Cyanobacteria as dominant mediator of altitudinal gradient effects on phytoplankton community diversity in freshwater ecosystems: Evidences from the freshwater Lakes along the Hu Line

Freshwater salinization is the process of changing ion concentrations (e.g., Na+, Mg2+, K+, Cl−, , ) relative to background levels due to human activities (e.g., agriculture, application of road de-icing salts, water and resource extraction, climate change, and sea-level rise; Williams 2001; Cañedo-Argüelles et al. 2016). Although considerably less studied than other environmental issues (Cañedo-Argüelles 2020), salinization is widely accepted as presenting major challenges to freshwater and coastal biodiversity (Cunillera-Montcusí et al. 2022). Existing data and research show a clear rise in freshwater salinization worldwide (Dugan et al. 2017; Cañedo-Argüelles 2020; Jeppesen et al. 2020; Kaushal et al. 2021), yet key knowledge gaps and management challenges remain due to the complexity (Kaushal et al. 2018) and prevalence of the problem (Cañedo-Argüelles 2020; Jeppesen et al. 2020). Current literature has neglected to provide unbiased geographic coverage (Cunillera-Montcusí et al. 2022), and ecosystem-level responses (e.g., functions and services) are rarely assessed (Herbert et al. 2015). Compelling calls for research agendas that address the need for salinization research at multiple scales (e.g., global, regional, local) are well timed (Cunillera-Montcusí et al. 2022). One identified research gap points to the need for networks of researchers working together at regional scales using experimental approaches to identify impacts on biodiversity, community salinity thresholds, and landscape-scale drivers. Here, we document the results of a networked Global Salt Initiative (GSI) that performed in situ experiments on lakes to look at ecosystem-level impacts: their findings suggest that North American and European water quality guidelines for salt are far too low to prevent ecosystem-level impacts. The further purpose of this Special Issue (SI) is to document the results of ecosystem-level impacts of increasing salinity on lake and coastal area biodiversity and ecosystem functioning from a variety of perspectives.

AIM: The aim of the present study was to study the vertical variation in phytoplankton community in a subtropical coastal lake and to verify the temporal variation of this community following variation in temperature and dissolved nitrogen and phosphorus. METHODS: Sampling of phytoplankton and abiotic variables were performed monthly from June/2009 to January/2011 at four depths from the central part of Peri Lake. The data were analyzed using analysis of variance, correlation and canonical correspondence analysis. RESULTS: Vertical variation in the phytoplankton community and limnological data did not occur but temporal variation was found. The lake was limited by light and nutrients and this light limitation selected the Cyanobacteria species from Sn and S1 functional groups. Phytoplankton community was composed of five groups, with 31 freshwater taxa, in which Cyanobacteria was the most important with 87.7% of total density and Chlorophyta with 11.8%. Cylindrospermopsis raciborskii was dominant during almost the whole study period because when temperature and phosphorus increased and wind speed decreased Limnothrix sp. density was boosted. Different species of Cyanobacteria filamentous showed correlation with variables in different ways, indicating that some species can co-exist, each of them having distinct niches or can compete by the same resource. CONCLUSION: The phytoplankton presented periodicity driven by annual change in water temperature and nutrients availability. Peri Lake's features allow for the occurrence of a vertically homogeneous water column and the dominance of cyanobacterial functional groups adapted to low underwater light and nutrients deficiency

Phytoplankton are commonly used as an ecological tool in assessing water quality and indicating ecosystem health. The purpose of this study was to explore the effects of geospatial and physicochemical variables on variation in phytoplankton community composition and biodiversity in lakes across the State of Oklahoma. We hypothesized that variation in phytoplankton communities is primarily driven by both geospatial and physicochemical variables, specifically precipitation, longitude, nitrogen, and phosphorus. To test this hypothesis, we acquired 438 surface water samples collected during a 3‐year period from 109 lakes in Oklahoma through a statewide water quality monitoring program. All phytoplankton samples were counted using compound light microscopy and identified to genus level. Community data analyses were performed to assess spatial variation in community composition and whether the variation can be explained by the physicochemical and geospatial variables. We identified 106 unique phytoplankton taxa, with cyanobacteria comprising an average of 68% of the total biovolume across lakes. We also found significant relationships between phytoplankton biodiversity and urban land, chlorophyll a , electrical conductivity, water temperature, biovolume, and turbidity. The analyses identified one geospatial variable and six physicochemical variables as significantly correlated with phytoplankton community composition, suggesting that physicochemical variables are more predictive of variation in community composition than geospatial variables. Overall, we concluded that although geospatial variables were not strongly predictive of overall phytoplankton community structure, rare phytoplankton taxa (i.e., Haptophyta and Charophyta) do respond to geospatial variation while phytoplankton community composition driven by common taxa (i.e., Cyanobacteria, Chlorophyta, and Bacillariophyta) is structured by physicochemical variables. Our findings emphasize the continued need to focus on in‐lake characteristics for maintaining water quality standards and preserving diverse lake ecosystems.

Phytoplankton is the primary producer and the basis of most aquatic food webs. Characterising the variations in phytoplankton communities and the factors affecting these variations in a fluctuating environment are central issues in ecology and essential to developing appropriate conservation strategies. In the present study, seasonal variations in the phytoplankton community and the driving environmental factors were analysed based on data from Lake Nansihu in 2013. In all, 138 phytoplankton species were identified. The phytoplankton community exhibited seasonal variations, with a mean abundance that ranged from 5.00 × 105 cells L–1 in winter to 4.57 × 106 cells L–1 in summer and a mean biomass that varied from 0.44 mg L–1 in winter to 3.75 mg L–1 in summer. A spring algal bloom did not appear in this warm, temperate monsoon lake, but an algal bloom did appear in summer when the temperature and nutrient concentrations were high. There were substantial seasonal variations in the dominant phytoplankton taxa, from Chlorophyta, Bacillariophyta and Euglenophyta in spring to Chlorophyta and Bacillariophyta in summer, followed by dominance of Chlorophyta in autumn and Bacillariophyta in winter. Results of canonical correspondence analysis indicated that although the environmental factors affecting the seasonal variations in different phytoplankton species varied, water temperature, total nitrogen, total phosphorus and ammonia nitrogen appeared to be the most dominant. These four variables were also the main environmental factors driving the seasonal variations in the phytoplankton community in the lake. The results of the present study will be useful in guaranteeing the water quality and ecological security of Lake Nansihu.

Inland freshwater shallow lake ecosystem degradation is indistinctly intertwined with human-induced factors and climate variability. Changes in climate and human-induced factors significantly influence the state of lake ecosystems. This study provides evidence of the driver, pressure, state, impact, and response (DPSIR) indicators for freshwater lake ecosystem dynamics, taking Lake Malombe in Malawi as a case study. We used the DPSIR framework and Tobit model to achieve the study’s objectives. The study’s findings indicate that top-down processes gradually erode Lake Malombe’s ecosystem state. The lake resilience is falling away from its natural state due to increasing rates of drivers, pressures, and impacts, indicating the lake ecosystem’s deterioration. The study shows that demographic, socio–economic, climatic drivers, pressures, state, and responses significantly (p < 0.05) influenced the lake ecosystem’s resilience. The study suggests that substantial freshwater ecosystem management under the current scenario requires a long-term, robust, and sustainable management plan. The findings from this study provide a roadmap for short-term and long-term practical policy-focused responses, particularly in implementing a freshwater ecosystem restoration programs in Malawi and Africa more broadly.

Numerous studies have shown that changes in environmental factors can significantly impact and shift the structure of phytoplankton communities in marine ecosystems. However, little is known about the association between the ecological stoichiometry of seawater nutrients and phytoplankton community diversity and stability in subtropical bays. Therefore, we investigated the relationship between the phytoplankton community assemblage and seasonal variation in the Beibu Gulf, South China Sea. In this study, we found that the abundance of Bacillariophyceae in spring was relatively greater than in other seasons, whereas the abundance of Coscinodiscophyceae was relatively low in spring and winter but greatly increased in summer and autumn. Values of the alpha diversity indices gradually increased from spring to winter, revealing that seasonal variations shifted the phytoplankton community structure. The regression lines between the average variation degree and the Shannon index and Bray–Curtis dissimilarity values showed significantly positive correlations, indicating that high diversity was beneficial to maintaining community stability. In addition, the ecological stoichiometry of nutrients exhibited significantly positive associations with Shannon index and Bray–Curtis dissimilarity, demonstrating that ecological stoichiometry can significantly influence the alpha and beta diversity of phytoplankton communities. The C:N:P ratio was not statistically significantly correlated with average variation degree, suggesting that ecological stoichiometry rarely impacted the community stability. Temperature, nitrate, dissolved inorganic phosphorous, and total dissolved phosphorus were the main drivers of the phytoplankton community assemblage. The results of this study provide new perspectives about what influences phytoplankton community structure and the association between ecological stoichiometry, community diversity, and stability in response to environmental changes.

Seasonal variations in phytoplankton community and some physico-chemical features of Lake Karamuk (Afyonkarahisar-Turkey).

As part of the joint Finnish-Russian research and development project “Assessment of the ecological state of the transboundary waters”, seasonal and spatial variations in the phytoplankton communities of Lake Pyhajarvi were studied in order to identify possible long-term (1963–2002) changes and to present recent data (since 2002) on phytoplankton biomass and species composition. Some changes in both phytoplankton biomass and species composition, particularly in the littoral zone and northern basins of the lake, were obvious at the end of the 1980s; in particular, the density of blue-greens increased during that period. Biomasses increased five-fold in 1980, decreased after 1990 and have remained low (0.14 mg l−l) to the present time. The effective water protection measures applied, especially reducing the phosphorus load from municipal wastewaters and airborne pollution, can now be seen to have improved the water quality. Although no significant temporal differences were found in phytoplankton biomass during the intensive biweekly sampling in 2002, considerable spatial variation was seen within the lake. An obvious change in the species composition of phytoplankton and an increase in biomass were seen even in the loaded parts of the lake. Despite the spatial differences in phytoplankton biomass and community structure, the changed species composition in the northern part of the lake indicated a clear recovery from the blue-green and Chrysophyceae dominated high biomass of the 1980s.

To explore the temporal and spatial variations in phytoplankton community in small estuaries, we collected surface water samples from Yongjiang River estuary during wet, normal, and dry seasons and determined the main driving factors of phytoplankton community. A total of 358 species belonging to nine phyla and 123 genera were identified in all seasons. During wet, normal, and dry seasons, species number was 276, 154 and 151, and the abundance was (170.45±225.43)×103, (51.92±30.28)×103 and (31.65±12.79)×103 cells·L-1, respectively. Diatoms dominated the phytoplankton community, and the main dominant species were Cyclotella meneghiniana, Skeletonema costatum, and Paralia sulcata. Shannon diversity and Pielou evenness indices decreased from inside mouth to outside mouth in wet season, but there was no obvious spatial difference in normal season or dry season. Results of non-metric multidimensional scaling analysis and analysis of similarities showed that phytoplankton community composition differed significantly among different regions (inside, at and outside mouth) and different seasons. In wet season, phytoplankton abundance was significantly positively correlated with temperature, dissolved inorganic nitrogen, and dissolved reactive phosphorus, but significantly negatively correlated with salinity. In normal season, phytoplankton abundance was significantly negatively correlated with temperature. In dry season, it was not significantly correlated with environmental factors. Results of redundancy analysis showed that temperature, salinity, ammonium and dissolved reactive phosphorus explained the variations in phytoplankton community by 19.5%, 11.9%, 9.4% and 8.2%, respectively. These results revealed high dominance of diatoms and the main driving factors (temperature, salinity and nutrients) of phytoplankton community in Yongjiang River estuary.

Chapter 4 - Spatio-temporal patterns of bacterial diversity along environmental gradients and bacterial attachment to organic aggregates

The East China Sea (ECS) is the largest marginal sea in the northern western Pacific Ocean. In comparison to various physical studies, little information on the seasonal patterns in community structure of phytoplankton is currently available. Based on high performance liquid chromatography (HPLC) pigment analysis, spatiotemporal variations in phytoplankton community compositions were investigated in the northern ECS. Water temperature and salinity generally decreased toward the western part of the study area but warmer conditions in August led to strong vertical stratification of the water column. In general, major inorganic nutrient concentrations were considerably higher in the western part with a shallow water depth, and consistent with previous results, had no discernable vertical pattern during our observation period except in August. This study also revealed PO4-limited environmental conditions in May and August. The monthly averaged integral chlorophyll-a concentration varied seasonally, highest (35.2 ± 20.22 mg m−2) in May and lowest (5.2 ± 2.54 mg m−2) in February. No distinct vertical differences in phytoplankton community compositions were observed for all the sampling seasons except in August when cyanobacteria predominated in the nutrient-deficient surface layer and diatoms prevailed at deep layer. Canonical correlation analysis results revealed that nutrient distribution and the water temperature were the major drivers of the vertical distribution of phytoplankton communities in August. Spatially, a noticeable difference in phytoplankton community structure between the eastern and western parts was observed in November with diatom domination in the western part and cyanobacteria domination in the eastern part, which were significantly (p < 0.01) correlated with water temperature, salinity, light conditions, and nutrient concentrations. Overall, the two major phytoplankton groups were diatoms (32.0%) and cyanobacteria (20.6%) in the northern ECS and the two groups were negatively correlated, which holds a significant ecological meaning under expected warming ocean conditions.

Phytoplankton community dynamics assessed by ships-of-opportunity sampling in the northern Baltic Sea: A comparison of HPLC pigment analysis and cell counts

Distribution of phytoplankton community in relation to environmental parameters in cage culture area of Sepanggar Bay, Sabah, Malaysia

The resting stages of phytoplankton are usually regarded as the seed bank and source of harmful algal blooms because of the recruitment of phytoplankton from sediment to the water column under suitable environmental conditions. Information about resting stages of phytoplankton is abundant in shallow lakes and littoral sea; yet, studies on river–reservoir systems are rare. The river–reservoir continuum shows a unique structuring of longitudinal gradients of hydrological and hydrodynamic conditions. We hypothesized that the seed bank and algal blooms in reservoirs are influenced by the hydrodynamic conditions of each reservoir. We used Illumina Miseq sequencing to examine the spatio-temporal variation in the phytoplankton community in the sediment as reservoir drawdown and in surface water during algal blooms in Pengxi River, a tributary of China’s Three Gorges Reservoir. The results show that the cyanobacteria community in sediment is significantly influenced by temperature, total carbon, maximum flow velocity, and total phosphorous, the eukaryotic phytoplankton community in sediment is significantly influenced by total phosphorous, temperature, total carbon, maximum flow velocity, and total nitrogen. Additionally, the dominant species in sediment is significantly different from that in surface water during algal blooms. Our results suggest that the dominant species in surface water during algal blooms is more influenced by the environmental factors and hydrodynamic conditions in the water column than the seeds in the sediment. These findings are fundamental for further research on the influence of hydrodynamic conditions on algal blooms in artificially regulated river-reservoir systems.

Kang, J.J.; Lee, J.H.; Kim, H.C.; Lee, W.C.; Lee, D.; Jo, N.; Min, J.-O., and Lee, S.H., 2018. Monthly variations of phytoplankton community in Geoje-Hansan bay of the southern part of Korea based on HPLC pigment analysis. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 356–360. Coconut Creek (Florida), ISSN 0749-0208.Seasonal variations in environmental parameters such as temperature, salinity, and nutrients can significantly affect the community structure of phytoplankton, the primary food source of a marine ecosystem. To understand the influences of environmental factors on phytoplankton community structure, phytoplankton pigments analysis were conducted in the Geoje-Hansan bay situated at the southern part of Korea during January to December, 2016 on monthly basis. Salinity in the water was observed to be fairly stable throughout the study period except for the rainy periods during the summer season (August: 30.3 ± 0.3 and September: 31.1 ± 0.2 psu). Water temperature showed typical seasonal patterns similar to the temperate oceans with maximum values during summer seasons (24.9 ± 0.9 °C). Major nutrients (nitrogen, phosphate, and silicate; hereafter N, P, Si) showed similar patterns of seasonal variation with averages of 3.677 ± 2.707μM, 0.338 ± 0.270μM, and 17.614 ± 9.287μM, respectively, with peak values during December. Phytoplankton community composition estimated using the CHEMTAX program showed distinctive seasonal variations during the study period. The results showed a dominance of dinoflagellates during November – March (>64%) with an exception in December whereas diatoms appeared to be dominant during May – October (60.1%). Dinoflagellates exhibited a negative correlation with temperature, whereas diatoms showed a positive correlation with temperature based on principal components analysis (PCA). Given these findings, a diatom-dominant ecosystem would be expected throughout the year under ongoing ocean warming conditions, which could provide different food qualities to upper trophic levels in the Geoje-Hansan bay.