Limnology and Oceanography Letters最新文献

In this study, we explored the realized thermal sensitivities of various phytoplankton groups in natural seawater, a crucial aspect for understanding the dynamics of marine ecosystems under climate change. Utilizing a decadal pigment dataset (2002–2015) from China Seas and employing generalized additive mixed models coupled with maximum entropy modeling, we discerned thermal sensitivity differentiations among nine phytoplankton groups, encompassing the full-size spectrum. Our findings revealed that cryptophytes were exceptionally thermally sensitive, with a strong correlation between temperature changes and biomass variance. Characterized by a preference for cooler waters, cryptophytes had a low mean temperature niche and a narrow niche breadth. Notably, they exhibited the lowest temperature tipping point, highlighting their heightened vulnerability to warming trends. These findings underscored the significance of cryptophytes, an often-overlooked group, in understanding ecosystem responses to climate shifts, and emphasized their potential role as key indicators in marine ecological studies under global warming.

Streams are significant emitters of carbon dioxide (CO₂) to the atmosphere that are influenced by diel CO₂ dynamics. However, we know little about diel CO₂ variability within streams, the diel dynamics of CO₂ in the air above streams, and the consequences for emission calculations. We studied five pre-alpine streams by equipping three sites per stream in close proximity (~ 1 km apart) with automatic logging stations that continuously recorded water and air CO₂ partial pressures (pCO₂) for 2–4 d. All streams and sites showed increased pCO₂ at night and decreased pCO₂ during the day, however, with fourfold higher diel amplitudes for atmospheric pCO₂ compared to the water. Calculating diffusive CO₂ fluxes with fixed compared to dynamic measured atmospheric CO₂ resulted in negligible to 431% lower estimates. We might thus currently overestimate fluvial CO₂ emissions and should include diel water and air CO₂ variability to more accurately assess stream CO₂ emissions.

Terrestrial groundwater travels through subterranean estuaries before reaching the sea. Groundwater-derived nutrients drive coastal water quality, primary production, and eutrophication. We determined how dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved organic nitrogen (DON) are transformed within subterranean estuaries and estimated submarine groundwater discharge (SGD) nutrient loads compiling > 10,000 groundwater samples from 216 sites worldwide. Nutrients exhibited complex, nonconservative behavior in subterranean estuaries. Fresh groundwater DIN and DIP are usually produced, and DON is consumed during transport. Median total SGD (saline and fresh) fluxes globally were 5.4, 2.6, and 0.18 Tmol yr⁻¹ for DIN, DON, and DIP, respectively. Despite large natural variability, total SGD fluxes likely exceed global riverine nutrient export. Fresh SGD is a small source of new nutrients, but saline SGD is an important source of mostly recycled nutrients. Nutrients exported via SGD via subterranean estuaries are critical to coastal biogeochemistry and a significant nutrient source to the oceans.

Giant kelp (Macrocystis pyrifera) forests are common along the California coast. Attached on the rocky bottom at depths of approximately 5–25 m, the kelp, when mature, spans the water column and develops dense, buoyant canopies that interact with waves and currents. We present two novel results based on observations of surface gravity waves in a kelp forest in Point Loma, California. First, we report short wave (1–3 s) attenuation in kelp, quantified by an exponential decay coefficient $��\alpha �\sim �O�\left(�{10}^{�-�3�}�m^{�-�1�}�\right)�$—comparable to the dampening effect of sea ice. Second, we identify seasonal and tidal changes in attenuation, peaking mid-summer with maximum kelp cover, and during low tide when a greater proportion of the fronds are at the surface. Thus, the naturally occurring surface canopies of kelp forests can act as temporally varying, high-frequency filters of wave energy.

Biodiversity generally increases productivity in ecosystems; however, this is mediated by the specific functional traits that come with biodiversity loss or gain and how these traits interact with environmental conditions. Most biodiversity studies evaluate the effects of species richness alone, despite our increasing understanding that intraspecific diversity can have equally strong impacts. Here, we manipulate both species richness and intraspecific richness (i.e., number of distinct strains) in marine diatom communities to explicitly test the relative importance of species and strain richness for biomass and trait diversity in six distinct temperature/nutrient environments. We show that species and strain richness both have significant effects on biomass and growth rates, but more importantly, they interact with each other, indicating that cross-species diversity effects depend on within-species diversity and vice versa. This intertwined relationship thus calls for more integrative approaches quantifying the relative importance of distinct biodiversity components and environmental context on ecosystem functioning.

The (sub)tropical western North Pacific is potentially an area of intense nitrogen (N₂) fixation in the global ocean, despite limited understanding of the flux and controlling factors. We conducted high-resolution observations from 2016 to 2021 in this region and used machine learning algorithms to simulate N₂ fixation flux. Models estimated an N₂ fixation flux from 5.72 to 6.45 Tg N yr⁻¹, with strong seasonal variation and peak rates in summer. The western North Pacific Subtropical Gyre and the Kuroshio Current contributed more to N₂ fixation flux than did the adjacent areas. Models suggested that sea surface temperature, photosynthetically available radiation, and nutrient supply were most strongly correlated with seasonal and spatial variations in N₂ fixation. This study provides an improved estimation of N₂ fixation in the western North Pacific and advances our understanding of its role in ocean productivity.

The PEG (Plankton Ecology Group) model predicts differences in phenology between eutrophic and oligotrophic lakes regarding the occurrence, timing and magnitude of annual chlorophyll maxima and minima. While these predictions have been tested between lakes, hardly any tests exist using long-term data. We test these predictions using chlorophyll time-series (1980–2019) from Lake Constance in which trophic status shifted from eutrophic to oligotrophic conditions. We show that oligotrophication subsequently resulted in reduction of the summer and spring blooms, and finally the loss of the clear-water phase. In contrast to the PEG model the spring bloom was not delayed, but advanced with oligotrophication. Warming modified the seasonal patterns via advancing clear-water timing. Oligotrophication did not only influence phenologies, but also the importance of independent variables driving phenologies. Thus, the decline of nutrients was the dominant factor in shaping the seasonal patterns of chlorophyll in Lake Constance during the last four decades.

Microbial biodiversity is fundamental to maintain ecosystem functioning in seasonally variable ecosystems. However, it remains unclear how alterations in water availability caused by episodic drying compromise the ability of stream microbes to maintain multiple functions simultaneously (e.g., primary production and carbon cycling). Using data from 32 streams, we investigated how the phenology of annual drying influences stream sediment microbial biodiversity and their capacity to sustain multifunctionality. Our results showed that stream multifunctionality and most bacteria did not respond to changes in drying phenology. Only two bacterial groups, the drying-resistant Sphingobacteriia and the drying-sensitive Acidobacteria_Gp7, exhibited positive associations with multifunctionality; whereas, bacterial diversity showed a negative correlation with functions. Among these biodiversity aspects, Sphingobacteriia showed the strongest capacity to maintain multifunctionality at low and moderate performance levels. Our findings will help to better understand the mechanisms through which biodiversity sustains the functioning of seasonally variable streams and their responses to global change.

Recent rapid changes in climate and environmental conditions have significantly impacted coastal ecosystem functioning. However, the complex interplay between global and local effects makes it challenging to pinpoint the primary drivers. In a multi-ecosystem study, we analyzed pluri-decadal trends of bivalve-δ¹³C as recorder of global environmental changes. These trends were correlated with large-scale natural and anthropogenic climate proxies to identify whether coastal biota responded to global effects. Our findings revealed decreasing bivalve-δ¹³C trends in all sea regions, mainly linked with increased temperature and atmospheric-CO₂ concentrations, the later generating a decrease in atmospheric-CO₂ δ¹³C values (Suess effect) because of fossil-fuel burning. After removing the Suess effect from bivalve-δ¹³C trends, ongoing global climate variability continues to affect most ecosystems, possibly intensified by combined, interacting regional or local effects. These results highlight the need to consider large-scale effects to fully understand ecosystem and food web responses to the multiple effects of global change.