An analysis of MODIS-derived algal and mineral turbidity in Lake Erie

Satellite-derived estimates of chlorophyll concentrations based on colour ratio algorithms traditionally fail in turbid waters such as those found in Lake Erie, resulting in chlorophyll concentrations often orders of magnitude in error and spatial distributions mirroring that of known suspended sediment distributions. Methods are presented here that were used to simultaneously extract algal and mineral suspended particulate matter for Lake Erie from the red and near-infrared bands of NASA's MODIS-Aqua sensor. Results produced spatially and temporally distinct seasonal cycles in agreement with bio-geo-physical processes on the lake. Derived imagery was used to monitor seasonal cycles of both algal and mineral particulate matter on the lake and determine areas of persistently elevated concentrations that may highlight regions of potential water quality concern.     

Reporting on the status,trends, and drivers of algal blooms on Lake of the Woods using satellite-derived bloom indices (2002–2021)

Despite significant declines in external phosphorus loads, Lake of the Woods continues to experience severe recurring cyanobacterial harmful algal blooms (cHABs) covering as much as 80% of the lake surface area. Satellite-derived bloom indices were used to assess the status, trends, and drivers of cHAB conditions for the period 2002 to 2021 in support of developing ecosystem objectives and response indicators for the lake. Areas of greatest potential concern, with the most prolonged bloom occurrences, were in the southeast of the lake. Significant decreases in bloom indices suggest the lake may now be responding to historical nutrient reductions. The greatest rates of decrease were within the main water flow paths, with little change in the more isolated embayments, suggesting flushing plays a key role in regulating regional bloom severity. Significant inter-annual variability in bloom phenology was observed, with blooms peaking later in recent years, which may be in response to climate-induced changes in the lake and watershed. The absence of a direct relationship between external phosphorus loads and annual bloom severity reflects the complexity of the lake’s response to eutrophication and the potential roles of other drivers including climate and a strong legacy effect of sedimentary nutrients. A case study of the 2017 bloom season captures the compounding interaction of meteorological variability and seasonal nutrient delivery in regulating the bloom response. Results highlight the need for greater understanding of seasonal and regional variability of bloom drivers to aid in forecasting the lake’s recovery under both nutrient management and climate change scenarios.     

Spatial and temporal variability of inherent and apparent optical properties in western Lake Erie: Implications for water quality remote sensing

Lake Erie has experienced dramatic changes in water quality over the past several decades requiring extensive monitoring to assess effectiveness of adaptive management strategies. Remote sensing offers a unique potential to provide synoptic monitoring at daily time scales complementing in-situ sampling activities occurring in Lake Erie. Bio-optical remote sensing algorithms require knowledge about the inherent optical properties (IOPs) of the water for parameterization to produce robust water quality products. This study reports new IOP and apparent optical property (AOP) datasets for western Lake Erie that encapsulate the May–October period for 2015 and 2016 at weekly sampling intervals. Previously reported IOP and AOP observations have been temporally limited and have not assessed statistical differences between IOPs over spatial and temporal gradients. The objective of this study is to assess trends in IOPs over variable spatial and temporal scales. Large spatio-temporal variability in IOPs was observed between 2015 and 2016 likely due to the difference in the extent and duration of mid-summer cyanobacteria blooms. Differences in the seasonal trends of the specific phytoplankton absorption coefficient between 2015 and 2016 suggest differing algal assemblages between the years. Other IOP variables, including chromophoric, dissolved organic matter (CDOM) and beam attenuation spectral slopes, suggest variability is influenced by river discharge and sediment re-suspension. The datasets presented in this study show how these IOPs and AOPs change over a season and between years, and are useful in advancing the applicability and robustness of remote sensing methods to retrieve water quality information in western Lake Erie.     

城市河湖水华防治技术研究

城市河湖的富营养化给城市水环境造成了许多不利因素,改善水质,消除藻类水华是一个不容忽视的重要问题。阐述了应用于富营养化水体中藻类控制的物理、化学和生物技术的内容、存在的问题和不足。指出了各种方法有机结合,进一步研究出高效的控制策略才能更加有效地控制水华现象的发生。     

High-resolution hydrodynamic modelling to study year-round circulations and inter-basin exchanges in Lake Winnipeg

A new high-resolution (500 × 500 m), three-dimensional hydrodynamic model was applied to Lake Winnipeg to study summer and winter water circulation, temperature, and ice-cover during 2016–17. The model was run with a combination of buoy-based observations and the outputs from the Global Environmental Multiscale model forcing. Four primary riverine inflows and two outflows were considered in the model. The bathymetry from a previous study by the authors was revised using a 2018 survey covering the South Basin and the Narrows. Comparisons of this new model with the previous model setup (2 km resolution) show noticeable improvements in all simulated parameters. In the Narrows, where seiche-driven flows have predominant oscillation periods of ~27 h and ~17 h, the RMSE of simulated currents is 0.1 m s^?1, half of that of the previous simulations. The new model was able to reasonably simulate the spatial development of ice-cover over the lake. The ice-free period circulation results show that there are two clockwise and counterclockwise gyres in the North Basin, and a weak seasonal clockwise gyre in the South Basin. Monthly circulation patterns differ from those during short wind events due to spatiotemporal variability of wind patterns. The materials from the Red and the Winnipeg Rivers need ~50 days to reach the Narrows before transported from the South Basin to the North Basin. The daily inter-basin exchange flow oscillations during the ice-free period can range up to ~3.5 × 10⁴ m³ s^?1, while under-ice daily exchanges are always northwards with values depending on inflowing riverine discharge up to ~0.5 × 10⁴ m³ s^?1.     

First estimation of the diffusive methane flux and concentrations from Lake Winnipeg,a large,shallow and eutrophic lake

Freshwater lakes are increasingly recognized as significant sources of atmospheric methane (CH₄), potentially offsetting the terrestrial carbon sink. We present the first study of dissolved CH₄ distributions and lake-air flux from Lake Winnipeg, based on two-years of observations collected during all seasons. Methane concentrations across two years had a median of value of 24.6 nmol L^-1 (mean: 41.6 ± 68.2 nmol L^-1) and ranged between 5.0 and 733.8 nmol L^-1, with a 2018 annual median of 24.4 nmol L^-1 (mean: 46.8 ± 99.3 nmol L^-1) and 25.1 nmol L^-1 (mean: 38.8 ± 45.2 nmol L^-1) in 2019. The median lake-air flux was 1.1 µmol m^?2 h^?1 (range: 0.46–70.1 µmol m^?2h^?1, mean: 2.9 ± 10.2 µmol m^?2 h^?1) in 2018, and 5.5 µmol m^?2h^?1 (range: 0.0–78.4 µmol m^?2 h^?1, mean: 2.7 ± 8.5 µmol m^?2 h^?1) in 2019, for a total diffusive emission of 0.001 Tg of CH₄-C yr^?1. We found evidence of consistent spatial variability, with higher concentrations near river inflows. Significant seasonal trends in CH₄ concentrations were not observed, though fluxes were highest during the fall season due to strong winds. Our findings suggest Lake Winnipeg is a CH₄ source of similar mean magnitude to Lake Erie, with lower concentrations and fluxes per unit area than smaller mid- to high-latitude lakes. Additional work is needed to understand the factors underlying observed spatial variability in dissolved gas concentration, including estimations of production and consumption rates in the water column and sediments.     

Temporal variations in the pelagic fish community of Lake Winnipeg from 2002 to 2019

Lake Winnipeg has undergone extensive changes in environmental conditions and fish community structure during recent decades. The presence of cyanobacteria and invasive species as well as eutrophication, flow regulation, fishing pressure, and climate change all have potential impacts on the native fish community. Since 2002, pelagic forage fish species and early life stages of large-bodied fish species in the pelagic zone in Lake Winnipeg (Manitoba, Canada) have been monitored. Catch data were used to study the temporal variation in species-specific occurrence and catch-per-unit-effort (CPUE) and to analyse the effects of lake condition on species occurrence and CPUE estimates. To account for the temporal variation observed for commonly caught prey species in Lake Winnipeg, we used a Bayesian approach, Integrated Nested Laplace Approximation (INLA), to compare the effects of environmental variables on occurrence and CPUE. The pelagic fish community composition varied among years, and CPUE declined by 2.2-fold between 2005–2008 and 2015–2018. Emerald shiner was the most dominate prey fish species but decreased in the catches since the early 2000’s, while rainbow smelt have almost entirely disappeared from the catches in recent years. Overall, we observed a decrease in CPUE in four of six most caught, pelagic species. Important environmental variables explaining occurrence and CPUE of the six most caught species in the survey were temperature and Secchi, trawl, and water depths. The trawl survey serves as a valuable long-term monitoring tool to study trends in responses of both native and non-native species to ecosystem changes in Lake Winnipeg.     

Association of aerobic anoxygenic phototrophs and zebra mussels,Dreissena polymorpha,within the littoral zone of Lake Winnipeg

While nutrient loading has affected all levels of Lake Winnipeg’s ecology, its greatest influence has likely been on the microbial community. In addition to eutrophication, zebra mussels (Dreissena polymorpha) have recently invaded the ecosystem and threaten food web dynamics. Their filter-feeding predation and association with bacteria, specifically phototrophs, was investigated. A sampling trip to Lake Winnipeg in October 2017, focused on the isolation, enumeration, and identification of aerobic anoxygenic phototrophs in littoral water, sediment, and tissues of mussels. Gimli, Patricia, and Grand beaches, separated by >15 km across the South Basin, had similar bacterial counts when cultivated on rich organic, BG-11, purple non-sulphur, and K₂TeO₃-supplemented media. Culture-based enumeration on rich organic medium revealed 1.74% of heterotrophs from littoral waters were aerobic anoxygenic phototrophs, and represented 13.98% within sediments. In contrast, 0.48, 1.15, and 0.16% of cultured heterotrophs were aerobic anoxygenic phototrophs within zebra mussel gill, gut, and gonadal tissues, respectively. High-throughput sequencing of bacterial 16S V4 rDNA maintained similar trends in respective bivalve organs, where 0.22, 1.13, and 0.20% of total 16S genes belonged to these phototrophs. Several Sphingomonadaceae isolates were recovered from gut tissues, all with filamentous morphology large enough for predation. Bioaccumulation of metals was also studied in D. polymorpha. All tested associated aerobic anoxygenic phototrophs were capable of resisting the metalloid oxide tellurite. The consistent distribution of aerobic anoxygenic phototrophs within microbial communities across Lake Winnipeg, and their predominance in the gut tissues of zebra mussels suggested bacterial consumption by this invasive species.     

鄱阳湖水质时空相关性及其因素分析

利用2011年鄱阳湖监测点全年的水环境参数数据,基于相关系数法,对鄱阳湖污染物时空相关性及时空变化规律进行了研究。结果表明,鄱阳湖水质存在时空相关性,枯水期空间分异性较大,1月份TR值最大,这与鄱阳湖水位变化相关;鄱阳湖南北湖区空间分异性从主湖区都昌处沿远离都昌方向分别向北部、南部地区随着距离的增大而逐渐减少,其中监测点L7的PR值最小,这主要受到周溪地区珍珠蚌类水产养殖的影响。     

Strategy of water pollution prevention in Taihu Lake and its effects analysis

Taihu Lake, the third largest freshwater lake in China, is located in the Chanjiang Delta of the Yangtze River. Its waters are used by agriculture, industry and as major drinking water for several cities including Shanghai and Wuxi. The lake also is important for tourism, aquaculture and flood control. Taihu Lake and its surrounding areas are facing three major water-related threats: deteriorating water quality with inflow and runoff from its watershed; flooding during the rainy seasons; and water shortages during drier months. Noxious algae blooms are occurring with increasing frequency and water quality continues to decline. Remedial actions implemented to date have been ineffective. This paper proposes that the problems could be remedied by constructing a by-pass channel (BPC), which would divert low-quality water from the lake during low precipitation periods and allow better quality water to flow into the lake during high flow periods. This remedial action would simultaneously deal with the deteriorating water quality of Lake Taihu and maintain its water level at a desired level. A preliminary assessment of this strategy shows that, if the BPC were implemented, the water quality of Taihu Lake would be improved significantly in few years, the flood disaster would be greatly mitigated, and the water shortage problem in the basin would be alleviated.     

Commentary: Achieving phosphorus reduction targets for Lake Erie

Harmful Algal Blooms (HABs), which were largely absent from Lake Erie from the 1980s until the mid-late 1990s, have been growing steadily worse in intensity. While much of the phosphorus loading into the lake prior to 1972 was caused by point-source pollution, approximately 88% to 93% of current loading comes from nonpoint sources, of which agriculture is the dominant land use. A reduction target of 860?metric?tons, or 40% of the total phosphorus spring loading in 2008, has been set with the expectation that such a reduction could limit the size and associated impact of HABs in 9 out of every 10?years. We review the effectiveness of recommended practices aimed at reducing phosphorus loss in agriculture and pair this knowledge with behavioral data on likely adoption to identify how best to achieve the reduction target. The data suggests that the target is feasible as a majority of the farming population is willing to consider many of the recommended practices. However, increases in adoption over time have been minimal, and farmers will need better cost-benefit information, site-specific decision support tools, and technical assistance in order to more rapidly adopt and execute the placement of recommended practices. A combination of voluntary and mandatory approaches may be needed, but policies and programs promoting voluntary adoption should be designed to better target known barriers and maximize voluntary program effectiveness.     

Investigating the invasion of the nonindigenous zooplankter, Eubosmina coregoni, in Lake Winnipeg,Manitoba, Canada

The spread of nonindigenous species (NIS) over land and via interconnecting water bodies is threatening aquatic ecosystems worldwide. This study examines the invasion of the first known NIS zooplankter, Eubosmina coregoni, into Lake Winnipeg, Manitoba, Canada. Analyses of cladoceran microfossils from a sediment core collected in the North Basin of the lake indicate this species first appeared in sediments dated to the late 1980s. An increase in total cladoceran accumulation rates coupled with increasing N, C, P, and chlorophyll a over the last 40 years provides evidence of eutrophication. Extant samples from fall 2002-2005 indicate that E. coregoni is mainly restricted to the North Basin while Bosmina longirostris is present throughout the lake. Results from this study provide baseline data regarding the invasion and establishment of E. coregoni, a precursor to future NIS that may have substantial ecological and economic impacts on the Lake Winnipeg ecosystem.     

Evidence from field measurements and satellite imaging of impact of Earth rotation on Lake Iseo chemistry

During an initial field survey in 2012, we observed an unexpected asymmetry of dissolved oxygen distribution between the western and eastern side in northern Lake Iseo. Motivated by this apparent anomaly, we conducted a detailed field investigation, and we used a physical model of the northern part of the lake to understand the influences that might affect the distribution of material in the northern section of the lake. These investigations suggested that the Earth's rotation has significant influence on the inflow of the lake's two main tributaries. In order to further crosscheck the validity of these results, we conducted a careful analysis at a synoptic scale using images acquired during thermally unstratified periods by Landsat-8 and Sentinel-2 satellites. We retrieved and post-processed a large set of images, providing conclusive evidence of the role exerted by the Earth's rotation on pollutant transport in Lake Iseo and of the greater environmental vulnerability of the north-west shore of this lake, where important settlements are located. Our study confirms the necessity for three-dimensional hydrodynamic models including Coriolis effect in order to effectively predict local impacts of inflows on nearshore water quality of medium-sized elongated lakes of similar scale to Lake Iseo.     

From River to Lake: Phosphorus partitioning and algal community compositional changes in Western Lake Erie

The Maumee River is an important source of phosphorus (P) loading to western Lake Erie and potentially a source of Microcystis seed colonies contributing to the development of harmful algal blooms in the lake. Herein, we quantified P forms and size fractions, and phytoplankton community composition in the river–lake coupled ecosystem before (June), during (August), and after (September) a large Microcystis bloom in 2009. Additionally, we determined the distribution and density of a newly emergent cyanobacterium, Lyngbya wollei, near Maumee Bay to estimate potential P sequestration. In June, dissolved organic phosphorus (DOP) was the most abundant P form whereas particulate P (partP) was most abundant in August and September. Green algae dominated in June (44% and 60% of total chlorophyll in river and lake, respectively) with substantial Microcystis (17%) present only in the river. Conversely, in August, Microcystis declined in the river (3%) but dominated (32%) the lake. Lake phytoplankton sequestered < 6% of water column P even during peak Microcystis blooms; in all lake samples < 112 μm non-algal particles dominated partP. Lyngbya density averaged 19.4 g dry wt/m², with average Lyngbya P content of 15% (to 75% maximum) of water column P. The presence of Microcystis in the river before appearing in the lake indicates that the river is a potential source of Microcystis seed colonies for later lake blooms, that DOP is an important component of early summer total P, and that L. wollei blooms have the potential to increase P retention in nearshore areas.     

Cladophora (green algae) and dreissenid mussels over a nutrient loading gradient on the north shore of Lake Ontario

Benthic algae, much of it the green alga Cladophora, blanket the nearshore lakebed of the north shore of Lake Ontario. Nearshore field studies in Toronto, Ajax, Oshawa and Cobourg in 2012 and 2013, and Toronto in 2015 examined the distribution of Cladophora over a nutrient gradient on the north shore of the lake. Concentrations of total phosphorus, dissolved phosphorus and total inorganic nitrogen in the water column decreased from west to east over the gradient corresponding with decreasing watershed development and size. However, high surface cover and nuisance levels of Cladophora biomass were found across the gradient, including the least developed study area where total phosphorus concentrations were similar to those in the open lake. The abundance of Dreissena, high in all areas, was measured concurrently with Cladophora biomass and correlated positively at depths of 6 to 10 m. External loading of phosphorus provides a basis for abatement of Cladophora; however, the influences of enrichment along the shoreline, internal loading at the lakebed and lake trophic status in sustaining growth remain obscure. Nuisance levels of Cladophora are not isolated to locations experiencing elevated external loading and should be viewed in the context of interacting area-specific and lake-wide nutrient supplies.     

再生水回用于景观水体磷营养盐对叶绿素a和藻密度的影响研究

以北京市某再生水厂出水为研究对象,人工配制各浓度梯度的营养盐,试验研究补给再生水后景观水体水质指标的变化,重点考察磷对叶绿素a和藻密度的影响情况.试验结果表明叶绿素a和藻密度主要受水体中氮磷比和磷酸盐浓度的影响.在磷酸盐保持在1 mg/L以下,氨氮在2 mg/L以下,硝酸盐氮在8 mg/L以下,将再生水一次性补给景观水体是完全可行的,不会产生藻类暴发;当磷酸盐浓度增加至1.5 mg/L,藻密度将显著增加.     

Nutrient footprints on the Toronto-Mississauga waterfront of Lake Ontario

The extent of nutrient enrichment over the urbanized shoreline of western Lake Ontario bordering the Cities of Toronto and Mississauga was investigated in 2018. Concentrations of total phosphorus were higher and more wide-ranging compared with nearshore reference areas in eastern Lake Ontario. Area-weighted chlorophyll a was higher over the shoreline from the mouth of the Credit River to Humber Bay west of Toronto Harbour compared with that to the east from the Toronto Beaches to the Rouge River, a pattern also seen broadly in concentrations of phosphorus fractions and nitrates. Concentrations of phosphate measured by mass spectrometry, and using an internal standard to minimize sampling losses, were higher in Toronto Inner Harbour, near wastewater outfalls, river mouths, and to varying extent over the mixing areas of these discharges. Chlorophyll a suggested broadly oligotrophic to oligo-mesotrophic conditions despite areas with nutrient fractions suggestive of more productive conditions. Toronto Inner Harbour was mesotrophic, with wide-ranging levels of phosphorus fractions strongly influenced by the variable loading from the Don River into the harbour. Phosphorus fractions in the harbour quays which also receive CSOs discharges were elevated at times. Blooms or scums of planktonic algae were not observed. Elevated concentrations of phosphate were found at shallow depths suitable for growth of the green algae Cladophora. As these urban areas continue to grow, the potential for additional nutrient loading to exacerbate growth of algae should be watched given the present conditions that indicate variable but pervasive nutrient enrichment.     

Small eddies observed in Lake Superior using SAR and sea surface temperature imagery

Making use of the fine resolution of satellite SAR imagery, we observe small eddies during the spring and summer months in several locations in Lake Superior. During these months there is a thermal gradient between warmer nearshore waters and colder offshore waters which enhances cyclonic coastal currents. Using spaceborne SAR imagery from the European Space Agency's ERS-1 and ERS-2 missions from 1992 to 1998, we observe small eddies, identifying and mapping basic eddy characteristics including diameter, location, and rotational sense. In total, 45 eddies were located, of which 41 were cyclonic and 4 anticyclonic. Average diameter was 9.8 km and average distance to shore was 8.1 km. Based on sea surface temperature data from AVHRR, the eddies are located within the region of sharp thermal gradients of order 3–5 °C per 3 km. Spatial and temporal coverage was uneven, however, more eddies were seen in SAR images taken in late summer along the southern and eastern shores as well as areas where the boundary current interacts with topographic features including islands and promontories.