Algal growth in warm temperate reservoirs: Kinetic examination of nitrogen, temperature, light, and other nutrients

Nutrient limited growth of the phytoplankton assemblage in two Texas reserv oirs was studied by a combination of nutrient addition experiments and stat istical modeling. Dilution bioassays were run to ascertain-the qualitative and quantitative patterns in nutrient limitation. Algal growth was frequent ly and strongly nutrient limited, particularly when temperature was >22 deg rees C. By itself, N was more often stimulatory than P, though strong addit ional enhancement of growth by P and trace nutrients was often detected. Mo nod growth kinetics indicated that half-saturation constants for N limited growth for the entire algal assemblage were in the range 20-200 mu g N/L, r elatively high compared to literature values, and increased with increasing temperature. Maximal growth was also an increasing function of temperature . A single temperature-dependent model was fit to the growth dynamics for a ll experiments showing N-limitation. The model mu = 0.0256.T([DIN]/66.0 + [ DIN]) where mu is specific growth rate (d(-1)), T is temperature (degrees C ) and [DIN] is dissolved inorganic N (mu mol/L) fit the experimental result s reasonably well (r(2) = 0.82). However, only a modest predictive power fo r growth in the controls (our best estimate of growth in situ) was achieved (r(2) = 0.26). Thus, even with unusually detailed, site-specific fitting o f model parameters, accurately modeling algal growth in natural ecosystems can remain a challenge. (C) 1998 Published by Elsevier Science Ltd. All rig hts reserved.