Negligible isotopic fractionation of nitrogen within temperate <i>Zostera</i> spp. meadows
<p>Seagrass meadows form an ecologically important ecosystem in the coastal zone. The <span class="inline-formula"><sup>15</sup>N∕<sup>14</sup>N</span> ratio of seagrass is commonly used to assess the extent to which sewage-derived nitrogen may be...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-12-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/15/7225/2018/bg-15-7225-2018.pdf |
| _version_ | 1818416533639004160 |
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| author | D. G. Russell W. W. Wong P. L. M. Cook |
| author_facet | D. G. Russell W. W. Wong P. L. M. Cook |
| author_sort | D. G. Russell |
| collection | DOAJ |
| description | <p>Seagrass meadows form an ecologically important ecosystem in the
coastal zone. The <span class="inline-formula"><sup>15</sup>N∕<sup>14</sup>N</span> ratio of seagrass is commonly used to
assess the extent to which sewage-derived nitrogen may be influencing seagrass
beds. There have, however, been few studies comparing the <span class="inline-formula"><sup>15</sup>N∕<sup>14</sup>N</span>
ratios of seagrass beds, their associated sediments and, of critical
importance, the porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="f83a9f1907f38a5589c34b239e10518b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00001.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00001.png"/></svg:svg></span></span> pool, which is most bioavailable.
Here, we undertook a study of the <span class="inline-formula"><sup>15</sup>N∕<sup>14</sup>N</span> ratios of seagrass
tissue, sediment porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="68d940fa21d9c6691de36bd82f3e56d8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00002.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00002.png"/></svg:svg></span></span> pool and the bulk sediment to
elucidate the extent of any fractionating processes taking place during
organic matter mineralisation and nitrogen assimilation. The study was
undertaken within two coastal embayments known to receive nitrogen from a
range of sources including marine, urban and sewage sources. There was close
agreement between the bulk sediment <span class="inline-formula"><i>δ</i><sup>15</sup></span>N and seagrass
<span class="inline-formula"><i>δ</i><sup>15</sup></span>N (<span class="inline-formula"><i>r</i><sup>2</sup></span> of 0.92 and mean offset of 0.9 ‰),
illustrating a close coupling between the plant and sediment pools. The
<span class="inline-formula"><i>δ</i><sup>15</sup></span>N of porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="1828c3f6b34695d5ee1ef7c7b60e0fa3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00003.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00003.png"/></svg:svg></span></span> was strongly correlated with
the <span class="inline-formula"><i>δ</i><sup>15</sup></span>N of both the sediment and the seagrass tissue. For both of
these relationships, however, the intercept of the line was not significantly
different from 0 and the slopes were not <span class="inline-formula">1:1</span>, reflecting an enrichment of
the porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="9d8f7ee8bf88d657d75cdcf077dbe3e2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00004.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00004.png"/></svg:svg></span></span> <span class="inline-formula"><i>δ</i><sup>15</sup></span>N pool relative to seagrass
tissue and bulk sediment <span class="inline-formula"><i>δ</i><sup>15</sup></span>N at high <span class="inline-formula"><i>δ</i><sup>15</sup></span>N values. We
suggest that nitrogen fixation is the most likely explanation for the
observation that the <span class="inline-formula"><i>δ</i><sup>15</sup></span>N of seagrass tissue is lower than
porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M18" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="7b888eb222795ca6a6dd2ceb535b59a0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00005.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00005.png"/></svg:svg></span></span>. Conversely, we suggest that the most likely
explanation for the enrichment of porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="b054521cc8a5d2267742c16e315b1d01"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00006.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00006.png"/></svg:svg></span></span> above bulk
sediment was through the preferential mineralisation of isotopically enriched
algal material (nitrogen derived from sewage sources) within the sediment as
<span class="inline-formula"><i>δ</i><sup>15</sup></span>N increased in the vicinity of a sewage treatment plant.</p> |
| first_indexed | 2024-12-14T11:52:24Z |
| format | Article |
| id | doaj.art-e83e1f4546584ca09f9260df6d8c8d03 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-14T11:52:24Z |
| publishDate | 2018-12-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-e83e1f4546584ca09f9260df6d8c8d032022-12-21T23:02:16ZengCopernicus PublicationsBiogeosciences1726-41701726-41892018-12-01157225723410.5194/bg-15-7225-2018Negligible isotopic fractionation of nitrogen within temperate <i>Zostera</i> spp. meadowsD. G. Russell0W. W. Wong1P. L. M. Cook2Water Studies Centre, School of Chemistry, Monash University, Clayton, 3800, AustraliaWater Studies Centre, School of Chemistry, Monash University, Clayton, 3800, AustraliaWater Studies Centre, School of Chemistry, Monash University, Clayton, 3800, Australia<p>Seagrass meadows form an ecologically important ecosystem in the coastal zone. The <span class="inline-formula"><sup>15</sup>N∕<sup>14</sup>N</span> ratio of seagrass is commonly used to assess the extent to which sewage-derived nitrogen may be influencing seagrass beds. There have, however, been few studies comparing the <span class="inline-formula"><sup>15</sup>N∕<sup>14</sup>N</span> ratios of seagrass beds, their associated sediments and, of critical importance, the porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="f83a9f1907f38a5589c34b239e10518b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00001.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00001.png"/></svg:svg></span></span> pool, which is most bioavailable. Here, we undertook a study of the <span class="inline-formula"><sup>15</sup>N∕<sup>14</sup>N</span> ratios of seagrass tissue, sediment porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="68d940fa21d9c6691de36bd82f3e56d8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00002.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00002.png"/></svg:svg></span></span> pool and the bulk sediment to elucidate the extent of any fractionating processes taking place during organic matter mineralisation and nitrogen assimilation. The study was undertaken within two coastal embayments known to receive nitrogen from a range of sources including marine, urban and sewage sources. There was close agreement between the bulk sediment <span class="inline-formula"><i>δ</i><sup>15</sup></span>N and seagrass <span class="inline-formula"><i>δ</i><sup>15</sup></span>N (<span class="inline-formula"><i>r</i><sup>2</sup></span> of 0.92 and mean offset of 0.9 ‰), illustrating a close coupling between the plant and sediment pools. The <span class="inline-formula"><i>δ</i><sup>15</sup></span>N of porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="1828c3f6b34695d5ee1ef7c7b60e0fa3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00003.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00003.png"/></svg:svg></span></span> was strongly correlated with the <span class="inline-formula"><i>δ</i><sup>15</sup></span>N of both the sediment and the seagrass tissue. For both of these relationships, however, the intercept of the line was not significantly different from 0 and the slopes were not <span class="inline-formula">1:1</span>, reflecting an enrichment of the porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="9d8f7ee8bf88d657d75cdcf077dbe3e2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00004.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00004.png"/></svg:svg></span></span> <span class="inline-formula"><i>δ</i><sup>15</sup></span>N pool relative to seagrass tissue and bulk sediment <span class="inline-formula"><i>δ</i><sup>15</sup></span>N at high <span class="inline-formula"><i>δ</i><sup>15</sup></span>N values. We suggest that nitrogen fixation is the most likely explanation for the observation that the <span class="inline-formula"><i>δ</i><sup>15</sup></span>N of seagrass tissue is lower than porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M18" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="7b888eb222795ca6a6dd2ceb535b59a0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00005.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00005.png"/></svg:svg></span></span>. Conversely, we suggest that the most likely explanation for the enrichment of porewater <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="b054521cc8a5d2267742c16e315b1d01"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7225-2018-ie00006.svg" width="24pt" height="15pt" src="bg-15-7225-2018-ie00006.png"/></svg:svg></span></span> above bulk sediment was through the preferential mineralisation of isotopically enriched algal material (nitrogen derived from sewage sources) within the sediment as <span class="inline-formula"><i>δ</i><sup>15</sup></span>N increased in the vicinity of a sewage treatment plant.</p>https://www.biogeosciences.net/15/7225/2018/bg-15-7225-2018.pdf |
| spellingShingle | D. G. Russell W. W. Wong P. L. M. Cook Negligible isotopic fractionation of nitrogen within temperate <i>Zostera</i> spp. meadows Biogeosciences |
| title | Negligible isotopic fractionation of nitrogen within temperate <i>Zostera</i> spp. meadows |
| title_full | Negligible isotopic fractionation of nitrogen within temperate <i>Zostera</i> spp. meadows |
| title_fullStr | Negligible isotopic fractionation of nitrogen within temperate <i>Zostera</i> spp. meadows |
| title_full_unstemmed | Negligible isotopic fractionation of nitrogen within temperate <i>Zostera</i> spp. meadows |
| title_short | Negligible isotopic fractionation of nitrogen within temperate <i>Zostera</i> spp. meadows |
| title_sort | negligible isotopic fractionation of nitrogen within temperate i zostera i spp meadows |
| url | https://www.biogeosciences.net/15/7225/2018/bg-15-7225-2018.pdf |
| work_keys_str_mv | AT dgrussell negligibleisotopicfractionationofnitrogenwithintemperateizosteraisppmeadows AT wwwong negligibleisotopicfractionationofnitrogenwithintemperateizosteraisppmeadows AT plmcook negligibleisotopicfractionationofnitrogenwithintemperateizosteraisppmeadows |