Freshwater Reservoir Research Articles

IMPACT OF SALINITY INTRUSION ON HEALTH OF COASTAL PEOPLE: REFLECTIONS FROM DACOPE UPAZILA OF KHULNA DISTRICT, BANGLADESH

Increasing salinity in ground water, arable lands and many rivers of the southwest coastal area are important consequences of sea level rise as well as climate change. The scarcity of fresh drinking water was the very initial impact of salinity intrusion that possessed multidimensional threats on human existence. Thus, the current study is designed to know the potential problems caused by salinity intrusion and the protective measures and coping mechanisms adopted by coastal people for salinity. To meet the objectives, two southwest coastal villages Joynagar and Parjoynagar of Kamarkhola union at Dacope upazila in Khulna district of Bangladesh were selected purposively as over past few decades along with other southwest coastal areas these two villages were suffering from increasing salinity intrusion. A collection of qualitative techniques including case study, FGDs and KIIs were adopted to gather vivid data. The results of the study found that apart from physical and psychological health salinity intrusion also possessed adverse impact on social health. The very common physical problems include acidity, stomach problem, several skin diseases and psychological problems include hypertension. Besides, there happened social health problem because of the physical and psychological problem. For example, early marriage happened because salinity gradually changed the skin color from light to gray. However, the findings also presented that all preventive measures of community and authority were taken only for securing fresh drinking water instead of taking preventive measures for purifying washing and cooking water that led to several diseases and problems. In conclusion, it can be recommended that increasing freshwater reservoirs can be a suitable solution for salinity intrusion of the coastal areas.

Evolution of Ramasetu region as a link between India and Sri Lanka during the late Pleistocene and Holocene

AbstractHigh-resolution seismic data of the Ramasetu region revealed three subaerial unconformities S1, S2, and S3. S1 is the youngest subaerial unconformity, whereas S3 is the oldest. These subaerial unconformities have been determined based on the presence of channel-incision signatures. Identified buried channels originated in the Palk Strait and debouched in the Gulf of Mannar. Youngest buried channels became most active during MIS 3 (~60–29 ka) and were buried entirely at ~7.0 ka. The study suggests that the Palk Strait evolved as a large multi-centered freshwater reservoir during the last glacial period and remained a freshwater reservoir until seawater started encroaching the region at ~8.5 ka. The Ramasetu region was a potential habitat zone for foragers, with fresh and saline water ecosystems available at opposite banks. During the Microlithic and terminal Pleistocene, Homo sapiens needed to cross high-energy rivers using floaters/rafts in wet seasons of MIS 2 and 3. At the same time, they used a direct walkable land link in the extreme dry season of MIS 2. During the early to mid-Holocene, foragers required floaters/rafts or artificial structures (such as bandh/bridge) to cross shallow, low-energy estuarine patches of the Ramasetu. The Palk Strait region was not crossable without using boats/ships in the last ~7 ka except during minor sea-level falls.

Groundwater conditions the effectiveness of surface water diversion in the remediation of the eutrophicated volcanic lake of Furnas, Azores archipelago.

Volcanic lakes in oceanic islands represent extremely important areas for biodiversity and offer exceptional conditions for nature-based tourism as one of the main pillars of economic growth in these regions. Nitrogen and phosphorus fertilizers are being used extensively at the Azores archipelago, similarly to other places in the world, to increase agricultural production and is causing severe pollution and eutrophication of surface freshwater reservoirs. This work concentrates on the evaluation of the efficiency of surface water diversion as a remediation measure to reduce nutrient loading and reverse eutrophication of Furnas crater lake on the island of São Miguel. Nutrient loading was monitored using an extensive water quality monitoring program in the main watershed of the eutrophicated lake that, together with watershed-scale mass balance methods and groundwater and solute transport models, allowed us to identify an average 98% efficiency in the reduction of nitrate loading. However, phosphorus total load in the discharged water to Furnas lake was observed to only be decreased by 33% due to the groundwater origin of phosphorus. Results from modelling suggested that nutrients were emitted from both point (nitrates) and diffuse (phosphorus) sources as surface runoff and as groundwater seepage, respectively. The results obtained recognized a partially successful surface water diversion, since groundwater path was not initially identified, thus highlighting the importance of groundwater flow regime in the design of such remediation measures. This work also provides a perspective on surface water diversion to revert eutrophication under a volcanic formation, where lakes can be naturally more nutrient rich.

Genome sequence of freshwater nontoxigenic Limnoraphis associated with microcystin-producing blooms.

A sample from a 2019 cyanobacterial bloom in a freshwater reservoir in eastern Oregon, USA, was used to produce a metagenome from which the complete, circular 7.3 Mbp genome of Limnoraphis sp. WC205 was assembled. The Limnoraphis sp. WC205 genome contains gas vesicle genes, genes for N2-fixation and genes for both phycocyanin- and phycoerythrin-containing phycobilisomes. Limnoraphis was present in Willow Creek Reservoir throughout the summer and fall, coexisting with various other cyanobacteria in blooms that were associated with microcystin. The absence of cyanotoxin genes from the Limnoraphis sp. WC205 genome showed this cyanobacterium to be non-toxigenic, although it is predicted to produce cyanobactins closely related to Microcystis aeruginosa microcyclamides. DNA sequence corresponding to the Microcystis mcyG gene identified Microcystis as the microcystin producer in this lake.

Characterization of Bacterial Communities from the Surface and Adjacent Bottom Layers of Water in the Billings Reservoir.

Here, we describe the bacterial diversity and physicochemical properties in freshwater samples from the surface and bottom layers of the Billings Reservoir, the largest open-air storage ecosystem in the São Paulo (Brazil) metropolitan area. Forty-four samples (22 from the surface and 22 from the bottom layers) were characterized based on 16S rRNA gene analysis using Illumina MiSeq. Taxonomical composition revealed an abundance of the Cyanobacteria phylum, followed by Proteobacteria, which were grouped into 1903 and 2689 different genera in the surface and the deep-water layers, respectively. Chroobacteria, Actinobacteria, Betaproteobacteria, and Alphaproteobacteria were the most dominant classes. The Shannon diversity index was in the range of 2.3–5.39 and 4.04–6.86 in the surface and bottom layers, respectively. Flavobacterium was the most predominant pathogenic genus. Temperature and phosphorus concentrations were among the most influential factors in shaping the microbial communities of both layers. Predictive functional analysis suggests that the reservoir is enriched in motility genes involved in flagellar assembly. The overall results provide new information on the diversity composition, ecological function, and health risks of the bacterial community detected in the Billings freshwater reservoir. The broad bacterial diversity indicates that the bacterioplankton communities in the reservoir were involved in multiple essential environmental processes.

Sapropel as a source of nutrients in feeding of cattle

Modern agriculture needs new highly effi cient feed and feed additives. Sapropel is a type of finegrained and loose sediments rich in organic matter. The properties of sapropel and the sufficiently wide possibilities of its extraction make it an important natural resource that can be used mainly in agriculture. Sapropel and its processed products are environmentally safe, non-toxic, with a certain content of nutrients. Another important reason for studying sapropel is its widespread distribution and availability in freshwater reservoirs, which leads to the discovery of new ways of extraction and bioeconomically efficient use of this most valuable natural resource, available in economically significant amount with high opportunities for its use in animal husbandry. The purpose of the work was to analyze the use of sapropel as a source of nutrients in cattle feeding. In order to study the influence of sapropel on dairy productivity of cows, a scientifi c and economic experiment was carried out under the conditions of an educational and experimental farm of the Federal State Budgetary Educational Institution of Higher Education “Northern Trans-Ural State Agricultural University”. It was found as a result of the experiment that when using sapropel at the doses of 250 and 500 g/head/day, there was an increase in dairy productivity of cows. Thus, milk yield during the experiment period in the 1st experimental group increased by 1,48 % compared to the control group, and in the 2nd experimental group by 7,2 %, milk quality indicators also improved. Sapropel did not have a negative influence on the health of animals, which was confirmed by hematological indicators. Therefore, the use of sapropel in cattle feeding is effective.

Regional factors as major drivers for microbial community turnover in tropical cascading reservoirs.

The turnover of microbial communities across space is dictated by local and regional factors. Locally, selection shapes community assembly through biological interactions between organisms and the environment, while regional factors influence microbial dispersion patterns. Methods used to disentangle the effects of local and regional factors typically do not aim to identify ecological processes underlying the turnover. In this paper, we identified and quantified these processes for three operational microbial subcommunities (cyanobacteria, particle-attached, and free-living bacteria) from a tropical cascade of freshwater reservoirs with decreasing productivity, over two markedly different dry and rainy seasons. We hypothesized that during the dry season communities would mainly be controlled by selection shaped by the higher environmental heterogeneity that results from low hydrological flow and connectivity between reservoirs. We expected highly similar communities shaped by dispersal and a more homogenized environment during the rainy season, enhanced by increased flow rates. Even if metacommunities were largely controlled by regional events in both periods, the selection had more influence on free-living communities during the dry period, possibly related to elevated dissolved organic carbon concentration, while drift as a purely stochastic factor, had more influence on cyanobacterial communities. Each subcommunity had distinct patterns of turnover along the cascade related to diversity (Cyanobacteria), lifestyle and size (Free-living), and spatial dynamics (particle-attached).

Hydrological influence on the variation of the terrestrial gravity field in Manaus, Amazonas, Brazil

The influence of groundwater on the hydrological cycle has been studied at large-scale across the Amazon Basin, one of the largest freshwater reservoirs in the world. Considering this Basin's importance in the global hydrological cycle, local studies also are critical. Here, we focus on the local hydrological cycle in Manaus, at the center of the Amazon Basin. We observed the variability of local gravity, fluvial height, soil moisture, precipitation, evapotranspiration and groundwater in the rainy (December–May) and dry (June–November) seasons, during drought (2016) and flood (2017) years. In general, in the beginning of the rainy season, soil moisture is instantaneously influenced by the first precipitation, increasing gravity. After, the soil becomes saturated and the variation in soil moisture achieves maximum values, which are sustained until the end of rainy season. After soil saturation by infiltration, the groundwater starts to be fed by percolation and the water table starts to rise. Thus, variation in local gravity reflects mainly variations in groundwater level. After the dry season starts, the soil loses moisture (soil moisture values decrease), while the gravity signal maintains high values, representing the sustained behavior of the groundwater. Modeling the vertical gravity component influenced by soil moisture and by groundwater results, respectively, in 49.63 nm/s2 and 314.70 nm/s2. In comparison with the gravity measurement of 368.02 nm/s2, we confirm that the groundwater is the main contributor to the gravity signal. We also find a strong correlation between fluvial height and the gravity signal, but demonstrate with 3D modeling that the Negro River height variation does not directly influence the gravity signal. Instead, we explain the similarity in fluvial height and the gravity signal by the connection between fluvial height and groundwater, and the correlation between groundwater and gravity variations.

Mainland-coastal interactions in East Borneo: Inter-site comparison and Bayesian chronological models of two Late Pleistocene–Holocene sequences (Liang Abu and Kimanis rock shelters)

In recent decades, East Borneo has become an increasingly important archaeological “hot-spot” in Island Southeast Asia as a result of early dates for rock art ca. 38,000 BP and the greater number of excavated sites that support a much longer period of human occupation. However, the chronology of settlement and adaptation to environmental changes during the Pleistocene–Holocene transition is still poorly known. Here we report on an excavation at the Liang Abu rock shelter which has contexts dating from the Late Pleistocene (12,660 ± 58 uncal. BP) to the present day, indicating a terminus ante quem (TAQ) for human occupation at 23,790 BP. We present the results of an attempt to systematically integrate and compare data from Liang Abu and Kimanis, a geographically close site with a previously published sequence. Particular attention is paid to post-depositional issues in tropical settings and to data compatibility, reuse, and reproducibility, relying on open-source software for data processing (R scripts) and Bayesian chronological modeling. Two Bayesian models are built and compared using the ChronoModel software, which can handle outliers and uncertainty (e.g., freshwater reservoir effect). This first inter-site comparison for Borneo results in a new chronology of human settlement and mainland–coastal interactions in East Borneo and paves the way for future regional synthesis.

Chlorophyll soft-sensor based on machine learning models for algal bloom predictions

Harmful algal blooms (HABs) are a growing concern to public health and aquatic ecosystems. Long-term water monitoring conducted by hand poses several limitations to the proper implementation of water safety plans. This work combines automatic high-frequency monitoring (AFHM) systems with machine learning (ML) techniques to build a data-driven chlorophyll-a (Chl-a) soft-sensor. Massive data for water temperature, pH, electrical conductivity (EC) and system battery were taken for three years at intervals of 15 min from two different areas of As Conchas freshwater reservoir (NW Spain). We designed a set of soft-sensors based on compact and energy efficient ML algorithms to infer Chl-a fluorescence by using low-cost input variables and to be deployed on buoys with limited battery and hardware resources. Input and output aggregations were applied in ML models to increase their inference performance. A component capable of triggering a 10 upmug/L Chl-a alert was also developed. The results showed that Chl-a soft-sensors could be a rapid and inexpensive tool to support manual sampling in water bodies at risk.

Variability of Biological Features of a Mugilidae Chelon Ramada in Two Tunisian Reservoirs

Mullet is the most massively harvested species, representing the third of the total freshwater fish landing in Tunisia. To ensure freshwater fish farming durability and development in the country, reservoirs have been stocked with Mugilidae fry which was collected from coastal and estuaries areas after a short adaptation period. The objective of this paper is to compare and contrast Chelon ramada’’s age, growth, and mortality in two Tunisian freshwater reservoirs (Seliana and Kasseb). The sample species were caught with a multi-mesh gillnets and were classified into five age groups. The study of the age and growth demonstrated variability between Chelon ramada species’ features. The optimal size of the captured mullet (Lopt) was equal to 37.62 cm for M=0.48, L∞=57.05 and K=0.31 in Siliana Reservoir. Whereas, it measured 31.42cm in Kasseb Reservoir, for M=0.795, L∞=48.15 and K=0.31. It has also been found that the fishing mortality rate is very high at Siliana Reservoir when compared to Kasseb Reservoir. This work is a contribution to the identification of the biological features of Chelon ramada that lives in Siliana and Kasseb Reservoirs. It seeks to ensure a rational and sustainable exploitation of fishery resources in these Tunisian freshwater reservoirs and it recommends the development and preservation of mullet fisheries.

Integrative monitoring strategy for marine and freshwater harmful algal blooms and toxins across the freshwater-to-marine continuum.

Many coastal states throughout the USA have observed negative effects in marine and estuarine environments caused by cyanotoxins produced in inland waterbodies that were transported downstream or produced in the estuaries. Estuaries and other downstream receiving waters now face the dual risk of impacts from harmful algal blooms (HABs) that occur in the coastal ocean as well as those originating in inland watersheds. Despite this risk, most HAB monitoring efforts do not account for hydrological connections in their monitoring strategies and designs. Monitoring efforts in California have revealed the persistent detection of cyanotoxins across the freshwater-to-marine continuum. These studies underscore the importance of inland waters as conduits for the transfer of cyanotoxins to the marine environment and highlight the importance of approaches that can monitor across hydrologically connected waterbodies. A HAB monitoring strategy is presented for the freshwater-to-marine continuum to inform HAB management and mitigation efforts and address the physical and hydrologic challenges encountered when monitoring in these systems. Three main recommendations are presented based on published studies, new datasets, and existing monitoring programs. First, HAB monitoring would benefit from coordinated and cohesive efforts across hydrologically interconnected waterbodies and across organizational and political boundaries and jurisdictions. Second, a combination of sampling modalities would provide the most effective monitoring for HAB toxin dynamics and transport across hydrologically connected waterbodies, from headwater sources to downstream receiving waterbodies. Third, routine monitoring is needed for toxin mixtures at the land-sea interface including algal toxins of marine origins as well as cyanotoxins that are sourced from inland freshwater or produced in estuaries. Case studies from California are presented to illustrate the implementation of these recommendations, but these recommendations can also be applied to inland states or regions where the downstream receiving waterbody is a freshwater lake, reservoir, or river. Integr Environ Assess Manag 2023;19:586-604. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Effects of Typhoon on Saltwater Intrusion in a High Discharge Estuary

AbstractSaltwater intrusion in the Changjiang Estuary occurs in winter and dry season, which may affect drinking water supply in Shanghai. An atypical saltwater intrusion event, observed under high river discharge (>20,000 m3/s) in October 2018, coincided with the passage of super typhoon Kong‐rey. The response of the estuarine salt field is reproduced here with a numerical model for analysis with a Eulerian framework. Model results show that saltwater intrusion was mainly due to the landward advection of salt (∼260 t/s), which was driven by the storm surge (∼0.4 m) and landward Ekman transport under typhoon winds. The sheared salt flux (∼145 t/s) significantly contributes to the total landward flux, especially when the surge recedes after the typhoon has passed. Northwesterly winds increased vertical shear and stratification during the event. The maximum saltwater intrusion occurred about a day after the typhoon passage, and the salinity at the freshwater reservoir intake exceeds the local drinking standard of 0.45 psu. A numerical experiment shows that if Kong‐rey had passed during spring tide, the saltwater intrusion would have been weaker due to a stronger northward transport near the coast and a landward transport in the southern channels.

Depth Profiles of Dissolved Oxygen (DO) and Hydrogen Sulfide (H2S) Concentration in a Tropical Freshwater Reservoir

This study aims to determine the profile of dissolved oxygen and H2S based on depth in the Jatiluhur Reservoir related to fish culture in floating net cages. The scope of this research is focused on the location of floating net cage cultivation. Dissolved oxygen distribution is classified as a positive heterograde type where dissolved oxygen levels higher in the metalimnion layer due to the photosynthesis process that occurs effectively by aquatic plants and phytoplankton. Jatiluhur Reservoir shows signs of organic pollution, with BOD5 and COD levels exceeding the quality standard. This organic substance comes from the waste of floating net cages. BOD5 and COD values that exceed the quality standard result in increased oxygen consumption during the decomposition process; therefore, a hypoxic layer occurs. This occurrence can cause water conditions to become anoxic, producing H2S gas. The H2S value in the Jatiluhur Reservoir was observed to exceed 0.002 mg/L and showed an increase in the metalimnion layer.

Pseudomonas boanensis sp. nov., a bacterium isolated from river water used for household purposes in Boane District, Mozambique

A Gram-negative rod with a single polar flagellum was isolated from a freshwater reservoir used for household purposes in Boane District, near Maputo, Mozambique, and designated as strain DB1T. Growth was observed at 30-42 °C (optimum, 30-37 °C) and with 0.5-1.5 % NaCl. Whole-genome-, rpoD- and 16S rRNA-based phylogenies revealed this isolate to be distant from other Pseudomonas species with Pseudomonas resinovorans, Pseudomonas furukawaii and Pseudomonas lalkuanensis being the closest relatives. Phenotypic analyses of strain DB1T showed marked differences with respect to type strains P. resinovorans CCUG 2473T, P. lalkuanensis CCUG 73691T, P. furukawaii CCUG 75672T and Pseudomonas otiditis CCUG 55592T. Taken together, our results indicate that strain DB1T is a representative of a novel species within the genus Pseudomonas for which the name Pseudomonas boanensis is proposed. The type strain is DB1T (=CCUG 62977T=CECT 30359T).

Lacustrine diatom oxygen isotopes as palaeo precipitation proxy - Holocene environmental and snowmelt variations recorded at Lake Bolshoye Shchuchye, Polar Urals, Russia

The diatom oxygen isotope composition (δ18Odiatom) from lacustrine sediments helps tracing the hydrological and climate dynamics in individual lake catchments, and is generally linked to changes in temperature and δ18Olake. Lake Bolshoye Shchuchye (67°53′N; 66°19′ E; 186 m a.s.l) is the largest and deepest freshwater reservoir in the Polar Urals, Arctic Russia. The diatom oxygen isotope interpretation is supported by modern (isotope) hydrology, local bioindicators such as chironomids, isotope mass-balance modelling and a digital elevation model of the catchment.The Bolshoye Shchuchye δ18Odiatom record generally follows a decrease in summer insolation and the northern hemisphere (NH) temperature history. However, it displays exceptional, short-term variations exceeding 5‰, especially in Mid and Late Holocene. This centennial-scale variability occurs roughly contemporaneously with and similar in frequency to Holocene NH glacier advances. However, larger Holocene glacier advances in the Lake Bolshoye Shchuchye catchment are unknown and have not left any significant imprint on the lake sediment record. As Lake Bolshoye Shchuchye is deep and voluminous, about 30–50% of its volume needs to be exchanged with isotopically different water within decades to account for these shifts in the δ18Odiatom record. A plausible source of water with light isotope composition inflow is snow, known to be transported in surplus by snow redistribution from the windward to the leeward side of the Polar Urals. Here, we propose snow melt variability and associated influx changes being the dominant mechanism responsible for the observed short-term changes in the δ18Odiatom record. This is the first time such drastic, centennial-scale hydrological changes in a catchment have been identified in Holocene lacustrine diatom oxygen isotopes, which, for Lake Bolshoye Shchuchye, are interpreted as proxy for palaeo precipitation and, on millennial timescales, for summer temperatures.

Detecting, extracting, and mapping of inland surface water using Landsat 8 Operational Land Imager: A case study of Pune district, India.

Background: Recent developments in optical satellite remote sensing have led to a new era in the detection of surface water with its changing dynamics. This study presents the creation of surface water inventory for a part of Pune district (an administrative area), in India using the Landsat 8 Operational Land Imager (OLI) and a multi spectral water indices method. Methods: A total of 13 Landsat 8 OLI cloud free images were analyzed for surface water detection. Modified Normalized Difference Water Index (MNDWI) spectral index method was employed to enhance the water pixels in the image. Water and non-water areas in the map were discriminated using the threshold slicing method with a trial and error approach. The accuracy analysis based on kappa coefficient and percentage of the correctly classified pixels was presented by comparing MNDWI maps with corresponding Joint Research Centre (JRC) Global Surface Water Explorer (GSWE) images. The changes in the surface area of eight freshwater reservoirs within the study area (Bhama Askhed, Bhatghar, Chaskaman, Khadakwasala, Mulashi, Panshet, Shivrata, and Varasgaon) for the year 2016 were analyzed and compared to GSWE time series water databases for accuracy assessment. The annual water occurrence map with percentage water occurrence on a yearly basis was also prepared. Results: The kappa coefficient agreement between MNDWI images and GSWE images is in the range of 0.56 to 0.96 with an average agreement of 0.82 indicating a strong level of agreement. Conclusions: MNDWI is easy to implement and is a sufficiently accurate method to separate water bodies from satellite images. The accuracy of the result depends on the clarity of image and selection of an optimum threshold method. The resulting accuracy and performance of the proposed algorithm will improve with implementation of automatic threshold selection methods and comparative studies for other spectral indices methods.

Next-Generation High-Throughput Sequencing to Evaluate Bacterial Communities in Freshwater Ecosystem in Hydroelectric Reservoirs.

The quality of aquatic ecosystems is a major public health concern. The assessment and management of a freshwater system and the ecological monitoring of microorganisms that are present in it can provide indicators of the environment and water quality to protect human and animal health. with bacteria is. It is a major challenge to monitor the microbiological bacterial contamination status of surface water associated with anthropogenic activities within rivers and freshwater reservoirs. Understanding the composition of aquatic microbial communities can be beneficial for the early detection of pathogens, improving our knowledge of their ecological niches, and characterizing the assemblages of microbiota responsible for the degradation of contaminants and microbial substrates. The present study aimed to characterize the bacterial microbiota of water samples collected alongside the Madeira River and its small tributaries in rural areas near the Santo Antonio Energia hydroelectric power plant (SAE) reservoir in the municipality of Porto Velho, Rondonia state, Western Brazil. An Illumina 16s rRNA metagenomic approach was employed and the physicochemical characteristics of the water sample were assessed. We hypothesized that both water metagenomics and physicochemical parameters would vary across sampling sites. The most abundant genera found in the study were Acinetobacter, Deinococcus, and Pseudomonas. PERMANOVA and ANCOM analysis revealed that collection points sampled at the G4 location presented a significantly different microbiome compared to any other group, with the Chlamidomonadaceae family and Enhydrobacter genus being significantly more abundant. Our findings support the use of metagenomics to assess water quality standards for the protection of human and animal health in this microgeographic region.

Severe cyanobacterial blooms in an Australian lake; causes and factors controlling succession patterns

Cyanobacterial blooms have major impacts on the ecological integrity and anthropogenic value of freshwater systems. Chrysosporum ovalisporum, a potentially toxic cyanobacteria has been rare in Australian waters until recently when is has bloomed in a number of lake and river systems. The aim of this study was to determine drivers of its growth and growing dominance. We performed regular monitoring of Mannus Lake, a small freshwater reservoir in South-Eastern Australia that has recently undergone extremely dense bloom events. Blooms of the diazotrophic Chrysosporum ovalisporum occurred in both summers of the 19 month study during periods of persistent thermal stratification. Following the C. ovalisporum blooms, non-diazotrophic taxa (Microcystis aeruginosa and Woronichinia sp.) dominated the phytoplankton community under less stratified conditions. Thermal stratification and nitrogen availability appeared to be the primary drivers of changes in cyanobacterial community structure. We propose that the observed transition from C. ovalisporum to M. aeruginosa and/or Woronichinia sp. may be a result of nitrogen limitation in early summer, which combined with persistent thermal stratification led to an ecological advantage for the nitrogen-fixing C. ovalisporum. Mixing events caused the senescence of the C. ovalisporum bloom, likely supplementing the nutrient budget of the lake with atmospherically derived N and alleviating N limitation to non-diazotrophic taxa. Non-diazotrophic cyanobacterial growth then increased, albeit at much lower biovolumes compared to the initial bloom. Overall, the results demonstrate the role of thermal stratification and nutrient cycling in structuring the cyanobacterial community and provide insights into the environmental factors driving the proliferation of the relatively new, potentially toxic cyanobacterium C. ovalisporum in Australian waters.

What’s It Worth? Estimating the Potential Value of Early Warnings of Cyanobacterial Harmful Algal Blooms for Managing Freshwater Reservoirs in Kansas, United States

Cyanobacterial blooms are an issue drawing increasing concern in freshwater lakes and reservoirs in the United States due to the real and sometimes perceived harms they can cause through cyanotoxin production or other effects. These types of blooms are often referred to as cyanobacterial harmful algal blooms (cyanoHABs). Cyanotoxin exposure can potentially lead to human health effects through recreation and consumption of drinking water and may impact fisheries, wildlife, domestic pets, and livestock. Characterizing the societal impacts of cyanotoxin production, exposure, and effects and estimating the potential value of information of an early warning system can inform and support freshwater lake and reservoir management decisions and future research directions. A Bayesian decision tree analysis was utilized to identify uses, users, and benefits of the information provided by this research. Specifically, the potential value related to a cyanoHAB early warning system, based on potential toxicity, was analyzed that would provide information two additional days earlier relative to cyanoHAB toxicity. The evaluation considers the application of this information for freshwater lake management - whether or not to post an advisory or warning to avoid recreational water contact. The model was parameterized with data from the state of Kansas and the value of avoided foregone recreation and avoided health effects was derived. The estimated annual value of information ranges between $565 thousand to $2.3 million (2018 United States Dollars (USD)) for the state of Kansas alone based on provided assumptions. The results demonstrate a lower bound of the value of a cyanoHAB early warning system and suggest additional research to understand how the use and value of this information could support research prioritization and further illustrate the return on research investment. This analysis does not incorporate the full suite of potential societal costs that may be associated with a cyanoHAB event such as drinking water treatment, impacts to irrigation, or power generation.