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Original Article • Braz. J. Biol. 86 • 2026 • https://doi.org/10.1590/1519-6984.309050 linkcopy

Open-access Floristic survey and environmental impacts in seasonally floodable grasslands of the Baixada Maranhense Environmental Protection Area, Brazil

Levantamento florístico e impactos ambientais em campos sazonalmente inundáveis da Área de Proteção Ambiental da Baixada Maranhense, Brasil

Abstract

This study aimed to conduct a floristic survey of aquatic and palustrine plants and to assess environmental impacts in two municipalities of the Baixada Maranhense. Between January and August 2024, we recorded 99 species, distributed in 68 genera and 39 families. We report the first records of Wolffiella neotropica and Luziola subintegra for Northeastern Brazil, Euploca lagoensis for Maranhão, eight new records for the Amazon region of Maranhão, and three for the Baixada Maranhense. Cyperaceae, Onagraceae, and Poaceae had the highest species richness (8 spp. each), followed by Fabaceae (7 spp.). Ludwigia and Cyperus were the most diverse genera (8 and 6 spp., respectively). Palustrine (58 spp.) and emergent (9 spp.) life forms predominated. Floating life forms comprised seven free-floating and seven rooted-floating species. The most widespread impacts were fires, irregular waste disposal, and urban expansion. Inventories are essential in poorly studied wetlands, as they contribute to understanding environmental dynamics and support biodiversity conservation.

Keywords:
Amazon region of Maranhão; wetlands; floodable grasslands; new occurrences; Ramsar Site

Resumo

Este trabalho teve como objetivo realizar um levantamento de plantas aquáticas e palustres e analisar os impactos ambientais em dois municípios da Baixada Maranhense. Catalogamos 99 espécies, 68 gêneros e 39 famílias, entre janeiro e agosto de 2024. Reportamos o primeiro registro de Wolffiella neotropica e Luziola subintegra para o Nordeste, Euploca lagoensis para o Maranhão, oito novos registros para a Amazônia maranhense e três para a Baixada maranhense. As famílias Cyperaceae, Onagraceae e Poaceae apresentaram a maior riqueza específica (8 spp., cada), seguidas por Fabaceae (7 spp.). Ludwigia e Cyperus foram os gêneros mais diversos (8 e 6 spp., respectivamente). As formas de vida palustres (58) e emergentes (9) predominaram. As flutuantes somaram (7 spp., cada). Os impactos de maior alcance foram as queimadas, o descarte irregular de lixo e a expansão urbana. Inventários são necessários em áreas úmidas pouco estudadas, para entender a dinâmica dos ambientes e conservar a biodiversidade.

Palavras-chave:
Amazônia maranhense; áreas úmidas; campos inundáveis; novas ocorrências; Sítio Ramsar

1. Introduction

Wetlands are ecosystems of high ecological relevance, located at the interface between aquatic and terrestrial environments, either natural or artificial, and characterized by the permanent or periodic presence of water and by hydromorphic soils (Junk et al., 2014; Nunes da Cunha et al., 2015). These environments play a central role in maintaining biodiversity, regulating climate, and providing ecosystem services, such as groundwater recharge and support for biological diversity (Piedade et al., 2012).

In Brazil, wetlands are estimated to cover approximately 20% of the national territory (Junk et al., 2011, 2024a), with emphasis on the Northeastern region, where the Baixada Maranhense Environmental Protection Area (BM EPA) is located and has been recognized as a Ramsar Site since the 2000s. The BM EPA is situated at the easternmost edge of the Brazilian Amazon and consists of extensive seasonally floodable plains that favor the establishment of plant communities composed of aquatic and palustrine plants (A&P plants).

A&P plants comprise species adapted to flooded environments that are capable of tolerating permanent or seasonal submersion of the root system through morphophysiological adaptations, including aerenchyma, hollow stems, and cuticular modifications (Cook, 1996; Amaral et al., 2008). These plants colonize both lentic and lotic environments and shape the ecological dynamics of aquatic ecosystems by cycling nutrients and providing shelter for fauna (Thomaz and Esteves, 2011).

Aquatic and wetland plants play essential roles in the structure and functioning of wetlands. These plants participate in nutrient cycling, promote sediment stabilization, contribute to reducing erosion and the resuspension of particles and pollutants, and aid in carbon sequestration and climate regulation (Thomaz, 2023; Maranho and Gomes, 2024). Additionally, aquatic and wetland plants provide shelter, substrate, food resources, and nesting sites for various aquatic organisms, thereby contributing to the maintenance of biodiversity in wetlands (Brito et al., 2021; Fares and Michelan, 2024).

As in the BM EPA, aquatic ecosystems may exhibit periods of flooding and drought and high environmental heterogeneity, resulting in habitat mosaics that can sustain substantial floristic diversity (Costa-Neto et al., 2002; Barbieri and Carreiro, 2017). Despite the ecological relevance of these ecosystems, floristic studies involving A&P plants remain incipient in Maranhão. Previous investigations in wetlands of Northeastern Brazil have focused on specific localities or environmental typologies, such as reservoirs, restingas, and urban areas (Lima et al., 2011; Moura-Júnior et al., 2013; Sabino et al., 2015; Barbieri and Carreiro, 2017; Silva and Fontes, 2018; Arouche et al., 2021; Pestana et al., 2024; Alves et al., 2024; Paiva et al., 2025). These studies have contributed to knowledge of the regional flora, but they still reveal gaps regarding species distribution and the understanding of the ecological dynamics of floodable grasslands.

A recent study in the BM EPA reported a new record for Maranhão and for the Northeastern region (Ferreira et al., 2025), reinforcing the importance of these environments as biodiversity reservoirs and priority areas for botanical research and conservation. Thus, research on the A&P flora of municipalities within the BM EPA is justified, especially regarding taxon checklists, regional comparisons, and the assessment of environmental impacts on vegetation. Additionally, the wetlands of the BM EPA have been subjected to increasing anthropogenic pressures, including urban expansion, agricultural and livestock activities, the introduction of invasive species, and effluent discharge, all of which may compromise biodiversity and associated ecosystem services (Andrade et al., 2018; Simkin et al., 2022; Duré et al., 2025; Pestana et al., 2026). Floristic surveys therefore constitute fundamental tools for characterizing vegetation, supporting conservation strategies, and guiding sustainable management and environmental education actions (Pimentel et al., 2024).

In this context, the present study aimed to conduct a floristic survey of A&P plants in the municipalities of Santa Helena and Turilândia, located in the northern portion of the BM EPA, with the purpose of expanding knowledge of regional plant diversity and describing environmental impacts in these wetlands, thereby supporting conservation actions and contributing to the understanding of the flora associated with floodable grasslands in the Amazon region of Maranhão.

2. Material and Methods

2.1. Study area

The study was conducted in the municipalities of Santa Helena and Turilândia in the Amazon phytogeographic domain of western Maranhão within the BM EPA (Figure 1). These municipalities contain natural floodable grasslands that constitute one of the largest lake systems in northeastern Brazil (Theodosio et al., 2023). The landscape features seasonally flooded depressions interspersed with flat to gently undulating terrain, connected by a meandering drainage network from the lower courses of the Mearim, Pindaré, Pericumã, and Turiaçu rivers (Costa-Neto et al., 2002; Barbieri and Carreiro, 2017; Theodosio et al., 2023 – Figure 2). The regional climate is Tropical Savanna (Aw) according to the Köppen climate classification (Alvares et al., 2013). Mean annual temperature is 26.5 °C and mean annual precipitation is approximately 1,780 mm, concentrated primarily in the first half of the year (Climate-Data.org, 2025).

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Figure 1
Map showing the location of the study area and collection points in the municipalities of Turilândia and Santa Helena, Maranhão, Brazil.
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Figure 2
Representative environments sampled in the study area. (A) Turiaçu River near the bridge crossing that separates the municipalities of Santa Helena (left bank) and Turilândia (right bank); (B) riverbank of the Turiaçu River with small boats during the dry season; (C,D) Lago Bacabal, showing flooded grassland with buffalo and surrounded by palm vegetation; (E) Lago Preto, with aquatic vegetation and a forested river margin with dense riparian vegetation. (F) Lago Jenipapo.

2.2. Collection and processing of botanical material

The floristic survey was carried out through three field expeditions conducted between January and August 2024, covering both the flood period, in January, and the dry period, in July and August. Sampling was distributed across 13 collection sites in the Baixada Maranhense, including lentic and lotic aquatic environments, such as lakes, rivers, floodable grasslands, and temporarily flooded areas in the municipalities of Santa Helena and Turilândia (Figure 2). At all sites, fertile botanical material was collected using the free exploratory walking method, with systematic walks along the margins of floodable grasslands and water bodies, as well as within aquatic environments when access was possible, to ensure a continuous survey of the vegetation.

During fieldwork, plants were photographed, habitat and habit data were recorded, and geographic coordinates were obtained using a GPS device. Small boats were used occasionally and complementarily when necessary to access deeper environments or to collect floating specimens located far from the margins. Collections were conducted intensively on weekends, on Saturdays and Sundays, from 8:00 a.m. to 5:00 p.m., totaling approximately 8 hours of active sampling per day. Fieldwork logistics included institutional land vehicles provided by the University, small motorboats, and foot transit, depending on site accessibility. Travel between sampling sites totaled approximately 40 km across the study areas in the sampled municipalities. Collection authorization was obtained through submission of a request to SISBio (License No. 96470-1) and State Secretariat (A34-2024). After collection, specimens were pressed and dehydrated in an oven for approximately 72 h at 60 °C, following standard herborization protocols (Fidalgo and Bononi, 1989). The resulting exsiccates were deposited in the Herbarium Rosa Mochel (SLUI) (Thiers, 2025).

2.3. Taxonomic identification and data treatment

Specimens were identified using taxonomic keys and specialized literature (Pott and Pott, 2000; Piedade et al., 2018; Souza and Lorenzi, 2019), supplemented by comparisons with herbarium specimens and consultations of the speciesLink (SpeciesLink, 2025) and Flora e Funga do Brasil (Flora e Funga do Brasil, 2025). Classification followed the Angiosperm Phylogeny Group IV (Angiosperm Phylogeny Group, 2016) system for angiosperms and the Pteridophyte Phylogeny Group I (PPG, 2016) system for ferns. Scientific name spellings and authority designations were verified against Flora e Funga do Brasil (2025). New records were determined by cross-referencing specimen data with SpeciesLink, Flora e Funga do Brasil, and GBIF. Records were considered new when no previous occurrences were found in these databases.

Species life forms were classified in the field following Pott and Pott (2000) and Amaral et al. (2008) (Figure 3), with validation using specialized literature when required. The floristic data obtained were organized into taxonomic lists containing families, genera, species, life forms, and ecological information, allowing comparative analyses with surveys previously conducted in the region.

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Figure 3
Growth forms of A&P plants based on the categories proposed by Pott and Pott (2000) and Amaral et al. (2008): (1) Palustrine or Amphibious; (2) emergent; (3) rooted floating; (4) free-floating; (5) rooted submerged; (6) free-submerged; (7) epiphytes. Source: Extracted from Alves et al. (2024).

2.4. Species accumulation and richness estimation

Floristic data were organized into a species-by-site incidence matrix, where rows represented the 99 recorded species and columns represented the 13 sampling points. Species occurrences were recorded as presence (1) or absence (0). Sampling adequacy was assessed using a species accumulation curve based on incidence data, treating each sampling point as an independent sampling unit. The curve was constructed using the random permutation method with 999 permutations (Gotelli and Colwell, 2001). In addition to observed species richness, the non-parametric richness estimators Chao2 and Jackknife 1 were recalculated after each increment in sampling effort across the permutations. This approach allowed estimation trajectories to be compared directly with the observed accumulation curve (Chao, 1987; Colwell and Coddington, 1994). All analyses were performed in the R environment (R Core Team, 2025) using the vegan (Oksanen et al., 2025) and ggplot2 (Wickham, 2016) packages for statistical computations and data visualization, respectively.

2.5. Analysis of environmental impacts

Environmental impacts were analyzed in three stages: (i) inventory and characterization of anthropogenic and natural components to delimit geoenvironmental units and diagnose the main environmental problems; (ii) assessment of future trends based on the current environmental scenario; and (iii) identification of legal instruments and management strategies applicable to environmental planning (Leopold et al., 1971; Oliveira-Folharini et al., 2018).

3. Results

3.1. Floristic composition and sampling effort

A total of 99 species distributed in 68 genera and 39 botanical families were recorded (Table 1; Figures 4, 5 and 6). Cyperaceae, Onagraceae, and Poaceae exhibited the highest species richness, with 8 species (8.1%) each, while Fabaceae accounted for 7 species (7.1%). Other representative families were Araceae, Convolvulaceae, Euphorbiaceae, Heliotropiaceae, and Plantaginaceae, with 4 species each (4.1%). The remaining families had three or fewer species. Regarding generic richness, Ludwigia L. stood out as the most diverse genus, with 8 species (8.1%), followed by Cyperus L., with 6 species (6.1%). The genera Bacopa Aubl., Ipomoea L., Lindernia All., and Pontederia L. each had 3 species (3%), whereas most genera were represented by a single species.

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Table 1
Taxa of aquatic and palustrine plants recorded in the municipalities of Santa Helena and Turilândia, Baixada Maranhense, Maranhão, Brazil.
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Figure 4
Representative families and species of aquatic and palustrine plants recorded in Santa Helena and Turilândia, Maranhão, Brazil. (A) Acanthaceae – Justicia laevilinguis; (B) Alismataceae – Echinodorus paniculatus; (C, D) Araceae – Lemna aequinoctialis and Pistia stratiotes, respectively; (E) Cabombaceae – Cabomba aquatica; (F) Cleomaceae – Tarenaya longicarpa; (G) Convolvulaceae – Ipomoea carnea; (H) Cyperaceae – Cyperus blepharoleptos; (I) Euphorbiaceae – Caperonia castaneifolia; (J, K) Fabaceae – Neptunia oleracea and Mimosa dormiens; (L) Gentianaceae – Schultesia guianensis; (M, N) Heliotropiaceae – Euploca lagoensis and Heliotropium elongatum; (O, P) Lentibulariaceae – Utricularia foliosa and U. gibba.
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Figure 5
Representative families and species of aquatic and palustrine plants recorded in Santa Helena and Turilândia, Maranhão, Brazil. (A) Linderniaceae – Lindernia dubia; (B) Lythraceae – Cuphea carthagenensis; (C) Malvaceae – Malachra radiata; (D) Marsileaceae – Marsilea polycarpa; (E) Menyanthaceae – Nymphoides humboldtiana; (F) Nymphaeaceae – Nymphaea amazonum; (G, H, I) Onagraceae – Ludwigia decurrens, L. sedioides, and L. erecta, respectively; (J) Passifloraceae – Passiflora foetida; (K) Plantaginaceae – Bacopa sessiliflora; (L, M) Poaceae – Echinochloa polystachya and Luziola subintegra; (N) Polygalaceae – Senega paniculata; (O, P) Pontederiaceae – Pontederia crassipes and P. rotundifolia.
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Figure 6
Representative families and species of aquatic and palustrine plants recorded in Santa Helena and Turilândia, Maranhão, Brazil. (A, B) Rubiaceae – Borreria scabiosoides and Pentodon pentandrus, respectively; (C, D) Salviniaceae – Azolla microphylla and Salvinia auriculata; (E) Sphenocleaceae – Sphenoclea zeylanica; (F, G) Turneraceae – Piriqueta cistoides and Turnera subulata; (H, I) Verbenaceae – Phyla betulifolia and Stachytarpheta cayennensis; (J) Vitaceae – Cissus erosa.

Palustrine species were the predominant life form distribution with 58 taxa (58.5%), followed by emergent species with 9 species (9.1%). Free-floating and rooted-floating forms each accounted for 7 species (7.1%). The remaining species exhibited more than one life form, reflecting ecological plasticity. Regarding origin, native species totalled 88 species (88.9%) and naturalized species 11 species (11.1%).

Phytogeographic analysis revealed broad ranges across multiple domains, predominantly the Amazon and Cerrado, with additional occurrences in the Caatinga, Atlantic Forest, Pantanal, and Pampa. The survey yielded significant range extensions, including new records for the Baixada Maranhense (Sesuvium portulacastrum (L.) L., Trichospira verticillata (L.) S.F.Blake, and Schultesia guianensis (Aubl.) Malme) and the Amazonian region of Maranhão (Cyperus surinamensis Rottb., Fimbristylis littoralis Gaudich., Aeschynomene rudis Benth., Vigna luteola (Jacq.) Benth., Marsilea polycarpa Hook. & Grev., Ludwigia hyssopifolia (G.Don) Exell, Senega paniculata (L.) J.F.B.Pastore & J.R.Abbott, and Eragrostis tenella (L.) P.Beauv. ex. Roem. & Schult.). Furthermore, Euploca lagoensis (Warm.) Diane & Hilger is recorded for the first time in the state of Maranhão, and Wolffiella neotropica Landolt and Luziola subintegra Swallen are new records for northeastern Brazil.

The species accumulation curve exhibited a pronounced increase across the initial sampling points, with the rate of species addition declining progressively as sampling effort increased (Figure 7). Consequently, the maximum observed richness of 99 species was reached when all 13 sampling points were incorporated. The non-parametric richness estimators indicated a high degree of inventory completeness, as the observed richness corresponded to 96.4% of the Chao2 estimate (~102 species) and 89.9% of the Jackknife 1 estimate (~110 species).

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Figure 7
Species accumulation curve for observed and estimated richness of aquatic and palustrine plants in Santa Helena and Turilândia, Maranhão, Brazil. The solid line with open circles represents the observed species richness, whereas the surrounding shaded band depicts the standard deviation derived from 999 random permutations; the dotdashed and dotted lines represent the Chao2 and Jackknife1 richness estimators, respectively.

3.2. Analysis of environmental impacts

Different types of human actions were identified, among which fires, irregular waste disposal, inadequate cattle and buffalo raising in natural grasslands, municipal effluent discharge into floodable ecosystems, urban expansion, and the introduction of invasive flora stood out (Figure 8).

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Figure 8
Environmental impacts observed in seasonally flooded grasslands. (A) Water buffaloes in the landscape of the municipality of Turilândia. (B) Cattle in the landscape of the municipality of Santa Helena. (C) Solid waste on the riverbank in Turilândia. (D) Anthropogenic modification of the flooded grasslands landscape in Santa Helena.

Fires were observed in Turilândia, in the areas of the Jenipapo, Sumidouro, and Palmeiral lakes. In Santa Helena, this practice was not recorded at the sampled sites. Irregular waste disposal was evident in several areas in both municipalities. In Santa Helena, waste was observed on the banks of the Turiaçu River. In Turilândia, waste was observed near Ponte das Três Ilhas, Lagoa Permanente, and also along the Turiaçu River.

Inadequate cattle and buffalo raising was identified in Turilândia, in the localities Lagoa da Ubá, Lago Bacabal, and the village of Viola. In Santa Helena, no significant records were found. Regarding municipal effluent discharge, the most affected sites in Santa Helena and Turilândia were along the banks of the Turiaçu River. Urban expansion was recorded in Santa Helena, in areas close to the Turiaçu River. In Turilândia, urban pressure was identified at Ponte das Três Ilhas and in the vicinity of the Turiaçu River. Finally, the introduction of invasive plant species was identified in Turilândia (Ponte das Três Ilhas, village of Viola, and igarapé), especially the occurrence of Lemna valdiviana Phil. and Pontederia crassipes Mart.; the latter was also present in Santa Helena.

4. Discussion

The high floristic richness recorded in the wetlands of the BM EPA reinforces the importance of these environments for maintaining regional plant biodiversity. Floristic studies conducted in wetlands of Maranhão and other tropical regions show that these ecosystems often harbor high diversity of A&P plants, although they remain relatively undersampled from a botanical perspective (Barbieri and Carreiro, 2017; Silva and Fontes, 2018; Córdova et al., 2022; Pestana et al., 2024; Alves et al., 2024). In addition to floristic richness, this survey resulted in new species records for the Baixada Maranhense, the Amazon region of Maranhão, and the state of Maranhão, including species such as Euploca lagoensis and Senega paniculata (Flora e Funga do Brasil, 2025; Specieslink, 2025). In addition, Luziola subintegra and Wolffiella neotropica represent new records for Northeastern Brazil (Flora e Funga do Brasil, 2025).

The predominance of the families Cyperaceae, Onagraceae, Poaceae, and Fabaceae follows the pattern observed in floristic surveys of tropical aquatic environments, in which these families show high representativeness due to their broad ecological plasticity and capacity to adapt to seasonally floodable environments (Cook, 1996; Thomaz and Esteves, 2011). Similarly, the higher richness observed for the genera Ludwigia and Cyperus has already been reported in aquatic A&P plants inventories, reflecting the affinity of these groups with environments subject to hydrological variation and different flooding regimes (Sabino et al., 2015; Santos et al., 2017).

The alternation between flooding and drying phases influences biodiversity and the ecological organization of floodplain environments (Jean Milien et al., 2023). In these environments, substrates may remain periodically or permanently waterlogged and are often hypoxic or anoxic, requiring species adapted to such environmental conditions (Junk et al., 2024b). Therefore, the high representativeness of palustrine species (58.5%) observed in this study may be explained by the hydrological dynamics of the floodable grasslands of the Baixada Maranhense, where seasonal flooding and subsequent exposure during drier periods favor species with high ecological plasticity and tolerance to environmental variation (Thomaz and Esteves, 2011; Conceição-Gomes and Aoki, 2015). The occurrence of emergent and free- or rooted-floating species further indicates the environmental heterogeneity of these systems, which include areas ranging from temporarily flooded sites to permanent aquatic environments (Cook, 1996).

The dominance of native species (88.9%) indicates relative maintenance of the regional flora in the studied areas. However, the presence of naturalized species, although in a lower proportion, may be associated with anthropogenic pressures such as urban expansion, fires, inadequate waste disposal, and agricultural and livestock activities, factors already identified as influencing the floristic composition of wetlands and as capable of favoring opportunistic species (Spinelli-Araújo et al., 2016; Barbieri and Carreiro, 2017). The broad phytogeographic distribution of the recorded species, with occurrences in the Amazon and Cerrado domains and additional records for the Caatinga, Atlantic Forest, Pantanal, and Pampa, highlights the transitional character of the Baixada Maranhense. This condition favors the coexistence of species with broad ecological amplitude, adapted to different environmental conditions and frequently associated with tropical wetland ecosystems (Costa-Neto et al., 2002; Silva-Junior et al., 2020).

The evaluation of the survey effort showed a progressive reduction in the rate of species accumulation, while high inventory completeness estimated by Chao2 (96.4%) and Jackknife1 (89.9%) indicated that the sampling was adequate to characterize the flora of A&P plants of Santa Helena and Turilândia. Although the accumulation curve did not reach a complete asymptote, the close agreement between observed and estimated richness suggests that most species present in the study area were recorded. According to Chao2, approximately four additional species would be expected with further sampling, whereas Jackknife1 indicates that richness could increase by about 10%.

These results indicate high inventory completeness, suggesting that additional sampling would primarily detect infrequent species rather than substantially increase total richness (Gotelli and Colwell, 2001; Chao et al., 2014; Chao and Chiu, 2016). Remaining difference between observed and estimated richness is expected for aquatic plant communities, where many species occur at low frequencies or are restricted to particular habitats (Thomaz and Esteves, 2011; Murphy et al., 2019). The study area includes lakes, seasonally floodable grasslands, and floodplains that differ in water depth, hydroperiod, and connectivity. Such environmental variation favors species turnover and contributes to the occurrence of locally uncommon species, increasing the likelihood that some taxa remain undetected even after intensive sampling (Cook, 1996; Chambers et al., 2008).

Regarding the environmental impacts observed in Turilândia, fires mainly result from agricultural practices during soil preparation for planting and from the expansion of agriculture and livestock activities for pasture formation (Silva-Junior et al., 2016; Rodrigues et al., 2022). These pasture areas are used mainly for extensive cattle and buffalo raising. The raising of these animals, incorporated as an economic activity, has caused ecological impacts, such as soil compaction by trampling and vegetation removal through grazing, which reduces the regeneration capacity of these environments, as well as social impacts, especially due to the introduction of buffalo into the grasslands, the disorderly growth of herds, and urban expansion in the region, directly affecting the structure and functioning of these ecosystems (Costa-Neto et al., 2002; Muniz, 2006; Neto et al., 2022). Cattle raising may indirectly affect aquatic and palustrine vegetation by promoting vegetation loss. A preference for emergent species may also occur, as observed for Pacourina edulis Aubl. (Asteraceae) in the Baixada Maranhense, where plants were heavily grazed by water buffaloes (Ferreira et al., 2025). In parallel, cattle raising may cause soil erosion, sediment input into streams, and changes in groundwater dynamics. In impacted streams, sediment deposition may cover colonizable surfaces, hindering the establishment of aquatic and palustrine species (Junk et al., 2024b).

In addition to the environmental impacts mentioned above, inadequate disposal of municipal effluents and solid waste into the Turiaçu River should also be highlighted. These results corroborate a recent study on bathing suitability and sanitary perception in the municipality of Santa Helena, which demonstrated the existence of effluent discharge points along the river course (Pacheco et al., 2021). This problem is intensified by irregular waste disposal, which compromises water quality and favors eutrophication, creating a suitable environment for the proliferation of invasive species such as Pontederia crassipes (water hyacinth) and Lemna valdiviana (duckweed) in the sampled environments (Addo-Bankas et al., 2022; Kato and Kato-Noguchi, 2026).

In a climate change scenario, potential changes in flood duration and seasonal water availability may increase the vulnerability of the wetlands of the Baixada Maranhense, especially when combined with the environmental impacts recorded in this study, such as fires, irregular waste disposal, livestock pressure, and urban expansion. The conservation of these areas is especially relevant under global climate change because wetlands help maintain water in the landscape, reduce erosion and sediment transport, and store considerable amounts of carbon in soils and living biomass (Lind et al., 2022; Junk et al., 2024b).

5. Conclusions

This study expands the knowledge on A&P plants in the BM EPA by documenting 99 species in the wetlands of Santa Helena and Turilândia, including new geographic records at local, state, and regional scales. The richness estimators indicated that the sampling effort adequately represented the flora of the surveyed wetlands, although additional species may be recorded with further collecting. The recorded environmental impacts indicate that these wetlands are subject to multiple stressors capable of altering vegetation structure and ecosystem functioning. These results reinforce the urgency to strengthen conservation strategies and implement integrated management actions, especially in areas adjacent to the Turiaçu River and other highly degraded sites. The protection of these floodable fields is essential to preserve plant diversity, ecological processes, and associated ecosystem services.

The generated floristic data constitute a relevant baseline for biodiversity monitoring and environmental planning in the Baixada Maranhense. Long-term monitoring programs are recommended to evaluate changes in aquatic macrophyte composition related to natural hydrological dynamics and increasing anthropogenic pressures. In this context, the recurrent occurrence of Pontederia crassipes in impacted environments suggests that this species has the potential to be evaluated in future studies as a bioindicator of environmental changes, particularly in areas affected by eutrophication and nutrient enrichment. Continuous inventories and ecological studies will be fundamental to support conservation policies, guide restoration initiatives, and improve the management of wetlands in the eastern Amazon.

Acknowledgements

We thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico-CNPq (process 404619/2023-1, “Diversidade florística em áreas de lacuna de informação Botânica para o Maranhão”) for funding this research. We also thank the Programa Institucional de Bolsas de Iniciação Científica (PIBIC); the Grupo de Pesquisa em Biodiversidade e Interdisciplinaridade em Ensino de Ciências Naturais for assistance with identification and herborization; UFMA for logistical support; Dra. Francisca Helena Muniz, curator of SLUI herbarium at UEMA.

Data Availability Statement

The entire dataset supporting the results of this study is included in the article.

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*

e-mail: raysa.valeria@ufma.br

Editor:

Takako Matsumura Tundisi

Publication Dates

  • Publication in this collection
    17 Aug 2026
  • Date of issue
    2026

History

  • Received
    24 May 2026
  • Accepted
    09 July 2026
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