2.2 Sampling technique
The monitoring scheme followed in this study utilised hydrological and ecological monitoring principles (Gruijter et al., 2006). The scheme was designed for status monitoring (Loaiciga et al., 1992; Dixon & Chiswell, 1996). The two factors of interest during the monitoring period were the receding water levels, as monitoring was conducted during the dry season, and the effects of changing environmental on the freshwater ecosystem.
2.2.1 Sampling sites
2.2.1.1 Upstream catchment (USC)
The USC constitutes the upland urban areas of the watershed from where drainage and tributary streams to the Ngwerere River originate. These include the northern central business district (CBD) of Lusaka city, the industrial area on the western side, and low- and high-density suburbs northwards. The three sampling sites located in the USC were Garden Olympia
Park (GOP), Garden Petroda Filling Station (GPFS), and the Lumumba Mandevu Junction (LMJ). GOP is located on the fringe of the Olympia park suburb and Garden compound along Katima Mulilo Road. It receives drainage from the upstream Northmead, Luangwa, and Olympia suburbs. This site was selected as it receives a significant amount of drainage from these locations and channels it into Ngwerere River. The GPFS sampling site was located on the periphery of Katima Mulilo Road in the Garden compound, but in proximity to the Great North Road (GNR) junction. The drainage channel in this location receives runoff and drainage from the CBD areas, areas around the Zambia Electricity Supply Corporation (ZESCO) headquarters, Rhodes Park, Thorn Park, Villa Elizabeth, Chilulu, Emmasdale, and parts of the Garden and Northmead residential areas. This site was selected as it would enable the assessment of water quality attributable to these areas before entering the main channel of Ngwerere River. The LMJ sampling site was located on the periphery of Lumumba Road before the GNR junction. The drainage channel on LMJ receives runoff from parts of the industrial area, Villa Elizabeth, and the western parts of the Emmasdale and Buseko commercial areas. This enabled the assessment of runoff from these locations before merging with the main course of the Ngwerere River.
2.2.1.2 Midstream catchment (MSC)
The MSC primarily contains settlement areas. From the fringes of USC into the Ngwerere area, there are commercial farming settlements. The major land use
types in this area are settlements, arable land, savannah, sparse woodlands, and commercial farms. The sampling sites located in the MSC were Mazyopa Community (MC), Galaunia Roan Farm (GRF), and the Confluence of Chamba Valley Stream and Ngwerere (CCVN) River. The MC sampling site was in the Mazyopa community area on the boundary with the Roma Park residential area, and was the final sampling location before the commercial farm zones. It lies at the bottom of the three sampling sites under USC. The MC site was selected as it is the area where the flow from the three sampling sites combine under USC and thus enabled the assessment of WQ changes arising from the combined effects of the three locations. The GRF site was located along Ngwerere road, on the edge of Galaunia Roan commercial farm. It was located
downstream of the MC site. It was chosen as it would allow WQ assessment after the introduction of runoff from commercial farming fields. The CCVN site was located further downstream, beyond the GRF site. The CCVN site was selected as it captured flow after merging with the Chamba Valley stream, a major tributary to the Ngwerere River. The Chamba Valley stream collects runoff from Munali, Kaunda Square, and the Minestone residential areas, then traverses some smallholder vegetable gardens before merging into the Ngwerere River.
2.2.1.3 Downstream catchment (DSC)
The DSC is situated in the lower lands of the watershed. Major land use types in this area are forests, savannah, arable lands, and rural dwellings. However, urban settlements such as the Ndeke Mean wood settlement in the north-eastern area have begun to stretch into this catchment,
The sampling sites in DSC were Galaunia Ngwerere Farm (GNF), Zambia National Service Airport (ZNSA), and Ngwerere Chongwe Confluence at Kasenga (NCCK). The GNF site is located on a tributary stream that receives drainage from the Galaunia Ngwerere and Dimondale commercial farms. The ZNSA site is situated on another minor stream that receives drainage from the upland areas adjacent to KKIA and the commercial farms for ZNS. The NCCK site is the furthest point downstream of the Ngwerere River before it merges into the Chongwe River, flowing in from the north-west in a south-easterly direction.
2.3 Hypothesis tests
Three propositions were tested in this study, as follows:
i. There are no statistically significant differences for WQ parameters between the watershed positions of USC, MSC, and DSC.
iii. There are no statistically significant differences between WQ parameters associated with the months of sampling, i.e. August, September, October, and November.µ
Thus, the test hypotheses for the three propositions can be symbolically stated as follows:
i. \(H_o\ =\ x_{usc\ }\ =x_{msc}\ =\ x_{dsc}\)
ii. \(H_o:\ x_{GPFS\ }=x_{gop}\ =x_{lmj}\ =x_{mc}\ =x_{grf}\ =\ x_{ccvn}\ =x_{gnf}\ =x_{znsa}\ =x_{ncck}\)
iii. \(H_o:\ x_{Aug}\ =x_{Sept}\ =x_{Oct}\ =x_{Nov}\)
2.4 Characterization of pH, Salinity, BOD, TDS, COD, Na and TSS in Ngwerere River
Spatial assessment of the chemical contamination of Ngwerere River was conducted by assessing selected WQ parameters. Data were collected from nine sampling locations within the NPW (Fig. 1). The water quality parameters assessed included pH (Speight et al., 2005), salinity (Clean Water Team (CWT), 2004), total dissolved solids (TDS) (CWT, 2004), chemical oxygen demand (COD) (Domini et al., 2006), Na+ (Hendershot et al., 1993), and total suspended solids (TSS) (United States Geological Survey (USGS), 2000).
3 Results
3.1 Water quality parameter characterization
Table 1 presents a statistical summary of the water quality parameters for NPW. Figure 2 includes box plots for the data characteristic of the WQ parameters considered in this study. Total dissolved solids and TSS data had the largest variation around the mean, with standard deviations (σ) equal to 82.4 and 209.73, respectively.