The role of warm, dry summers and variation in snowpack on phytoplankton dynamics in mountain lakes.

Climate change is altering biogeochemical, metabolic, and ecological functions in lakes across the globe. Historically, mountain lakes in temperate regions have been unproductive because of brief ice-free seasons, a snowmelt-driven hydrograph, cold temperatures, and steep topography with low vegetation and soil cover. We tested the relative importance of winter and summer weather, watershed characteristics, and water chemistry as drivers of phytoplankton dynamics. Using boosted regression tree models for 28 mountain lakes in Colorado, we examined regional, intraseasonal, and interannual drivers of variability in chlorophyll a as a proxy for lake phytoplankton. Phytoplankton biomass was inversely related to the maximum snow water equivalent (SWE) of the previous winter, as others have found. However, even in years with average SWE, summer precipitation extremes and warming enhanced phytoplankton biomass. Peak seasonal phytoplankton biomass coincided with the warmest water temperatures and lowest nitrogen-to-phosphorus ratios. Although links between snowpack, lake temperature, nutrients, and organic-matter dynamics are increasingly recognized as critical drivers of change in high-elevation lakes, our results highlight the additional influence of summer conditions on lake productivity in response to ongoing changes in climate. Continued changes in the timing, type, and magnitude of precipitation in combination with other global-change drivers (e.g., nutrient deposition) will affect production in mountain lakes, potentially shifting these historically oligotrophic lakes toward new ecosystem states. Ultimately, a deeper understanding of these drivers and pattern at multiple scales will allow us to anticipate ecological consequences of global change better.

Toward the improvement of total nitrogen deposition budgets in the United States.

Frameworks for limiting ecosystem exposure to excess nutrients and acidity require accurate and complete deposition budgets of reactive nitrogen (Nr). While much progress has been made in developing total Nr deposition budgets for the U.S., current budgets remain limited by key data and knowledge gaps. Analysis of National Atmospheric Deposition Program Total Deposition (NADP/TDep) data illustrates several aspects of current Nr deposition that motivate additional research. Averaged across the continental U.S., dry deposition contributes slightly more (55%) to total deposition than wet deposition and is the dominant process (>90%) over broad areas of the Southwest and other arid regions of the West. Lack of dry deposition measurements imposes a reliance on models, resulting in a much higher degree of uncertainty relative to wet deposition which is routinely measured. As nitrogen oxide (NOx) emissions continue to decline, reduced forms of inorganic nitrogen (NHx = NH3 + NH4+) now contribute >50% of total Nr deposition over large areas of the U.S. Expanded monitoring and additional process-level research are needed to better understand NHx deposition, its contribution to total Nr deposition budgets, and the processes by which reduced N deposits to ecosystems. Urban and suburban areas are hotspots where routine monitoring of oxidized and reduced Nr deposition is needed. Finally, deposition budgets have incomplete information about the speciation of atmospheric nitrogen; monitoring networks do not capture important forms of Nr such as organic nitrogen. Building on these themes, we detail the state of the science of Nr deposition budgets in the U.S. and highlight research priorities to improve deposition budgets in terms of monitoring and flux measurements, leaf- to regional-scale modeling, source apportionment, and characterization of deposition trends and patterns.

Prospective evaluation of the impact of covert hepatic encephalopathy on quality of life and sleep in cirrhotic patients.

BACKGROUND: Minimal hepatic encephalopathy (HE) and HE grade 1 (HE1) according to the West Haven criteria have recently been grouped as one entity named-covert HE- (CHE). Data regarding the impact of CHE on health-related quality of life (HRQoL) and sleep quality are controversial. AIM: First, to determine whether CHE affects HRQoL and sleep quality of cirrhotic patients and second, whether minimal HE (MHE) and HE1 affect HRQoL and sleep quality to a comparable extent. METHODS: A total of 145 consecutive cirrhotic patients were enrolled. HE1 was diagnosed clinically according to the West Haven criteria. Critical flicker frequency and the Psychometric Hepatic Encephalopathy Score were used to detect MHE. Chronic Liver Disease Questionnaire (CLDQ) was used to assess HRQoL and Pittsburgh Sleep Quality Index (PSQI) was applied to assess sleep quality. RESULTS: Covert HE was detected in 59 (40.7%) patients (MHE: n = 40; HE1: n = 19). Multivariate analysis identified CHE (P < 0.001) and female gender (P = 0.006) as independent predictors of reduced HRQoL (CLDQ total score). CHE (P = 0.021), low haemoglobin (P = 0.024) and female gender (P = 0.003) were identified as independent predictors of poor sleep quality (PSQI total score). Results of CLDQ and PSQI were comparable in patients with HE1 and MHE (CLDQ: 4.6 ± 0.9 vs 4.5 ± 1.2, P = 0.907; PSQI: 11.3 ± 3.8 vs 9.9 ± 5.0, P = 0.3). CONCLUSION: Covert HE was associated with impaired HRQoL and sleep quality. MHE and HE1 affected both outcomes to a comparable extent supporting the use of CHE as a clinically useful term for patients with both entities of HE in clinical practice.