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1. Effects of climate change and episodic heat events on cyanobacteria in a eutrophic polymictic lake.

   https://doi.org/10.1016/j.scitotenv.2019.07.220  

   Bartosiewicz, Maciej (January 2019, Science of the total environment)

   null (Ed.)

   Changes in mixing regimes and CO2 availability may promote harmful cyanobacterial blooms in polymictic lakes and ponds globally, but the underlying mechanisms still remain unclear. We integrated results from a natural experiment comprising an average-wet year (2011) and one with heat waves (2012), a long-term meteorological dataset (1960–2010), historical phosphorus concentrations and corresponding sedimentary pigment records, to determine, on different temporal scales, the mechanistic controls of cyanobacterial blooms in a eutrophic polymictic lake. Intense warming in 2012 was associated with: 1) increased stability of the water column with buoyancy frequencies exceeding 40 cph at the surface, 2) high phytoplankton biomass in spring (up to 125 mg WW L-1), 3) reduced downward transport of heat and 4) persistently depleted epilimnetic CO2 concentrations. CO2 depletion was effectively maintained by intense uptake by phytoplankton (influx up to 30 mmol m-2 d-1) in combination with reduced carbon inputs from the watershed during dry periods. Under eutrophic conditions these effects triggered massive bloom of buoyant cyanobacteria (up to 300 mg WW L-1). Complementary evidence from polynomial regression modelling using long-term datasets revealed that warming is the most important predictor of cyanobacterial abundance during the second half of the last century explaining 78% of the observed positive trend, whereas phosphorus concentration explained only 10% thereof. Together the results from the interannual comparison and the multi-decadal record indicate that hotter and drier climates increase water column stratification and decrease CO2 availability in eutrophic polymictic lakes. This combination catalyzes blooms of buoyant cyanobacteria. 

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2. Exploring How Cyanobacterial Traits Affect Nutrient Loading Thresholds in Shallow Lakes: A Modelling Approach

   https://doi.org/10.3390/w12092467  

   Chang, Manqi; Teurlincx, Sven; Janse, Jan; Paerl, Hans; Mooij, Wolf; Janssen, Annette (September 2020, Water)

   null (Ed.)

   Globally, many shallow lakes have shifted from a clear macrophyte-dominated state to a turbid phytoplankton-dominated state due to eutrophication. Such shifts are often accompanied by toxic cyanobacterial blooms, with specialized traits including buoyancy regulation and nitrogen fixation. Previous work has focused on how these traits contribute to cyanobacterial competitiveness. Yet, little is known on how these traits affect the value of nutrient loading thresholds of shallow lakes. These thresholds are defined as the nutrient loading at which lakes shift water quality state. Here, we used a modelling approach to estimate the effects of traits on nutrient loading thresholds. We incorporated cyanobacterial traits in the process-based ecosystem model PCLake+, known for its ability to determine nutrient loading thresholds. Four scenarios were simulated, including cyanobacteria without traits, with buoyancy regulation, with nitrogen fixation, and with both traits. Nutrient loading thresholds were obtained under N-limited, P-limited, and colimited conditions. Results show that cyanobacterial traits can impede lake restoration actions aimed at removing cyanobacterial blooms via nutrient loading reduction. However, these traits hardly affect the nutrient loading thresholds for clear lakes experiencing eutrophication. Our results provide references for nutrient loading thresholds and draw attention to cyanobacterial traits during the remediation of eutrophic water bodies. 

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3. Physical drivers facilitating a toxigenic cyanobacterial bloom in a major Great Lakes tributary

   https://doi.org/10.1002/lno.11558  

   Matson, Paul G.; Boyer, Gregory L.; Bridgeman, Thomas B.; Bullerjahn, George S.; Kane, Douglas D.; McKay, Robert M.; McKindles, Katelyn M.; Raymond, Heather A.; Snyder, Brenda K.; Stumpf, Richard P.; et al (January 2020, Limnology and Oceanography)

   The Maumee River is the primary source for nutrients fueling seasonal Microcystis-dominated blooms in western Lake Erie’s open waters though such blooms in the river are infrequent. The river also serves as source water for multiple public water systems and a large food services facility in northwest Ohio. On 20 September 2017, an unprecedented bloom was reported in the Maumee River estuary within the Toledo metropolitan area, which triggered a recreational water advisory. Here we (1) explore physical drivers likely contributing to the bloom’s occurrence, and (2) describe the toxin concentration and bacterioplankton taxonomic composition. A historical analysis using 10-years of seasonal river discharge, water level, and local wind data identified two instances when high-retention conditions occurred over ≥ 10 d in the Maumee River estuary: in 2016 and during the 2017 bloom. Observation by remote sensing imagery supported the advection of cyanobacterial cells into the estuary from the lake during 2017 and the lack of an estuary bloom in 2016 due to a weak cyanobacterial bloom in the lake. A rapid-response survey during the 2017 bloom determined levels of the cyanotoxins, specifically microcystins, in excess of recreational contact limits at sites within the lower 20 km of the river while amplicon sequencing found these sites were dominated by Microcystis. These results highlight the need to broaden our understanding of physical drivers of cyanobacterial blooms within the interface between riverine and lacustrine systems, particularly as such blooms are expected to become more prominent in response to a changing climate. 

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4. PDO and AMO Modulation of the ENSO–Asian Summer Monsoon Teleconnection During the Last Millennium

   https://doi.org/10.1029/2023JD039638  

   Wang, Na; Dee, Sylvia; Hu, Jun; Steiger, Nathan; Thirumalai, Kaustubh (December 2023, Journal of Geophysical Research: Atmospheres)

   Abstract Observations show that the teleconnection between the El Niño‐Southern Oscillation (ENSO) and the Asian summer monsoon (ASM) is non‐stationary. However, the underlying mechanisms are poorly understood due to inadequate availability of reliable, long‐term observations. This study uses two state‐of‐the‐art data assimilation‐based reconstructions of last millennium climate to examine changes in the ENSO–ASM teleconnection; we investigate how modes of (multi‐)decadal climate variability (namely, the Pacific Decadal Oscillation, PDO, and the Atlantic Multidecadal Oscillation, AMO) modulate the ENSO–ASM relationship. Our analyses reveal that the PDO exerts a more pronounced impact on ASM variability than the AMO. By comparing different linear regression models, we find that including the PDO in addition to ENSO cycles can improve prediction of the ASM, especially for the Indian summer monsoon. In particular, dry (wet) anomalies caused by El Niño (La Niña) over India become enhanced during the positive (negative) PDO phases due to a compounding effect. However, composite differences in the ENSO–ASM relationship between positive and negative phases of the PDO and AMO are not statistically significant. A significant influence of the PDO/AMO on the ENSO–ASM relationship occurred only over a limited period within the last millennium. By leveraging the long‐term paleoclimate reconstructions, we document and interrogate the non‐stationary nature of the PDO and AMO in modulating the ENSO–ASM relationship. 

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5. Teleconnection of Regional Drought to ENSO, PDO, and AMO: Southern Florida and the Everglades

   https://doi.org/10.3390/atmos10060295  

   Abiy, Anteneh Z.; Melesse, Assefa M.; Abtew, Wossenu (June 2019, Atmosphere)

   Drought variability is associated with global oceanic and atmospheric teleconnections driven by, among others, the Pacific Decadal Oscillation (PDO), the Atlantic Multidecadal Oscillation (AMO), and El Niño–Southern Oscillation (ENSO). Climate teleconnections with a region’s rainfall, with drought and flooding implications, should be part of short- and long-term water management planning and operations. In this study, the link between drought and climatic drivers was assessed by using historical data from 110 years of regional rainfall in southern Florida and the Everglades. The objective was to evaluate historical drought and its link with global oceanic and atmospheric teleconnections. The Standardized Precipitation Index (SPI) assesses regional historical drought in 3-, 6-, 12-, 24-, 36-, 48-, and 60-month periods. Each of the SPIs was used to analyze the association of different magnitudes of drought with ENSO, AMO, and PDO. Historical drought evaluated in different time windows indicated that there is a wet and dry cycle in the regional hydrology, where the area is currently in the wet phase of the fluctuation since 1995 with some drought years in between. Regional historical rainfall anomaly and drought index relationships with each driver and combination of drivers were statistically evaluated. The impact of ENSO fluctuation is limited to short-period rainfall variability, whereas long-period influence is from AMO and PDO. 

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