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| Titel |
A multi-proxy lake core record from Lago Lungo, Rieti Basin, Lazio, Italy and its relation to human activities in the catchment during the last century |
| VerfasserIn |
Paula Noble, Irene Tunno, Scott Mensing, Gianluca Piovesan |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250129594
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| Publikation (Nr.) |
 EGU/EGU2016-9729.pdf |
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| Zusammenfassung |
| The lakes of the Rieti Basin have experienced extensive human modification dating back to
pre-Roman times, yet lake archives indicate that the most profound changes to the aquatic
ecosystem have occurred during the last century. Analysis of the upper ∼120 cm segment of a
sediment core from Lago Lungo, dating back to ∼1830 CE, show changes in water quality
and hydrologic inflow largely attributed to 20th century reclamation and land use activities.
Lago Lungo is a shallow, small, eutrophic, hard water lake situated in an intermontaine
alluvial plain ∼90 km NE of Rome. It is one of several remnant lakes in a poorly drained
wetland area fed by numerous springs. Reclamation activities over the last century have
substantially altered the drainage network affecting water delivery to the lakes and their
connectivity. There are 3 interesting signals in the core. First, small Stephanodiscus species,
associated with hypereutrophic conditions, appear after 1950, peak ∼1990, and may be
attributed to increased use of chemical fertilizers and intensification of local agriculture.
Elemental proxies from scanning XRF data (abundances of Ti, Si/Ti, and Ca) are
consistent with increased eutrophication starting ∼1950. A decline in Stephanodicsus
after 1990 reflects some improvement to the water quality following the lake’s
incorporation into a nature preserve and creation of a narrow vegetation buffer.
Intermittent water quality measurements from 1982 onward corroborate the changes in
trophic status interpreted from the core record. Second, a large change in the core
stratigraphy, elemental geochemistry, and diatom composition occurs ∼1940 and is
associated with several major reclamation efforts, including the rerouting of the Santa
Susanna channel, which redirected large volumes of artesian inflows away from
the lakes and estuarine system. Upstream, dams on the Turano and Salto rivers
were also constructed, further affecting hydrological inflows into the basin. From
∼1900-1940 there is an abundance in Aulacoseira, which dominates the adjacent
Lago di Ripasottile and may suggest increased connectivity between these two
lakes prior to 1940. Third, the largest compositional change occurs ∼1900, before
which Cyclotella distinguenda and periphyton are larger components, and there is a
lower ratio of diatom frustules to silt. Prior to ∼1900, the lake may have received
additional hydrological inputs, including drainage from wetlands that were diverted after
1900. Causally, we put forth 2 hypotheses for the abrupt shift ∼1900. The first
hypothesis relates to a period of increased seismic activity circa 1900, including the
June 28 1898 earthquake that was felt strongly in the town of Rieti, ∼10 km to
the south of Lago Lungo. Seismic activity could have potentially impacted the
plain to alter drainage patterns in basin. Alternatively, following the hypothesis of
alternative stable states in lakes, the 1900 shift may simply represent an ecological
change from a clear water state dominated by macroalgae and periphyton, to a turbid
water state dominated by phytoplankton. In this alternative interpretation, the 1900
shift may represent the initial step in a 3-phased succession of lake eutrophication
throughout the 1900s, where the initial step predated the 1940 reclamation efforts. |
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