Relationship between toxic cyanobacterial blooms, physico-chemical factors and multiple source excreta contamination in affected watershed
Notice bibliographique
Résumé
Missisquoi Bay (MB) is a temperate eutrophic freshwater ecosystem located in an agricultural watershed and it frequently experiences toxic Microcystis-dominated cyanobacterial blooms. Cyanobacterial population dynamics are influenced by a plethora of factors that may differ from system to system, requiring a site-specific assessment of bloom-promoting factors to design more effective bloom prevention or remediation strategies. This is the first biomonitoring study that combined data from high-throughput 16S rRNA gene amplicon sequencing, qPCR and environmental parameters from temporal and spatial samples to identify the main bloom-promoting factors. In addition, high-throughput amplicon sequencing of mitochondrial DNA genes was performed to qualitatively identify potential external sources of nutrients originating from animal excreta. Particular emphasis was placed on 1) determining whether there was a link between nutrients from external sources and cyanobacterial blooms and 2) analyzing in situ the effect of environmental factors (particularly nitrogen (N) and phosphorus (P) concentrations) on the dynamics of cyanobacterial community composition, abundance and toxicity.The concentrations of total P (TP) and total N (TN) in MB in 2009 correlated significantly with the abundance of total cyanobacterial cells, the Microcystis 16S rRNA and mcyD genes and intracellular microcystin. The results suggest that external sources of nutrients, such as surface runoff and animal excreta, played a significant role in the load of nutrients into the bay and thus in the proliferation of toxic cyanobacterial blooms. This was indicated by the detection of non-aquatic mitochondrial DNA hosts in the bay and the relationships between the pattern of surface runoff, nutrient concentrations, E. coli counts and total cyanobacterial abundance. Potential sources of nutrients from non-aquatic animal excreta in the system comprised rodents, birds, cattle and humans, indicating that efforts are required to control pollution from animal excreta in MB. During the growing season, the major cyanobacterial taxa were members of the orders Chroococcales and Nostocales. The genus Microcystis was identified as the main mcyD-carrier and main microcystin producer, hence the most problematic taxon in the cyanobacterial bloom. The correlations observed with environmental parameters suggest that increasing nutrient concentrations and TN:TP (mass) ratios approaching 11:1, coupled with an increase in temperature, promoted Microcystis-dominated toxic cyanobacterial blooms. Although the importance of nutrient ratios and absolute concentrations on cyanobacterial and Microcystis dynamics has been documented, this is the first time that an optimum TN:TP ratio for Microcystis dominance has been observed in the field. This observation provides further support to the theory that nutrient supply ratios are an important determinant of species composition in natural phytoplankton assemblages. Although the validity and prediction potential of this optimum ratio for Microcystis dominance has yet to be verified through longer-term studies, it may provide practical guidelines for nutrient management strategies to avoid the proliferation of this toxin producing cyanobacterial genus in MB.
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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) | 0,000 | 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 ».