Gola d
i Lago
is a small (ca. 3 ha), m
inerotroph
ic peatland
in Canton T
ic
ino, southern Sw
itzerland. Chem
ical analysesof peat show remarkable concentrat
ions of As, Se, and U.Cor
ing at regular
intervals (19 s
ites) revealed severalzones of pronounced accumulat
ion, w
ith As concentrat
ionsup to 350 mg kg
-1 (2000 mg kg
-1 on a m
ineral matterbas
is). Both Fe and S are also enr
iched at th
is depth,suggest
ing that redox-related transformat
ions have affectedall three elements. H
igh concentrat
ions of Se (up to 28mg kg
-1) and U (up to 470 mg kg
-1) were also detected,represent
ing on a m
ineral matter bas
is 350 and 2900 mg kg
-1,respect
ively. An
interm
ittent stream enter
ing the peatlandconta
ined up to 400
![](/<font color=)
images/ent
it
ies/mgr.g
if">g of As L
-1, but the permanentstream leav
ing the m
ire conta
ins <2
![](/<font color=)
images/ent
it
ies/mgr.g
if">g L
-1. A three-d
imens
ional map of the spat
ial d
istr
ibut
ion of As showsthat the ma
in source of As
is the
interm
ittent stream andnot the basal, m
ineral sed
iment underly
ing the peatland.Arsen
ic
is h
ighly enr
iched not only
in shallow peat layersat the
interface between the stream and peatland todaybut also
in deeper peat layers
in the center of the m
ire, atwhat must have been the stream-peat
interface
in thepast. By sequent
ial extract
ion of fresh peat samples, 100%of the As could be extracted from a shallow sample butonly 19% from a sample taken from the deeper layers. In bothcases, most of the As was assoc
iated w
ith the organ
icmatter fract
ion (73% and 57% respect
ively). Although th
ispeatland
is an effect
ive geochem
ical trap for As
in thestream waters, the mechan
isms of removal rema
in unclear.