ABSTRACT
On the basis of a one-year program of monthly in situ bioassays and sampling at 10 stations near the incubation site, a study on the effect of petroleum on the massive algal blooms in the northeastern coastal area of Lake Maracaibo has been made. Experiments were conclusive in showing that, although crude oil by itself has an inhibitory effect on phytoplankton, in combination with other factors, mainly a nitrogen/phosphorus (NIP) ratio of 16:1, it can cause a sharp increase in the algal population, favoring Cyanophyta, particulary Anacystis, but generally inhibiting the other two divisions in the lake, Chlorophyta and Chrysophyta.
Statistically significant stimulatory interactions of three factors were observed in four experiments, the most striking one being that among oil, NIP ratio, and formation waters, the other three being oil + N/P + EDTA (ethylenediamine tetra acetic acid). True interactions between petroleum and N/P were also observed in five experiments, stimulus running to over 100 times the control assay. The composition of the algal blooms resembled much more closely that of the bioassays when the petroleum was present.
Data available supports the explanation that blue-green algae indigenous to Lake Maracaibo, mainly Anacystis, are tolerant of crude oil, while green algae and diatoms are severely inhibited by it, which gives bluegreens an effective advantage in the competition for the nutrients. It adds to the physical, chemical and biological advantages already enjoyed by Cyanophyta in the lake, contributing to an additional promotion of the lake eutrophication.