Glossary S – T

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S

The Saffir-Simpson Hurricane Scale

The Saffir-Simpson Hurricane Scale rates a hurricane's present intensity on a scale from 1-5. This scale is used to provide an estimate of the potential flooding and property damage that may be expected from a cyclone. Wind speed is the determining factor in the scale

Saline intrusion

Saline intrusion is the influx of sea water into an area that is not normally exposed to high salinity levels. More information

Salinity

Salinity is the mass fraction of salts in water. More information

Saltflats

Saltflats, or saline supratidal mudflat facies, occur in dry evaporative environments (often in the tropics) that undergo infrequent tidal inundation. More information

Saltmarsh

A coastal saltmarsh is a community of plants and animals that grow along the upper-intertidal zone of coastal waterways. More information

Salt-wedge

An intrusion of sea water into a coastal waterway in the form of a wedge along the seabed. The lighter fresh water from riverine sources overrides the denser salt water

Sand

Grains with diameters between 0.06 mm to 2 mm. Sand is commonly divided into five sub-categories: very fine sand (0.0625 mm - 0.105 mm), fine sand (0.125 mm - 0.21 mm), medium sand (0.25 mm - 0.42 mm), coarse sand (0.5 mm - 0.84 mm), and very coarse sand (1 mm - 1.68mm).

Satellite remote sensing

Satellite remote sensing is the collection of information about the earth's surface using sensors mounted to satellites.

Seagrass

Marine flowering plants which generally attach to the substrate with roots. See more information in Seagrass Species and Changes in Seagrass Areas.

Seawater intrusion

Seawater intrusion is the influx of sea water into an area that is not normally exposed to high salinity levels. More information

Secchi depth

Secchi depth is assessed by lowering a black and white circular plate (Secchi disk) into the water column. It is a two-way vertical attenuation reading in the respect that light travels to the disk and back up again to the observer. The depth at which the disk is no longer visible is called the Secchi depth. More information

Sediments assessment scheme

Background

An initial qualitative condition assessment of the 970 estuaries on the seaboard of Australia was completed during the National Land and Water Resources Audit based on observable human impact to catchments and waterways. The next stage will be to gather environmental data for modified estuaries. Since 1996, The Environmental Geology Group at the University of Sydney has been undertaking a systematic contaminant study of sediments in estuaries, lagoons and coastal lakes of New South Wales (NSW). Sediments in 30 of the largest and most contaminated 130 estuaries in NSW have been investigated. Strict conformity in field and laboratory techniques have resulted in a large, comparable, GIS-based data set of over 4000 estuarine sediments analysed for a suite of metals. A smaller number of other toxicants (e.g. organochlorine pesticide, polycyclic aromatic hydrocarbon, polybiphenol) and nutrient analyses have also been undertaken in the more important waterbodies. The most contaminated parts of estuaries in the Sydney region have been tested for sediment toxicity using a raft of ecotoxicological tools.

Sediments are being used in this assessment in preference to water and the scheme adopted in this regional investigation is outlined below.

Use of Sediments in Marine Environmental Assessments

Sediments are being used to monitor these coastal environments because sediments faithfully record and time-integrate the environmental status of an aquatic system. Contaminant concentrations are high in sediments, and thus they are easily, cheaply and accurately analysed. Sediments can be an important secondary source of pollutants, and because they integrate contaminants over time, sediments provide useful spatial and temporal information. Sediment quality influences the nature of overlying and interstitial waters through physical, chemical and biological processes. Because sediments play a major role in the transport and storage of contaminants, they are important in identification of contaminant sources and determining dispersion pathways. Sediments also provide an important habitat for animals and are a food source for many species. Sediment quality thus determines, to a large degree, biodiversity and ecological health in aquatic systems, and they are economically attractive in environmental assessment of coastal environments.

Previous Approach to Describe Contaminant Status of Estuaries

Until recently, the contaminant status of an estuary was described by basic statistical parameters, e.g. mean, maximum and minimum concentrations. To make meaningful comparisons between these estuaries, it has been necessary to size-normalise the data to minimise the confounding introduced by variable grain size, as well as to keep field, laboratory and analytical techniques consistent. However, these parameters provide little information that is useful to environmental managers and strategic planners in the governance of these estuaries.

New Approach to Describe Estuarine Health

The new approach being used at Sydney University is to:

  • assess sediment quality;
  • determine severity of impact, and
  • identify contaminant sources and establish dispersion pathways.

To make this information available, it is necessary to provide both total sediment and normalised contaminant data.

Assessment of Sediment Quality

Sediment quality is the ability of sediment to support a healthy benthic population. The Australian and New Zealand Environmental and Conservation Council (ANZECC) recently adopted sediment quality guidelines (ANZECC/ARMCANZ [1]) largely based on a scheme developed by the U. S. National Oceanic and Atmospheric Administration (NOAA) [2,3]. This scheme provides two values, ERL and ERM, which delineate three concentration ranges for a particular chemical. The concentrations below ERL values represent a minimal-effects range, which is intended to estimate conditions where biological effects would be rarely observed. Concentrations equal to, or greater than ERL, but below ERM, represent a range within which biological effects occur occasionally. Concentrations at, or above ERM values represent a probable-effects range within which adverse biological effects frequently occur. The ANZECC sediment quality guidelines (SQGs) use the Interim Sediment Quality Guidelines-Low (ISQG-L) value (equivalent to ERL) as a threshold level that triggers the requirement for additional investigative work.

To estimate the adverse effects of mixtures of chemicals, NOAA uses mean ERM quotients which are determined by normalising the concentration of each substance to its ERM value, summing the quotient for each substance, and dividing the resultant sum by the total number of contaminants for which guidelines are available. In the Sydney University regional assessment of the contaminant status of NSW estuaries, the mean ERM quotient (MERMQ). is determined for three metals (Cu, Pb and Zn) only (MERMQ3m). The advantages of this approach are that analysis of these metals is cheap and accurate, these metals are ubiquitous and concentrations are available for all NSW estuaries. Also, for urban estuaries at least, concentrations of these metals follow trends for other metals and organic contaminants [4].

Severity of Impact

The extent to which chemicals exceed ‘natural', ‘pristine', or ‘pre-anthropogenic' concentrations is a measure of the degree of impact in estuarine sediments. To measure the magnitude of this exceedence requires an accurate determination of pre-anthropogenic, or ‘background' concentrations of contaminants. Enrichment is the extent to which contaminant concentrations exceed geochemical background levels. This can be expressed as an enrichment factor (EF) = Cn/Bg, where Cn is the concentration of the contaminant and Bg is the background concentration. When evaluating EFs, it is important to consider uncertainties in acquiring the data, e. g. spatio-temporal variation and field error. Enrichment factors above a certain threshold should be considered indicative of contamination. This threshold varies between studies, but is usually between 1.5 and 3. Other methods of estimating the degree of contamination, e. g. the Index of Geoaccumulation (Igeo) [5] have been attempted, but EFs have been adopted in the University of Sydney study for simplicity and clarity. Classes of enrichment are: EF<1 indicates no enrichment, <3 is minor; 3-5 is moderate; 5-10 is moderately severe; 10-25 is severe; 25-50 is very severe; and >50 is extremely severe.

Identification of Source and Dispersion Pathways

The other information required by environmental managers and planners is the source of contamination and to what extent toxicants have been dispersed through the system. To acquire this type of information necessitates the use of normalised contaminant data to minimise the confounding introduced by variable grain size. Normalisation can be undertaken by physical separation and analysis of a certain size fraction of the sediment (size normalisation), by elemental normalisation and by a post-extraction normalisation (PEN) procedure [6]. The latter two techniques use total chemical data, which is faster, more economical and employs only one chemical analysis, but if accurate and detailed results are required, size normalisation should be undertaken. All three techniques are used in the Sydney University study for most of the estuaries investigated.

  1. ANZECCARMCARZ, 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality. Australian and New Zealand Environment and Conservation Council/Agricultural and Resource Management Council of Australia and New Zealand, Canberra.
  2. Long. E. R., MacDonald, D. D., Smith, L. and Calder, F. D., 1995. ‘Incidence of Adverse Biological Effects Within Ranges of Chemical Concentrations in Marine and Estuarine Sediments', Environmental Management, 19, 81-97.
  3. Long, E. R. and MacDonald, D. D., 1998. ‘Recommended uses of empirically derived sediment quality guidelines for marine and estuarine ecosystems', Human and Ecological Risk Assessment, 4/5, 1019-1039.
  4. Birch, G. F. and Taylor, S. E., 2002. The use of sediment quality guidelines in the environmental assessment of Port Jackson estuary, Sydney, Australia. Hydrobiologia, 472, 19-27.
  5. Fostner and Muller, 1981
  6. Birch, G. F., in press. A test of normalisation methods for marine sediments, including a new post-extraction normalisation (PEN) technique. Hydobiologia.

Author

Gavin Birch, Environmental Geology Group, School of Geosciences, The University of Sydney, NSW, 2006.

Sedimentation rates

Sedimentation rates refer to the amount of material (organic and mineral) deposited by the action of water over a given interval of time. More information

Sheet runoff (or Surface Runoff)

The flow across the land surface of water that accumulates on the surface when the rainfall rate exceeds the infiltration capacity of the soil.

Sheetwash

Sheetwash or 'sheet erosion' refers to the removal of a thin layer of surface soil by run-off. The problem is often imperceptible until there has been severe soil loss. It is most acute in areas that are bare due to over-grazing, on fallow soils or on soils that have been repeatedly cultivated. Sheetwash removes valuable soil and it becomes a source of turbidity and particulate nutrients in some rivers and coastal waterways.

Shore

The "shore" is defined as the zone between low tide and the highest point reached by waves or tides (2). 2. Watt, A. (1982). Longman Illustrated Dictionary of Geology. Harlow, Essex, England, Longman Group: 192 pp.

Shorebirds

Shorebirds, (waders, gulls and terns) are birds principally found along the shores of beaches, estuaries, rock platforms and wetlands. More information

Sidescan sonar

A sidescan sonar is an echosounder that comprises one or two arrays of sonar transducers mounted obliquely to the vessels direction of travel, which are capable of imaging the seabed in a wide swath on either side of the vessel. The sonar emits a fan-shaped acoustic pulse (or 'ping') perpendicular to the path of the sensor through the water. The intensity of sound reflected from the seabed and its time of arrival are recorded in across-track slices for each ping, and when combined produce a swath image. Multiple swaths can also be combined to form an image for a wide area of the seabed, and are commonly used for identification of various substrate types (e.g. sand, seagrass, rock), and feature detection (e.g. presence of navigation hazards). The sound frequencies used in side-scan sonar usually range from 100 to 500 kHz. Sidescan sonars are suitable for assessing the nature (e.g. roughness, presence of objects such as rocks) of the seabed, however most do not provide accurate depth (or bathymetry) information. Higher frequencies enable more efficient object detection but have reduced range. A sidescan may be mounted on the hull of a vessel, or towed behind the vessel (on a torpedo-shaped 'towfish') at the desired depth.

Silt

Grains with diameters between 0.002 mm to 0.06 mm

Single Beam Echosounder

A single beam echosounder or 'depth sounder' is a system capable of accurately measuring the water depth below a vessel (Figure 1). This is achieved by measuring the two-way travel time (e.g. from the ship to the seabed, and back again) of an acoustic pulse (or a burst of sound) emitted by the sonar transducer. The acoustic pulse typically ranges in frequency from 12 - 200 kHz, with lower frequencies required in deeper water. The reliability of the depth calculation is dependant on accurately knowing the sound velocity in sea water, which is usually around 1500 m/s depending on water temperature, salinity, and other factors. Single beam echosounders are routinely mounted on most sea-going vessels, and when attached to a GPS and recording device, provide an inexpensive seabed mapping tool.

Example of the components of a single beam echosounder mounted on a small boat.

Figure 1. Example of the components of a single beam echosounder mounted on a small boat.

Sorting

An expression of the range of grain sizes present in a sediment. A well-sorted sediment has a narrow range of grain sizes, whereas a poorly sorted sediment has a wide range of grain sizes.

Specific conductance

The presence of charged ionic species in solution enables water to conduct an electrical current. This is referred to as conductivity, electrical conductivity (EC) or conductance, and it is directly related to the total dissolved salt concentration. Conductivity is best measured in the field using an electronic probe that applies a voltage between two electrodes. EC is sensitive to water temperature. The international standard temperature for laboratory conductivity measurements is 25 oC. Most modern field instrumentation will correct and standardise conductivity readings to this temperature and then refer to the measurement as specific conductance. It is worth mentioning that different standard temperatures were used in the past, so the water temperature at which the measurement was taken should always be reported. Up until around the late 1970s the units of EC were micromhos per centimetre (µmhos cm-2) after which they were changed to microSiemens cm-2 (1µS cm-1 = 1 µmho cm-1).

Spring Tide/King Tide

Tide greater than the mean tidal range. Occurs about every two weeks, when the Moon is full or new.

Stakeholders

Specific groups (community groups, government organisations, investors) or individuals who have an interest ("stake") in the outcome of the project. More information

Stormwater

Stormwater runoff comprises all forms of runoff from urban areas. It is enhanced by the web of impervious surfaces, including roads, roofs, footpaths, car parks and other structures, and is conveyed to coastal waterways by natural and man-made conduits and drains. More information

Strand Plain

A series of dunes, typically associated with and parallel to a beach, and sometimes containing one or more small creeks or lakes. More information.

Stratification

Physical layering of the water column resulting from density differences caused by salinity or temperature variation.

Streambed & Streambank Erosion

By their very nature, rivers are the drains of the landscape, and are natural agents of erosion. But what is their natural or ‘normal' rate of erosion? And just how much has erosion been accelerated through poor management of drainage systems?

There has been a recent conceptual leap in understanding stream and river erosion within Australia. Previously, riverbank and streambank erosion - the removal of river banks by flowing water - was targeted as the major erosional problem to be addressed. However, we now understand that streambank erosion is an obvious symptom of a more fundamental problem within the drainage feature, the lowering of the streambed. This phenomenon may be much less obvious, but can be identified through the active sites, nick points and their resultant renewed instability of the streambanks.

An eroding bank in Tantulean Creek in NSW (photo courtesy of Upper Shoalhaven Landcare Council)

Photo 1. An eroding bank in Tantulean Creek in NSW (photo courtesy of Upper Shoalhaven Landcare Council)

What is a Nick Point?

A nick point is an incised headcut within a stream bed, and indicates a sudden lowering of streambed level. This erosive feature is most obvious in coherent or semi-consolidated river bed material, usually as a small waterfall. In a gravel-bottomed stream, a nick point may be as subtle as a small incised channel within a riffle zone. In even finer gravels and sands, this feature is generally not recognisable. As the streambed erodes and lowers at this active headcut, the nick point migrates upstream, thereby creating progressive bed lowering of the entire stream. There can be many nick points active in a stream at any one time.

An example of a nick point in Durran Durra Creek, Upper Shoalhaven Catchment (photo courtesy of Upper Shoalhaven Landcare Council)

Photo 2. An example of a nick point in Durran Durra Creek, Upper Shoalhaven Catchment (photo courtesy of Upper Shoalhaven Landcare Council)

What is Stream Bed Lowering?

This is the result of migrating nick points. Where there is active erosion within the bed of a stream or river channel, the bed may be steadily lowered, creating relatively higher banks up onto the adjoining floodplain or terrace. The banks become increasingly steepened and unstable as this erosion is active at the toe of the slope. Streambed collapse and erosion occurs, and the channel commonly widens in conjunction with bed lowering. Other evidence of stream bed erosion can be the exhumation of roots of trees within the channel, or the exposure of foundations of man-made structures. If you have a good memory, or have historical reference levels to bridge or causeway foundations, these can generally provide the best indication to the longer-term changes in your stream.

Bombay Creek in NSW is a highly incised stream exacerbated by streambed erosion (photo courtesy of Upper Shoalhaven Landcare Council)

Photo 3. Bombay Creek in NSW is a highly incised stream exacerbated by streambed erosion (photo courtesy of Upper Shoalhaven Landcare Council)

Rapid Buildup of Sediment in your Stream

Where there is erosion, sediment is mobilised and it may accumulate further downstream where flood energy conditions are not as severe. So if you observe siltation, or sediment buildup in a stream bed, it may indicate significant erosion is occurring upstream.

Potential Impacts on Coastal Waterways

Erosion from streambanks and gullys can generate as much as 90% of the sediment yield from a catchment [1,2]. The sediment is a major source of turbidity and particulate nutrients in some rivers and coastal waterways [1].

Further Insights

In the past, much of the work on streambank erosion directly addressed the symptom without perhaps fully questioning or understanding the cause. Today we think we understand processes a little better. It is now apparent that through stabilising or raising stream bed levels, bank erosion is also suppressed. This, in conjunction with appropriate revegetation of the banks, riparian zones and the various floodplain terraces in proximity to the channel, can only increase the resistance to erosional events in the future. The stabilising of the banks with vegetation also helps absorb the energy of the river during flood, and helps retain valuable topsoil.

With streambed lowering, and the related increased height of the banks and widening of the channel, floodwaters will not overbank as frequently. This may seem like progress to some in that there is less damage to fences and roads on the floodplains, and less standing water on valuable pasture, but it also means less silt deposition and rejuvenation on the floodplain, lower groundwater levels, loss of wetlands, and possible saline discharges from the base of gullys and streambanks. As usual, there is no free ride for long, and the sustainable use of floodplains comes with a responsibility and a ‘price'.

Modifications to a river do have long-reaching consequences, but in the end, if the modifications are not compatible with the natural scale of energy-dissipating processes of the river, they will ultimately fail.

Because the condition of a river is a dynamic balance between all forces impinging on it, every modification made to it has an ensuing reaction. Rivers are not always in equilibrium with the dynamic balance where they should be, and there can be a considerable lag in time until the appropriate ‘event' provides the readjustment of levels or sediment supply or change of geometry in the channel.

In the bigger picture and longer timeframe, the river and its floods will always win out. But we also know that with appropriate measures and application of technology for erosion prevention, we can stall for time. We can help retain the riverine assets, as we now experience them, a little longer to maintain or improve the agricultural productivity, have satisfaction in conservation, and enjoy the recreational benefits. The unknown is for how many years?

  1. Hughes, A.O., Prosser, I.P., Stevenson, J., Scott, A., Lu, H., Gallant, J., and C. Moran. 2001. Gully erosion mapping for the National Land and Water Resources Audit. CSIRO Land and Water Canberra, Technical Report 26/01.
  2. Olley, J.M., Murray, A.S.. Mackenzie, D.M., Edwards, K. 1983. Identifying sediment sources in a gullied catchment using natural and anthropgenic radioactivity. Water Resources Research 29, 1037-1043.

Author

Bruce Radke, NSW Department of Land and Water Conservation.

Stress

From an ecological perspective, a stress is a change that causes a response in a system or population of interest. See also stressors

Stressors

Stressors are Physical, chemical and biological stressors are major components of the environment that, when changed by human or other activities, can result in degradation to natural resources. [1].

  1. Scheltinga, D., Counihan, R., Moss, A., Cox, M., Bennett, J. 2004, Users' Guide to Estuarine, Coastal and Marine Indicators for Regional NRM Monitoring, Report to DEH, MEW, ICAG, Coastal Zone CRC.
More information

Structural Macro Biota (SMB)

Similar to a "Vegetated" class, such as mangrove, saltmarsh and seagrass, but also including cover forming macroinvertebrates that create a structured habitat with a significant vertical dimension on the seabed, such as corals and sponges.

Subaerial

Occurring on land or at the earth's surface, as opposed to underwater or underground.

Sub-bottom profilers

A sub-bottom profiler is effectively an echosounder that transmits a relatively low-frequency acoustic pulse that can penetrate the seabed. This signal is reflected off sub-surface boundaries between sediment or rock layers that have different acoustic impedance, which is related to density and sound speed within each layer (Figure 1). The strength of the reflected signal depends on the degree of impedance contrast. The returning sound waves are recorded by an array of hydrophones (towed behind the vessel), or by a transducer/transceiver, depending on the type of system. The first useful signal received represents the seabed-water interface, and shows the morphology of the seabed in a manner similar to a single beam echosounder. The time of arrival and intensity of subsequent impulses provides information about layers that exist below the seabed.

Several physical parameters of the acoustic signal emitted, such as output power, signal frequency, and pulse length affect the performance of the instrument and influence its usefulness in various marine environments. Increased output power allows greater penetration into the substrate. However, in the case of harder seabeds (e.g. gravels or highly compacted sands) or very shallow water, higher power will result in multiple reflections and more noise in the data. Higher frequency systems (up to 20 kHz) produce high definition data of sediment layers immediately below the seabed, and are able to discriminate between layers that are close together (e.g. 10's of cms). Lower frequency systems give greater substrate penetration, but at a lower vertical resolution. Longer pulse length transmissions (or 'pings') yield more energy and result in greater penetration of substrate. However, they decrease the system resolution. The depth of penetration also depends on the hardness of the upper layers and is significantly limited by the presence of gas deposits.

Deployment of various shallow-water sub-bottom profiling systems.

Figure 1. Deployment of various shallow-water sub-bottom profiling systems.

Substrate

The sediment and other material that comprises the seabed (or floor of coastal waterway).

Sub-tidal

Permanently below the level of low tide, an underwater environment.

Sulfate reduction, biological

Organic matter decomposition can be a consequence of sulfate reduction in the sediments of coastal waterways (and other aquatic systems) [1]. The process is performed by anerobic sulfate-reducing bacteria. The bacteria require: metabolisable organic matter; an anoxic environment (or microenvironment); and dissolved sulfate. Hydrogen sulfide gas (H2S) and alkalinity are generated in the process (see simplified reaction 1).

(Eq. 1) SO42- + 2(CH2O) = H2S + 2HCO32-

Sulfate reduction is often a dominant process in eutrophic systems, occurring after the oxygen-consuming bacteria have removed dissolved oxygen. If dissolved oxygen is present in the water column, organic matter is preferentially decomposed by oxygen-consuming bacteria.

A conceptual model of sulfate reduction and hydrogen sulfide and iron sulfide production in a coastal lake. SRB - Sulfate reducing bacteria.

Figure 1. A conceptual model of sulfate reduction and hydrogen sulfide and iron sulfide production in a coastal lake. SRB - Sulfate reducing bacteria.

The fate of hydrogen sulfide

Some hydrogen sulfide from sulfate reduction can be released to the atmosphere (Figure 1). Hydrogen sulfide can be oxidised to sulfate or sulfur (So), or can react with iron sulfide minerals in the sediment (Figure 1 and 2). Iron monosulphides (FeS) form first, but are readily converted to pyrite (FeS2; Figure 2). The overall reaction is shown in Equation 2 [7].

(Eq. 2) Fe2O3 + 4S2-(mostly from H2S) + 6H+ = 2FeS2 + 3H2O + 2e

Diagram of iron

Figure 2. Diagram of iron

Consequences of sulfate reduction

  • H2S smells like rotten eggs, and can detract from the aesthetic amenity of coastal waterways when it is released to the atmosphere [2,5].
  • H2S is toxic to a wide range of aquatic organisms [3];
  • H2S can inhibit nitrification [4]. When nitrification is inhibited, coupled nitrification-denitrification is also inhibited.
  • Ammonium (NH4+) is released from organic matter during degradation by sulfate reduction (Equation 3) [6]. Ammonium is a bioavailable and is readily taken up by plants.

    • (Eq. 3) 106(CH2O)16(NH3)(H3PO4) + 53SO42- → 106 CO2 + 16 NH3 + H3PO4 + 106 H2O + 53 S2-

  • Iron sulfides (e.g. pyrite), formed during sulfate reduction, are an active component of acid sulfate soils (ASS), and problems with acid production and drainage can arise if the pyrite is oxidised.
  • Iron sulfides cannot bind phosphate. Therefore, when iron oxyhydroxides are converted to iron sulfides during sulfate reduction, phosphate can be released to the water column [9].
  1. Skyring, G.W. 1987. Sulfate Reduction in Coastal Ecosystems. Geomicrobiology Journal 5, 3/4, 295-374.
  2. Murray, E. 2002. GA nose about smelly lake. AusGEO News 65, 7-9.
  3. Connell, D.W., and Miller, G.J. 1984. Chemistry and Ecotoxicology of Pollution. John Wiley & Sons, N.Y.
  4. Joye, S.B. and Hollibaugh, J.T. 1995. Influence of sulfide inhibition of nitrification on nitrogen regeneration in sediments. Science 270, 623-625.
  5. Murray, E.J. and Heggie, D.T. 2002. Factors influencing extensive sulphate reduction in Lake Wollumboola, and intermittently closed/open lake (ICOLL) on the NSW south coast, Proceedings of the annual conference of the Australian Marine Sciences Association, 10-12 July 2002, Fremantle WA.
  6. Froelich, P. N., Klinkhammer, G. P., Bender, M. L., Luedtke, N., Heath, G. R., Cullen, D., Dauphin, P., Hammond, D., Hartman, B., and Maynard, V. (1979). Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic; suboxic diagenesis. Geochimica et Cosmochimica Acta Pergamon, Oxford. 43, 1075-1090.
  7. Berner, R.A. 1971. Principles of Chemical Sedimentology. McGraw Hill, Inc, U.S.A, 192-209
  8. Berner, R.A. 1983. Sedimentary pyrite formation: An update Geochemica et Cosmochimica Acta 48, 605-615
  9. Roden, E.E. and Edmonds, J.W. 1997. Phosphate mobilization in iron-rich anaerobic sediments: microbial Fe(iii) oxide reduction versus iron-sulphide formation. Arch. Hydrobiol. 139, 347-378.

Contributors

Emma Murray, Geoscience Australia
Graham Skyring, Skyring Environment Enterprises

Supra-tidal

Above the level of high tide, a terrestrial environment.

Suspended Sediment

Sedimentary material subject to transport by flowing water (e.g. currents) that is carried in suspension. Typically comprises relatively fine particles that settle at a lower rate than the upward velocity of water eddies. More information.

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T

Target(s)

In Natural Resource Management, targets are numerical values or descriptive statements that must be met within a specified period of time to protect a set of environmental values (i.e. aquatic ecosystem protection, recreation and aquaculture/human consumption).

TBL

Commonly used abbreviation for triple bottom line.

Territorial baseline

The Territorial Sea Baseline (often simply referred to as the Baseline) is a line from which Australia's Territorial Sea, Coastal Waters, Contiguous Zone and Exclusive Economic Zone are measured. It is drawn in accordance with the provisions of the United Nations Convention on the Law of the Sea and the Seas and Submerged Lands Act (1973). In most cases the baseline it is the line of Lowest Astronomical Tide however the line jumps across rivers and some bays and also between near offshore islands in some situations. It also includes the low water line around islands and some reefs. More information

Threat

A source of impending danger or harm to the condition of natural resource assets or the services they provide. Can include both pressures and stressors

Three-dimensional models

3D (three dimensional) models of coastal environments are digital representations of coastal environments (e.g. bays and estuaries) that have the appearance of width, height and depth.More information

Tidal Creek

Coastal waterways in which tides are the principal factor that shape the overall geomorphology. Typically occur on prograding, muddy coasts and contain a narrow channel that drains the immediate hinterland that is fringed by intertidal habitats. More information.

Tidal Current

An alternating, horizontal movement of water associated with the rise and fall of the tide, these movements being caused by gravitational forces due to the relative motions of Moon, Sun and Earth.

Tidal Prism

Volume of water moving into and out of an estuary or coastal waterway during the tidal cycle.

Tidal sand banks

Tidal sand banks are sedimentary features commonly found within tide-dominated estuaries, deltas and tidal creeks. Tidal sand banks are typically subtidal to intertidal in elevation, and consist of elongate linear to sinuous sand bars comprised of moderate- to well-sorted fine muds to sands. More information

Tide-dominated Delta

Coastal waterway in which tides are the principal factor that shapes the overall geomorphology, and river input is sufficient to have filled the basin. Typically funnel-shaped, and the wide entrance may form a coastal protuberance that contains elongate tidal sand banks that fringed by inter- and supra-tidal habitats. More information.

Tide-dominated Estuary

Coastal waterway in which tides are the principal factor shaping the overall geomorphology. Typically funnel-shaped with a wide entrance containing elongate tidal sand banks. The margins are fringed by extensive intertidal habitats, separated by tidal channels. More information.

Total dissolved nitrogen

Total dissolved nitrogen (TDN) consists of dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen (DON). More information

Total Inorganic Carbon Dioxide (TCO2)

The total inorganic CO2 content of a sample can be calculated from the following equation:

TCO2 = [CO2(aq.)] + [H2CO3] + [HCO3-] + [CO32-]

Other known abbreviations for TCO2 are åCO2 and CT.

Total nitrogen

Total nitrogen (abbreviated TN) is a measure of all forms of dissolved and particulate nitrogen present in a water sample. More information

Total phosphorus

Total phosphorus (abbreviated TP) is a measure of all forms of dissolved and particulate phosphorus present in a water sample. More information

Total suspended matter

Total suspended matter is a gravimetric measure of the mass of suspended material in a given volume of water sample that does not pass though a filter (usually with a pore size of 0.45 µm). More information

Toxicants

Toxicants are chemical contaminants that may harm living organisms at concentrations found in the environment. More information

Trajectory/Phase

An aspect of the system that varies with time e.g. wet/dry season and open/closed estuary.

Transgressive Coastlines

Coastal regions which have recently been inundated by the sea due to a rise in sea level relative to the land are called trangressive coastlines.

Transmissometry

Transmissometry is a kind of turbidity measurement in which a calibrated beam of light is projected through the water to a light detector over a set distance (usually less than 300mm). The loss in the intensity or absorption of light is then measured and correlated to the turbidity. More information

Tributyltin

Tributyltin (TBT) is the active agent in many biocides. It has been used throughout the world as an antifoulant paint on ship and boat hulls, fishnets and buoys, and docks, to discourage the growth of marine organisms (e.g. barnacles, tubeworms, mussels, bacteria and algae). Other TBT compounds (collectively referred to as 'organotins') are used as wood preservatives, disinfectants, and stabilizers in PVC resin, and in pulp and paper mills, breweries, leather-processing plants and textile mills. The use of TBT in antifouling paints may affect nontarget aquatic organisms (e.g. mussels, clams, and oysters) causing changes in their structure and growth [2]. In some gastropod species, TBT exposure causes imposex. TBT is also extremely toxic to crustaceans [3]. The use of organotins is now restricted or prohibited in most countries.

  1. See page 8.1-20 of ANZECC/ARMCANZ (October 2000) Australian Guidelines for Fresh and Marine Water Quality.
  2. Michigan Department of Natural Resources "Fact Sheet on Tributyltin Compounds." April 24, 1987
  3. U.S. Environmental Protection Agency. Office of Pesticide Programs. Tributyltin support document. 1985.

Trigger Values

Trigger values, in the context of the ANZECC/ARMCANZ Water Quality Guidelines, are concentrations of key indicators, above or below which there is a risk of adverse biological effects [1]. Default trigger values have been set for 'core' water quality indicators for different bioregions in Australia, and are based mainly on statistical distributions.

Section 3.3.2.3 (page 3.3-5) in the Guidelines outlines approaches for deriving trigger values. Percentile values (80th and 20th) derived from statistical distributions were used to set 'default' trigger values for different indicators (e.g. TP, FRP, TN, NOX, NH4, pH, chlorophyll a and dissolved oxygen saturation) in different bioregions.

The default trigger values have subsequently been adopted as default water quality targets for use in regional planning.

  1. ANZECC/ARMCANZ (October 2000) Australian Guidelines for Fresh and Marine Water Quality.

Triple bottom line (TBL)

Decisions that consider economic, social and environmental factors.

Trophic Status

The trophic status of a coastal waterway refers to the rate at which organic matter is supplied [1]. Trophic status should not be confused with eutrophication which is an increase in the RATE of supply of organic matter. A preliminary trophic scheme has been proposed for Australian coastal waters based on relationships between carbon loading (i.e. measured by the carbon dioxide flux), denitrification efficiencies and benthic production/respiration ratios [2]:

  • oligotrophic (<48 mmol C m-2 d-1)
  • mesotrophic (48 - 96 mmol C m-2 d-1)
  • eutrophic (>96 - 144 mmol C m-2 d-1)
  • hypereutrophic (>144 mmol C m-2 d-1)
  1. Nixon, S.W. 1995. Coastal marine eutrophication: A definition, social causes, and future concerns. Ophelia 41, 199-219.
  2. Eyre, B. and A.J.P. Ferguson 2002. Sediment biogeochemical indicators for defining sustainable nutrient loads to coastal ecosystems, Proceedings of Coast to Coast 2002 - "Source to Sea", Tweed Heads, pp. 101-104.

Turbidity

Turbidity is a measure of water clarity or murkiness. It is an optical property that expresses the degree to which light is scattered and absorbed by molecules and particles. Turbidity results from soluble coloured organic compounds and suspended particulate matter in the water column. More information

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