Water Quality, Soil Characteristics and Vegetation Diversity Along Euent-dominated Rivers in Western Rajasthan, India

This study aimed at analysing water quality of euent-dominated seasonal rivers and its impacts on soil and vegetation. Euent-inicted, river-edge and non-polluted areas were selected at 5 places along Luni, Bandi and Jojari rivers in western Rajasthan. Water of rivers exhibited high pH (7.6-8.6), electrical conductivity (EC 2.45-38.3 dSm -1 ), total dissolved and suspended solids, alkalinity and Na (1.50-30.00 gL -1 ), K, Ca and Mn (25.2-2439.3 µgL 1 ) concentrations and low NH 4 -N (1.08-20.69 mgL -1 ), NO 3 -N (0.44-9.10 mgL -1 ) and PO 4 -P (3.10-13.40 mgL -1 ). Most variables were highest for Luni and lowest for Bandi River. Cu, Co, Se, Cd and Pb concentrations were <180 µgL -1 . Soil pH, EC and PO 4 -P were highest along Bandi, whereas NH 4 -N, NO 3 -N and K were highest along Jojari River in both 0-30 and 30-60 cm soil layers. Euent-inicted soils exhibited high pH, EC and PO 4 -P, whereas non-polluted soils showed high NH 4 -N, NO 3 -N and K availability. These soil variables decreased downstream. Plant species number ranged between 34 along Luni and 20 along Jojari (total 10 trees, 10 shrubs and 29 herbaceous). Species richness (R) and diversity (H’) of trees were highest along Bandi. Shrubs and herbaceous R, H’ and evenness (e’) were high along Luni. Least diverse vegetation was along Jojari. Non-polluted area exhibited high tree R and H’, whereas river-edge showed high herbaceous R and H’. Euent-inicted area showed high salts and low diversity, but dominated by Aeluropus lagopoides, Paspalum virgatum, Phragmites karka, Tamarix ericoides, etc., which can be used in restoring such degraded urban areas.


Introduction
Urbanization is the fastest growing and one of the most destructive land-use type to local ecosystems. Urban population has been increased in India by 14.5-fold over the period 1901-2011, i.e. from a modest base of 25.8 million persons in 1901 to 377.11 million in 2011. Such urbanization contributes to accelerated loss of many native species because of deleterious effects of water pollution caused by municipal and industrial e uents of industrial and urban areas (Kaur et al. 2012). In India, the amount of sewage and industrial wastewater generated are 61.75 billion liter and 0.5 billion liter per day, respectively against the treatment capacity of 21.96 billion liter per day only (Roy 2020). In most of the cases, a major portion of the generated e uents are discharged into nearby water bodies, drainage lines or river systems (Preisner 2020). Luni River and its tributaries like Bandi and Jojari are examples that receive industrial e uents from Balotra (Barmer), Pali and Jodhpur cities in arid western Rajasthan affecting their natural environment (Bothra 2019).These seasonal rivers have now become e uent dominated systems in terms of ow, water quality and systems integrity (Bischel et al. 2013; Luthy et al. 2015).
Depending on e uent quality and the amount of organic and inorganic loads, the quality of newly developed habitat may be enhanced or adversely affected, with varying consequences for different ora and fauna along the river courses (Drury et al. 2013; Ahmed et al. 2014).Changes in composition of sediment deposited also in uence habitats quality for some species. Continuous discharge of e uents also transforms these seasonal rivers into perennial ones altering oral and faunal composition and facilitates the establishment of some new species based on adaptation towards modi ed environment (Brooks et al. 2006;Bothra 2019).
Despite some positive effects of maintaining stream ow, protecting ecological integrity and sustaining societal bene ts like novel riparian and aquatic habits, improved aesthetic values and ground water recharge in arid environment such discharged e uents deteriorate soil quality and affects abundance of native vegetation and agricultural production as well (Ali et  Therefore, the objectives of this work were to: (i) assess quality of water owing in Luni, Bandi and Jojari rivers in arid western Rajasthan; (ii) quantify vegetation diversity along these river systems; and (iii) to identify dominant species growing in e uent dominated river areas for their use in phytoremediation programmes.

Site conditions
This study was conducted along Luni, Bandi and Jojari rivers located in Barmer (24° 58′ to 26° 32′ N and 70° 05′ to 72° 52′ E), Pali (24° 45′ to 26° 29′ N and 72° 47′ to 74° 18′ E) and Jodhpur (26° 00′ to 27° 37′ N and 72° 55′ to 73° 52′ E) districts situated in arid western Rajasthan (Fig. 1). The climate of the region is characterized by extremes of temperatures, uncertain rainfall, high potential evapotranspiration and strong winds. Landscape of the region is variable ranging between sandy plains to isolated hills. Maximum temperature rises up to 50°C, whereas minimum temperature drops down to freezing point during winter season. Rainfall in the studied areas showed high temporal and spatial variations. Average annual rainfall in Barmer, Pali and Jodhpur are 346.8 mm, 607.3 mm and 309.3 mm respectively with 70% coe cient of annual rainfall variations indicating inter-annual variability in rainfall and in uence vegetation composition and production. Rainfall was greater in Barmer and Pali districts in August than other months, whereas it was greater in July in Jodhpur district as compared to the other months (Fig. 2). Most of the rain fell between July to September by southwest monsoon, which begins in the last week of July and lasts till middle of September. Soils are sandy to sandy loam in texture with low soil organic carbon and nutrients. Soil depth varies with physiographic conditions of the area. The vegetation of the area is xerophytic in nature and most of the plant species are spiny and smaller in leaf size (Champion and Seth 1968; Bhandari 1990).

Experimental design and vegetation survey
River Luni (Barmer), Bandi (Pali) and Jojari (Jodhpur) receive e uents from Balotra (Barmer), Pali and Jodhpur city respectively (Fig. 1). Five sites were selected along each river for sampling of water samples and study of vegetation structure and composition (Fig. 1a). Different sites were located between Dhundhara and Tilwara in Barmer district along Luni River, Punayata in Pali and Nehra dam in Barmer along Bandi River and between Kharada Randhir in Jodhpur and Doli in Barmer along the Jojari River. At each site, three micro-habitats like e uent-in icted riverbed, river edge and a non-polluted control were identi ed. Survey was conducted during nonmonsoon period of January to March 2018. Thus water sampling site were 15 (5 along each river) and vegetation study plots were 45 (3 river × 5 site × 3 micro-habitats).
Trees and shrubs were enumerated and measured 72 km stretch along the Luni, 38 km stretch along the Bandi and 48 km stretch along the Jojari Rivers by laying out plots of 20 m × 20 m size at e uent-in icted riverbed, river edge and non-polluted control areas. For herbaceous species nested plots of 1 m × 1 m size were laid in the centre of above mentioned plots. Thus there were 15 main plots along each river course. All trees and shrubs species available in the plots were counted for their population and measured for diameter at breast height (dbh, 1.37 m height)/collar diameter (15 cm above soil surface) and total height. Plants were identi ed as per taxonomical classi cation using standard literature (Bhandari 1990). In case of multiple stem particularly for the shrubs, individual tillers were measured and converted to a single value using equation (Chojnacky 1999 Here CD in single value collar diameter and d is diameter of individual tiller.

Water collection and analysis
Water sample were collected from the selected ve sites of each river mentioned above and were transported to laboratory for analysis (Fig. 1a). These water samples were ltered through Whatmann 42 lter paper and stored at 4 ºC. Each sample was analyzed for pH, electrical conductivity (EC), total dissolved solid (TDS), total suspended solid (TSS), alkalinity, basic cations, and concentrations of macro-and micro-nutrients (OMA 1990).
TSS, TDS, total alkalinity, nitrogen and phosphorus were determined following standard methods (OMA 1990).

Soil and plant sampling and analysis
Soil samples were collected from ve sites along the river and in 0-30 and 30-60 cm soil layers from e uentin icted, river-edge and non-polluted (control) micro-habitats. Leave samples of Prosopis juli ora and Salvadora persica were collated from e uent in icted and non-polluted micro-habitats. All soil samples were brought to laboratory and air dried, ground and passed through 2 mm sieve for further analysis. Sieved soil samples were subjected to various physico-chemical and nutrients like pH, EC, available ammonium nitrogen, available nitrate nitrogen, available phosphorous and available potassium (Jackson 1973 Table 1). Waters of these rivers were alkaline (pH 7.6-8.6) and highly saline   (Fig. 3). While considering the rivers, soil pH (p < 0.05), EC and available PO 4 -P were highest along Bandi River, whereas NH 4 -N, NO 3 -N and K (p < 0.05) were highest along Jojari River (Fig. 3A left panels). Lowest value of soil pH was along Jojari River, EC, PO 4 -P and K along Luni River, and NH 4 -N and NO 3 -N along the Bandi River.
Among micro-habitats, soils of e uent-in icted areas were high in pH, EC and PO 4 -P ( Fig. 3A middle panels).
Availability of NH 4 -N, NO 3 -N and K were highest in non-polluted soils (control area), whereas their lowest values were at river edge ( Fig. 3B

Plant mineral status
Different mineral elements like As, Cd, Cr, Cu, Fe, Pb, Hg, Sn and Zn were estimated in two tree species viz. P. juli ora and S. persica growing in the e uent-in icted as well as non-polluted soils. Concentrations of these mineral elements were greater in the leaves of the plants growing in e uent-in icted soils as compared to those growing in the normal soils (Table 3). However, concentrations of Cd and Cr were relatively high in leaves of S. persica as compared to the leaves of P. juli ora, whereas the concentrations of As, Cu, Fe, Pb, Hg and Zn were greater in leaves of P. julilora than in S. persica. Concentration of Sn observed almost similar in both the species.    Low tree and shrubs diversity in the e uent-in icted and river-edge areas than that in non-polluted ones were because of wastewater that had enhanced alkalinity, salinity and metal concentration in the soils and resulted in to the emergence of some new species adapting to the modi ed environment and in uenced the plant diversity and community structure along these rivers (Ahmed et al. 2014).
Occurrence of P. juli ora, P. cineraria, T. ericoides, P. karka, A. lagopoides, Blumea spp., C. dactylon, P. virgatum, G. lotoides, H. curassavicum, S. articulates, S. surattense, S. fruticosa and T. angustifolia in e uent-in icted area indicated dominance of herbaceous species and was because of their high tolerance to the new environment and adaptation to survive in the soils with high pH, EC and available PO 4 -P and other metallic ions. However, relatively more number of species ourishing along the river edge than e uent-in icted area was because of increased aeration and nutrient and water availability in this micro-habitat (Dorotoviaova 2013). High values of herbaceous R, H' and e' in e uent-in icted and river-edge areas as compared to non-polluted area was due to growth of selective species favoured by water and relatively high salts and mineral concentrations in this contaminated soils. It was also shown by positive correlations of herbaceous R, H' and e'with water NH 4

Conclusion And Recommendations
Soils properties and plant diversity in the studied region were in uenced by climatic conditions and physicochemical characteristics of the e uents discharged into the rivers. High pH, salinity, TDS, TSS, alkalinity and Na, K, Ca and Mn concentrations and low NH 4 -N, NO 3 -N and PO 4 -P had not only made the e uent-dominated water of these rivers un t for irrigation Bandi < Jojari < Luni, but had also in uenced the soil characteristics (high pH, EC and PO 4 -P along Bandi and high NH 4 -N, NO 3 -N and K along Jojari River) and vegetation composition negatively along the river courses. Combined effects of e uent and vegetation had resulted in high pH, EC and PO 4 -P in e uent-in icted and NH 4 -N, NO 3 -N and K in non-polluted soils with 0.24 unit, 5.96-fold, 1.40-fold, 1.34-fold, 1.23fold, and 1.52-fold variation in respective parameter between the micro-habitats. Arid climate, rainfall and e uentdominated water were the factors responsible low diverse vegetation, i.e. 49 species with dominance of herbaceous species. Trees and herbaceous diversities were favoured by rainfall (soil water) and shrub diversity by soil water stress. Non-polluted area was more diverse with typical arid vegetation, whereas e uent-in icted area had vegetation tolerant to high soil salt and saline water. River edge area was medium in diversity with limited number of shrubs and trees. P. juli ora, P. cineraria, A. nilotica, S. persica, T. ericoides, P. karka, C. procera, A. persica, A. lagopoides, Blumea spp., C. dactylon, P. virgatum, G. lotoides, H. curassavicum, S. articulates, S. fruticosa and T. angustifolia growing in e uent-in icted and river edge areas were tolerant to wastewater contaminated soils and have remediation capacity and hence can be utilised in increasing green cover and enhancing environmental quality of urban areas. Focus should be given on enhancing the remediation e ciency and rehabilitation centering to the plants contributing to social and economic development of the regional population.

Declarations
Figures Figure 1 Location of study site and sampling sites along Luni, Bandi and Jojari Rivers in western Rajasthan (a), e uents discharged from Jodhpur, Pali and Balotara cities owing through Jojari (b), Bandi (c) and Luni River (d), respectively. Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors. Rainfall pattern in different districts in western Rajasthan