A systematic literature review of forecasting and predictive models for cyanobacteria blooms in freshwater lakes

Authors

Benny Zuse Rousso, Edoardo Bertone, Rodney Stewart, David P. Hamilton

Cyanobacteria harmful blooms (CyanoHABs) in lakes and reservoirs represent a major risk for water authorities globally due to their toxicity and economic impacts. Anticipating bloom occurrence and understanding the main drivers of CyanoHABs are needed to optimize water resources management. An extensive review of the application of CyanoHABs forecasting and predictive models was performed, and a summary of the current state of knowledge, limitations and research opportunities on this topic is provided through analysis of case studies. Two modelling approaches were used to achieve CyanoHABs anticipation; process-based (PB) and data-driven (DD) models. The objective of the model was a determining factor for the choice of modelling approach. PB models were more frequently used to predict future scenarios whereas DD models were employed for short-term forecasts. Each modelling approach presented multiple variations that may be applied for more specific, targeted purposes. Most models reviewed were site-specific. The monitoring methodologies, including data frequency, uncertainty and precision, were identified as a major limitation to improve model performance. A lack of standardization of both model output and performance metrics was observed. CyanoHAB modelling is an interdisciplinary topic and communication between disciplines should be improved to facilitate model comparisons. These shortcomings can hinder the adoption of modelling tools by practitioners. We suggest that water managers should focus on generalising models for lakes with similar characteristics and where possible use high frequency monitoring for model development and validation.

Cyanobacteria in inland waters: new monitoring, reporting, modelling and ecological research

 

Authors

Simon M. Mitrovic, Tsuyoshi Kobayashi and Daniel L. Roelke

Cyanobacteria in freshwater environments are a natural part of the phytoplankton community but can cause human health and ecosystem issues through the production of toxins (Paerl et al. 2001). The toxins produced by cyanobacteria (cyanotoxins) are
varied, and include hepatotoxins, neurotoxins, cytotoxins and skin irritants (Bartram and Chorus 1999; Wiegand and Pflugmacher 2005). Cyanotoxins can have adverse effects on human health, particularly by exposure through drinking water (Carmichael et al. 2001) or recreation (such as swimming; Pilotto et al. 1997). Cyanotoxins are also known to affect livestock and native animals drinking contaminated water (Stewart et al. 2008) and aquatic organisms such as fish (Drobac et al. 2016), zooplankton (Bownik 2016) and aquatic macrophytes (Mitrovic et al. 2004, 2005). The risks from cyanotoxins increase with the density of cyanobacterial blooms, so understanding the drivers of cyanobacterial growth and dominance, as well as the risks of cyanotoxins, is important for management. Cyanobacterial blooms are anticipated to expand and change their distribution, frequency and intensity in inland waters with increasing global warming and climate change (Paerl and Huisman 2009). This is concerning due to the potential impact of blooms in new locations and increased bloom intensity in previously affected areas. This special issue of the Journal brings together papers that use new and diverse scientific tools available for monitoring, reporting and modelling cyanobacterial growth, as well as ecological research on cyanobacteria and their toxins that can help expand our research and management capabilities. These approaches to the monitoring of cyanobacteria within waterways may give further insights into risks and management approaches.

Quantifying the dependence of cyanobacterial growth to nutrient for the eutrophication management of temperate-subtropical shallow lakes

Authors

Wei Zou, Guangwei Zhu, Yongjiu Cai, Hai Xu, Mengyuan Zhu, Zhijun Gong, Yunlin Zhang, Boqiang Qin

The increasing global occurrence of cyanobacterial blooms, attributed primarily to human-induced nutrient enrichment, significantly degrades freshwater ecosystems and poses serious risks to human health. The current study examined environmental variables and cyanobacterial biovolume (B_Cyano) of 28 shallow lakes in the eastern China plains during the spring and summer of 2018. We used a 95% quantile regression model to explore season-specific response of B_Cyano to total nitrogen (TN), or total phosphorus (TP), and robust linear relationships were observed between log(B_Cyano+0.001) and log(TN), or log(TP) in both spring and summer periods. Based on these regressions, regional-scale and season-specific TN and TP thresholds are proposed for these lakes to ensure the safety for recreational waters and drinking water source. However, actual B_Cyano for a given concentration of TN (or TP) for many observations were considerably lower than the results of the 95% regression model predict, indicating that other factors significantly modulated nutrient limitation of B_Cyano. Generalized additive model and quantile regression model were used together to explore potentially significant modulating factors, of which lake retention time, macrophytes cover and N: P ratio were identified as most important. Thus, it is necessary to develop type-specific nutrient thresholds with the consideration of these significant modulating factors. Furthermore, nutrient-B_Cyano relationships of our studied lakes with lake retention time>100 days and no macrophyte were further explored and nutrient thresholds of this lake type were proposed. Nutrient thresholds proposed in this study may play an essential role in achieving a cost-effective eutrophication management for shallow lakes both in the eastern China plains and elsewhere with similar climatic background. On a broader scale, the approaches and findings of this study may provide valuable reference to formulate reasonable nutrient reduction targets for other ecoregions with different climatic conditions.

Mitigating eutrophication and toxic cyanobacterial blooms in large lakes: The evolution of a dual nutrient (N and P) reduction paradigm

Authors

Hans W. Paerl, Karl E. Havens, Hai Xu, Guangwei Zhu, Mark J. McCarthy, Silvia E. Newell, J. Thad Scott, Nathan S. Hall, Timothy G. Otten, Boqiang Qin

Cyanobacterial harmful algal blooms (CyanoHABs) are an increasingly common feature of large, eutrophic lakes. Non-N₂-fixing CyanoHABs (e.g., Microcystis) appear to be proliferating relative to N₂-fixing CyanoHABs in systems receiving increasing nutrient loads. This shift reflects increasing external nitrogen (N) inputs, and a > 50-year legacy of excessive phosphorus (P) and N loading. Phosphorus is effectively retained in legacy-impacted systems, while N may be retained or lost to the atmosphere in gaseous forms (e.g., N₂, NH₃, N₂O). Biological control on N inputs versus outputs, or the balance between N₂ fixation versus denitrification, favors the latter, especially in lakes undergoing accelerating eutrophication, although denitrification removal efficiency is inhibited by increasing external N loads. Phytoplankton in eutrophic lakes have become more responsive to N inputs relative to P, despite sustained increases in N loading. From a nutrient management perspective, this suggests a need to change the freshwater nutrient limitation and input reduction paradigms; a shift from an exclusive focus on P limitation to a dual N and P co-limitation and management strategy. The recent proliferation of toxic non-N₂-fixing CyanoHABs, and ever-increasing N and P legacy stores, argues for such a strategy if we are to mitigate eutrophication and CyanoHAB expansion globally.

Review: Toward management of urban ponds for freshwater biodiversity

Authors

Beat Oertli, Kirsten M. Parris

Many cities around the world are expanding and this trend in urbanization is expected to sharply increase over coming decades. At the same time, the integration of green and blue spaces is widely promoted in urban development, potentially offering numerous benefits for biodiversity. This is particularly relevant for urban waterbodies, a type of ecosystem present in most cities. However, site managers often lack the knowledge base to promote biodiversity in these waterbodies, which are generally created to provide other ecosystem services. To address this, our review presents guidelines for promoting biodiversity in urban ponds. We found a total of 516 publications indexed in ISI Web of Sciences related to this topic, of which 279 were retained for the purposes of our review. The biodiversity of urban ponds, measured by species richness, appears to be generally lower than in rural ponds; however, urban ponds often support threatened species. Furthermore, if well managed, urban ponds have the potential to support a much greater biodiversity than they currently do. Indeed, this review shows that a range of urban factors can impair or promote pond biodiversity, including many that can easily be controlled by site managers. Local factors include design (surface area, pond depth, banks and margins, shade, shoreline irregularity), water quality (conductivity, nutrients, heavy metals), and hydroperiod and biotic characteristics (stands of vegetation, fish, invasive species). Important regional factors include several indicators of urbanization (roads, buildings, density of population, impervious surfaces, car traffic), and the presence of other wetlands or green spaces in the surrounding landscape. We considered each of these factors and their potential impact on freshwater biodiversity. Taking into account the management measures listed in the publications reviewed, we have proposed a framework for the management of urban ponds, with guidelines to promote biodiversity and other ecosystem services, and to avoid ecosystem disservices or the creation of ecological traps. At the city scale, the biodiversity of a pondscape benefits from a high diversity of pond types, differing in their environmental characteristics and management.

Do benthic algae provide important information over and above that provided by macrophytes and phytoplankton in lake status assessment? – Results from a case study in Norway

Authors

Susanne C. Schneider, Dag Hjermann, Hanne Edvardsen

To test if phytobenthic algae provide additional important information to macrophytes and phytoplankton for lake monitoring, we sampled two large lakes in Norway. In each lake, we analyzed water chemistry and phytoplankton above the deepest site, recorded macrophytes and non-diatom phytobenthic algae at 20 sites around the shoreline and estimated site-specific nutrient input from land cover. Since no ready-to-use phytobenthos index exists for lakes in Norway, we tested the PIT index developed for rivers, commonly perceived signs of disturbance such as high algal cover, and taxon richness as well as similarity patterns. Both lakes were nutrient poor, but had potential local nutrient inputs (villages, agriculture). In neither of the lakes did phytobenthos indicate a worse overall ecological status than macrophytes and phytoplankton. Our data therefore, did not suggest that it would be useful to add phytobenthos into surveillance monitoring of lakes in Norway. There was a loose correlation between macrophyte and phytobenthic site-specific taxon richness and similarities. This means that macrophytes and phytobenthos do indeed give partly redundant information. High algal cover was found at sites with both high and low phosphorus input. Using algal cover as indicator of site-specific nutrient input is therefore overly simplistic. Urban and cultivated areas were associated with a more eutrophic PIT. This indicates that the PIT, despite being developed for lotic waters, may be used to detect site specific nutrient input in lakes.

Assessment of large-scale patterns of hydrological alteration caused by dams

Authors

Francisco J. Peñas, José Barquín

Nowadays, alteration of the natural flow regime is considered one the most widespread and damaging impacts for river ecosystems. Hence, increasing our understanding of large-scale hydrological alteration patterns would help us design more effective water use policies. The present study aims to establish general patterns of hydrological alteration caused by dams on a national level, with Spain as a case study. First, we developed a classification of the natural flow regime of the Spanish river network, which served as the reference to assess the degree of hydrological alteration of 139 altered-river gauges. In addition, using the flow series of the altered-river gauges we defined a set of 7 types of altered regimes (TARs), which allowed the stratification of the analyses. The results revealed that the magnitude and direction of hydrological alteration depended on the natural flow class of the altered rivers. In this regard, major effects of dams on Spanish rivers were related to the modification of the intra-annual variability of daily flow, the magnitude of seasonal maximum and minimum flows and the patterns of high flow events. Our results also showed that the distribution of the TARs partially followed a geographic order, but associations between TARs and natural flow classes were not straightforward. In addition, we highlighted that the nature of the hydrological alteration was independent of the registered dam uses.

Incorporating reservoir impacts into flood frequency distribution functions

Authors

Shida Gao, Pan Liu, Zhengke Pan, Bo Ming, Shenglian Guo, Lei Cheng, Jinxing Wang

Assessing flood frequency is pivotal for hydrology, with implications for many fields ranging from river science to the insurance industry. Reservoir regulation may alter the characteristics of the flood frequency distribution function. This paper incorporates reservoir impacts as an inherent variable to derive an analytical solution of outflow peaks and proposes new flood frequency distributions. Steps are as follows: (1) the original flood without reservoir impacts is assumed to follow a Pearson type III distribution, (2) linear and nonlinear reservoir models, including numerical integration and triangular area calculation methods, are proposed to simulate the relationships between inflow and outflow peaks, and (3) the flood frequency distributions resulting from reservoir impacts are derived. Derived equations are applied to the Shuibuya and Wuqiangxi reservoirs in China. Results show that: (1) although the numerical integration method with the nonlinear model is comparable with the reservoir flood routing, the triangle area calculation method with the nonlinear model is recommended for its accuracy and simplicity, (2) the reservoir regulation changes the flood frequency distribution function entirely in the nonlinear reservoir model, while only change the parameter in the linear reservoir model, and (3) downstream flood’s CV can be increased or decreased, which depends on the reservoir regulating capacity. It is indicated that altering the parameters of the flood frequency distribution is not sufficient to characterize watershed under reservoir control. This paper proposes the analytical solution about inflow and outflow peaks, which can point out the possible changes in the watershed with reservoir construction in plan.

Enhanced real-time cyanobacterial fluorescence monitoring through chlorophyll-a interference compensation corrections

 

Authors

F. Choo, A. Zamyadi, R. M. Stuetz, G. Newcombe, K. Newton, R. K. Henderson

In situ fluorometers can be used as a real-time cyanobacteria detection tool to maintain safe drinking and recreational water standards. However, previous studies into fluorometers have established issues arising mainly from measurement inaccuracies due to green algae interference. Therefore, this study focusses on developing correction factors from a systematic study on the impact of green algae as an interference source. This study brings a novel technique where the chlorophyll-a (Chl-a) and phycocyanin measurements are used to correct the fluorometer output for interference bias; four fluorometers were tested against three key cyanobacterial species and the relationship between phycocyanin output, green algae and cyanobacteria concentrations were investigated. Good correlation (R² > 0.9, p-value < 0.05) was found between the fluorometer phycocyanin output and increasing green algae concentration. The optimal correction method was selected for each of the fluorometer and cyanobacteria species pairs by validating against data from the investigation of green algae as an interference source. The correction factors determined in this study reduced the measurement error for almost all the fluorometers and species tested by 21%–99% depending on the species and fluorometer, compared to previous published correction factors in which the measurement error was reduced by approximately 11%–81%. Field validation of the correction factors showed reduction in fluorometer measurement error at sites in which cyanobacterial blooms were dominated by a single species.

Multivariate design of socioeconomic drought and impact of water reservoirs

Authors

Xinjun Tu, Haiou Wu, Vijay P. Singh, Xiaohong Chen, Kairong Lin, Yuting Xie

Socioeconomic drought in association with minimum instream flow against the backdrop of local water supply was investigated. An integrated procedure for design combinations of drought properties, such as duration, severity, and peak, involving the truncation of drought events, the goodness-of-fit of joint and marginal distributions of drought properties, the determination of design combinations of these properties for a given Kendall return period, and the evaluation of uncertainty of the combinations, was developed. In multivariate design of socioeconomic droughts in a case study, univariate, bivariate and trivariate design values of drought properties and their alterations due to the regulation of water reservoirs were computed. Results showed that any two properties of drought exhibited a high positive dependence. For a given bivariate return period, the pairs of cumulative frequencies of drought properties formed a symmetric curve for truncated samples and a symmetric curving-belt for large quantities of simulated samples. For a given trivariate return period, the pairs of cumulative frequencies of duration and peak showed a symmetry, but the pairs of duration and severity or severity and peak were remarkably scattered on the side of severity and comparatively concentrated on the side of duration or peak. For the confidence interval of probability of 0.95, the range of trivariate design values was larger than that of bivariate design. The differences between drought design values of univariate, bivariate, and trivariate designs were small, which resulted from high correlations of drought properties, the use of Kendall frequency, and approximate identical cumulative frequencies in design combinations. The decrease of socioeconomic drought properties under the regulation of water reservoirs was significant, but the drought spell, total volume, and monthly maximum of water deficit for a 5-year return period still accounted for 3.06–3.27 months, 0.426–0.470 billion m³, and 0.211–0.217 billion m³, respectively, provided that the local water supply was met.