EFFECT OF MIXED INDUSTRIAL WASTEWATER ON SOIL, TREE BIOMASS PRODUCTION AND TRACE METAL UPTAKE

Abstract

Although the agricultural use of wastewater raises some environmental and human health concerns, irrigation with wastewater is usually carried out by smallholders in dry areas. The present study reports on the physiological effect of several dilutions of the raw wastewater of the Hudiara drain on Dalbergia sissoo and Eucalyptus camaldulensis plants. Six-month old seedlings were established in pots and irrigated for 18 months with: tap water (control, T 0 ); 25% wastewater (T 1 ); 50% wastewater (T 2 ); 75% wastewater (T 3 ); and 100% wastewater (T 4 ). Results showed that the plant growth parameters decreased as the percent of wastewater increased. At T 4 the shoot length, number of leaves, leaf fresh weight, and leaf oven dry weight were reduced by 17%, 72%, 72%, and 70% in Dalbergia sisoo and 5%, 17%, 23%, and 29% in Eucalyptus camaldulensis plants respectively, compared to the control (T 0 ). The content of chlorophyll a, chlorophyll b and total chlorophyll increased in Dalbergia sissoo plants treated with wastewater at 25%, but decreased in the T 2 , T 3 , and T 4 treatments. Whereas chlorophyll a, chlorophyll b and total chlorophyll increased up to T 2 in E. camaldulensis, in treated pots beyond that percentage, a decline in chlorophyll was observed. As the percentage of wastewater in the treatments increased, the accumulation of Na, Cd and Cr in tissues increased, while the concentration of K, P, Mg, and Fe decreased. Similarly, Eucalyptus camaldulensis and Dalbergia sissoo plants were irrigated with synthetic wastewater containing Cd and Cr for 18 months. Treatments were T 0 = Tap water (control); T 1 = 0.05+1.0 mg L -1 conc. of Cd(II)+ Cr(VI); T 2 = 0.10+2.0 mg L -1 conc. of Cd(II)+ Cr(VI); T 3 = 0.20+4.0 mg L -1 conc. of Cd(II)+ Cr(VI) and T 4 = 0.40+8.0 mg L -1 conc. of Cd(II)+ Cr(VI). Results showed that plants at T 1 grew more compared to the control, but beyond that level, a gradual decline in growth was recorded with a maximum reduction in T 4 treated plants. Cd and Cr accumulation in tissues increased (roots>shoot>leaves) as external metal concentration increased, while nutrient accumulation (K, P, Mg, Fe) and chlorophyll content declined. However, the application of synthetic wastewater containing various concentrations (0, 10, 20, 40 and 80 mg L -1 ) of Cd and Cr on the growth of Dalbergia sissoo at the seedling stage for four weeks under controlled conditions in a growthii chamber (300 μmol m -2 s -1 of photosynthetically active radiation with 16:8 hours photoperiod) revealed a decline in growth after 10 mg L -1 and 40 mg L -1 for Cr and Cd, respectively. A combined application of Cd and Cr wastewater showed a growth reduction at doses above 20 mg L -1 . Results showed that Cr was more toxic to Dalbergia sissoo plants at the seedling stage than Cd. The present study suggests that wastewater from the Hudiara drain diluted to 25% and 50% with tap water is a feasible option for the growth of D. sissoo and E. camaldulensis plants in Lahore, Pakistan. A phytosociological survey using the Braun-Blanquet’s approach was undertaken to investigate the influence of the Hudiara drain wastewater on the surrounding vegetation. Multivariate analysis of vegetation data classified the vegetation into two major communities including, Cynodon dactylon and Boerhaavia diffusa, and Parthenium hysterphorus and Xanthium strumarium groups. The fervent growth of these species designated the area as wasteland. The patterns of floral diversity exhibited considerable variation. Canonical Correspondence Analysis (CCA) revealed that the distribution of vegetation correlates with environmental variables, but their role in the grouping of species was not significant. However, soil EC played a role in the grouping of Stellaria media and Fagonia cretic. Similarly, some species, namely Riccinus communis, Boerhaavia diffusa and Phragmites karka showed a correlation with Fe and Cr respectively, suggesting Phragmites karka as a suitable candidate for chromium contaminated sites.