Abstract
In the South African National Water Act (NWA, No 36 of 1998), the ecological Reserve is defined as the quality and quantity of water required to ensure appropriate protection of water resources, so as to secure ecologically sustainable development and use. Aquatic ecosystems are recognised as the core location of water resources, and although considerable progress has been made in developing methods for quantifying environmental flow requirements, this paper describes and discusses the first agreed method for quantifying environmental water quality requirements in an ecological Reserve assessment. Integration of flow and water quality is emphasised, and is based on the philosophy that environmental flows should be motivated to provide ecologically important flow-related habitat, or geomorphological function, but should not be motivated to solve water quality problems by dilution. Water quality is multivariate, and not all variables can be considered in an ecological Reserve assessment, but core water quality variables include: system variables (salts, dissolved oxygen, turbidity, temperature), nutrients (phosphate, nitrite, nitrate) and toxic substances (those listed in the South African Water Quality Guidelines for Aquatic Ecosystems, including toxic metal ions, toxic organic substances, and/or substances from a chemical inventory of an effluent or discharge). In addition, biological indicator data (e.g. SASS data), chlorophyll-a (e.g. phytoplankton and periphyton data) and toxicity test data may be used. For each variable, a concentration range or response is linked to a class within a water resource classification system, where classes range from minimally to severely modified. There are five main stages in the environmental water quality method: • Initiate study and determine scope of assessment. • Delineate water quality sub-units. • Select sites and collect data and information. • Determine benchmarks, including generic boundary values (literature-based concentrations related to classes); the unimpacted, natural or reference condition; the present ecological state; and the contribution of water quality to the overall ecosystem importance and sensitivity. • Provide quantified and qualitative water quality objectives for each ecosystem health class, and each variable in each resource unit. These steps are integrated with environmental flow assessment procedures. After environmental flows have been recommended to achieve a selected level of protection (class), flow-concentration relationships are modelled, and the likely water quality consequences of modified flows are provided to resource managers, who then decide on whether to allocate water for dilution and/or to address the pollution problem directly using source controls. Water SA Vol. 31 (2) 2005: pp.161-170
Highlights
IntroductionThe two founding principles of the South African National Water Act (No 36 of 1998) (NWA) are “sustainability” and “equity” (NWA, 1(1)(xviii)(b))
The ecological ReserveThe two founding principles of the South African National Water Act (No 36 of 1998) (NWA) are “sustainability” and “equity” (NWA, 1(1)(xviii)(b))
If there is a trend, the earlier part of the record may be appropriate for reference condition determination while the more recent data record may be appropriate for a present ecological state assessment. o There may be a water quality monitoring point upstream of any impacts in the resource unit which may be suitable for reference condition assessment
Summary
The two founding principles of the South African National Water Act (No 36 of 1998) (NWA) are “sustainability” and “equity” (NWA, 1(1)(xviii)(b)). Each of the classes is associated with a level of ecosystem health and integrity (Table 1), and the potential to offer a particular range of goods and services (Palmer et al, 2002; 2004) This classification is related to the A - F categories used in early ecological Reserve determinations (DWAF, 2001). Ecological Water Requirements (Rivers) assessments for water quality require that an assessment be made of reference (unimpacted) condition This is to benchmark the default boundary values provided in the methods (Palmer et al, 2004, Appendix 1) for the categories and determine whether natural background levels are different from those values provided. Toxic substances: Data: NH3 (calculate from NH4 data), Al, As, Atrazine, Cd, Cr, Cu, Cyanide, Endosulfan, F, Pb, Phenol, Hg. Assess whether ASPT score from Refer- Compare ASPT scores from resource unit with ence site is >5% different to default Natural relevant boundary table. The more recent data record can be used. o Assess whether it is necessary, and appropriate, to use water quality data from dam outflow. o not specified by the method, box-and-whisker plots of monthly medians, 25% and 75% of selected water quality variables provide a useful visualisation of seasonal changes, and provides the necessary information required for flow-concentration modelling
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