| Abstract: | ABSTRACT: An agricultural nonpoint source polluted stream in northern Idaho was examined to determine seasonal and longitudinal patterns of periphyton chlorophyll α. Chlorophyll a was measured at eight sites along Lapwai Creek, a fifth order stream impacted by agricultural runoff containing nutrients and eroded soils. Seasonally, periphyton chlorophyll α was lowest in the spring (cumulative x?= 60.4 mg m?2) and highest in the summer (cumulative x?= 222 mg m?2). Winter concentrations were higher than expected (cumulative x?= 168.6 mg m?2). The headwaters, flowing through an open grassy meadow, had the lowest concentrations of the study (two-year x?= 49.7 mg m?2). Immediately below a small, eutrophic reservoir, periphyton chlorophyll α increased markedly (two-year x?= 155.8 mg m?2) and remained high through a deep canyon (two year x?= 135.5 mg m?2) and down to the mouth of the stream (two-year x?= 172.3 mg?2). Periphyton chlorophyll α in Lapwai Creek was at least two times greater than values reported in the literature for comparable, undisturbed Idaho streams. We suggest that increased nutrient concentrations via agricultural nonpoint source pollution and increased light penetration from the removal of large, woody riparian vegetation have resulted in high periphyton chlorophyll α along the continuum of Lapwai Creek. |
