https://aurora.auburn.edu/handle/11200/49375 2026-04-04T23:25:52Z https://aurora.auburn.edu/handle/11200/50761 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. https://aurora.auburn.edu/handle/11200/50745 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. https://aurora.auburn.edu/handle/11200/50728 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. https://aurora.auburn.edu/handle/11200/50691 Long-term research on hedgerow pruning management for alley cropping in Haiti: implications for soil fertility maintenance and sustainability in low resource farming in the tropics One of the basic concepts of alley cropping as practiced in the tropics is that the leaves and stems are used to add nitrogen and organic matter to the soil and recycle other plant nutrients. As I discussed the system with project leaders, I was made aware that the leaves and small stems of the trees were being removed to feed livestock or the hedgerows were heavily grazed by livestock. One of the purposes of designing this trial was to demonstrate the benefits to the crop of applying the hedgerow prunings to the alleys rather than removing them to feed livestock. Because of previous experience carrying out an alley cropping experiment in the Democratic Republic of Congo, I had become aware of the importance of managing the competition between the tree hedgerows and the associated crop through the timing of pruning operations. Therefore, I also felt it important to focus on identifying the proper timing and frequency of pruning operations during a growing season. Although this research was carried out in Haiti, the results relating to hedgerow management will be beneficial to those practicing alley cropping in other areas of the tropical world. In 1990, this study was designed to carry out agroforestry research in Haiti in support of extension activities of two development agencies, CARE International and the Pan American Development Foundation (PADF), as part of the Agroforestry II project, funded by USAID. The primary focus of the project was tree planting on agricultural lands, but the project also promoted planting of leguminous trees as hedgerows for soil conservation on sloping land. Food crops were planted between the hedgerows. My assignment was to design trials that would address the needs of CARE and PADF with respect to tree hedgerows. Success of the hedgerow planting effort in the project was reported in terms of “soil saved,” with the assumption that by preventing soil loss and planting leguminous trees, they were also improving soil fertility. That was a questionable assumption given the way in which the hedgerows were managed.