A simple method for approximating the supportive capacities and metabolic constraints in lakes and reservoirs

Abstract

1. A method for calculating and comparing the stoichiometric yields of phytoplankton standing crop (as chlorophyll a) is presented. 2. Some worked examples show how the model distinguishes lakes in which the supportive capacity is constrained mainly by the available phosphorus or by the nitrogen supply or by the light availability. Sites are identified where control moves among the constraining factors. 3. An instance of lake management is given where the diagnosis, remedy and the remediation have conformed closely to the model predictions.

Phytoplankton biomass is mainly controlled by hydrology and phosphorus concentrations in tropical hydroelectric reservoirs

“…The following indexes based on Kosten et al (2009) were used to test nutrient limitation for phytoplankton growth in the systems: (i) TN:TP ratio (atomic); if the median of a reservoir is below 20, the system is considered limited by N; and above 38, limited by P (Sakamoto, 1966); (ii) DIN:SRP ratio (atomic), if the median is below 13, the reservoir is considered limited by N; and above 50, limited by P (Morris & Lewis, 1988); (iii) DIN and SRP were compared to halfsaturation constants for phytoplankton growth: below 10 lg P L -1 (*0.3 lmol P/L), P was considered limiting (Sas, 1989), and below 100 lg N l -1 (*6-7 lmol N/L), N was considered limiting (Reynolds, 1997); (iv) phytoplankton biomass (carbon content) in the reservoirs was compared to the theoretical biomass expected when estimated from the bioavailable nutrient loading, thus determining the carrying capacity of the systems according to the approach of Reynolds (1992b) and Reynolds & Maberly (2002). The following formulas were used: (a) 5.6 g C (g N) -1 and (b) 41 g C (g P) -1 , considering the theoretical stoichiometric yield of phytoplankton cell carbon for DIN and SRP availability, respectively.…”

Phytoplankton Regulation in a Eutrophic Tidal River (San Joaquin River, California)

“…The general procedure of Reynolds and Maberly (2002) was used to estimate the phytoplankton carrying capacity from macronutrient availability. Total nitrogen (N tot ) and total phosphorus (P tot ) were used to calculate carrying capacities for nitrogen and phosphorus, in order to determine maximum values and to avoid the uncertainty in estimating the bioavailable fraction of nutrients.…”

“…The derived equation of Reynolds (Reynolds and Maberly 2002) was used to estimate the supportive capacity of light, B max (µg chlorophyll a L -1 ):…”

“…The parameter values suggested by Reynolds and Maberly (2002) were also used: κ = 0.01, P r = 15, and I k = 20. Γ and I max were determined as above.…”

“…K was estimated from Equation 5. There is much uncertainty in the parameter values chosen by Reynolds and Maberly (2002), and therefore corresponding uncertainty in the estimates of B max . Although there are other ways to arrive at maximum biomass estimates, they all suffer from similar uncertainties.…”