Open AccessTracing anthropogenic inputs in stream foods webs with stable carbon and nitrogen isotope systematics along an agricultural gradient
Author(s) -
Kern Y. Lee,
Lisa Graham,
Daniel E. Spooner,
Marguerite A. Xenopoulos
Publication year - 2018
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0200312
Subject(s) - trophic level , δ15n , riparian zone , δ13c , isotopes of nitrogen , dominance (genetics) , environmental science , ecology , stable isotope ratio , environmental chemistry , dissolved organic carbon , nitrate , biology , nitrogen , chemistry , biochemistry , physics , organic chemistry , quantum mechanics , habitat , gene
Stable carbon ( 13 C) and nitrogen isotopes ( 15 N) are useful tools in determining the presence of agricultural influences in freshwater ecosystems. Here we examined δ 15 N and δ 13 C signatures in nitrate, fish, and mussel tissues, from rivers in Southern Ontario, Canada, that vary in their catchment proportion of agriculture land use, nutrients and organic matter quality. We found comparatively 15 N-enriched δ 15 N values in animal tissues and dissolved nitrates, relative to expected values characterized by natural sources. We also observed a strong, positive correlation between riparian agriculture percentages and δ 15 N values in animal tissues and nitrates, indicating a significant influence of agricultural land use and the probable dominance of organic fertilizer and manure inputs in particular. The use of a 15 N-based equation for the estimation of fish trophic position confirmed dietary analyses is showing all fish species to be tertiary consumers, with a relatively consistent 15 N-enrichment in animal tissues between trophic levels. This indicates that variability in 15 N-trophic fractionation is minor, and that fish and mussel tissue δ 15 N values are largely representative of source nitrogen. However, the trophic fractionation value varied from accepted literature values, suggesting strong influences from either local environmental conditions or dietary variation. The δ 13 C datasets did not correlate with riparian agriculture, and animal δ 13 C signatures in their tissues are consistent with terrestrial C3 vegetation, suggesting the dominance of allochthonous DOC sources. We found that changes in water chemistry and dissolved organic matter quality brought about by agricultural inputs were clearly expressed in the δ 15 N signatures of animal tissues from all trophic levels. As such, this study confirmed the source of anthropogenic nitrogen in the studied watersheds, and demonstrated that this agriculturally-derived nitrogen could be traced with δ 15 N signatures through successive trophic levels in local aquatic food webs. The δ 13 C data was less diagnostic of local agriculture, due to the more complex interplay of carbon cycling and environmental conditions.