A modern isotope record of changes in water and carbon budgets in a groundwater‐fed lake: Blue Lake, South Australia
Bibliographic record
Abstract
Groundwater is often a major component of lake water and chemical balances. Alteration in catchment subsurface water balances through land‐use change and pumping can affect lake biogeochemical cycles through changes in groundwater flow rates. We present a modern (~200 yr) sediment isotope record ( δ18Ocarb, δ13Ccarb, and δ13Corg) of changes to the water and carbon budget of Blue Lake, which is situated in karstic limestone in South Australia and is mostly fed by groundwater. The 3.5‰ decrease in δ18Ocarb and δ13Ccarb deposited in lake sediments since ~1850 reflects higher rates of groundwater through‐flow due to rainfall variability, land‐use change, and increased rates of pumping over the past 40 yr. Calculated water residence times, based on the isotopic data, were 23 ± 2 yr before 1850 and decreased by the late twentieth century to 8 ± 2 yr. Concomitant dissolved inorganic carbon (DIC) residence times were 3.8 and 2.2 yr, respectively. Although burial rates of CaCO3 have increased by about threefold over the past 40 yr, there is no evidence that substantial changes in organic carbon deposition has occurred. The shorter DIC residence time is largely due to increased input and higher CO2 evasion rates. About 88% of Ccarb and ~96% of Corg generated within the water column is remineralized, but the isotopic composition is essentially unaltered in the sediments. The measured variations in δ13Ccarb and δ13Corg of sediments are thought to reflect changes to DIC residence time and increased CO2(aq) concentrations rather than changes in lake productivity.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".