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Sampling and analysis of lakes in the

Corangamite CMA region Report to the Corangamite Catchment Management Authority CCMA Project WLE/42-009: Client Report 3 Annette Barton, Andrew Herczeg, Jim Cox and Peter Dahlhaus

CSIRO Land and Water Science Report 34/06

September 2006

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From CSIRO Land and Water File: S:\CCMA\GDE_project\Photographs\SiteVisit23-25July2006, No1 Description: The dry crater which was Deep Lake. Photographer: Bob Smith, Ballarat of University © 2006 CSIRO

ISSN: 1446-6171

Identification and review of the groundwater dependent ecosystems in the Corangamite CMA Page i

Report Title

Sampling and analysis of the lakes of the Corangamite CMA region

Authors

Dr Annette Barton 1, 2

Dr Andy Herczeg1, 2 Dr Jim Cox 1, 2

Mr Peter Dahlhaus 3, 4

Affiliations/Misc

1. CSIRO Land and Water, PMB 2, Glen Osmond, SA, 5064 2. CRC for LEME, PO Box 1130, Bentley, WA, 6151 3. University of Ballarat, PO Box 663, Ballarat VIC, 3353 4. Dahlhaus Environmental Geology Pty Ltd, PO Box 318, Buninyong, VIC, 3357

CSIRO Land and Water Science Report 34/06

September 2006

Identification and review of the groundwater dependent ecosystems in the Corangamite CMA Page ii

Table of Contents 1. Introduction......................................... ............................................................................ 3 2. Lakes Inspection and Sampling........................... ......................................................... 3 3. Chemical Analyses................................... ...................................................................... 5

3.1. Field measurements.............................................................................................................. 5 3.2. Chemistry.............................................................................................................................. 5 3.3. Radon count.......................................................................................................................... 9 3.4. Stable isotopes ................................................................................................................... 10

4. Further Work ........................................ ......................................................................... 13 5. Acknowledgements..................................... ................................................................. 13 References ......................................... .................................................................................. 13

Identification and review of the groundwater dependent ecosystems in the Corangamite CMA Page 3

1. Introduction This is the third milestone report for the Corangamite Catchment Management Authority (CCMA) project WLE/42-009 – Understanding the processes causing salinity of the groundwater dependent ecosystems of the CCMA.

The objectives of this third project report are to report on work undertaken during the third quarter-year phase, provide feed-back and chart future directions. Work to date has included the inspection and water sampling of 23 lakes in the CCMA region and chemical analyses of the water samples for radon, stable isotopes and major ions.

2. Lakes Inspection and Sampling Between 23-25 July a site visit was undertaken to sample as many lakes as possible in the CCMA region. Sampling was undertaken by Annette Barton, CSIRO, and Bob Smith, University of Ballarat. Table 1 gives a listing of the 46 lakes visited and a brief comment on the condition of these lakes. Specific sampling localities are shown in Figure 1.

Approximately half of these lakes were dry or the water depth so small as to make it all but impossible to take a sample of water without disturbing and sampling lake sediments in the process. In a number of instances deep mud obstructed access, although for these cases it was thought that even if the water’s edge had been reached it would have been too shallow to sample.

Figure 1. Lake sampling sites.


Table 1. Listing of CCMA lakes Visited and Comment on Condition.

Lake Name/Reference Condition

Deep Lake Completely dry. No sample.

Lake Logan Assumed dry. No sample.

Lake Tooliorook Sample taken.

Kooraweera Lakes (3) Water running into lake on Westbank Rd. Spring? Otherwise dry. Sample taken.

Lake Milangil Virtually dry. Water too shallow to sample.

Lake Round Dry. No sample.

Lake Kariah Dry. No sample.

Lake Colongulac Camperdown WWTP. Did not access due to signage from the South West Water Authority. Water visible.

Lake Bullen Merri Sample taken.

Lake Gnotuk Suds around rim. Sample taken.

Lake Purrumbete Sample taken.

Lake Koreetnung Dry (farmer’s advice). No sample.

Lake Weeranganuk Dry. No sample.

Lake Corangamite Dry in northern part. Very shallow in others and difficult to access due to mud. Only a small sample obtained.

Lake Terangpom Shallow. Sample taken.

Lake Coradgill Dry. Lakes Bulkil Narra, Punpundal & Tatutong assumed likewise.

Lake Gnarpurt Dry. No sample.

Lake Struan Sample taken.

Lake Rosine Sample taken.

Cundare Pool/Lake Martin Water running into inlet. Otherwise dry. Sample taken of inlet water.

Weering Lake Sample taken.

Upper Lough Calvert Shallow. Sample taken.

Middle Lough Calvert Dry. No sample.

Lower Lough Calvert Dry. No sample.

Lake Cundare Sample taken.

Thomas Lake Dry. No sample.

Lake Beeac Water at surface. No sample.

Lake Ondit Dry. No sample.

Lake Purdiguluc Completely dry. Lakes Coragulac & Gnalinegurk assumed likewise.

The Basins (2) Water in both lakes. Sample taken from West Basin.

Lake Colac Sample taken.

Lake Thurrumbong Dry. No sample.

Lake Burn Very shallow. Could not access due to mud. No sample.

Murdeduke Lake Sample taken.

Gherang Lake Dry. No sample.

Modewarre Lake Sample taken.

Breamlea Wetlands Mostly dry. Sample taken from small pool.

Reedy Lake Mostly dry. Sample taken from small pool.

Connewarre Lake Much algae in water. Sample taken.

Connewarre Swamp Sample taken.

Barwon Estuary/Mouth Sample taken.

Murtnagurt Swamp Mostly dry. No sample.

Victoria Lake Sample taken.


Sampling involved collecting a grab sample (most often using a bucket) and extracting a radon sample on site. Some chemical parameters were measured in the field including electrical conductivity (EC), pH, dissolved oxygen (DO) and temperature. Water and radon samples were freighted back to the CSIRO laboratory in Adelaide for analyses.

Of particular interest was the sample collected from the Kooraweera Lakes at Westbank Road. Both the lake sampled, and others in the chain, appeared essentially dry however at this location a streamlet was discharging into one of the lakes and had formed a sizeable pond at its northern tip. Local knowledge suggests that the water emanates from Larra Spring which runs down from Mt Elephant to the north-west and feeds into the Kooraweera chain of lakes (pers. comm. D. Smithyman). This would indicate that the water sampled is groundwater and that these lakes typically have some groundwater dependence.

3. Chemical Analyses

3.1. Field measurements Field measurements for 23 of the 24 lakes sampled are given in Table 2. No field measurements were taken for Sample 6 (Lake Corangamite) as only a small amount of water was obtained due to the shallowness of the water body and the mud impediment. Electrical conductivity (EC) ranges from 134 mS/m for Kooraweera Lakes to 22 400 mS/m for Lake Weering. The higher EC values are likely to underestimate the salinity due to the non-linearity of EC to TDS relationship at high salinity. pH values tend to be in the alkaline range from 7.84 to 9.24 and these are reflected in high measured total alkalinity (Table 3). Most of the surface water had DO concentration less than 100% of that of atmospheric equilibrium indicating active biogeochemical oxidation occurring due to high organic matter concentrations.

3.2. Chemistry The dissolved solutes of the Corangamite Lakes are dominated by Na+ and Cl- except for the most dilute lakes (Kooraweera Lakes and Lake Purrumbete) which have a slightly higher proportion of HCO3

- as anions. In general, the dominance of Na+ and Cl- over the other ions increases linearly as a function of TDS (Figure 2 and Figure 3). Most notably, Ca2+ and HCO3

- remain low throughout the entire salinity range indicating control of these dissolved ions through precipitation of carbonate minerals. The low salinity VVP groundwater and lake waters (TDS <2,500 mg/L) have higher proportion of HCO3

- and alkaline earth ions (Mg2+ and Ca2+) relative to other ions than the more saline surface and ground waters (>2,500 mg/L). These waters probably have a majority of their solutes derived from mineral weathering and a lesser fraction from marine aerosols.

The composition of the more saline lake waters (>2,500 mg/L) are similar to that of seawater and the more saline groundwaters of the VVP. Therefore, the source of most of the dissolved ions for both these lakes and groundwaters are derived from marine aerosols deposited by rainfall. The ratio of Cl-/Br- in all lakes are slightly higher than that of seawater (290) which demonstrates the dominance of the marine origin of Cl- and by inference Na+. In all cases, the ultimate salinity level is determined by the extent of evaporation in the respective lakes rather than amount or source of salt input. The concentration of Si quoted in Table 3 are lower than those measured in the VVP groundwaters (Dighton et al., 2006) and suggest that this element is consumed by in-lake production of phytoplankton such as diatoms.


0

2 104

4 104

6 104

8 104

1 105

1.2 105

1.4 105

1.6 105

0 50000 100000 150000 200000 250000 300000

Corangamite Lakes - anions

ClSO4HCO3

Ani

ons

(mg/

L)

TDS (mg/L) Figure 2. Relationship between lake water anions as a function of TDS

0

2 104

4 104

6 104

8 104

1 105

0 50000 100000 150000 200000 250000 300000

Corangamite Lakes - cations

Na

Mg

Ca

Ion

con

cent

ratio

n (m

g/L)

TDS (mg/L) Figure 3. Relationship of lake water cations as a function of TDS

The ratio of HCO3-/Cl- ranges over nearly three orders of magnitude with an overall decrease

with increasing TDS (Figure 4). The freshest lakes (<2,500 mg/L) tend to have higher HCO3-

/Cl- which is indicative of surface and inter-flow runoff components which tends to have higher component of HCO3

- due to mineral-solution reactions that produce HCO3- as a by-

product. Lakes with salinities >2,500 mg/L show HCO3-/Cl- <0.08 reflecting a higher saline

groundwater component to the water balance. Therefore one may be able to separate the lakes into two groups – low salinity (<2,500 mg/lL) and high HCO3

-/Cl- (>0.08) that are surface water and inter-flow dominated, and higher salinity (>2,500 mg/L) and low HCO3

-/Cl- (<0.01) that are groundwater dominated. The four intermediate samples shown in Figure 4 may represent mixing between the two end-members.

0.001

0.01

0.1

1

10

0 50000 100000 150000 200000 250000 300000

HCO3

-/Cl- vs. TDS

HC

O3- /C

l- (m

ass)

TDS (mg/L) Figure 4. HCO 3

-/Cl- as a function of Cl - concentration


Table 2. Field Measurements for CCMA Lakes

Field Measurements

EC pH DO Temp Wetland Number

Rank Wetland Date Time Sample Number

Easting

MGA Z54

Northing

MGA Z54 µS/cm % oC

994938 99 Lake Tooliorook 23-Jul 10:00 1 700559 5794238 21300 8.94 57 7.5

988822 34 Kooraweera Lakes 23-Jul 10:30 2 698844 5783057 1340 8.82 112 6.9

840643 74 Lake Bullen Merri 23-Jul 12:06 3 684503 5765735 15620 8.98 78 11.9

839675 73 Lake Gnotuk 23-Jul 13:05 4 683654 5766668 93600 8.23 104 13.8

950604 123 Lake Purrumbete 23-Jul 14:00 5 696235 5760044 872 8.8 104 12.1

120710 8 Lake Corangamite 23-Jul 15:10 6 704550 5768249

38768 6 Lake Terangpom 23-Jul 15:30 7 703782 5776211 23000 9.11 114 13.8

121897 86 Lake Struan 23-Jul 16:30 8 712047 5789332 20800 9.04 157 11.1

255870 87 Lake Rosine 23-Jul 17:30 9 726521 5787234 65400 9.24 124 11.4

280809 16 Cundare Pool/Lake Martin 24-Jul 9:00 10 731157 5782465 10360 8.55 85 6.5

351812 90 Lake Weering 24-Jul 10:00 11 736464 5780861 224000 7.91 65 8.1

362762 29 Upper Lough Calvert 24-Jul 11:15 12 734908 5774818 175000 8.1 86.1 10.8

292738 17 Lake Cundare 24-Jul 11:40 13 728850 5772372 187300 8.24 83 14.2

268572 67 Lake Colac 24-Jul 13:30 14 728642 5760999 7840 8.89 106 12.2

139554 39 West Basin 24-Jul 14:50 15 713948 5755079 132300 8.98 115 13.9

540707 10 Lake Murdeduke 25-Jul 9:20 16 755564 5769910 104800 8.73 90 9.6

470630 93 Lake Modewarre 25-Jul 10:10 17 773178 5763114 30900 9.65 82 10

704580 72 Breamlea Wetlands 25-Jul 11:05 18 796532 5756637 76800 8.91 78 11.4

Barwon River 25-Jul 11:45 19 805764 5757426 55000 8.33 69 12.8

782634 3 Connewarre Swamp 25-Jul 12:15 20 807049 5758251 53000 8.25 68 13.3

893610 120 Lake Victoria 25-Jul 12:50 21 815369 5757870 107000 7.84 57 13

770658 2 Connewarre Lake 25-Jul 14:05 22 804848 5764559 45500 8.33 68.8 14.3

739680 12 Reedy Lake 25-Jul 14:40 23 800989 5765422 4840 7.88 63.7 14.2

Barwon River 25-Jul 15:10 24 796488 5766430 2460 8.38 71 11.5


Table 3. Laboratory analysis results for CCMA Lake s

Wetland Number

Rank Wetland pH Tot Alk

Carb Alk

Cl Br - SO4-- Ca K Mg Na S Σcat Σan Diff Si Sr

meq/l meq/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mmol(+/-)/l mg/l mg/l

994938 99 Lake Tooliorook 8.7 11 1.2 6990 19 385 37 46 772 3407 148 214 217 -0.7 <2.0 2.3

988822 34 Kooraweera Lakes 8.3 6.0 191 0.49 20 34 32 52 146 8 13 12 4.9 18 0.3

840643 74 Lake Bullen Merri 8.8 12 1.1 4830 11 8 18 102 250 2886 2 150 148 0.4 <2.0 <1.0

839675 73 Lake Gnotuk 8.5 14 0.9 38000 94 105 118 716 2339 19990 31 1085 1086 0.0 6.3 8.4

950604 123 Lake Purrumbete 8.1 3.0 136 0.23 17 23 6 31 88 6 7.7 7.2 2.8 1.0 0.3

120710 8 Lake Corangamite 7.7 15 108800 470 4330 72 770 4520 64700 1479 3207 3173 0.5 <10 10

38768 6 Lake Terangpom 9.1 30 5.1 7180 18 294 17 184 576 4225 111 236 239 -0.5 <5.0 <2.5

121897 86 Lake Struan 8.5 6.5 0.4 6870 19 423 211 32 729 3073 153 205 210 -1.1 <5.0 5.5

255870 87 Lake Rosine 8.9 10 2.1 24990 68 1110 136 109 2179 12386 400 727 739 -0.9 <5.0 9.9

280809 16 Cundare Pool/Lake Martin 7.9 3.9 3106 8 299 160 20 340 1408 110 98 98 -0.4 <5.0 <2.5

351812 90 Lake Weering 7.7 6.6 152000 438 17528 224 1065 10283 88056 6100 4710 4670 0.4 <10 13

362762 29 Upper Lough Calvert 8.1 4.0 82800 202 3912 73 185 2848 50824 1470 2452 2428 0.5 <10 22

292738 17 Lake Cundare 8.2 3.8 92500 209 6900 27 386 859 61751 2450 2766 2763 0.1 <10 9.9

268572 67 Lake Colac 8.7 7.6 0.4 2302 5 86 78 34 183 1265 30 75 74 0.3 <2.0 1.6

139554 39 West Basin 8.8 28 5.9 56249 147 1815 17 937 1732 34449 622 1665 1651 0.4 <10 <5.0

540707 10 Lake Murdeduke 8.6 30 4.1 42599 121 1711 39 216 2671 23669 590 1255 1267 -0.5 <10 6.3

470630 93 Lake Modewarre 9.4 19 5.7 10620 19 120 21 48 640 5847 39 309 321 -1.9 <5.0 2.5

704580 72 Breamlea Wetlands 8.6 3.0 29400 80 3590 632 560 1720 15767 1240 872 909 -2.0 <5.0 11

Barwon River 8.0 2.1 19600 54 2560 399 412 1216 10633 915 592 611 -1.6 <5.0 7.4

782634 3 Connewarre Swamp 7.9 2.1 18900 51 2490 388 398 1176 10276 890 573 590 -1.5 <5.0 7.2

893610 120 Lake Victoria 7.6 3.8 42500 120 5790 926 925 2668 23938 2110 1330 1333 -0.1 <10 18

770658 2 Connewarre Lake 8.1 2.6 15900 42 2070 330 331 1001 8607 751 481 497 -1.7 <5.0 6.1

739680 12 Reedy Lake 7.4 2.4 1102 2.5 598 152 30 129 642 220 47 47 -0.4 <2.0 1.4

Barwon River 7.9 2.7 601 1.1 80 41 11 64 319 29 21 21 -0.1 0.3 0.5


3.3. Radon count Analytical results for radon-222 (222Rn) are listed in Table 4. In the main the values were very low with only two lakes showing values above 0.15 Bq/L. These were samples 11 (Cundare Pool/Lake Martin inlet) and 23 (Reedy Lake).

Table 4. Results of Radon and Stable Isotopes Anal yses

Radon Isotopes

Quantity Error δ18O δ

2H Wetland Sample Number

Bq/L Bq/L ‰rel SMOW ‰rel SMOW

Lake Tooliorook 1 0.07 0.02 3.06, 3.17 22.2

Kooraweera Lakes 2 0.08 0.02 -4.47 -23.6

Lake Bullen Merri 3 0.00 0.01 2.54 18.4

Lake Gnotuk 4 0.03 0.01 3.10 20.4

Lake Purrumbete 5 0.11 0.02 1.77 11.0

Lake Corangamite 6 0.76 8.0

Lake Terangpom 7 0.11 0.02 0.15 6.5

Lake Struan 8 0.05 0.01 2.78 18.9

Lake Rosine 9 0.08 0.02 3.07 23.5

Cundare Pool/Lake Martin 10 0.35 0.03 -1.44 -10.5

Lake Weering 11 0.00 0.01 -3.02 -12.3

Upper Lough Calvert 12 0.12 0.02 -1.06 -2.1, -2.6

Lake Cundare 13 0.04 0.01 -1.18 -4.0

Lake Colac 14 0.04 0.01 2.32 19.9

West Basin 15 0.08 0.02 3.87 20.1

Lake Murdeduke 16 0.03 0.01 3.16 18.9

Lake Modewarre 17 0.12 0.02 2.93 23.2

Breamlea Wetlands 18 0.07 0.02 0.97 12.7

Barwon River 19 0.00 0.01 0.44 5.9

Connewarre Swamp 20 0.00 0.01 0.41, 0.42 4.6

Lake Victoria 21 0.09 0.02 1.54 10.9

Connewarre Lake 22 0.13 0.02 0.15 1.5

Reedy Lake 23 0.38 0.04 -0.10 -0.8

Barwon River 24 0.08 0.02 -2.83 -16.2

Geyh, 2000, gives background to the use of Rn-222 for identification of groundwater in surface water bodies. Rn-222 is produced by radioactive decay of Radium-226 and is a noble gas with a half-life of 3.6 days. Radium is water-soluble and moves into groundwater by dissolution from rock and alpha recoil of Thorium-230 (230Th). “The presence of the short-lived radon in groundwater always means that the source radium is not too distant.” After discharging to the surface radon degasses completely, hence the presence of radon in surface water bodies may imply recent groundwater inflow.

The analytical results obtained for radon-222 are in general very low. Possible explanations include:

1. there is very little groundwater input to the surface water bodies;

2. due to the shallowness of the lakes groundwater degassing occurs very quickly;

3. sampling did not occur at or near the point of groundwater intrusion;

4. due to the lack of rain, the lakes have become decoupled from the groundwater and hence there has been no recent groundwater input.


As stated above the only exceptions are Cundare Pool/Lake Martin and Reedy Lake; analytical results may indicate the presence of some groundwater in these waterbodies. It is known that the water sampled for Cundare Pool/Lake Martin was essentially stream (Woady Yalloak River) inflow, hence it is possible that, due to the preceding extensive dry period, much of this water could be from the base flow below the river.

In general, however, the radon results have been inconclusive. Radon sampling was undertaken to ascertain if this method might provide insight into the groundwater dependence of the Corangamite CMA lakes, but the results have revealed very little. No further radon sampling is proposed at this stage.

3.4. Stable isotopes The stable isotopes of water (2H/1H and 18O/16O) are considered to be one of the most useful tracers in establishing a lake water balance, particularly with respect to the subsurface components (Rozanski et al., 2000) Evaporation processes lead to measurable increases in the ratio of 2H/1H and 18O/16O with the isotopic concentrations evolving linearly in δ2H - δ18O space. The degree of evaporative enrichment is dependent on atmospheric relative humidity over the lake and the surface water temperature.

Analytical results for stable isotopes deuterium (δ2H) and oxygen-18 (δ18O), for the CCMA lakes sampled, are given in Table 4. In Figure 6 the isotope data have been presented in δ2H - δ18O space and compared with monthly isotopic data for Melbourne rain.

Work undertaken for the Groundwater Flow Systems project (Smitt et al., 2005b, Smitt et al., 2005a and Dighton et al., 2006) included the sampling and analysis of bores in the vicinity of many of the lakes discussed in this report. Results for the stable isotopes δ2H and δ18O for the bore samples have generally plotted within the domain of the average monthly values for Melbourne rainfall shown in Figure 6. It can be seen from this same figure that the δ2H, δ18O coordinates for the Kooraweera Lakes plot within this same range, while all others plot on a line beyond this range. This provides further corroborative evidence to the hypothesis that the Kooraweera Lakes sample was essentially groundwater (refer §2).

Those lakes that lie further to the right along the trend shown in Figure 6 have undergone a greater degree of evaporation relative to the rate of inflow. The lake water balance can be simply represented by a balance between the relatively light isotopic composition of inflow, and the tendency of evaporation to remove the lighter isotope preferentially to the heavier isotope thereby enriching the remaining water in the heavier isotope. In a semi-quantitative way the lakes increase in residence time (Residence time = total volume/total inputs) the further they lie to the right of line beginning at the Kooraweera point and ending at West Basin.

One can assume that the isotopic composition of groundwater is slightly more negative than surface water (refer Figure 6) but for the purposes of this discussion it may be assumed to be indistinguishable. Therefore, the evaporation trend observed for the lakes in Figure 6 would be identical for the two types of inflow. However, if groundwater inflow were substantial and large, one could do an experiment where during a dry period without surface water inflows, say in summer, a time series of selected lakes would assist with determining if groundwater is a significant contributor by monitoring the isotope composition of lake water with respect to the theoretical path of evaporation.

Another way of expressing the data is to use the deuterium excess (δxs = δ2H – 8*δ18O) which is a number that reflects the deviation of a given sample from the meteoric water line. Lower values indicate increasing influence of evaporation. Most of the groundwater samples have a deuterium excess of between 7 – 12, which is slightly less than the local meteoric water values of 13. The lake waters have a δxs between 5 and -5, and if there was a large flow-through of groundwater, then the δxs would be higher (that is approaching the groundwater δxs values). However plotting the δxs values data as a function of HCO3

-/Cl- (Figure 5) can at least qualitatively distinguish between the relative importance of surface water, groundwater and evaporation dominated lakes. Type 1: High δxs, low HCO3

-/Cl- - groundwater dominated, through-flow; Type 2: Low δxs, low HCO3

-/Cl- - groundwater


dominated, long residence time; Type 3: High δxs, high HCO3-/Cl- – surface water dominated,

through-flow.

-10

-5

0

5

10

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

D-e

xces

s (‰

,VS

MO

W)

HCO3

-/Cl- (mass) Figure 5. Deuterium-"excess" versus HCO 3

-/Cl -

In Table 5 the lakes have been grouped into their various types on the basis of deuterium “excess”. This categorisation represents the end members and there a continuum between the three.

Table 5. Wetland delineation on the basis of deute rium “excess”

Wetland Type Type Description Wetland Names

Type 1 High δxs, low HCO3-/Cl- :

high groundwater flow-through

Lake Corangamite; Cundare Pool/Lake Martin; Lake Weering; Upper Lough Calvert; Lake Cundare; Breamlea Wetlands; Connewarre Swamp; Connewarre Lake.

Type 2 Low δxs, low HCO3-/Cl- :

groundwater dominated, long residence time

Lake Tooliorook; Lake Gnotuk; Lake Struan; Lake Rosine; West Basin; Lake Murdeduke; Lake Victoria.

Type 3 High δxs, high HCO3-/Cl- :

surface water dominated

Kooraweera Lakes; Lake Bullen Merri; Lake Purrumbete; Lake Terangpom; Lake Colac; Lake Modewarre; Reedy Lake;.

Surface water dominated through-flow lakes

Groundwater dominated through-flow lakes

Groundwater/ evaporation dominated


y = 5.9x + 2.7

y = 7.9x + 11.5

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

10.00

20.00

30.00

-8.00 -6.00 -4.00 -2.00 0.00 2.00 4.00

d18O

d2 H

Melbourne Rain

Kooraweera

Weering

Reedy

Murdeduke

Rosine

ColacModewarre

Corangamite

Terangpom

W. BasinGnotuk

Breamlea

Barwon R.

StraunBullen Merri

Purrumbete

Victoria

Conn. Swamp

Conn. Lake

Upper Lough Calv.

Lake Cundare

Inlet Cundare Pool

Barwon R.Upstream L. Reedy

Tooliorook

Figure 6. Lake stable isotopes shown in δ

2H - δ18O space together with average monthly values for Me lbourne rain.


4. Further Work The solute and stable isotope investigations begun in this last quarterly period have the potential to contribute valuable information towards the understanding of the groundwater dependence of the CCMA lakes. It is therefore proposed that sampling and testing of the lakes be continued on a regular (3 monthly) basis, in order to ascertain the behaviour of the lakes on a temporal basis, and in particular to evaluate the seasonal changes in groundwater dependence. It is also proposed that several lakes be monitored for detailed investigation (weekly monitoring) during the drier summer months when the influence of surface water is minimized and the groundwater dynamics may be investigated with greater precision.

A better understanding of the present hydraulic gradients is also needed. It is important to carefully measure (where required) and document water levels in the lakes and in the groundwater on an absolute AHD scale to established potential gradients to the lakes for both the phreatic and deep lead groundwater systems.

5. Acknowledgements Acknowledgement is given of the help and assistance of Dr Jeffrey Turner, CSIRO Land and Water, Wembley, WA, with respect to isotope analysis. Bob Smith, University of Ballarat kindly assisted with the field work logistics and sampling of the lakes. Phil Davies, CSIRO Land and Water produced Figure 1.

References

Dighton, J., Dahlhaus, P., Davies, P., Cox, J., Barton, A., Smitt, C. and Smith, B. (2006) Defining groundwater flow systems on the basalt plains to accurately assess the risk of salinity and impacts of changed landuse, Third milestone report: Groundwater chemistry, Report to the Corangamite Catchment Management Authority, CSIRO Land and Water, Urrbrae, SA.

Geyh, M. (2000) Groundwater: Saturated and Unsaturated Zone, Volume IV, Environmental istotopes in the hydrological cycle: Principles and applications Technical documents in hydrology, No. 39, Vol. IV, UNESCO/IAEA, Paris

Rozanski, K.,Froehlich, K., and Mook, W.G. (2000) Surface Water, Volume III, Environmental isotopes in the hydrological cycle: Principles and applications Technical documents in hydrology, No. 39, Vol. III, UNESCO, Paris

Smitt, C., Cox, J., Dahlhaus, P., Dighton, J. and Davies, P. (2005a) Defining groundwater flow systems on the basalt plains to accurately assess the risk of salinity and impacts of changed landuse, Second milestone report, Report to the Corangamite Catchment Management Authority, CSIRO Land and Water, Urrbrae, SA.

Smitt, C., Cox, J., Dahlhaus, P. and Fitzpatrick, A. (2005b) Defining groundwater flow systems on the basalt plains to accurately assess the risk of salinity and impacts of changed landuse, First milestone report, Report to the Corangamite Catchment Management Authority, CSIRO Land and Water, Urrbrae, SA.

sampling and analysis of lakes in the corangamite cma region · corangamite cma region report to...

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