Journal of the Royal Society of Western Australia, 86(4), December 2003 
Table 1 
Salinity values (g L' 1 ), Lake Clifton, 1985-86. Transects and sites are shown in Fig 1. Salinities in bold represent an average of differing 
top and bottom values. 
23 
May 
8 
July 
9-10 
Aug 
1985 
20 
Sept 
11-13 
Oct 
9-10 
Nov 
13-15 
Dec 
21-22 
Jan 
18-20 
Feb 
1986 
14-16 
Mar 
18-19 
Apr 
16-18 
June 
20-22 
July 
A1 
32* 
20 
20 
18 
17 
18 
22 
26 
30 
30 
31.5 
31 
27 
A2 
32* 
20 
20 
18 
17 
18 
22 
25.5 
30 
30 
32 
31 
27.5 
A3 
31* 
20 
20 
18 
17 
18 
20 
25.5 
30 
30 
32 
31 
28.5 
B1 
26** 
19 
16 
16 
18 
22 
27 
32 
30 
30 
30 
28 
B2 
27** 
20 
17.5 
17 
17.5 
21.5 
26.5 
30 
32 
32 
30.5 
29 
B3 
27** 
20 
17 
15.5 
18 
21 
26 
32 
32 
32 
30 
28 
Cl 
30.5* 
15 
15 
15 
16 
16 
22 
30 
38 
36 
38 
33 
28 
C2 
30* 
14 
16 
14.5 
16 
16 
22 
30 
38 
36 
38 
33 
27 
C3 
32* 
14 
16 
14 
16 
16 
22 
31 
26 
29 
D1 
26* 
13 
10 
12 
13 
15 
22 
30 
43 
45 
48 
36 
26 
D2 
26* 
14 
10 
12 
13.5 
15 
22 
34 
42 
43 
48 
38 
26 
D3 
26* 
14 
10 
12 
12 
15 
22 
36 
47 
42 
28 
* 23 May 1985; ** 31 May 1985. 
each of four transects (Table 1) showed ranges in the 
permanent, northern basin, transects A and B, of 17-32 
and 15.5-32 g L* 1 respectively. Salinity gradients reflect 
interactions between the position of freshwater inflow 
along the eastern margin, lake bathymetry and wind 
strength, which are sufficient to mix this lake vertically, 
but not horizontally. Salinity increased from north to 
south during the period of low water level (January- 
March 1986, Table 1), due to the increasing impact of 
evaporative concentration on successively shallower 
southern bodies of water. The gradient is reversed with 
high water level (in spring e.g. October 1985, Table 1); the 
northern basin (transect A) is most saline because of the 
higher salt load in the larger volume of water contained 
in the deeper basin. Successively lower salinities occurred 
along transects B-D during high water level, reflecting 
the greater impact of the freshwater input in shallower 
basins. Aquifer input was sufficient to generate an east- 
west salinity gradient, from 2 g L' 1 immediately over the 
aquifer outflow, to 15 g L' 1 at the edge of the rushes 
(Juncus sp; 23 August 1984, CM Burke & B Knott, 
unpublished data). Gilgies, Cherax quinquecarinatus 
(Gray), were active in this lens of fresher water at night. 
A series of ad hoc salinity readings late in the 1990s 
suggest that salinity has increased since the 1980s. Values 
recorded at times of low water level have been; 44 g L' 1 
(adjacent to transect A; 17 May 1997, Konishi 1997); 49-34 
g L' 1 at site 2 (adjacent to transect C), and 45-25 g L* 1 at 
site 3 (adjacent to transect D; Gartrell 1998); 48 g L' 1 
(adjacent to transect A, 24 April 1999). During the 1990s 
salinity values at times of high water level, too, have 
been higher than those noted in the 1980s; 25 g L' 1 (both 
adjacent to transect A, 22 September 1999, and again on 5 
September 2000). 
Despite the limited evidence available, the data 
indicate that there has been an increase in salinity since 
the 1980s. The total annual rainfall at the two nearest 
meteorological stations, Bunbury and Mandurah, are 
plotted against water levels measured at Lake Clifton in 
September 1986 to 1999 (at the end of the rainy season) in 
Fig 2A. It is clear that there is a direct correlation between 
rainfall and water level in the lake. Measurements of 
salinity during the same period are shown in Fig 2B (J 
Lane, CALM, unpublished data). As expected, there is an 
inverse correlation between water level and salinity. 
However, if rainfall was the only driving factor in 
determining the lake's salinity, then increased rainfall in 
the late 1990s and the subsequent water level rise should 
have returned the salinity to the lower levels observed in 
the 1980s (during years of similar rainfall and water 
level). This trend has not been observed. An approximate 
estimation of the total salt content of the lake was 
calculated as the salinity multiplied by the total lake 
volume. Measurements of salinity were made in 
September when the lake was fully mixed, and lake 
volume was calculated as a function of water level based 
on bathymetry data supplied by the Water and Rivers 
Commission. These calculations indicate that although 
the mass of salt in Lake Clifton remained relatively 
constant from 1985 to 1992, it has since increased by 40% 
from 1993 to 2000 (Fig 2C). Since this calculation is 
independent of rainfall, this indicates a possible increase 
in proportion of brackish ground water to fresh ground 
water inflow into the lake. Clearly, further investigations 
are necessary to substantiate whether the observed 
increases in salinity of Lake Clifton are permanent, and if 
so what are the cause(s). 
Consequences 
If the salinity of Lake Clifton is increasing and 
continues to do so, then changes in the pattern of 
microbialite growth, reduction in faunal diversity within 
the lake, and change in usage by waterbirds, are 
inevitable consequences unless the cause(s) are identified 
and corrected. Even if the salinity is increasing, any 
ecological perturbations already in train may not yet be 
irreversible given immediate remedial action. The 
limnology of Lake Hayward altered substantially during 
the dry summer of 1987/1988, but subsequently returned 
to its pre-drought pattern, probably through internal 
homeostatic mechanisms (Burke & Knott 1997). With a 
permanent change to hypersalinity, the international 
scientific significance of the lake may well be lost. It must 
120 
