SULFATE CONTROL OF PHOSPHORUS AVAILABILITY IN LAKES - A TEST AND REEVALUATION OF HASLER AND EINSELE MODEL

During summer stratification large amounts of phosphorus (P) accumulat e in anoxic bottom waters of many lakes due to release of P from under lying sediments. The availability to phytoplankton of this P is invers ely related to the Fe:P ratio in bottom waters. Using data from 51 lak es, we tested the hypothesis that sulfate concentration in lake water may be critical in controlling the Fe:P ratio in anoxic bottom waters. Results showed that Fe:P ratios in bottom waters of lakes were signif icantly (p<0.001) related to surface water sulfate concentrations. The higher Fe:P ratios in low sulfate systems is due not only to higher i ron concentrations in anoxic bottom waters but also to lower P concent rations in anoxic waters. Thus, our results suggest that anthropogenic ally induced increases in sulfate concentrations of waters (e.g. from fossil fuel burning) may have a double effect on P cycling in lakes. H igher sulfate concentrations can both increase the magnitude of P rele ase from sediments as well as increase the availability of P released from sediments into anoxic bottom waters.