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Biological and Geochemical Record of Anthropogenic Impacts in Recent Sediments from Lake Pupuke, Auckland City, New Zealand |
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| Authors: | Paul Augustinus Michael Reid Sofia Andersson Yanbin Deng Mark Horrocks |
| Institution: | 1. Department of Geology, School of Geography and Environmental Science, University of Auckland, PB 92019, Auckland, New Zealand 2. National Institute of Water and Atmospheric Research, Christchurch, New Zealand 6. School of Resource, Environment and Heritage Sciences, University of Canberra, 2601, ACT, Australia 3. Earth Sciences Centre, G?teborg University, G?teborg, S-405 30, Sweden 7. Department of Physical Geography and Quaternary Geology, Stockholm University, S-106 91, Stockholm, Sweden 4. School of Biological Sciences, University of Auckland, PB 92019, Auckland, New Zealand 5. School of Geography and Environmental Science, University of Auckland, PB 92019, Auckland, New Zealand |
| Abstract: | Frozen sediment cores from Lake Pupuke in Auckland City, New Zealand, contain a high resolution decadal to annual scale record of changing lake paleoenvironments and geochemistry that reflects changing landuse and hydrology in the catchment over the past c. 190 years. A reliable chronology is available from AMS 14C and 210Pb dating of the sediments, with the timing of the older part of the record supported by the first appearance of pollen of introduced Pinus and Plantago lanceolata associated with European settlement of Auckland in the early 1840s. Diatom stratigraphy, sediment elemental and carbon isotope geochemistry reflect changes in sediment sources and lake conditions commensurate with European development of the Lake Pupuke catchment, in particular enhanced algal productivity controlled by the influx of nutrients after c. 1920 AD. Attempts to prevent nuisance algal blooms in 1933, 1934 and 1939 using CuSO4 addition produced Cu spikes in the sediment that allowed confirmation of the accuracy of the 210Pb chronology. Hence, the elemental and isotopic composition of the Lake Pupuke sediments reflect the timing of significant anthropogenic activities, rather than climatic variations, that have occurred within the watershed over the past c. 190 years. The comparison of records of land use change in the catchment with the multi-proxy record of changes in the sediments usually allowed unambiguous identification of the signatures of change and their causes. |
| Keywords: | Diatoms Eutrophication Lake sediment Pollen Trace elements Transfer function |
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