AN INVESTIGATION INTO THE POSSIBLE SOURCES OF NUTRIENTS IN THE CATCHMENT AND THE COST IMPLICATIONS TO RAND WATER

Gyedu-Ababio, T.

Kruger National Park, P/Bag X1021, Phalaborwa 1390. Tel: 082 908 7729. E-mail: [email protected]

ABSTRACT

Rand Water supplies potable water to about 10 million people in and surrounding areas. Nutrients generated in the catchment end up in the Vaal Dam, which is the main abstraction source of raw water for Rand Water. Nutrients in the Vaal Dam cause the proliferation of algae with associated treatment costs to Rand Water. The historical water quality data in the various sub-catchments were analysed and various activities that might contribute to the nutrient loads investigated. It was realised that the size of the catchment, size of agricultural fields and sewage effluents had positive correlation with the loads of nutrients leaving the respective sub-catchments. It was also realised that the contributes a greater proportion of nutrients in the Vaal Dam as compared to the . The water from the LHWP has “buffered” the quality of the recipient system. The chemical and other treatment costs of Rand Water was found to increase with the increasing nutrient loads. It is suggested that all wastewater treatment plants be monitored closely to ensure efficient and effective performance. Best management practices in the agricultural and industrial set-ups be enforced in the Vaal Dam Catchment to reduce the nutrient loads in the Vaal Dam. Rand Water’s contribution towards the management of the Vaal Dam Catchment should be considered when negotiating the raw water tariffs.

Keywords: Nutrients, sewage effluents, catchment, treatment costs, Vaal Dam

INTRODUCTION

The patterns of cycling nutrients in the ecosystem involve not only metabolism by living organisms, but also a series of strictly abiotic chemical reactions. Despite the fact that nitrogen, N, and phosphorus, P, are natural elements in water and essential for animal and plant life, their levels in many surface waters are too high leading to eutrophication. Domestic and industrial waste water arising from sewage treatment plants furnished with insufficient infrastructure, intensive agriculture with overuse and/or misuse of pesticides and fertilisers, uncontrolled livestock breeding, irrigation and storm water are named as the major sources of diffuse pollution in many catchment areas. Among these sources, agricultural fertilisers have for a long time been considered as the main sources of nutrients worldwide on a global scale (1). The difficulty in identifying such sources both qualitatively and quantitatively is that they are highly governed by natural conditions such as spatial (topography, location, incidence of surface runoff) and temporal (precipitation, evaporation), soil characteristics (soil texture, structure and permeability) and land management (land use, cultivation trends, fertiliser application and frequency)(2).

Agricultural nutrient losses have been demonstrated to accelerate eutrophication in aquatic systems in many countries. Phosphorus and other nutrients stimulate the growth of aquatic plants including undesirable algae (3, 4). In the Vaal Dam Catchment, a greater proportion of land is used for agricultural purposes. The Vaal River catchment is more industrialized than the Wilge catchment. Sewage treatment plants abound in the Vaal Dam Catchment and their malfunctioning has been a source of concern to the Catchment Management Section of Rand Water.

Proceedings of the 2004 Water Institute of Southern Africa (WISA) Biennial Conference 2 –6 May 2004 ISBN: 1-920-01728-3 Cape Town, Produced by: Document Transformation Technologies Organised by Event Dynamics Nutrient enrichment and stimulation of plant growth limits the potential use of the affected water and it is a cost to the community (5). The Vaal River is the most important and most regulated in South Africa. It is also a eutrophic system on account of high chlorophyll-a and inorganic nitrogen and phosphorus concentrations (6).

Rand Water buys raw water (from the Vaal system) from the Department of Water Affairs and Forestry (DWAF). The cost of raw water keeps increasing. Operational and chemical costs together with raw water costs constitute more than 50% of Rand Water’s annual budget. Nutrients in the Vaal Dam cause proliferation of algae, which in turn cause quality problems associated with the potable water. Rand Water therefore has to spend more money in the purification of water. It costs Rand Water approximately R9761.33 to transform one mega-litre of raw water to potable water (7, 8, 9, 10, 11, 12). The above notwithstanding, Catchment Management Section of Rand Water do an excellent job in protecting the source water, the cost of which is not considered in the negotiation of raw water tariffs.

This research focuses on the sources of the nutrients and the cost implication on Rand Water should the nutrient levels in the Vaal Dam increase. The main objectives of the study were to: • identify the subcatchment that produces higher nutrient loads into the Vaal Dam • project a financial scenario as to the nutrient pollution of the source water and • provide some tools to management to be used in the negotiation on raw water tariffs

METHODS OF STUDY

The data for the study were obtained by routine and adhoc surveys of the Vaal Dam Catchment; Water Quality data from Rand Water CIMDSS; flow data from the Department of Water Affairs and Forestry (DWAF, Pretoria); interviews with Human Resource and Finance personnel at Rand Water. Farmers in the catchment were also consulted.

Description of the Study Area The Vaal Dam Catchment covers an area of about 39 143 km2. It is situated in the regions of; 28o07’E, 26o45’S; 30o15’E, 26o15S and 28o52’E, 28o45’S. It is further divided into the Wilge and Vaal sub-catchments.

Figure 1. Map of the Vaal Dam catchment showing the two sub catchments and Rand Water’s sampling points. Thus, the Vaal Dam Catchment consists of two main sub-catchments; the Vaal River and the Wilge River Catchments. The land cover for the two catchments is 20 442 km2 and 18 151 km2 for the Vaal and Wilge respectively. The landscape is characterised by mountains, up to the height of 2200 m in the fringes of the catchment. A larger proportion of the land, especially the Vaal sub-catchment is below 2000 m. The towns indicated on the map have got sewage treatment plants which have been undergoing repairs or upgrading due to the influx of people into these towns for the past few years.

Nutrient Analysis and Loads All nutrients analysis was done at Rand Water Laboratories using Rand Water’s methods. The nutrient load calculation was done using the concentration of the specified nutrients, (nitrate, phosphate, TKN, and TP) and the volume of water passing through such sampling points per month and per annum. Load = AC x AV; where AC = average concentration and AV = average volume per month. Loads were converted to Kg/month or Kg/year. Calculations were therefore done for sites with weirs (volume or continuous flow meters). Calculations were made from 1995/6 to 2000/1 where data was available. The three main sampling points in the Wilge/Liebenbergsvlei catchment, WL, WLA and WAF have flow values from the beginning of 1998 when the LHWP water was released into the Ash River.

RESULTS OF THE STUDY

The types of fertiliser being used in the Vaal Dam Catchment are mainly ammonium nitrate, ammonium sulphate, potassium sulphate, triple supper phosphate (TSP), 20.20.20, 15.15.15 composite fertilisers and urea.

Correlation Between Catchment Size and Nutrient Loads The sizes of the sub-catchments in which the monitoring was done differ. A regression analysis was done for all the quaternary catchment areas within each leg and the loads of the various nutrients used in this study.

Table 1. Regression analysis between size of catchment and nutrient loads. Vaal Catchment Wilge Catchment Nutrient R2 P-value R2 P-value

Nitrate (NO3) 0.029 0.500 0.071 0.52

Phosphate (PO4) 0.241 0.038 0.046 0.07 Total K. Nitrogen (TKN) 0.355 0.009 0.248 0.208 Total Phosphorus (TP) 0.284 0.022 0.486 0.054

There was significant correlation between the catchment size and all the nutrients studied with the exception of nitrate in the Vaal sub-catchment. The opposite is true for the Wilge sub-catchment. There was no significant correlation between the nutrients and the size of the catchment in the Wilge. This might be due to the fact that not enough data was available on yearly basis for this particular analysis in the Wilge sub-catchment. The common land use in the two catchments have been compared in Table 2 as percentage land cover.

It can be seen from Table 2 that, apart from mines and quarries, unimproved grassland, cultivated temporal dry land and barren rock, percentage land use is similar in the two catchments. The Vaal catchment has a higher percentage of mines and quarries than the Wilge. The Vaal also has a greater percentage of unimproved grassland as compared to the Wilge but the Wilge dominates in the percentage temporal cultivated dry land. Table 2. Comparison of the land use in the two catchments, Vaal and Wilge. Percentage cover Land use Vaal Wilge Barren rock 0.0088 0.3347 Cultivated: permanent - commercial irrigated 0.0023 0.0156 Cultivated: temporary - commercial dryland 27.7831 36.9825 Cultivated: temporary - commercial irrigated 0.1970 0.1073 Cultivated: temporary - semi-commercial/subsistence dryland 0.1130 0.0726 Degraded: unimproved grassland 0.0092 0.8633 Dongas & sheet erosion scars 0.0204 0.0046 Forest plantations 0.4487 0.3619 Improved grassland 0.0411 0.0028 Mines & quarries 0.2376 0.0008 Thicket & bushland (etc) 0.4946 1.1072 Unimproved grassland 68.9147 57.5985 Urban / built-up land: commercial 0.0152 0.0224 Urban / built-up land: industrial / transport 0.1438 0.0155 Urban / built-up land: residential 0.5686 0.7438 Urban / built-up land: residential (small holdings: grassland) 0.0034 0.0119 Water bodies 0.7737 1.2508 Wetlands 0.2204 0.3410

Table 3. Nutrient loads at selected sites in the Vaal Dam catchment. Wilge leg (most downstream point) Vaal leg (most downstream point) NO3 WF NO3 WAE+VGB Oct-Sep Kg/yr Oct-Sep Kg/yr 1995/96 12694.52 1995/96 31620.24 1996/97 12754.42 1996/97 20865.24 1997/98 21699.69 1997/98 12387.58 1998/99 3075.31 1998/99 3127.04 1999/00 7561.58 1999/00 8888.01 2000/01 8711.21 2000/01 3928.51 Avg 11082.79 Avg 13469.44

PO4 WF PO4 1995/96 2521.11 1995/96 4658.29 1996/97 2729.81 1996/97 4992.19 1997/98 2557.92 1997/98 2981.59 1998/99 2424.19 1998/99 2094.17 1999/00 1611.87 1999/00 2686.26 2000/01 710.45 2000/01 3223.43 Avg 2092.56 Avg 3439.32

TKN WF TKN 1995/96 37282.75 1995/96 64793.15 1996/97 39157.90 1996/97 28057.25 1997/98 14878.57 1997/98 23047.95 1998/99 12351.33 1998/99 7496.09 1999/00 44397.59 1999/00 50444.67 2000/01 55666.49 2000/01 48332.59 Avg 33955.77 Avg 37028.62

Table 3. continued. TP WF TP 1995/96 11537.78 1995/96 20040.55 1996/97 9795.21 1996/97 9091.3 1997/98 5840.58 1997/98 6796.42 1998/99 7713.32 1998/99 5014.11 1999/00 8699.37 1999/00 8962.83 2000/01 3934.8 2000/01 4025.16 Avg 7920.18 Avg 8988.40

It can be seen from Table 3 that the Vaal leg contributed higher loads (in almost all the identified nutrients) than the Wilge leg.

Impact of Water from Lesotho Water was released from the LHWP into the Ash River, which drains into the Liebenbergsvlei in early 1998. The Liebenbergsvlei is a tributary of the Wilge River, one of the main sources of water in the Vaal Dam. The graphs below show the loads of the identified nutrients in the rivers, before and after the release of the Lesotho water.

Figure 2. Nitrate loads measured at selected points in the Wilge.

Figure 3. Phosphate loads measured at selected points in the Wilge. It is evident from Figures 2 & 3 that the loads of Nitrates and phosphate reduced drastically in the receiving river, Liebenbergsvlei at WL, just before the confluence with the Wilge River. This subsequently caused the load in the Wilge River after the confluence with the Liebenbergsvlei to decrease considerably during 1998 (WF). It can therefore be inferred from the above analysis that water from Lesotho actually reduced the load of the identified nutrients in the receiving waters and in the Vaal Dam as a whole.

Cost of Chemicals and Operating Expenses Table 4 gives an illustration and trends of cost of chemicals and other operating expenses.

Table 4. Percentage variation in the cost of chemicals for the production of potable water (1997-2002).

Item Percentage variation in item (%) 1997 1998 1999 2000 2001 2002 Cost of sales (water 31 39 43 43 44 45 purchased) Operating expenses 45 41 44 42 45 42 Chemicals 5 3 3 3 4 3 Actual cost of chemicals (R million) 49 690 853 53 684 211 47 927 402 65 405 000 82133 809 74 958 424 Net finance costs 4 7 7 7 7 7 Profit for the year 18 13 7 7 4 8

As indicated in Table 4, Rand Water spends about R60m on average on chemicals for the treatment of water on annual basis. Operating expenses takes up to 45% of Rand Water’s annual budget. When eutrophication occurs and the algae produces toxins in the source water, more chemicals e.g. chlorine and particulate activated carbon (PAC) are used to counter the effect of the toxins. Toxins, among others cause some tasty discomfort in the final product.

It has been repeatedly emphasised that the proliferation of algae as a result of higher nutrient concentrations also leads to the production of toxins. Toxins, though not regular in Rand Water’s source water, occur during the warmer months. It gives the potable water consumers a bad taste and as a result a bad image about Rand Water’s product they receive as tap water. A special Powdered Activated Carbon (PAC) plant has to be installed by Rand Water to remove toxins from the source water. The PAC plant and its installation cost Rand Water a staggering amount of R15.2 million (13). The plant needs PAC to work and the cost of the two types of quality grades on the market bought by Rand Water is tabled below.

Table 5. Types of PAC and their cost to Rand Water. Name of chemical Also known as Tons bought Cost per ton Total cost (recorded in inventory) R R PAC (chem. 0078) Jacobi aquasorb 261,60 8990 2 351 784 A5 PAC (chem. 0085) Norit SA super 283,40 10950 3 103 230 Total amount used on PAC 5 455 014 Total wasted (tons) Amount wasted (R) 31 309070

These analyses suggest that Rand Water spends about R 5.5 million only on PAC. Although the two types of PAC have got long life span, over R 300, 000 are lost through wastage of this chemical.

DISCUSSION AND CONCLUSION

As indicated in the results, the size of the catchment can influence the amount of nutrients generated in the Vaal Catchment. The impact of agricultural activities and WWTW have not been singled out or quantified in this study and as a result might affect the results of the catchment size correlation. The physical and chemical qualities of source water affect the quality of the potable one. The colour, odour and taste mainly result from algae. Chlorophyll-a produced by the algae can affect the colour of the potable water if not treated properly during the transformation process of converting raw water into potable water. The decomposition of the algae adds some odour to the raw water which might be not be easily detected during the transformation process. The algae also produce toxins in the raw water, which if not checked or removed during the transformation process, will add unpleasant tastes to the final product (potable water). It was also realised that cost of potable water takes into account operational cost and source water protection. It is therefore a logical conclusion that source water protection affects chemical costs in the production of potable water. The effective management and protection of the source/raw water reduces chemical costs.

Effective control of the transformation processes, quality control of all the inputs in the conversion cycle (from the protection of raw/source water till the potable water gets to the consumer), implies that world class potable water can be sold to the consumer at relatively cheaper cost. It can also be inferred that the cost and quality of source water, to a greater extent, depends on the efficient management and protection of the source water.

Financial Implications of Pollution (Nutrient) Control A permanent staff component of twelve people in the Catchment Management Section of Rand Water and their associated Weed gang have an average budget of about 3% of the Water Quality & Environmental Services (MWQES) budget and about 0.13% of the total income of Rand Water. This amount makes up to 0.25% of Rand Water’s operational expenses. The cost of raw water, cost of protection of source water and chemical costs together consumes a whooping 55% of Rand Water’s annual budget.

It has been substantiated that nutrient loads in the Vaal Dam originates from the Vaal and Wilge sub catchments, the former contributing a greater proportion of the nutrient load. The water from LHWP into the ash river in 1998 actually reduced the nutrient load in the receiving waters. The only way to reduce the heavy loads of nutrients in the Vaal Dam will be to prevent pollution at the source. Catchment Management Section should be able to proactively reduce point source pollution by using source directed measures. The implementation of the studies on a possible pipeline from the Ash river outfall to Rand Water’s purification plants is recommended as it will avoid the pollution of the water by nutrients by agricultural activities and WWTW. It is suggested that all wastewater treatment plants be monitored closely to ensure efficient and effective performance. Best management practices in the agricultural and industrial set-ups be enforced in the Vaal Dam Catchment to reduce the nutrient loads in the Vaal Dam. Negotiation with DWAF/Catchment Management Agencies (CMA) should be entered into to allow Rand Water to perform all source water protection or catchment management activities in the Vaal Dam Catchment. This is possible according to the National Water Act (14). The cost of catchment management activities could be deducted from raw water costs.

If Rand Water is to succeed in supplying water to its customers on a sustainable basis over a long period of time, then the strategy of negotiation with DWAF should be redesigned. “The winners of tomorrow will deal proactively with chaos; will look at the chaos per se as the source of market advantage, not as a problem to be got around” (15). The “chaos” in the tariff system should be managed taking into account the activities of the Catchment Management and cost implications of the quality of the raw water.

REFERENCES

1. V. Novotny, Diffuse pollution from agriculture – A worldwide outlook. Wat. Sci. Tech. 39(3): 1-13 (1999). 2. L. Heathwaite and A. Sharpley, Evaluating measures to control the impact of agricultural phosphorus on water quality. Wat. Sci. Tech. 39(12): 149-155 (1999). 3. A.N. Sharpley, S.J. Smith, Prediction of bio available phosphorus loss in agricultural runoff. J. Environ. Qual. 21: 32-37 (1992). 4. A.N. Sharpley, S.J. Smith & J.W. Nany, Environmental impact of Agricultural nitrogen and phosphorus use. J. Agric. Food Chem. 35: 812-817 (1987). 5. D.M. Nash and J.D. Halliwell, Tracing phosphorus transferred from grazing land to water. Wat. Res. 34 (7): 1975-1985 (2000). 6. A.J.H. Pieterse & S.J. van Vuuren, An investigation into Phytoplankton Blooms in the Vaal River and the Environmental variables responsible for their development and decline. WRC Report No. 359/1/97, (1997). 7. Rand Water’s Annual Financial statement, Published by Rand Water Head Office, Johannesburg, South Africa (1997). 8. Rand Water’s Annual Financial statement, Published by Rand Water Head Office, Johannesburg, South Africa (1998). 9. Rand Water’s Annual Financial statement, Published by Rand Water Head Office, Johannesburg, South Africa (1999). 10. Rand Water’s Annual Financial statement, Published by Rand Water Head Office, Johannesburg, South Africa (2000). 11. Rand Water’s Annual Financial statement, Published by Rand Water Head Office, Johannesburg, South Africa (2001). 12. Rand Water’s Annual Financial statement, Published by Rand Water Head Office, Johannesburg, South Africa (2002). 13. S. Mia (Rand Water Engineering Dept) Pers. comm. Cost of and installation of PAC plant at Veeriniging. 14. South Africa, National Water Act (36 of 1998). Government Printer, Pretoria. South Africa (1998). 15. Ulrich and Wieserma, The changing role of marketing in the organisation. Handouts of GIMT and Rand Water Advanced Management Programme 2002 (1998).