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- Climatic
control on
rapid
exhumation
along the
Southern
Himalayan
Front: Earth and
Planetary
Science
Letters, Vol.
222, No. 3-4.
(15 June
2004), pp.
791-806.Along
the Southern
Himalayan
Front (SHF),
areas with
concentrated
precipitation
coincide with
rapid
exhumation, as
indicated by
young mineral
cooling ages.
Twenty new,
young (80% of
the annual
precipitation.
AFT cooling
ages reveal a
coincidence
between rapid
erosion and
exhumation
that is
focused in a
~50-70-km-wide
sector of the
Himalaya,
rather than
encompassing
the entire
orogen.
Assuming
simplified
constant
exhumation
rates, the
rocks of two
age vs.
elevation
transects were
exhumed at
~1.4±0.2 and
~1.1±0.4 mm/a
with an
average
cooling rate
of ~40-50
°C/Ma during
Pliocene-Quart
ernary time.
Following
other recently
published
hypotheses
regarding the
relation
between
tectonics and
climate in the
Himalaya, we
suggest that
this
concentrated
loss of
material was
accommodated
by motion
along a
back-stepping
thrust to the
south and a
normal fault
zone to the
north as part
of an
extruding
wedge.
Climatically
controlled
erosional
processes
focus on this
wedge and
suggest that
climatically
controlled
surface
processes
determine
tectonic
deformation in
the internal
part of the
Himalaya.
Source: Earth and Planetary Science Letters, Vol. 222, No. 3-4. (15 June 2004), pp. 791-806. - PCB sources,
transformation
s, and
contributions
in recent Fox
River,
Wisconsin
sediments
determined
from receptor
modeling: Water
Research, Vol.
36, No. 14.
(August 2002),
pp.
3449-3462.The
PCB
contamination
in lower Fox
River
sediments was
investigated
in order to
identify
possible PCB
sources,
contributions,
and
transformation
s, using two
receptor
models.
Congener
specific
sediment PCB
data from
sites
immediately
upstream of
DePere dam to
Green Bay that
had been
gathered for
the Green
Bay/Fox River
Mass Balance
Study, were
used in this
analysis. The
first receptor
model is a
self training
factor
analysis (FA)
model with
non-negative
constraints
that was
applied to
identify the
PCB sources
and
significant
congener
patterns. The
second is a
chemical mass
balance model
(CMB) in which
published
Aroclor
sources,
inferred from
our FA model,
were used to
apportion
these Aroclors
to each
sample. The FA
model
indicated two
significant
factors, the
major one
being Aroclor
1242 and the
other, a
profile
dominated by
low
chlorinated
congeners,
indicating a
possible PCB
alteration
profile. This
profile had
significant
contributions
to samples at
or around
sites with
total PCB
concentrations
higher than 50
ppm,
indicating a
potential
anaerobic
dechlorination
activity. It
was also
deduced from
the FA model
that very
small
contributions
of more highly
chlorinated
Aroclors may
be present in
the system.
The results
from the CMB
model
confirmed that
the system is
dominated by
Aroclor 1242.
Its average
contribution
was 95%, with
small amounts
of Aroclor
1254 (2%) and
1260 (1%). Two
of the
samples,
located in the
vicinity of
point sources,
showed high
contributions
of Aroclor
1016 by the
CMB model.
This is
interpreted as
an altered
Aroclor
profile
resembling the
less
chlorinated
Aroclor 1016.
Contributions
obtained form
the CMB and FA
models show
similar
patterns.
Source: Water Research, Vol. 36, No. 14. (August 2002), pp. 3449-3462. - Linking land
use, erosion
and sediment
yields in
river basins: Hydrobiologia,
Vol. 410, No.
0. (1999), pp.
223-240.Result
s obtained
from erosion
plots and
catchment
experiments
provide clear
evidence of
the
sensitivity of
erosion rates
to land use
change and
related human
activity.
Evidence for
the impact of
land use on
the sediment
yields of
world rivers
is less clear,
although
examples of
rivers where
sediment
yields have
both increased
and decreased
in recent
decades can be
identified.
The apparent
lack of
sensitivity of
river sediment
loads to land
use change
reflects, at
least in part,
the buffering
capacity
associated
with many
river basins.
This buffering
capacity is
closely
related to the
sediment
delivery ratio
of a river
basin, in that
basins with
high sediment
delivery
ratios are
likely to
exhibit a
reduced
buffering
capacity.
Investigations
of the impact
of land use
and related
human activity
on sediment
yields should
consider the
overall
sediment
budget of a
catchment
rather than
simply the
sediment
output.
Information on
the sediment
budget of a
drainage basin
is difficult
to assemble
using
traditional
techniques,
but recent
developments
in the
application of
fingerprinting
techniques to
establish
sediment
sources and in
the use of
environmental
radionuclides,
such as
caesium-137
and lead-210,
to document
sediment
storage offer
considerable
potential for
providing such
information.
Sediment
storage within
a river basin
can give rise
to
environmental
problems where
sediment-assoc
iated
pollutants
accumulate in
sediment
sinks. The
accumulation
of phosphorus
on river
floodplains as
a result of
overbank
sedimentation
can, for
example,
represent an
important
phosphorus
sink.
Source: Hydrobiologia, Vol. 410, No. 0. (1999), pp. 223-240. - Distribution
and seasonal
biomass of
drift
macroalgae in
the Indian
River Lagoon
(Florida, USA)
estimated with
acoustic
seafloor
classification
(QTCView,
Echoplus): Journal of
Experimental
Marine Biology
and Ecology,
Vol. 326, No.
1. (6 December
2005), pp.
89-104.Three
areas of the
Indian River
Lagoon,
Florida (USA)
were surveyed
to show
seasonal
changes in the
distribution
and biomass of
macroalgae and
seagrass.
Acoustic
seafloor
discrimination
based on first
and second
echo returns
of a 50 kHz
and 200 kHz
signal, and
two different
survey systems
(QTCView and
ECHOplus) were
used. System
verification
in both the
field and a
controlled
environment
showed it was
possible to
distinguish
acoustically
between
seagrass,
sparse algae,
and dense
algae.
Accuracy of
distinction of
three classes
(algae,
seagrass, bare
substratum)
was around
60%. Maps were
produced by
regridding the
survey area to
a regular grid
and using a
nearest-neighb
or
interpolation
to provide
filled
polygons.
Biomass was
calculated by
counting
pixels
assigned to
substratum
classes with
known
wet-weight
biomass values
(sparse algae
250 g m- 2,
dense algae
2000 g m- 2,
seagrass 100 g
m- 2) that
were measured
in the field.
In three study
areas
(Melbourne,
Sebastian
Inlet, and
Cocoa Beach),
a dependence
of algal
biomass on
depth and
season was
observed.
Seagrass most
frequently
occurred in
water less
than 1 m deep,
and in
November,
seagrass beds
tended to be
covered by
dense algae
that also
extended up-
and downstream
of shoals in
the Lagoon. In
March, the
pattern was
similar, with
the exception
that some
areas of
previously
dense algae
had started
thinning into
sparse algae.
Macrophyte
biomass was
lowest in May
in the
Melbourne and
Cocoa Beach
study areas,
with the
opposite
situation in
the Sebastian
Inlet study
area. In May,
seagrass areas
were largely
devoid of
dense algae
and most algae
accumulations
were sparse.
In August,
dense algae
covered large
areas of the
deep Lagoon
floor while
shoals were
largely free
of algae or
had only
sparse cover.
We suggest
this summer
pattern to
reflect
moribund algae
being washed
from the
shallows to
deeper
channels and
from there
being removed
from the
lagoonal
ecosystem
either through
tidal passages
into the open
ocean or by
degradation
and breakdown
in situ. The
differences
between the
study areas
indicate high
spatial and
temporal
variability in
biomass and
distribution
of macrophyte
biomass in the
Indian River
Lagoon.
Source: Journal of Experimental Marine Biology and Ecology, Vol. 326, No. 1. (6 December 2005), pp. 89-104. - Fluvial
landscape
models and
catchment-scal
e sediment
transport: Global and
Planetary
Change, Vol.
39, No. 1-2.
(October
2003), pp.
31-51.The need
for the
ability to
make
quantitative
predictions
regarding the
transport of
sediment
within
watersheds and
from
watersheds to
the sea has
never been
more important
than it is
today.
Sediment
transport is
at the heart
of a
surprising
number of
practical
problems,
ranging from
the prevention
of soil loss
to the
tracking of
contaminants,
and this has
resulted in a
rich but
scattered
literature. In
many of these
contexts,
observational
data has been
used to
develop
empirical
sediment
transport
laws. For
example, the
Revised
Universal Soil
Loss Equation
(RUSLE) has
been developed
for use at the
farm-plot
scale, and the
equation of
Syvitski et
al. [Water
Resour. Res.
36(9) (2000)
2747] was
developed for
the world's
largest river
basins. In the
context of
fluvial
geomorphology,
several
different but
closely
related
sediment
transport laws
have been used
to construct
fluvial
landscape
models. The
sediment
transport
formulas used
by these
models are a
generalized
form of
several
physically
based bed-load
transport
formulas.
Based on
studies of
fluvial
landscape
models, we now
know that many
measurable
attributes of
channelized
landscapes,
such as
junction
angles, Horton
ratios,
hydraulic
geometry
exponents,
valley
geometry, and
longitudinal
profiles, vary
in a
predictable
manner with a
few
well-constrain
ed, physical
parameters.
One important
consequence of
this success
in forward
modeling is
that it is now
feasible to
solve the
inverse
problem of
calculating
regional
sediment
transport
parameters
from
measurements
(such as long
profiles) that
can easily be
made from
digital
elevation
models (DEMs).
This may also
make it
possible to
make a
rational
selection
between
alternate
sediment
transport
laws. Since
fluvial
landscape
models
represent the
state of the
art in
catchment
sediment
transport
modeling, the
three-fold
purpose of
this paper is
to: (1)
explain the
key concepts
and
simplifying
assumptions
that are
common to
these models;
(2) explain
how several
current models
differ from
one another;
and (3)
highlight a
few of the
significant
results that
have been
obtained in
recent years.
While serving
mostly as an
expository or
overview
paper, some
new results
for a steady
state fluvial
landscape
model are also
included.
Source: Global and Planetary Change, Vol. 39, No. 1-2. (October 2003), pp. 31-51.
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