Contrasting seasonal cycling of arsenic in a series of subarctic shield lakes with different morphometric properties

The subarctic shield near Yellowknife, Northwest Territories (NWT), is populated with thousands of small lakes (\u3c1.5 km2) and several large lakes. Historic mining activities in the region have left a legacy of environmental impacts and widespread arsenic (As) contamination in both aquatic and terrestrial environments. In particular, several small subarctic lakes near Yellowknife have been previously documented to be contaminated with high levels of As. Subarctic lakes are characterized by seasonal ice-cover that can persist for more than half of the year, yet little is known about the under-ice spatial and seasonal dynamics of As cycling. The objective of this study is to contrast seasonal changes in As cycling within and among a series of lakes with different basin morphologies during ice-cover and into the ice-free seasons. In this study, a combination of data including water profile sampling, sediment cores, snow and ice measurements, and bathymetric mapping were collected in four lakes from November 2020 to October 2021. Continuous monitoring of lake physical properties (dissolved oxygen, temperature, and light) was conducted via data loggers installed at 1 m depth intervals in each lakes’ water column. Detailed profiles of water chemistry were collected monthly at the deepest part of each lake, examining numerous key water chemistry elements with a focus on dissolved and particulate As concentrations. Key results from this study indicated: 1) Distinct seasonal variation in As over the ice-on and open-water periods, 2) The important role of lake mixing regimes in the mobility of As, 3) Field evidence of Fe attenuation of As from the water column. This project contributes important information on the winter cycling of As, which will help to inform our understanding of the chemical recovery of subarctic lakes from As pollution

Fluctuating light takes crop photosynthesis on a rollercoaster ride

Crops are regularly exposed to frequent irradiance fluctuations, which20 decrease their integrated CO2 assimilation and affect their phenotyp

Blue light dose–responses of leaf photosynthesis, morphology, and chemical composition of Cucumis sativus grown under different combinations of red and blue light

The blue part of the light spectrum has been associated with leaf characteristics which also develop under high irradiances. In this study blue light dose–response curves were made for the photosynthetic properties and related developmental characteristics of cucumber leaves that were grown at an equal irradiance under seven different combinations of red and blue light provided by light-emitting diodes. Only the leaves developed under red light alone (0% blue) displayed dysfunctional photosynthetic operation, characterized by a suboptimal and heterogeneously distributed dark-adapted Fv/Fm, a stomatal conductance unresponsive to irradiance, and a relatively low light-limited quantum yield for CO2 fixation. Only 7% blue light was sufficient to prevent any overt dysfunctional photosynthesis, which can be considered a qualitatively blue light effect. The photosynthetic capacity (Amax) was twice as high for leaves grown at 7% blue compared with 0% blue, and continued to increase with increasing blue percentage during growth measured up to 50% blue. At 100% blue, Amax was lower but photosynthetic functioning was normal. The increase in Amax with blue percentage (0–50%) was associated with an increase in leaf mass per unit leaf area (LMA), nitrogen (N) content per area, chlorophyll (Chl) content per area, and stomatal conductance. Above 15% blue, the parameters Amax, LMA, Chl content, photosynthetic N use efficiency, and the Chl:N ratio had a comparable relationship as reported for leaf responses to irradiance intensity. It is concluded that blue light during growth is qualitatively required for normal photosynthetic functioning and quantitatively mediates leaf responses resembling those to irradiance intensity

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Chlorophyll fluorescence as a tool for describing the operation and regulation of photosynthesis in vivo

In very broad terms, photosynthesis begins with the absorption of light (the photosynthetically active kind) and ends with assimilation—the fixation of CO2—a process that is fundamental to trophic networks in the biosphere. In between the absorption of light and the act of assimilation, there are the intermediate processes of photosynthesis: photochemistry, electron transport and energy transduction, metabolism, and gaseous diffusion processes. The rate of assimilation will ultimately be determined by the limiting activity of these processes. There are also complex regulatory networks that coordinate the activities of the many subprocesses of photosynthesis whose combined activity is necessary for assimilation. To understand the relationship between light absorption and assimilation, it is necessary to understand operation of the intermediate processes, how they interact with each other, and how they individually or collectively limit the overall efficiency of assimilation. In this chapter, we will describe the principles and use of a major, widely used nondestructive method for measuring the operation and regulation of PSII not only in leaves and similar photosynthetic plant tissues but also in in vitro samples: steady-state chlorophyll fluorescence

A model for the irradiance responses of photosynthesis

The analysis of the irradiance responses of photosynthetic processes, such as the quantum efficiencies of electron transport by photosystems I and II (PSI and PSII) or the rate of carbon dioxide fixation, is limited by the lack of mechanistically based analytical model for these processes. Starting with a model of P700 redox state, we develop a series of analytical functions which can be used to fit the irradiance responses of the quantum yields for electron transport by PSI and PSII, the irradiance responses of electron transport by PSI and PSII, and even the irradiance response of the fixation rate of carbon dioxide. These functions depend on two or three parameters so they can be fit to typical irradiance response data. We illustrate by example the use of these functions in various applications and discuss further use and development of the basic model described in detail here