Limnology and Oceanography Letters最新文献

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.

Worldwide river deltas are impacted by human activities and climatic change, but it has been challenging to quantify their contributions due to nonlinear natural processes and a lack of long-term geomorphological data. Time-series bathymetric data were collected at submarine Hengsha Shoal in the Yangtze Delta during 11 repeat surveys over 60 yr. Our results show that the minimum riverine sediment supply to maintain the shoal's morphology was 229–258 Mt yr⁻¹. Without human impacts, it would have been experiencing net erosion since the operation of the Three Gorges Dam in 2003. However, this shoal has been growing in certain periods. Specifically, the accumulation/erosion during the project's period was much stronger than those during the pre- and post-projects periods. Morphological change due to deltaic engineering was as high as 19 times of that induced by sediment decline. For future research, it is critical to quantify the impact of deltaic human activities during the Anthropocene Epoch.

Anthropogenic pressures like ocean warming, acidification, rising N : P ratios, and marine heatwaves (MHWs) are affecting eukaryotic plankton diversity, though their combined impacts are rarely studied. To address this, we conducted a mesocosm experiment on a North Sea plankton community, testing the influence of a MHW under ambient and future environmental conditions. Using 18S rRNA amplicon sequencing, we found that global change generally reduced protist diversity, in particular that of phototrophic organisms. While heterotrophs were largely unaffected by heatwaves, phototrophic diversity declined especially during cooling and only recovered under ambient conditions. Global change shifted the community from nano- to pico-sized phototrophs and increased harmful algae bloom species and parasites, while heatwaves elevated marine ochrophytes. The coccolithophore Gephyrocapsa oceanica thrived under both stressors. Our findings suggest that changing baseline conditions and extreme events can differentially impact heterotrophic and phototrophic diversity, with potential consequences for the metabolic balance of eukaryotic plankton communities.

Brachiopods have been employed for environmental and climatic reconstructions in the near and geological past. Traditionally, one datapoint is obtained per shell, providing time-averaged bulk signals. However, brachiopods also have the potential to provide time-resolved information on (sub)annual timescales, but this has been understudied due to difficulties in accounting for brachiopod shell growth. We investigated the distribution of δ¹⁸O, δ¹³C and Element/Ca along growth profiles of three Recent terebratulides from temperate and polar latitudes. We employed a novel approach using the Brody–Bertalanffy equation to transform shell distances into ages, permitting the study of periodicity in the measured signatures. We show that, superimposed on ontogenetic trends, faster-growing temperate species record annual and intrannual changes at collection sites, whereas slower-growing Antarctic species are also controlled by endogenous cycles. δ¹⁸O profiles reflect annual and intrannual variations in midlatitudes and interannual variations at high latitudes. δ¹³C and Element/Ca are additionally influenced by vital effects.

Rivers produce and decompose large amounts of carbon globally due, in part, to high rates of gross primary production (GPP) and ecosystem respiration (ER), collectively known as ecosystem metabolism. Water temperature is a major driver of ecosystem metabolism, and in-stream temperatures are increasing globally, including extreme temperature events called heatwaves. This study used published estimates of daily GPP and ER from 48 stream and river locations in the United States to examine how ecosystem metabolism responds to riverine heatwaves. During low-severity heatwaves, GPP and ER increase proportionally, resulting in no net difference. However, during severe and extreme heatwaves, GPP declined up to 82% while ER increased up to 47%, resulting in greater rates of heterotrophy (ER > GPP). While rivers were typically heterotrophic outside of heatwave conditions, these results suggest that during heatwaves, rivers become stronger sources of carbon dioxide.