Surface Water Quality Nutrient Retention Efficiency in Streams Receiving Inputs from Wastewater Treatment Plants Euge `nia Marti,* Jordi Aumatell, Lluı´s Gode ´ , Manel Poch, and Francesc Sabater ABSTRACT documented declines in water quality (Howarth et al., 1996). Degradation of water quality is a universal issue We tested the effect of nutrient inputs from wastewater treatment because it directly affects human health and the ecologi- plants (WWTPs) on stream nutrient retention efficiency by examining the longitudinal patterns of ammonium, nitrate, and phosphate con- cal integrity of freshwater ecosystems. centrations downstream of WWTP effluents in 15 streams throughout Human well-being and economic development are Catalonia (Spain). We hypothesized that large nutrient loadings would highly dependent on freshwater quantity and quality. saturate stream communities, lowering nutrient retention efficiency There is an obvious need to implement management (i.e., nutrient retention relative to nutrient flux) relative to less pol- strategies that minimize degradation of freshwaters. luted streams. Longitudinal variation in ambient nutrient concentra- During the last 50 yr, massive effort has been directed tion reflected the net result of physical, chemical, or biological uptake on developing wastewater treatments to reduce direct and release processes. Therefore, gradual increases in nutrient concen- sewage input to streams (Tchobanoglous and Bur- tration indicate that the stream acts as a net source of nutrients to ton, 1991). In this sense, wastewater treatment plants downstream environments, whereas gradual declines indicate that the (WWTPs) have certainly improved water quality. How- stream acts as a net sink. In those streams where gradual declines in nutrient concentration were observed, we calculated the nutrient up- ever, some aspects of the water quality problem remain take length as an indicator of the stream nutrient retention efficiency. unsolved because (i) nonpoint sources are difficult to No significant decline was found in dilution-corrected concentrations control by infrastructure, (ii) the removal efficiency of of dissolved inorganic nitrogen (DIN) and phosphate in 40 and 45% WWTP nutrient loads is technologically limited, and of streams, respectively. In the remaining streams, uptake length (esti- (iii) world population and associated activity continue mated based on the decline of nutrient concentrations at ambient levels) to increase. Under these conditions there is a need to ranged from 0.14 to 29 km (DIN), and from 0.14 to 14 km (phosphate). identify and implement alternative solutions to enhance Overall, these values are longer (lower retention efficiency) than those water quality. from nonpolluted streams of similar size, supporting our hypothesis, Physical, chemical, and biological processes within and suggest that high nutrient loads affect fluvial ecosystem function. streams influence the transport, transformation, and re- This study demonstrates that the efficiency of stream ecosystems to remove nutrients has limitations because it can be significantly altered tention of nutrients during downstream transport (Stream by the quantity and quality of the receiving water. Solute Workshop, 1990). Several studies have reported high efficiency of first to third order streams in nutrient retention (Mulholland et al., 1985; Triska et al., 1989; Munn and Meyer, 1990; Marti and Sabater, 1996; Valett A tight linkage between terrestrial and aquatic eco- et al., 1996; Marti et al., 1997; Peterson et al., 1997; systems is indicated by the influence of watershed Mulholland et al., 2000; Peterson et al., 2001). This in- processes on stream water nutrient concentrations (Dil- trinsic property, the so-called “self-purifying capacity,” lon and Kirchner, 1975; Webster et al., 1983; Likens and of stream ecosystems could partially ameliorate water Bormann, 1995). Direct anthropogenic inputs greatly quality problems by reducing the nutrient loads within affect terrestrial solute exports from either point sources relatively short distances (Elosegui et al., 1995) if this (e.g., wastewater treatment plants), or through diffuse capacity is not overwhelmed by excessive nutrient load- pathways (Casey et al., 1993; Jordan and Weller, 1996), ing. Most existing data on nutrient retention efficiency which increase stream loads. Anthropogenic nutrient has been obtained from nearly pristine streams, and sources are a major cause of large increases in stream there is limited study on retention under “polluted con- nutrient concentrations measured worldwide, often with ditions” (Haggard et al., 2001). Based on the “Subsidy- Stress Hypothesis” (Odum et al., 1979), we hypothesized E. Marti, J. Aumatell, and M. Poch, Laboratori d’Enginyeria Quı ´mica i Ambiental, Facultat de Cie ` ncies, Universitat de Girona, Campus that large, long-term nutrient loads (such as those from Montilivi, s/n, 17071 Girona, Spain; L. Gode ´, Age ` ncia Catalana de WWTP effluents) would stress the stream communities l’Aigua, Departament de Medi Ambient, Generalitat de Catalunya, and lower the nutrient retention efficiency relative to Provenc ¸a 204-208, 08036 Barcelona, Spain; and F. Sabater, De- less polluted streams. The objective of this study was partament d’Ecologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain. E. Marti, present address: Centre d’Estudis Avan- to examine the effect of large nutrient inputs, caused c ¸ats de Blanes (CSIC), Acce ´ s a la Cala St. Francesc 14, 17300 Blanes, by point sources, on stream nutrient retention efficiency Girona, Spain. Received 2 Oct. 2002. *Corresponding author (eugenia@ (N and P) by (i) evaluating the effects of nutrient inputs ceab.csic.es). Abbreviations: ACA, Catalan Water Treatment Agency; DIN, dis- Published in J. Environ. Qual. 33:285–293 (2004).  ASA, CSSA, SSSA solved inorganic nitrogen; DOC, dissolved organic carbon; WWTP, wastewater treatment plant. 677 S. Segoe Rd., Madison, WI 53711 USA 285 Published January, 2004