The hydrologic classification of dilute lakes

Abstract

Dilute lakes, herein defined as having an electrical conductivity ≤25 µS cm−1, are considered valuable culturally, as water and recreational resources; biologically, as unique ecosystems; and scientifically, as sentinels of climate change. However, research and interest has been spread over many disciplines focusing on various issues, making hydrologic comparisons somewhat difficult. Here, 15 dilute lakes are subdivided into lake subtypes based on the dominant hydrologic input and output using annual water balance data. Dilute conditions occur in lakes dominated by all hydrologic inputs (precipitation, surface inflow, and groundwater) and outputs (evaporation, surface outflow, and groundwater), though not all possible input/output combinations produce dilute conditions. Of the nine possible hydrologic lake subtypes (three input by three output fluxes), dilute conditions have been reported in six lake subtypes, not just the traditional seepage and drainage lakes typically suggested in the literature. When annual water balance data are plotted on a “Piper‐type” graph, these six hydrologic lake subtypes are grouped into three hydrologic clusters emphasizing specific hydrologic landscape characteristics and limiting conditions hydrology may impose on naturally dilute lakes. Implications of such a classification system and possible future research questions are discussed.