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P <br />C <br />0 <br />6 <br />ratios to fall below 1.0 (heterotrophic) when turbidity increased <br />in artificial streams. Teal (1957) showed a temperate cold water <br />spring to become heterotrophic with the introduction of allochthonous <br />materials. Investigations by Thomas and O'Connell (1966) revealed <br />similar results. <br />The efficiency with which algal cells produce oxygen (assimila- <br /> tion ratios) similarly reveals information regarding aquatic <br />. ecosystems. Ratios, are obtained by measuring the amount of gross <br /> primary production per chlorophyll a (P/C). The usefulness of this <br /> parameter relies on'the fact that, of all chlorophyll types found <br /> in plant cells, only chlorophyll a participates directly in photo- <br /> synthesis (Rhyther 1956). Light, temperature, and nutrients, as <br /> previously stated, can affect rates of gross production.. <br /> Light intensity may similarly affect chlorophyll a concentrations. <br /> McIntyre et al. (1964) found concentrations to range from 0.40 <br /> g/m2 at 2100 lux to 0.80 g/m2 at 6,000 lux in artificial streams. <br /> McConnell (1958) found periphyton grown in shaded communities of <br /> the Logan River to contain up to 50 percent less chlorophyll. a than <br /> that from areas of greater insolation. Steeman-Nielsen et al. (1962) <br />a <br />a <br />found algal cells from shade adapted communities to be smaller and <br />contain more chlorophyll a per cell than communities grown in high <br />light. Under low light conditions, communities adapted to low <br />light intensities are more efficient producers than communities <br />grown under high light intensities (Steeman-Nielsen 1961a). <br />Detritus levels play an important role regarding the trophic <br />0 <br />state of lotic communities. Cummins (1974) notes that increased <br />