Leibniz Institute For Baltic Sea Research Warnemünde
Dispersal of anthropogenic nitrogen along the coast 15 of Beibu Gulf, southern China, as traced by δ N David Kaiser a, * | Daniela Unger a, ** | Qiu Guanglong b a
Leibniz Center for Tropical Marine Ecology (ZMT), Bremen, Germany b Guangxi Mangrove Research Center (GMRC), Beihai, PR China * Current address: Leibniz Institute for Baltic Sea Research Warnemünde (IOW), Germany;
[email protected] ** Current address: Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany
Introduction Human watershed activities, such as agriculture and aquaculture, often increase dissolved inorganic nitrogen (DIN) input to estuaries and enhance coastal eutrophication. The coast of Guangxi, southern China, is characterized by heterogeneous land use. Some areas enjoy national-level protection. Others are subject to high anthropogenic pressure1, presenting a potential source of pollutants to less affected areas. High DIN loading is often accompanied by elevated nitrogen isotope signatures (δ15N)2, allowing the use of particulate δ15N in tracing anthropogenic nitrogen within and between systems.
Background N2 δ15N = 0‰
Guangxi coast Huangzhu River and Pearl Bay
nitrogen fixation (Haber-Bosch process)3
Nanliu River and Lianzhou Bay
Shankou Mangrove Forest
synthetic fertilizer application δ15DIN ≈ -3 to 3‰4
high stream δ15DIN >7‰6
high δ15N of leaf tissue8
sedimentation litter fall
China Beibu Gulf
South China Sea
high δ15DIN in sediment9
Results
water
mangroves
filtration
water SPM photometry13 flourometry14
DIN
sed.
leaf
GMS15
δ15N
=NO3 +NO2 +NH4
100 50
high-tide (32 psu)
150
DIN [µM]
low-tide (19 psu)
Sampling
Discussion
Pearl Bay
200
Huanzhu River
Approach
0 10 8
SPM δ15N [‰]
6 4 2 0 10 8
mangrove δ15N [‰]
For assistance during field and lab work we thank Sun Ting (OUC), Qui Guanglong (GMRC), Christina Staschock (ZMT), Julia Lange (Uni Bremen), and Dorothee Dasbach (ZMT). The German Federal Ministry for Education and Science (BMBF; project no.: 03F 0607 B) financed this research
References 1 Kaiser
et al. 2013, Sci Tot Environ 450–451: 92-107 2 Middelburg and Herman 2007, Mar Chem 106: 127-147 3 Galloway et al. 2008, Science 320, 889-892 4 Panno et al. 2006, J Environ Quality 35: 495-504 5 Anderson and Cabana 2006, Sci Tot Environ 367: 968-978 6 Harrington et al. 1998, Chem Geol 147: 281-294 7 Middelburg and Nieuwenhuize 1998, Mar Chem 60: 217-225 8 Costanzo et al. 2003, Estuaries 26: 857-865 9 Bao et al. 2003, Cont Shelf Res 57: 82-91 10 Chen et al. 2011, J Oceanogr 67:709–718 11 Morell and Corredor 1998, Est Coast Shelf Sci 37: 203-212 12 Kaiser et al. submitted to Cont Shelf Res 13 Grasshoff et al. 1983, ISBN 3–527-2599-8 14 Kéroul and Aminot 1997, Mar Chem 57: 265-275 15 Herbeck and Unger 2013, Mar Ecol Prog Ser 478: 71-86
0 Huangzhu
Nanliu
n.a.
sediment
sediment
leaf
sed.
leaf
4 2
• High human N input causes high average DIN and δ15NSPM in the Nanliu River. • High δ15N of mangrove leaves and sediments reflect anthropogenic nitrogen pollution in Nanliu/Lianzhou Estuary. • Low-tide, mangrove influenced SPM in Shankou shows low δ15NSPM, reflecting natural conditions. • Enhanced δ15NSPM of high-tide marine particles, demonstrates tidal import of an external source of pollution. Elevated mangrove sediment δ15N indicates deposition of allochthonous human impacted material in the Shankou Mangrove. • Low DIN and δ15NSPM in the small Huangzhu River reflect minimal anthropogenic impact from the watershed/hinterland. • Minor nitrogen pollution import is evident in Huangzhu/Pearlbay Estuary from low δ15N of mangrove leaves and sediments. • Mangrove leaf and sediment δ15N reflect longer temporal integration of environmental conditions and confirm the persistence of a gradient of decreasing pollution from Lianzhou to Shankou and Pearl Bay.
6
Acknowledgements
- multiple human activities - low human activity - strong tidal exchange with Beibu Gulf - no river; open topography - strong commercial exploitation - national-level protection
Generalized distribution of diluted river water after Chen et al. 201110 year round only in autumn
Lianzhou Bay
high δ15N of suspended particles7
uptake by higher plants
Nanliu River
uptake by phytoplankton
- low human activity in hinterland - enclosed bay (6 km wide mouth) - protected estuarine environment
Vietnam
loss of 14N on watershed through e.g. plant uptake, volatilization, denitrification5
Shankou
• DIN in Nanliu River is dominated by NO3 (93%), reflecting its anthropogenic source.1 • Low-tide DIN in Shankou is dominated by NH4 (83%), reflecting strong mangrove influence.11,12 • Elemental, isotopic, and amino acid analyses of C and N show that SPM-nitrogen derives mostly from phytoplankton.12
• The higher dispersal of impacted riverine material to Shankou than to Pearl Bay is unexpected from coastal current patterns. The semienclosed morphology of Pearl Bay and riverine flushing reduce intrusion of polluted coastal water. The open morphology and lack of river runoff in Shankou facilitate tidal import of human impacted material.
Conclusions • Land use in intensively cultivated watersheds influences ecological parameters of remote, protected coastal areas along the southern Chinese coast. • Transfer of land based pollution to coastal ecosystems depends on local morphological and hydrological conditions as well as on large scale current patterns. This complicates the protection of designated coastal areas. Analyses of particulate δ15N may aid short term (SPM) and longer term (sediments) monitoring of pollution dispersal.
