2023 Early Hearing Detection & Intervention Conference

March 5-7, 2023 • Cincinnati, OH

5/21/2018 | 9:30 AM - 9:45 AM | NITROGEN LOADING IN AN OLIGOTROPHIC RESERVOIR: INFLUENCE ON FOOD WEB DYNAMICS | 330 B

NITROGEN LOADING IN AN OLIGOTROPHIC RESERVOIR: INFLUENCE ON FOOD WEB DYNAMICS

Land-use alterations and other anthropogenic sources increase nutrient availability globally. Lake Koocanusa, an oligotrophic reservoir, exemplifies these changes and provides an opportunity to examine the response of organisms through time. We use 35+ years of monthly monitoring data to examine relationships among reservoir operations, water quality, phytoplankton, zooplankton, and fisheries. Increased mining activity in the upper Kootenai River watershed has contributed to increased nitrate loading into Lake Koocanusa. Nitrogen concentrations have more than doubled since 2000 while the remainder of water quality parameters have been relatively consistent; for example, mean TP from 2000-2016 was 6.2 ± 0.4 ppb (mean ± SE). Thus, N:P ratios have increased to be in excess of 100:1. Although lower trophic levels may be somewhat resilient to these changes, characteristics of the fisheries have changed. Kokanee length growth has declined by 0.6 mm yr-1 from 38 mm yr-1 in 1987 to 20 mm yr-1in 2016. Similarly, weight growth has declined by 2.2 g yr-1 from 113 g yr-1 in 1987 to 48 g yr-1in 2016. Increased N loading in oligotrophic reservoirs may influence food web dynamics.

Nitrogen
Nutrients
Water Quality

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Presenters/Authors

Lisa Kunza (), South Dakota School of Mines and Technology, lisa.kunza@sdsmt.edu;