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Journal ArticleDOI

Laghi di Monticchio (Southern Italy, Region Basilicata): genesis of sediments—a geochemical study

01 Jul 2008-Journal of Paleolimnology (Springer Netherlands)-Vol. 40, Iss: 1, pp 529-556
TL;DR: In this article, the authors investigated the sedimentation record of Lago Grande di Monticchio (LGM) and elucidated spatial variations of sediment genesis within the lake basin and the importance of various depth sections for the lake's internal nutrient cycling.
Abstract: The sedimentation record of Lago Grande di Monticchio (LGM) is one of the most prominent paleoclimatic archives in the on-glaciated areas of Europe. However, the modern lake system has never been the subject of intense limnological studies. On the basis of hydrochemical water profiles, detailed investigations of sediment short cores and in situ pore water profiles from the littoral to the profundal zone, we elucidate spatial variations of sediment genesis within the lake basin and the importance of various depth sections for the lake's internal nutrient cycling. Sediments from the smaller meromictic Lago Piccolo di Montichio are discussed as a reference. Our study demonstrates: (i) distinctly higher sediment accumulation for the centre of the lake basin by focussing of the settling particle flux; (ii) decline of carbonate from the littoral to the profundal zones; (iii) nonsynchronous change of calcite net-accumulation for various water depths; (iv) exceptionally high cation release from sediments covering the steeply inclining sector of the lake basin; (v) relatively constant dissolved silica concentrations in the pore waters (SiO2 *42 mg/l) independent of water depth and sediment composition; (vi) influx of oxygen-bearing groundwater into the anoxic hypolimnion after heavy rainfall and the associated precipitation of Fe-oxihydroxides; (vii) higher release of NH4 by anaerobic degradation of organic matter at a water depth of 23 m than for sediments at a maximum water depth of 32 m, whereby the latter reflects the importance of seasonal sediment re-oxidation for anaerobic degradation of organic debris; (viii) although seasonal reoxidation of sediments from various water depths is quite different, Oxygen Index values of LGM sediments fall in a small range, which reflects rapid microbial consumption of seasonally re-generated easily bio-degradable organic molecules.

Summary (3 min read)

Introduction

  • Sediment from Lago Grande di Monticchio (LGM, Fig. 1a–c) represents one of the most prominent European terrestrial paleoenvironmental archives with a continuous 100 kyr record spanning the Eem interglacial to the modern industrial period (Allen et al. 1999).
  • The oldest volcanic products of the Monte Vulture are the Foggianello sub-unit deposits of Fara d’Olivo ignimbrite (Crisci et al. 1983).
  • The lake level of LGM shows seasonal fluctuations, with high levels in early spring (pers. comm., local residents 1994).

Sampling

  • On 22 August 1994 and 19 September 1994, temperature profiles of the water column were taken at the deepest part of both lakes.
  • Divers placed dialysis cells along a transect (Fig. 1b) in the surface sediments of LGM at various water depths such that the uppermost dialysis chamber fit with the sediment/water interface (see Schwedhelm et al. 1988 for cell construction).
  • The vertical distance between each chamber was 1 cm with 2 chambers at each depth level.
  • Short gravity cores ( 70 cm) were taken from the centre of lake LPM and along a transect (Fig. 1b) from LGM using a Niemistö gravity corer (Niemistö 1974).
  • The cores were continuously sampled at 3 cm slices by vertical extrusion; sample slices were immediately stored in a refrigerated box.

Water samples

  • The determination of fluoride, chloride, nitrate and sulphate was carried out by ion exchange chromatography (DX 100, Dionex).
  • Soluble Reactive Phosphorus (SRP) and ammonium were determined colorimetrically (FIAS, Perkin Elmer) using the molybdenum-blue method for SRP measurements and spectro-photometry of an indicator solution after separation of NH3 through a Teflon membrane (for details see Müller et al. 1992).
  • Dissolved inorganic carbon (DIC) of lake water samples was measured coulometrically.
  • Dissolved silica and cations were measured sequentially by ICP-AES (ARL 35000).
  • Temperature profiles of the lakes were taken by means of a water-tight single channel logger with an integrated thermistor temperature sensor (XL-100) manufactured by Richard Brancker Research, Canada.

Sediment samples

  • Sediment samples were frozen on return to the laboratory (1–2 days after sampling) and later freeze-dried.
  • The total carbon and nitrogen were determined after thermal decomposition at 1,350°C in an oxygen-gas-flow by IR-spectrometry and heat-conductivity detection, respectively (CNS 2000, LECO).
  • Elemental sulphur was determined after methanol-extraction (reflux, 7 min) by reversed phase liquid chromatography (eluent: 80% methanol, column: C-18, UV-detection 254 nm, DX 100, Dionex, see Möckel 1984).
  • Detector efficiency calibration for 46.539 keV was based on αspectrometric measurements using a 208Po recovery spike.

Lake water characteristics

  • Increase of Ca and DIC in the hypolimnion of LGM towards the lake bottom reflects post-depositional dissolution of autochthonous carbonate.
  • During summer stratification, the SO4 concentration had significantly decreased in the anoxic deep water, but increased again by the inflow of groundwater (Fig. 3i).
  • The LGM lake water is moderately mineralized, so the authors could not obtain hints for subsurface inflow of highly saline waters that could trigger development of meromictic conditions.

Radiometric data

  • Unsupported 210Pb in the upper 15 cm of the LPM core and in the LGM core from 4 m depth shows similar high activity values and a distinct decline in the upper sections of these cores (Fig. 4a–d, Table 1).
  • The 137Cs profiles confirm that sediment accumulation at the 23 m site distinctly exceeds that of the profundal LPM sediments and that of LGM sediments from the shallow water (Fig. 4e–h).
  • The initial unsupported 210Pb activity of 760 mBq/g calculated on the basis of CIC assumptions probably exceeds that of earlier sedimentation periods.
  • The geochemical signatures of deeper sediments at the 8 m depth, showing distinctly lower Al contents (Fig. 5g), could reflect the presence of minerogenic debris with a geochemical composition that completely differs from those of the other LGM cores.
  • They may also reflect in situ sulphide precipitation within discrete sulphate reduction zones and the diffusive flux of Fe dissolved in pore water towards these zones.

Pore water chemistry

  • Pore water profiles can be used to assess microbial activity within sediments and the diffusive exchange between sediments and the overlying water.
  • The pore water profile of the 12 m site is characterized by overall higher Ca and DIC concentrations and shows a distinct decline of the concentration gradients between 35 cm and the sediment water interface.
  • The NH4 pore water profile recovered from the 12 m depth shows a different pattern with a maximum at 42 cm and a concentration gradient towards the sediment/water boundary.
  • The SRP pore water profile reflects well the different phosphorus release at various depth levels.
  • Sediments of the smaller LPM show higher TOC/N values than LGM sediments (Fig. 5a).

Synopsis

  • (1) Sediments of LGM document gradually increasing contributions from dead planktonic matter in the course of the recent sedimentation history and show clear variations in their geochemical composition depending on water depth.
  • Autochthonous calcite is characterized by a distinctly higher Ca/Sr ratio than the coexisting lake water.
  • Relatively higher accumulation of macrophytic organic remnants and littoral CaCO3 does not counterbalance focussing of the particle flux towards the centre of the lake basin.
  • Re-precipitation of pore water dissolved Fe as Fe-oxihydroxide is accompanied by substantial co-precipitation of U and Mo. Enhanced chemical alteration in the steeply inclining sector of LGM is documented in pore water profiles from the 12 m site that show distinctly elevated Na, K, Mg, Ca, Mn and DIC concentrations with strong gradients towards the sediment/water interface.
  • (5) Silica pore water concentrations, which should largely originate from the post-depositional dissolution of biogenic opal, have a uniform value of ca. 42 mg/l SiO2 in LGM sediments.

Figures

  • The basis of assumed values for porosity (ϕ) and density of the solid sediment (ρs).
  • The depth estimate for the year 1963 in core 6 m (b) was calculated on the basis of CRS assumptions minerogenic sediment constituent on CaCO3-free base for an assumed Al2O3 content of 15.6 wt% of the bulk siliciclastic sediment fraction (Al2O3 value for mean continental crust composition after Taylor (1964), see (g) for Al concentration data).
  • (h–l) Profiles of selected element ratios, characterizing the siliciclastic sediment fraction: LaN/TmN, ratio of Chondrite-normalized REE concentrations (used data for normalization from Taylor and McLennan (1985)).
  • Distinctly enhanced Fe/Al, U/Al and Mo/Al values in the profiles from the 8 m sampling site reflect intense chemical alteration and re-distribution of Fe, U and Mo. Increase of Fe/Al and Mo/Al in the LPM sediments coinciding with Stotal increase, (n) indicates sulphide-precipitation of Fe and Mo in the modern LPM, (m) excess.
  • Fe balanced for an assumed Fe/Al mass ratio of 0.9 for the minerogenic debris.

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Laghi di Monticchio (Southern Italy, Region Basilicata):
genesis of sediments-a geochemical study
Georg Schettler, Patrick Albéric
To cite this version:
Georg Schettler, Patrick Albéric. Laghi di Monticchio (Southern Italy, Region Basilicata): genesis of
sediments-a geochemical study. Journal of Paleolimnology, Springer Verlag, 2008, 40 (1), pp.529-556.
�10.1007/s10933-007-9180-4�. �insu-00252989�

Laghi di Monticchio (Southern Italy, Region Basilicata): genesis
of sediments—a geochemical study
Georg Schettler
1
and Patrick Albéric
2
(1) GeoForschungsZentrum Potsdam, Section Climate Dynamics and Sediments,
Telegrafenberg C328, 14473 Potsdam, Germany
(2) Institut des Sciences de la Terre d’Orléans (ISTO), UMR 6113 CNRS-Université
d’Orléans, Bâtiment Géosciences, BP 6759, Rue de St Amand, 45067 Orléans Cedex 2,
France
Abstract The sedimentation record of Lago Grande di Monticchio (LGM) is one of the most
prominent paleoclimatic archives in the non-glaciated areas of Europe. However, the modern
lake system has never been the subject of intense limnological studies. On the basis of
hydrochemical water profiles, detailed investigations of sediment short cores and in situ pore
water profiles from the littoral to the profundal zone, we elucidate spatial variations of
sediment genesis within the lake basin and the importance of various depth sections for the
lake’s internal nutrient cycling. Sediments from the smaller meromictic Lago Piccolo di
Montichio are discussed as a reference. Our study demonstrates: (i) distinctly higher sediment
accumulation for the centre of the lake basin by focussing of the settling particle flux; (ii)
decline of carbonate from the littoral to the profundal zones; (iii) non-synchronous change of
calcite net-accumulation for various water depths; (iv) exceptionally high cation release from
sediments covering the steeply inclining sector of the lake basin; (v) relatively constant
dissolved silica concentrations in the pore waters (SiO
2
~42 mg/l) independent of water depth
and sediment composition; (vi) influx of oxygen-bearing groundwater into the anoxic
hypolimnion after heavy rainfall and the associated precipitation of Fe-oxihydroxides; (vii)
higher release of NH
4
by anaerobic degradation of organic matter at a water depth of 23 m
than for sediments at a maximum water depth of 32 m, whereby the latter reflects the
importance of seasonal sediment re-oxidation for anaerobic degradation of organic debris;
(viii) although seasonal re-oxidation of sediments from various water depths is quite different,
Oxygen Index values of LGM sediments fall in a small range, which reflects rapid microbial
consumption of seasonally re-generated easily bio-degradable organic molecules.
Keywords Lacustrine sediments - Geochemistry - Genesis
Introduction
Sediment from Lago Grande di Monticchio (LGM, Fig. 1a–c) represents one of the most
prominent European terrestrial paleoenvironmental archives with a continuous 100 kyr record
spanning the Eem interglacial to the modern industrial period (Allen et al. 1999). During the
last decade, a reliable chronology for the LGM sedimentation record has been developed
based on varve counting, AMS
14
C-dating, and tephrochronostratigraphy (Newton and
Dugmore 1993; Zolitschka and Negendank 1993, 1996; Narcisi 1996; Huntley et al. 1999;
Wulf et al. 2004). Contributions to local vegetation development as a mirror of paleoclimate
change have been given by Watts (1985), Watts et al. (1996a, b, 2000), Huntley et al. (1999)
and Allen et al. (2000, 2002). Diatom assemblages in LGM sediments as a proxy for
paleoenvironmental change were investigated by Nimmergut et al. (1999). A pioneering
geochemical study of a 50 m sedimentation record from LGM was done by Robinson (1994).
Further geochemical sediment profiles were published by Creer and Morris (1996), Ramrath

et al. (1999) and Brauer et al. (2000). Still missing is a deeper understanding of sediment
genesis in LGM, which constrains paleoclimatic interpretation of geochemical and
geomagnetic sediment profiles that are partially based on sediment cores from various water
depths (see contributions by Creer and Morris 1996; Brandt et al. 1999).
Here, a study of the modern LGM, based on snapshots of thermal and chemical lake
stratification, in situ pore water profiles and investigation of short sediment cores taken along
a transect from the littoral zone to the centre of the lake during summer stratification, is
presented. The study was carried out to assess: (1) principal differences in sediment
characteristics at various water depths, (2) differences in sediment accumulation between the
shallow water area and the centre of the lake basin, (3) geochemical implications for
groundwater inflow, (4) post-depositional redistribution of chemical elements and (5) the
importance of various depth sections for the nutrient and sulphur cycle in LGM.
Geological setting and hydrological conditions
The Laghi Grande and Piccolo di Monticchio are maar lakes embedded in a collapsed
structure on the southwestern slopes of the Monte Vulture volcanic complex (Fig. 1c). The
suite of the local volcanic rocks is divided into two major units: the older Monte Vulture
complex and the younger Monticchio unit. The oldest volcanic products of the Monte Vulture
are the Foggianello sub-unit deposits of Fara d’Olivo ignimbrite (Crisci et al. 1983). The Fara
d’Olivo trachytic ignimbrite exhibits an age of 742 ± 11 kyr after Villa (1988). Buettner et al.
(2006) suggested an age of 740 ± 7 kyr for the lower and <740 kyr for the upper Fara d’Olivo
unit. The largest local volcanic rocks by volume are primary and epiclastic deposits of the
Barile unit. Volcanic products of this unit were ejected between ca. 673 and 610 kyr BP (see
Table 7-2 in Buettner et al. 2006 and references therein).
After a period of quiescence, the Monte Vulture volcano became dismembered by faulting
(Valle dei Greggi-Fosso del Corbo fault system). Volcanism resumed with volumetrically
subordinate eruptions assigned to the Monticchio unit (Laghi di Monticchio unit:
132 ± 12 kyr, Brocchini et al. 1994; 141 ± 11 kyr suggested by Buettner et al. 2006). Faulting
caused subsidence of the southern half of the Vulture complex and collapse of its
southwestern part. Eruptive activity of the Monticchio unit scattered along the active fault
systems and was dominantly linked to diametric structures, two of which are located under the
Monticchio Lakes (Giannandrea et al. 2006).
The igneous rocks of the Vulture complex comprise phonolites, tephri-phonolites, phonolitic-
foidites, and foidites (Principe et al. 2006 and references therein). Enhanced sulphur contents
associated with the occurrence of hauyne (Na,Ca)
4–8
[Al
6
Si
6
O
24
](SO
4
,S)
1–2
are peculiarities of
these rocks. High SO
4
contents of Vulture lavas are thought to be caused by magma
interaction with sedimentary SO
4
-rich brines from the basement of the volcano covering
Cretaceous to Pliocene sediments (La Volpe et al. 1984; De Fino et al. 1986). Substantial
hydrothermal calcite, gypsum, and anhydrite vein deposits were detected during explorations
in the hydrothermal fields of Tuscany and Latinum; Triassic marine evaporites are seen as the
major SO
4
source of these mineralizations (Marini and Chiodini 1994 and references therein)
and may also represent a major SO
4
source for hauyne-rich Vulture volcanites (see Table 1 in
De Fino et al. 1986 for hauyne contents). This interpretation is supported by relatively
positive δ
34
S values of metasomatic hauyne phenocrysts (+6.1, +6.6‰) from the Vulture
volcano (Cavarretta and Lombardi 1990). According to an alternative explanation, the
sulphate is primarily of magmatic origin: reduced sulphur became oxidized in the magma with

a high oxygen fugacity to SO
2
/SO
3
, and the escape of gaseous SO
2
/SO
3
left heavy
34
S behind
(see for detailed discussion Cavarretta and Lombardi 1990). The Laghi di Monticchio unit,
which is exposed in the western surroundings of LGM, involves a carbonatite-melilitite tuff
sequence abundant in mantle xenoliths (Stoppa and Principe 1998; Jones et al. 2000; Downes
et al. 2002). Formation of the maar lakes is associated with phreatomagmatic eruptions during
the final stage of volcanic activity.
The modern Lago Piccolo di Monticchio (LPM) has a maximum water depth of 38 m, a
surface area of 1.6 × 10
5
m
2
, and a water volume of 3.9 × 10
6
m
3
and receives sub-surface
inflow from a catchment area of 1.05 × 10
6
m
2
(Zolitschka and Negendank 1996). Lago
Piccolo di Monticchio is meromictic with a chemocline at about 13 m (Chiodini et al. 1997
and references therein). Monimolimnion waters in LPM are anoxic with high CO
2
content and
show a temperature increase with depth. Salinity increases to 1.8 g/l in the deepest part of the
lake basin (monitoring data 1995: Chiodini et al. 1997). The lake level of LPM is held
artificially 1 m above the lake level of LGM (~656 m asl).
The surface area of the dimictic LGM is 4.05 × 10
5
m
2
, and its water volume is 3.5 × 10
6
m
3
(Zolitschka and Negendank 1996). The lake receives sub-surface drainage from a catchment
of 3.04 × 10
6
m
2
, including that of LPM, and has one outlet. The morphology of the LGM
basin has been characterized by sonar measurements (Hansen 1993). Lago Grande di
Monticchio has an extended shallow area (Fig. 1b) with abundant submerged vegetation
(Ceratophyllum demersum) and a littoral fringe rich in Nympha alba and Polygonum
amphibum.
Mean annual precipitation (815 mm) is relatively high due to the elevation of the site (e.g.
Monte Vulture: 1,262 m asl), although a pronounced dry period commonly occurs in the
summer. The hillside is densely forested and dominated by Beech (Fagus sylvatica) and
Turkey Oak (Quercus cerris) (Watts et al. 1996b). A high percentage of precipitation does not
drain but undergoes evapotranspiration. For an assumed evapotranspiration of 80% in the
catchment, the above hydrological data suggest a water residence time of ~7 years for LGM.
Loosely deposited pyroclastics in the catchment of LGM favour the seepage of precipitation.
Drainage by surface runoff into the lakes, however, may occur during the melting of snow
when the top-soils are frozen.
The lake level of LGM shows seasonal fluctuations, with high levels in early spring (pers.
comm., local residents 1994). During late spring and summer, the lake level commonly
decreases by one to two metres. Water level increase is limited by a canal built by monks of
the monastery San Ippolito that was founded within the Piano Comune tuff ring depression in
AD 1059 and discharges Lago Grande waters into the river Ofanto. During the winter of
1993/1994, both lakes were ice-covered. A clearly visible terrace, ca. 5 m above the modern
lake level, indicates that the lake level was higher in the past. The lands surrounding Monte
Vulture are cultivated, especially for cereals.
Sampling
On 22 August 1994 and 19 September 1994, temperature profiles of the water column were
taken at the deepest part of both lakes. Divers placed dialysis cells along a transect (Fig. 1b) in
the surface sediments of LGM at various water depths such that the uppermost dialysis
chamber fit with the sediment/water interface (see Schwedhelm et al. 1988 for cell
construction). The vertical distance between each chamber was 1 cm with 2 chambers at each

depth level. At each cell site, water samples were taken approximately 0.5 m above the
surface sediment. To determine the amount of cations, an aliquot of the water sample was
membrane-filtered (0.45 μm) and stabilized with nitric acid. Upon removal by divers on 19
September 1994, the single dialysis chambers were immediately sampled with syringes in
7 ml polypropylene tubes with a screw closure, manufactured by Sarstedt (Germany). One
sample from each depth was stabilized by addition of 20 μl HNO
3
.
Short gravity cores (70 cm) were taken from the centre of lake LPM and along a transect
(Fig. 1b) from LGM using a Niemistö gravity corer (Niemistö 1974). The cores were
continuously sampled at 3 cm slices by vertical extrusion; sample slices were immediately
stored in a refrigerated box. Sediments from the deepest part of LGM had very high gas
contents (methane), precluding taking a core from the deepest part of LGM.
Analytical methods
Water samples
The determination of fluoride, chloride, nitrate and sulphate was carried out by ion exchange
chromatography (DX 100, Dionex). Soluble Reactive Phosphorus (SRP) and ammonium were
determined colorimetrically (FIAS, Perkin Elmer) using the molybdenum-blue method for
SRP measurements and spectro-photometry of an indicator solution after separation of NH
3
through a Teflon membrane (for details see Müller et al. 1992). Dissolved inorganic carbon
(DIC) of lake water samples was measured coulometrically. The DIC of pore water samples
was determined by a commercial laboratory (ANTEUM, Berlin) by adding a small sample
volume to phosphoric acid and performing IR-spectrometry of the released carbon dioxide
(TOC 5000, Shimadzu). Dissolved silica and cations were measured sequentially by ICP-AES
(ARL 35000). Temperature profiles of the lakes were taken by means of a water-tight single
channel logger with an integrated thermistor temperature sensor (XL-100) manufactured by
Richard Brancker Research, Canada.
Sediment samples
Sediment samples were frozen on return to the laboratory (1–2 days after sampling) and later
freeze-dried. The <185 μm fraction was separated from the freeze-dried material by sieving. It
comprised almost 100% of the total sample. After a HNO
3
/HClO
4
/HF/HCl-decomposition of
0.25 g solid sample, the determination of major and minor elements, including phosphorus
and sulphur, was carried out by sequential ICP-AES (ARL 35000) and external calibration.
Selected trace elements were measured by ICP-MS using a VG Plasma Quad PQ2+.
Beryllium-9,
115
In and
187
Re were used for internal standardization. The total analytical errors
for ICP-MS measurements were below ±10%. Inorganic carbon was measured
coulometrically after decomposition with hot phosphorus acid (Coulomat 702, Ströhlein). The
total carbon and nitrogen were determined after thermal decomposition at 1,350°C in an
oxygen-gas-flow by IR-spectrometry and heat-conductivity detection, respectively (CNS
2000, LECO). Organic carbon was calculated by difference using the total and inorganic
carbon results. Elemental sulphur was determined after methanol-extraction (reflux, 7 min) by
reversed phase liquid chromatography (eluent: 80% methanol, column: C-18, UV-detection
254 nm, DX 100, Dionex, see Möckel 1984). The chromatographic method enables the
detection of polysulphides and sulphur of various chain- and ring-size, respectively.
Octagonal ring-sized sulphur (S
8
) was the dominant sulphur modification in the examined
methanol-extracts. Only its peak area was considered for quantitative analyses of total
elemental sulphur.

Citations
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Journal ArticleDOI
TL;DR: In this article, chemical and isotopic features of dissolved gases (CH4 and CO2) from four meromictic lakes hosted in volcanic systems of Central-Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture).
Abstract: This paper focuses on the chemical and isotopic features of dissolved gases (CH4 and CO2) from four meromictic lakes hosted in volcanic systems of Central–Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH4 and CO2. The δ13C-CH4 and δD-CH4 values of dissolved gas samples from the maximum depths of the investigated lakes (from −66.8 to −55.6 ‰ V-PDB and from −279 to −195 ‰ V-SMOW, respectively) suggest that CH4 is mainly produced by microbial activity. The δ13C-CO2 values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from −5.8 to −0.4 ‰ V-PDB) indicate a significant CO2 contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO2 source feeding the regional thermal and cold CO2-rich fluid emissions. In contrast, the relatively low δ13C-CO2 values (from −13.4 to −8.2 ‰ V-PDB) of Lake Averno indicate a prevalent organic CO2. Chemical and isotopic compositions of dissolved CO2 and CH4 at different depths are mainly depending on (1) CO2 inputs from external sources (hydrothermal and/or anthropogenic); (2) CO2–CH4 isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO2 and CH4 concentrations. In the hypolimnion, where the δ13C-CO2 values progressively increase with depth and the δ13C-CH4 values show an opposite trend, biogenic CO2 production from CH4 using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water–bottom sediment interface. Theoretical values, calculated on the basis of δ13C-CO2 values, and measured δ13CTDIC values are not consistent, indicating that CO2 and the main carbon-bearing ion species (HCO3 −) are not in isotopic equilibrium, likely due to the fast kinetics of biochemical processes involving both CO2 and CH4. This study demonstrates that the vertical patterns of the CO2/CH4 ratio and of δ13C-CO2 and δ13C-CH4 are to be regarded as promising tools to detect perturbations, related to different causes, such as changes in the CO2 input from sublacustrine springs, that may affect aerobic and anaerobic layers of meromictic volcanic lakes.

51 citations


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Abstract: . Sedimentation processes occurring in the most recent maar lake of the French Massif Central (Lake Pavin) are documented for the first time based on high resolution seismic reflection and multibeam bathymetric surveys and by piston coring and radiocarbon dating on a sediment depocentre developed on a narrow sub aquatic plateau. This new data set confirms the mid Holocene age of maar lake Pavin formation at 6970±60 yrs cal BP and highlights a wide range of gravity reworking phenomena affecting the basin. In particular, a slump deposit dated between AD 580–640 remoulded both mid-Holocene lacustrine sediments, terrestrial plant debris and some volcanic material from the northern crater inner walls. Between AD 1200 and AD 1300, a large slide scar mapped at 50 m depth also affected the southern edge of the sub aquatic plateau, suggesting that these gas-rich biogenic sediments (laminated diatomite) are poorly stable. Although several triggering mechanisms can be proposed for these prehistoric sub-aquatic mass wasting deposits in Lake Pavin, we argue that such large remobilisation of gas-rich sediments may affect the gas stability in deep waters of meromictic maar lakes. This study highlights the need to further document mass wasting processes in maar lakes and their impacts on the generation of waves, favouring the development of dangerous (and potentially deadly) limnic eruptions.

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Journal ArticleDOI
TL;DR: In this paper, a sediment trap that was cleared monthly was deployed in Lake Challa, a deep stratified freshwater lake on the eastern slope of Mt. Kilimanjaro in southern Kenya.
Abstract: From November 2006 to January 2010, a sediment trap that was cleared monthly was deployed in Lake Challa, a deep stratified freshwater lake on the eastern slope of Mt. Kilimanjaro in southern Kenya. Geochemical data from sediment trap samples were compared with a broad range of limnological and meteorological parameters to characterize the effect of single parameters on productivity and sedimentation processes in the crater basin. During the southern hemisphere summer (November–March), when the water temperature is high and the lake is biologically productive (nondiatom algae), calcite predominated in the sediment trap samples. During the “long rain” season (March–May) a small amount of organic matter and lithogenic material caused by rainfall appeared. This was followed by the cool and windy months of the southern hemisphere winter (June–October) when diatoms were the main component, indicating a diatom bloom initiated by improvement of nutrient availability related to upwelling processes. The sediment trap data support the hypothesis that the light–dark lamination couplets, which are abundant in Lake Challa cores, reflect seasonal delivery to the sediments of diatom-rich particulates during the windy months and diatom-poor material during the wet season. However, interannual and spatial variability in upwelling and productivity patterns, as well as El Nino–Southern Oscillation (ENSO)-related rainfall and drought cycles, exert a strong influence on the magnitude and geochemical composition of particle export to the hypolimnion of Lake Challa.

33 citations

Journal ArticleDOI
TL;DR: Analysis of δ18O of lake water and invertebrate remains, including head capsules of chironomid larvae and resting eggs of planktonic Cladocera, in surface sediments from 31 large, deep, and stratified lakes along a latitudinal transect through Europe found a systematic offset between the absolute δ 18O values of ch ironomids and cladocerans.
Abstract: An understanding of modern relationships between the stable oxygen isotope composition (δ18O) of lake water and aquatic invertebrates is essential for the interpretation of paleoclimate records based on δ18O of organic remains of these organisms. We analyzed δ18O of lake water and invertebrate remains, including head capsules of chironomid larvae and resting eggs (ephippia) of planktonic Cladocera, in surface sediments from 31 large, deep, and stratified lakes along a latitudinal transect through Europe. The δ18O values measured for both lake water and aquatic invertebrate remains were compared to estimated δ18O in precipitation. A strong linear relationship between mean annual air temperature and δ18O of precipitation was observed along the north–south transect (r = 0.97), whereas the relationship between precipitation δ18O and lake-water δ18O was weaker (r = 0.80). A strong positive correlation was observed between δ18O in lake water and aquatic invertebrates (r = 0.95 and 0.94 for chironomids and cladocerans, respectively). Although slopes of linear regressions between lake-water δ18O and δ18O of both aquatic invertebrate groups are similar, a systematic offset between the absolute δ18O values of chironomids and cladocerans was observed; chironomids were on average 2.4‰ heavier than Cladocera. We attribute this offset to differences in ecology, metabolism, and/or behavior between benthic chironomid larvae and planktonic Cladocera. δ18O records based on subfossil chironomid and cladoceran remains have the potential to quantitatively characterize past lake-water δ18O and, indirectly, past climatic changes.

22 citations

Journal ArticleDOI
TL;DR: The first detailed description of the Monticchio maar lakes based on high-resolution conductivity-temperature-depth (CTD) profiles, chemical and isotopic (H and O) compositions of the water, and the amounts of dissolved gases (e.g., He, Ar, CH4, and CO2) was provided in this paper.
Abstract: [1] We report on the first geochemical investigation of the Monticchio maar lakes (Mt. Vulture volcano, southern Italy) covering an annual cycle that aimed at understanding the characteristic features of the physical structures and dynamics of the two lakes. We provide the first detailed description of the lakes based on high-resolution conductivity-temperature-depth (CTD) profiles, chemical and isotopic (H and O) compositions of the water, and the amounts of dissolved gases (e.g., He, Ar, CH4, and CO2). The combined data set reveals that the two lakes, which are separated by less than 200 m, exhibit different dynamics: one is a meromictic lake, where the waters are rich in biogenic and mantle-derived gases, while the other is a monomictic lake, which exhibits complete turnover of the water in winter and the release of dissolved gases. Our data strongly suggest that the differences in the dynamics of the two lakes are due to different density profiles affected by dissolved solutes, mainly Fe, which is strongly enriched in the deep water of the meromictic lake. A conceptual model of water balance was constructed based on the correlation between the chemical composition of the water and the hydrogen isotopic signature. Gas-rich groundwaters that feed both of the lakes and evaporation processes subsequently modify the water chemistry of the lakes. Our data highlight that no further potential hazardous accumulation of lethal gases is expected at the Monticchio lakes. Nevertheless, geochemical monitoring is needed to prevent the possibility of vigorous gas releases that have previously occurred in historical time.

13 citations


Cites background or result from "Laghi di Monticchio (Southern Italy..."

  • ...A previous investigation of the geochemistry of sediment found both pyrite and siderite in the sediment [Schettler and Alberic, 2008], and hence, the chemistry of deeper LPM waters is controlled by the stability of minerals and the inflow of CO2....

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  • ..., 2000] and the genesis of its sediments [Schettler and Albéric, 2008]....

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  • ...In contrast, investigations of LGM have mainly focused on paleoclimatic aspects [Brauer et al., 2000] and the genesis of its sediments [Schettler and Albéric, 2008]....

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  • ...In contrast to previous reports [Schettler and Albéric, 2008] which classified classifying LGM as a warm monomictic lake, we observed complete overturning of the water in winter 2009 and a subsequent new chemical stratification during spring 2009....

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References
More filters
Journal ArticleDOI
Biancamaria Narcisi1
TL;DR: In this article, the authors defined the chronological framework of the 51 m deep sedimentary sequence (core D) from Lago Grande di Monticchio (Mt Vulture volcano) with the aim of defining the main late Quaternary explosive events from Ischia, Vesuvius and the Phlegrean Fields districts of the Campanian area.

83 citations


"Laghi di Monticchio (Southern Italy..." refers methods in this paper

  • ...During the last decade, a reliable chronology for the LGM sedimentation record has been developed based on varve counting, AMS (14)C-dating, and tephrochronostratigraphy (Newton and Dugmore 1993; Zolitschka and Negendank 1993, 1996; Narcisi 1996; Huntley et al. 1999; Wulf et al. 2004)....

    [...]

  • ...During the last decade, a reliable chronology for the LGM sedimentation record has been developed based on varve counting, AMS 14C-dating, and tephrochronostratigraphy (Newton and Dugmore 1993; Zolitschka and Negendank 1993, 1996; Narcisi 1996; Huntley et al. 1999; Wulf et al. 2004)....

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Journal ArticleDOI
TL;DR: In this article, a time scale covering the last 76.3 ka is provided by interpolation of sedimentation rates, based on the annual laminations of Lago Grande di Monticchio (southern Italy).

83 citations

Journal ArticleDOI
TL;DR: In this paper, a mathematical model for the study of early diagenesis in lake sediments is presented, which includes microbial and geochemical reactions, inorganic chemical speciation of the dissolved components, and diffusion of the individual species between the boxes.

83 citations


"Laghi di Monticchio (Southern Italy..." refers background in this paper

  • ...…parameter that determines the molecular diffusive flux of SO4 into the sediments, where it is used as an electron acceptor for anaerobic bacterial respiration and microbial mediated anaerobic oxidation of methane (e.g. Furrer and Wehrli 1996; Iversen and Jørgensen 1985 and references therein)....

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  • ...Sulphate is utilized as an electron acceptor for the bio-degradation of organic matter in the absence of other preferentially used electron acceptors (O2, NO3, reactive Fe(III), e.g. Furrer and Wehrli 1996) and is consumed by anaerobic methane oxidation (e.g. Iversen and Jørgensen 1985)....

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Journal ArticleDOI
TL;DR: The Monticchio Lakes Formation MLF as mentioned in this paper is a newly identified carbonatite-melilitite tuff sequence which is exposed in the southwestern sector of the Vulture volcano.

77 citations


"Laghi di Monticchio (Southern Italy..." refers background or methods in this paper

  • ...The Laghi di Monticchio unit, which is exposed in the western surroundings of LGM, involves a carbonatite-melilitite tuff sequence abundant in mantle xenoliths (Stoppa and Principe 1998; Jones et al. 2000; Downes et al. 2002)....

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  • ...A prominent geochemical signature of the igneous rocks of the Monte Vulture complex including the LGM carbonatite-melilitite formation is the distinct enrichment of light rare earth elements (LREEs), as seen in data presented by De Fino et al. (1986) and Stoppa and Principe (1998)....

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Journal ArticleDOI
TL;DR: Spinel peridotite xenoliths from the Monte Vulture carbonatite-melilitite volcano have been derived from the subcontinental lithospheric mantle beneath central southern Italy.
Abstract: Spinel peridotite xenoliths found in the Monte Vulture carbonatite–melilitite volcano have been derived from the subcontinental lithospheric mantle beneath central southern Italy. Clinopyroxene-poor lherzolites and harzburgites are the most common rock types, with subordinate wehrlites and dunites. Small quantities of phlogopite and carbonate are present in a few samples. The peridotites record a large degree of partial melting and have experienced subsequent enrichment which has increased their LILE and LREE contents, but in most cases their HFSE contents are low. Despite being carried to the surface by a carbonatite–melilitite host, the whole-rock and clinopyroxene compositions of the xenoliths have a trace-element signature more closely resembling that of silicate-melt metasomatised mantle rather than carbonatite-metasomatised peridotites. 87Sr/86Sr and 143Nd/144Nd isotopic ratios for clinopyroxene from the Vulture peridotites are 0.7042–0.7058 and 0.51260–0.5131 respectively. They form a trend away from the depleted mantle to the composition of the host magmas, and show a significant enrichment in 87Sr/86Sr compared with most European mantle samples. The mantle beneath Monte Vulture has had a complex evolution – we propose that the lithosphere had already undergone extensive partial melting before being affected by metasomatism from a silicate melt which may have been subduction-related.

74 citations


"Laghi di Monticchio (Southern Italy..." refers background in this paper

  • ...The Laghi di Monticchio unit, which is exposed in the western surroundings of LGM, involves a carbonatite-melilitite tuff sequence abundant in mantle xenoliths (Stoppa and Principe 1998; Jones et al. 2000; Downes et al. 2002)....

    [...]

Frequently Asked Questions (21)
Q1. What are the contributions in "Laghi di monticchio (southern italy, region basilicata): genesis of sediments-a geochemical study" ?

Sediments from the smaller meromictic Lago Piccolo di Montichio are discussed as a reference. Their study demonstrates: ( i ) distinctly higher sediment accumulation for the centre of the lake basin by focussing of the settling particle flux ; ( ii ) decline of carbonate from the littoral to the profundal zones ; ( iii ) non-synchronous change of calcite net-accumulation for various water depths ; ( iv ) exceptionally high cation release from sediments covering the steeply inclining sector of the lake basin ; ( v ) relatively constant dissolved silica concentrations in the pore waters ( SiO2 ~42 mg/l ) independent of water depth and sediment composition ; ( vi ) influx of oxygen-bearing groundwater into the anoxic hypolimnion after heavy rainfall and the associated precipitation of Fe-oxihydroxides ; ( vii ) higher release of NH4 by anaerobic degradation of organic matter at a water depth of 23 m than for sediments at a maximum water depth of 32 m, whereby the latter reflects the importance of seasonal sediment re-oxidation for anaerobic degradation of organic debris ; ( viii ) although seasonal re-oxidation of sediments from various water depths is quite different, Oxygen Index values of LGM sediments fall in a small range, which reflects rapid microbial consumption of seasonally re-generated easily bio-degradable organic molecules. 

Pore water profiles can be used to assess microbial activity within sediments and the diffusive exchange between sediments and the overlying water. 

The diffusive penetration of oxygen into surface sediments, which depends on the oxygen concentration of the overlying water and the oxygen consumption rate in the sediment (mainly aerobic mineralization of organic matter and oxidation of reduced sulphur), determines the sediment depth where sulphate reduction can principally proceed from a thermodynamic viewpoint. 

Besides groundwater inflow, post-depositional ion release from this debris, in particular release of mono- and divalent cations and silica may significantly contribute to the DSC of the lake water. 

Presuming that LGM and LPM are fed by groundwater inflow of similar composition, an inhibited P-cycle in LPM due to meromixis should be the major reason for the overall higher Si consumption in the lake water of LGM. 

Sulphate is utilized as an electron acceptor for the bio-degradation of organic matter in the absence of other preferentially used electron acceptors (O2, NO3, reactive Fe(III), e.g. Furrer and Wehrli 1996) and is consumed by anaerobic methane oxidation (e.g. Iversen and Jørgensen 1985). 

Co-precipitation with FeOOH is an important mechanism that can transfer dissolved oxy-anions of U(VI) and Mo(VI) from the water column into the sediments (e.g. Bruno et al. 1995; Gustafsson 2003). 

In the nearly non-calcareous sediments from deeper parts of the lake basin, seasonal production of alkalinity associated with sulphate reduction is important. 

Elemental sulphur seems to play a key role in the formation of pyrite, which is less sensitive to oxidation (unpublished personal experimental results). 

Assuming a substantial post-depositional dissolution of autochthonous calcite, pore water in the surface sediments should reflect the Ca/Sr signature of the autochthonous calcite. 

Diffusive nutrient exchange across the sediment/water interface is further influenced by a complex of interacting parameters including, e.g. temperature, oxygen availability, vertical and temporal variations in H2S production by SO4 reduction, abundance of bio-degradable organic matter, PO4 retention or release associated with authigenic mineral formation. 

After a HNO3/HClO4/HF/HCl-decomposition of 0.25 g solid sample, the determination of major and minor elements, including phosphorus and sulphur, was carried out by sequential ICP-AES (ARL 35000) and external calibration. 

Increase of Ca and DIC in the hypolimnion of LGM towards the lake bottom reflects post-depositional dissolution of autochthonous carbonate. 

During the exposure of the dialysis cell, changes in interstitial water chemistry can occur, which is why in situ dialysis pore water profiles detected in this manner give an integral picture over the exposure time of the dialysis cells. 

Hydrogen sulphide produced by SO4 reduction releases PO4 from its precipitates with Fe. Inflow of SO4-bearing groundwater may therefore indirectly influence the P-cycle of LGM. 

Lowering of the pH seems to be sufficient to prevent precipitation of Ca and Mn, which show elevated concentrations in the pore water at the 12 m site. 

In the lower core section (31.5–55.5 cm) of the 4 m profile, however, unsupported 210Pb values vary between 38 and 69 mBq/g without showing a declining trend versus depth. 

If the authors consider TOC and N contents, biogenic opal accounts for approximately 50 wt% in the nearly non-calcareous sediments from the 23 m site. 

Three mechanisms may explain the lower Feexc of the profundalLGM sediments: (i) The dissolved Fe influx into the deep water and possible focussing of the settling FeOOH flux towards the centre of the lake basin does not counterbalance the Feexc loss by deposition of FeOOH particles in the shallow water area during overturn. 

Because of the permanent absence of oxygen in the LPM deep water, it appears astonishing that OI values of LPM sediments exceed the average OI of LGM sediments by a factor of ~1.5. 

The geochemical signatures of deeper sediments at the 8 m depth, showing distinctly lower Al contents (Fig. 5g), could reflect the presence of minerogenic debris with a geochemical composition that completely differs from those of the other LGM cores.