Dissolved organic carbon mobilized from organic horizons of mature and harvested black spruce plots in a mesic boreal region
Bibliographic record
Abstract
Abstract. Boreal forests are subject to a wide range of temporally and spatially variable environmental conditions driven by seasonal and regional climate variations, in addition to disturbances such as forest harvesting and climate change. Among the various ecological mechanisms affected by disturbance, is the transport rate of dissolved organic carbon (DOC) from surface soil organic (O) horizons to deeper mineral SOC pools and the adjacent aquatic systems. Here, we examine the transport of DOC from surface O horizons across a boreal forest landscape using passive pan lysimeters in order to identify controls and hot moments of DOC mobilization from this key C source. To do so, we specifically addressed (1) how DOC fluxes from O horizons vary on a weekly to seasonal basis in both forest and harvested plots, and (2) how soil temperature, soil moisture and water inputs relate to DOC fluxes in these plots over time. The total annual DOC flux from O horizons was greater in the warmer harvested plots than in the forest plots (54 g C m−2 vs 38 g C m−2 respectively; p = 0.008), despite smaller aboveground C inputs and smaller SOC stocks in the harvested plots. Water input, measured as rain, throughfall and/or snowmelt depending on season, was positively correlated to temporal variations in soil water and DOC fluxes. Soil temperature was positively correlated to temporal variations of DOC concentration ([DOC]) of soil water and negatively correlated with water fluxes, but no relationship existed between soil temperature and DOC fluxes. Soil moisture was negatively correlated to temporal variations in [DOC] in the harvested plots only. The relationship between water input to soil and DOC fluxes was seasonally dependent in both plot types. In summer, a water limitation on DOC flux existed where weekly periods of no flux alternated with periods of large fluxes, suggesting that increased water fluxes over this period would result in proportional increases in DOC fluxes. In contrast, a flushing of O horizons occurred during increasing water inputs and decreasing soil temperatures in autumn, prior to snowpack development. Soils of both plot types remained snow-covered all winter, which protected soils from frost and limited winter soil water fluxes. The largest water input and soil water fluxes occurred during spring snowmelt, but did not result in the largest fluxes of DOC, suggesting a production limitation on DOC fluxes over both the wet autumn and snowmelt periods. While future increases in annual precipitation could lead to increased DOC fluxes, the response may be dependent on the intra-annual distribution of this increase. Increased water input during the already wet autumn, for instance, may not lead to increased fluxes if the DOC pool is not replenished. Potential reductions in snow cover, however, leading to a reduction in soil insulation and increased occurrence of soil frost in addition to increases in winter-time water fluxes, could be an important mechanism of increased DOC production and fluxes from O horizons in winter.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".