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Lakes are important components for regulating carbon cycling within landscapes. Most lakes are regarded as CO2 sources to the atmosphere, except for a few eutrophic ones. Algal blooms are common phenomena in many eutrophic lakes and can cause many environmental stresses, yet their effects on the net exchange of CO2 (FCO2) at large spatial scales have not been adequately addressed. We integrated remote sensing and Eddy Covariance (EC) technologies to investigate the effects that algal blooms have on FCO2 in the western basin of Lake Erie--a large lake infamous for these blooms. Three years of long-term EC data (2012-2014) at two sites were analyzed. We found that at both sites: (1) daily FCO2 significantly correlated with daily temperature, light, and wind speed during the algal bloom periods; (2) monthly FCO2 was negatively correlated with chlorophyll-a concentration; and (3) the year with larger algal blooms was always associated with lower carbon emissions. We concluded that large algal blooms could reduce carbon emissions in the western basin of Lake Erie. However, considering the complexity of processes within large lakes, the weak relationship we found, and the potential uncertainties that remain in our estimations of FCO2 and chlorophyll-a, we argue that additional data and analyses are needed to validate our conclusion and examine the underlying regulatory mechanisms. [ABSTRACT FROM AUTHOR]

In 2011, Lake Erie experienced the largest harmful algal bloom in its recorded history, with a peak intensity over three times greater than any previously observed bloom. Here we show that long-term trends in agricultural practices are consistent with increasing phosphorus loading to the western basin of the lake, and that these trends, coupled with meteorological conditions in spring 2011, produced record-breaking nutrient loads. An extended period of weak lake circulation then led to abnormally long residence times that incubated the bloom, and warm and quiescent conditions after bloom onset allowed algae to remain near the top of the water column and prevented flushing of nutrients from the system. We further find that all of these factors are consistent with expected future conditions. If a scientifically guided management plan to mitigate these impacts is not implemented, we can therefore expect this bloom to be a harbinger of future blooms in Lake Erie. [ABSTRACT FROM AUTHOR]

Microcystis spp. blooms have occurred annually in western Lake Erie since about 1995. Microcystis produce a group of toxins known as microcystins which can be harmful to livestock and to humans. In this study, surface water samples were collected from six sites during six sampling events from July to October in 2007. In situ environmental data (e.g. pH, temperature) and laboratory analyses (e.g. nutrients) were carried out to characterize the six sites. The Microcystis spp. density ranged from 10² to 107 cells/ml. Microcystin-LR concentration of 20 of all 36 samples were below the detection limit (0.15-5 ppb), while the microcystin-LR concentration in the 16 remaining samples ranged from 0.5 to 3 x 10³ μg per gram dry weight. The aim of this research was to investigate the relationships between sampling location, environmental parameters, Microcystis spp. concentration, and microcystin-LR concentration. The results suggest that temperature, nutrient concentration, turbidity, and wind speed and direction ( P < 0.05) are factors which affected Microcystis spp. density. Sampling site 8M, located 13m from the Maumee River, provided an advantage for Microcystis spp. growth, presumably due to intermediate water depth (5.5 m) combined with impact from the river. No relationship was found between Microcystis spp. density and microcystin-LR concentration. Temperature, nutrient concentration and DO ( P < 0.05) were associated with the production of microcystin-LR. [ABSTRACT FROM AUTHOR]

Long-term records of phytoplankton blooms in freshwater lakes are necessary both for understanding basin-scale changes to watersheds and for providing a key constraint for assessing processes driving blooms. However, due to the inherent constraints of in situ sampling and the short time period covered by modern space borne sensors, few long-term records exist. Historical data from sensors such as Landsat offer strong potential for creating new records of past blooms. Here, we use a novel evaluation procedure based on multiple metrics to assess algorithm suitability and robustness for generating long-term bloom records using Landsat 5 imagery. Evaluation metrics are based on bloom presence, spatial distribution, magnitude and timing, using both in situ Microcystis biovolume and remotely-sensed Cyanobacterial Index (CI) data from MERIS for 2002–2011. Applying this procedure for a test case focusing on Lake Erie's western basin, an algorithm based on a near infrared threshold with simple atmospheric correction through subtraction of the shortwave infrared band, combined with an additional “greenness” filter based on a hue threshold, performs best. Implementing this algorithm for 1984–2001 reveals the long-term trends in peak bloom magnitude prior to the start of the MERIS and MODIS record (2002–2015), and more than doubles the period of record that can be used to understand bloom occurrence and growth for this system. More broadly, we demonstrate that Landsat observations can be used to identify macro-scale features of blooms. For Lake Erie, the performance of the final Landsat algorithm is comparable to that of the MERIS CI algorithm, despite Landsat's broad spectral bands and long revisit time. [ABSTRACT FROM AUTHOR]

Since the mid-1990s, harmful algal blooms have plagued the waters of western Lake Erie with increased frequency. These blooms adversely affect water quality in terms of aesthetics, recreational use, and potentially, human health. In vessel-based observations made from 2002-2007, the most common nuisance species was Microcystis aeruginosa, a cyanobacteria that forms blooms during summer months. Microcystis blooms from 2002-07 were quantified using biweekly plankton tows (N=145) and a density separation method to separate Microcystis from other species. Patterns of bloom timing and density were then compared to USGS data from a major nearby tributary, the Maumee River, that is linked to bloom development by delivering the algal nutrients phosphorus and nitrogen to Lake Erie. Highest summer bloom volumes occurred in years with highest summer river flow (2003, 2004), while the lowest Microcystis volume occurred in the driest summer (2002). In addition to Microcystis, another cyanobacteria species, Lyngbya wollei, previously unreported in Lake Erie, formed large benthic mats along the southern shoreline of Maumee Bay in late summer of 2006. In September 2006, Lyngbya mats washed ashore, fouling beaches, private marinas, and shoreline property with layers of biomass up to 1.3 m thick. Early observations of Lyngbya mats suggest that the extent of shoreline fouling may depend on wind direction and water currents during the period in late summer when mats become mobile. [ABSTRACT FROM AUTHOR]

Growth of the toxic cyanobacteria, Microcystis sp., has increased in recent years in Maumee Bay and western Lake Erie resulting in harmful algal blooms (HABs) during summer months. To investigate environmental causes of HABs, it is important to quantify differences in algal abundance between months and years. However, because cell counts of Microcystis are time-consuming, it is difficult to processes sufficient samples to adequately characterize multiple blooms. We developed a density separation technique that permitted relatively rapid quantification of Microcystis volume in archived zooplankton tows from western Lake Erie. We report the results of sample analysis for 2002-2006. Microcystis volume in samples collected approximately biweekly at six sites (N = 145) was determined in calibrated Imhoff cones and some samples (N=60) were further processed to determine Microcystis cell density. Total cells in the sample and cell density in the lake water increased linearly with volume of Microcystis in samples (r² = 0.84 and 0.89), indicating that volume estimates can be used as a surrogate for cell counts. Averaging Microcystis cell density on a monthly basis for all sites allowed for temporal representation of bloom intensity, whereas monthly density by site allowed for a spatial illustration of the blooms. From heaviest to lightest Microcystis blooms (average monthly Microcystis volume·m-2 summed over July, August, September), the years are ranked as follows: 2003 (355.2 ml·m-2), 2004 (311.4 ml·m-2), 2006(233.5 ml·m-2), 2005 (120.8 ml·m), 2002 (54.5 ml·m-2). [ABSTRACT FROM AUTHOR]

Abstract: For almost two decades, the western basin of Lake Erie has been plagued with recurring toxic algal blooms dominated by the colonial cyanobacterium, Microcystis spp. Since the Maumee River is a major source of nutrients and sediment inputs into the lake, and Microcystis spp. has been identified as a member of the upstream river algal assemblage, the possibility exists that the river Microcystis species serve as a seed population for the toxic blooms occurring in the lake. Genetic profiling of toxic cyanobacteria using the microcystin synthesis gene, mcyA, clearly indicates that the toxic cyanobacteria of the river are distinct from the toxic Microcystis spp. of Lake Erie. Indeed, mcyA sequences are almost exclusively from toxic Planktothrix spp., similar to what has been documented previously for Sandusky Bay. UniFrac statistical analysis of cyanobacterial community composition by comparison of 16S–23S ITS sequences also show that the Maumee River and Lake Erie communities are distinct. Overall, these data show that despite the importance of nutrient inputs and sediments from the river, the toxic cyanobacterial blooms of Lake Erie do not originate from toxic species endemic to the Maumee River and instead must originate elsewhere, most likely from the lake sediments. [Copyright &y& Elsevier]