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Art: This afternoon we're out on the
Neuse River in North Carolina collecting
bed-sediment samples. This is part of a
large national project that's intended
to calculate and determine the concentration
and masses of sediment-associated
off-continent flux of a variety of
chemical constituents. We're sampling
the sediment because the sediment is a
major carrier for things like trace
elements, nutrients, and a number of
organic pollutants like DDT, and PCBs.
Ordinarily, we would use suspended sediment,
but it would take a very long time to get a
sufficient mass of it to work with. So,
we're using bed sediment as a surrogate,
but we're not using the entire component
of all of the bed sediment, we're just
looking at the less than 63-micron fraction.
Those samples that we're collecting
are representative cross-sectional ones,
so that we've collected aliquots as
we've gone across the stream bed and
composited it, so that it represents
the entire river cross section.
And ultimately, we'll be collecting the
same kind of material at 130 river sites
all around the coast of the United States,
starting in Maine and going to the tip
of Florida, going from the tip of Florida
all the way over to the Texas-Mexico
border. And then, from Baja California,
all the way up the west coast and into
Washington because we're also gonna
collect samples from rivers that
discharge into Puget Sound.
What's the bottom feel like?
Erik: Mud with a lot of clams.
Art: Oh good!
Erik: Or oysters.
Art: That's what I needed.
Michelle: So Art, what's this you're using to collect sediment samples with?
Art: This is a petite PONAR and it's spring
loaded, and what happens is as long as
I keep tension on the line, the springs
stay shut because the two bars keep the
thing in place. When I hit the bottom,
the spring pops out. And, when I pull
up, it closes and that's how I collect the sample.
Michelle: And about how much of the sediment layer do you get with it?
Art: Well, it depends on the bottom and
how heavy it is. If the bottom is fairly
soft, we probably go down about six to
eight inches. But, we're only trying
to collect the upper one to two centimeters.
We got something. Well, we got a big clam.
Erik: Is there a minimum amount that you need or?
Art: Well, we can do the analysis on
two grams or less, but I want a representative sample.
Figure, roughly by about where that post is –
Art: – and we'll start there. We'll see what the water depth is.
Michelle: So Art, what are your expected results from this study?
Art: Well, we ultimately will come up with
a mass and concentrations for all the constituents
that we're measuring. Right now, approximately
260 megatons of sediment are discharged
to the Atlantic, Gulf, and Pacific. And,
those sediments contain high concentrations
of a variety of constituents. Some of
them are within a normal range, some of
them exceed those ranges. But, we won't
really know until we actually carry out
a chemical analysis on them.
The information we get from this will
give us a baseline level of chemical
transport, which can be used, in part,
to assess climate- change effects, so
it changes from climate change. It will
also help us identify those rivers that
have excessive concentrations and might
require additional monitoring.
One of the major aspects of this study is
to evaluate various factors that can affect
sediment chemistry. So, as part of this
study, we're collecting a lot of ancillary
data. We're collecting land-use
distributions within each basin, covering
such things as the amount of agriculture,
the amount that's forested, the amount
that's urbanized, the amount that's
undeveloped, and we're also looking at population density.
Previous work has shown that both the
population density and the amount of
urbanization, are the strongest or
single most important factors that
affect the sediment chemistry, and
also nutrient sediment chemistry.
At the end of this project, we will have
a series of calculated values that we
can compare against the actual measured
values in the samples we're collecting.
The calculated values will be first
baseline values, based on NAWQA bed-sediment
samples that were collected at 450 sites
around the U.S. The second will be based
on worldwide published averages for
suspended sediment. The third, will be based
on land-use distributions within each
basin. And then, the last will be based
on population density within each basin.
And, those calculated values will ultimately
be compared against the actual measured
values and hopefully, we'll have a
better idea of the factors that affect
sediment chemistry and we will actually
have values to evaluate those factors
against, because we're collecting real
samples that we're going to ultimately analyze.
Erik: You did it.
Art: It also looks like it's empty-- Totally clean.
It's about four feet. I don't think
you can hit it, well you might
be able to hit is with the paddle.
It's just sand.
We'll go downstream about a couple hundred yards.
Michelle: So Art, what do you think the
effects of climate change will be on the flux, sediment flux?
Art: Well, the two most significant effects
of climate change are going to be temperature
changes and changes in precipitation
patterns. Precipitation patterns are
going to affect the amount of sediment
that's being discharged because
it's a function of runoff, and
temperature changes will affect
weathering, which will affect the
chemistry of the sediment. So, both affects.
Michelle: How empty are we Erik?
Erik: Quite empty.
Art: Got sediment this time, not a lot,
but some. I'll take this and take a
duplicate and then we'll go home.
The major outcome of this exercise,
which will take about two years in
total, will be to establish a baseline
level for off-continent flux against
which we can measure subsequent changes
and hopefully, ascribe them to
climate effects or climate change.
[End of Audio]
Title: The Off-Continent Flux Project
Art Horowitz (U.S. Geological Survey) describes the U.S. Geological Survey study to estimate amounts of chemicals washed to the oceans from the continental United States.
Date Taken: 5/1/2011
Video Producer: Douglas A. Harned , National Water-Quality Assessment Program (NAWQA), USGS, North Carolina Water Science Center, Raleigh, NC
Note: This video has been released into the public domain by the U.S. Geological Survey for use in its entirety. Some videos may contain pieces of copyrighted material. If you wish to use a portion of the video for any purpose, other than for resharing/reposting the video in its entirety, please contact the Video Producer/Videographer listed with this video. Please refer to the USGS Copyright section for how to credit this video.
Additional Video Credits:
Art Horowitz: Scientist
Douglas Harned: Producer, Video, Editor
Michelle Moorman: Video
Erik Staub: Video
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