Cyanobacterial Bloom Development, Nitrogen Fixation and Community Change: Insights on Rapid Change From a Shallow Lake
Notice bibliographique
Résumé
ABSTRACT Nutrient‐rich lakes are highly susceptible to cyanobacterial blooms. During blooms, the consumption of dissolved inorganic nutrients can be rapid, but nitrogen (N) limitation can be mitigated through N 2 fixation by cyanobacterial diazotrophs. Despite the importance of N 2 fixation in many blooms, key gaps remain in our spatial and temporal understanding of N 2 fixation. We explored the trajectory of cyanobacterial bloom development by assessing phytoplankton community dynamics, N 2 fixation rates and physical and chemical conditions in a shallow, polymictic and eutrophic lake. Using high‐frequency sensors and discrete‐sampling measurements, we characterised the phases of the bloom and determined the importance of N 2 fixation to bloom development across one open water season. The pre‐bloom phase (defined as the period prior to rapid growth and biomass accrual) saw increases in cyanobacterial biomass (predominantly diazotrophic Dolichospermum flos‐aquae ), associated with annual maxima of photosynthetically active radiation (PAR) and water temperature. Ammonium in surface water reached a peak leading up to the major bloom, following a period of stratification. With the onset of the bloom phase, high rates of N 2 fixation (up to 3.7 μg L −1 h −1 ) were observed in surface water (0.1 or 0.3 m depth) during transient thermal stratification events which coincided with peak cyanobacterial biomass and peak N 2 fixation rates. Midway through the major bloom phase, as water temperatures and PAR decreased, we observed a shift from high biomass dominated by diazotrophs to lower biomass dominated by non‐diazotrophic taxa, predominantly the lower‐light adapted taxa Planktothrix agardhii . Nuisance surface scums are often associated with blooms in this lake and were observed across all bloom phases, although scums were most prevalent during the major bloom phase, often co‐occurring with stratification. Interestingly, taxa that dominated scums differed from the taxa that dominated the shallow water column, with Dolichospermum flos‐aquae‐ dominated surface scums seen atop Planktothrix agardhii ‐dominated phytoplankton communities at 0.3 m, indicative of fine‐scale niche differentiation. Surface scums displayed a very high potential for N 2 fixation reflecting the potential for scum formation to lead to biogeochemical hotspots and hot moments. Scum events with their extremely high rates of N 2 fixation represent an under‐studied biogeochemical hotspot that may help sustain bloom conditions. Cyanobacterial blooms demonstrate extremely high spatial and temporal variability, changing in response to environmental drivers, and driven by changes caused by blooms themselves. Scums, an understudied, but frequently observed symptom of cyanobacterial blooms, can represent sites of extreme variability, and extreme biological activity, influencing bloom dynamics through potential for extremely high rates of N 2 fixation.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».