An integrated approach to quantify groundwater transport of phosphorus to Narrow Lake, Alberta

Abstract

An integrated approach was used to quantify groundwater phosphorus flux to Narrow Lake, a small glacial-terrain lake in central Alberta. Data from a drilling program, major ion concentrations, environmental isotopes, and computer simulations indicated that the lake gains water through the nearshore region from a small, shallow groundwater flow system; at deep offshore regions, water moves from the lake to the groundwater flow system. Seepage flux was quantified by water budget, Darcy’s equation with data from wells near the lake, Darcy’s equation with data from minipiezometers in the lake, and seepage meters. Whole-lake seepage flux determined from minipiezometer data (30 mm yr−1) was only 10–25% of the other estimates (mean, 221 mm yr −1; range, 133–332 mm yr−1 from seepage meter and water budget data, respectively). Groundwater contributed ∼30% of the annual water load to the lake. The P concentration, [P], in pore water from lake sediments (mean, 175 mg m−3) was 8 times higher than groundwater from wells near the lake (mean, 21 mg m−1). Thus, if well water was used to estimate the [P] of the seepage water, the rate of groundwater P loading to the lake would be underestimated. The rate of groundwater P loading to the lake computed from average seepage flux and average pore-water [P] was 39 mg m−2 yr−1, and groundwater may be the largest single source of P to epilimnetic water in the lake.