Multi-metric biomonitoring of a seasonally flooded Baraila wetland using benthic macroinvertebrates as indicator organisms in the middle Ganga River Basin (Vaishali), India

Wetlands are arguably the most productive freshwater ecosystems on earth, serving as an essential reservoir that supports a diverse array of flora, fauna, and microbial life (Dorche et al. 2019; Singh & Sharma 2020; Sripanya et al. 2023). Despite their ecological significance, a global decline in wetlands has been reported owing to multiple anthropogenic stressors, such as land use changes, overexploitation, destruction or degradation of habitat, agricultural expansion, and water pollution (Best & Darby 2020; Yang et al. 2022). Wetland depletion has been documented worldwide, ranging from the rapid disappearance of the Florida Everglades in the United States to the drastic deterioration of the Sundarbans in Bangladesh and India (Sklar et al. 2019; Sahana et al. 2022). Nearly 91.12% of the wetland degradation has been reported as a negative impact of human development activities on the ecological stability of wetlands in the Jiangsu province in China (Wang et al. 2023). Similarly, Dar et al. (2021) found nutrient input from the agricultural runoffs and other sources of organic wastes have led the wetland to a hyper-eutrophic state.

Moreover, poor wetland management and monitoring framework are two of the potential reasons behind the rapid decline in global wetlands. To build a sustainable conservation and management plan it is crucial to understand the hydrodynamics of the wetland ecosystem. The interrelationship between aquatic health, and human activity, the source of impairment, and the impact of disturbances on biological entities cannot be explained by the traditionally followed physicochemical method (Stein et al. 2008; Johnson & Ringler 2014; Khatri et al. 2021; Mezgebu 2022). Biomonitoring, on the other hand, can explain the biological response of aquatic fauna toward stressors indicating a change in water quality (Mehari et al. 2014). According to Carter et al. (2006), biomonitoring provides a moving picture of the past and present conditions, whereas physicochemical approaches rather a snapshot, primarily reflecting the water quality condition of the time water has been sampled. Among various groups of bio-indicators, macroinvertebrates are the preferred organism for the biomonitoring program by researchers across the globe (Duran & Suicmez 2007; Morse et al. 2007; Orwa et al. 2014; Lakew & Moog 2015; Neetu et al. 2019; Shabani et al. 2019; Akyildiz & Duran 2021; Dirisu & El Surtasi 2021; Balisco et al. 2022; Sripanya et al. 2023). Benthic macroinvertebrates are used as preferable organisms over other aquatic species due to their high diversity, sedentary nature, long life cycles, easy and economical sampling efforts, and a strong and broad variety of responses toward environmental stressors (Patang et al. 2018). Several indices based on the biomonitoring data have been developed to assess the quality of the freshwater ecosystem (Nguyen et al. 2014; Tampo et al. 2021; Wang et al. 2023). However, relying on the result of a single index usually fails to reflect the accurate status of aquatic water bodies, exposed to various kinds of human-induced disturbances. Biomonitoring approaches using a multi-metric index overcome these limitations, and strengthen the findings of the biomonitoring dataset (Carter et al. 2006). In agreement with the above discussions, Johnson & Ringler (2014) found inclusion of biological data in ecological studies can provide a better understanding of the factors that affect the biological organisms, and water quality of a wetland. Dorche et al. (2019) working in the Choghakhor wetland of Iran reported an effective application of biotic indices, as it shows reasonable consistency with the water quality classification.

Like many regions across the globe, India has witnessed a decline of 70% in wetland areas from 1990 till today, due to failure to manage water pollution, usage of water resources, and human negligence (Singh et al. 2020). Wetland comprises 4.7% of the total geographical area in India, and shares 6.53% of global wetland biodiversity. Therefore, the degradation and loss of wetlands have been reportedly linked with the loss of biodiversity, and other ecological services in many regions of the Gangetic plains. The Baraila wetland has been considered a potential contender to be categorized under the Ramsar site, after Kabar Tal, in 2020 (Comptroller and Auditor General (CAG) of India 2017). In addition to supporting a population size of 49,819 individuals, and native bird species, it hosts the largest international bird communities in India, from countries like Siberia, Mongolia, Africa, Eurasia, and Japan (Aslam et al. 2021; Vaishali 2022). The macroinvertebrates of the wetlands constitute a significant part of the food chain for many of these waterbirds (Meyer et al. 2015). The occurrence, distribution, and habitat selection of these migratory birds have been previously reported to be linked with the assemblages of the aquatic benthic macroinvertebrates (Rooney & Bayley 2012). Unfortunately, the biodiversity and water dynamics of the Baraila wetland have been reportedly under multiple anthropogenic pressures, which mainly include encroachment, overexploitation, frequent droughts, eutrophication, habitat degradation, etc. Several studies have been conducted assessing the water quality, geochemistry, irrigation suitability, and mineralogy of the Baraila wetland (Aslam et al. 2021, 2023a, 2023b), and have outlined a conservation plan for the wetland (SAPCC 2015; CAG 2017). No comprehensive evaluation using biomonitoring approaches has been conducted in the wetland, emphasizing the critical need to fill this research gap. Therefore, the study aims to (1) assess the water quality of the Baraila wetland using a multi-metric biomonitoring approach and to (2) investigate the relationship between the water quality parameters and community assemblage of benthic macroinvertebrates at the Baraila wetland. This research will not only assess the Baraila wetland's ecological state but also contribute valuable insights into the authorities concerned in developing a conservation strategy, and further encourage similar approaches to various fragile habitats worldwide.

The study was carried out at the Baraila wetland, which is a seasonally flooded wetland in the Vaishali District of North Bihar. It covers a substantial area of 12.7 km² expanding from 25°45′58″ & 25°45′37″ N to 85°31′48″ & 85°34′50″ E. The wetland is underlain with a quaternary alluvial floodplain created by the consolidation of the River Ganga, and its associated tributaries, including the Gandak, Noon, and Baya rivers (Galy et al. 2008; CGWB 2013; Kumar et al. 2021). It lies in the middle Ganga River basin, in which deposits of clay minerals and monotonous flat topography are prevalent (Kumar et al. 2022; Sulaiman et al. 2023). The climatic conditions of the study area fall within the sub-tropical to sub-humid type, with temperatures varying from approximately 26 to 40 °C during summer, and 4–15 °C in winter (Aslam et al. 2023a, 2023b). The district experiences an average annual rainfall of 1,170 mm, with substantial precipitation in July and August. The wetland has been identified as an eco-sensitive zone and is given protected status under the official gazette notification of the government (WII 2017). In addition, the Baraila wetland has been recognized as a wetland of national significance through the National Wetland Conservation and Management Programme (NWCMP), and could potentially be added to the Ramsar database in the future. According to WII (2017), the wetland holds great significance as it serves as one of the main destinations for a wide variety of migratory bird species around the world.

The site selection was done after visually analyzing the habitat and anthropogenic stressors at the Baraila wetland. In this study, a Land Use Land Cover (LULC) map for the Baraila wetland was generated utilizing 30-m resolution data for the year 2021 from ESRI and processing it through the ArcGIS version 10.5 software. The research adopted an unsupervised classification method, identifying and categorizing spectral signatures of various land cover types into distinct classes. The maximum area of the wetland was categorized as rangeland (66.97%), followed by flooded vegetation (29.40%) in the year 2021. Additionally, elevation and delineation maps were produced using digital elevation models (DEMs) satellite data from USGS. The wetland was noted with streamflow mainly in the southern regions, with only 37.05% of the region having an elevation beyond 48 m. Therefore, the accessibility of collecting both water and benthic samples from the same location has mainly governed the site selection process. The names of the selected sampling sites were as follows: site 1 – Loma, site 2 – Dulwar, site 3 – Chakaiya, and site 4 – Kawai Baraila (Figure 1).

Water samples were collected during the pre-monsoon period of March and April, and the post-monsoon period of September and October 2022. A total of 24 water samples, three from each site in both seasons, were collected in a 2.5-L polythene bottle at a depth of about 10 cm below the surface water. The water samples were then transported to the laboratory and kept in a cool place for further analysis. Altogether 13 physicochemical parameters were assessed, where the water temperature (WT), depth (d), transparency, pH, free CO₂, and dissolved oxygen (DO) were estimated in situ using a water analysis kit. The remaining parameters were analyzed following the standard methods of APHA (2017), and Trivedy & Goel (1984). The turbidity of the samples was analyzed using a Turbidimeter (Thermo Scientific Eutech. TN-100), TSS, and Biological Oxygen Demand (BOD₅) has been analyzed using Gravimetric and Winkler's Iodometric methods (APHA 2017). The nitrogen parameters such as ammonia (⁠⁠), nitrate (⁠⁠), total nitrogen (TN), and total phosphorus (TP) were estimated within 48 h after collection. High-quality analytical-grade reagents were utilized during the analytical procedures, and the respective equipment underwent calibration before analysis (Sulaiman & Kamari 2024).

For the qualitative and quantitative assessments of the benthic macroinvertebrates, samples were collected following the grab sampling method, with the help of an Eckman dredge of size 15.2 cm × 15.2 cm at each location, for the mentioned study periods. Subsequently, the dredged material was sieved through a 425-μm metallic sieve, and the benthic samples were carefully transferred from the sieve to a white enamel tray. The benthic macroinvertebrates with hard shells were manually handpicked with forceps, while the soft body organisms were collected with the help of a brush followed by their preservation in 10% formalin in a plastic jar and glass vial, respectively. Furthermore, the macroinvertebrates were meticulously sorted and identified up to the species level using appropriate taxonomic keys and manuals (Subba Rao 1989; Dey 2007; Nesemann 2007).

The macroinvertebrate's numeric features such as taxa richness, abundance, and tolerance scores are used to assess the water quality of the wetland as a function of different community-level metrics. The use of biotic indices is effective in assessing the responses of biota to organic pollution, though they may fall short in detecting various other types of pollution. The diversity indices, on the other hand, offer a broader perspective by gauging environmental stress, with higher species richness typically associated with unpolluted environments (Mason 2002). However, it becomes difficult to interpret whether the sensitive species or the tolerant species have contributed to the higher diversity index value in a wetland. Hence, an integrated approach employing both biotic and diversity indices holds promise for a more comprehensive evaluation of wetland water quality. The metrics used, their classification, and their corresponding interpretations that reflect the water quality of the wetland have been shown in Table 1. Here, the study incorporates a slight modification in the BMWP score given by Mason (2002) called the BMWP-Baraila lake (BMWP-BL) score. The widely used approach in biomonitoring freshwater ecosystems, known as the Biological Monitoring Working Party (BMWP) score, is a method that measures organic pollution based on the presence and absence of species belonging to a specific family. The highest BMWP scores are assigned to the most sensitive families of macroinvertebrates, and the lowest scores to those most tolerant. These family scores are then combined to assess the overall BMWP score. The given BMWP method evaluates the water quality based on the presence and absence of species belonging to a family, that are given a particular score. However, a family given a high score might not be relatively abundant, than those given a lower score. In such cases, the assessment might deviate from the actual conditions of the wetland. The study incorporates the weighted score to the previously given formula of the BMWP score method. The weighted score was given based on the %relative abundance (%RA) of the taxa, given 1, 2, 3, 4, 5 when %RA was between 0 and 20, 21 and 40, 41 and 60, 61 and 80, 81 and 100, respectively, and is calculated using the formula given in Table 1.

The statistical range, mean, and standard deviation of the physicochemical parameters of water, and the values of different ecological metrics used in the study were calculated in Microsoft Excel (2021). The resulting data of the ecological metrics were subjected to Nested ANOVA to assess variations at a 5% significance level, between the studied seasons, and the different sites, respectively. The seasonal difference in the RA of the benthic families was depicted as bar graphs using Microsoft Excel (2021), whereas the comparative differences between seasons for the ecological metrics were shown as a box plot, carried out in SPSS (version 22.0) software. Furthermore, the dendrogram showing preferential assemblages of benthic fauna was plotted using the paired group (UPGMA) method with the Bray Curtis similarity index in PAST software (version 4.03). The software R studio (version 4.3.1), with a vegan package, was used to construct Mantel Corrplot, between physicochemical variables and clusters of benthic macroinvertebrates.

The statistical results of various ecological metrics used in the study to assess the water quality of Baraila wetlands have been summarized in Table 4. None of the studied sites has noted a Margalef's richness index value exceeding 2.5, indicating low species richness in the study area. The Pielou's evenness index ranged between 0.64 and 0.92 in the pre-monsoon and ranged between 0.73 and 0.79 in the post-monsoon. A value of the evenness index nearing 1 suggests the absolute even distribution of species encountered at the study sites. Site 3 of Baraila wetland, having the lowest taxa richness among all the studied sites, is more evenly distributed than others. The value of the Shannon diversity index was recorded highest at site 4 (2.1) in the pre-monsoon season, whereas it ranges from 1.74 to 1.86 in the post-monsoon. It falls between 1 and 3 at all the studied sites, which indicates moderately polluted water conditions in the study area. Assessing water quality based on diversity indices somehow fails to incorporate.

The severity of wetland degradation is often misunderstood by conventional physicochemical monitoring programs. Biomonitoring, especially through sedentary organisms like benthic macroinvertebrates, has notably given better insights into the degree of degradation in a wetland (Miserendino et al. 2008; Mehari et al. 2014; Banda et al. 2023; Sripanya et al. 2023). The abundance and diversity of benthic fauna are the function of the physical and chemical characteristics of habitat conditions, as it quickly responds to any change in water quality (Neetu et al. 2019). Therefore, the study uses a multi-metric index based on macroinvertebrate community to evaluate the water quality and ecological conditions at the Baraila Wetland. The study area lies in a semi-urban region predominated by agricultural activities near the watershed area of the wetland. Besides excessive nutrient input from agricultural fertilizer, the region is being encroached upon with human settlement, where overexploitation and habitat degradation are some most notable anthropogenic stressors (Aslam et al. 2023b). Moreover, the decline in the mean annual rainfall, the infiltration of weeds, heavy siltation, the channeling of river water through canals, clogging up the water resource from the river into wetland, and the local dispute among the inhabitants have caused water scarcity in the Baraila wetland (Aslam et al. 2021, 2023b).

Like many other seasonally flooded wetlands of the world the dilution effect of various chemical constituents in the water is largely dependent on the timing, duration, and magnitude of flooding by nearby rivers (Dube et al. 2017). The abiotic environment of an ecosystem plays a vital role in a structuring biotic community. The abiotic factors that mainly govern the composition and assemblage of benthic macroinvertebrates include WT, depth, DO, nutrient level, TSS in water, the vegetation, and substrate composition of a wetland. It has been well established that water bodies with high DO favor the proliferation of a diverse range of benthic macroinvertebrates (Mehari et al. 2014; Mezgebu et al. 2019), where rapid fluctuation in DO can lead to the elimination of many species of insects and bivalves from the aquatic ecosystem (Tripathy & Mukhopadhayay 2015). Mishra et al. (2015) reported alkaline conditions, and temperatures up to 30 °C favor many species of molluscs which coincides with the findings of the observed results. A relatively higher temperature accelerates the egg hatching, larval development, and survival of various benthic fauna (Baaloudj et al. 2022). The absence of many species of insect family has been mainly because of the low water depth throughout the studied region (Basu et al. 2013). However, most of the physicochemical parameters in the study area were found to be within the optimal range to flourish the macroinvertebrate community except for the low water depth, turbidity, remarkably higher nutrient load, and increased TSS concentration during the post-monsoon season.

As revealed by the results, the studied region was predominated by the families of Bithyniidae, Viviparidae, Planorbidae, Lymnaeidae, and Thiaridae over the others. The low abundance of Ephemeropteran and Trichopteran, with a relatively higher diversity of semi-tolerant to tolerant species of benthic macroinvertebrates, indicates a moderate level of organic pollution. Furthermore, the absence of bivalves strengthens the discussion of moderate organic pollution in the wetland, as it usually prefers clean and well-oxygenated water conditions (Singh et al. 2019). Many previous studies have noted that the sensitive taxa are replaced by semi-tolerant to tolerant fauna in response to organic pollution in a wetland (Miserendino et al. 2008; Keddy 2010; Barkia et al. 2014). The dominance of benthic fauna of class gastropods in the wetland implies the significance of vegetation and shallow water in structuring their community at the Baraila wetland. In addition, the degree of organic pollution in the wetland was also validated by various indices used in the study, which classified the wetland under the moderately polluted category. There is an insignificant impact of season on structuring the benthic community at the study area as p > 0.05 between seasons. However, a decline in taxa richness during the post-monsoon season might be due to an increase in turbidity, TSS, and nutrient levels in the wetland (Velásquez Guarniz 2018). The higher taxonomic richness of benthic macroinvertebrates in pre-monsoon than in post-monsoon agrees with the findings of Molina et al. (2014), González et al. (2013), and Coayla-Peñaloza et al. (2023). Coayla-Peñaloza et al. (2023) also found disturbance by flooding after monsoon increases the flow, turbidity, and nutrient load to the lentic ecosystem, which negatively affects the development of benthic fauna.

The results of HCA have grouped benthic fauna into three clusters, where it appears that the sensitivity toward organic pollution and habitat preferences has mainly governed the assemblage of benthic macroinvertebrate community in the study area. The Alboglossiphonia species have been observed to remain associated with the leafy vegetation, or are found on the shell of gastropods including species of Pila, which eventually validates the results. The clustering of the species of Lymnaeidae, with Chironomidae and Hirudidae explains their tolerance toward pollution (Singh et al. 2020). A study by Mezgebu et al. (2019) also spotted the species of Lymnaeidae, Chironomidae, Psychodidae, and Oligochaeta at highly impacted sites. The preference for habitat in shaping benthic community is very much evident in clusters 2 and 3, where species such as A. oxytropis, Gabbia orcula, Gyralus convexiculus, and Digoniostoma cerameopoma favoring stagnant water, and dense submerged vegetation are grouped (Tripathy & Mukhopadhayay 2015). The assemblage of B. bengalensis, B. micron, B. dissimilis, and N. oligobranchia is because all of them favor silty habitat conditions with relatively sparse vegetation. Similar observations have also been reported by the studies of Leitner et al. (2015), Gething et al. (2020), and Sripanya et al. (2023).

Contrary to the findings of other studies, that have noted a negative correlation of TSS with the benthic community, the significant association of TSS with benthic macroinvertebrates suggests the suspended particles in wetlands might primarily consist of organic matter that serves as food for benthic fauna (Rahman et al. 2021). Several studies have suggested that dead phytoplankton and other organic components contribute to the increased level of TSS in a wetland (Hernández et al. 2014; Jyväsjärvi et al. 2014; Tampo et al. 2021). The semi-tolerant to tolerant families of Lymnaeidae, Planorbidae, Hirudidae, and Chironomidae have been noted to thrive in the conditions with enriched nitrogen and ammonia concentration in the water. However, it has to be mentioned here that the level of ammonia in water has ranged from 0.07 to 0.17 mg/L, which has not exceeded the limit to cause acute toxicity even in the tolerant species (Nutile & Solan 2019). Moreover, the findings concur with the observations of Yang et al. (2020), who found a significant correlation of benthic macroinvertebrates with TP and TN. Shabani et al. (2019) working on a plain wetland in North-East China found TN, NH₄-N, N, and turbidity are among the significant variables that have impacted the distribution of filter-feeding benthos. The species of Lymnea, Gyralus, Tubifex, Chironomus, and Limnodrilus have been reported from disturbed and organically contaminated sites, which is largely influenced by high TP and biological oxygen demand.

The study offers a comprehensive understanding of the wetland's true condition, surpassing conventional water quality assessment approaches. This study notably reveals the wetland's moderate pollution status, predominantly attributed to agricultural expansion and human encroachment. The overexploitation, habitat degradation, and inadequate wetland management have resulted in diminished species richness across the wetland, despite suitable water quality conditions. The survival of species, resilient to moderate pollution, with the absence of sensitive fauna, shedding light on the adverse impact of multiple anthropogenic stressors. In addition, the cluster analysis, followed by Mantel's correlogram approach in biomonitoring, has well-documented the role of water quality parameters in shaping macroinvertebrate communities. However, a holistic study on the impact of anthropogenic stressors and the habitat conditions remains an imperative limitation of the research work, which can be acknowledged for further exploration. The research underscores the urgent necessity for proactive conservation measures and informed management strategies to safeguard this potential Ramsar wetland in the near future. Furthermore, the global significance of this study resonates strongly with similar threatened wetlands facing water scarcity, and encroaching urbanization, emphasizing the relevance of these findings on a broader scale.

The authors are thankful to all members of the Environmental Biology Laboratory at Patna University, Patna.

D. conceptualized, investigated, did formal analysis, did data curation, wrote the original draft, and did software analysis. A.K. conceptualized and supervised the study, provided resources, wrote, reviewed, and edited the article.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.