River algal blooms are well predicted by antecedent environmental conditions

Authors

Rui Xia, Gangsheng Wang, Yuan Zhang, Peng Yang, Zhongwen Yang, Sen Ding, Xiaobo Jia, Chen Yang, Chengjian Liu, Shuqin Ma, Jianing Lin, Xiao Wang, Xikang Hou, Kai Zhang, Xin Gao, Pingzhou Duan, Chang Qian

River algal blooms have become a challenging environmental problem worldwide due to strong interference of human activities and megaprojects (e.g., big dams and large-scale water transfer projects). Previous studies on algal blooms were mainly focused on relatively static water bodies (i.e., lakes and reservoirs), but less on the large rivers. As the largest tributary of the Yangtze River of China and the main freshwater source of the South-to-North Water Diversion Project (SNWDP), the Han River has experienced frequent algal blooms in recent decades. Here we investigated the algal blooms during a decade (2003–2014) in the Han River by two gradient boosting machine (GBM) models with k-fold cross validation, which used explanatory variables from current 10-day (GBMc model) or previous 10-day period (GBMp model). Our results advocate the use of GBMp due to its higher accuracy (median Kappa = 0.9) and practical predictability (using antecedent observations) compared to GBMc. We also revealed that the algal blooms in the Han River were significantly modulated by antecedent water levels in the Han River and the Yangtze River and water level variation in the Han River, whereas the nutrient concentrations in the Han River were usually above thresholds and not limiting algal blooms. This machine-learning-based study potentially provides scientific guidance for preemptive warning and risk management of river algal blooms through comprehensive regulation of water levels during the dry season by making use of water conservancy measures in large rivers.

Effects of land use on streams: traditional and functional analyses of benthic diatoms

Authors

Csilla Stenger-Kovács, Edina Lengyel, Viktor Sebestyén & Beáta Szabó

Agriculture and urbanisation, the two forms of land use, represent serious threats to the ecological status of aquatic ecosystems, especially in the case of small streams at low altitudes. In this study, 75 Hungarian streams were analysed to explore the effects of these land use types on the composition of benthic diatom communities and their richness. In the Carpathian region, species and trait composition, as well as species richness, varied primarily according to the local environmental variables followed by the shared effects of the environmental factors and land use types. At the same time, functional richness was chiefly explained by the pure effects of land use. However, the difference in trait composition between areas dominated by forest (low profile guild, small cell size) and agriculture (motile ecological guilds with middle size, linear-lanceolate shape) was obvious. Higher proportion of water and artificial surfaces might support the spread of diatom species with specific traits: low profile guild with a slightly elongated outline. Nevertheless, no effect of urbanisation on the set of traits, species composition and richness was detected at either local or catchment scale, which might be due to the relatively small portion of artificial surfaces in the watersheds as a whole.

Harmful algae at the complex nexus of eutrophication and climate change

Author

Patricia M.Glibert

Climate projections suggest–with substantial certainty–that global warming >1.5 °C will occur by mid-century (2050). Population is also projected to increase, amplifying the demands for food, fuel, water and sanitation, which, in turn, escalate nutrient pollution. Global projections of nutrient pollution, however, are less certain than those of climate as there are regionally decreasing trends projected in Europe, and stabilization of nutrient use in North America and Australia. In this review of the effects of eutrophication and climate on harmful algae, some of the complex, subtle, and non-intuitive effects and interactions on the physiology of both harmful and non-harmful taxa are emphasized. In a future ocean, non-harmful diatoms may be disproportionately stressed and mixotrophs advantaged due to changing nutrient stoichiometry and forms of nutrients, temperature, stratification and oceanic pH. Modeling is advancing, but there is much yet to be understood, in terms of physiology, biogeochemistry and trophodynamics and how both harmful and nonharmful taxa may change in an uncertain future driven by anthropogenic activities.

Temporal and spatial variability of terrestrial diatoms at the catchment scale: controls on communities

Authors

Jasper Foets​, Carlos E. Wetzel, Adriaan J. Teuling, Laurent Pfister

Diatoms are generally regarded as inhabitants of water bodies. However, numerous taxa are able to survive and reproduce in a variety of non-aquatic ecosystems. Although terrestrial diatoms are discussed extensively in the literature, most of those studies covered floristic aspects and few information exists on their ecology. This lack of knowledge thwarts their potential use as environmental markers in various applications. As a way forward, we investigated the seasonal patterns and the role of different disturbances on the community composition. We collected soil diatom samples in 16 sites across the Attert River basin (Luxembourg) every 4 weeks for a period of 14 months. Our results indicate that forests create a stable microhabitat for diatoms and that temporal variation of the diatom communities is mainly controlled by farming practices rather than seasonal changes in environmental variables. We also found out that communities need one to 2 months to reestablish a new, stable community after a significant change in the environment. We were able to confirm the applicability of the Pollution-Sensitivity Index (IPS) to identify anthropic disturbances.

Large-scale geographical and environmental drivers of shallow lake diatom metacommunities across Europe

Authors

Omar Rodríguez-Alcalá, Saúl Blanco, Jorge García-Girón, Erik Jeppesen, Ken Irvine, Peeter Nõges, Tiina Nõges, Elisabeth M. Gross, Eloy Bécares

Disentangling the relative role of species sorting and dispersal limitation in biological communities has become one of the main issues for community ecologists and biogeographers. In this study, we analysed a data set of epiphytic diatoms comprising 34 lakes from six European countries. This data set covers a relatively large latitudinal gradient to elucidate which processes are affecting the distribution of diatom communities on a broad spatial extent. Our results show strong environmental effects on the composition of the diatom communities, while the spatial factor effects were weak, emphasising that compositional variation was mainly due to species turnover. Our data support information from the literature that local abiotic factors are the main predictors controlling the compositional variation of diatom assemblages in European shallow lakes. More specifically, changes in species composition were driven mainly by nutrient content in Northern Europe, whereas lakes located in Southern Europe were more affected by conductivity and lake depth. Our results solve pending questions in the spatial ecology of diatoms by proving that species turnover is stronger than nestedness at any spatial scale, and give support to the use of epiphytic diatoms as biological indicators for shallow lakes.

Interactive effects of warming and eutrophication on population dynamics and stalk production of epiphytic diatoms in transitional waters

Authors

M. D. Belando, P. M. Martínez, M. Aboal

The interactive effects of temperature and nitrogen:phosphorus stoichiometry were assessed by an experiment that involves cultures of the stalked epiphytic diatom Licmophora colosalis at different N:P ratios (5, 10, 16, 21 and 42) and temperatures (26, 31 and 36 °C) to simulate predictions of global warming effects on a Mediterranean coastal lagoon. At 26 °C, which seemed optimal for L. colosalis, it grew well at the N:P ratios within the 16–21 range, but a different stoichiometry reduced cell growth. The 5 °C increase had deleterious effects on diatom fitness as growth reduced, mortality increased and carbohydrates accumulation amplified under N or P deficiency. In contrast, this temperature stress was better overcome at N:P = 16. The 36 °C temperature proved lethal. Stalk production was specifically stimulated when growth was P-limited at both 26 °C and 31 °C, which suggests that a high proportion of stalks, which would form macroscopic colonies, may serve as an indicator of warming and high N:P ratios in transitional waters.

Spatial and temporal patterns of diatom assemblages, and their drivers, in four US streams: evidence from a long-term dataset

Authors

Camille A. Flinders, Renee L. Ragsdale, Joan Ikoma, William J. Arthurs, Jess Kidd

Bioassessment to evaluate stream integrity and determine changes related to point-source discharges is typically focused in wadeable streams, with limited understanding of seasonal and annual variation. We used a multi-year (n = 13), multi-site (n = 5–7), seasonally (spring and fall) sampled dataset to evaluate spatial and temporal patterns in diatom assemblages relative to measured environmental variables, land use, and pulp and paper mill discharges in a wadeable stream (Codorus Creek, PA) and three non-wadeable rivers (Leaf River, MS; McKenzie and Willamette rivers, OR). Analysis of variance (ANOVA) and permutational ANOVA (PERMANOVA) showed that significant spatial differences in commonly used diatom biotic integrity/diagnostic metrics and assemblage structure were common in the wadeable stream, but rare in the non-wadeable rivers. Season-specific diatom patterns were observed in all streams regardless of size, but annual variation was more prevalent in the non-wadeable rivers. Environmental variables explained 35–58% of the variability in diatoms in the spring and 33–50% in the fall, with physical habitat characteristics associated with stream morphology and seasonality more important than those associated with anthropogenic inputs such as land use and point sources. Findings from this study highlight the value of spatially and temporally comprehensive datasets in understanding and interpreting diatom assemblage patterns.

Responses of benthic algae to nutrient enrichment in a shallow lake: Linking community production, biomass, and composition

Authors

Amanda R. McCormick, Joseph S. Phillips, Anthony R. Ives

1. Understanding how nutrient limitation affects algal biomass and production is a long‐standing interest in aquatic ecology. Nutrients can influence these whole‐community characteristics through several mechanisms, including shifting community composition. Therefore, incorporating the joint responses of biomass, taxonomic composition, and production of algal communities, and relationships among them, is important for understanding effects of nutrient enrichment.
2. In shallow subarctic Lake Mývatn, Iceland, benthic algae compose a majority of whole‐lake primary production, support high secondary production, and influence nutrient cycling. Given the importance of these ecosystem processes, the factors that limit benthic algae have a large effect on the function and dynamics of the Mývatn system.
3. In a 33‐day nutrient enrichment experiment conducted in Lake Mývatn, we measured the joint responses of benthic algal biomass, primary production, and composition to nitrogen (N) and phosphorus (P) supplementation. We enriched N and P using nutrient‐diffusing agar overlain by sediment, with three levels of N and P that were crossed in a factorial design.
4. We found little evidence of community‐wide nutrient limitation, as chlorophyll‐aconcentrations showed a negligible response to nutrients. Gross primary production (GPP) was unaffected by P and inhibited by N enrichment after 10 days, although the inhibitory effect of N diminished by day 33.
5. In contrast to biomass and primary production, community composition was strongly affected by N and marginally affected by P, with some algal groups increasing and others decreasing with enrichment. The taxa with the most negative and positive responses to N enrichment were Fragilariaceae and Scenedesmus, respectively.
6. The abundances of particular algal groups, based on standardised cell counts, were related to GPP measured at the end of the experiment. Oocystis was negatively associated with GPP but was unaffected by N or P, while Fragilariaceae and Scenedesmus were positively associated with GPP but had opposite responses to N. As a result, nutrient‐induced compositional shifts did not alter GPP.
7. Overall, our results show that nutrient enrichment can have large effects on algal community composition while having little effect on total biomass and primary production. Our study suggests that nutrient‐driven compositional shifts may not alter the overall ecological function of algal communities if (1) taxa have contrasting responses to nutrient enrichment but have similar effects on ecological processes, and/or (2) taxa that have strong influences on ecological function are not strongly affected by nutrients.

Factors influencing the heterogeneity of benthic diatom communities along the shoreline of natural alpine lakes

Authors

Frédéric Rimet, Léa Feret, Agnès Bouchez, Jean-Marcel Dorioz, Etienne Dambrine

Littoral benthic diatom communities are pivotal indicators which react to coastline sources of pollution. Littoral communities, however, may be also strongly influenced by other environmental factors: we assumed that even in lakes without anthropogenic pressure, communities could be heterogeneous. To investigate the natural causes of community heterogeneity along shoreline, we sampled 58 pristine high-altitude lakes in the French Alps. Inside each lake, three different littoral stations were sampled. Water chemical composition was measured with major environmental settings. Lakes with homogeneous communities along their shoreline were dominated by pioneer species adapted to strong physical disturbances. The water renewal time in these lakes was short (a few days) and this conveyed strong turbulences. Lakes with heterogeneous communities along their shore had longer water renewal time and were dominated by high-profile diatoms that were able to compete for light and nutrients. The within-lake heterogeneity could be explained by the variability in coastline terrestrial habitats. This study illustrates how water turbulences can limit the expression of some ecological processes like interspecific competition and reduce heterogeneity when it is an overriding stressor. Finally, implications for lake managers are given in terms of monitoring efforts.

Use of phytobenthos to evaluate ecological status in lowland Romanian lakes

 

Authors

M.G. Kelly, G. Chiriac, A. Soare-Minea, Carmen Hamchevici, S. Juggins

In contrast to diatom assemblages in lakes in most other parts of Europe, those in lowland lakes in Romania appear to be determined primarily by biochemical oxygen demand (BOD) and conductivity rather than by nutrients. This has confounded the development of a Water Framework Directive-compatible phytobenthos assessment system for Romanian lakes and led, instead, to the development of a new metric, the Romanian Diatom Index (RDI), which captures these gradients. The primary anthropogenic stressor is assumed to be BOD whilst conductivity is a product of background geology and climate. The RDI is strongly correlated with BOD, and ecological quality ratios (EQRs) are computed by dividing the observed RDI by an expected value, determined from the 90^th percentile of the relationship between RDI and conductivity. This equates to the “best available” RDI at any point on the conductivity gradient and, in the absence of true “reference sites”, has been assumed to represent the boundary between high and good status. The boundary between good and moderate status has been set at the point where the sum of valves of taxa tolerant to elevated BOD exceeds the sum of valves of taxa that are sensitive to elevated BOD. The position of this boundary has been further validated by the use of a Threshold Indicator Species Analysis (TITAN). In view of the susceptibility of conductivity to climate warming, 2010 values of conductivity have been used to ensure a stable benchmark against which future changes can be measured. This study highlights the challenges involved in performing reliable ecological assessments in situations that are, by the standards of much of Europe, atypical.