Using Above-Water Radiometric Measurements in Crow Pond to Validate Satellite Retrievals from Small Eutrophic Waters

Principal Investigators: Dr. Lorena Pinheiro-Silva, Dr. Rebecca North

Institution and/or Affiliation: University of Missouri


Project Description Missouri’s water landscape is predominantly shaped by man-made reservoirs, a consequence of increased construction over the past 50 years. Small impoundments are widespread across the state and exhibit high nutrient levels, primarily attributed to their expansive watersheds dominated by agricultural land use. Observable shifts in the color of Missouri reservoirs, transitioning from brown to green, indicate an increase in phytoplankton biomass. This alteration raises concerns about accelerated eutrophication in the agricultural Midwest, since lakes with elevated nutrients, chlorophyll-a (the dominant pigment of phytoplankton), and poor water clarity are susceptible to harmful algal blooms, negatively affecting aquatic foodwebs and recreation.

In eutrophic lakes and reservoirs, the concentration and community composition of phytoplankton largely govern water quality and color. Satellite remote sensing is a valuable tool to improve our understanding of how anthropogenic drivers interact and affect ecosystem structure and function in inland waters (Topp et al., 2021). These data can extend our observational record in space and time, which in turn can help deconvolve secular trends from ephemeral event-scale phenomena such as harmful algal blooms (Coffer et al., 2021). However, despite the recent advancements in high spatio-temporal resolution space-based sensors, some fundamental challenges remain regarding the remote sensing of small and/or productive water bodies, which hinder its widespread application.

Here, we propose to employ satellite remote sensing data from Sentinel 2 (MSI) whose higher spatial resolution (10 – 60 m) permits water quality retrievals in smaller water bodies (Pahlevan et al., 2020). We will develop an open-source pipeline using Google Earth Engine that will retrieve satellite derived lakewide averages of chlorophyll-a concentrations in Crow Pond for available imagery between 2016-2025. The satellite data will be validated against above-water radiometry measurements made with hyperspectral radiometers at Crow Pond. The primary aim of this study is to establish recent phenological patterns of algal biomass and water quality in non-winter months for Crow Pond. The specific goals are as follows: 1) quantify adjacency effects for Crow Pond, 2) evaluate three freely available atmospheric corrections (Polymer, Accolite and MAIN) applicable to inland water systems, 3) compare of satellite reflectance to in-situ radiometric measurements where such co-located data exist, and 4) evaluate a suite of chlorophyll-a retrieval algorithms suited to small eutrophic inland waters.