Crop, Soil and Environmental Sciences (General)

Data for: Cyanobacteria and aquatic ecosystem dynamics across 28,000 years of environmental changes in subtropical North America

Data for: Cyanobacteria and aquatic ecosystem dynamics across 28,000 years of environmental changes in subtropical North America Ecological pressures on aquatic ecosystems have increased over recent centuries due to human activities and climate change. However, contextualizing ecosystem deterioration is often challenging due to limited knowledge of environmental changes over millennial timescales. Subtropical Carolina bays in North Carolina, USA, have remained unglaciated, preserving paleolimnological records that extend back to the last glacial period. Here, we analyzed a sediment core from the ecologically rich Lake Waccamaw spanning more than 28,000 years for aquatic proxies of nutrients, photosynthetic pigments, cyanotoxins, carbon isotopes, and terrestrial proxies of pollen and charcoal. The study explored paleolimnological changes in the aquatic environment connected to land changes and climate during the late Quaternary in the southeastern Atlantic Coastal Plain. Results reveal that while current levels of colonial cyanobacteria are high, past levels of cyanobacteria, other primary producers, and cyanotoxins were higher under natural climate variability. Abrupt ecosystem responses to increasing trophic conditions during Interstadial 3 (27.8-26.4 cal ka BP) and the early Holocene (11.4-7 cal ka BP) were marked by increases in primary producer abundance, deciduous vegetation expansion, and fire activity. Cyanobacteria remained dominant throughout the record, with colonial forms prevailing during the Holocene. Increases in pigment concentrations aligned with Quercus and were primarily driven by hydroclimatic variability and nutrient stoichiometry. Transitions between Pinus and Quercus pollen matched stadials and interstadials in the δ18Ο record from the North Greenland Ice Core Project (NGRIP). This study highlights the value of multi-proxy millennial-scale paleolimnological records for understanding aquatic ecosystem responses to climate conditions during the late Pleistocene.

Photosynthetic pigment and cyanotoxin data for: Cyanotoxin production in shallow subtropical lakes is driven by nutrient enrichment and primary producer abundance on the millennial scale

Photosynthetic pigment and cyanotoxin data for: Cyanotoxin production in shallow subtropical lakes is driven by nutrient enrichment and primary producer abundance on the millennial scale Increased cyanotoxin concentrations from harmful algal blooms (HABs) in lake systems pose a global challenge to water quality. Although progress has been made in monitoring cyanotoxins in modern environments over recent decades, identifying the triggers of cyanotoxin release by cyanobacteria has yielded mixed results from experimental and analytical studies. Paleolimnological reconstructions can reveal whole-lake long-term changes, but few studies have directly measured cyanotoxins alongside other water quality proxies. Here, we investigated the drivers of sedimentary total microcystin (MC) concentrations on millennial scales in hypereutrophic Lakes Dora and Marian in central Florida, USA. We analyzed dated sediment records using paleolimnological techniques to reconstruct nutrient deposition, cyanobacteria abundance (photosynthetic pigments), and cyanotoxins (total MCs). The objective was to investigate the linkage between MC concentrations in the sediments with both biotic (cyanobacteria and other primary producers) and abiotic factors (nutrients and climate). We found that MC production occurred throughout the ∼7000-year period, progressing from periods of moderate to low, and then to high concentrations in both lakes. Statistical analyses showed that historical MC concentrations were correlated with sedimentary measurements of total phosphorus (TP), cyanobacteria abundance, and other primary producer groups, such as cryptophytes. However, there was only a minimal correspondence with climate proxies, such as charcoal and pollen, suggesting that internal nutrient cycling and human pressures were the dominant drivers of MC deposition. Our study demonstrates that cyanotoxins have occurred for millennia in both lakes with maintained relationships to nutrients and other environmental factors that existed both in historic and modern limnological conditions.

A Comparison of Dating Models for Reservoir Sediment Records using Mass Accumulation, Radioisotopes, and Bayesian Statistics

A Comparison of Dating Models for Reservoir Sediment Records using Mass Accumulation, Radioisotopes, and Bayesian Statistics Paleolimnological investigations of reservoirs (i.e. human-made lakes) are becoming more common, establishing a need to explore dating approaches for sediment records from reservoirs. Traditional dating methodologies such as Constant Rate of Supply (CRS), 137Cs, and Mass Accumulation Rate (MAR) have been utilized for sediment records from reservoirs for decades. However, with the advent of newer Bayesian approaches, such as the Bacon and Plum models, there is a need to understand the tradeoffs between the outputs of each method. This study investigated the differences, not the accuracy, among age model outputs (dates and sedimentation rates) generated with CRS, MAR, Plum, and Bacon for three reservoirs in the Southeastern United States. Though they are all viable age models, their utility varies with research question, application, and financial cost. MAR and Bacon produced similar linear age models. The sedimentation rate for MAR was a static value throughout the record, while Bacon’s had more variable and significantly larger sedimentation rate than MAR for each reservoir studied. Both MAR and Bacon are more practical when there is a limited budget or less time for analysis. CRS and Plum produced similar non-linear age models, with CRS and Plum having the smallest and second smallest region of error, respectively. Similarly, CRS and Plum sedimentation rates exhibited aligned variations of sedimentation rates for two of the three sediment records analyzed. CRS and Plum dates and sedimentation rates were more similar when sediment records had a larger excess 210Pb total inventory. We found the smallest differences among model outputs, <5% difference based on a RMSE normalized ‘record age ratio’, when models utilized the same input data (i.e. top-bottom dates for MAR with Bacon and radioisotope for CRS with Plum). Generally, CRS and Plum would be preferred when there is ample time and funds for the lengthy radioisotope analysis and its higher costs. If there are additional known dates to incorporate into a model, we encourage the use of Plum. We have provided a decision-making framework for selecting dating models for reservoir sediment records in an effort to help standardized future dating model approaches and applications.

Data for Linking Phosphorus Dynamics with Hypereutrophic Conditions on the Millennial Scale: The Paleolimnology of Shallow and Subtropical Lake Wauberg, Florida, USA

Data for Linking Phosphorus Dynamics with Hypereutrophic Conditions on the Millennial Scale: The Paleolimnology of Shallow and Subtropical Lake Wauberg, Florida, USA Eutrophication of aquatic ecosystems results in the proliferation of harmful algal blooms (HABs), posing a global challenge to water quality and ecosystem services. Whereas eutrophication has been linked to nutrient additions of nitrogen and phosphorus in conjunction with human activities over the last few decades, much less understanding has developed on water quality trends when nutrient additions persist for centuries or even millennia. Here, we used paleolimnological techniques to reconstruct eutrophication and cyanobacteria dynamics in Lake Wauberg, FL, USA, a lake that has experienced millennial-scale nutrient additions from natural phosphate geology. We measured photosynthetic pigments, cyanotoxins, and nutrient concentrations on a sediment core spanning the last ~6,900 years of lake history. Our primary hypothesis is that the long-term total phosphorus (TP) additions caused constant cyanobacteria dominance throughout the entire history of the lake. Results show that long-term P deposition in Lake Wauberg existed within two different hydrological conditions. Focusing on the last 5 ka BP, which represent the period of constant lake conditions, photosynthetic pigments and cyanotoxins demonstrated a strong positive relationship with TP over other nutrients. By dividing TP inputs into three levels, primary producers positively increased with low and high TP inputs but showed no change under moderate levels. Under high (2.2-3 mg g⁻¹) and extreme (>3 mg g⁻¹) TP sedimentary concentrations over the last 0.3 ka BP, substantial increases in cyanobacteria abundance, rapid production of microcystins (MCs), and a possible shift to N-fixation occurred. These data show that chronic and additive TP inputs can produce asynchronous responses in the primary producer community and MC concentrations with substantial increases occurring at higher TP thresholds. Linking the historic ecological response to TP periods with current limnological conditions could provide new directions in forecasting and managing aquatic ecosystems that experience chronic TP inputs.