Wetlands are productive aquatic ecosystems of earth that have natural cleansing capacity providing important ecological services. However, polluted wetlands with their poor water quality pose a threat to the aquatic life, agriculture and health and well-being of the local community. The burgeoning population of the cities and intensification of industries implies that large quantities of solid and/or liquid wastes in the form of either sewage or industrial effluents are released into the water bodies and/or land. The Industrial wastes containing high quantities of dissolved and suspended solids, high Biological Oxygen Demand-(BOD) and Chemical Oxygen Demand-(COD) values, heavy metals, organic and inorganic chemicals, pesticide run-offs, oils and grease harms aquatic life when discharged into the water bodies (Kaur and Brraich 2022). The contaminants gets to accumulate in wetland plants and sediments through such anthropogenic activities, leading to biomagnification in aquatic organisms, particularly in the tissues of fish.
India has a total of 75 Ramsar wetlands and out of that Punjab state has six. The Ramsar site no. 1161 (RSIS) located at Rupnagar, Ropar District in the state of Punjab, India (31°01'N 076°30'E) is a 1,365-ha national wetland site. In Punjab, numerous canals draw their water from the Sutlej River as their primary source. A diversion barrage on the Sutlej River was constructed to supply drinking and irrigation waters to distant areas through the Sirhind and Bist Doab canals in 1952. This led to the formation of the Ropar wetland which was declared a Ramsar site in 2002. The conservation efforts of this man-made freshwater riverine and lacustrine wetland were initiated in 1998 (EIACP). The site is a breeding ground for 55 fish species, 318 migratory bird species, Sambar, nationally protected reptiles, Hogdeer, smooth Indian Otter, and Indian Pangolin (endangered). Additionally, it serves as a crucial waterfowl migration staging area (EIACP). The site is an important location for recreation where visitors and nature lovers come to watch birds and the natural beauty of the placid waters in the backdrop of the Shivalik Hills.
The urea fertilizer plant (Naya Nangal), thermal power plant (Ghanauli village), cement manufacturing plant (Daburji Village) and increasing industrialization in the catchment area is causing major degradation of this wetland’s water quality. The inflow of chemical pollutants, such as, run-off from agriculture fields, and sewage from city's higher reaches viz., Anandpur Sahib, Nangal, Naya Nangal, Kiratpur Sahib, Nurpur Bedi are posing threats to this site affecting the local fish industry (www.punenvis.nic.in). The effluent from Nalagarh and Baddi industries, the majority of which are pharmaceutical industries; is discharged into the Sutlej River through the Sirsa rivulet which also discharges huge amounts of sediment near the Guru Gobind Singh Super Thermal Power Plant. The Thermal Plant uses the lake water as a coolant and discharges warm water into the lake which in turn lowers the heated water’s oxygen level thus affecting fish production. The Nangal fertilizer facility releases excessive amounts of ammonia into Ropar Lake, where at one point the fish population was wiped out. (Verma et al. 1998).
Some physico-chemical and spatiotemporal studies have been conducted in the past highlighting the importance of wetland’s water quality, in Punjab, India (Sharma et al. 2016; Kaur et al. 2017; Ahada & Suthar 2018; Akhter& Brraich 2020a and 2020b; Singh et al. 2022; Zhan et. al. 2022; Kaur & Brraich 2022). The Ranjit Sagar wetland's physico-chemical characteristics were studied between 2012 and 2014 by Brraich and Saini (2015) wherein the Water Quality Index (WQI) indicated the poor water quality unsuitable for consumption purposes. A similar study for 4 seasons was carried out on the Ropar wetland between 2015–2017 (Akhter and Brraich 2020b). The physico-chemical parameters were observed to have seasonal variation with higher values in summer and monsoon seasons and lower in the winter season because of low fluctuation in water level, high turbidity, increase phytoplankton productivity and decrease in photosynthetic activity. Sharma et al. (2016) examined the groundwater, soil and wheat samples grown in the Ropar wetland region in the pre-monsoon season of 2013 and found that arsenic concentration ranged between- “2.90–10.56 µg L− 1, 0.06 to 0.12 mg kg− 1 and 0.03 to 0.21 mg kg− 1,” respectively. Phosphate and arsenate ions are equivalent in physicochemical terms; hence, plants may absorb them in a competitive manner (Zhao et al. 2010). Iron and manganese oxides or hydroxides in subsoil take up arsenic and discharge it in groundwater under a diminished redox condition and arsenic gets conveniently accessible to plants (Ramanathan et al. 2015). Plants that accumulate arsenic are susceptible to necrosis, growth retardation, chlorosis and finally collapse of the plant. (Gulz et al. 2005). The IARC (2004) has declared arsenic and its derivatives to be carcinogenic (category 1) to humans. The hydro-chemical analysis of the Malwa region, Punjab (India) during the 2013–2014 period revealed high groundwater contamination in major locations out of the 24 locations studied exceeding WHO parameters as well as standards for drinking water in India (Kaur et al. 2017). For both seasons, the main cations and anions were abundant in the sequence:
“ (Na+ > Ca2+ > Mg2+ > K+ > and HCO3 > SO4 2− > Cl− )”. The author observed that fluorides, calcium, EC, alkalinity, sulphates and total hardness were higher than the BIS (Bureau of Indian Standards) permissible limits in the large number of samples. High levels of fluoride and total arsenic content of more than 10 µg/L fixed by WHO and BIS rendered it unfit for drinking purposes. Another groundwater study performed in the Malwa belt of Punjab, investigated the hydrochemistry (pH, EC, TDS, Cl−, TH, SO42−, PO43−,, Na2+, K+, Mg2+, Ca2+, F− and NO3 −) of 76 thoroughly cultivated sites covering 14 districts of the Punjab state (Ahada & Suthar 2018). Although, TH, K+, Mg2+, Ca2+, TDS and Cl− were confined in the limit majority of locations as per BIS; the proportion of SO42− was found higher than PO43− concentration in most of the sites. High concentration of Sodium ion was found in the range of 26.05–735.5 mg/L whereas fluoride ranged between 1.59–5.07 mg/L, higher than the permitted range. One common anthropogenic mineral found in groundwater was NO3▔. The WQI indices indicated that about 80.3% of the sites were found to have water not suitable for drinking. The overall groundwater was not found suitable for either drinking or agricultural purposes. Recently, Zhan et al. (2022) assessed the seasonal variation in groundwater quality near and around Ropar wetland, Punjab from 18 sites used frequently by villagers. More number of samples had higher levels of hardness, Ca2+, Mg 2+, SO42−, and heavy metals such as Pb, Cd, Cu and Cr contamination during the winter season exceeding BIS limits. The fly ash from coal-powered thermal power plants and the cement industry close to the Ropar wetland were identified as the primary sources of the heavy metal contamination. Studies conducted between 2015-17 by Akhter and Brraich (2020a) analysed physico-chemical parameters from 4 representative sites in the Ropar wetland. It was inferred that quality of water at Ropar wetland varies between “Poor” to “Very Poor” category based upon sampling site. Surface water samples taken in 2017 from ten distinct places in Buddha Nullah, Ludhiana, and Punjab indicated that the stream was hazardous for irrigation due to heavy metal pollution. An investigation of the mutagenic and genotoxic properties of surface water samples taken from 13 distinct locations within the Harike wetland in Punjab, utilizing the plasmid nicking test using pBR322 and the histidine reversion point mutation assay in the Salmonella typhimurium (TA98) strain was taken up by Kaur et al. (2017). The water samples from sites, fed by river Sutlej demonstrated significant mutagenic and genotoxic activity. Eighteen locations near the Ropar Wetland in Punjab provided groundwater samples that were found to be hard, non-saline, and slightly alkaline conditions that would make the water ideal for agriculture. (Sharma et al. 2019). Among 18 samples, few samples exceeded the permissible BIS limits (mg L− 1) for cadmium and chromium. Analysis of 5 wetlands of international importance including Ropar wetland and 2 of national importance located in Punjab state was found to be amidst good and poor in the course of studied seasons in the year 2019 (Singh et. al. 2022). The WQI values found both Nangal wetlands as well as Ranjit Sagar to have good water quality whereas Ropar, Harike, Kanjli and other wetlands of national importance to have poor water quality. The study conducted on Harike and Nangal wetlands concluded the WQI and HPI of Harike wetland as 56.68 (“poor”) and 144.9 while for Nangal it was 39.54 (“good”) and 3.12 respectively (Kaur and Brraich 2022) indicating significant heavy metal pollution at Harike. The water quality characteristics of a wetland such as physical, chemical, and biological determines its goodness; hence it is important to maintain the same. Water monitoring parameters influence management decisions on its suitability for designated use, aquaculture or to improve its conditions.
Contaminated water can be cleaned up using a variety of approaches, most of which fall into the physical, biological,chemical environmental, and technological categories. (Md. Anawar and Chowdhury 2020). A hybrid method called aeration that combines biological, chemical, and engineering processes can occasionally be successful in treating heavily contaminated river water at the field level (Sheng et al. 2013). The process can remove > 70% of (COD)Chemical Oxygen Demand, (BOD) Biological Oxygen Demand and also Odour from the polluted water.
“Water hyacinth, reed, water lettuce (Zimmels et al. 2008), Whorl-leaf watermilfoil, pondweed, cattail, duckweed, and canna” are examples of aquatic plants that have the ability to detoxify polluted water through either retention or adsorption, accumulation, and degradation of pollutants (Md Anawar et al. 2008). This low-cost widely accepted phytoremediation technique using native aquatic plants can be adopted along the riverbank or in wetlands conveniently. The stabilization of contaminated wetlands through vegetation restoration can reduce pollution and stabilize the area. The process primarily relies on identifying the physical and chemical features of the contaminated wetland and selecting appropriate plant species that work in tandem with the rhizosphere microbes to promote plant establishment and growth. In this context, plants such as vetiver grass, water hyacinth and wild mustard freely available in the Indian subcontinent have the potential to absorb heavy metals from contaminated sites. High levels of toxic metal(loid) concentrations, such as those of (Cu) 50–100 mg kg–1, (Cr) 50–100 mg kg–1, (Pb) > 1500 mg kg–1, (Ni) 100 mg kg–1, (Se) > 74 mg kg–1, (Zn) > 750 mg kg–1, and (As) 100–250 mg kg–1,” can be tolerated by vetiver (Chen et al. 2004; Danh et al. 2010). Vetiver is also efficient in reducing Biochemical Oxygen Demand and removing total phosphorus (TP) and total nitrogen (TN) hydrocarbons and PAH from contaminated water. Vetiver is resilient to a number of abiotic stimuli, such as protracted drought, flooding, submersion, severe temperatures, pH, alkalinity, and elevated levels of heavy metals—all of which are frequently found in contaminated areas (Truong & Baker, 1998; Truong, 1999). Water hyacinth, a free-floating aquatic plant is an effective phytoremediation alternative for heavy metals. Several studies indicated that water hyacinths are capable of cleaning up the heavy metals content from the wastewater effluents up to 70–90% of their initial concentration in 4–6 days (PN and Madhu 2011; Akinbile et al. 2012; Adekunle et al. 2012; Panneerselvam and Priya 2023). Indian mustard (Brassica juncea) with natural phytoextraction potential can concentrate high concentrations of metals in its shoots. High phytoextraction efficiency (PE) and phytoextraction rate (PR) of mustard plants grown in contaminated sites have been seen in the past (Hall 2002); (Rathore et al. 2013); (Ansari et al. 2015); (Rathore et al. 2019). In order to protect itself against heavy metal stress, mustard uses processes such as active efflux, decreasing diffusion across the cell membrane, and binding metals with the cell wall (Hall 2002). Since the heavy metals are kept out of the functional system, they are kept in the apoplast and vacuoles (Boominathan and Doran 2003; Ma et al. 2005). Through defensive enzymes namely, ascorbate peroxidase, superoxide dismutase, carnitine-acylcarnitine translocase, glutathione peroxidase, and glutathione reductase, the cells of mustard plants decrease damage from oxidation caused by heavy metal accumulation (Mani et al. 2013).
Hence, the conservation and management of Ropar wetland warrants monitoring of industrial effluents, and monitoring its physical, chemical and biological characteristics regularly. In the past, the majority of scientific work focused on groundwater around Ropar Wetland, primarily examining concentrations of a limited number of heavy metals. Examining and assessing surface water quality parameters, including total alkalinity, total hardness, pH, electrical conductivity, total dissolved solids, dissolved oxygen, and heavy metals, in water samples taken from sampling locations all the way across the wetland and its surrounding areas was the goal of the current study. This surface water either converges or diverges from the Sutlej River, a vital source of drinking and irrigation water. Additionally, this surface water infiltrates and poses a contamination risk to the groundwater. Additionally, the study explored the increasing heavy metal pollution concern in the wetland and the potential of phytoremediation as a bioremediation tool. The water quality index (WQI) and heavy metal index (HMI) were calculated to provide an overall assessment of water quality in the wetland. Native plant species capable of phytoextraction viz., vetiver grass, water hyacinth and Indian mustard were sampled to examine their efficiency in removing heavy metals from the contaminated sites.