Fieldwork in New Zealand: Comparisons Between Northern and Southern Hemisphere Wetlands
Fieldwork on the North Island of New Zealand is contributing to a more global view of how wetlands function and how they may respond to climate change and other human-driven impacts. USGS scientist Karen McKee spent 5 months conducting research alongside New Zealand colleagues and other collaborators.
From January 10 to May 25, 2010, McKee participated in two projects aimed at a better understanding of wetlands in both the Southern and Northern Hemispheres. One project focused on freshwater wetlands in New Zealand and their vulnerability to nutrients; the other investigated the southernmost populations of mangrove, a subtropical/tropical coastal tree, and how climate change and other factors may affect mangrove expansion where their distribution overlaps with temperate salt marsh.
Where is New Zealand and What Was it Like to Do Fieldwork There?
New Zealand, which consists of two main islands and numerous smaller islands, is located in the Southern Hemisphere about 1,250 miles southeast of Australia and 1,500 miles north of Antarctica. The country is characterized by dramatic topography (from low-lying coastal areas to the peaks of the Southern Alps) and a complex climate (warm subtropical in the north, cool temperate in the south, severe alpine in mountainous regions). This varied landscape is contained within only 103,483 square miles (about the size of Oregon) and has a human population of just over 4 million. New Zealand straddles the Pacific and Australian tectonic plates and is characterized by periodic earthquakes and volcanism. Because of its long isolation from the rest of the world, New Zealand boasts an extraordinary biota—about 80 percent of its plant species are endemic. However, since European settlement, much of the native forest has been cleared, and many nonnative species of plants and animals have been introduced.
Fieldwork in New Zealand was often challenging. Researchers had to traverse large expanses of pasture and dodge grazing livestock to access freshwater wetlands, which were often located in isolated pockets far from roads and navigable waterways. Access to mangrove study sites along the coast required considerable hiking and was complicated by the large (6-9 ft) tide range—researchers had to plan carefully to avoid being stranded. Fortunately, there are few dangerous animals in New Zealand, ticks and tick-borne diseases are rare, and there is only one species of venomous spider. Except for stinging nettles (Urtica species), there are few poisonous plants.
Why Study Wetlands in New Zealand?
Temperate wetlands in the Northern Hemisphere have been well studied, and this 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. New Zealand wetlands contain unique indigenous flora and fauna, which are found nowhere else. These wetlands provide many of the same goods and services as do northern, temperate wetlands and are consequently important natural resources. Also, as in many other locations worldwide, New Zealand has lost a substantial portion of its wetlands to fragmentation, conversion to other uses, nutrient enrichment, and invasive species.
This study will help determine to what extent our understanding of biodiversity and ecosystem processes, based on northern, temperate wetlands, can be applied to New Zealand and other Southern Hemisphere locations. Of perhaps greater importance, information from Southern Hemisphere wetlands can be used in conjunction with that from Northern Hemisphere to develop a broader database with which questions regarding resilience and impacts of global change can be addressed at a broader scale. This type of information is particularly needed to predict how wetlands worldwide will respond to climate change, sea-level rise, and eutrophication (the process by which a body of water becomes enriched in dissolved nutrients that stimulate the growth of aquatic plant life, commonly resulting in excessive algal blooms and the depletion of dissolved oxygen).
Effects of Nutrients on New Zealand Freshwater Wetlands
McKee joined an international team of scientists led by Landcare Research, one of several Crown (government) Research Institutes in New Zealand, to investigate effects of nutrient enrichment on freshwater wetlands. Recent land-use conversion to dairy farming has greatly promoted polluted runoff into wetlands and invasion by weeds. Wetlands in the United States are similarly threatened by nutrient enrichment and invasive species, although the species involved as well as pollution sources and extent of influence may differ.
According to Bev Clarkson of Landcare Research, the goal of the New Zealand research program is to "improve management and restoration strategies for landowners, managers, and policymakers." To address this goal, research is focused on gaining a "functional understanding of how modification of water and nutrient regimes impacts biodiversity, cultural values and ecosystem services in a range of wetland types." A unique aspect of this research program is its explicit involvement of native Maori in restoration case studies, development of cultural indicators, training of emerging researchers, and development of end-user products, such as a Web-based handbook on restoration of cultural wetlands.
McKee is participating in a study of freshwater wetlands to determine if they are functionally similar to temperate wetlands in the Northern Hemisphere, despite floristic differences. The study involves experimental additions of nutrients (nitrogen and phosphorus) to wetlands at different successional stages and hypothesized sensitivity to enrichment.
McKee's role is to provide expertise in assessing belowground (roots) responses to nutrients by wetland plants of New Zealand and to participate in and advise on other aspects of the research. During this initial fieldwork, McKee and other project participants began measurements of belowground productivity, which will be completed in 2011.
A Comparison of Mangroves at Northern and Southern Limits of Distribution
McKee also participated in a second project, which focused on coastal wetlands and involved colleagues from the National Institute for Water and Atmospheric Research (NIWA) (New Zealand), the University of Queensland (Australia) and the Smithsonian Institution (United States). Fieldwork on this project was initiated several years ago and assessed nutrient controls on mangroves in the Southern Hemisphere (Australia and New Zealand).
New Zealand has a single indigenous species of mangrove, Avicennia marina subsp. australacasica, which is restricted to the North Island of New Zealand, New Caledonia, Lord Howe Island, and the southern tip of Australia. Its Northern Hemisphere counterpart, Avicennia germinans (black mangrove), grows at its northernmost limits in Louisiana, where McKee also has study sites. At their northern and southern limits, mangroves intergrade with temperate marsh plants, with which they compete for space, light, and nutrients. In both settings, mangroves are expanding in area, although the causes for expansion appear to differ.
In previous research, McKee has examined effects of elevated carbon dioxide on A. germinans in Louisiana and effects on competition with salt marsh species; she and her colleague Jill Rooth published a paper on this subject in Global Change Biology (2008, vol. 14, p. 971-984, http://dx.doi.org/10.1111/j.1365-2486.2008.01547.x). In addition, McKee coauthored a book chapter on salt marsh-mangrove interactions in Australia and the Americas for inclusion in Coastal Wetlands, An Integrated Ecosystem System Approach, published in 2009 by Elsevier (http://www.elsevier.com/wps/find/bookdescription.cws_home/716674/description).
During fieldwork in New Zealand, McKee examined characteristics of mangroves for comparison with mangroves at their northern limits along the Gulf of Mexico. She traveled along both coasts of the North Island in New Zealand conducting measurements and making observations of mangroves and associated marsh vegetation.
Wetland Restoration in New Zealand
McKee also visited wetland restoration sites to observe methods and learn about cooperative efforts between government researchers and private companies. Peat mining, which involves surface excavation of peat bogs, is an important industry in New Zealand. Some mining companies are cooperating with New Zealand scientists to restore the native bog vegetation in mined areas to allow for future peat formation. McKee visited one mine in the Hauraki Plains region, where researchers had conducted a study to determine the best planting, fertilization, and cultivation techniques to promote rapid revegetation by the primary peat-forming plants and to minimize invasion by weeds. The results of this study will assist the mining operation in designing protocols for postharvest restoration.
By studying and comparing diverse wetlands, USGS scientists can develop more accurate models to predict future changes due to human activities as well as to natural disturbances. Research on wetlands outside of the United States, especially with respect to global change factors, is necessary to fully understand and predict how wetlands in general may respond in the future. By identifying how differences and similarities in structure and function influence wetland resilience, scientists can better predict how specific wetlands in the United States will fare in the future and to design appropriate management and restoration plans. In addition, participation in international research projects leads to new ideas and methods for protecting and conserving the Nation's natural resources.
in this issue:
Comparisons Between Northern and Southern Hemisphere Wetlands