Spatial characteristics of surface-deposited diatoms in Weishan Lake and their relationship with the water environment (Shandong Province, China)

Abstract

The Weishan Lake serves as a crucial reservoir and regulating lake in the Eastern Route of the South-to-North Water Diversion Project and the ecological health of its lake ecosystem directly impacts the water quality for water diversion. Diatoms are particularly sensitive to changes in water environments, and the composition of diatom communities serves as a significant indicator of the health of aquatic ecosystems. To understand the composition of diatom communities in Weishan Lake and their relationship with environmental factors, thereby providing scientific grounds for the protection of the lake’s ecological environment, surface sediment diatoms, water samples, and sediments were collected and analyzed. The study revealed that there are 64 species from 19 genera of diatoms in Weishan Lake, predominantly comprising epiphytic and planktonic species. Dominant species include Fragilaria brevistriata, Achnanthes minutissima, and Stephanodiscus parvus, indicating an overall meso-eutrophic status. According to the diatom composition and biodiversity index, the diatom community was divided into three combination zones. Redundancy analysis (RDA) results indicated that the water environmental factors influencing the composition and distribution of diatom communities in Weishan Lake are TP, TOC, DO, NO₂⁻–N, and Ca²⁺, collectively explaining 35.60% of the variation in diatom community composition. Due to the influence of agricultural and industrial wastewater runoff, domestic sewage discharge, and cage aquaculture, Weishan Lake is in a mesotrophic eutrophication state. Therefore, it is recommended that strict control over inappropriate human activities in the lake area be implemented in the future to ensure the safety of water quality for water diversion.

Keywords:

• Diatom
• environment factors
• spatial distribution
• Weishan lake
• redundancy analysis

1. Introduction

Weishan Lake, as a critical reservoir in the eastern segment of the South-to-North Water Diversion Project, plays a pivotal role in determining the quality of water transported to its destination. However, recent years have seen an escalation in the detrimental impact of human activities on its ecosystem, manifesting in the rise of industrial wastewater, domestic sewage, and aquaculture pollution (Jiao et al. 2020; Zhu et al. 2019). Particularly since the beginning of the twenty first century, escalating concentrations of nitrogen and phosphorus have transformed Weishan Lake into a paradigmatic eutrophic body of water. Concurrently, the proliferation of cage culture operations has led to a reduction in the lake’s surface area, triggering a regression in aquatic vegetation. Consequently, the water quality of the eastern segment of the South-to-North Water Transfer Project faces imminent peril (Xu et al. 2022). Thus, it becomes paramount and pressing to comprehensively understand the historical hydrological fluctuations and eutrophication patterns of the lake, and to undertake measures for the restoration and preservation of Weishan Lake’s ecological equilibrium.

Diatoms, as vital primary producers in aquatic ecosystems, exhibit characteristics such as wide distribution, short life cycles, rapid reproduction, and sensitivity to environmental conditions, with distinct suitability and tolerance thresholds for specific ecological factors (Yang et al. 2020). Alterations in environmental parameters exert direct influence on diatom composition, rendering them effective indicators of shifts in water quality, encompassing acidity levels and eutrophication status (Cvetkoska et al. 2018). Furthermore, diatom remnants possess the unique ability to endure in sediment over extended periods (Rühland et al. 2015), thereby enabling the reconstruction of long-term environmental dynamics through analysis of their changing assemblages. Consequently, to unravel the historical diatom community structure and reconstruct the lake’s protracted hydrological evolution and eutrophication trajectory utilizing diatom species, it is imperative to explore the intricate interplay between contemporary diatom composition and environmental variables.

In recent decades, significant strides have been made by numerous paleoecologists in investigating the relationship between sediment diatoms and environmental factors (Yang et al. 2003; Wu et al. 2020; Guan et al. 2021). For instance, through an analysis of the correlation between diatoms and environmental parameters in 40 lakes across the Tibetan Plateau, Yang et al. (2003) identified conductivity (salinity) as the primary determinant influencing diatom distribution in the region. Consequently, they formulated a diatom-conductivity (salinity) conversion function, facilitating the quantitative reconstruction of salinity variations over the past century in Chen Co and Nam Co. Similarly, the diatom assemblage of Longtan Lake was utilized to elucidate changes in regional water quality over the preceding century, with diatoms deemed particularly sensitive to fluctuations in pH and nutrient levels (Guan et al. 2021). Analysis of fossil diatoms and pigments by Rowland Hall et al. was used to examine the effects of land management practices on the nutritional status of Williams Lake, a eutrophic lake in central British Columbia, Canada (Hall et al. 1997). Qin et al. conducted a regional assessment of water phosphorus changes in eutrophic lakes in eastern China since 1900, demonstrating that a large-scale integration of spatial information from paleontological records can highlight eutrophication processes and further benefit current lake management (Qin et al. 2023). Moreover, leveraging the composition, abundance, and ecological characteristics of diatoms in the Pearl River estuary, Wu et al. 2020 delineated the environmental evolutionary sequence of the area since the Late Pleistocene.

While considerable advancements have been made in diatom studies, research focusing on modern diatom ecology within Weishan Lake remains comparatively scarce. Consequently, our analysis of diatom composition, spatial distribution, and their relationship with environmental factors in the lake’s surface sediment fills a critical gap, offering insights into past diatom assemblages and facilitating the long-term reconstruction of hydrological changes and eutrophication history. This endeavor serves to enhance our understanding of Weishan Lake’s ecological dynamics, thereby aiding in its ecological restoration efforts. In future studies, the diatom-environmental factor conversion function can be constructed and provide a basis for the environmental evolution of reducing lakes in the future.

2. Research area and methods

2.1. Research area

Located in Weishan County, Shandong Province, China, Weishan Lake (116°57′∼ 117° 21′ E, 34°27′∼ 34°53′N) forms part of the Nansi Lake system, alongside Nanyang Lake, Dushan Lake, and Zhaoyang Lake (Figure 1). The Nansi Lake system was bifurcated into an upper lake and a lower lake by a dam constructed in 1958. The northern section of the dam constitutes the upper lake, encompassing Nanyang Lake, Dushan Lake, and a segment of Zhaoyang Lake (Tan et al. 2022), while the southern portion forms the lower lake, primarily comprising Weishan Lake and a portion of Zhaoyang Lake (Figure 1). With an area of 660 km², Weishan Lake is characterized by shallow depths, boasting an average water length of 1.59 m and a maximum depth of 2.9 m. The lake experiences a temperate monsoon climate, with an average annual temperature ranging from 14.9 to 16 °C and an average annual precipitation of 750 mm, with approximately 70% of precipitation occurring during the summer months (Wei et al. 2015). Serving as a pivotal storage hub for the eastern leg of the South-to-North Water Diversion Project, Weishan Lake fulfills a multitude of functions including flood control, irrigation, transfer, and tourism, thereby playing a vital role in upholding regional ecological equilibrium.

Figure 1. Bitmap of Weishan Lake area.

2.2. Data acquisition and processing

Considering the northwest section of the lake as a river-type with a narrow water surface, juxtaposed with the open waters in the south, and factoring in the surrounding environmental conditions, 41 sampling points were established across Weishan Lake in 2019. Surface sediment diatoms and water samples were concurrently collected from these 41 sites, with on-site measurements conducted for water temperature (WT), dissolved oxygen (DO), Secchi disc transparency (SD), and pH levels. The suite of water quality parameters tested primarily encompassed physical and chemical indicators, including Chl.a, CODMn, TP, TN, NH₃–N, NO₃⁻–N, NO₂^—N, DOC, PO₄ and eight major ions (SO₄²⁻, Ca²⁺, Cl⁻, K⁺, Mg²⁺, Na⁺, NH₄⁺, NO₃⁻). The water depth is measured by the portable depth sounder, the transparency is measured by the transparency plate, and the water temperature, pH and dissolved oxygen are measured by the water quality monitor. The eight ions, total nitrogen, total phosphorus, chlorophyll a and chemical oxygen demand were analyzed in the laboratory of Liaocheng University. The total nitrogen data were obtained by ultraviolet spectrophotometry after potassium persulfate digestion, total phosphorus was determined by ammonium molybdate spectrophotometry, and concentrations of Ca²⁺, K⁺, Mg²⁺ and Na⁺ ions were determined by IPC-AES. The concentrations of Cl⁻ and SO₄²⁻ were obtained by ion chromatography (Table 1).

Table 1. Statistical table of environmental factors.

Environmental factors	Mean value	Standard deviation
SD (m)	0.827	0.263
T (°C)	18.024	0.592
DO (mg/L)	9.351	1.164
pH	8.627	0.548
Chl.a (mg/m^3)	7.075	3.924
CODMn (mg/L)	4.934	0.656
TP (mg/L)	0.086	0.014
TN (mg/L)	2.367	0.523
PO4 (mg/L)	0.066	0.048
NH3–N (mg/L)	0.471	0.112
NO3^−–N (mg/L)	0.717	0.311
NO2^−–N (mg/L)	0.022	0.022
Doc (mg/L)	6.670	0.506
SO4^2−	116.629	20.581
Ca^2+	41.277	7.701
Cl^−	92.519	9.418
K^+	8.853	0.834
Mg^2+	19.533	2.703
Na^+	77.457	10.156
NH4^+	0.945	0.604
NO3^−	14.990	1.952

Diatom sample preparation adhered to standardized methodologies. Approximately 0.5 g of each sample was transferred into a small beaker, where 10 mL of 10% hydrochloric acid was added to dissolve calcium carbonate, followed by the addition of 10 mL of 30% hydrogen peroxide to eliminate organic matter. Upon completion of the reaction, the samples underwent centrifugation at a speed of 2500 r·min⁻¹ for 10 min, followed by the addition of 10 mL of distilled water to each tube. Subsequently, the samples were individually pipetted onto coverslips, air-dried overnight, and sealed with a drop of toluene to finalize the preparation of diatom slides. A Naphrax gum film was applied after thorough steaming. Diatom species were identified under a 1000-fold Leica biomicroscope, with approximately 300 diatom valves enumerated per slide as the minimum threshold requirement, primarily referencing the taxonomic works of Krammer and Lange-Bertalot (1986-1991).

2.3. Statistical analyses

Data processing and graphing were performed using Excel 2010 and Origin 2018, while clustering analysis of diatom assemblages was conducted using SPSS 24. Ordination analysis, aimed at exploring relationships between diatom assemblages and environmental variables, was carried out using Canoco 5 for Windows software.

2.3.1. Biological evaluation

The Shannon-Wiener index (H′’), Pielou index (E), Margalef index (D) and the Simpson index (D) were used to calculate the richness, diversity, and evenness (Strong 2016). The calculation formulas are shown in that:

Shannon–Wiener (1) $$H^{\prime }=-{{\displaystyle \sum }}_{i=1}^s\left(\frac{n_i}{N}\right)\cdot \text{ln\hspace{0.17em}}\left(\frac{n_i}{N}\right)$$(1)

Pielou (2) $$E=\frac{\hspace{0.17em}{H}^{\prime }}{\text{ln\hspace{0.17em}}S}$$(2)

Margalef (3) $$\text{D =}\frac{\mathrm{S}-1}{\mathrm{\text{ln}}\hspace{0.17em}N}$$(3)

Simpson (4) $$D\text{=1}-{\sum }_{i=1}^s\frac{n_i(n_i-1)}{N(N-1)}$$(4)

Note: S: The number of species of diatom species; N: The number of all species of diatoms; $n_i$: The number of individual diatom species.

2.3.2. Index analysis

In order to mitigate potential errors, diatom species with abundances greater than 10% were retained. Initially, detrended correspondence analysis (DCA) gradient length was employed to determine the appropriate ordination analysis method for the diatom species data. A gradient length greater than 2 for axis 1 indicates the selection of the unimodal model, whereas a gradient length less than 2 favors the linear model (Lepš and Šmilauer 2003; Dong et al. 2019). Experimental analysis revealed that the gradient length of SD (=1.49) was below 2, suggesting a linear response of diatoms to environmental factors. Consequently, redundancy analysis (RDA) was deemed more suitable for examining the relationship between diatoms and environmental elements.

To mitigate bias in the data, the diatom species data underwent squaring, while the environmental variables underwent log (x + 1) transformation before conducting RDA. A collinearity diagnosis was conducted on all environmental factors included in the RDA analysis, with factors exhibiting large variance expansion coefficients (VIF ≥ 5) being removed. Subsequently, Monte Carlo permutation (p < 0.05, n = 499) was employed to test and analyze the significance of the environmental indicators. DCA and RDA analyses were executed using CANOCO 5.

3. Results

3.1. Composition and spatial distribution characteristics of diatom community

A total of 64 species belonging to 19 genera were identified in the 41 surface sediment samples collected from Weishan Lake. The dominant species consisted predominantly of epiphytic and planktonic species, with relatively few benthic species present. Among these, 15 diatom species exhibited a species richness exceeding 10%, with the percentage composition of the major diatom species depicted in Figure 2.

Figure 2. Diatom assemblage of Weishan Lake.

The main genera comprising the diatom community in Weishan Lake were Fragilaria brevistriata (24.92%), Achnanthes minutissima (13.78%), and Stephanodiscus parvus (11.48%), collectively accounting for 50.18% of the total counts. F. brevistriata was the most abundant species in Weishan Lake and exhibited a distribution extending from the lake shore to the lake center. This species preferred neutral to alkaline waters, with an optimum pH range of 6.3–7.9, and demonstrated high counts in meso-eutrophic environments (Yang 2008). A. minutissima was prevalent in most samples, with its ecological optimum value for total phosphorus in lakes in the middle and lower reaches of the Yangtze River estimated at around 50 μg/L. It thrived in alkaline, nutrient-rich environments and dominated in lakes with elevated pH levels (Dong et al. 2006). S. parvus exhibited widespread distribution in eutrophic lakes and served as an indicator species for assessing the eutrophication status of lakes. Overall, the diatoms primarily comprised meso-eutrophic species, and the alkaline water quality of the lake could be inferred from the diatom species and their ecological preferences. Based on biodiversity indices and diatom characteristics, the diatom assemblages of Weishan Lake were categorized into three combination zones (Figure 2) using SPSS 24, with specific change characteristics as follows:

Zone I: The Shannon-Wiener index, Pielou index, and Simpson index exhibited the lowest values among the three zones, with consistent trends observed for all indices except the Margalef index. The composition of diatom assemblages mirrored the trend reflected by the biodiversity indices, indicating a low abundance of diatoms in this zone across all samples and an uneven distribution of individuals among species. Sample sites within Zone I encompassed sites 1–5 and 32–33, characterized by S. parvus as the dominant species, accounting for an average content of 64.66%. While A. minutissima, F. brevistriata, Cocconeis placentula, Meneghiniana cyclotella, and Cymbella microcephala were present, their contents were relatively low, with the remaining diatom species exhibiting even lower abundances.

S. parvus, a common species in eutrophic lakes (Dong et al. 2006), emerged as the predominant species in this zone, indicating severe eutrophication in the vicinity of the sampling sites. These sites, located in the shallow southeastern area of Weishan Lake, were surrounded by cage culture areas and ironworks. The discharge of fish excreta, exogenous bait, decaying aquatic plants, and industrial and agricultural wastewater elevated nitrogen and phosphorus concentrations, deteriorating the water environment and exacerbating lake eutrophication, thus facilitating S. parvus dominance in this zone.

Zone II: The Shannon-Wiener index, Pielou index, Margalef index, and Simpson index exhibited the highest values among the three zones. Trends across the indices were consistent, indicating uniformity in species composition among the sampling sites. Sample sites within Zone II encompassed sites 6–20, 23, 29–31, 34–39, and 41, with the dominant diatom species predominantly comprising epiphytic species such as F. brevistriata (maximum content 42.73%, average content 18.77%), A. minutissima (maximum content 45.94%, average content 16.84%), and Fragilaria construens (maximum content 22.31%, average content 10.46%).

S. parvus content was higher at sites 37 and 38, correlating with experimental results indicating higher total nitrogen (TN) content at these sites (3.59 mg/L and 2.28 mg/L, respectively). Elevated TN content and the prevalence of eutrophic species suggested more severe eutrophication at these sites, which were situated near cage culture areas where fish excretion and bait retention contributed to nitrogen and phosphorus accumulation, along with increased organic matter content, intensifying eutrophication levels.

Zone III: The Margalef index exhibited the lowest values among the three zones, while the Shannon-Wiener index, Pielou index, and Simpson index were higher than in Zone I. The variation trends of all four indices were consistent, with low values observed at sampling site 21, indicating low uniformity in diatom species. Sample sites within Zone III encompassed sites 21–22, 24–28, and 40, characterized by F. brevistriata dominance, alongside the presence of F. construens and A. minutissima (Figure 3).

Figure 3. Diatom assemblage zoning map of Weishan Lake.

3.2. Redundancy analysis of diatom communities and environmental factors

In the DCA analysis, the maximum gradient length of species change was 1.49, which was less than 2, indicating a linear response of the diatom community to environmental factors. Subsequently, RDA was employed to unveil the primary factors influencing the composition and spatial distribution of diatom communities.

The eigenvalues of the first and second axes in the RDA were 0.256 and 0.058, respectively, signifying that the distribution of diatom species was influenced by the joint effect of both axes. RDA results revealed that the composition of the diatom community in Weishan Lake was predominantly influenced by five significant factors: Ca²⁺(F = 2.8, p = 0.008), NO₂⁻–N (F = 5.5, p = 0.002), TP (F = 2.3, p = 0.042), TOC (F = 3.4, p = 0.008), DO (F = 3.0, p = 0.006), collectively explaining 35.60% of the variability in the diatom community.

According to Figure 4a, Cyclotella pseudostelligera, Aulacoseira granulate, and Aulacoseira ambigua exhibited a significant positive correlation with DO, while eutrophic species such as S. parvus and Cyclotella meneghiniana were significantly positively correlated with NO₂⁻–N. Metro-eutrophic species such as A. minutissima and F. brevistriata showed a positive correlation with TOC and TP, but a negative correlation with NO₂⁻–N. Cocconeis placenta exhibited a high correlation with Ca²⁺.

Figure 4. Results of RDAs, with significant variables.

As depicted in Figure 4b, sample sites 3, 5, 32, and 33 exhibited a high correlation with NO2–N, with eutrophic species S. parvus dominant in the sampling area. Sample sites 2, 34, 37, and 38 demonstrated higher Ca²⁺ concentrations. Sites 7–8, 10–14, 16–20, 23, and 29–30 exhibited a positive correlation with DO concentration, indicating better self-purification ability of water in these areas. Conversely, sites 15, 21–22, 24–28, and 31 were scattered in areas with higher TP and TOC concentrations, suggesting nutrient enrichment and eutrophication in the lake.

4. Discussion

Based on the results of the RDA analysis, the primary environmental factors influencing changes in diatom communities in Weishan Lake were TOC and DO, followed by TP, NO₂⁻–N, and Ca²⁺.

4.1. Effect of DO on diatom community change in Weishan Lake

DO serves as a key indicator reflecting water oxygen concentration and is vital for gauging water self-purification capacity, as well as maintaining lake water quality and health. Anoxic and anaerobic conditions can detrimentally impact lake ecosystems (Yu et al. 2017). Diatom growth and reproduction necessitate DO consumption, with their photosynthesis and respiration closely tied to oxygen levels (Chen et al. 2021). Elevated DO concentration fosters a stable ecosystem, facilitating the growth and reproduction of certain diatom species. For instance, C. pseudostelligera, Aulacoseira granulata, and A. ambigua exhibited positive correlations with DO concentration.

Moreover, the average DO concentration across the 41 sample sites was 9.35 mg/L, with 15 sites in diatom assemblage Zone II demonstrating a positive correlation with DO concentration, including sites 7, 8, 10–14, 16–20, 23, 29, and 30. The average dissolved oxygen concentration of 9.85 mg/L suggests high oxygen levels in the vicinity of these 15 sites, indicative of robust water self-cleaning capabilities.

4.2. Effect of TOC on diatom community change in Weishan Lake

TOC, as a crucial environmental factor, significantly influences diatom composition and distribution. TOC represents the organic matter content of lake sediments and serves as a metric for lake productivity (Zang et al. 2019). Human activities substantially impact TOC levels. For instance, a study on sediment organic matter in Taihu Lake found a positive relationship between organic matter distribution and human interference activities (Mao et al. 2020), with estuarine organic matter content notably increasing (Gao et al. 2016). Human activities, including increased cash crop cultivation and pesticide and chemical fertilizer use, have boosted sediment organic matter input into lakes. This, coupled with net-pen aquaculture methods, has further elevated sediment organic carbon content. In this study, diatom community composition significantly correlated with TOC, explaining 22.3% of diatom community change information. Diatom species such as F. brevistriata, C. microcephala, Amphora libyca, and A. minutissima demonstrated a greater ability to utilize TOC, indicating the pronounced impact of TOC.

4.3. Effect of nutrients on diatom community change in Weishan Lake

RDA analysis highlighted that the composition and distribution of diatom communities were primarily influenced by nutrients. Nitrogen and phosphorus indicators have long been recognized as pivotal variables affecting diatom composition and distribution (Jamileh et al. 2020). For example, studies have underscored the significance of total phosphorus in shaping diatom distribution in lakes across the middle and lower reaches of the Yangtze River, with environmental factors such as TN, NH₃–N, NO₃⁻–N, and TP exerting considerable influence on diatom composition in the Hanjiang River basin (Liu et al. 2018). Studies pertaining to Nansi Lake have also identified nitrogen and phosphorus nutrients, along with temperature and pH, as key environmental indicators driving diatom community changes. During photosynthesis, diatoms rely on nutrient supplies such as nitrogen and phosphorus, with increased nutrient contents often signaling nutrient enrichment.

Sample sites 21, 22, 24, 25, 26, 27, 28, and 31 in Zone III were situated at the positive end of TP, indicative of mild eutrophication in the area, with medic-eutrophic species like A. minutissima, A. ambigua, and F. brevistriata dominating. Improved cage culture technology and increased fishery output have prompted fishermen to eradicate vegetation like reeds and lotus while expanding cage culture operations. However, low utilization and conversion rates of bait for animals such as crabs and fish, coupled with improper feed placement, result in significant residual bait accumulation in the water. Decay and decomposition of residual roots further contribute to nitrogen and phosphorus accumulation, hastening lake eutrophication. Cage culture activities can also directly damage aquatic vegetation and diminish the water purification capacity of submerged plants. Sample sites 21 and 22, located in areas influenced by cage culture, exhibited high nutrient levels as well.

NO₂⁻–N poses a threat to both human health and lake organisms when its concentration exceeds permissible levels (Padisák et al. 2018; Dou et al. 2016). Its primary sources include domestic sewage, industrial wastewater, and fertilizer effluents. In recent years, heightened nitrogen and phosphorus concentrations in the Weishan Lake area have resulted from economic development, population growth, and increased pollutant discharge. The inefficient use of agricultural fertilizers has led to substantial runoff into the lake during precipitation events. Industrial and domestic effluents, along with agricultural runoff, carry suspended particles containing nitrogen, phosphorus, and other nutrients into Weishan Lake without adequate treatment, deteriorating water quality and exacerbating eutrophication. Moreover, Typhoon “Lichima” has exacerbated nutrient influx into Weishan Lake by causing rivers to transport significant nutrient loads into the lake. NO₂⁻–N, as a nitrogen source, at certain concentrations, promotes the growth of diatom species (Xiang et al. 2018). Sample sites 3, 5, 32, and 33 in diatom assemblage I exhibited positive correlations with NO₂⁻–N, indicating a mildly eutrophic state. These sites were dominated by eutrophic species like S. parvus and C. meneghiniana. Sites 3 and 5, located near the purse-seine culture area and steel mills, exhibited high nutrient levels due to feed delivery, fish excretion, fish residues, and industrial wastewater. Sample site 32, near Weishan Island, had a NO₂⁻–N concentration of 0.037 mg/L, significantly higher than the average of 0.021 mg/L, likely due to frequent human activities. Site 33, situated near the inlets of the Dasha River, Shizi River, and Panlong River, likely received a substantial nutrient load from these rivers, resulting in mild eutrophication.

Metal elements in water bodies, at appropriate concentrations, facilitate diatom growth and reproduction. Conversely, below-threshold metal concentrations inhibit diatom growth. Calcium ions maintain diatom normalcy, regulating their development, metabolic activities, and cell membrane stability (He et al. 2020). Studies indicate that inadequate calcium ion concentrations hinder diatom growth rates, while excessive concentrations inhibit growth. However, optimal calcium ion concentrations enhance diatom development and physiological metabolism, mitigating the adverse effects of heavy metals and promoting diatom genus and species growth (Bai et al. 2019). RDA analysis revealed a strong positive correlation between diatom genera such as F. brevistriata, A. minutissima, and F. construens, and calcium ion concentration. Notably, certain alkaliphilic diatom genera, like Achnanthes, Cocconeis, and Gomphonema, exhibit higher calcium ion acclimation values, the significant positive correlation between C. placentula and calcium ions in this study.

5. Conclusion

In 2019, a total of 64 diatom species belonging to 19 genera were identified in the surface sediments of Weishan Lake. These species were predominantly epiphytic and planktonic, with relatively few benthic species. The dominant species observed were F. brevistriata, A. minutissima, and S. parvus, primarily representing meso-eutrophic species. Based on diatom composition and biodiversity index, the diatom species were categorized into three zones. The water environment conditions inferred from diatom species in these zones closely aligned with the actual environmental conditions.Redundancy analysis (RDA) revealed significant environmental variables influencing the composition and distribution of the diatom community in Weishan Lake. These variables included Ca²⁺, NO₂⁻–N, TP, TOC, DO, collectively explaining 35.60% of the variability in the diatom community. Notably, TOC and DO exerted the greatest impact, indicating that diatoms were primarily affected by nutrient and water pollution in the lake. Weishan Lake exhibited a slight eutrophic state, likely influenced by industrial and agricultural wastewater, domestic sewage discharge, and cage culture practices. To ensure the safety of water quality for water transfer purposes, it is imperative to rigorously control improper human activities in the lake area in the future.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability

The data presented in this study are available upon request from the corresponding author.

Additional information

Funding

This study was funded by the National Natural Science Foundation of China (Grant Nos. 41807430 and 41871073).