Section 11
Chapter 10,317

Chlorophyll maxima in mountain ponds and lakes, Mount Rainier National Park, Washington State, USA

Larson, G.L.

Lake and Reservoir Management 16(4): 333-339


ISSN/ISBN: 1040-2381
DOI: 10.1080/07438140009354240
Accession: 010316967

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Hypolimnetic chlorophyll maxima are common in dear lakes and often occur at depths with between 1 and 0.1 % of the surface incident light. Little is known, however, about the concentrations of chlorophyll in thermally unstratified mountain ponds and how these concentrations compare to epilimnetic and hypolimnetic concentrations in mountain lakes. The objectives of this study were to document the concentrations of chlorophyll in thermally unstratified ponds and stratified lakes in Mount Rainier National Park (MORA) and to compare the results with concentrations and distributions of chlorophyll in clear-deep lakes in the Oregon Cascade Range and the Sierra Nevada Range. Thirty-two ponds (<2.5 m deep) and 14lakes (>9.9 m deep) were sampled primarily during the summers of 1992 to 1996 at MORA. Water samples from near the surface (0.1-0.5 m) of ponds and near the surface and near the bottom of lakes were collected over the deepest part of each system. One exception, Mowich Lake, was sampled at seven depths between the surface and 50 m (Z=58.6 m). Chlorophyll concentrations were low in all systems, but higher in ponds (average 1.8 mugcntdotL-1) than in lakes. Chlorophyll concentrations were higher in hypolimnetic lake samples (average 0.7 mugcntdotL-1) than in epilimnetic lake samples (average 0.2 mugcntdotL-1). Elevated concentrations of chlorophyll in mountain ponds, relative to those in hypolimnetic lake samples, may have been influenced by increased nutrient availability from interactions at the mud-water interface and, in this park, defecation by elk that used many of the ponds as wallows. Mowich Lake showed a chlorophyll maximum (apprx1.5 mugcntdotL-1) near the lake bottom. Based on Secchi disk clarity readings, the depth of 1.0 % incident surface solar radiation was greater than the maximum depths of the ponds and lakes. Comparative data from other clear-deep lakes in the Oregon Cascade Range and Sierra Nevada Range suggested that deep-chlorophyll maxima (apprx1.5 mugcntdotL-1) occurred at <1.0% and>0.1% of the incident surface solar radiation, and that the typical maximum depths ranged between 75 and 140 m during thermal stratification.

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