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Estuarine microplankton ecology an experimental approach

University of British Columbia

The data presented in this thesis are the result of laboratory experiments, executed concurrently with a year-long field study. Microcosms (20 1 volume) were filled with mixtures of natural low and high salinity waters in order to give a salinity range from ≤ 5 ppt, 10 ppt, 18 ppt to ≥ 26 ppt. The mixed waters were enriched so as to simulate the entrainment of nutrient-rich, saline water in a salt wedge estuary. Nitrate-N (20 μg-at 1⁻¹), phosphate-P (2 μg-at 1⁻¹) and silicate-Si (50 μg-at 1⁻¹) were added to the highest salinity microcosm, proportionally less to lower salinities. A distinct pattern of autotrophic and heterotrophic growth developed resembling natural events in the Fraser River estuary during the period between winter and late spring. Despite seasonal variability of the source waters, the simulated spring bloom was reproducible under constant laboratory conditions, thus allowing the continued performance of experiments. Skeletonema costatum and Thalassiosira spp. were consistently dominant in the simulated bloom, as they are in the Strait of Georgia. The salinity values influenced the microplankton ecology with respect to phytoplankton species composition and heterotrophic activity. In Light- and Dark-experiments nutrient uptake and growth kinetics of bacteria and algae were studied, as well as the role of heterotrophic microflagellates. The interactions of the microplankton were described in numerical models. In the presence of high substrate concentrations (5 mg 1⁻¹ glucose = 2 mg 1⁻¹ glucose-C), the glucose cell quota of bacteria determined the timing of the heterotrophic bloom, while grazing parameters and the gross growth efficiency of the microflagellates determined the absolute numbers. With an ecological efficiency of 57% between the two trophic levels, the Dark-model represented a system which was neither substrate nor predator controlled, but something in between. The Light-model gave an estimate of nitrogen recycling by microflagellates. In perturbation experiments the impact of high organic load (glucose), shading, Cu, a heavy metal mixture, and the herbicide 2,4-D on the microplankton populations was monitored. Naturally occurring perturbations had much greater impact on estuarine ecology than anthropogenic ones, even when pollutants were added at concentrations exceeding those in moderately polluted estuaries.

Text

2010-06-13

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http://hdl.handle.net/2429/25686

Oceanography

University of British Columbia

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