USGS Multimedia Gallery: (Video)--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 old…although 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 we’re 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: We’ve got the main peat-forming species, which is Empodisma minus, which is in the Restionaceae; it’s a restiad. We’ve also got some sedges here, and we’ve 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..they’ve been trampled…
>>Dr. McKee: Oh..wow!
>>Dr. Clarkson: I’ll..no…I’ll get you a nice one over here. Ahmm. And they actually grow upwards. The…ahhm..negatively geotropic. And that actually forms the bulk of the peat.
>>Dr. McKee: Oh…OK.
>>Dr. Clarkson: See..I mean it’s..it’s sort of like…just 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 we’ve done is we’ve removed a core from the marsh soil. And you can see it’s very organic. It’s peat. And what we’re 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 I’m going to do is insert it into the hole. And…it goes in quite easily but it’s a fairly tight fit. And then I’ll 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 we’ll be able to measure the biomass of roots that has grown into that ingrowth bag and that’ll give us an estimate of belowground productivity in this marsh.
>>Dr. Mendelssohn: So we’re just laying this…it’s about a 55 centimeter cotton strip. This is actually artist’s canvas, which has mostly cellulose and so we’re going to put it into the ground vertically….so we can measure the rate of tensile strength loss, which is an index of decomposition over..ah..over the time period that we’re going to have these in the ground. I’m going to pick up the shovel quickly so the strip stays in the ground.
>>Scott Bartlam: OK. Well, what I’m doing is…measuring the temperature of the soil at the plots. And I’m 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 the…it’s..the climate here is 14.7 degrees Celsius.
[sounds of walking through brush]
>> Dr. Mendelssohn: [sound of pulling material from ground]…without 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.