Advancing Water Quality Monitoring and Hydrologic Optics Studies for Inland Waters through An Individual Particle Analysis Technique in Characterizing Suspended Mineral Particles

Light attenuation by suspended particles in aquatic systems is an important physical process regulating underwater light field (important to primary production) and water clarity (thus water quality), as well as the magnitudes and the spectral features of remote-sensing reflectance. Mineral (or inorganic) particles are a key component of the optical regimes of inland waters because of their higher refractive indices as compared with algal and detrital particles, and generally much higher concentrations than in open oceans. A unique individual particle analysis (IPA) technique (scanning electron microscopy interfaced with automated image and X-ray analyses) has been used to provide detailed characterizations (size, shape, and composition) of individual mineral particles collected from diverse freshwater systems in North America, including the Great Lakes and the Finger Lakes of New York. A summary metric, the projected area concentrations of mineral particles, has been demonstrated to strongly regulate some critical water quality parameters, such as turbidity, Secchi depth, and particulate phosphorus concentrations. In addition, IPA results can be used as inputs for theoretical calculations of optical coefficients (e.g., absorption, scattering, and backscattering) of the mineral particle populations (i.e., the inherent optical properties, IOPs). Here we present some highlights from our water quality and optics studies supported by this IPA technique: (1) demonstration of the regulating effects of mineral area concentrations on common water quality metrics, (2) partitioning of the bulk particulate IOPs into contributing components (e.g., algal particles, calcite, clay minerals), (3) pursuit of optical modeling (particulate scattering and backscattering) closure with bulk measurements (promising results documented), (4) development of bio-optical models parameterized on particulate organic carbon content for an inland lake, and (5) advancement of remote-sensing algorithm development through ‘ground-truthing’ optics surveys.