Glossary I – L

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Commonly used abbreviation for the Intergovernmental Coastal Advisory Group.


Acronym - Intermittently Closed and Open Lakes and Lagoons, referring to Coastal Lagoons and some Wave-Dominated Estuaries under low runoff conditions.

IMCRA, IMCRA regions

The Interim Marine and Coastal Regionalisation for Australia (IMCRA) [1] is a near-shore regionalisation that consists of 60 meso-scale regions (100-1000's of km) that cover the area between the coast and the edge of the continental shelf around Australia. IMCRA was based mainly on fish (pelagic and demersal) diversity and species richness data, and has been adopted both nationally and internationally.

Figure 4 on the near-pristine estuaries page is an interactive map that enables users to enlarge and view the states (or parts of states) and the coastal IMCRA regions found there.

IMCRA Technical Group 1998. Interim M long microtidal estuaries [17] ersion 3.3. Interim Marine and Coastal Regionalisation for Australia Technical Group, the Department of Environment, Water, Heritage and the Arts, Commonwealth Government, Department of the Environment, Canberra. More information


Impoundments include dams, locks, weirs, reservoirs and farm dams. The regulation of rivers through the construction of these structures has changed natural flow regimes and altered environmental flows. More information


Imposex is the occurrence of induced male sex characteristics superimposed on normal female gastropods, with the development of male sex organs, the penis and/or the vas deferens. More information

Index of habitat variability

The index of habitat variability is a measure of the distribution and abundance of habitats in Australia's estuaries and coastal waterways based on the presence and absence of a suite of geomorphic and sedimentary environments. More information

Indicators, environmental

For the purposes of State of the Environment Reporting, environmental indicators are physical, chemical, biological or socio-economic measures that best represent key elements of a complex ecosystem or environmental issue. In the context of Natural Resource Management, indicators are the medium through which one converts qualitative environmental values and management goals into measurable water quality objectives. More information

Indigenous Vegetation

Indigenous vegetation consists of plant species that existed in a given state prior to European arrival [1].

  1. NSW Department of Land and Water Conservation 1997. Definitions and Exemptions, State Environmental Planning Policy No. 46, Protection and Management of Native Vegetation, Amendment No. 2, pp. 26.


Animals that live within the sediment. More information.

Australia's Intensive Land Use Zone

Australia's Intensive Land Use Zone Based on the National Land and Water Resources Audit

Figure 1. Australia's Intensive Land Use Zone Based on the National Land and Water Resources Audit

Intergovernmental Coastal Advisory Group

The Intergovernmental Coastal Advisory Group (ICAG) manages the implementation of the Framework for a National Cooperative Approach to Integrated Coastal Zone Management. It comprises representatives from the Australian Government, each state government, the Northern Territory Government and the Australian Local Government Association (ALGA). ICAG members meet several times a year to share experiences and to work on Framework implementation.


The environment between the level of high tide and low tide.

Intertidal mud flats

Intertidal mud flats are un-vegetated, generally low gradient and low energy environments that are subject to regular tidal inundation, and that consist of poorly- to moderately-sorted sandy mud and muddy sand. More information

Introduced species

Introduced species ('exotic', 'invasive' or 'alien' species) are species moved to locations outside their natural range by human-mediated dispersal. More information

Ion Activity

The activity of an ion is its 'effective' concentration in solution. The reason that the effective concentration of an ion is different than the actual concentration (as measured in a water sample) is because ions form uncharged pairs in solution (see Figure 1). The extent of ion-pair formation increases with salinity. There is little difference between the activities and concentrations of most ions at salinty's below about 3 ppt.

Figure showing that the extent of uncharged (designated with 'o') ion pair formation increases with salinity, and this reduces the 'effective' concetration of ions

Figure 1. The extent of uncharged (designated with 'o') ion pair formation increases with salinity, and this reduces the 'effective' concentration of ions.

There are several software packages that can be used to to calculate activity coefficients for ions based on Debeye-Huckel theory or Pitzer equations. The Pitzer approach is most suitable when salinity's are in the seawater range.


Isohalines are lines (or contours) that join points of equal salinity in an aquatic system. Isohaline position refers to the distance (kilometres) of a near-bottom isohaline (usually 2 ppt) from the mouth of a coastal waterway (Figure 1). More information

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A kill is an unexpected and generally short-lived event marked by the conspicuous death of large numbers of fish (e.g. fish kill) or other organism (e.g. usually birds). More information

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A coarse-grained residue left behind after finer particles have been transported away, due to the inability of the transporting medium to move the coarser particles.


Raised embankment of a river, showing a gentle slope away from the channel. It results from periodic overbank flooding, when coarser sediment is immediately deposited due to a reduction in velocity.


The Lifespan of a coastal waterway is the length of time available before estuarine habitats are lost (e.g. central basin and intertidal areas) due to infilling, and only deltaic habitats remain (mainly channels and swamp areas). More information

Limiting Nutrients

A limiting nutrient is a nutrient or trace element that is essential for plants to grow, but that is available in smaller quantities than are required by the plants and algae to increase in abundance. Therefore, if more of a limiting nutrient is added to an aquatic ecosystem, larger algal populations will develop until nutrient limitation or another environmental factor ( e.g. light or water temperature) curtails production, although at a higher threshold than previously.

It is often said that nitrogen is the limiting nutrient in marine and coastal waters, however this general assumption is often incorrect [1]. Phosphorus, carbon, silica and iron can also limit production in marine and coastal waters, and different trophic groups within the same ecosystem can be limited by different elements and nutrients [2].

  1. ANZECC/ARMCANZ (October 2000) Australian Guidelines for Water Quality Monitoring and Reporting.
  2. Sundareshwar, P.V., Morris, J.T., Koepfler, E.K., and B. Fornwalt. 2003. Phosphorus limitation of coastal ecosystem processes. Science 299, 563-565.

Lithic, Lithified

Geological term referring to in situ indurated, consolidated, cemented or rocky materials (generally hard, albeit some may be relatively soft by reason of being weathered or only semi-lithified).

Low water mark

Low water mark is a term generally used to describe the low tide line. Under Common Law this term is usually considered to be Mean Low Water. Some Australian States have amended this Common Law understanding via legislation. For example, Queensland has legislation defining the Low Water Mark as Mean Low Water Springs.

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