Cultural eutrophication is the leading cause of water quality degradation worldwide. The traditional monitoring of eutrophication is time-consuming and not integrative in space and time. Here, we examined the use of carbon (δ13C) and nitrogen (δ15N) isotopic composition to track the degree of eutrophication in a bay of Lake Titicaca impacted by anthropogenic (urban, industrial and agricultural wastewater) discharges. Our results show increasing δ13C and decreasing δ15N signatures in macrophytes and suspended particulate matter with distance to the wastewater source. In contrast to δ15N and δ13C signatures, in-between aquatic plants distributed along the slope were not only affected by anthropogenic discharges but also by the pathway of carbon uptake, i.e., atmospheric (emerged) vs aquatic (submerged). A binary mixing model elaborated from pristine and anthropogenic isotope end-members allowed the assessment of anthropogenically derived C and N incorporation in macrophytes with distance to the source. Higher anthropogenic contribution was observed during the wet season, attributed to enhanced wastewater discharges and leaching of agricultural areas. For both seasons, eutrophication was however found naturally attenuated within 6 to 8 km from the wastewater source. Here, we confirm that carbon and nitrogen stable isotopes are simple, integrative and time-saving tools to evaluate the degree of eutrophication (seasonally or annually) in anthropogenically impacted aquatic ecosystems.
Bibliographical noteFunding Information:
This work is a contribution to the EUTITICACA project (founded by the Impuestos Directos a los Hidrocarburos IDH administrated by the Universidad Mayor de San Andr_es, PI: D. Acha: email@example.com), COMIBOL project (INSU CNRS/IRD EC2CO Program, PI: D. Point: firstname.lastname@example.org) and LA PACHAMAMA project (ANR CESA program, No ANR-13-CESA-0015-01, PI: D. Amouroux: email@example.com). We wish to thank, J. Gardon, A. Terrazas, C. Gonzalez, N. Clavijo, L. Salvatierra, R. Rios, J.C. Salinas, A. Castillo, M. Claure, J. Tapia, J.L. Duprey (IRD Bolivia), la Familia Catari (Don Ramon, Don Maximo, Don Eric, Don Ruben and Donia Maria) and Don German Calizaya (Fishermen Association, Machacamarca, Bolivia) for their help and assistance during the field campaigns.
- Anthropogenic discharges
- Carbon stable isotopes
- Lake Titicaca
- Nitrogen stable isotopes