Due to ongoing climate change, northern lakes have become warmer. Warming is predicted to influence dissolved oxygen (DO) availability, indirectly. However, few studies have investigated this indirect role of warming as a controlling factor of DO. Here, we experimentally tested impacts of warming (+ 3 C) on DO availability of four enclosures compared to four ambient-condition enclosures. The results showed that DO is significantly lower in the heated enclosures compared to the ambient, rather than light availability (PAR) was higher in the heated enclosures during the experiment. DO in both groups of enclosures was significantly correlated to water temperature (WT) and phytoplankton chlorophyll-a (Chl-a) concentration, not to PAR and nutrients. While phytoplankton Chl-a was not correlated to nutrient concentrations, it was negatively impacted by warming treatment compared to ambient enclosures. We can conclude that warming, rather than nutrient availability and increased PAR, could indirectly reduce DO for the whole-ecosystem in shallow lakes. Our results confirm the idea of including primary trophic levels in the studies that trying to understand drivers of DO availability with ongoing climate warming, especially, in shallow lake ecosystems.
The first results obtained by the numerical physicochemical modeling of uranium and thorium behavior in the radon-rich waters of southern Siberia are presented. The studied waters are characterized by a wide variation of geochemical parameters (pH varies from 5.9 to 10.1; Eh from − 500 to + 285 mV), have diverse chemical composition, with dominating HCO3 Mg–Ca, HCO3 Na–Ca and Cl–SO4 –HCO3 Na, SO4–HCO3 Na–Mg–Ca types, with TDS value varying from 0.2 to 2.6 g/dm3 and silicon content 0.52–32.90 mg/dm3. The possibility for uranium minerals to be formed from the radioactive waters of southern Siberia has been established: In particular, uraninite and thorianite can be most actively precipitated within rather broad range of redox conditions, while uranium black is to occur less frequently. The possibility for thorium minerals to occur in trace amounts is also determined, with thorianite ThO2 as the most probable one. At pH values around 5, the formation of thorium sulfate Th(SO4)2 is also possible. In an acidic, strongly reducing environment with Eh < − 300 mV, trace amounts of ThS2 and Th2S3 may be deposited.
This study investigated the sources of carbon and nitrogen in a small, silicate-dominated catchment (Oplotnica River, Pohorje, Slovenia) with two creeks, Lukanjski and Javorski, from 2012 to 2014. Additionally, carbon and nitrogen cycling in soil profiles was studied at Javorski Creek. Isotopic analyses of river water, particulates, and sediments provided a more holistic view of the sources of carbon and nitrogen, weathering contributions, and the evasion or sequestration of CO2 in the atmosphere within the catchments. The weathering of rocks, such as granodiorite and quartz diorite, influences water geochemistry. The Oplotnica River and its tributaries were characterized by the ion composition: Na+ > Ca2+ > Mg2+ > K+ and HCO3− > SO42− > Cl− > NO3−. Partial pressure of CO2 concentrations in river and creeks ranged from 1.1 to 13.4 times that of atmospheric pressure, representing a source of CO2 to the atmosphere. The carbon isotope value of dissolved inorganic carbon (δ13CDIC) ranged from − 9.8 to − 1.4‰ in river, while in the creeks, it ranged from − 26.1 to − 4.7‰, reflecting the degradation of organic matter and exchange with the atmosphere. The intensity of bicarbonate weathering for the Oplotnica River at its gauging station was 10.4 mmol/(l⋅km2⋅s), characteristic of silicate watersheds. The isotopic composition of carbon (δ13C) and nitrogen (δ15N) in river sediments reflects values typical of soil and temperate (C3) plants. This study is significant on both local and global levels, as it addresses the contribution of weathering rates and the release of CO2 to the atmosphere from small silicate watersheds.
In the face of rapidly compounding climate change impacts, including ocean acidification (OA), it is critical to understand present-day stress exposure and to anticipate the biogeochemical conditions experienced by vulnerable ecosystems like coral reefs. To meaningfully predict nearshore carbonate chemistry, we must account for the complexity of the local benthic community, as well as connectivity between habitats and relevant endmember carbonate chemistry. Here, we adopt a system-scale approach to predict site-scale effects of benthic metabolism on the carbonate system of the Florida Reef Tract (FRT). We utilize bimonthly carbonate chemistry data from ten cross-shelf transects spanning 250 km of the FRT to model changes in dissolved inorganic carbon (DIC) and total alkalinity (TA). Benthic habitat maps were used to broadly classify communities known to impact carbonate chemistry. A SLIM 2D hydrodynamic model with mesh resolution reaching 100 m over reefs and along the coastline was used to determine the relevant water mass histories and identify the upstream benthic communities shaping local carbonate chemistry. These historical metabolic footprints, or “flowsheds”, were used to build predictive models of the change in DIC and TA at each station. The best predictive models included the chemical impacts of benthic ecosystem metabolism, as defined by water mass trajectories, weighted endmember chemistry, volume, time, and other environmental parameters (light, temperature, salinity, chlorophyll-a, and nitrate). Considering water mass for 5 days prior to sample collection yielded the highest model skill.
The elemental records of the sediments from two IODP cores, U1501C (Oligocene and Late Miocene-Pliocene) and U1499A (Pliocene to Pleistocene) in the Northern South China Sea have been studied here to understand the variability in the sedimentary provenance and depositional environment, which are impacted by the tectonic and East Asian monsoon evolution through time. The major oxides and REE abundances indicate the sources of sediment influx to be significantly from the South China, North and North eastern parts of SCS since 33 Ma, and prominent contributions from Pearl River, Hainan Island and Taiwanese rivers since 8.3 Ma. The depositional redox is corroborated by the Ce anomaly and trace element proxies such as U/Th, V/Cr, V/(V + Ni), and Ni/Co. The chemical weathering intensity, evidenced by the Chemical Index of Alteration and major elements (Ca/Ti, Na/Ti, Al/K, Al/Ti, AL/Na), and La/Sm ratios, was observed to be low. Early Oligocene witnessed the deposition of littoral sediments, caused by the initial rifting and spreading in SCS. During the late Miocene ( 8.3 Ma), sedimentation was influenced by the prevailing arid climate and intensification of East Asian Winter monsoon (EAWM). Since Pliocene–Pleistocene ( 5.3 Ma−0.01 Ma), the sediment deposition remained unaffected by tectonism, but was majorly influenced by the intensification of EAWM and the glacial-interglacial cycles.
