Sewage contamination under water scarcity effects on stream biota: biofilm, grazers, and their interaction
One of the most common anthropogenic impacts on river ecosystems is the effluent discharge from wastewater treatment plants. The effects of this contamination on stream biota may be intensified in Mediterranean climate regions, which comprise a drought period that leads to flow reduction, and ultimately to stagnant pools. To assess individual and combined effects of flow stagnation and sewage contamination, biofilm and gastropod grazers were used in a 5-week experiment with artificial channels to test two flow velocity treatments (stagnant flow/basal flow) and two levels of organic contamination using artificial sewage (no sewage input/sewage input). Stressors’ effects were determined on biofilm total biomass and chlorophyll (Chl) content, on oxygen consumption and growth rate of the grazers (Theodoxus fluviatilis), and on the interaction grazer-biofilm given by grazer’s feeding activity (i.e., biofilm consumption rate). The single effect of sewage induced an increase in biofilm biomass and Chl-a content, simultaneously increasing both grazers’ oxygen consumption and their feeding activity. Diatoms showed a higher sensitivity to flow stagnation, resulting in a lower content of Chl-c. Combined stressors interacted antagonistically for biofilm total biomass, Chl-b contents, and grazers’s feeding rate. The effect of sewage increasing biofilm biomass and grazing activity was reduced by the presence of flow stagnation (antagonist factor). Our findings suggest that sewage contamination has a direct effect on the functional response of primary producers and an indirect effect on primary consumers, and this effect is influenced by water flow stagnation.
KeywordsOrganic load Nutrients Flow velocity Grazing Multiple stressors Primary productivity Chlorophyll, Mesocosms
The authors are grateful to José António Santos for the assistance in the laboratory work during chlorophyll determination.
This work was financially supported by the Foundation for Science and Technology (Portugal)—FCT, through the following: strategic projects UID/MAR/04292/2013 granted to MARE and UID/GEO/04035/2013 granted to GeoBioTec and grant from FLUVIO PhD program (PD/BD/52510/2014) attributed to Ana Raquel Calapez.
- Graça MAS, Serra SRQ, Ferreira V (2012) A stable temperature may favour continuous reproduction by Theodoxus fluviatilis and explain its high densities in some karstic springs. Limnetica 31:129–140Google Scholar
- Kelly MG, Gómez-Rodríguez C, Kahlert M, Almeida SFP, Bennett C, Bottin M, Delmas F, Descy J-P, Dörflinger G, Kennedy B, Marvan P, Opatrilova L, Pardo I, Pfister P, Rosebery J, Schneider S, Vilbaste S (2012) Establishing expectations for pan-European diatom based ecological status assessments. Ecol Indic 20:177–186CrossRefGoogle Scholar
- Lear G, Dopheide A, Ancion P-Y, Roberts K, Washington V, Smith J, Lewis GD (2012) Biofilms in freshwater: their importance for the maintenance and monitoring of freshwater health. In: Lear G, Lewis GD (eds) Microbial Biofilms: Current Research and Applications. Caister Academic Press, UK, pp 129–152Google Scholar
- McIntire CD (1966) Some effects of current velocity on periphyton communities in laboratory streams. Hydrobiologia 27 (3-4):559–570Google Scholar
- OECD (2001) Test No. 303: Simulation test - aerobic sewage treatment - A: activated sludge units; B: biofilms In: OECD Guidelines for the Testing of Chemicals, Section 3.Google Scholar
- Prenda J, Gallardo-Mayenco A (1996) Self-purification, temporal variability and the macroinvertebrate community in small lowland mediterranean streams receiving crude domestic sewage effluent. Arch Hydrobiol 136:159–170Google Scholar
- Romaní AM, Amalfitano S, Artigas J, Fazi S, Sabater S, Timoner X, Ylla I, Zoppini A (2013) Microbial biofilm structure and organic matter use in mediterranean streams. Hydrobiologia 719 (1):43–58Google Scholar
- Schindler DW (2006) Recent advances in the understanding and management of eutrophication. Limnology and Oceanography 51 (1part2):356–363Google Scholar
- Tachet H, Richoux P, Bournaud M, Usseglio-Polatera P (2010) Invertébrés d’eau douce, Nouvelle Edition. Centre National de la Recherche Scientifique Press. Paris.Google Scholar
- Woodward G, Gessner MO, Giller PS, Gulis V, Hladyz S, Lecerf A, Malmqvist B, McKie BG, Tiegs SD, Cariss H, Dobson M, Elosegi A, Ferreira V, Graça MAS, Fleituch T, Lacoursière JO, Nistorescu M, Pozo J, Risnoveanu G, Schindler M, Vadineanu A, Vought LB-M, Chauvet E (2012) Continental-scale effects of nutrient pollution on stream ecosystem functioning. Science 336:1438–1440CrossRefGoogle Scholar