macrophytes. Disturbance from elevated nutrients and/or turbidity resulting in low water clarity can shift a wetland to have turbid, nutrient rich water, which then favours phytoplankton[9][5]. Feedback mechanisms between low clarity, high nutrients and turbidity prevent regrowth of macrophytes.

Certain corals prefer clear water, while others have adapted to the low light conditions of turbid water. In marine environments with low water clarity, autotrophs such as corals may become dominated by taxa capable of heterotrophy, such as Goniopora and Turbinaria[2].

Reduced water clarity can indicate negative impacts of development and human activity on a waterbody. Water clarity may be reduced through excessive erosion and transport of sediment derived from land clearing, agricultural practices or construction activities. Erosion control in coastal catchments may contribute to health of coastal waters by preventing transport of suspended sediments to the coast, where they can impact seagrass, seaweed and corals through reducing light availability[1][6].

References

1. ^ Abal, E & Dennison, W (1996), 'Seagrass depth range and water quality in southern Moreton Bay, Queensland, Australia', Marine and Freshwater Research. [online], vol. 47, no. 6, p. 763. Available at: http://www.publish.csiro.au/?paper=MF9960763 [Accessed 12 September 2023].
2. ^ Anthony, KRN & Fabricius, KE (September 2000), 'Shifting roles of heterotrophy and autotrophy in coral energetics under varying turbidity', Journal of Experimental Marine Biology and Ecology. [online], vol. 252, no. 2, pp. 221-253. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0022098100002379 [Accessed 12 September 2023].
3. ^ ANZECC/ARMCANZ (2000), National Water Quality Management Strategy: Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand.
4. ^ Environment and Resource Management Department, BC (1997), Ambient Water Quality Criteria for Colour in British Columbia: Technical Appendix. [online] Available at: https://www2.gov.bc.ca/assets/gov/environment/air-land-water/water/waterquality/water-quality-guidelines/approved-wqgs/colour-tech.pdf.
5. ^ Hilt, S, Brothers, S, Jeppesen, E, Veraart, AJ & Kosten, S (1 October 2017), 'Translating Regime Shifts in Shallow Lakes into Changes in Ecosystem Functions and Services', BioScience. [online], vol. 67, no. 10, pp. 928-936. Available at: http://academic.oup.com/bioscience/article/67/10/928/4210695/Translating-Regime-Shifts-in-Shallow-Lakes-into [Accessed 12 September 2023].
6. ^ Lambert, V, Bainbridge, ZT, Collier, C, Lewis, SE, Adams, MP, Carter, A, Saunders, MI, Brodie, J, Turner, RDR, Rasheed, MA & O'Brien, KR (August 2021), 'Connecting targets for catchment sediment loads to ecological outcomes for seagrass using multiple lines of evidence', Marine Pollution Bulletin. [online], vol. 169, p. 112494. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0025326X21005282 [Accessed 12 September 2023].
7. ^ National Health and Medical Research Council (2011), AUSTRALIAN DRINKING WATER GUIDELINES 6. [online], Commonwealth of Australia. Available at: https://www.nhmrc.gov.au/about-us/publications/australian-drinking-water-guidelines#block-views-block-file-attachments-content-block-1.
8. ^ Queensland Museum (2022), Wetlands of Queensland Book, p. 437, Queensland Museum, Brisbane, Queensland.
9. ^ Scheffer, M (2004), 'Ecology of shallow lakes', Population and community biology series, p. 374, Springer-Science+Business Media, Dordrecht.
10. ^ Turbidity and Water | U.S. Geological Survey. [online] Available at: https://www.usgs.gov/special-topics/water-science-school/science/turbidity-and-water [Accessed 23 October 2023].
11. ^ a b US EPA, OW (10 January 2014), Indicators: Water Clarity. [online] Available at: https://www.epa.gov/national-aquatic-resource-surveys/indicators-water-clarity [Accessed 11 September 2023].

Last updated: 11 September 2023