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- Isles, Peter D. F., et al.
(författare)
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Climate-driven changes in energy and mass inputs systematically alter nutrient concentration and stoichiometry in deep and shallow regions of Lake Champlain
- 2017
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Ingår i: Biogeochemistry. - : SPRINGER. - 0168-2563 .- 1573-515X. ; 133:2, s. 201-217
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Tidskriftsartikel (refereegranskat)abstract
- Concentrations of nitrogen (N) and phosphorus (P) in lakes may be differentially impacted by climate-driven changes in nutrient loading and by direct impacts of temperature and wind speed on internal nutrient cycling. Such changes may result in systematic shifts in lake N:P under future climate warming. We used 21 years of monitoring data to compare long-term and intra-annual trends in total N (TN), total P (TP) and TN:TP at 15 sites in Lake Champlain to concurrent measurements of watershed nutrient inputs and meteorological drivers. TN:TP declined sharply lake-wide, particularly in the past decade, yet the drivers of this trend varied based on site depth. In deep sites, declines were driven by changes in watershed loading of dissolved P and N and (in some cases) by decreases in hypolimnetic dissolved oxygen. In shallow sites, declines in TN:TP were primarily driven by long-term increases in temperature and decreases in wind speed, and exhibited systematic seasonal variability in TN:TP due to the timing of sediment P loading, N removal processes, and external nutrient inputs. We developed a conceptual model to explain the observed trends, and suggest that while climate drivers have affected nutrient dynamics in shallow and deep sites differently, both deep and shallow sites are likely to experience further declines in N:P and increases in cyanobacteria dominance if recent climate trends continue.
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| 2. |
- Isles, Peter D. F., et al.
(författare)
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Modeling the drivers of interannual variability in cyanobacterial bloom severity using self-organizing maps and high-frequency data
- 2017
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Ingår i: Inland Waters. - : TAYLOR & FRANCIS LTD. - 2044-2041 .- 2044-205X. ; 7:3, s. 333-347
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Tidskriftsartikel (refereegranskat)abstract
- It is well established that cyanobacteria populations in shallow lakes exhibit dramatic fluctuations on both interannual and intraannual timescales; however, despite extensive research, disentangling the drivers of interannual variability in bloom severity has proved challenging. Critical thresholds of abiotic drivers such as wind, irradiance, air temperature, and tributary inputs may control the development and collapse of blooms, but these thresholds are difficult to identify in large and complex datasets. In this study, we compared high-frequency estimates of oxygen metabolism in a shallow bay of Lake Champlain to concurrent measurements of physical and chemical parameters over 3 years with very different bloom dynamics. We clustered the data using supervised and unsupervised self-organizing maps to identify the environmental drivers associated with key stages of bloom development. We then used threshold analysis to identify subtle yet important thresholds of thermal stratification that drive transitions between bloom growth and decline. We found that extended periods with near-surface temperature differentials above 0.20 degrees C were associated with the initial development of bloom conditions, and subsequent frequency and timing of wind mixing events had a strong influence on interannual variability in bloom severity. The methods developed here can be widely applied to other high frequency lake monitoring datasets to identify critical thresholds controlling bloom development.
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