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CHAPTER 5 3.1.12 3.1.12 SAGI (Salinity Association Group Index)

The Salinity Association Group Index (SAGI) can be calculated using data at family or mixed (species) taxonomic level.
The index works in a similar way to LIFE (Section 3.1.9) Taxa are classified into five groups, termed Salinity Association
Groups (SAGs). The assignment of groups was based primarily on the results of a literature search, followed by expert
and to fill gaps in the published material.
(94)
opinion, to sense-check the results of the literature search

SAGI (Salinity Association Group Index)

This index is used to assess the impact of saline intrusion on invertebrate communities.

Table 5. 6
Definition of Salinity Association Groups, from Pickwell (2012) (26)

Salinity Association Group definition*
Group (SAG)

Macroinvertebrate taxa which tolerate only salinities below 2.5gL , approximately
-1
I 1.73PSU. Typically freshwater taxa; may be tolerant of slightly brackish conditions, or
completely intolerant.

-1
Macroinvertebrate taxa which can tolerate salinities over 2.5gL (1.73PSU) up to a
II salinity of 10gL (7.63PSU). Taxa may be present at slightly higher salinities, but only in
-1
small numbers. Freshwater taxa tolerant of mild brackish conditions.

Macroinvertebrate taxa which are characterised by the largest abundance occurring
in the salinity range 8–20gL (5.99–16.22PSU). Taxa are tolerant of the salinity range
-1
III 4–25gL (2.85–20.73PSU), but may also be recorded at salinities greater, or less,
-1
than those specified in this range. Characteristic brackish water taxa, tolerant of a wide
range of salinity conditions from long-term brackish to near freshwater.

Macroinvertebrate taxa which tolerate salinities below 20gL-1 (16.22PSU) down to
-1
IV 14gL (14.99PSU). Taxa may be present at slightly lower salinities, but only in small
numbers. Long-term brackish taxa tolerant of lower salinities, ie transition zones.

Macroinvertebrate taxa which tolerate only salinities greater than 20gL ,
-1
V approximately 16.22PSU. Full coastal seawater taxa rarely moving into nominally
freshwater habitats.

*Definitions using salinity concentrations are in regular font style, whilst the descriptive definitions of the
groups are in italic font style.

The index value for each taxon depends not only on its SAG but also its RIVPACS Log 10 abundance category.
SAGI should only be calculated from samples collected by standard RIVPACS methods, described in Chapter 2.

The index has been used in the south-east of England where there is saline intrusion. The index is likely to detect
salinization from industrial discharges and salt mining, but it has not been tested on these yet.

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