Limnology and Oceanography Letters最新文献

Ultraviolet radiation (UV) is the most energetic waveband of incident solar radiation and has wide-ranging effects in the aquatic environment. Our analysis of an 18-year record of underwater irradiance and related limnological variables in sub-alpine, ultra-oligotrophic Lake Tahoe revealed orders of magnitude changes in UV transparency associated with interannual climate perturbations. The large-scale shifts between years were caused by pronounced changes in the loading of allochthonous particulate matter and colored dissolved organic matter associated with regional dry–wet cycles, while autochthonous factors explained the seasonal variations in UV under average weather conditions. Water clarity in the photosynthetically available radiation (PAR) waveband showed less variation, resulting in large interannual differences in the UV : PAR ratio. Clearwater lakes are likely to experience increasingly large fluctuations in underwater UV and spectral irradiance due to ongoing climate change and precipitation extremes, with potential impacts on their ecosystem structure and function.

Subterranean estuaries (i.e., seawater-fresh groundwater mixing zones at coastal aquifers) are highly reactive boundaries between continental groundwater and coastal surface seawater. Because particulate organic matter is retained in shallow sediments, internal microbial transformations rely on dissolved organic matter (DOM) supply and bioavailability. Here, we investigated DOM carbon content and optical characteristics in two nearby subterranean estuaries with contrasting oxygenation. Coastal organic carbon processing in the anoxic subterranean estuary resulted in the export of DOM enriched in recalcitrant compounds compared to the oxygenated one, which was a net sink of DOM. This contrasting behavior was not driven by opposite redox conditions but from the fast transfer of labile DOM and oxygen to the beach interior of the oxygenated subterranean estuary. There, heterotrophic processes, which rely almost exclusively on DOM, are enhanced, resulting in net DOM consumption prior discharge to surface waters.

Cobalt is a central component of cobalamins, which are nutrients essential for various metabolic processes in marine organisms. Dissolved cobalt in seawater is mostly bound to organic ligands, and the prevailing assumption to date is that these ligands are cobalamin-related compounds, yet the identity and impact of these ligands on cobalt bioavailability remain unknown. In this study, we examined cobalt ligand distributions and cobalamin cycling in surface waters across a North Pacific meridional transect. While we did not detect cobalamin derivatives in the dissolved cobalt ligand pool, the detection of transcripts associated with cobalamin synthesis and salvage pathways suggests that cobalamins may not be accumulating in seawater as cobalt-binding ligands and thus represent only a small fraction of the cobalt ligand pool in the North Pacific.

DelSontro, T., J. J. Beaulieu, and J. A. Downing. 2018. “Greenhouse Gas Emissions from Lakes and Impoundments: Upscaling in the Face of Global Change.” Limnology and Oceanography Letters 3: 64–75. https://doi.org/10.1002/lol2.10073.

In the abstract of this article, “CO₂-equivalents” should have been stated as “C-CO₂-equivalents.”

We apologize for this error.

Rivers transport ~200 Tg of particulate organic carbon (POC) to the global ocean annually, of which 30% is known to be buried in continental-shelf sediments. The fate of the remaining “missing” terrestrial POC (POC_terr) remains uncertain, with proposed explanations including rapid remineralization or transport to the remote deep ocean. Here, based on δ¹³C and ²³⁴Th tracers, we show that the vertical fluxes of POC_terr to the deep sea (~2.7 Tg C yr⁻¹) account for the “missing” portion in the northwestern Pacific marginal seas. The East China Sea and East/Japan Sea are ideal for testing this hypothesis, given substantial POC_terr inputs and extensive shelf areas connected to a semi-enclosed deep sea. We found that sediment resuspension and the refractory nature of POC_terr facilitate its effective transport to the deep sea, which serves as its major sink. These findings provide crucial insights into the fate of POC_terr in the global ocean.

Aquatic heatwaves are increasing in frequency, intensity, and duration worldwide. While increases in mean water temperatures are linked to enhanced phytoplankton biomass, it is unclear how heatwaves alter phytoplankton dynamics in lakes at an ecosystem scale. We investigated changes in surface chlorophyll during 29 summer heatwaves between 2008 and 2019 in 3 north temperate lakes. These lakes vary in staining and were either references or manipulated with nutrients and top predator additions. The manipulations provided a variety of nutrient, grazing, and light conditions during heatwave and non-heatwave conditions. Surface chlorophyll concentrations increased during 24 out of 29 heatwaves. In the low-nutrient reference lake the mean increase in chlorophyll was 57% while in the two experimental lakes the mean increases were 127% and 183%. Overall, the effects of the whole-lake experiments were variable but still provided context for possible patterns amid a diverse set of food web and nutrient conditions.

Understanding the spatial ecology of migratory species is uniquely challenging using conventional approaches. In fisheries such as for Pacific salmon, genetic stock identification (GSI) and isotope-based methods have emerged as strategies for reconstructing spatial ecology but are limited by the spatial resolution of genetic differentiation and isotopic heterogeneity. We show that integrating these complementary datasets improve the spatial resolution of provenance assignments. To do so, we reconstructed basin-wide estimates of natal origin locations for Chinook salmon in the Yukon River using samples (n = 247) from an experimental fishery designed to assess in-season run timing. A combined framework improved precision of likely provenance assignments (stream km > 0.7 posterior probability) by 92% over genetic assignments and 52% over strontium isotope methods. In doing so, we illustrate watershed scale estimates of natal origin distributions with a greater resolution available from GSI or isotope data alone.

The major marine nitrogen-fixing cyanobacterium, Crocosphaera watsonii, is restricted to warm tropical and subtropical oceans, while the underlying mechanisms remain unclear. C. watsonii fixes nitrogen (oxygen-sensitive) and carbon (oxygen-evolving) during night and day, respectively. By diel analyses of physiological rates and transcriptome at its optimal (28°C) and a lower temperature (23°C), we found that the low temperature delayed the enhancement of respiration (oxygen-consuming) and the onset of nitrogen fixation during nighttime. Transcription of the master regulator of circadian gene expression, circadian genes, and major metabolic pathways (e.g., respiration, nitrogen fixation, and photosynthesis) was delayed at the low temperature, suggesting that low temperature might decouple intracellular and environmental diurnal cycles and cause resource limitation and reduced growth. We propose that temperature might mediate the circadian clock, thereby regulating diurnal rhythm of nitrogen and carbon fixation, explaining the temperature dependence (particularly the lower thermal limit) and biogeography of C. watsonii.

The Cofán communities rely on the Cofán Bermejo Ecological Reserve for their survival and cultural practices. Due to the rugged and inaccessible topography of the reserve in the Northern Ecuadorian Amazon region, limited biomonitoring and ecological characterization studies of the ecosystem health have been conducted. We investigated the community composition and functional structure of benthic macroinvertebrates in the Bermejo River basin by identifying bioindicators and measuring physicochemical variables. Our results indicated that predators were consistently the dominant taxa in all sampled sites, and that the taxonomic abundance was positively correlated with richness and the collector taxa. We also observed positive relations between pH and taxonomic abundance, and between water temperature and the biological monitoring working party metric. Primary associations were also found between feeding guilds, pollution-sensitive taxa, and ecological water indices. This work provided a first characterization of the macroinvertebrate communities and physicochemical parameters in the Bermejo River basin.