Evidence for mild sediment Pb contamination affecting leaf-litter decomposition in a lake
Much work has focused on the effects of metal-contaminated sediment on benthic community structure, but effects on ecosystem functions have received far less attention. Decomposition has been widely used as an integrating metric of ecosystem function in lotic systems, but not for lentic ones. We assessed the relationship between low-level sediment lead (Pb) contamination and leaf-litter decomposition in a lentic system. We measured 30-day weight loss in 30 litter-bags that were deployed along a Pb-contamination gradient in a cypress-forested lake. At each deployment site we also quantified macrobenthos abundance, dissolved oxygen, water depth, sediment organic content, sediment silt/clay content, and both total sediment and porewater concentrations of Cd, Cu, Ni, Pb and Zn. Principal components (PC) analysis revealed a negative relationship between Pb concentration and benthic macroinvertebrate abundance, and this covariation dominated the first PC axis (PC1). Subsequent correlation analyses revealed a negative relationship between PC1 and percent leaf-litter loss. Our results indicate that leaf-litter decomposition was related to sediment Pb and benthic macroinvertebrate abundance. They also showed that ecosystem function may be affected even where sediment Pb concentrations are mostly below threshold-effects sediment quality guidelines—a finding with potential implications for sediment risk assessment. Additionally, the litter-bag technique used in this study showed promise as a tool in risk assessments of metal-contaminated sediments in lentic systems.
KeywordsDecomposition Leaf litter Lead Sediment metal Ecological integrity
This work was funded with student grants from the University of Louisiana at Lafayette Graduate Student Organization, and the Ecology Center of the University of Louisiana at Lafayette. We thank Marvin “Trey” Mace III for assistance with field work, and Dr. Paul Leberg for advice on statistical analyses.
Conflict of interest
The authors declare that they have no conflicts of interest regarding this work.
- Ahmed W, Shaukat SS (2012) Effect of heavy metal pollution on leaf litter decomposition of two species of mangroves, Avicennia marina and Rhizophora mucronata. J Basic Appl Sci 8:696–701Google Scholar
- Box GEP, Cox DR (1964) An analysis of transformations. J Roy Stat Soc B 26:211–252Google Scholar
- Hoffman DJ, Rattner BA, Burton AB Jr, Cairns J Jr (1995) Handbook of ecotoxicology. CRC Press, Boca RatonGoogle Scholar
- McCune B, Grace JB (2002) Analysis of ecological communities. MjM Software Design, Gleneden BeachGoogle Scholar
- Newman MC, Ownby DR, Mezin LCA, Powell DC (2000) Applying species-sensitivity distributions in ecological risk assessment: assumptions of distribution type and sufficient numbers of species. Environ Toxicol Chem 19:508–515Google Scholar
- Schäfer RB, Bundschuh M, Rouch DA, Szöcs E, von der Ohe PC, Pettigrove V, Schulz R, Nugegoda D, Kefford BJ (2012) Effects of pesticide toxicity, salinity and other environmental variables on selected ecosystem functions in streams and the relevance for ecosystem services. Sci Total Environ 415:69–78CrossRefGoogle Scholar
- USEPA (2001) Methods for collection, storage and manipulation of sediments for chemical and toxicological analyses: technical manual. WashingtonGoogle Scholar
- USEPA (2007) Method 3051a: microwave assisted acid digestion of sediments, sludges, soils, and oils. U.S. Environmental Protection Agency, Washington. http://www.epa.gov/osw/hazard/testmethods/sw846/pdfs/3051a.pdf. Accessed 5 Sep 2013
- Wilson JT (2003) Occurrence of and trends in selected sediment-associated contaminants in Caddo Lake, east Texas, 1940–2002. Water-Resources Investigations Report 03-4253. U.S. Geological Survey, WashingtonGoogle Scholar