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Shabir R, Li Y, Megharaj M, Chen C. Biopolymer as an additive for effective biochar-based rhizobial inoculant. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 912:169263. [PMID: 38092216 DOI: 10.1016/j.scitotenv.2023.169263] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Revised: 11/19/2023] [Accepted: 12/08/2023] [Indexed: 12/17/2023]
Abstract
Biochar is an efficient and inexpensive carrier for bacteria that stimulate plant development and growth. In this study, different biopolymer additives (cellulose, xanthan gum, chitin and tryptone) were tested with different addition ratios (1:0.1, 1:0.5 and 1:1) on further enhancing biochar capacity for supporting the growth and activity of Bradyrhizobium japonicum (CB1809). We utilized pine wood biochar (PWBC) pyrolyzed at 400 °C as the base inoculum carrier. The shelf life and survival rate of CB1809 were counted using the colony-forming unit (CFU) method for up to 120 days. Peat served as a standard reference material against which all treatments were compared. Subsequent experiments evaluated the ability of carrier inoculants to promote Glycine max L. (soybean) plant growth and nodulation under different watering regimes, i.e., 55 % water holding capacity (WHC) (D0), 30 % WHC (D1) and, 15 % WHC (D2) using sandy loam soil. Results revealed that among different additives; xanthan gum with 1:0.5 to PWBC [PWBC-xanthan gum(1:0.5)] was observed as a superior formulation in supporting rhizobial shelf life and survival rate of CB1809. In pot experiments, plants with PWBC-xanthan gum(1:0.5) formulation showed significant increase in various physiological characteristics (nitrogenase activity, chlorophyll pigments, membrane stability index, and relative water content), root architecture (root surface area, root average diameter, root volume, root tips, root forks and root crossings), and plant growth attributes (shoot/root dry biomass, shoot/root length, and number of nodules). Additionally, a reduced enrichment of isotopic signatures (δ13C, δ15N) was observed in plants treated with PWBC-xanthan gum(1:0.5), less enrichment of δ15N indicates an inverse link to nodulation and nitrogenase activity, while lower δ13C values indicates effective water use efficiency by plants during drought stress. These results suggest that biopolymers supplementation of the PWBC is useful in promoting shelf life or survival rate of CB1809.
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Affiliation(s)
- Rahat Shabir
- Australian Rivers Institute, School of Environment and Science, Griffith University, Nathan, Campus, 4111, Queensland, Australia; Cooperative Research Centre for High Performance Soils, Callaghan, NSW, Australia
| | - Yantao Li
- Australian Rivers Institute, School of Environment and Science, Griffith University, Nathan, Campus, 4111, Queensland, Australia; Cooperative Research Centre for High Performance Soils, Callaghan, NSW, Australia; College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
| | - Mallavarapu Megharaj
- Cooperative Research Centre for High Performance Soils, Callaghan, NSW, Australia; Global Centre for Environmental Remediation, College of Engineering, Science and Environment, The University of Newcastle, University Drive, Callaghan, NSW 2308, Australia
| | - Chengrong Chen
- Australian Rivers Institute, School of Environment and Science, Griffith University, Nathan, Campus, 4111, Queensland, Australia; Cooperative Research Centre for High Performance Soils, Callaghan, NSW, Australia.
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Bahadori M, Chen C, Lewis S, Wang J, Shen J, Hou E, Rashti MR, Huang Q, Bainbridge Z, Stevens T. The origin of suspended particulate matter in the Great Barrier Reef. Nat Commun 2023; 14:5629. [PMID: 37699913 PMCID: PMC10497579 DOI: 10.1038/s41467-023-41183-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2022] [Accepted: 08/24/2023] [Indexed: 09/14/2023] Open
Abstract
River run-off has long been regarded as the largest source of organic-rich suspended particulate matter (SPM) in the Great Barrier Reef (GBR), contributing to high turbidity, pollutant exposure and increasing vulnerability of coral reef to climate change. However, the terrestrial versus marine origin of the SPM in the GBR is uncertain. Here we provide multiple lines of evidence (13C NMR, isotopic and genetic fingerprints) to unravel that a considerable proportion of the terrestrially-derived SPM is degraded in the riverine and estuarine mixing zones before it is transported further offshore. The fingerprints of SPM in the marine environment were completely different from those of terrestrial origin but more consistent with that formed by marine phytoplankton. This result indicates that the SPM in the GBR may not have terrestrial origin but produced locally in the marine environment, which has significant implications on developing better-targeted management practices for improving water quality in the GBR.
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Affiliation(s)
- Mohammad Bahadori
- Australian Rivers Institute, Griffith University, Nathan, QLD, 4111, Australia
- School of Environment and Science, Griffith University, Nathan, QLD, 4111, Australia
| | - Chengrong Chen
- Australian Rivers Institute, Griffith University, Nathan, QLD, 4111, Australia.
- School of Environment and Science, Griffith University, Nathan, QLD, 4111, Australia.
| | - Stephen Lewis
- Catchment to Reef Research Group, Centre for Tropical Water and Aquatic Ecosystem Research, James Cook University, Townsville, QLD, Australia
| | - Juntao Wang
- Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, Australia
- Global Centre for Land-Based Innovation, Western Sydney University, Penrith, NSW, Australia
| | - Jupei Shen
- School of Geographical Sciences, Fujian Normal University, Fuzhou, PR China
| | - Enqing Hou
- Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China
| | - Mehran Rezaei Rashti
- Australian Rivers Institute, Griffith University, Nathan, QLD, 4111, Australia
- School of Environment and Science, Griffith University, Nathan, QLD, 4111, Australia
| | - Qiaoyun Huang
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, China
| | - Zoe Bainbridge
- Catchment to Reef Research Group, Centre for Tropical Water and Aquatic Ecosystem Research, James Cook University, Townsville, QLD, Australia
| | - Tom Stevens
- Catchment to Reef Research Group, Centre for Tropical Water and Aquatic Ecosystem Research, James Cook University, Townsville, QLD, Australia
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3
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Li Z, Wang S, Nie X, Sun Y, Ran F. The application and potential non-conservatism of stable isotopes in organic matter source tracing. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 838:155946. [PMID: 35569649 DOI: 10.1016/j.scitotenv.2022.155946] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Revised: 05/10/2022] [Accepted: 05/10/2022] [Indexed: 06/15/2023]
Abstract
Organic matter (OM) tracing is critical for understanding the processes of soil redistribution and global carbon cycling. It effectively supports ecological management and global climate change prediction. Stable isotopes are generally more source-specific compared with other tracers and identify OM sources with a higher level of accuracy. Nevertheless, stable isotopes may be enriched or depleted by physical and biochemical processes such as selective migration of particles and OM mineralization in transport and sedimentary environments, making it difficult to establish links between the source and sink regions. Literature on OM source identification tends to assume a direct link between stable isotope sources and sinks, ignoring the non-conservatism of stable isotopes. There is further literature on understanding and modeling the processes that link the sources to sinks in terms of the non-conservatism of stable isotopes. The disagreement in response to the non-conservatism lies in the lack of comprehensive understanding of stable isotope fingerprinting systems and non-conservatism. The development of stable isotope fingerprinting technology is full of challenges. This review outlines the applicability of stable isotope tracers, identification mechanisms, and associated quantitative models, intending to improve the stable isotope fingerprinting system. We highlight the non-conservatism of stable isotopes in space and time caused by physical and biochemical processes. Additionally, a decision tree is established to determine the quantitative tools, evaluation indicators, and procedures related to non-conservatism. This decision tree clarifies the process from non-conservatism detection to threshold determination of statistical quantification, which can guide the end-users to better apply stable isotope to trace OM sources.
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Affiliation(s)
- Zhongwu Li
- College of Geographic Sciences, Hunan Normal University, Changsha 410081, China; College of Environmental Science and Engineering, Hunan University, Changsha 410082, China
| | - Shilan Wang
- College of Geographic Sciences, Hunan Normal University, Changsha 410081, China
| | - Xiaodong Nie
- College of Geographic Sciences, Hunan Normal University, Changsha 410081, China.
| | - Yize Sun
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China
| | - Fengwei Ran
- College of Geographic Sciences, Hunan Normal University, Changsha 410081, China
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Marion GS, Jupiter SD, Radice VZ, Albert S, Hoegh-Guldberg O. Linking isotopic signatures of nitrogen in nearshore coral skeletons with sources in catchment runoff. MARINE POLLUTION BULLETIN 2021; 173:113054. [PMID: 34744009 DOI: 10.1016/j.marpolbul.2021.113054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 09/20/2021] [Accepted: 10/10/2021] [Indexed: 06/13/2023]
Abstract
We use a multi-tracer approach to identify catchment sources of nitrogen (N) in the skeletons of nearshore Porites corals within the Great Barrier Reef. We measured δ15N, δ13C and C:N ratios of particulate organic matter (POM) sampled from the Pioneer River catchment and identified five distinct end-members: (1) marine planktonic and algal-dominated matter with higher δ15N values from the river mouth and coastal waters; (2) estuarine planktonic and algal matter with lower δ15N values associated with estuarine mixing; (3) lower river freshwater phytoplankton and algal-dominated matter in stratified reservoirs adjacent to catchment weirs, with the 15N-enriched source likely caused by microbial remineralization and denitrification; (4) upper river low δ15N terrigenous soil matter eroded from cane fields bordering waterways; and (5) terrestrial plant detrital matter in forest streams, representing a low δ15N fixed atmospheric nitrogen source. The δ15N values of adjacent, nearshore Porites coral skeletons is reflective of POM composition in coastal waters, with 15N-enriched values reflective of transformed N during flood pulses from the Pioneer River.
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Affiliation(s)
- Guy S Marion
- ARC Centre of Excellence for Coral Reef Studies, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Stacy D Jupiter
- ARC Centre of Excellence for Coral Reef Studies, The University of Queensland, Brisbane, QLD 4072, Australia; ARC Centre of Excellence for Coral Reef Studies, Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia; Wildlife Conservation Society, Melanesia Program, 11 Ma'afu St, Suva, Fiji.
| | - Veronica Z Radice
- ARC Centre of Excellence for Coral Reef Studies, The University of Queensland, Brisbane, QLD 4072, Australia; Old Dominion University, Norfolk, VA, USA
| | - Simon Albert
- School of Civil Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Ove Hoegh-Guldberg
- ARC Centre of Excellence for Coral Reef Studies, The University of Queensland, Brisbane, QLD 4072, Australia; School of Biological Sciences, The University of Queensland, Brisbane, QLD 4072, Australia; Global Change Institute, The University of Queensland, Brisbane, QLD 4072, Australia
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5
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Bahadori M, Chen C, Lewis S, Boyd S, Rashti MR, Esfandbod M, Garzon-Garcia A, Van Zwieten L, Kuzyakov Y. Soil organic matter formation is controlled by the chemistry and bioavailability of organic carbon inputs across different land uses. THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 770:145307. [PMID: 33515882 DOI: 10.1016/j.scitotenv.2021.145307] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 01/15/2021] [Accepted: 01/16/2021] [Indexed: 06/12/2023]
Abstract
Soil organic matter (SOM) formation involves microbial transformation of plant materials of various quality with physico-chemical stabilisation via soil aggregation. Land use and vegetation type can affect the litter chemistry and bioavailability of organic carbon (OC), and consequently influence the processing and stabilisation of OC into SOM. We used 13C nuclear magnetic resonance (13C NMR) and hot-water extraction to assess the changes in chemical composition and labile OC fractions during the transformation processes from leaf to litter to SOM depending on land use and vegetation type. The hot-water-extractable OC (HWEOC) decreased from leaf (43-65 g kg-1) to litter (19-23 g kg-1) to SOM (8-16 g kg-1) similar in four land use types: grassland, sugarcane, forest and banana. These trends demonstrated the uniform converging pathways of OC transformation and increasing stability by SOM formation. The preferential decomposition and decrease of labile OC fractions (∑% di-O-alkyl, O-alkyl and methoxyl) from leaf (54-69%) to SOM (41-43%) confirmed the increasing stability of the remaining compounds. Despite differences in the biochemical composition of the leaf tissues among the vegetation types, the proportions of labile OC fractions in SOM were similar across land uses. The OC content of soil was higher in forest (7.9%) and grassland (5.2%) compared to sugarcane (2.3%) and banana (3.0%). Consequently, the HWEOC per unit of soil weight was higher in forest and grassland (2.0 and 1.2 g kg-1 soil, respectively) compared to sugarcane and banana (0.3 and 0.4 g kg soil-1, respectively). The availability of labile SOM is dependent on the quantity of SOM not the chemical composition of SOM. In conclusion, labile OC fractions in SOM, as identified by 13C NMR, were similar across land use regardless of vegetation type and consequently, SOM formation leads to convergence of chemical composition despite diversity of OC sources.
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Affiliation(s)
- Mohammad Bahadori
- Australian Rivers Institute, Griffith University, Brisbane, QLD 4111, Australia; School of Environment and Science, Griffith University, Brisbane, Queensland 4111, Australia
| | - Chengrong Chen
- Australian Rivers Institute, Griffith University, Brisbane, QLD 4111, Australia; School of Environment and Science, Griffith University, Brisbane, Queensland 4111, Australia.
| | - Stephen Lewis
- Catchment to Reef Research Group, Centre for Tropical Water and Aquatic Ecosystem Research, James Cook University, Townsville, QLD 4811, Australia
| | - Sue Boyd
- School of Environment and Science, Griffith University, Brisbane, Queensland 4111, Australia
| | - Mehran Rezaei Rashti
- Australian Rivers Institute, Griffith University, Brisbane, QLD 4111, Australia; School of Environment and Science, Griffith University, Brisbane, Queensland 4111, Australia
| | - Maryam Esfandbod
- Australian Rivers Institute, Griffith University, Brisbane, QLD 4111, Australia; School of Environment and Science, Griffith University, Brisbane, Queensland 4111, Australia
| | - Alexandra Garzon-Garcia
- Australian Rivers Institute, Griffith University, Brisbane, QLD 4111, Australia; Department of Environment and Science, GPO Box 5078, Brisbane 4001, Australia
| | - Lukas Van Zwieten
- Australian Rivers Institute, Griffith University, Brisbane, QLD 4111, Australia; NSW Department of Primary Industries, Wollongbar Primary Industries Institute, Wollongbar, NSW 2477, Australia
| | - Yakov Kuzyakov
- Department of Soil Science of Temperate Ecosystems, University of Göttingen, 37077 Göttingen, Germany; Agro-Technological Institute, RUDN University, 117198, Moscow, Russia; Institute of Environmental Sciences, Kazan Federal University, 420049 Kazan, Russia
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McCloskey GL, Baheerathan R, Dougall C, Ellis R, Bennett FR, Waters D, Darr S, Fentie B, Hateley LR, Askildsen M. Modelled estimates of fine sediment and particulate nutrients delivered from the Great Barrier Reef catchments. MARINE POLLUTION BULLETIN 2021; 165:112163. [PMID: 33640848 DOI: 10.1016/j.marpolbul.2021.112163] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 02/02/2021] [Accepted: 02/05/2021] [Indexed: 06/12/2023]
Abstract
The eWater Source modelling framework has been modified to support the Great Barrier Reef (GBR) Dynamic SedNet catchment modelling concept, which is used to simulate fine sediment and particulate nutrient generation, loss, and transport processes across GBR catchments. Catchment scale monitored data sets are used to calibrate and evaluate models. Model performance is assessed qualitatively and quantitatively. Modelling predicts that approximately half of generated sediment is delivered to the GBR lagoon; the remainder is deposited on floodplains, trapped in reservoirs or lost through other minor processes (e.g. irrigation extractions). Gullies are the major source of sediment, with comparable contributions from hillslopes and streambanks. Hillslope sources are considered the major source of particulate nutrients across the GBR catchments. We demonstrate that using locally developed, customised models coupled with a complementary monitoring program can produce credible modelled estimates of pollutant loads and provide a platform for testing catchment scale assumptions and scenarios.
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Affiliation(s)
- G L McCloskey
- Department of Resources, Queensland Government, Australia.
| | - R Baheerathan
- Department of Resources, Queensland Government, Australia
| | - C Dougall
- Department of Resources, Queensland Government, Australia
| | - R Ellis
- Department of Environment and Science, Queensland Government, Australia
| | - F R Bennett
- Department of Environment and Science, Queensland Government, Australia
| | - D Waters
- Department of Resources, Queensland Government, Australia
| | - S Darr
- Department of Resources, Queensland Government, Australia
| | - B Fentie
- Department of Environment and Science, Queensland Government, Australia
| | - L R Hateley
- Department of Resources, Queensland Government, Australia
| | - M Askildsen
- Department of Resources, Queensland Government, Australia
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Potential Pollution Sources from Agricultural Activities on Tropical Forested Floodplain Wetlands Revealed by Soil eDNA. FORESTS 2020. [DOI: 10.3390/f11080892] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Tropical floodplain wetlands are found in low-lying areas that are periodically inundated. During wet periods, these wetlands can receive large amounts of suspended and dissolved material from the catchment, including many potential pollutants. In this study, we use traditional isotope tracers (δ15N and δ13C) along with soil eDNA to investigate the sources of transported materials and potential contaminants in seven forested floodplain wetlands in tropical Australia. We hypothesised that eDNA and isotope tracers in the soil would reflect the land use of the catchment. Our goal was to test whether eDNA could be used as a potential tool to identify and monitor pollutants in floodplain wetlands. The sampling sites were located within catchments that have a mosaic of land types, from well-conserved rainforests to intensive agricultural land uses, such as grazing, sugar cane, wood production, and horticulture. The soil eDNA was comprised of a mix of plant species consistent with the land use of the catchments. Most of the eDNA pool was derived from native trees, accounting for 46.2 ± 6.5% of the total; while cultivated species associated with agricultural activities contributed to 1–24% of the total. From the cultivated species, highest contributions (>5%) were from Sorghum sp. used for grazing, banana (Musa ornata), melons (Cucumis melo), and Pinus radiata and Juniperus sp. grown for wood production. Interestingly, tropical wetlands on sites 15 km offshore had soil eDNA from agricultural activities of the mainland, highlighting the connectivity of these wetlands, probably during extensive floods. Overall, soil eDNA, more than isotopic tracers, showed promising results for tracing and monitoring potential pollutants in tropical floodplain wetlands that are highly connected and susceptible to environmental degradation.
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Bahadori M, Chen C, Lewis S, Rashti MR, Cook F, Parnell A, Esfandbod M, Stevens T. Tracing the sources of sediment and associated particulate nitrogen from different land uses in the Johnstone River catchment, Wet Tropics, north-eastern Australia. MARINE POLLUTION BULLETIN 2020; 157:111344. [PMID: 32658700 DOI: 10.1016/j.marpolbul.2020.111344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Revised: 06/02/2020] [Accepted: 06/02/2020] [Indexed: 06/11/2023]
Abstract
While the ecosystem of the Great Barrier Reef (GBR), north-eastern Australia, is being threatened by the elevated levels of sediments and nutrients discharged from adjacent coastal river systems, the source of these detrimental pollutants are not well understood. Here we used a combined isotopic (δ13C, δ15N) and geochemical (Zn, Pt and S) signatures and stable isotope analysis in R (SIAR) mixing model to estimate the contribution of different land uses to the sediment and associated particulate nitrogen delivered to the Johnstone River. Results showed that rainforest was the largest contributor of suspended and bed sediments in the river estuary (both 33.1%), followed by banana (26.7%, 20.4%), sugarcane (21.5%, 21.4%) and grazing (18.7%, 25.1%). However, bananas and sugarcane land uses had the highest contribution to sediments delivered to the coast per unit of area. This will help land managers to prioritise on-ground activities to improve water quality in the GBR lagoon.
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Affiliation(s)
- Mohammad Bahadori
- Australian Rivers Institute, Griffith University, Brisbane, QLD 4111, Australia; School of Environment and Science, Griffith University, Brisbane, Queensland 4111, Australia
| | - Chengrong Chen
- Australian Rivers Institute, Griffith University, Brisbane, QLD 4111, Australia; School of Environment and Science, Griffith University, Brisbane, Queensland 4111, Australia.
| | - Stephen Lewis
- Catchment to Reef Research Group, Centre for Tropical Water and Aquatic Ecosystem Research, James Cook University, Townsville, QLD 4811, Australia
| | - Mehran Rezaei Rashti
- Australian Rivers Institute, Griffith University, Brisbane, QLD 4111, Australia; School of Environment and Science, Griffith University, Brisbane, Queensland 4111, Australia
| | - Freeman Cook
- Australian Rivers Institute, Griffith University, Brisbane, QLD 4111, Australia; Freeman Cook & Associates Pty Ltd, Australia
| | | | - Maryam Esfandbod
- Australian Rivers Institute, Griffith University, Brisbane, QLD 4111, Australia; School of Environment and Science, Griffith University, Brisbane, Queensland 4111, Australia
| | - Thomas Stevens
- Catchment to Reef Research Group, Centre for Tropical Water and Aquatic Ecosystem Research, James Cook University, Townsville, QLD 4811, Australia
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Coral skeletons reveal the history of nitrogen cycling in the coastal Great Barrier Reef. Nat Commun 2020; 11:1500. [PMID: 32198372 PMCID: PMC7083840 DOI: 10.1038/s41467-020-15278-w] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Accepted: 02/25/2020] [Indexed: 11/08/2022] Open
Abstract
Anthropogenic nutrient discharge to coastal marine environments is commonly associated with excessive algal growth and ecosystem degradation. However in the world's largest coral reef ecosystem, the Great Barrier Reef (GBR), the response to enhanced terrestrial nutrient inputs since European settlement in the 1850's remains unclear. Here we use a 333 year old composite record (1680-2012) of 15N/14N in coral skeleton-bound organic matter to understand how nitrogen cycling in the coastal GBR has responded to increased anthropogenic nutrient inputs. Our major robust finding is that the coral record shows a long-term decline in skeletal 15N/14N towards the present. We argue that this decline is evidence for increased coastal nitrogen fixation rather than a direct reflection of anthropogenic nitrogen inputs. Reducing phosphorus discharge and availability would short-circuit the nitrogen fixation feedback loop and help avoid future acute and chronic eutrophication in the coastal GBR.
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