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Phosphorus Limitation of Lotic Periphyton Growth Rates: An Intersite Comparison Using Continuous-Flow Troughs (Thompson River System, British Columbia)

Max L. Bothwell
Limnology and Oceanography
Vol. 30, No. 3 (May, 1985), pp. 527-542
Stable URL: http://www.jstor.org/stable/2836399
Page Count: 16
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Phosphorus Limitation of Lotic Periphyton Growth Rates: An Intersite Comparison Using Continuous-Flow Troughs (Thompson River System, British Columbia)
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Abstract

Periphyton growth rates and relative degrees of phosphorus deficiency were compared with onsite, continuous-flow troughs in three parts of the Thompson River system. Soluble reactive phosphorus (SRP) in the lower Thompson, North Thompson, and South Thompson Rivers averaged 3.4, 1.1, and $0.7 \mu g liter^-1$. Several physiological and chemical composition parameters ranked the degree of P deficiency in the rivers in the same sequence as did SRP. Among these were alkaline phosphatase activity, $V_max$ for $^32 PO_4^3-$ uptake, and cellular N:organic P, Chl a:ATP, C:ATP, and C:organic P. Specific growth rates $(\mu)$ estimated by biomass accrual and by $^14 CO_2$ uptake usually, but not always, indicated higher $\mu$ with greater availability of P. However, relative specific growth rates $(\mu:\mu_max)$ consistently reflected the influence of P limitation. As assessed from N:organic P and by application of the Droop and Goldman-Carpenter equations, $\mu : \mu_max$ was 0.8-0.9 at the lower Thompson, 0.3-0.6 at the North Thompson, and 0.0-0.3 at the South Thompson sites. Hence, periphyton growth rates in the lower Thompson River were near the maximum set by temperature and light at ambient SRP of only $3-4\mu g liter^-1$. Evidence of P-limited growth rates in the South Thompson and North Thompson Rivers was found at temperatures approaching $0^\circ C$.

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