Clay turbidity inhibits the phytoplankton production of lakes. This research will investigate a compensatory role for clays in an alternate trophic pathway. It is hypothesized that dissolved organic matter (DOM) is more available to higher trophic levels through concentration on clay particles. Specifically: (1) clay particles adsorb significant quantities of DOM (the nutritional value of which varies with the source) to facilitate bacterial production; and (2) as a result of bacterial surface growth, clay particles with adsorbed DOM aggregate into larger particles. The research will examine the relative importance of autotrophy and heterotrophy, and the mechanisms by which clay particles are important in lake food webs. The project answers four questions: (1) Does the quantity of clay turbidity affect the absolute as well as the relative amounts of bacterial production and phytoplankton production? (2) Does the quantity of clay turbidity affect bacterial use of phytoplankton exudates? (3) Does the sorptive or aggregative capacity of the clays vary with the nature of the DOM (allochthonous vs. autochthonous)? (4) Does bacterial growth on aggregates affect the size of the clay-organic-bacteria aggregates? Lake Chapala's predictable spatial and temporal gradients of suspended clay concentrations allows a combination of laboratory and field experimentation to test hypotheses. Answers will permit a new trophic model appropriate to lakes and reservoirs with high clay turbidity. Managers may be able to replace management practices (water quality and fisheries) based on traditional models. This alternate pathway is especially important in tropical lakes because year-around warm waters enable consistently high bacterial activity. This project is funded under the RUI initiative. It is unique in its involvement of undergraduates in field work in the tropics and through its use of international collaborators.
