Browsing by Author "Lovelock, CE"
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- ItemMangrove forest and soil development on a rapidly accreting shore in New Zealand(Springer, 2010-04) Lovelock, CE; Sorrell, BK; Hancock, N; Hua, Q; Swales, AMangrove forests are rapidly expanding their distribution in New Zealand, which is at the southern limit of their range. We investigated how these expanding mangrove forests develop through time. We assessed patterns in forest structure and function at the Firth of Thames, which is a rapidly accreting mangrove site in New Zealand where 1 km of mangrove of Avicennia marina has established seaward since the 1950s. Across the intertidal region, mangrove forest structure was highly variable. We used bomb-pulse radiocarbon dating to age the forest. Two major forest establishment events were identified; one in 1978–1981 and another in 1991–1995. These events coincided with sustained El Niño activity and are likely the result of reduced wind and wave energy at the site during these periods. We used the two forests of different ages to assess whether mangroves in New Zealand mature at similar rates as other mangroves and whether they conform to classic models of succession. The timing of forest maturation is similar in New Zealand as in more tropical locations with trees exhibiting features of mature forests as they age from about 10 to about 30 years. In older forest (~30 years old) trees become larger and stands more homogenous than in the younger forest (~10 years old). Carbon and nutrient concentrations in soils increased and soils become more aerobic in older forest compared to younger forest. Additionally, using fertilization experiments, we established that despite reduced growth rates in older forests, nitrogen remained limiting to growth in both older and young forests. However, in contrast to classic successional models leaf tissue nutrient concentrations and nutrient conservation (nutrient resorption from senescence leaf tissue) were similar in forests of differing ages and did not vary with fertilization. We conclude that mangrove forest expansion in New Zealand is influenced by climatic factors. Mangrove forests mature rapidly, even at the limits of their range and they satisfy many of the successional patterns predicted by Odum (1969) for the early stages of forest succession. © 2010, Springer.
- ItemNatural and regenerated saltmarshes exhibit similar soil and belowground organic carbon stocks, root production and soil respiration(Springer Nature Limited, 2019-04-10) Santini, NS; Lovelock, CE; Hua, Q; Zawadzki, A; Mazumder, D; Mercer, TR; Muñoz-Rojas, A; Hardwick, SA; Madala, BS; Cornwell, W; Thomas, T; Marzinelli, EM; Adam, P; Paul, S; Vergés, ASaltmarshes provide many valuable ecosystem services including storage of a large amount of ‘blue carbon’ within their soils. To date, up to 50% of the world’s saltmarshes have been lost or severely degraded primarily due to a variety of anthropogenic pressures. Previous efforts have aimed to restore saltmarshes and their ecosystem functions, but the success of these efforts is rarely evaluated. To fill this gap, we used a range of metrics, including organic carbon stocks, root production, soil respiration and microbial communities to compare natural and a 20-year restoration effort in saltmarsh habitats within the Sydney Olympic Park in New South Wales, Australia. We addressed four main questions: (1) Have above- and belowground plant biomass recovered to natural levels? (2) Have organic carbon stocks of soils recovered? (3) Are microbial communities similar between natural and regenerated saltmarshes? and (4) Are microbial communities at both habitats associated to ecosystem characteristics? For both soil organic carbon stocks and belowground biomass, we found no significant differences between natural and regenerated habitats (F(1,14) = 0.47, p = 0.5; F(1,42) = 0.08, p = 0.76). Aboveground biomass was higher in the natural habitat compared to the regenerated habitat (F(1,20) = 27.3, p < 0.0001), which may result from a site-specific effect: protection from erosion offered by a fringing mangrove forest in the natural habitat but not the regenerated habitat. Our microbial community assessment indicated that restored and natural saltmarsh habitats were similar at a phylum level, with the exception of a higher proportion of Proteobacteria in the rhizosphere of saltmarshes from the regenerated habitat (p < 0.01). Abundance of both Desulfuromonas and Geobacter was associated with high carbon and nitrogen densities in soils indicating that these genera may be key for the recovery of ecosystem characteristics in saltmarshes. Our restored and natural saltmarsh soils store at 30 cm depth similar levels of organic carbon: 47.9 Mg OC ha−1 to 64.6 Mg OC ha−1. Conservation of urban saltmarshes could be important for ‘blue carbon’ programmes aimed at mitigating atmospheric carbon dioxide. © 2019 Springer Science+Business Media, LLC, part of Springer Nature
- ItemRadiocarbon dating and wood density chronologies of mangrove trees in arid Western Australia(Public Library of Science, 2013-11-12) Santini, NS; Hua, Q; Schmitz, N; Lovelock, CEMangrove trees tend to be larger and mangrove communities more diverse in tropical latitudes, particularly where there is high rainfall. Variation in the structure, growth and productivity of mangrove forests over climatic gradients suggests they are sensitive to variations in climate, but evidence of changes in the structure and growth of mangrove trees in response to climatic variation is scarce. Bomb-pulse radiocarbon dating provides accurate dates of recent wood formation and tree age of tropical and subtropical tree species. Here, we used radiocarbon techniques combined with X-ray densitometry to develop a wood density chronology for the mangrove Avicennia marina in the Exmouth Gulf, Western Australia (WA). We tested whether wood density chronologies of A. marina were sensitive to variation in the Pacific Decadal Oscillation Index, which reflects temperature fluctuations in the Pacific Ocean and is linked to the instrumental rainfall record in north WA. We also determined growth rates in mangrove trees from the Exmouth Gulf, WA. We found that seaward fringing A. marina trees (similar to 10 cm diameter) were 48 +/- 1 to 89 +/- 23 years old (mean +/- 1 sigma) and that their growth rates ranged from 4.08 +/- 2.36 to 5.30 +/- 3.33 mm/yr (mean +/- 1 sigma). The wood density of our studied mangrove trees decreased with increases in the Pacific Decadal Oscillation Index. Future predicted drying of the region will likely lead to further reductions in wood density and their associated growth rates in mangrove forests in the region. © 2013 Santini et al.
- ItemReconstructing extreme climatic and geochemical conditions during the largest natural mangrove dieback on record(European Geosciences Union (EGU), 2020-02-28) Sippo, JZ; Santos, IR; Sanders, CJ; Gadd, PS; Hua, Q; Lovelock, CE; Santini, NS; Johnston, SG; Harada, Y; Reithmeir, G; Maher, DTA massive mangrove dieback event occurred in 2015–2016 along ∼ 1000 km of pristine coastline in the Gulf of Carpentaria, Australia. Here, we use sediment and wood chronologies to gain insights into geochemical and climatic changes related to this dieback. The unique combination of low rainfall and low sea level observed during the dieback event had been unprecedented in the preceding 3 decades. A combination of iron (Fe) chronologies in wood and sediment, wood density and estimates of mangrove water use efficiency all imply lower water availability within the dead mangrove forest. Wood and sediment chronologies suggest a rapid, large mobilization of sedimentary Fe, which is consistent with redox transitions promoted by changes in soil moisture content. Elemental analysis of wood cross sections revealed a 30- to 90-fold increase in Fe concentrations in dead mangroves just prior to their mortality. Mangrove wood uptake of Fe during the dieback is consistent with large apparent losses of Fe from sediments, which potentially caused an outwelling of Fe to the ocean. Although Fe toxicity may also have played a role in the dieback, this possibility requires further study. We suggest that differences in wood and sedimentary Fe between living and dead forest areas reflect sediment redox transitions that are, in turn, associated with regional variability in groundwater flows. Overall, our observations provide multiple lines of evidence that the forest dieback was driven by low water availability coinciding with a strong El Niño–Southern Oscillation (ENSO) event and was associated with climate change. © Author(s) 2020.
- ItemSpatial and temporal variation in carbon storage in subtropical seagrass meadows(World Seagrasses Association, 2016-10-17) Samper-Villarreal, J; Lovelock, CE; Saunders, MI; Roelfsema, C; Hua, Q; Mumby, PJSeagrass meadows are one of three habitats that serve as marine carbon sinks, preserving up to thousands of years of carbon stored in their sediments. However, seagrass meadows are highly threatened and are continuing to decline worldwide. Seagrass management and conservation initiatives require adequate understanding of the spatial and temporal variability of carbon storage in these ecosystems, which is currently limited. This study aimed to identify how varying environmental and biological conditions influence spatial and temporal variability of carbon storage in subtropical seagrass meadows. Seagrass biomass and sediment cores were collected between the years 2012 and 2013 at multiple locations across a water quality gradient within Moreton Bay, Australia. The number of cores collected were 298 biomass cores, 298 shallow sediment cores, and 20 deeper sediment cores of up to 2 m sediment depth. Sediment carbon content and seagrass structural complexitywere determined for each location. Environmental variables were determined from field data (water quality) and modelled data (wave height). Spatial variability of carbon content was found among sites and linked to variations in seagrass canopy complexity, water turbidity, depth and wave energy. Sediment isotopic composition varied among locations, indicating variations in the contribution of carbon sources. Seasonal variability was limited and overshadowed by spatial variability. Millennial variation was observed, by dating the deeper sediment cores using 210PB and 14C. Carbon content, vertical accretion, isotopic composition, and carbon accumulation rates varied through the sediment column in Moreton Bay and were higher following European settlement. This study provides comprehensive results on spatial and temporal variability of seagrass sediments in Moreton Bay, which provides useful information for the developmentand implementation of blue carbon conservation and management initiatives.
- ItemUsing stable isotope analysis of archaeological pandanus nutshell to understand past rainfall at Madjedbebe, northern Australia(Australian Nuclear Science and Technology Organisation, 2021-11-17) Florin, A; Roberts, P; Marwick, B; Patton, NR; Schilmeister, J; Lovelock, CE; Barry, LA; Hua, Q; Nango, M; Djandjomerr, D; Fullagar, R; Wallis, LA; Faibairn, AS; Clarkson, CArchaeological research provides a long-term perspective on how humans live with various environmental conditions over tens of thousands of years. However, to do this, archaeologists rely on the existence of local and temporally comparable environmental proxies, which are often not available. Our research at Madjedbebe, a ~65,000-year-old archaeological site on Mirarr country in northern Australia, developed an on-site proxy for past rainfall from pandanus nutshell, a remnant of ancient meals eaten at the site. This talk will discuss how we can use ancient food scraps, such as pandanus nutshell, to document past rainfall and what the results of this research mean for communities living at Madjedbebe in the past.