The concentration of dissolved oxygen in aquatic systems helps to regulate biodiversity1'2, nutrient biogeochemistry3, greenhouse gas emissions4, and the quality of drinking water5. The long-term ...declines in dissolved oxygen concentrations in coastal and ocean waters have been linked to climate warming and human activity6,7, but little is known about the changes in dissolved oxygen concentrations in lakes. Although the solubility of dissolved oxygen decreases with increasing water temperatures, long-term lake trajectories are difficult to predict. Oxygen losses in warming lakes may be amplified by enhanced decomposition and stronger thermal stratification8,9 or oxygen may increase as a result of enhanced primary production10. Here we analyse a combined total of45,148 dissolved oxygen and temperature profiles and calculate trends for 393 temperate lakes that span 1941 to 2017. We find that a decline in dissolved oxygen is widespread in surface and deep-water habitats. The decline in surface waters is primarily associated with reduced solubility under warmer water temperatures, although dissolved oxygen in surface waters increased in a subset of highly productive warming lakes, probably owing to increasing production of phytoplankton. By contrast, the decline in deep waters is associated with stronger thermal stratification and loss of water clarity, but not with changes in gas solubility. Our results suggest that climate change and declining water clarity have altered the physical and chemical environment of lakes. Declines in dissolved oxygen in freshwater are 2.75 to 9.3 times greater than observed in the world's oceans6,7 and could threaten essential lake ecosystem services2,3,5'11.
The concentration of dissolved oxygen (DO) is an important attribute of aquatic ecosystems, influencing habitat, drinking water quality, biodiversity, nutrient biogeochemistry, and greenhouse gas ...emissions. While average summer DO concentrations are declining in lakes across the temperate zone, much remains unknown about seasonal factors contributing to deepwater DO losses. It is unclear whether declines are related to increasing rates of seasonal DO depletion or changes in seasonal stratification that limit re‐oxygenation of deep waters. Furthermore, despite the presence of important biological and ecological DO thresholds, there has been no large‐scale assessment of changes in the amount of habitat crossing these thresholds, limiting the ability to understand the consequences of observed DO losses. We used a dataset from >400 widely distributed lakes to identify the drivers of DO losses and quantify the frequency and volume of lake water crossing biologically and ecologically important threshold concentrations ranging from 5 to 0.5 mg/L. Our results show that while there were no consistent changes over time in seasonal DO depletion rates, over three‐quarters of lakes exhibited an increase in the duration of stratification, providing more time for seasonal deepwater DO depletion to occur. As a result, most lakes have experienced summertime increases in the amount of water below all examined thresholds in deepwater DO concentration, with increases in the proportion of the water column below thresholds ranging between 0.9% and 1.7% per decade. In the 30‐day period preceding the end of stratification, increases were greater at >2.2% per decade and >70% of analyzed lakes experienced increases in the amount of oxygen‐depleted water. These results indicate ongoing climate‐induced increases in the duration of stratification have already contributed to reduction of habitat for many species, likely increased internal nutrient loading, and otherwise altered lake chemistry. Future warming is likely to exacerbate these trends.
A study of more than 400 lakes revealed climatic warming contributed to an increase in stratification duration along with greater volumes of oxygen‐depleted water during the summer. This will likely reduce habitat availability, increase internal nutrient loading, and otherwise alter lake chemistry. Further warming will exacerbate these trends.
Lake surface temperatures are warming in many regions and have the potential to alter seasonal thermal stratification. However, the effects of climate change on thermal stratification can be ...difficult to characterize because trends in thermal stratification can be regulated by changes in multiple climate variables and other characteristics, such as water clarity. Here, we use long‐term (1993–2017) data from near‐pristine Crater Lake (Oregon) to understand long‐term changes in the depth and strength of summer stratification, measured by the center of buoyancy and Schmidt Stability, respectively. The depth of stratification has shoaled significantly (2.4 m decade−1), while stratification strength exhibited no long‐term trend. Empirical observations and modeling scenarios demonstrate that atmospheric stilling at Crater Lake is associated with the 25‐year shoaling trend as spring wind speeds declined over the observation period. While summer lake surface water and air temperatures warmed during the study period, spring air temperatures were variable and correlated with summer Schmidt Stability. Our results indicate that warmer spring air temperature resulted in earlier onset of stratification and stronger summer stratification. The observed shoaling of stratification depth at Crater Lake may have important ecological consequences, especially for non‐motile primary producers who can become constrained within a thinner epilimnion and exposed to higher solar radiation and reduced upwelling of nutrients. Driven by climate changes, many large lakes may be experiencing similar trends in seasonal stratification.
Widespread long‐term increases in dissolved organic carbon (DOC) concentrations (i.e., “browning”) have been observed in many lakes, but the ecological consequences are poorly understood. Some ...studies suggest a unimodal relationship between DOC and primary productivity, with peak productivity at intermediate DOC concentrations. This peak is hypothesized to result from the tradeoff between light absorbing properties of DOC, and increases in limiting nutrients with browning. Nevertheless, it is unclear whether nutrient stoichiometry is constant as lakes brown. Across both regional and national surveys, we found a positive linear relationship between DOC and both total and organic forms of nitrogen and phosphorus. However, long‐term data from a suite of browning lakes indicates that total nutrients do not increase as DOC increases through time. Our results show that DOC and limiting nutrients are coupled spatially, but not temporally, and that this temporal mismatch challenges previous conceptualizations of the long‐term effects of browning on productivity.
Freshwater is a vital natural resource currently under threat from multiple anthropogenic stressors. The effects of watershed and atmospheric disturbances often present themselves in lakes, given ...their deep-lying position within a watershed. Water transparency in many north-temperate lakes is rapidly decreasing due to increasing loads of terrestrial dissolved organic matter (“DOM”); commonly referred to as lake browning. At the same time, the planet is undergoing rapid and widespread changes in climate. Lake surface temperatures are warming at record rates following increases in air temperatures. Further, wide-spread declines in surface wind speeds have been observed across much of the northern hemisphere; a phenomenon referred to as “atmospheric stilling”. Watershed and atmospheric changes can fundamentally alter lake ecosystem structure and function, which in turn will reduce many of the ecosystem services lakes provide such as safe drinking water, angling, and recreational opportunities. This dissertation investigates how changes in water transparency and climate interact to alter physical and chemical lake features, and further examines how these changes will ultimately alter habitat availability and growth rates of common sport fish.Though a clear pattern has been shown between lake surface temperatures and climate warming, less is known about how the multiple factors of climate change affect summer thermal stratification. Summer stratification depth and strength are two characteristics that regulate many in-lake processes including the creation of a distinct vertical thermal gradient, which strongly regulates the distribution of many organisms. Understanding the role climate plays on stratification depth and strength can be difficult because non-climate factors like water transparency can strongly influence stratification features. In the first study, I utilized a lake in a protected National Park as a case study in order to isolate the effects of climate change on stratification depth and strength. Crater Lake is a near-pristine lake which has exhibited little changes in water transparency and watershed land use over the last 25 years. I examined long-term trends in water temperature profiles and meteorological conditions to determine how summer stratification characteristics changed from 1993 to 2017. I next calibrated a hydrodynamic model and performed scenarios to investigate how changes in climate variables (mainly air temperature and windspeed) alter stratification characteristics. Summer depth and strength of stratification were regulated by different climate variables. I found that the depth of stratification decreased by 55% across the 25-year period, and that this decline was most likely driven by a decrease in wind speeds. While there was no clear long-term pattern in summer stratification strength, I found variability in stratification strength was largely driven by variation in air temperature, with warmer air temperatures resulting in stronger stratification. Notably, I found that spring time conditions in both wind speed and air temperature strongly influenced summer stratification characteristics. Since wind speeds are declining elsewhere and air temperatures are warming across the globe, other large lakes may be experiencing similar stratification changes.North temperate lakes have been browning across North America and Europe following recovery from acid deposition, and changes in precipitation and land use practices. Browning associated decreases in water transparency can strongly influence lake productivity due to the light absorbing nature of DOM. However, limiting nutrients (i.e., phosphorus and nitrogen) could be associated with DOM, which may help compensate for the negative light absorbing effects of DOM on lake productivity. I utilized two spatial surveys across the United States and a long-term lake survey of 28 lakes in the Adirondacks to understand how limiting nutrients and DOM characteristics were related. Across space, limiting nutrients were strongly positively related with DOM concentrations (quantified here as dissolved organic carbon concentration; “DOC”) and DOM specific absorbance. Adirondack lakes strongly increased in DOC concentration and became browner from 1994 to 2012, but limiting nutrients did not increase. Instead, phosphorus concentrations largely stayed the same while nitrogen concentrations decreased. Further, modeling of lake photosynthetic potential in each of the 28 lakes indicates that most lakes have likely decreased in whole-lake productivity from 1994-2012. Contrasting trends in DOM and limiting nutrients suggests that the strongest effect of lake browning will likely be a decrease in lake productivity through time.Many north temperate lakes are warming and browning at the same time. Both warming temperatures and decreases in water transparency have the potential to threaten lake dissolved oxygen (“DO”) levels. The relative importance of each driver and the combined effects of warming and browning are not well understood. The third study investigates how warming air temperatures and browning affect DO levels via hydrodynamic and biogeochemical modeling scenarios across a 30-year period (1990 – 2019). I calibrated a hydrodynamic and coupled biogeochemical model to Lake Giles in Pennsylvania. Lake Giles has a robust long-term data record and is a small oligotrophic lake, which is representative of many north temperate lakes. After model validation, I recreated Lake Giles across three different initial DOC concentrations to represent a wide initial range of DOC. For each of the three lakes, I simulated trends in browning and climate warming across the 30-year period and calculated annual summer DO metrics. Lakes with more DOC tended to have less DO. Browning tended to reduce DO in clear lakes quicker than in lakes with higher initial DOC concentrations. Climate warming had a smaller negative effect on DO concentrations. Browning increased the prevalence of anoxia and hypoxia in the summer, and the combined browning and warming scenarios generated the highest levels of summer anoxia and hypoxia. An increase in DOC from 1 to 5 mg L-1 shifted the onset of anoxia and hypoxia up to one and half months earlier. This study has major water quality implications, as the onset of anoxia and hypoxia can release nutrients stored in the sediments, which can fuel algae blooms in the surface waters.Browning traps more heat at the lake surface, which leads to warmer surface waters and cooler deep waters in the summer. Fish are ectotherms, and as such many functions including metabolism and growth are temperature dependent. Browning therefore has the potential to alter growth rates in fish. In this last study, I again used Lake Giles as a case study. I used a hydrodynamic model to recreate Lake Giles at different DOC concentrations from 1 to 15 mg L-1 during a typical year. I then examined how the growth of two common fish with different temperature preferences varied in response to browning-induced changes in water temperature. Largemouth Bass (Micropterus salmoides) are a common warm-water species present in many north temperate lakes. As DOC concentrations increased, summer surface temperatures warmed and shifted closer to bass optimal temperatures. Thus, increases in DOC led to larger growth rates for bass, most noticeable in the 1 to 3 mg L-1 range. Brook Trout (Salvelinus fontinalis) are a common cold-water sport fish that inhabits deeper parts of the lake in the summer. Browning led to a slight decrease in deep water temperatures, especially in the spring. As a result, trout growth in the spring slightly reduced with browning, but the overall affects were minimal. Though trout growth was minimally affected by DOC, I estimated that trout would have to move shallower in the water column to track their preferred temperature, which could lead to changes in behavior and interspecific competition. Overall, I found differential effects of lake browning on fish growth via temperature depending on fish type (i.e., warm-water vs cold-water fish). Lakes may become dominated by warm water species as lakes continue to brown if food supplies remain suitable.
Sensory systems transform the external world into time-varying spike trains. What features of spiking activity are used to guide behavior? In the mouse olfactory bulb, inhalation of different odors ...leads to changes in the set of neurons activated, as well as when neurons are activated relative to each other (synchrony) and the onset of inhalation (latency). To explore the relevance of each mode of information transmission, we probed the sensitivity of mice to perturbations across each stimulus dimension (i.e., rate, synchrony, and latency) using holographic two-photon optogenetic stimulation of olfactory bulb neurons with cellular and single-action-potential resolution. We found that mice can detect single action potentials evoked synchronously across <20 olfactory bulb neurons. Further, we discovered that detection depends strongly on the synchrony of activation across neurons, but not the latency relative to inhalation.
•Perceptual detection of neural stimulation probed by two-photon holographic optogenetics•Mice can reliably detect single action potentials across <20 olfactory bulb neurons•Detection depends strongly on neuronal synchrony, but not latency relative to inhalation
Using two-photon holographic optogenetics, Gill, Lerman et al. show that mice can reliably detect single spikes across small sets of targeted olfactory bulb neurons. They find that detection performance depends strongly on neuronal synchrony, but not on latency relative to inhalation.
We evaluated the ability of several outcome prognostic scales to predict poor 1-year outcomes and mortality after endovascular thrombectomy.
In this retrospective analysis from the stroke registry of ...a large integrated health system, consecutive patients presenting from August 2020 to September 2021 with an anterior circulation large-vessel occlusion stroke treated with endovascular thrombectomy were included. Multivariable logistic regression was performed to determine the ability of each scale to predict the primary outcome (1-year modified Rankin Scale mRS score of 4–6) and the secondary outcome (1-year mortality). Area under the curve analyses were performed for each scale.
In 237 included patients (mean age 68 ±15 years; median National Institutes of Health Stroke Scale score 16 11–21), poor 1-year outcomes were present in 116 patients (49%) and 1-year mortality was 34%. The CLEOS (Charlotte Large Artery Occlusion Endovascular Therapy Outcome Score), which incorporates age, baseline National Institutes of Health Stroke Scale score, initial glucose level, and computed tomography perfusion cerebral blood volume index, had a significant association with poor 1-year outcomes (per 25-point increase; odds ratio, 1.0134; P = 0.02). CLEOS and PRE (Pittsburgh Response to Endovascular Therapy) were both significantly associated with 1-year mortality. Area under the curve values were comparable for CLEOS, PRE, Houston Intra-Arterial Therapy 2, and Totaled Health Risks in Vascular Events to predict 1-year mRS score 4–6 and mortality. Only 1 of 18 patients with CLEOS ≥690 had a 1-year mRS score of 0–3.
CLEOS can predict poor 1-year outcomes and mortality for patients with anterior circulation large-vessel occlusion using prethrombectomy variables.
Decompressive hemicraniectomy (DHC) is a treatment of space-occupying hemispheric infarct. Current surgical guidelines use criteria of age <60 years and surgery within 48 hours of stroke onset.
The ...purpose of this study was to evaluate the neurologic outcome after DHC and evaluate the relationship of stroke volume and outcomes.
A retrospective review was performed of patients undergoing DHC for cerebral infarct from 2016 to 2019. Unfavorable outcome was defined as modified Rankin Scale (mRS) score >3. Patients with precraniectomy magnetic resonance imaging were selected as a subset for volumetric stroke volume analysis using RAPID software (iSchemaView, Redwood City, California), with stroke volume defined as apparent diffusion coefficient <620 on diffusion-weighted imaging.
Fifty-two patients met the inclusion criteria. At 90 days, favorable outcome was achieved in 11 patients (21.2%), and 41 patients (78.8%) had unfavorable outcomes (15 29% died). Surgery after 48 hours, age >60 years, and multivessel distribution did not significantly affect 90-day mRS score (P = 0.091, 0.111, and 0.664, respectively). In volumetric subset analysis, 10 patients of 41 (31.3%) achieved favorable outcomes, and no patients with volume of infarct >280 mL had a favorable outcome. There was a trend of lower volumes associated with favorable outcomes, but this did not meet significance (favorable 207 ± 68.7 vs. unfavorable 262 ± 117.1; P = 0.163).
Outcomes after DHC for malignant hemispheric infarct were not affected by current accepted guidelines. Volume of infarct may have an effect on outcome after DHC. Further research to aid in predicting which patients benefit from decompressive craniectomy is warranted.
Reversible cerebral vasoconstriction syndrome (RCVS) presents with a thunderclap headache, often prompting brain imaging. Most patients fully recover with supportive care and time, but oral calcium ...channel blockers are often used in patients with severe vasoconstriction. In this case report, we present a patient with severe vasoconstriction leading to weakness refractory to oral calcium channel blockers. Intrathecal nicardipine was administered via an external ventricular drain and the patient subsequently showed improvement of her weakness and significant improvement of vasospasm on Computed Tomography Angiography. We suggest further studies to determine the efficacy of intrathecal nicardipine in patients with RCVS not responsive to oral calcium channel blockers.
•Reversible cerebral vasoconstriction syndrome (RCVS) is an under-diagnosed cause of severe headache.•Oral calcium channel blockers can be used for severe cases.•Intrathecal calcium channel blockers via EVD have been used to treat aneurysmal vasospasm.•Intrathecal nicardipine may be a treatment option for cases of refractory RCVS with neurologic deficit.
Purpose
Pediatric basilar artery aneurysms are rare and challenging to treat. Microsurgical options and standard endovascular coiling are often undesirable choices for treatment of this pathology. ...Additional endovascular strategies are needed.
Methods
Presentation, diagnosis, and management of pediatric basilar aneurysms were reviewed, with an emphasis on endovascular treatment strategies. Our case series of 2 patients was presented in detail, one treated with flow diversion and vessel sacrifice and one treated with stent-assisted coiling. An extensive review of the literation was performed to find other examples of pediatric basilar artery aneurysms treated with endovascular techniques.
Results
Twenty-nine studies met inclusion criteria. Fifty-nine aneurysms in 58 patients were treated using endovascular techniques. Mortality rate was 10.3% (6/58) and a poor outcome (GOS 1–3) occurred in 15.5% (9/58). There were 4 reported recurrences requiring retreatment; however, only 46.5% of patients had reported follow-up of at least 1 year. 71.1% (42/59) were dissecting aneurysms.
Conclusion
Basilar artery aneurysms in the pediatric population are rare, commonly giant and fusiform, and often not amenable to microsurgical or coiling techniques. The surrounding vasculature, location, size, and morphology of the aneurysm along with the durability of treatment must be considered in treatment decisions. With proper patient selection, stent-assisted coiling and flow diversion may increase the durability and safety of endovascular treatment in this population.
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