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Anthropogenic impact on the development of coastal marine ecosystems through the last millenium: comparing presumably high (German Bight) with low impact (Bay of Plenty, NZ) regions

The aim of this study is to decipher the human impact on the long-term development of the two key regions of the INTERCOAST research training group – the German Bight and Bay of Plenty in New Zealand. Both regions have been influenced by human interactions for almost the entire last millennium, beginning with early diking in the German Bight and the arrival of Polynesians in New Zealand. In the course of history both regions experienced intensification of land use and later on the onset of industrialization, presumably with different extents of impact. Additional trigger mechanisms of palaeoenvironmental variability are natural climate variations like the Little Ice Age and the 20th century global warming. High resolution sedimentary records, partly existing and partly to be newly collected, will serve as the base of investigations in this study.

Main study questions within the thesis will be:
  1. How have humans influenced the two study regions and is this reflected in the sediment?
  2. Have natural climate variations occurred and are these reflected in the sediments?
  3. How can the process-based understanding of past developments be used to contribute to the development of sustainable management strategies for the future development of the regions?
So far, background information about the setting and state-of-the-art in the region of Tauranga Harbour has been collected and summarized in a short outline (see excerpt below):
The estuary system of Tauranga Harbour has probably been influenced by human interventions for the last 700 years. While direct evidence by means of human footprints and cultural remains have been found in ash layers of the Rangitoto eruption from 1400 AD, first deforestation signals were found even earlier slightly underneath the tephra layers of Mt. Tarawera eruption (‘Kaharoa event’) from 1314 AD. Therefore, the beginning of human colonization of the North Island of New Zealand by Polynesians is dated back to the end of the 13th century. Abrupt changes in boreal pollen values and the appearance of microscopic charcoal particles are seen in sediment cores all over the North Island, especially also in a peat core from Matakana Island. Pollen and charcoal evidence suggests furthermore, that anthropogenic deforestation happened rapidly and extensively. Throughout the phase of Maori settlement indigenous forests decreased from 80% to about 50% of total land coverage. A second colonization phase started, when Europeans arrived in New Zealand around 1840 AD. With the arrival of Europeans also the sheep population increased and indigenous grasslands were fire-cleared for grazing. The introduction of refrigerated shipping in 1882 AD led to an expansion phase, a further removal of forests and expansion of pasture.
Since the hinterland is drained by several rivers, evidence of colonization and its different stages as well as hints of natural climate variations or of variances in sediment provenance will be found in the sediments of Tauranga Harbour. For example, fire deforestation by the first Maori probably led to enhanced erosion and therefore sedimentation rates may have increased. To determine the age of the sediments, shells may be used for analysis of radiocarbon. For verification matters, tephra layers of the Kaharoa event in 1314 AD and the Tarawera eruption from 1886 AD may be of help. Younger sediments may be determined by 210Pb, whereas the 137Cs isotope likely doesn’t assist in age determination because it was not detectable during former studies. The onset of deforestation is accompanied by increased values of charcoal particles, which may then be transported to the estuary. A change in vegetation may also be seen in pollen and seed numbers. With the arrival of Europeans, enhanced nutrient entry due to farming activities with higher live stocks may be reflected in nitrogen isotopic composition of organic matter in the sediments. A very recent increase in human activity and the onset of industrialization may be seen in the heavy metal composition of the sediments. Lead, for example, reaches the atmosphere via burning leaded and other fossil fuels as well as incineration of waste and gets washed out by rain. Another input of eroded and plant material as well as human contaminations from close and also more remote areas is delivered by wind.
Of course, sedimentation is not only a matter of what derives from land, but also of which processes are occurring in the water column and the sediment itself. The remains of benthic or pelagic foraminifer shells, for example may give us ideas about water temperature and/or salinity during their formation. Salinity changes may derive from changes in fresh water input or changes in the width of the tidal inlets. As water temperature has been shown to have a strong coupling to wind, a temperature proxy may indicate changes in wind patterns. Very productive areas may show depleted oxygen levels in the sediment and enhanced organic carbon values.

As this project is still at its very beginning, the Workshop in NZ (15.02.2013-02.03.2013) will be used (a) to further define the project during the first thesis committee meeting and related discussions, (b) to discuss future sampling campaigns in New Zealand, (c) to plan the research stay in New Zealand, and (d) to interact with fellow INTERCOAST PhD students and their supervisors in order to develop multi-project collaborations.

Members

Proponents:Prof. Dierk HebbelnUniversity of Bremen
:Dr. Willem de LangeUniversity of Waikato
PhD Candidate:Florian Boxberg (Sanja Asendorf)University of Bremen

Publications

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Miscellaneous

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