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					TITLE:              ASSESSMENT OF THE WATER QUALITY OF
                    THE EBENEZER DAM



REPORT NUMBER:      N/B800/02/DEQ/2699



PROJECT:            TROPHIC STATUS PROJECT



STATUS OF REPORT:   FINAL



DATE:               AUGUST 1999
INTRODUCTION
This report was compiled following the request of the Water Control Officer (WCO) for data of
the Ebenezer Dam. It is essential that samplers that have been sampling for the IWQS at
different impoundments should have access to the results to allow samplers to understand
the purpose of sampling and receive feedback. This is also proposed as one way of
acknowledging the samplers for years of hard work. Interpretation of data was also
undertaken to assist WCO with the assessment of the data.

BACKGROUND
The Ebenezer Dam was included in the Trophic Status Project. This initiated a sampling
programme that was conducted by the Water Control Officer at the dam. The IWQS provided
all the equipment for the sampling programme. Analysis of samples was done at IWQS for the
following variables:

      Inorganic chemical constituents
      Total nutrients
      Chlorophyll a
      Algal composition
      Turbidity (Secchi disc readings)
      Suspended solids
      Phaeophytin

This data has now been assessed and this report is the result there-off.

SITE BACKGROUND
The Ebenezer Dam is situated in the upper reaches of the Groot Letaba River catchment on
the confluence of the Broederstroom and Helpmekaar rivers (Figure 1). The catchment is in
mountainous area with mainly natural vegetation. The small rural town of Haenartsburg is in
the catchment of the Ebenezer Dam.

The dam wall was completed in 1960 and the water was mainly intended for irrigation
purposes (RSA, 1964). Lately pipelines have been installed to supply water to a great number
of rural communities in the Northern Province.

WATER QUALITY OF THE EBENEZER DAM
The chemical water samples received at IWQS were analysed for inorganic variables and
total nutrients. The results are stored on the main database of the Department of Water
Affairs and Forestry in Pretoria. The statistics for the chemical variables measured are shown
in Table 1. The variables are organised in alphabetical order.

Table 1.             The statistical analysis for all chemical variables in the Ebenezer Dam (1989-
                     1998)

    Variable                        Minimum 5 Percentile Mean Median 95 Percentile Maximum No. samples
    Ammonium (NH4-N)                  0.01      0.02     0.14  0.12      0.30        0.49       83
    Calcium (Ca)                       0.0      2.0       2.8   3.0       4.0         5.0       82
    Chloride (Cl)                      0.0      3.0       5.4   5.0       9.0        13.0       82
    Electrical Conductivity (EC)       3.6      4.6       5.5   5.4       7.0         8.0       83
    Fluoride (F)                      0.00      0.00     0.14  0.10      0.30        0.50       82
    Kjeldahl nitrogen (KN)            0.23      0.29     0.49  0.48      0.73        1.06       69
    Magnesium (Mg)                     0.0      1.0       1.8   2.0       2.0         3.0       82
    Nitrate & nitrite (NO3+NO2-N)     0.00      0.02     0.08  0.07      0.21        0.23       83
    Ortho-phosphorus (PO4-P)         0.000     0.002     0.011 0.010    0.021       0.069       83
    pH                                 4.7      6.5       7.4   7.4       8.0         8.3       83
    Potassium (K)                      0.0      0.5       1.1   0.8       2.3         3.2       82
    Silicon (SI)                       2.8      3.0       4.4   4.5       5.2         5.8       83
    Sodium (Na)                        0.0      1.1       3.3   3.0       5.0         6.0       82
    Sulphates (SO4)                    0.0      1.0       5.1   5.0      10.9        21.0       82
    Total alkalinity (TAL)             0.0      8.0      15.5  16.0      23.0        25.0       82
    Total dissolved salts (TDS)         0        28       39    38        53          63        82


                                                                                                         1
Inorganic chemistry
The      mean     total   dissolved   solids                                                          1998.
concentration, which is an indication of the
salinity in the system, is 39 mg/l. This low                                                          Figure 2.                  Pie diagram showing the
concentration indicates that there are no                                                                                        contribution of the major ions to
saline impacts on the impoundment. As                                                                                            the TDS concentrations in
the TDS concentration is a total of the                                                                                          Ebenezer Dam.
major ions in the system the contribution
of the different major ions to the TDS
concentration is shown in Figure 2. The
changes in time for the mean annual,
major ion concentrations, total alkalinity
(TAL) and electrical conductivity are
shown in Figure 3a and 4. It can be seen
that concentrations have remained fairly
constant with the possible exception of
sulphate and TAL. This also indicates the
impact of activities on salinity is minimal.
Figure 3b show the minimum, 5 percentile,
mean, 95 percentile and maximum
concentrations of the main ions found in
the Ebenezer Dam for the period 1989 to


                                    10
                                                                                                                                                      Na
                     Conc. (mg/l)




                                     8                                                                                                                K
                                     6                                                                                                                Ca
                                     4                                                                                                                Mg
                                                                                                                                                      Cl
                                     2
                                                                                                                                                      SO4
                                     0
                                               89 - 90

                                                         90 - 91

                                                                   91 - 92

                                                                              92 - 93

                                                                                         93 - 94

                                                                                                   94 - 95

                                                                                                             95 - 96

                                                                                                                       96 - 97

                                                                                                                                  97 - 98

                                                                                                                                            98 - 99




                                                                             Hydrological Year



                                    25

                                    20
                     Conc. (mg/l)




                                                                                                                                                      Min.

                                    15                                                                                                                5%
                                                                                                                                                      Mean
                                    10                                                                                                                95%
                                     5                                                                                                                Max.

                                     0
                                                   Na              K                    Ca           Mg                Cl              SO4
                                                                                        Variable
                                                                                                                                                             b




                                     Na
            SO4                     17%
            26%
                                           K
                                          6%

                                           Ca
                                          14%

              Cl                    Mg
             28%                    9%




                                                                                                                                                                 2
Figure 3.   a) The mean annual concentration for the main ions (N, K, Ca, Mg, Cl & SO 4)
            in the Ebenezer Dam (1989 to 1998). b) The minimum, 5th percentile, mean,
            95th percentile and maximum concentrations of the main ions (N, K, Ca, Mg,
            Cl & SO4) for the whole period.




                                                                                      3
                                             25




                 Conc. (mg/l)
                                             20
                                             15                                                                                                                                                                         EC
                                             10                                                                                                                                                                         TAL
                                              5
                                              0




                                                    89 - 90

                                                                         90 - 91

                                                                                              91 - 92

                                                                                                                   92 - 93

                                                                                                                                    93 - 94

                                                                                                                                                   94 - 95

                                                                                                                                                                95 - 96

                                                                                                                                                                           96 - 97

                                                                                                                                                                                     97 - 98

                                                                                                                                                                                                98 - 99
                                                                                                                   Hydrological Year



Figure 4.      Mean annual electrical conductivity (EC) and total alkalinity (TAL)
               concentration in the Ebenezer Dam (1989 to 1998).


Nutrients
The main nutrients measured, include ammonium (NH4), nitrate & nitrite (NO3 &NO2), Kjeldahl
nitrogen (KN), ortho-phosphorus (PO4) and total phosphorus (TP).

Figure 5 indicates that in the Ebenezer Dam, the mean annual TP and PO4 concentrations for
the period 1989 to 1998, were consistently within the required Phosphorous Management
Objective (PMO) of 130 µg/ P (DWA 1988, ANON 1988a, ANON 1988b). The mean annual
TP and PO4 concentrations were also below the 47 µg/ that were suggested by WALMSLEY
and BUTTY (1980) and there is also no increase in the concentrations during the period. The
impoundment is, therefore, not very productive in terms of eutrophication and plant
production.

The mean annual nitrogen concentrations in the Ebenezer Dam are reflected in Figure 6 and
indicate that the nitrogen concentrations within the impoundment were continuously within the
TWQR and consistently below 1 mg/. There were no distinct increases in the nitrogen
species concentrations during the study period.

The mean annual TN:TP ratios for the Ebenezer Dam are shown in Figure 7. The TN:TP
ratios indicate that the water quality in the Ebenezer Dam is phosphorous limited indicating
that eutrophic conditions are unlikely to occur. Ratios have also remained fairly consistent,
therefore no problem is expected to occur in the near future. The nutrient contents of the
impoundment indicate that the water quality of the system is of a desirable quality when
eutrophication is considered.
                 Phosphorus species (mg/l)




                                             0.25

                                             0.20

                                             0.15                                                                                                                                                                             PO4-P
                                                                                                                                                                                                                              TP
                                             0.10                                                                                                                                                                             PMO
                                             0.05

                                             0.00
                                                              89 - '90

                                                                                   90 - '91

                                                                                                        91 - '92

                                                                                                                             92 - '93

                                                                                                                                              93 - '94

                                                                                                                                                             94 - '95

                                                                                                                                                                          95 - '96

                                                                                                                                                                                     96 - '97

                                                                                                                                                                                                  97 - '98

                                                                                                                                                                                                             98 - '99




                                                                                                                             Hydrological Year



Figure 5.      Changes in mean annual TP and PO4 concentrations in the Ebenezer Dam
               (1989–1998). PMO = Phosphorous Management Objective for total
               phosphorous concentrations




                                                                                                                                                                                                                                      4
                   Nitrogen species (mg/l)
                                             5.0

                                             4.0
                                                                                                                                                                                                                                                                             NH4-N
                                             3.0                                                                                                                                                                                                                             NO3+NO2-N
                                             2.0                                                                                                                                                                                                                             KN
                                                                                                                                                                                                                                                                             TWQR
                                             1.0

                                             0.0




                                                     89 - '90

                                                                        90 - '91

                                                                                              91 - '92

                                                                                                                   92 - '93

                                                                                                                                 93 - '94

                                                                                                                                                  94 - '95

                                                                                                                                                                        95 - '96

                                                                                                                                                                                                96 - '97

                                                                                                                                                                                                                    97 - '98

                                                                                                                                                                                                                                    98 - '99
                                                                                                               Hydrological Year



Figure 6.       Mean annual concentration for KN, NO 3+NO2 and NH4 in the Ebenezer Dam
                (1989 – 1998) compared to the TWQR for NO3+NO2



                                             50

                                             40
                   TN:TP ratio




                                             30

                                             20

                                             10

                                              0
                                                      89 - '90


                                                                                   90 - '91


                                                                                                               91 - '92


                                                                                                                                    92 - '93


                                                                                                                                                             93 - '94


                                                                                                                                                                                              94 - '95


                                                                                                                                                                                                                         95 - '96


                                                                                                                                                                                                                                                96 - '97


                                                                                                                                                                                                                                                                       97 - '98


                                                                                                                                                                                                                                                                                     98 - '99
                                                                                                                                            Hydrological Year



Figure 7.       Mean annual TN:TP ratio in the Ebenezer Dam for the period 1989 to 1998

Biological characteristics
The chlorophyll a concentration (Figure 8) is an indication of the phytoplankton production in
the impoundment and is almost consistently below 10 µg/ in the Ebenezer Dam. Only during
1995 to 1996 was there an increase in mean annual chlorophyll a concentration. The
concentrations however never exceeded 30 µg/. Cyanobacteria (potential toxic) were
present as a part of the algal population during 1991 to 1993 (Figure 9) and there is,
therefore, little chance of toxic algal blooms. Either Chlorophyta or Chrysophyta dominated
the algal population during the study period.
                                                                                                                                                                                                                                               Secchi disc depth (m)
                   Percentage of time




                                                   100                                                                                                                                                                                0
                                                   80                                                                                                                                                                                 1                                           <10ug/l
                                                                                                                                                                                                                                      2                                           10-20ug/l
                                                   60                                                                                                                                                                                 3
                          (%)




                                                                                                                                                                                                                                                                                  20-30ug/l
                                                   40                                                                                                                                                                                 4
                                                                                                                                                                                                                                      5                                           >30ug/l
                                                   20                                                                                                                                                                                 6                                           SECCHI
                                                    0                                                                                                                                                                                 7
                                                                 89 - '90

                                                                                   90 - '91

                                                                                                    91 - '92

                                                                                                                      92 - '93

                                                                                                                                 93 - '94

                                                                                                                                               94 - '95

                                                                                                                                                                95 - '96

                                                                                                                                                                                   96 - '97

                                                                                                                                                                                                         97 - '98

                                                                                                                                                                                                                        98 - '99




                                                                                                           Hydrological Year




                                                                                                                                                                                                                                                                                                5
Figure 8.       Percentage of the time that chlorophyll a are within a range of concentrations
                and Secchi disc depths in the Ebenezer Dam, near the dam wall




                             Proportion of algal
                                                       100%




                               population (%)
                                                       80%
                                                       60%                                                                                                                                                          Euglenophyta

                                                       40%                                                                                                                                                          Phyrrophyta
                                                                                                                                                                                                                    Cryptophyta
                                                       20%
                                                                                                                                                                                                                    Chrysophyta
                                                        0%
                                                                                                                                                                                                                    Chlororphyta




                                                              89 - '90

                                                                         90 - '91

                                                                                                91 - '92

                                                                                                                92 - '93

                                                                                                                           93 - '94

                                                                                                                                       94 - '95

                                                                                                                                                  95 - '96

                                                                                                                                                                         96 - '97

                                                                                                                                                                                         97 - '98

                                                                                                                                                                                                    98 - '99
                                                                                                                                                                                                                    Cyanophyta


                                                                                                           Hydrological Year



Figure 9.       Mean annual dominance of algal groups in the Ebenezer Dam

Physical characteristics
Mean Secchi disc readings, a measurement for turbidity, are plotted in Figure 8. The
readings ranged between 1.8m and 6.3m, indicating that the impoundment is a clear system.
There is a slight positive correlation between the Chl a and the Secchi disc readings (r² =
0.38) in the Ebenezer Dam, indicating that the chlorophyll a might contribute to the turbidity in
the system, however, chlorophyll a is not the main contributor towards turbidity in the system.



                Feb                                                      Jun                                                                      Dec
                                            Temp. (°C)                                                         Temp. (°C)                                                               Temp. (°C)
                                        0          10 20    30                                             0        10 20             30                                            0       10 20              30
                                  0                                                                 0                                                                       0

                                  4                                                                 4                                                                       4

                                  8                                                                 8                                                                       8
                                                                                                                                                             Depth (m)
                 Depth (m)




                                                                                    Depth (m)




                              12                                                                 12                                                                      12

                              16                                                                 16                                                                      16

                              20                                                                 20                                                                      20

                              24                                                                 24                                                                      24



               Feb                                                       Jun                                                                      Dec
                                              O2 (mg/l)                                                        O2 (mg/l)                                                                O2 (mg/l)
                                        0          5   10   15                                             0          5    10         15                                            0         5     10         15
                                  0                                                                 0                                                                       0

                                  4                                                                 4                                                                       4

                                  8                                                                 8                                                                       8
                                                                                                                                                             Depth (m)
                 Depth (m)




                                                                                    Depth (m)




                              12                                                                 12                                                                      12

                              16                                                                 16                                                                      16

                              20                                                                 20                                                                      20

                              24                                                                 24                                                                      24




Figure 10.      Temperature and oxygen profiles in the Ebenezer Dam (February 1993, June
                1999 and December 1998)


The temperature profiles shown in Figure 10 show that there is distinct stratification
(temperature variation of approximately 10°C at a depth of around 8m) during the warm


                                                                                                                                                                                                                                   6
summer periods in the Ebenezer Dam and complete thermal mixing (temperature remains
consistent at approximately 15°C throughout all depths) during the colder winter months.
Surface water temperatures varied between 16.4°C and 23.7°C. Monthly oxygen profiles in
the Ebenezer Dam shows a distinct hypolimnion from between 10 m and 16 m, even during
the winter months.

Trophic status of the Ebenezer Dam
Table 2 indicates that the Ebenezer Dam is oligotrophic (low nutrient and plant growth) with
only periodically increased nutrient concentrations, towards mesotrophic conditions (higher
nutrient and plant production). The Ebenezer Dam water is of high quality in terms of its
trophic status and within acceptable levels. This is supported by the low salinity in the
impoundment and the chlorophyll a concentration that never exceeds 30 µg/.

Table 2.        Trophic status indicators in the Ebenezer Dam for the period 1989 –1998

      Year         Chlorophyll a              TP        Cyanobacteria        Mean Secchi         Trophic Status
                                                          dominance          disc reading
                 Mean         >30µg/        Mean            Mean               Mean
                 (µg/)         (%)          (mg/)           (%)                (m)

   1989-1990      3.0            0           0.014             0                  2.8                O & clear
   1990–1991      1.1            0           0.011             0                  3.3                O & clear
   1991-1992      3.3            0           0.026             0                  2.9                O & clear
   1992-1993      6.3            0           0.029             0                  2.3                O & clear
   1993-1994       -             -           0.037             0                  1.8                O & clear
   1994-1995      3.9            0           0.026             0                  1.8                O & clear
   1995-1996      9.6            0           0.023             0                  6.3                O & clear
   1996-1997      2.4            0           0.022             0                  2.8                O & clear
   1997-1998       -             -           0.016             0                  2.9                O & clear
   1998-1999      3.7            0             -               -                  3.0                    -


               The shading in the table is proportional to the eutrophication in the impoundment.
                          O = oligotrophic               M = mesotrophic
                          E = eutrophic                  HE = hyper-eutrophic


CONCLUSION
The Ebenezer Dam is oligotrophic with a tendency to being mesotrophic. There is no
noticeable salinity increases. The biological symptoms coupled to eutrophication indicators in
the form of nutrients also indicate that the water in the Ebenezer is of high quality.

RECOMMENDATIONS
Reports on the trophic status of impoundments should be compiled for:
 the information of Water Control Officers
 acknowledgement to samplers for the years that they contribute towards this information
   gathering

ACKNOWLEDGEMENTS
1.   Annelise Gerber, Alfred Seloana and Joyce Maluleka, the Technical Section of the
     IWQS, for their commitment towards the Trophic Status Project monitoring.
2.   The Water Control Officers at Ebenezer Dam for his continued effort to do the local
     sampling.
3.   Elna Vermaak for producing the map for this report.
4.   Toni Belcher for comments on the final report.




                                                                                                                  7
REFERENCES
ANON, (1988a) Phosphate standard now strictly enforced. SA Waterbulletin, vol. 14, no. 5
       p22. Pretoria.
ANON, (1988b) Special phosphate standard for sensitive catchments. Water sewage and
       Effluent, vol. 8, no. 4 pp 10-11. Pretoria.
DWA. (1988) Important announcement on implementation of the Special Phosphate standard
       in sensitive catchments. IMIESA (Johannesburg), vol13, no. 9, p 35.
DWAF, (1996) South African Water Quality Guidelines. First Edition. Department of Water
       Affairs, PRETORIA, South Africa.
RSA, (1964). Verslag oor die voorgestelde Pietersburgse streekwaterskema. Report by the
       secretary of Water Affairs. PRETORIA.
WALMSLEY, R.D. AND BUTTY, M., (1980) Guidelines for the control of eutrophication in South
       Africa. Special Report, Water Research Commission, PRETORIA, South Africa.




                                                                                        8

				
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