Compound Specific Isotope Analysis of Invertebrate Tissues: Determining Nitrogen Variability in Coastal Nova Scotia
Bibliographic record
Abstract
Anthropogenic nitrogen (N) loading in coastal marine environments causes eutrophication, alters food web structures, and degrades water quality. In Nova Scotia, anthropogenic N sources are introduced to coastal waters through multiple sources including sewage wastewater outfalls, seafood processing, aquaculture, and agricultural runo . Di erent N sources have characteristic isotopic ( 15N) signatures that can be traced using bioindicator organisms to map the spatial variability of 15N along the coastline. Organisms such as the blue mussel (Mytilus edulis) integrate the isotopic 15N composition of their local environment by feeding on particulate organic matter and integrating it into their tissues over several months. Mussels are ideal bio-indicators for this study because they are sessile organisms that are found along the rocky intertidal zone of the province's coastline, preserving the biogeochemical variability of their collection sites. This allows us to map the spatial variability of 15N to help identify sources of N in a region with few previous N measurements. Specimens of M. edulis were collected in triplicate from 21 sites across the province's Atlantic and Northumberland coasts. The adductor muscle of M. edulis was isolated from the rest of the tissue, removed, and freeze-dried for 15N analysis. Within-site variability was considerably low (mean of standard deviation = 0.56‰), indicating narrow variability within specimens at each site. There was, however, a wide range of mean 15N values between sites, ranging from 6.80 ± 0.27 ‰ to 11.08 ± 1.00 ‰ (n=21). To re ne these baseline 15N estimates independent of trophic fractionation, 8 sites with the largest 15N ranges were selected for compound speci c isotope analysis (CSI-AA). Amino acids were isolated for 15N analysis through acid hydrolysis, cation exchange and isopropyl TFAA derivatization. Individual amino acid values ranged from -7.5 ‰ to 18.1 ‰ (SD=5.5; n=250). Phenylalanine (Phe) is the best amino acid proxy for baseline 15N Phe values and ranged from 2.4 ± 1.2 ‰ to 7.8 ± 0.9 ‰; n=22. This variability re ects similar trends in the bulk 15N values, indicating that the local variability seen in M. edulis 15N likely re ects inputs of di erent nitrogen sources speci c to each sample site. This study pairs the novel CSI-AA approach with traditional nutrient data and bulk 15N analysis to generate estimates of baseline 15N variability for the Northumberland and Atlantic coasts of Nova Scotia.
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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 | 0.001 | 0.001 |
| 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".