Longitudinal patterns in nutrient chemistry and algal chlorophyll below point sources in three northern Ozark streams

Stream water quality is strongly influenced by nutrient enrichment from both diffuse and point sources (JARVIE et al. 2006). Initial regulatory efforts in the United States to improve water quality largely focused on point sources because they are more easily identified and controlled than diffuse sources. In many locations nutrient enrichment from municipal point sources has been substantially reduced. Nutrient removal is expensive, however, and few small wastewater treatment plants (WWTP) include tertiary treatment to remove nitrogen and phosphorus. Nutrients from WWTP are an important component o f the overallload received by many streams. Diffuse sources can also deliver large nutrient loads to streams (CARPENTER et al. 1998, PERKINS et al. 1998). In rural areas, the impact of agriculturalland use can far exceed that ofpoint sources (CLESCERI et al. 1986), and where agriculture is widespread the consequential effects of nutrient enrichment may be evident across entire river basins. In contrast, point source impacts may be localized but also more intense, and the impairment caused by high nutrient concentrations in stream reaches directly below WWTP can be severe (HAGGARD et al. 2001, MARTI et al. 2004). Our objective was to determine the impact of WWTP effiuent on 3 small Missouri streams by measuring how far downstream nutrient concentrations remained elevated above background levels attributable to diffuse input from agricultural and forested watersheds.