Mapping cyanobacterial blooms in the Great Lakes using MODIS

Toxin-producing Cyanobacteria have been documented in Lake Erie and Ontario in the last several years. We developed algorithms to discriminate potentially toxic cyanobacterial blooms from other harmless phytoplankton blooms and to extract relative phycocyanin abundances from Moderate Resolution Imaging Spectrometer (MODIS) satellite data. Lee's quasi-analytical algorithm was used to calculate total absorption and backscatter from the 250 m, 500 m and 1 km bands of MODIS scenes. A non-negative least square algorithm was then utilized to discern relative concentrations of Chlorophyta (green algae), phycocyanin-rich Cyanobacteria (blue-green algae), and colored dissolved organic matter and suspended sediments combined in lake waters using published absorption spectra for these components. MODIS-derived cyanobacterial concentrations and/or bloom distributions from 10 scenes acquired in the summers of 2004 and 2005 were successfully verified against contemporaneous calibrated measurements of pigments that were acquired from measurements made using continuous fluorimetric measurements of surface water (1 m depth) from six cruises, and three additional cyanobacterial blooms reported in the scientific literature between 2002 and 2006. These results demonstrate that this methodology could be used to develop a cost-effective practical screening method for rapid detection and warning of potentially toxic cyanobacterial blooms in the lower Great Lakes.     

Status,causes and controls of cyanobacterial blooms in Lake Erie

The Laurentian Great Lakes are among the most prominent sources of fresh water in the world. Lake Erie's infamous cyanobacterial blooms have, however, threatened the health of this valuable freshwater resource for decades. Toxic blooms dominated by the cyanobacterium Microcystis aeruginosa have most recently been one of primary ecological concerns for the lake. These toxic blooms impact the availability of potable water, as well as public health and revenues from the tourism and fishery industries. The socioeconomic effects of these blooms have spurred research efforts to pinpoint factors that drive bloom events. Despite decades of research and mitigation efforts, these blooms have expanded both in size and duration in recent years. However, through continued joint efforts between the Canadian and United States governments, scientists, and environmental managers, identification of the factors that drive bloom events is within reach. This review provides a summary of historical and contemporary research efforts in the realm of Lake Erie's harmful cyanobacterial blooms, both in terms of experimental and management achievements and insufficiencies, as well as future directions on the horizon for the lake's research community.     

Agricultural conservation practices could help offset climate change impacts on cyanobacterial harmful algal blooms in Lake Erie

Harmful algal blooms (HABs) are a recurring problem in many temperate large lake and coastal marine ecosystems, caused mainly by anthropogenic eutrophication. Implementation of agricultural conservation practices (ACPs) offers a means to reduce non-point source nutrient runoff and mitigate HABs. However, the effectiveness of ACPs in a changing climate remains uncertain. We used an integrated biophysical modeling approach to predict how Lake Erie cyanobacterial HAB severity (bloom biomass) may change under several climate and ACP implementation scenarios, using western Lake Erie and its largely agricultural watershed as our study system. An ensemble of general circulation model projections was used to drive spatially explicit land use and hydrology models of the Maumee River watershed, the output of which informed a predictive model of Lake Erie HAB severity. Results show that, in the absence of changes in ACPs, the frequency of severe HABs is projected to increase during coming decades, owing to increased inputs of nutrients from the watershed. These anticipated increases are due to increased total precipitation and more frequent higher-magnitude rainfall events. While further implementation of ACPs appears capable of reducing severe HAB events, widespread implementation would be necessary to reduce HAB severity below current management targets. This study highlights how continued climate change will only exacerbate the need for land management practices that can reduce nutrient runoff in agriculturally dominated ecosystems, such as Lake Erie. It also shows how interdisciplinary, biophysical modeling approaches can help identify strategies to mitigate HABs in the face of anthropogenic stressors.     

Needed: Early-term adjustments for Lake Erie phosphorus target loads to address western basin cyanobacterial blooms

For Lake Erie, it is already time to revise the phosphorus target loads set to address the problem of cyanobacterial blooms in the Western Basin. Current targets were proposed by the Annex 4 task group in 2015, adopted by U.S. and Canadian governments in 2016, and set as objectives of domestic action plans in 2017. These targets, applicable to all spring discharges below the 90th percentile, set a maximum load for both total phosphorus (TP) and dissolved reactive phosphorus (DRP) equivalent to 60% of their 2008 spring loads. This essentially mandates 40% reductions in both particulate phosphorus (PP) and DRP loading relative to 2008 loads. These targets do not explicitly incorporate the difference in bioavailability between DRP (~100% bioavailable) and PP (~25% bioavailable). From 2008 to 2017, DRP comprised 24% of the spring TP load and over half (~56%) of the total bioavailable phosphorus (TBAP) load, while PP comprised 76% of the TP load but only ~44% of the TBAP load. Subsequent deposition of PP in the estuarine and nearshore zones further reduces its significance in bloom development. By ignoring differences in bioavailability, the current targets provide no guidance for choosing among practices based on their relative effectiveness in reducing DRP or PP and their combined reductions in TBAP loading. Current targets place more emphasis on PP than needed to efficiently reach targeted cyanobacterial bloom reductions. To clarify appropriate management approaches and lead to greater success in reducing cyanobacterial blooms, target loads should be based on TBAP.     

Spatial analysis of toxic or otherwise bioactive cyanobacterial peptides in Green Bay,Lake Michigan

Cyanobacterial harmful algal blooms (cyanoHABs) are a growing problem in freshwater systems worldwide. CyanoHABs are well documented in Green Bay, Lake Michigan but little is known about cyanoHAB toxicity. This study characterized the diversity and spatial distribution of toxic or otherwise bioactive cyanobacterial peptides (TBPs) in Green Bay. Samples were collected in 2014 and 2015 during three cruises at sites spanning the mouth of the Fox River north to Chambers Island. Nineteen TBPs were analyzed including 11?microcystin (MC) variants, nodularin, three anabaenopeptins, three cyanopeptolins and microginin-690. Of the 19 TBPs, 12 were detected in at least one sample, and 94% of samples had detectable TBPs. The most prevalent TBPs were MCRR and MCLR, present in 94% and 65% of samples. The mean concentration of all TBPs was highest in the Fox River and lower bay, however, the maximum concentration of all TBPs occurred in the same sample north of the lower bay. MCs were positively correlated with chlorophyll and negatively correlated with distance to the Fox River in all cruises along a well-established south-to-north trophic gradient in Green Bay. The mean concentration of MC in the lower bay across all cruises was 3.0?±?2.3?μg/L. Cyanopeptolins and anabaenopeptins did not trend with the south-north trophic gradient or varied by cruise suggesting their occurrence is driven by different environmental factors. Results from this study provide evidence that trends in TBP concentration differ by congener type over a trophic gradient.     

Models for identifying significant environmental factors associated with cyanobacterial bloom occurrence and for predicting cyanobacterial blooms

Compared with microscopic indices such as biomass, inverted satellite images can reflect cyanobacterial blooms from a macroscopic perspective, can provide planar information for blooms, and can more definitely reflect the occurrence of visible cyanobacterial blooms. We therefore adopted inverted images (from MODIS imagery) to judge whether cyanobacterial blooms had occurred in a water area at a given time. We constructed two probit models for identifying significant environmental factors related to cyanobacterial bloom occurrence and for short-term forecasts of bloom occurrence. The models used the index of cyanobacterial bloom occurrence as the dependent variable and the predicted variable, respectively, and used three categories (water quality, hydrology, and weather) of monitoring variables as the independent variables (or predictive variables). We used the Hill Dagong water area of Lake Tai in China as a case study of the new methods. The results produced by the identification model are consistent with the general conclusions in this research field indicating the validity of the model. The mean relative error of the forecast model is 13.5%, which is close to or lower than that of two previous models. Compared with the previous models, our forecast model also has advantages in terms of spatial and temporal precision. The new models have both practical applicability and the ability to be generalized and can, therefore, be easily adapted for the prevention, control, and prediction of cyanobacterial blooms in other bodies of water.     

HJ-1B和Landsat卫星蓝藻水华监测能力评估——以洱海为例

蓝藻水华是富营养化湖泊共同面临的问题。遥感技术为快速、大范围水华监测提供了可能,选取遥感数据应首先明确不同卫星的水华监测能力。以洱海为例,对比分析HJ-1B和Landsat卫星在内陆中小湖泊水华监测的时间和空间监测能力,评价两者在水华监测中的适用性及优势。结果表明:两者均能有效识别水华,提取水华分布细节信息,相比MODIS更适合用于中小湖泊水华监测;进一步分析表明,综合两者数据监测蓝藻水华,可以更加客观统计水华时间特征,描述水华空间分布发展规律,对于其它中小湖泊利用遥感手段辅助水华监测具有参考意义。     

Diet of Invasive Adult White Perch (Morone americana) and their Effects on the Zooplankton Community in Missisquoi Bay,Lake Champlain

White perch (Morone americana) became established in Missisquoi Bay, Lake Champlain in the mid 1990s. Since that time, cyanobacteria blooms have become common in summer. Although introduced planktivorous fish often impact plankton communities through a reduction in Daphnia density, such effects can be difficult to predict in an opportunistic species such as white perch. In this study, we examined the extent of zooplanktivory exhibited by adult white perch in Missisquoi Bay. Adult white perch were collected from Missisquoi Bay on ten dates in spring and summer of 2005. White perch diet consisted of large numbers of Daphnia on dates when Daphnia densities exceeded 20 individuals/L and when Daphnia comprised more than 50% of the zooplankton assemblage. When Daphnia densities were below these threshold values, adult white perch diet consisted predominantly of benthic prey. Our results show that white perch feed on large numbers of Daphnia in Missisquoi Bay and select Daphnia over other zooplankton taxa when they are abundant. It is likely that adult white perch grazing in Missisquoi Bay has contributed to a reduction in Daphnia density which in turn may be contributing to summertime cyanobacteria dominance in this bay.     

Limnological characteristics, eutrophication and cyanobacterial blooms in an inland reservoir, Australia

Ben Chifley Reservoir, the only potable water supply for Bathurst, New South Wales, Australia, has been experiencing recurrent cyanobacterial bloom problems since 1991. A study was undertaken from June 1998 to July 1999 to assess the limnological characteristics pertinent to eutrophication and the associated cyanobacterial blooms. From January–May 1999, the reservoir exhibited significant numbers of cyanobacterial cells, totalling > 9000 cells mL^?1. The highest number of cells (> 27 000 cells mL^?1) was recorded during April 1999. The water quality characteristics of the reservoir, and the river inflow and climatic data, were grouped into three distinct periods; before, during and after cyanobacterial blooms. High water temperature (15–22°C), thermal stratification (ΔT = 2.7–2.8°C), depletion of dissolved oxygen and high nutrient concentrations, all of which are conducive to enhanced cyanobacterial blooms, were evident before and during the bloom periods. Based on its nitrogen to phosphorus molar ratio, Ben Chifley Reservoir can be considered as being phosphorus‐deficient, in contrast to nitrogen, which is readily available from a number of sources in its drainage basin, including atmospheric fixation. Thus, it is recommended that adopting management strategies to reduce the quantity of bioavailable phosphorus in the reservoir would be the most effective way to minimize the occurrence of algal blooms.     

Fungal community dynamics associated with harmful cyanobacterial blooms in two Great Lakes

Harmful algal blooms (HABs) impose major costs on aquatic ecosystems worldwide, including the Laurentian Great Lakes. Microbial consumers, including fungi, can have important interactions with bloom-forming algae and cyanobacteria, although relatively few studies have investigated the relationship between fungi and HABs. We examined changes in the aquatic fungal community coincident with the occurrence of large cyanobacterial blooms in two areas of the Great Lakes (western Lake Erie and Saginaw Bay, Lake Huron). We collected water samples over the course of bloom development, peak, and decline from 3 sites in western Lake Erie on 11 dates and 2 sites in Saginaw Bay on 4 dates. Single molecule sequencing (PacBio RS II) with two molecular markers (the internal transcribed spacer (ITS) of the rRNA locus using fungal-specific primers and the 18S rRNA with primers targeting early-diverging lineages of fungi) was used to estimate fungal community composition. Results indicate a diverse fungal community within the lakes, including several major fungal phyla. The Chytridiomycota were particularly well-represented (54.8% and 45.4% of ITS and 18S sequences, respectively), and we also found representation from both Cryptomycota and Aphelidiomycota, which are putatively obligate intracellular parasites. Further, we found associations between the fungal community (alpha diversity; community composition) and measures of bloom magnitude (chlorophyll a, phycocyanin, and microcystin concentrations) in western Lake Erie. Our results suggest potentially important spatial and temporal heterogeneity in the fungal community that motivates further research on functional importance of fungi in the Great Lakes and consequences for HABs and freshwater ecosystems more broadly.     

Understanding and management of cyanobacterial blooms in sub-tropical reservoirs of Queensland,Australia

A three year study of two sub-tropical water supply (potable and irrigation) reservoirs - Baroon Pocket and Leslie - aimed to develop an improved understanding and effective management strategy for the control of low level toxic cyanobacterial ‘blooms’. The two reservoirs appear to be typical of those elsewhere in tropical and sub-tropical Australia, being strongly stratified and monomictic if deep, or polymictic to monomictic (depending on inter-annual climatic variation) if shallow. In both reservoirs, thermal stratification appeared to be the key factor influencing the onset and demise of cyanobactenal blooms. Hypolimnetic deoxygenation was rapid during periods of stratification, and high rates of nitrogen and phosphorus release from bottom sediments occurred during anoxia. External nutrient inputs were dominated by episodic storm in-flows following the passing of (sub)tropical depressions, carrying massive sediment and nutrient loads into the reservoirs. As a consequence of this, and coupled with the high degree of internal nutrient recycling and the low national targets for cyanobacterial control in Australia, we believe that reduction of external nutrient inputs alone, through improved catchment management, may not be sufficient to prevent cyanobacterial blooms. Therefore, more emphasis should be given to ‘in-lake’ control strategies such as destratification, biomanipulation and in situ sediment treatment.     

太湖蓝藻监测及暴发情况分析

为了及时掌握太湖蓝藻发生和暴发状况,为保障流域供水安全和太湖富营养化治理提供必要的基础信息,以1996-2008年太湖各湖区藻类监测资料为基础,结合蓝藻历史变化状况,对太湖13 a的藻类群落组成、优势种的构成、数量和季节变化,以及蓝藻暴发情况进行分析,并对太湖9个湖区分区进行蓝藻暴发特征分析,探讨治理蓝藻水华的措施.结...     

First data on cyanobacterial biodiversity in benthic biofilms during mass mortality of endemic sponges in Lake Baikal

This study investigates in detail species diversity of cyanobacteria which proliferated on the surface of diseased sponges and bedrock in Lake Baikal (Siberia, Russia) during the ecological crisis that has been progressing in the littoral zone since 2011 and caused numerous negative changes in biota. In 2014–2015, we examined samples from diseased and healthy sponges as well as rock substrates using Sanger sequencing and high-throughput 16S rRNA gene analysis. Based on morphology, we identified 15 cyanobacterial species in biofoulings. Tychonema sp., Symplocastrum sp., Pseudanabaena galeata and Tolypothrix distorta dominated on diseased sponges. In communities of healthy sponges, we detected mainly picocyanobacteria Synechococcus. Fascicles of Symplocastrum sp. and T. distorta dominated on bedrock substrates. Phylogenetically, most 16S rDNAs clustered among Tychonema, Pseudanabaena, Geitlerinema, Kamptonema, Leptolyngbya, and Tolypothrix spp. Cyanobacterial proliferation in the littoral zone of Lake Baikal should be considered as one of the most important negative ecological processes in recent times which requires an urgent study in order to understand the causes of its emergence and development. Mat-forming cyanobacteria Tychonema characterized by the highest tropism to sponges plays a special role in the disease and death of sponges.     

基于卫星测高和实测数据的博斯腾湖水位变化分析

湖泊水位是湖泊水文观测必不可缺的要素,直接关系到湖泊物质交换和能量平衡,对研究湖泊运动和区域气候环境变化至关重要。为了掌握内陆湖泊水位的变化过程和空间特征,以新疆博斯腾湖为例,综合Jason-1&2、ENVISat&ERS、ICESat-1、ICESat-2等卫星测高资料,提取博斯腾湖湖泊水域瞬时水位和日均水位,并根据Hydroweb水位记录和1975-2020年博斯腾湖湖泊水位观测及水域面积数据,检验Jason-1&2、ENVISat&ERS、ICESat-1、ICESat-2测高数据的估计精度。借助趋势面分析方法,分析博斯腾湖水域水位变化的空间差异和特征。结果表明：Hydroweb水位记录、Jason-1&2、ENVISat&ERS、ICESat-1、ICESat-2卫星资料估计湖泊日均水位的绝对误差分别为0.24、0.34、0.28、0.18、0.08 m; 2020年博斯腾湖年均水位为1 048.10±0.12 m,与1975年年均水位相比增加了0.70±0.15 m;湖泊瞬时水位在空间尺度上存在一定水位差,ICESat-2测高数...     

Dolichospermum blooms in Lake Superior: DNA-based approach provides insight to the past,present and future of blooms

Cyanobacterial blooms are increasing in frequency, duration, and severity globally in freshwater ecosystems. The Laurentian Great Lakes are prone to toxin-producing cyanobacterial blooms and have experienced annually recurring blooms. Because of its oligotrophic nature, Lake Superior has been relatively free of bloom occurrences. However, in recent years, Dolichospermum blooms have occurred with increasing frequency, especially in the western arm. During a Dolichospermum bloom in 2018, opportunistic samples were collected from the offshore bloom and investigated with shotgun metagenomics. We identified a near-complete Dolichospermum genome that is highly similar to genomes from cultures recovered in Lakes Erie and Ontario. The genomes from the Laurentian Great Lakes are typified by their putative ability to produce a suite of secondary metabolites like anabaenopeptin, but not toxins like microcystin. Additionally, we recovered a Dolichospermum lemmermannii 16S rRNA gene from the bloom and using datasets collected from the epilimnion and sediments in Lake Superior show this organism is ubiquitous and that several strains may exist. While there is much to learn about Lake Superior cyanobacterial bloom development and triggers, understanding this organism is endemic to the region, what its genome is capable of and that specific strains may have provenance within the lake provides a distinct ecological basis for understanding and working towards a predictive framework for future blooms.     

Toxic cyanobacterial blooms in a shallow, artificially mixed urban lake in Colorado, USA

One of the most severe problems associated with eutrophication of urban freshwater ecosystems is the occurrence of increasingly frequent blooms of toxic cyanobacteria. Cyanotoxins might accumulate in the trophic web, producing diverse intoxication symptoms and chronic effects that are difficult to diagnose and prevent. High mortality of domestic animals and fish has been reported previously under these prevailing conditions. This study investigates the taxonomic composition of phytoplankton assemblages in Sheldon Lake during the summer of 2004, a year after the completion of a restoration project on the lake. The study analysed the physical and chemical changes caused by urban run‐off and artificial mixing, as well as the usefulness of microcystin molecular markers derived from the mcy gene cluster for the detection of toxic cyanobacterial strains in environmental samples from Sheldon Lake. This study clearly demonstrates that the artificial mixing rate alone was insufficient to cause a transition to a well‐mixed aquatic system, and that cyanobacteria remained dominant throughout the summer months. The presence of toxic cyanobacterial strains was confirmed with the use of molecular markers that detected the presence of the mcy gene cluster responsible for the production of toxin by Microcystis spp. This approach might have a great potential use in the routine analyses of urban aquatic ecosystems. It also might make toxicity monitoring more feasible, allowing for the early application of corrective actions, especially for cases such as Sheldon Lake, which is a public recreational focal point.     

联合Landsat影像和ICESat测高数据估计青海湖湖泊水量变化

湖泊既是陆地水资源的重要储蓄场所,也是区域和全球水文循环系统的重要组成部分,其水量波动对气候变化较为敏感。为了掌握湖泊面积、水位和水量的变化规律,借助1988-2018年Landsat TM/ETM/OLI影像和归一化差异水体指数NDWI（normalized difference water index）提取青海湖湖泊水域面积;利用ICESat-GLAS（ice, cloud, and land elevation satellite-geoscience laser altimeter system）测高数据提取青海湖湖泊水位变化,并结合观测资料检验陆地GLAS光斑脚点高程和湖泊水位的估测精度。根据湖泊面积与水位、水量与水位的关系,构建1988-2018年青海湖湖泊面积-水位-水量波动时变序列,并探讨湖泊水位、面积、水量的年内和年际变化特征。结果表明：GLAS光斑脚点高程与高程实测值的标准误差为0.14 m,与SRTM3高程标准误差为0.26 m;1988-2018年青海湖年均水位和水量总体上呈增加趋势,其中年均水位最低值出现于2004年,平均水位为(3 193.0±0.16) m,湖泊面积为(4 190±13) km²;与1988年年均水位相比,2018年青海湖年均水位上升了(1.93±0.22) m,湖泊年均面积扩张了(197.75±6.3) km²,湖泊水量增加了(8.93±0.12) km³。     

Mapping the spatial changes in Lake Volta using multitemporal remote sensing approach

Lake Volta is the world's largest man‐made lake by surface area, and the fourth largest by water volume. Located completely within Ghana, it has a surface area of about 8502 km² (3283 square miles). Like many other lakes on the African continent, Lake Volta is a major natural resource for Ghana, storing water for the operation of the hydroelectric dam, water supply for domestic, agricultural and industrial purposes, habitat for diverse aquatic species, an avenue for recreational activities, means of navigation between the north and south parts of the country, and a climate modulator for the tropical region. The lake has experienced variable water level and surface area changes attributable to climate change and excessive water abstractions. Using histogram thresholding techniques, this study produced binary images and vector maps of the lake. Spatial extent mapping of the lake using Landsat TM 1990, ETM + 2000 and ETM + 2007 images indicated the lake experienced both increased and decreased surface area changes during the study period. The lake's surface area varied by about 197 km² between 1990 and 2007, with the water level fluctuating between ±7 m. Factors thought to be contributing to these changes include human factors (regulated flows, deforestation, increased water abstractions and pollution) as well as natural phenomenon (climate change, water run‐off and subsequent sediment transport).