Anthropogenic eutrophication of Lake Titicaca (Bolivia) revealed by carbon and nitrogen stable isotopes fingerprinting

Cultural eutrophication is the leading cause of water quality degradation worldwide. The traditional monitoring of eutrophication is time-consuming and not integrative in space and time. Here, we examined the use of carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopic composition to track the degree of eutrophication in a bay of Lake Titicaca impacted by anthropogenic (urban, industrial and agricultural wastewater) discharges. Our results show increasing δ¹³C and decreasing δ¹⁵N signatures in macrophytes and suspended particulate matter with distance to the wastewater source. In contrast to δ¹⁵N and δ¹³C signatures, in-between aquatic plants distributed along the slope were not only affected by anthropogenic discharges but also by the pathway of carbon uptake, i.e., atmospheric (emerged) vs aquatic (submerged). A binary mixing model elaborated from pristine and anthropogenic isotope end-members allowed the assessment of anthropogenically derived C and N incorporation in macrophytes with distance to the source. Higher anthropogenic contribution was observed during the wet season, attributed to enhanced wastewater discharges and leaching of agricultural areas. For both seasons, eutrophication was however found naturally attenuated within 6 to 8 km from the wastewater source. Here, we confirm that carbon and nitrogen stable isotopes are simple, integrative and time-saving tools to evaluate the degree of eutrophication (seasonally or annually) in anthropogenically impacted aquatic ecosystems.

Diagenetic production, accumulation and sediment-water exchanges of methylmercury in contrasted sediment facies of Lake Titicaca (Bolivia)

Monomethylmercury (MMHg) concentrations in aquatic biota from Lake Titicaca are elevated although the mercury (Hg) contamination level of the lake is low. The contribution of sediments to the lake MMHg pool remained however unclear. In this work, seven cores representative of the contrasted sediments and aquatic ecotopes of Lake Titicaca were sliced and analyzed for Hg and redox-sensitive elements (Mn, Fe, N and S) speciation in pore-water (PW) and sediment to document early diagenetic processes responsible for MMHg production and accumulation in PW during organic matter (OM) oxidation. The highest MMHg concentrations (up to 12.2 ng L^-1 and 90% of THg) were found in subsurface PWs of the carbonate-rich sediments which cover 75% of the small basin and 20% of the large one. In other sediment facies, the larger content of OM restricted MMHg production and accumulation in PW by sequestering Hg in the solid phase and potentially also by decreasing its bioavailability in the PW. Diagenetically reduced S and Fe played a dual role either favoring or restricting the availability of Hg for biomethylation. The calculation of theoretical diffusive fluxes suggests that Lake Titicaca bottom sediments are a net source of MMHg, accounting for more than one third of the daily MMHg accumulated in the water column of the Lago Menor. We suggest that in the context of rising anthropogenic pressure, the enhancement of eutrophication in high altitude Altiplano lakes may increase these MMHg effluxes into the water column and favor its accumulation in water and biota.

Mercury contamination level and speciation inventory in Lakes Titicaca & Uru-Uru (Bolivia): Current status and future trends

Aquatic ecosystems of the Bolivian Altiplano (∼3800 m a.s.l.) are characterized by extreme hydro-climatic constrains (e.g., high UV-radiations and low oxygen) and are under the pressure of increasing anthropogenic activities, unregulated mining, agricultural and urban development. We report here a complete inventory of mercury (Hg) levels and speciation in the water column, atmosphere, sediment and key sentinel organisms (i.e., plankton, fish and birds) of two endorheic Lakes of the same watershed differing with respect to their size, eutrophication and contamination levels. Total Hg (THg) and monomethylmercury (MMHg) concentrations in filtered water and sediment of Lake Titicaca are in the lowest range of reported levels in other large lakes worldwide. Downstream, Hg levels are 3-10 times higher in the shallow eutrophic Lake Uru-Uru than in Lake Titicaca due to high Hg inputs from the surrounding mining region. High percentages of MMHg were found in the filtered and unfiltered water rising up from <1 to ∼50% THg from the oligo/hetero-trophic Lake Titicaca to the eutrophic Lake Uru-Uru. Such high %MMHg is explained by a high in situ MMHg production in relation to the sulfate rich substrate, the low oxygen levels of the water column, and the stabilization of MMHg due to abundant ligands present in these alkaline waters. Differences in MMHg concentrations in water and sediments compartments between Lake Titicaca and Uru-Uru were found to mirror the offset in MMHg levels that also exist in their respective food webs. This suggests that in situ MMHg baseline production is likely the main factor controlling MMHg levels in fish species consumed by the local population. Finally, the increase of anthropogenic pressure in Lake Titicaca may probably enhance eutrophication processes which favor MMHg production and thus accumulation in water and biota.

Asymptomatic Sensorineural Hearing Loss in Patients With Systemic Lupus Erythematosus

OBJECTIVE

Hearing loss can accompany systemic lupus erythematosus (SLE). The purpose of this study was to evaluate the prevalence of asymptomatic sensorineural hearing loss (ASNHL) in patients with SLE.

METHODS

Thirty-one unselected consecutive female patients with SLE (American College of Rheumatology criteria, 1982) were evaluated (in a prospective and descriptive study) for evidence of hearing abnormalities. Twenty-five healthy age-matched women served as controls. All patients and control groups underwent both a normal tympanoscopy and an audiometric testing as a prerequisite to be included in the study.

RESULTS

Patients with SLE had a mean age of 35 years (range, 19-64 years) and the follow-up time (median) was 48 months (range, 4-180 months). One of 31 patients was excluded because of middle ear infectious disease. Of the remaining 30 patients, 21 (70%) had impaired hearing; 20 (66%) had sensorineural loss at high frequencies in a bilateral and symmetric way, and one had conductive alteration. Ten patients had normal audiometric studies. Four women in the control group had alterations of the audiometric tests: 3 patients had conductive alteration and the other one had bilateral ASNHL. No statistically significant correlation was found among the presence of ASNHL, the detection of antiphospholipid antibodies, and the treatment with hydroxychloroquine. Also, no correlation was observed between impaired hearing and SLE activity.

CONCLUSION

If it can be established how often this ASNHL progresses to a clinical problem, it can be important that, as part of initial studies, patients with SLE undergo audiometric tests.

[Spinal cord metastasis of carcinoma of the lung: evaluation of magnetic resonance and computed tomography in its diagnosis]

A patient with lung adenocarcinoma had progressive myelopathy. Computed tomography of spinal cord with intravenous contrast and magnetic resonance scan were negative. At autopsy, a spinal cord metastasis was found. In patients with cancer and clinical suspicion of spinal cord metastasis, palliative treatment with radiotherapy is indicated in spite of negative radiological investigations, so as to prevent the progression of myelopathy.

[Hemangioma of the vertebrae: contribution of magnetic resonance to its study]

Vertebral hemangioma is a benign vascular tumor predominantly involving the dorsolumbar spine. Although most of these tumors are asymptomatic, they may result in radiculopathy and/or compressive myelopathy. Plain X-ray films and computed tomography (CT) generally permit the diagnosis by showing characteristic images with hypertrophic bone trabeculation in the vertebral body. We report three patients with vertebral hemangioma in which CT was diagnostic. Magnetic resonance (MR) with low intensity field was inferior to CT for the suggestion of the diagnosis of hemangioma, but had a better definition for subarachnoid space obliteration and spinal cord compression.