Variations of sedimentary Fe and Mn fractions under changing lake mixing regimes, oxygenation and land surface processes during Late-glacial and Holocene times.

Global spread of anoxia in aquatic ecosystems has become a major issue that may potentially worsen due to global warming. The reconstruction of long-term hypolimnetic anoxia records can be challenging due to lack of valid and easily measurable proxies. The sedimentary Mn/Fe ratio measured by X-ray fluorescence (XRF) is often used as a proxy for past lake redox conditions. Yet the interpretation of this ratio can be problematic when Fe and Mn accumulation is not solely redox driven. We used the varved sediments of Lake Moossee (Switzerland) to examine the partitioning of Fe and Mn in seven fractions by sequential extraction under various oxygen conditions over the last 15,000 years. We combined this data with XRF scans and an independent diagnostic proxy for anoxia given by a hyperspectral imaging (HSI)-inferred record of bacteriopheophytin, to validate the use of the XRF-Mn/Fe ratio as redox proxy. In the 15,000-year long record, Fe was bound to humins and amorphous, crystalline, sulfide and residual forms. Mn was mainly present in carbonate and amorphous forms. Higher erosion, prolonged anoxia, diagenesis and humic matter input affected Fe and Mn accumulation. Under holomixis the XRF-Mn/Fe ratio successfully reflected lake redox conditions. Periods with higher detrital Fe input obscured the applicability of the ratio. During phases of permanent anoxia, intensified early diagenetic processes trapped Mn in the sediments in carbonate, crystalline oxide and humic forms. Our study shows that the single use of the XRF-Mn/Fe ratio is often not conclusive for inferring past lake redox conditions. The application of the XRF-Mn/Fe as a proxy for anoxia requires taking into account the individual lake characteristics and changes in lake environmental conditions, which affect the accumulation of Fe and Mn in the sediments.

Persistent Hg contamination and occurrence of Hg-methylating transcript (hgcA) downstream of a chlor-alkali plant in the Olt River (Romania).

Chlor-alkali plants using mercury (Hg) cell technology are acute point sources of Hg pollution in the aquatic environment. While there have been recent efforts to reduce the use of Hg cells, some of the emitted Hg can be transformed to neurotoxic methylmercury (MeHg). Here, we aimed (i) to study the dispersion of Hg in four reservoirs located downstream of a chlor-alkali plant along the Olt River (Romania) and (ii) to track the activity of bacterial functional genes involved in Hg methylation. Total Hg (THg) concentrations in water and sediments decreased successively from the initial reservoir to downstream reservoirs. Suspended fine size particles and seston appeared to be responsible for the transport of THg into downstream reservoirs, while macrophytes reflected the local bioavailability of Hg. The concentration and proportion of MeHg were correlated with THg, but were not correlated with bacterial activity in sediments, while the abundance of hgcA transcript correlated with organic matter and Cl(-) concentration, indicating the importance of Hg bioavailability in sediments for Hg methylation. Our data clearly highlights the importance of considering Hg contamination as a legacy pollutant since there is a high risk of continued Hg accumulation in food webs long after Hg-cell phase out.

Lowering of furosemide dosage after clinical stabilization in patients with congestive heart failure.

OBJECTIVES: This study was performed to examine the safety of reducing the long-term doses of furosemide administered to patients with congestive heart failure (CHF) stabilized on a standard medical treatment. METHODS AND RESULTS: Twenty-nine patients with advanced CHF were treated with enalapril, digoxin, nitrates, and furosemide, as needed to alleviate their symptoms, and remained clinically stable for at least 3 months on those doses. Subsequently, the daily dose of furosemide was reduced to 1/3 of the previous dose, while the concomitant therapy was unchanged. All patients underwent a thorough clinical evaluation and right-heart catheterization before and 2 months after the furosemide dose reduction. After the treatment optimization the NYHA functional class decreased from 2.3 +/- 0.6 to 1.4 +/- 0.6 (p = 0.000), and the left ventricular ejection fraction increased from 22 +/- 10% to 32 +/- 13%, (p = 0.000). Clinical and haemodynamic evaluation before and after 2 months of treatment with lower furosemide doses showed that 24 of the 29 patients (83%) remained in a stable NYHA functional class and maintained a stable haemodynamic status. In the remaining 5 patients (17%), mean NYHA functional class increased from 1.8 +/- 0.4 to 2.4 +/- 0.6 (p = 0.07), accompanied by a significant increase of the right and left ventricular filling pressures from 4.2 +/- 2.7 to 9.0 +/- 3.0 mm Hg, p = 0.018 and from 8.6 +/- 3.0 to 19.8 +/- 3.6 mm Hg, p = 0.017, respectively. These 5 patients returned to a stable clinical status upon resumption of the prior doses of furosemide. CONCLUSIONS: Most patients with chronic CHF who were clinically stabilized on high doses of furosemide remained stable on a maintenance dose equal to one-third of the dose needed for their stabilization. Patients unable to tolerate the dose reduction regained their previous clinical status following the resumption of the prior diuretic doses.