The origin of the fluid mud layer in Lake Apopka, Florida

Abstract

Since it switched from a macrophyte-dominated state to a turbid, algal-dominated state in 1947, Lake Apopka has developed a layer of flocculent sediments with characteristics of fluid mud covering most of the lakebed and averaging 47 cm in thickness in 1996. Waves in this large, shallow lake frequently resuspend the upper portion of the fluid mud and frustrate programs designed to decrease the trophic state. We tested two hypotheses for its origin, one that the fluid mud layer represents the buildup of organic materials that had accumulated since 1947, the other that it was derived primarily by the liquefaction of the underlying macrophyte-derived consolidated sediments. We examined (1) changes in the mean depth of the lake relative to changes in fluid mud thickness; (2) 210 Pb dating of the sediments; (3) organic matter budget for the lake; (4) inorganic particle budget for the lake; and (5) chemical markers of sediments produced during the macrophyte stage (biogenic silica from sponges, long-chain n-alkanes from macrophytes, and 13 C) in the fluid mud. The evidence indicates that a major portion of the fluid mud can be attributed to the liquefaction of underlying consolidated sediments that were produced during the macrophyte stage of the lake. It follows that the fluid mud layer is less a direct consequence of eutrophication than a consequence of enhanced wave action on the lakebed following the loss of macrophyte dominance in this lake.

Persistence of naturally occurring and genetically modified Choristoneura fumiferana nucleopolyhedroviruses in outdoor aquatic microcosms

“…It cannot be assumed that once OBs have settled to the bottom they will remain stationary, since floc is easily disturbed. For example, water entering from the bottom can cause sediment to move upwards in lakes,57, 58 and wind and rain will resuspend unconsolidated sediment in shallow water bodies 59–61. Once resuspended in the water column, OBs attached to sediment particles/flocculent material could move off site through such processes as downstream transport and overland flow during flooding.…”

Extreme Weather Events and Climate Variability Provide a Lens to How Shallow Lakes May Respond to Climate Change

“…Some nutrient-enriched shallow lakes also have alternative states [47]: a clear state with macrophytes and turbid state with phytoplankton. A major disruption of submerged vegetation due to a hurricane, a drought, or a period of increased water depth could transform a lake to a turbid phytoplankton-dominated state and it may be very difficult for it to return to a clear-water plant-dominated state [48].…”

“…The lake switched and became a dark water lake and has only slowly recovered its transparency. Lake Apopka, Florida was by a variety of indicators a clear-water lake with vast coverage of SAV until 1946, when a hurricane tore up the SAV and pushed the lake into a phytoplankton-dominated condition that persists today [48]. What sets Lake Apopka apart from Okeechobee are two factors: (1) Okeechobee sediments contain a large percentage of inorganic solids that result in extreme light-limitation when they are suspended into the water column, preventing CyanoHABs from occurring or persisting; and (2) available information suggests that, in Apopka, all of the SAV was torn up and pulverized into particulate organic C and nutrients that fueled algal growth lake-wide.…”

“…This occurred in Lake Taihu, where dissolved nutrients were released from the sediments into the overlying water during the strong wind period, followed by a bloom period. It also occurred in Lake Okeechobee, and it likely is what stimulated the long-term dominance of cyanobacteria blooms in Lake Apopka, Florida [48]. 6.…”

Effects of Suspended Sediments on Seston Food Quality for Zebra Mussels in Lake Markermeer, The Netherlands

“…Van Duin et al (1992) observed a small oxidized layer on top of the soft mud layer, indicating that both layers were (to some extent) present in 1991-1992. Various earlier modeling studies on the TSM in Lake Markermeer (Vlag 1992) and numerous studies on other shallow lakes such as Lake Okeechobee (e.g., Ji 2004, Jin andSun 2007), Lake Apopka (Bachmann et al 1999(Bachmann et al , 2005, and Lake Taihu (Hu et al 2006) mentioned comparable mobile muddy layers and vertical gradients in suspended matter concentrations near the bottom during windy situations. To our knowledge, however, this was never before directly linked to effects on freshwater bivalves; therefore, ours is the first study to experimentally test this.…”