Ground-water component of lake water and nutrient budgets

Summary

The ground-water component of lake-water and nutrient budgets usually is calculated as the residual of the budget equation. This can lead to serious error and misinterpretation of a lake-water and nutrient budget because (1) overland runoff (nonchannelized surface flow) into the lake rarely is considered, and (2) errors in the measured parameters of inflow (usually precipitation and streamflow) and outflow (usually evaporation and streamflow) rarely are considered separately. Both factors thus become part of the residual along with ground-water. Recent theoretical studies of the interaction of lakes and ground-water show that the presence or absence of a continuous local ground-water flow-system boundary beneath a lake controls whether or not there is outseepage from the lake. The continuity of the flow-system boundary is controlled by the configuration of the water-table within the lake's drainage basin and the permeability contrasts within the ground-water system. The theoretical studies have helped define field analysis techniques for the determination of lake-ground water interrelationships that lead to realistic estimates of the ground-water component of lake- water and nutrient budgets. Knowledge of ground-water flow systems near lakes also can lead to improved understanding of ground-water chemistry near lakes. Often, because of the close proximity of a lake and a well, the ground-water sampled from the well is assumed to be related to the lake-water. However, the ground-water might not be related to the lake at all because the well might be completed in a regional flow system passing at depth beneath the lake.