Controls of Suspended Sediment Concentration, Nutrient Content, and Transport in a Subtropical Wetland

Abstract

Redistribution of largely organic sediment from low elevation sloughs to higher elevation ridges is a leading hypothesis for the formation and maintenance of the native ridge and slough landscape pattern found in peat wetlands of the Florida Everglades. We tested this redistribution hypothesis by measuring the concentration and characteristics of suspended sediment and its associated nutrients in the flowpaths of adjacent ridge and slough plant communities. Over two wet seasons we found no sustained differences in suspended sediment mass concentrations, particle-associated P and N concentrations, or sizes of suspended particles between ridge and slough sites. Discharge of suspended sediment, particulate nutrients, and solutes were nearly double in the slough flowpath compared to the ridge flowpath due solely to deeper and faster water flow in sloughs. Spatial and temporal variations in suspended sediment were not related to water velocity, consistent with a hypothesis that the critical sheer stress causing entrainment is not commonly exceeded in the present-day managed Everglades. The uniformity in the concentrations and characteristics of suspended sediment at our research site suggests that sediment and particulate nutrient redistribution between ridges and sloughs does not occur, or rarely occurs, in the modern Everglades.

Numerical Modeling of the Effects of Hydrologic Conditions and Sediment Transport on Geomorphic Patterns in Wetlands

“…These results agree with those of Noe et al (2009). The results of maximum increase in flow velocity up to 0.03-0.05 m/s as a pulsed condition also is not sufficient to change the bed elevation in the study area and therefore, higher flow velocity and larger pulsed flow conditions would be necessary to cause changes in bed elevation.…”

Recent and Historic Drivers of Landscape Change in the Everglades Ridge, Slough, and Tree Island Mosaic

“…The dominant size class of fine sediment (0.45-2.7 µm) and dominance of particulate P by the microbial, acid-hydrolyzable fraction suggest a bacterial origin within the water column , whereas entrainment of larger aggregates in ambient conditions is likely associated with bioturbation (see subsequent paragraphs). Suspended sediment biogeochemical characteristics, size distributions, and concentrations do not significantly differ between ridge and slough, though the greater discharge through sloughs results in greater unitwidth loading of suspended material compared to ridges (Noe et al, 2010).…”

“…Concentrations of larger detrital floc in suspension, measured with a digital floc camera over one day at a single site in central WCA-3A, were even lower (0.001-0.3 mg L −1 ; Larsen et al, 2009c). Concentrations of suspended sediment are generally unrelated to flow velocities (Larsen et al, 2009c;Noe et al, 2010), suggesting that ambient flow velocities are below the sediment entrainment threshold. The dominant size class of fine sediment (0.45-2.7 µm) and dominance of particulate P by the microbial, acid-hydrolyzable fraction suggest a bacterial origin within the water column , whereas entrainment of larger aggregates in ambient conditions is likely associated with bioturbation (see subsequent paragraphs).…”

“…Total dissolved P concentrations in ridge surface water and soil are slightly elevated (8% greater in surface water; Noe et al, 2010; 13% greater in pore water; Ross et al, 2006) above those of the slough. Relatively high leaching rates of sawgrass detritus (S.E.…”

“…Pulses (lasting less than a half-hour) of suspended sediment observed during a diel time series were not correlated with hydrologic and meteorological parameters and were likely caused by bioturbation by grass shrimp (Palaemonetes paludosus) and crayfish (Procambarus spp. ; Larsen et al, 2009c;Noe et al, 2010). Hurricane effects, while infrequent, are more widespread and long-lasting.…”