Categorizing “Muck” in the Indian River Lagoon, Florida, Based on Chemical, Physical and Biological Characteristics
Beckett, Katherine M
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During the past six decades, the thickness and areal extent of muck sediments have continually increased in the Indian River Lagoon (IRL), Florida. These sediments are anoxic, store and release nutrients, and destroy natural benthic habitats. The main objective of this research was to develop guidelines that help prioritize sites for muck removal based on the following: (1) biological abundance and diversity, (2) muck thickness, and (3) the physical and chemical composition of muck. Thinner muck deposits (20-40 cm), collected during two seasons at eight locations in the lagoon and adjacent creeks, had greater variability in sediment composition and ~5 times greater median biological abundance than thicker (≥100 cm), more uniform muck layers collected from nine locations during two seasons. No significant seasonal differences were found in mean biological abundance at each of the 17 stations when bottom water temperatures averaged ~19 and ~29°C, even though mean concentrations of dissolved ammonium and hydrogen sulfide increased by ~20% and 60%, respectively, when temperatures increased by ~10°C. A significantly lower effective number of species (ENS <7 on a scale of 1-9) was found at sites with higher porosity (>0.79), loss on ignition (LOI >7%), total organic carbon (TOC >2.0%) and total nitrogen (TN >0.2%). These sediments were categorized as low-diversity muck (LDM). The remaining sites were categorized as moderate-diversity muck with ENS values ≥7 and lower values for porosity, LOI, TOC and TN than the values listed above for LDM. All thicker muck stations and six of the eight thinner muck stations were categorized as LDM. Poor sediment quality and lower species diversity are considered key factors for prioritizing removal of LDM. This guideline for muck removal will help support restoration projects that can improve water and sediment quality and the health of the benthic communities in the IRL.