1 INTRODUCTION

Wetlands are essential for the balanced environment of this globe. In arid climates, the shrinkage of wetlands is more noticeable because they are more vulnerable to degradation. Various ecological functions are provided by these ecosystems. These are essential in dry regions because of their role in transporting water resources. Known as saline wetland lakes, these salt lakes can be found on every continent (Zadereev et al., 2020). It is not uncommon to find them in the vicinity of human settlements. In each continent, they are large in numbers and are widely distributed. The Caspian Sea is an important reservoir because it contains 70% of all inland saltwater (Afonina and Tashlykova, 2018). Saline water dominates many of the world's huge lakes.

From an economic standpoint, salt lakes are an abode of minerals (particularly halite, but also lithium, uranium, zeolites, and borax, among different minerals), water (through inflow diversion), fish, biochemical goods (glycerol and beta-carotene from Dunaliella spp., protein from Spirulina spp.), and aquaculture feedstock (especially Artemia cysts) (Foroumandi et al., 2022). In addition, many saline lakes have a historical or cultural value. For example, Mono Lake in California and the Great Salt Lake in Utah, both have high aesthetic values as naturally beautiful environments (habitats for unique organisms). However, in some cases, salt lakes may face greater threats than freshwater lakes due to the widespread belief that they are comparatively less in quantity. The most well-known salt lakes, such as the Dead Sea, Aral Sea, and Mono Lake, have all suffered significant degradation. Both the depth and the salinity have decreased by tens of meters in a relatively short period (Wurtsbaugh et al., 2017). The cumulative effects on the Aral Sea's human population, agricultural output, and the environment have been devastating. Salt lakes are particularly vulnerable to the effects of climate change and rising ultraviolet B radiation due to their shallowness, high levels of solar irradiation, and lack of natural cover compared to many freshwater bodies of water (Wurtsbaugh et al., 2017). Salt lake pollution is another major anthropogenic activity caused by the sporadic spread of exotic biota, particularly Artemia.

In saline wetlands, soil factors play a vital role in balancing the ecosystem. Their assessment becomes inevitable. An important concept in soil assessment is soil quality (SQ) that can be quantified in several ways. The quality of soil in many parts of the world is rapidly deteriorating (Bünemann et al., 2018). To keep ecosystems healthy for the long term, SQ is considered the building block of the process. SQ evaluation methods that are quantitative, documented, reproducible, and spatially explicit should be promoted to minimize the presence of subjectivity in the evaluation process (Doran et al., 2018). When determining the overall quality of soil, all physical, chemical, and biological factors play a role. Thus, by tracking soil quality parameters, we can gain a better understanding of what factors affects soil quality and what needs to be done to combat it (Bünemann et al., 2018). When it comes down to it, soil quality is a measure of how well soil functions in terms of maintaining productivity and preserving the environment as well as promoting the health of both plant and animal populations. In semi-arid areas, soil fertility and quality assessment (Husein et al., 2021; Selmy et al., 2021), soil quality of the semiarid rangelands (Raiesi and Salek-Gilani, 2021), and soil quality of semi-arid waste leachate (Nabiollahi et al., 2018) have all been studied (Yeilagi et al., 2021). However, studies on soil analysis required for the halophytes of these inland saline lakes are scarce. Soil quality assessment using GIS and remote sensing applications is critical for their assessment. These technologies provide spatio-temporal information, and allow for restoration plans to be implemented. Geostatistical approaches based on measurements at adjacent locations with specific weights assigned to each measurement are some of the assessment methods for soil property spatial variability. Geostatistical methods, such as ordinary inverse distance weighted interpolation and Kriging interpolation, have been extensively used to evaluate and analyze the spatial correlation and spatial variability of soil properties, such as physical, chemical, and biological properties, as well as their spatial correlation (Bouasria et al., 2021).

The use of interpolation procedures in science is a common practice, especially in the fields dealing with spatial data and continuous phenomena. An interpolation technique uses precise and qualitative sampling data to produce a continuous representation of the phenomenon under consideration. Interpolation results are strongly influenced by the precision of the input data. Because of the small-scale spatial variability of natural communities and the low light penetration in the water column, remote sensing methods alone cannot be used in these situations. Instead, spatial interpolation methodologies can be used to generate this information from in situ sampling points (Bouasria et al., 2021).

This research was carried out in Sambhar Salt Lake that was designated as a Ramsar site under criteria A due to its unique characteristics. It is the largest shallow saline site in India. Because of illegal saltpan encroachment, the use of illegal electric pumps for excessive underground water extraction, and the theft of brine worth 330 billion dollars from the global salt market, it is also under severe threat (Naik and Sharma, 2021), thus the existence of the lakes is at stake. To analyze the current status, this study aims to investigate the status of halophytes and soil properties.

2 MATERIAL AND METHODOLOGY 2.1 Study area

Sambhar Salt Lake (26°52′N–27°02′N; 74°54′E– 75°14′E) is present towards east of the Thar Desert as a playa wetland (Fig. 1), located in the foothills of the Aravali Mountain Range in India. Being an inland wetland, it is 230 km² (22.5 km in length and 1–3 km in width). A 5.16 km long dam was built for the reservoir (77 km²) and wetland area (113 km²). Its saline character is contributed by the presence of salts of sodium, calcium, potassium, and magnesium cations and chloride, carbonate, bicarbonate, and sulfate anions (Sharma et al., 2022). It appears white in areas where the salt content is high; grey in areas where the salt content is lower; and brown in areas where there is no salt content. Because it is located in a semi-arid climate zone, it receives approximately 500 mm of rainfall during the monsoon season and has access to water during the winter, when the temperature ranges between 11 ℃ and 24.4 ℃. When the temperature rises to 40.7 ℃ in the summer, it almost completely dries out. During the monsoon and summer seasons, the lake's vertical depth ranges from 3 m to 0.6 m, making it a shallow lake (Naik and Sharma, 2021). Its water system is supported by ephemeral streams like Mendha, Kharian, Rupnagar, and Khandel, forming a catchment of 5 520 km². This site is one of the most important stopping points for migratory water birds. It is also a popular destination for tourists. On March 23, 1990, it was designated as a Ramsar site (Sharma et al., 2021). Approximately 100 000 water birds, primarily flamingos, migrate to this lake during the winter months, and the majority of them are concentrated in the saltpan areas (Naik and Sharma, 2021). The water level of this lake has been rapidly decreasing because of illegal saltpan encroachment in recent years. As a result, regular monitoring of water birds and their distribution, as well as mapping of their habitats throughout entire flyways, are essential for their conservation and survival.

2.2 Methodology

First, a literature survey was done for halophytes, their classification, importance, and soil studies of the study area. The location of halophytes in the study area was considered the deciding factor in soil sample collection. Secondly, in areas where halophytes were present, the surface soil was used to determine the quality of the soil. The samples were collected on February 19–20, 2021. Since this is a shallow saline wetland, it is difficult to cover all of the wetland's areas. As a result, the spatial heterogeneity of final samples was observed. The study area was divided into four zones. Zones A and B are for Nagaur district, Zone C for Ajmer, and Zone D for Jaipur district. Stratified random sampling was carried out for each zone. Samples were collected only from the reachable portions of each stratum where halophytes were found. An auger was used to collect soil samples in the study area, and 16 samples were collected. The latitude, longitude, and photographs of each sampling point, as well as other features, were noted down. To prevent contamination, all soil samples were sealed in plastic bags and transported to the laboratory, where any undesirable substances were removed. All samples were dried naturally before being ground and sieved in preparation for laboratory analysis.

Following a review of the literature on inland saline wetlands, six basic indicators for soil-quality assessment were selected in advance. These indicators included soil moisture, pH, electrical conductivity, salinity, organic matter, and organic carbon. The soil samples were cleaned and dried after they were collected. Ten grams of each soil sample were taken and mixed with 10 mL of distilled water. Two hours were spent shaking them on the shaker. The solutions were then filtered through filter paper to remove any impurities. In addition, the cleaned solutions were centrifuged in order to produce more clear solutions. The soil solutions were then collected and stored for later analysis. The analysis was carried out following the methodology recommended by the American Public Health Association (APHA, 1995). Thirdly, Sentinel 2A satellite images from February 2021 were downloaded using the USGS earth explorer website for geospatial mapping. The bands were then layer stacked in ArcGIS 10.6 to create the final product. The study area was clipped with the help of the shape file of the Sambhar Lake. Results include the generation of inverse distance weighted interpolation maps for a variety of soil parameters. The methodology flowchart is given in Fig. 2, sampling points are given in Fig. 3, and field photographs are given in Fig. 4.

3 RESULT 3.1 Literature survey for halophytes 3.1.1 Classification

Halophytes have been classified by different authors based on their life cycle, based on geographic locations like coastal and inland species, based on soil and water requirement. Some of the common classifications of halophytes as discussed (Nikalje et al., 2018; Lopes et al., 2021; Biology Discussion, 2022). Based on soil-water requirements, these are classified as aquatic-haline, terrestro-haline (hygrohaline, meso-haline, xero-haline), and aero-haline. Based on the salt requirement, they are classified as oligo-haline that requires 0.01% to 0.1% NaCl, meso-haline that requires 0.1% to 1.0% NaCl, and poly-haline that requires salinity above 1%. Some of the halophytes can grow in 0.01% to 1.0% and are known as oligo-meso haline and other halophytes that can survive in all the salt concentrations are known as euhaline species. Based on salinity requirement in different phases of life, they are classified as obligatory halophytes (require salinity mandatorily), preferential halophytes (show optimum growth in saline habitat but may survive in non-saline areas), supporting halophytes (these can grow in saline habitat), and accidental halophytes (grow accidentally in marshy habitats). Based on succulence properties, classified as succulent (able to tolerate chloride ions in cell sap), non-succulent (resist high chloride concentration through desalinization by salt glands), and accumulating type (these plants do not have any salt mechanism, keep accumulating salt until they die). Based on soil and water requirement, they are also classified (Nikalje et al., 2019; Grigore, 2019; Castañeda-Loaiza et al., 2020). Hyper-halophytes require alkaline soil; tolerate up to Electrical conductivity of soil saturation extract (ECe) 100 dS/m. They require a minimum water table of 0.5 to 1.5 m; they have succulence-type of adaptive features. They have both C₃ and C₄ photosynthetic mechanisms. Hydro-halophytes opt for standing in fresh to brackish water, tolerate 100 000×10^-6 or more salinity, and follow C_{3 m} echanism. Euhalophytes grow in wet sandy, edge of salt fl ats, marshes, and salt deserts with a 1–2-m water table, they play the role as salt accumulation and exclusion and have C₄ photosynthetic mechanism. Haloxerophytes grow in soil with gypsum content, alkaline meadow, salt marshes, and sandy desert soil with a water table less than >4 m. Halogemimezophytes grow in alkaline soil, lakeshores, and riverbanks with at least 1.5–2.5-m water table. They opt for both C₃ and C₄ photosynthetic mechanisms. Halogemipetrophytes require stony skeletal saline soil and 1.5–4.0 m of the water table. Metallo-halophytes grow in metal-contaminated soils. The classification infographic is given in Fig. 5.

3.1.2 Importance of halophytes

Halophytes are used for many purposes as food sources such as halophytic cereal crops, leafy vegetables, and vegetable salads (El-Hack et al., 2018; Grigore and Toma, 2021; Caparrós et al., 2022). Suaeda fructicosa and Salicornia brachiata, Sesuvium portulacastrurn, Zera racemosa are a good source of greens food items. The sea fennel, Crithmum maritimum is widely utilized in salads. The young plants and shoots of Batis maritimum, Portulaca oleracea, Tetragonianoides sp., Salicornia spp., and Suaeda torreyana are commonly used for pickles. Salvadora olecides and S. perica provide edible fruits rich in fatty nutrients. They also give wood, fodder as well as shade. Scrirpus species yield tubers, which are a vital source of starch. These are also important sources of alcoholic beverages like nipa fruits. These are also used as barilla (Carbonate of soda). The ashes of chenopodiaceous halophytes such as Arthrocnemurn, Haloxylon, Salicornia sp., Salsola sp., and Suaeda sp. are obtained and used as raw material for the soap and glass industries (ElHack et al., 2018). Halophytes that are mangroves such as Excaecaria agallocha, Kandelia sp., Rhizophora sp., Ceriops sp. Sonnertia acida are good sources of tannin. Halophytes like Heritiera sp., Carapa sp., Avicennia sp., Sonnertia sp., Aegiceras majus etc. serve as a good source of timber for making cordage, mats, and baskets (Grigore and Toma, 2021). Halophytes such as Distichlis spicata are recently used for wasteland reclamation process by planting them in seaside areas, to reduce dust storms and also stabilize dry lake beds. These plants increase the soil holding capacity of coastal areas and protect them from submerging into the sea (Caparrós et al., 2022). Halophytes of desert areas like Simmondsia chinensis (Jojoba) are good sources of liquid wax. Infographics for different applications are given in Fig. 6.

3.1.3 Halophytes of Sambhar

Authors could not find a single research article, book chapter, conference proceedings, thesis, or any type of report dedicated to halophytes of the study area. There are numerous literatures on plants of the Thar Desert, and semi-arid zones but no specific articles for halophytes of this wetland. From the research article by Charan and Sharma (2016), the authors could find only two herb species. They are Haloxylon recurvumn that belong to Chenopodiaceae family and is a halo-xerophyte, and Suaeda fruticose, Amaranthaceae lunaki. These are euhalophytes. They come under near endangered category.

During the field visit, the authors could identify 10 halophytic species in the study area. The diversity and density of halophyte are very low. These are unevenly distributed in different zones. Comparatively, Zone D had the highest density among all the zones. Family Amaranthaceae has the highest number of species. It has four species including Haloxylon salicornicum, Salicornia brachiate, Salsola baryosma, and Suaeda fruticose. Family Poaceae has second highest number of species. It has two species: Cenchrus biflorus and Cynodon dactylon. Portulaceae family has only one species named as Portulaca oleracea, Fabaceae family has only one species which is Prosopis juliflora, Salvadoraceae family has one species named as Salvadora oleoides and Zygophyllaceae has one species which is Zygophyllum simplex. Out of the 10 species, three are monocotyledons that can withstand salinity between 0.5×10^-12 to 5.0× 10^-12. These are oligo-haline type of halophytes. Rest of the seven species are dicotyledons that can withstand 5.0×10^-12 to 18.0×10^-12. These are meso-haline type of halophytes. The study area has no polyhaline type of halophytes that can withstand 18.0 and above ×10^-12 of salinity. The details are given in Table 1.

3.2 Literature survey for the soil of Sambhar

The literature review was conducted for the soil parameters of the study area and is given in Table 1. It is found that the study on its soil parameters is very scare. Total of 11 publications could be retrieved (Baid, 1959; Chaudhuri et al., 1965; Lulla and Helfert, 1989; Yadav et al., 2007; Joshi et al., 2014; Singh and Gehlot, 2015; Pathak and Cherekar, 2015; Cherekar and Pathak, 2016; Naik and Sharma, 2021). The years of analysis are 1959, 1965, 1984, 1985, 2007, 2010, 2011, 2014, 2015, and 2019. Different authors have studied different parameters like pH, EC, TDS, dissolved oxygen, chemical oxygen demand, biological oxygen demand, sodium, calcium, magnesium, potassium, iron, manganese, chloride, carbonate, bicarbonate, nitrate, sulfate, sulfide, organic carbon, and organic matter. However, the most common parameters have been selected to be represented in Table 2. The highest pH value was 10.1 in 2010 and the lowest was 7.95 in 2015. The highest value of salinity was 164.04% in 2019 and the lowest was 8.665% in 1959. The highest value of carbonate was 518.5 mg/L in 2019 and the lowest was 404.21 mg/L in 2015. The highest value of bicarbonate was 41 500 mg/L in 2015 and the lowest was 18.33 mg/L in 2014. The highest value of sodium was 118 100.0 mg/L in 2015 and the lowest value was 1.24 mg/L in 2014. The highest value of chloride was 90 799.97 mg/L in 2019 and the lowest value was 5 175 mg/L in 2011. As the articles obtained were from random years, these could not be represented in any temporal scale. The values authors have provided information that lacks geographic coordinates. It was difficult to know which part of the lake was studied. Different authors have studied different parameters. Some of the studies were conducted in different seasons of the same year while other studies were conducted in the same season in subsequent years. Considering these challenges, it was difficult to draw any conclusion from these articles.

3.3 Laboratory analysis and mapping of soil

For the soil samples, both physical and chemical parameters have been analyzed. The details of each parameter are described in Figs. 7–12 and summarized in Table 3.

3.3.1 Physical parameter: pH

pH values have been categorized into five classes in Arc GIS software. They are neutral (7.31–7.91), slightly alkaline (7.91–8.30), moderately alkaline (8.30–8.54), highly alkaline (8.54–8.82), and very highly alkaline (8.82–9.37). Out of 16 sites, two points (Site 2 of Zone B and Site 3 of Zone D) are in neutral class. There are three points in the second class (Site 2 of Zone B, Sites 1 and 3 of Zone D). There are four points in the third class (Sites 2 and 5 of Zone A, Site 1 of zone C, and Site 7 of Zone D). There are four points in the fourth class (Sites 1 and 4 of Zone A, Sites 2 and 4 of Zone D) and there are four points in the fifth class (Site 3 of Zone A, Site 1 of zone B, Sites 5, 6, and 8 of Zone D). Focusing on each zone-wise, in Zone A, there are five sampling points. All the points have pH values above 8. Site 3 comes under very highly alkaline, Sites 1 and 4 come under highly alkaline, and Site 2 is moderately alkaline. Site 1 has 8.61, Site 2 has 8.4, Site 3 has 8.84, Site 4 has 8.71 and Site 5 has 8.24 pH value. In Zone B, there are two sampling points, out of which one is alkaline in nature and the other neutral. Site 1 has 9.27 and Site 2 has 7.31 pH value. In Zone C, there is only one sampling with pH value 8.45. Zone D has the highest number of sampling sites. There are eight points out of which two points have neutral pH values, three have above 8 and two points have above 9 pH values. Here, Site 1 has 7.96, Site 2 has 8.74, Site 3 has 7.66, Site 4 has 8.62, Site 5 has 9.04, Site 6 has 8.8, Site 7 has 8.34, and Site 8 has 9.37 pH value. It is important to note that, Zones B and D have both pH values with both alkaline and neutral pH. It is important to note that, Zones B and D have both alkaline and neutral pH values. The map is given in Fig. 7.

3.3.2 Physical property: electrical conductivity (EC)

The unit of EC is in mS/cm. EC values are classified into five classes. 0.38–4.87 is classified as very low conductivity, 4.87–6.85 as low conductivity, 6.85–8.63 as moderate conductivity, 8.63–11.10 as high conductivity, and 11.10–16.09 as very high conductivity. Under class 1 indicating very low conductivity, there are six points (Site 5 of Zone A, Site 2 of Zone B, Sites 1, 3, 4, and 7 of Zone D). Under class 2 indicating low conductivity, there are 6 points (Site 3 of Zone A, Site 1 of Zone B, Site 1 of Zone C, Site 3 of Zone D). Under class 3 indicating moderate conductivity, there is only 1 point (Site 1 of Zone A only). Under class 4, indicating high conductivity, there are 4 points (Site 4 of Zone A, Sites 2, 5, and 8 of Zone D). Under class 5 indicating very high conductivity, there are 2 points (Site 2 of Zone A, and Site 6 of Zone D). Focusing on each zone-wise, in Zone A, there are five sampling points. Site 1 has 7.89, Site 2 has 12.41, Site 3 has 4.92, Site 4 has 9.38 and Site 5 has 3.33 EC values. In Zone B, there are two sampling points. Site 1 has 6.7 and Site 2 has 3.12 EC values. In Zone C, there is only one sampling with EC value of 6.24. Zone D has the highest number of sampling sites. There are eight points. Here, Site 1 has 0.38, Site 2 has 9.4, Site 3 has 4.47, Site 4 has 3.41, Site 5 has 9.68, Site 6 has 16.1, Site 7 has 1.32, and Site 8 has 10.78 EC values. The map is given in Fig. 8.

3.3.3 Physical property: soil moisture

The unit of soil moisture is in percentage (%). Soil moisture values are classified into five classes. 1.12–7.31 is classified as very low moisture, 7.31– 10.80 as low moisture, 10.80–13.77 as moderate moisture, 13.77–16.99 as high moisture and 16.99– 23.36 as very high moisture. Under class 1 indicating very low moisture, there is only 1 point (Site 2 of Zone A). Under class 2 indicating low moisture, there are four points (Sites 1 and 5 of Zone A, Site 2 of Zone B, Site 7 of Zone D). Under class 3 indicating moderate moisture, there are four points (Site 3 of Zone A, Site 1 of Zone C, Sites 3 and 5 of Zone D). Under class 4, indicating high moisture, there are 2 points (Sites 2 and 4 of Zone D). Under class 5 indicating very high moisture, there are points (Site 4 of Zone A, Site 1 of Zone B, and Sites 4, 7, and 8 of Zone D). Focusing on each zone wise, in Zone A, there are five sampling points. Site 1 has 8.86, Site 2 has 5.29, Site 3 has 12.09, Site 4 has 23.37, and Site 5 has 8.36 moisture values. In Zone B, there are two sampling points. Site 1 has 21.35 and Site 2 has 9.45 moisture values. In Zone C, there is only one sampling with a moisture value 11.24. Zone D has the highest number of sampling sites. There are eight points. Here, Site 1 has 1.12, Site 2 has 15.72, Site 3 has 12.04, Site 4 has 16.07, Site 5 has 11.66, Site 6 has 19.02, Site 7 has 7.44, and Site 8 has 18.38 moisture values. The map is given in Fig. 9.

3.3.4 Chemical property: salinity

The unit of soil salinity is in ×10^-12. Soil salinity values are classified into five classes. 0.21–2.68 is classified as very low salinity, 2.68–3.77 as low salinity, 3.77–4.75 as moderate salinity, 4.75–6.11 as high salinity, and 6.11–8.85 as very high salinity. Under class 1 indicating very low salinity, there are 3 points (Site 5 of Zone A, Site 2 of Zone B, and Site 7 of Zone D). Under class 2 indicating low salinity, there are three points (Site 3 of Zone A, Site 1 of zone B, and Site 1 of zone C). Under class 3 indicating moderate salinity, there is only one point (Site 1 of Zone A). Under class 4, indicating high salinity, there are 2 points (Sites 2 and 4 of Zone A, Sites 2, 5 of Zone D). Under class 5 indicating very high salinity, there are 2 points (Site 2 of zone A and Site 6 of Zone). In Zone A, there are five sampling points. Site 1 has 4.34, Site 2 has 6.82, Site 3 has 2.7, Site 4 has 5.15, and Site 5 has 1.83 salinity values. In Zone B, there are two sampling points. Site 1 has 3.68 and Site 2 has 1.71 salinity values. In Zone C, there is only one sampling with a salinity value 3.43. Zone D has the highest number of sampling sites. There are eight points. Here, Site 1 has 0.21, Site 2 has 5.17, Site 3 has 2.46, Site 4 has 1.7, Site 5 has 5.31, Site 6 has 8.86, Site 7 has 0.72, and Site 8 has 5.92 salinity values. The map is given in Fig. 10.

3.3.5 Chemical property: organic carbon

The unit of soil organic carbon is in percent (%). Soil organic carbon values are classified into five classes. 0.15–1.03 is classified as very low organic carbon, 1.03–1.73 as low organic carbon, 1.73–2.41 as moderate organic carbon, 2.41–3.67 as high organic carbon, and 3.67–5.40 as very high organic carbon. Under class 1 indicating very low organic carbon, there are 6 points (Sites 1, 3, 4 of Zone A, Site 1 of Zone C, Sites 2 and 4 of Zone D). Under class 3 indicating low organic carbon, there are points (Sites 5, 6, and 8 of Zone D). Under class 3 indicating moderate organic carbon, there is only one point (Site 2 of Zone B). Under class 4, indicating high organic carbon, there are two points (Site 1 of Zone B and Site 1 of Zone D). Under class 5 indicating very high organic carbon, there is only one point (Site 2 of Zone A). In Zone A, there are five sampling points. Site 1 has 0.3, Site 2 has 5.41, Site 3 has 0.9, Site 4 has 0.3, and Site 5 has 0.15 organic carbon values. In Zone B, there are two sampling points. Site 1 has 3.29 and Site 2 has 2.81 values. In Zone C, there is only one sampling site with organic carbon value 3.43. Zone D has highest number of sampling sites. There are eight points. Here, Site 1 has 3.3, Site 2 has 0.45, Site 3 has 3, Site 4 has 0.3, Site 5 has 1.65, Site 6 has 1.5, Site 7 has 1.65, and Site 8 has 1.35 organic carbon values. The map is given in Fig. 11.

3.3.6 Chemical property: organic matter

The unit of soil organic matter is in percent (%). Soil organic matter values are classified into five classes. 0.15–1.03 is classified as very low organic matter, 1.03–1.73 as low organic matter, 1.73–2.41 as moderate organic matter, 2.41–3.67 as high organic matter, and 3.67–5.40 as very high organic matter. Under class 1 indicating very low organic matter, there are 6 points (Sites 1, 3, 4 of Zone A, Site 1 of Zone C, Sites 2 and 4 of Zone D). Under class 3 indicating low organic matter, there are points (Sites 5, 6, and 8 of Zone D). Under class 3 indicating moderate organic matter, there is only one point (Site 2 of Zone B). Under class 4, indicating high organic matter, there are two points (Site 1 of Zone B and Site 1 of Zone D). Under class 5 indicating very high organic matter, there is only one point (Site 2 of Zone A). In Zone A, there are five sampling points. Site 1 has 0.517, Site 2 has 9.326, Site 3 has 1.551, Site 4 has 0.517, and Site 5 has 0.258 organic matter values. In Zone B, there are two sampling points. Site 1 has 5.671 and Site 2 to has 4.844 values. In Zone C, there is only one sampling site with organic matter value 0.258. Zone D has highest number of sampling sites. There are eight points. Here, Site 1 has 5.689, Site 2 has 0.775, Site 3 has 5.172, Site 4 has 0.517, Site 5 has 2.844 4, Site 6 has 2.586, Site 7 has 2.844 6, and Site 8 has 2.327 organic matter values. The map is given in Fig. 12.

4 DISCUSSION

The current study aims to characterize the soil parameters where halophytes are growing. A literature survey was conducted for halophytes and soil characteristics. The study area was divided into four zones for stratified random sampling. Soil sampling was conducted for February 2021. The soil indicators for halophyte selected are pH, electrical conductivity, moisture, salinity, organic carbon, and organic matter. The obtained results were interpolated in the geospatial platform for soil characteristic mapping.

4.1 Current status of halophytes

As mentioned earlier, there are also no research studies on the halophytes of the study area, authors have tried to establish the relationship between the halophytes and the soil parameters from the literature on other saline lakes. It is found salinity and electrical conductivity has been the key survival factor for the halophytes, salinity being the ruling factor (Naz et al., 2010; Vineeth et al., 2020). Soil moisture and carbonate also affect their life cycle sometimes (Montagna et al., 2013). From the results, it is observed that the study area is dominated by meso-haline halophytes as compared to oligo-haline halophytes. However, this requires regular monitoring every season to understand the vegetation pattern of this lake.

4.2 Current status of soil

From Fig. 7 of pH, it is seen that there are only two sites with pH values above 9. Zone B of Nagaur district and Zone D in Jaipur. Zone A of Nagaur and Zone C of Ajmer do not indicate highly saline characteristics on their part. Results of EC are also demotivating the status of the lake as only one site each of Zones A and D have very high values. The soil moisture is highest towards the North direction in both the zones of Nagaur and a small portion of Jaipur in Zone D. It is observed that the center part of the wetland has less moisture percentage even during the winter season. Although this is a seasonal lake, it used to have water in the central part during monsoon and winter (Naik and Sharma, 2021), in the current study, it is observed that it has less moisture, indicating less water in the center part of the lake. It is important to emphasize that high moisture in the upper part of the lake is due to the illegal collection of surface brine and underground water using electrical pumps. Concern for the lake further intensifies when a soil salinity map is observed. Except two extreme sites of Zones A and D almost the whole lake comes under 2.66 to 3.77 salinity level. Sambhar, being an inland saline wetland, has such a low value of salinity. Salinity levels are reduced in halophyte growth sites and those sites also have fewer halophytes. The maps of soil organic carbon and organic matter show the highest values only at the western corner of Zone A that is also near to Aravalli hill range. The upper portion of Zone B and lower portion of Zone D also have a little organic content in the range of 2% to 4%.

4.3 Comparison with literature

Naik and Sharma (2021) have also analyzed soil parameters. Though the exact site locations do not match the results of each zone are comparable. Three basic parameters like pH, EC, salinity, and organic carbon can be compared to know if any changes occur. In Zone A of Nagaur part, the highest pH value of 2019 was 8.8 while in 2021 was 8.84, the lowest value of 2019 was 8.34 while of 2021 was 8.4. The highest EC value in 2019 was 8.39 while 12.41 in 2021, and the lowest value of 2019 was 2.23 while in 2021 was 3.33. The highest salinity value of 2019 was 4.34% while in 2021 it was 6.82%; the lowest of 2019 was 1.15% while in 2021 it was 1.83%. The highest value of organic carbon in 2019 was 0.33% while in 2021 it was 5.41%, the lowest value in 2019 was 0.04% while in 2021 it was 0.3%. In zone B (Nagaur), the highest value of pH in 2019 was 8.73 while 9.27 in 2021, and the lowest value was 8 in 2019 while 7.31 in 2021. The highest value of EC in 2019 was 1.1 while 6.7 in 2021, and the lowest value in 2019 was 5.77 while 3.12 in 2021. The highest value of salinity was 2.87% in 2019 while 3.68% in 2021, and the lowest value in 2019 was 0.6% while 1.71% in 2021. The highest value of organic carbon in 2019 was 0.54% while 3.29% in 2021, and the lowest value in 2019 was 0.08% while 2.81% in 2021. In Zone C (Ajmer) there is the single point of sampling for both 2019 and 2021. pH in 2019 was 8.71 while 8.45 in 2021, EC in 2019 was 7.62 while 6.24 in 2021. Salinity in 2019 was 3.89 while 3.43 in 2021 and organic carbon in 2019 was 0.5 while 0.15 in 2021. In Zone D (Jaipur), the highest pH was 9.56% while 9.37% in 2021, and the lowest value was 9.14% while 7.66% in 2021. The highest value of EC in 2019 was 10.5% while 16.1% in 2021, the lowest value was 0.52% in 2019 while 0.38% in 2021. The highest salinity is 2019 was 5.79% while 8.86% in 2021, the lowest value in 2019 was 0.31% while 0.21% in 2021. Highest value of organic carbon was 0.91% while 3.3% in 2021, the lowest value was 0.19% in 2019 while 0.3% in 2021.

From the above comparison, it is observed that in all Zones A, B, C, and D, the soil quality has increased in 2021 as compared to 2019. The values of pH have almost remained the same; however, EC and salinity have increased three to four times. Though there is an increase in values of carbonate, they are insignificant. The improving conditions of the parameters could be due to the positive impact of the COVID-19 lockdown, which is discussed in detail in the next paragraph.

Naik and Sharma (2021) stated that the lake has been shrinking at the decadal rate of 4.23% since 1969. Based on January 2019, they have predicted that by 2059, the wetland might be further shrunk by 4%, and saline soil and salt crust area might convert to barren. The saline lake has a very high chance for complete desiccation and conversion to a non-saline area due to illegal saltpan encroachment, excess groundwater extraction, and sewage dumping into the lake. The above factors could also affect adversely to the halophytes also.

In 2019, it was hit by first ever avian botulism (Naik and Sharma, 2021). More than 40 000 northern shoveler (Spatula clypeata) and other migratory birds died. All the economic activities were banned temporarily for a couple of months. In 2020, due to COVID-19 shutdown and repeated lockdowns, economic activities were under control as compared to pre-COVID days. Due to these conditions, many biotic and abiotic factors of this ecosystem have improved. Naik and Sharma (2021) have also suggested that the water regime has increased and more migratory birds are also visiting. Therefore, it is a good sign that the soil parameters of the lake have also improved with little financial investment for its restoration. This might also be the case for halophytes also. Since there is no literature on halophytes in the study area, no conclusion can be drawn in this regard. Just after the sampling and laboratory analysis, the second phase COVID-19 lockdown was declared. The site suitability modelling for halophytes was intended to be conducted using Analytical Hierarchical Process (AHP), but could not be achieved. This could have given a more robust idea for the halophytes of this lake.

Recently, in 2021, Sambhar Development Authority was formed for the conservation and management of the lake. The prime focus of the committee is the maintenance of water extent, as with the availability of water, there will be more halo-alkaliphiles. As a result, more migratory birds will be attracted to feed upon them. However, the conservational planning should also focus on the halophytes, as they are an integral part of the lake. These are highly ignored and no research has been done on them. The lake has been the point of interest for researchers of microbiology, biotechnology, soil-water chemistry, avian diversity, radioactive substances, the health status of salt workers, and brine quality. However, no literature is found specifically dedicated to the halophytes of these wetlands. There is an urgent for their regular survey, mapping, habitat suitability modelling, and ecological and economic importance.

Globally, most inland saline lakes are shallow and endorheic basins (Del Pilar Alvarez et al., 2022). This makes them particularly vulnerable to changes in soil parameters in an arid environment. Soil's physical and chemical properties in arid and semi-arid regions may change, which may lead to changes in the ecology and climate of these wetlands (Hassani et al., 2020). In arid and semiarid regions, the cumulative stress of soil moisture and salinity is one of the most important factors limiting wetland restoration (Zhao et al., 2021). For example, vegetation growth is stunted and land degradation occurs to some extent when a wetland and the surrounding vegetation are salinized. Ecological communities can also be disrupted, leading to a loss of wetland ecological function and productivity. The amount of water in the soil can be figured out by measuring the moisture content of the soil (Xu et al., 2019). Water-stressed environments can lead to desertification, decreased vegetation productivity, and changes in the local microclimate. Soil water and salt distribution and formation are critical to controlling natural disasters, such as land desertification and drought, as well as to protecting and restoring wetland ecosystems in arid and semi-arid areas. So, it becomes very important to focus both soil and halophytes on these inland saline wetlands.

5 CONCLUSION

In this research article, Sambhar Lake, India's largest shallow saline wetland, is being studied. Because of illegal saltpan encroachment, the use of illegal electric pumps for excessive underground water extraction, and the theft of brine worth 330 billion dollars from the global salt market, it is under severe threat. This type of activity is consistently degrading the ecosystem, resulting in an imbalance at each trophic level, from the primary producer down to the tertiary consumer. This study aimed to analyze the status of soil characteristics where halophytes are growing. In addition, the comprehensive results demonstrate the improvement in soil quality parameters that have occurred over the last three years. However, because no literature on halophytes was discovered, the future of this aspect of this Ramsar site is in doubt. If immediate conservation measures are not taken, the halophytes may be completely lost before they can be identified. This research would aid in the preservation of this ecosystem. There are 148 other inland saline Ramsar sites and other unidentified sites suffering from the same fate as this lake, and they should be given top priority during the UN Decade on Ecosystem Restoration.

6 DATA AVAILABILITY STATEMENT

All the data are present in Department of Environmental Science, Central University of Rajasthan.