Combined effects of cumulative nutrient inputs and biogeochemical processes that occur in freshwater under anthropogenic eutrophication could lead to myriad shifts in nitrogen (N):phosphorus (P) stoichiometry in global freshwater ecosystems, but this is not yet well-assessed. Here we evaluated the characteristics of N and P stoichiometries in bodies of freshwater and their herbaceous macrophytes across human-impact levels, regions and periods. Freshwater and its macrophytes had higher N and P concentrations and lower N : P ratios in heavily than lightly human-impacted environments, further evidenced by spatiotemporal comparisons across eutrophication gradients. N and P concentrations in freshwater ecosystems were positively correlated and N : P was negatively correlated with population density in China. These results indicate a faster accumulation of P than N in human-impacted freshwater ecosystems, which could have large effects on the trophic webs and biogeochemical cycles of estuaries and coastal areas by freshwater loadings, and reinforce the importance of rehabilitating these ecosystems.
Bibliographical noteFunding Information:
We thank L. P. Li and X. J. Zhao for providing data from field sampling. The authors also thank C. J. Ji at Peking University and the anonymous reviewers for their insightful comments on the manuscript. The research was supported by the National Natural Science Foundation of China (Project Nos. 41173083, 31321061 and 31330012), the Special Foundation of National Science and Technology Basic Research (2013FY112300) and National Key Basic Research Program of China (2014CB954202). J.P. and J.S. were funded by the European Research Council Synergy grant ERC-SyG-2013-610028 IMBALANCE-P, the Spanish Government grant CGL2013-48074-P and the Catalan Government grant SGR 2014-274. J.J.E. was supported by the US National Science Foundation RCN-SEES (Award #1230603).
- anthropogenic impacts
- decoupling of nitrogen and phosphorus cycles
- freshwater ecosystems
- global patterns