Nutrient Impacts on Wetlands: Field Studies New Zealand

Nutrient Impacts on Wetlands: Field Studies New Zealand


>>Narrator: Wetlands such as swamps and marshes
often receive nutrient runoff from agricultural lands, and changes in nutrient regime can
alter their structure and function. In this project, scientists from the U.S.
Geological Survey are collaborating with counterparts in New Zealand to investigate effects of nutrients
on freshwater wetlands. New Zealand is located in the Southern Hemisphere
about 1,200 miles southeast of Australia and 1,500 miles north of Antarctica. The country
consists of two main islands and numerous smaller islands. The landscape is characterized
by dramatic topography, which ranges from low-lying coastal areas to the Southern Alps
on the South Island, which reach over 12,000 feet high.
Due to its long isolation from the rest of the world, New Zealand boasts unique indigenous
plants and animals that are found nowhere else. The types of wetlands here vary from
salt marshes and mangroves along the coast to freshwater wetlands, which are the focus
of this video. Freshwater types include bogs, fens, swamps, and marshes.
Since European settlement, however, much of the native forest has been cleared, and many
non-native species of plants and animals have been introduced. In the past 150 years, New
Zealand has lost 90 percent of its original wetlands.
Because much of the land on the North Island of New Zealand has been converted to support
grazing livestock, sources of nutrients have increased substantially, and this change can
have a large effect on wetlands located within the same watershed. In this project, researchers
traverse large expanses of pasture and dodge sheep and cows to access wetlands located
in isolated pockets.>>Dr. Clarkson: The wetland as we see it
today was formed about 2000 years ago with the big Taupo eruption, when Lake Taupo erupted
and everything got blocked and came down the Waikato River. So it blocked up a whole lot
of the channels going into the Waikato River; so this all formed as a result of the blockage.
So we know this is only about 2,000 years oldÖalthough there would be portions that
would have deeper peats but not the wetland as we know it today. So we know this is a
relatively young one.>>Dr. Clarkson: We have ahhm..three different
wetlands. One is in the early successional, high-nutrient wetland. One is in a mid-successional,
medium-nutrient wetland. And this is a late-successional, low-nutrient wetland. So weíre expecting
different responses to the fertilizer across the different wetlands.
>>Narrator: By experimentally changing the amount of nutrients with different fertilizer
treatments, scientists can assess the effects on species composition and diversity as well
as on ecological functions such as peat formation.>>Dr. Clarkson: Weíve got the main peat-forming
species, which is Empodisma minus, which is in the Restionaceae; itís a restiad. Weíve
also got some sedges here, and weíve got a fern, swamp umbrella fern, which is here.
And over in the back here we have our late successional cane rush, which is also in the
Restionaceae, which is obviously a relative of the Empodisma down here. And this is also
a peat former.>>Narrator: . The low-nutrient, flooded conditions
in some of these wetlands can lead to massive accumulations of plant matter, called peat,
which is often mined for commercial purposes.>>Dr. Clarkson: That. That is actually the..what
we call cluster roots.>>Dr. McKee: Oh, yeah!
>>Dr. Clarkson: I mean..theyíve been trampledÖ>>Dr. McKee: Oh..wow!
>>Dr. Clarkson: Iíll..noÖIíll get you a nice one over here. Ahmm. And they actually
grow upwards. TheÖahhm..negatively geotropic. And that actually forms the bulk of the peat.
>>Dr. McKee: OhÖOK.>>Dr. Clarkson: See..I mean itís..itís sort
of likeÖjust like sphagnum.>>Dr. McKee: Uh huh.
>>Dr. Clarkson: You know it holds water and so on. This forms the bulk of the peat.
[background voices]>>Dr. Clarkson: Well, most of the peat is
this one. [sounds of walking through brush]
>>Dr. McKee: What weíve done is weíve removed a core from the marsh soil. And you can see
itís very organic. Itís peat. And what weíre going to do now is put in an ingrowth bag,
which is constructed of a..an open-weave, mesh, plastic material. And inside is sphagnum
peat that has been purchased commercially. So now what Iím going to do is insert it
into the hole. AndÖit goes in quite easily but itís a fairly tight fit. And then Iíll
use a tether..to tether it to a stake here so that we can easily find the bag a year
from now when we remove them. And recore this spot and weíll be able to measure the biomass
of roots that has grown into that ingrowth bag and thatíll give us an estimate of belowground
productivity in this marsh.>>Dr. Mendelssohn: So weíre just laying thisÖitís
about a 55 centimeter cotton strip. This is actually artistís canvas, which has mostly
cellulose and so weíre going to put it into the ground verticallyÖ.so we can measure
the rate of tensile strength loss, which is an index of decomposition over..ah..over the
time period that weíre going to have these in the ground. Iím going to pick up the shovel
quickly so the strip stays in the ground.>>Scott Bartlam: OK. Well, what Iím doing
isÖmeasuring the temperature of the soil at the plots. And Iím doing it from sort
of the start of the area where we put our plots and right through to the end. And just
checking that the soil temperatures are fairly consistent across there. The temperature of
theÖitís..the climate here is 14.7 degrees Celsius.
[sounds of walking through brush]>>Dr. Mendelssohn: [sound of pulling material
from ground]Öwithout ripping any of the material. And you can see that the upper part of the
strip has been in fairly dry soil, and then the lower part of the strip has been in much
moister soil. And these are installed in plots that have received different fertilizer treatments.
Either nitrogen, phosphorus, or nitrogen and phosphorus. So we are trying to identify which
of these nutrients or the combination of them limits the activity of these bacteria that
decompose cellulose.>>Narrator: Peat-forming wetlands are important
sinks for carbon, sequestering tons of peat over thousands of years. Plants fix carbon
dioxide in the atmosphere during photosynthesis, and the fixed carbon becomes buried over time
in the peat as the plants die and their tissues accumulate in the soil. By examining how changes
in nutrient input affect plant production and decomposition processes, scientists can
better predict how eutrophication may alter carbon storage and other ecosystem functions
in these wetlands.>>Narrator: Temperate wetlands in the Northern
Hemisphere have been well studied, and that research underlies much of what is known about
wetland structure and function. In contrast, much less is known about wetlands in the Southern
Hemisphere, particularly in geographically isolated locations such as New Zealand. The
results of this joint study will lead to a broader understanding of nutrient impacts
on wetlands and better ways to manage these important ecosystems.

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