Glossary Q – R

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Q

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Quartz

A highly resilient mineral based on silica (SiO2). More information

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R

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Radioisotope dating

It is possible to identify changes in sedimentation rates, as well as the timing of key historical events, in coastal lake or estuary catchments through measurement of radio-active isotopes. Of these, analysis of lead-210 (²¹⁰Pb) is the only method capable of providing high-resolution ages for sediments over the last 150 to 200 years. It is thus an ideal technique for those investigating post-colonial anthropogenic impacts in Australia.

Lead-210, which is part of the uranium-238 (²³⁸U) decay series, is absorbed onto sediment particles deposited in lakes and estuaries. It consists of both supported and unsupported components. The former refers to that component which is in equilibrium with all members of the decay chain which precede it. It is derived from the in situ decay of radium-226 (226Ra) that has been directly washed into the system as part of eroded material (Figure 1). Unsupported 210Pb is derived from radon-222 (²²²Rn) which diffuses as gas through the soil interstitial pore space into the atmosphere, where it rapidly decays to 210Pb. The ²¹⁰Pb then attaches to aerosol particles and settles out of the atmosphere as dry fallout or is washed out in rainfall events. This 'unsupported' ²¹⁰Pb can fall directly onto the lake sediments or be washed in at a later time from elsewhere in the catchment (see Figure 1). In either event, once deposited and incorporated in the sediment, the activity of unsupported 210Pb will be solely a function of the amount present initially and its half-life (half-life = 22.6 year). Thus, a ²¹⁰Pb-chronology can be determined for a sediment core by measuring the down-core activities of unsupported ²¹⁰Pb and comparing these with that measured for the modern sediments at the top of the core. The activity of supported 210Pb can be determined indirectly by measuring the activity of ²²⁶Ra using either alpha or gamma spectrometry. Unsupported 210Pb cannot be measured directly and so is inferred from the activity of total ²¹⁰Pb minus the activity of supported 210Pb. The activity of total 210Pb can be determined by either measuring ²¹⁰Pb directly using gamma spectrometry or measuring (using alpha spectrometry) the progeny ²¹⁰Po with which it is assumed to be in secular equilibrium.

Figure 1. Pathways by which ²¹⁰Pb reaches aquatic sediments (after Oldfield and Appleby, 1984) [1].

1. Oldfield, F., Appleby, P.G., 1984. Empirical testing of 210Pb-dating models for lake sediments. In: Hayworth EY and Lund JWG (Eds). Lake Sediments and Environmental History. Leicester University Press, 93-124.

Authors

Kate Harle, CSIRO
Henk Heijnis, ANSTO

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Redfield Ratio

The 'Redfield ratio' or 'Redfield stoichiometry' refers to the molar ratio of carbon (C), nitrogen (N) and phosphorus (P) in phytoplankton (principally diatoms). When nutrients are not limiting, most phytoplankton has the following molar ratio of elements:

C:N:P = 106: 16: 1

1. Redfield, A.C., Ketchum, B.H., and Richards, F.A. (1963). The influence of organisms on the composition of seawater. In The Sea, Vol. 2, (Ed. M.N. Hill), pp 26-79. (Wiley Interscience: New York).

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Redox Potential (Eh)

The redox potential, Eh, is the energy gained by transferring 1 mole of electrons from an oxidant to H₂. It is measured in volts relative to a hydrogen electrode which is at zero. Eh can be calculated from the Nernst equation:

Eh = E^o - RT/nF ln [products]/[reactants]

Where:
E^o is the standard potential of the redox reaction in volts;
R is the gas constant (8.3 x 10^-3) kJ K^-1;
T is the temperature measured in Kelvins (K);
F is Faraday's Constant (96.5 kJ V^-1);
n is the number of electrons in half reaction; and
[ ] is the activity of products and reactants.

It is negative in a reducing medium and positive in an oxidizing medium. EH and pE are related by the following:

pE = nF/2.303RT * Eh

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Regional Marine Planning Areas

At the core of the Oceans Policy is the development of Regional Marine Plans for large marine ecosystems or "Regional Planning Areas". These regions include: South-east, South-west, North-west, north and east. The profiles for these regions will set out the objectives for subsequent work to identify a network of Marine Protected Areas. More information

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Report Cards

Report cards rate the overall condition of marine and estuarine areas (or other), as well as aspects of habitat extent and quality. They generally represent the culmination of twelve months of scientific monitoring at sites within a specified jurisdiction.

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Residence Time

The average time a hypothetical particle of water spends in solution between the time it first enters and the time it is removed from a coastal waterway.

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Resolution

A measure of the closest distance between two unique identifiable features or the size of the smallest feature that can be mapped or sampled [1,2]. It is often divided into three subcategories:

• Observational resolution: the size of the smallest feature that can be mapped or sampled (also known as Ground Resolution Unit (GRU) or Minimum Discernable Unit (MDU)).
• Representational resolution: the smallest object that can be shown in a map/data layer (also known as the Minimum Mapping Unit (MMU))
• Management resolution: the smallest unit of relevance to a given management consideration (e.g. a biotopeor a microcommunity).

1. Burrough, P. A. and R. A. McDonnell (1998). Principles of Geographical Information Systems. Oxford University Press.
2. Delaney, J. and K. Van Neil (2007). Geographical Information Systems - An Introduction. Melbourne, Oxford University Press.

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Resuspension

Resuspension of bed sediments is the process by which currents and turbulence dislodge settled particles and mix them back into the water column. Fine sediments in the bed tend to stick together due to electrostatic forces. This cohesiveness is a property of the sediment mineralogy and also whether the sediment surface is covered by biogenic films or not. Such cohesive sediments may not resuspend until a critical flow speed is exceeded, which may be much higher than for coarser particles. In typical model formulations of the resuspension process, resuspension rates scale as the square of the flow speed so that doubling of flow speeds would quadruple resuspension rates.

Figure 1. Conceptual illustration of the resuspension process (modified after illustration in [1])

1. Webster, I.T., Ford, P.W., Robson, B., Margvelashvili, N., and Parslow, J.S. 2003. Conceptual Models of the Hydrodynamics, Fine-Sediment Dynamics, Biogeochemistry, and Primary Production in the Fitzroy Estuary. Cooperative Research Centre for Coastal Zone, Estuary & Waterway Management Technical Report #8.

Contributor

Ian Webster, CSIRO Land & Water

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Riparian Zone

The riparian zone is the vegetated corridor along streams and rivers. It serves a number of important functions that bear consideration in terms of farm management. The riparian zone:

• acts as a trap for sediments and nutrients heading from hill-slopes to streams, improving stream water quality;
• shades streams, lowering water temperature and altering food sources by preventing the growth of algae. This special environment is home to specifically adapted animals, which are lost following vegetation clearance;
• protects stream banks from collapse and trampling by stock, thus reducing streambank erosion and allowing for a diversity of bank habitats to form, e.g. bank overhangs favoured by the platypus;
• provides a source of litter and snags to channels, which form critical habitat to stream animals, e.g. Murray cod;
• provides food for terrestrial animals, especially in arid areas, and aquatic animals, particularly in small streams;
• provides habitat for birds, mammals and reptiles that live along the river; and
• hosts a number of interesting plants that have intrinsic value.

Photo 1. Riparian vegetation along Jacqua Creek in Windellama, NSW. (photo courtesy of Upper Shoalhaven Landcare Council)

For more information about the functions and management of the riparian zone, see the Riparian Land Management Technical Guidelines published by the Land and Water Resources Research and Development Corporation, now Land and Water Australia (LWA) in 1999. This comes in two volumes, one on the principals of riparian zone management and relevant legislation, and the second on management tools and techniques. To order a copy, visit the Land and Water Australia website. The rivers through forests parameter is the proposed indicator for riparian zone condition.

Author

Ralph Ogden, CSIRO Land and Water

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Risk

"Is a combination of the vulnerability of the system and the intensity of the pressure (stressor) on, a system - a highly vulnerable system exposed to a high level of pressure is considered at high risk." [1]

1. Moss A, Cox M, Scheltinga D, Rissik D (2006) 'Integrated estuary assessment framework.' Published by the Cooperative Research Centre for Coastal Zone, Estuary and Waterway Management (Coastal CRC), Indooroopilly Qld.

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Rocky reefs

Rocky reefs feature a hard substrate that may occur at supra-tidal to sub-tidal elevations. Surfaces are generally non-depositional and sometimes erosional, and are usually dominated by epifaunal and algal communities. More information

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