Foster, G.; Riegl, B.M.; Foster, K.A., and Morris, L.J., 2018. Acoustic detection and mapping of muck deposits in the Indian River Lagoon, Florida.

Locating significant deposits of muck (semifluid, fine-grained, organic-rich sediment) is an important aspect of estuarine conservation and management. The 38-kHz signal of a dual-frequency, single-beam acoustic survey of drift macroalgae was repurposed post hoc to locate and measure the horizontal and vertical extent of muck deposits within Indian River Lagoon, Florida. Raw echo returns were segmented into 5-cm strata of echo intensity, and a series of postprocessing algorithms were written to identify the characteristic pattern of backscatter associated with muck. Twenty-three deposits thicker than 0.5 m were identified within the 283-km2 survey area, nearly all of which were found within depressions of the Indian River (IR). The quantity of muck was estimated at 1.87 × 106 m3, roughly four times the quantity slated for removal from the Eau Gallie River and Elbow Creek (Florida) in 2016. The quantity of muck within the 110-km traverse of the IR Intracoastal Waterway (ICW) was estimated at 5.31 × 106 m3. Muck deposits within the 31-km traverse of the Banana River (BR) ICW were deeper (μ = 1.22 vs. 0.51 m), but muck volume was difficult to estimate because of the uncertain boundaries (i.e. channel width) of the BR ICW. The decision of whether to remove the significant volumes of muck within the 23 deposits and the ICW must consider ecological impact relative to concentrations of muck at the discharge of tributaries. Nonetheless, this extra layer of information was achieved with only a modest increase of surveying and postprocessing effort. Synergies such as this will be important in an era of monitoring and management cost constraints.

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