## 4 Conclusions  
The present study assessed heavy metal pollution and source identification in the Petrola Lake protected area. Our findings provide a better understanding of heavy metal accumulation not only in soils and lacustrine sediments affected by anthropogenic activities,  
Figure 4: PCA analysis of the log-transformed variables depicting the two main principal components (PC) of parameter loading with the two defined clusters labeled in green and orange (clusters A and B, respectively). The two PCA axes explain 81.4% of total variability in the dataset.  
but also in greater flamingo tissues. Our results highlight a certain degree of Pb and Cd accumulation in subsurface lake sediments and agricultural soils, respectively, and low bioaccumulation of the studied elements in flamingo tissues. Both the above elements are most likely derived from anthropogenic sources. Lead pollution in sediments is apparently dominated by organic matter binding and may be derived from human sources such as gasoline and gunshot pellets. Conversely, the highest Cd concentrations were found in agricultural soils (both irrigation and dryland), probably derived from the use of fertilizers, but still below the quality guideline levels to consider them as polluted. The remaining elements (Cu, Hg, and Zn) may have originated from a common source linked to siliciclastic weathering and carbonate mineral dissolution in the soil profile. The evidence from this study suggests that human activities have an impact on the accumulation of certain heavy metals such as Pb or Cd, regardless of whether these are below the pollution thresholds. Considerably more work will need to be carried out to assess the pollution risk of other elements that are commonly used in consumer and agricultural products, such as Cr or As. Further research is also required to understand how heavy metals bioaccumulate and adversely affect the health of natural bird populations.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12125769/s1](https://www.mdpi.com/article/10.3390/app12125769/s1)]([https://www.mdpi.com/article/10.3390/app12125769/s1](https://www.mdpi.com/article/10.3390/app12125769/s1)), Table S1: Complete results of the chemical analyses in sediment and soil samples; Table S2: Cu, Pb, and Zn concentrations from fractions F1-F6 during sequential extraction; Table S3: Complete results of the chemical analyses in flamingo tissue samples; Table S4: Pearson correlation analysis among total concentrations of heavy metals and organic matter content.  
Conceptualization, N.V. and F.J.; methodology, N.V. and A.P.; validation, N.V., A.P. and F.J.; formal analysis, N.V.; investigation, N.V.; resources, J.J.G.-A. and F.J.; data curation, N.V.; writing--original draft preparation, N.V., J.J.G.-A. and F.J.; writing--review and editing, N.V. and F.J.; visualization, N.V.; supervision, F.J.; project administration, N.V. and J.J.G.-A.; funding acquisition, N.V. and J.J.G.-A. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Ph.D. grant (BES-2012-052256) from the Spanish Ministry of Economy and Competitiveness, as well as projects FEDER/ Ministerio de Ciencia e Innovacion y Universidades-Agencia Estatal de Investigacion/CICYT-CGL2017-87216-C4-2-R from the Spanish government, PEIC-2014-004-P and SBPLY/17/180501/000296L projects from the Castilla-La Mancha Regional Government, and a research stay grant (EEBB-I-16-11376) from the Spanish Ministry of Economy and Competitiveness. The APC was funded by the University of Vienna.  
Not applicable.  
We thank [PERSON]. [PERSON] for English copyediting and his appreciated comments, the staff of the wildlife recovery center from Albacete (Junta de Comunidades de Castilla-La Mancha), and [PERSON] for his help in handling of flamingo samples. Open Access Funding by the University of Vienna.  
The authors declare no conflict of interest.