A Spatial Long-Term Trend Analysis of Estimated Chlorophyll-a Concentrations in Utah Lake Using Earth Observation Data

We analyzed chlorophyll-a (chl-a) concentrations in shallow, turbid Utah Lake using Landsat data from 1984 to 2021. is ~40 km by 21 km, has a surface area of ~390 km2, an average depth ~3 m, and loses ~50% inflow evaporation. This limits spatial mixing, allowing us evaluate impacts on smaller lake regions. evaluated long-term trends at the pixel level for areas related boundary conditions. created 17 study based differences shoreline development nutrient inflows. expected impacted exhibit increasing chl-a trends, as population growth watershed have been significant. used non-parametric Mann–Kendall test trends. The majority exhibited decreasing with few pixels Provo Goshen Bays exhibiting slight or no estimated trend magnitudes Sen’s slope fitted linear regression models. Trend all (and regions), both increasing, were small; largest being about ?0.05 ?0.005 µg/L/year, 0.1 0.005 µg/L/year slope, respectively. Over year-period, this would result decreases 2 0.2 µg/L increases 4 µg/L. All but monthly some rather than Monthly showed indications that algal blooms are occurring earlier, though evidence inconclusive. found essentially change either analysis regions since 1980?s; despite significant expansion; increased inflows; land-use changes. matches prior research supports hypothesis not limited direct inflows other factors.