Randall W. Parkinson

Red mangrove (Rhizophora mangle L.) litter fall response to selective pruning (Indian River Lagoon, Florida, U.S.A.)

This 33 month study quantified red mangrove (Rhizophora mangle L.) litter fall response to a selective pruning event using fringing forests located along the Indian River Lagoon, Florida, U.S.A. Selective pruning consisted of the removal of as many as 50% of the lateral branches originating between 2.1m (7ft) and 4.5m (15ft) above the forest floor while maintaining at least 50% of the forest canopy. Subcanopy light transmission data were used to estimate the impact of pruning on canopy closure and monthly measurements were obtained thereafter to monitor recovery. Estimates of litter fall were based upon biweekly sampling from ten 0.25 m2 traps randomly placed in four 5 × 10 m control and impact plots. Following selective pruning, subcanopy light transmission increased by more than 30%. This provided a favorable environment for enhanced mangrove propagule recruitment, but several exotic species, including Brazilian Pepper (Schinus terebinthifolius), also invaded the forest beneath canopy gaps. Subcanopy light transmission within the impact plots has steadily declined since pruning and within 12 months had approached control plot levels. The results of our BACI impact assessment suggest mean forest litter fall production before and after pruning was not significantly different. However, inspection of the graphical output suggest all components of litter fall declined immediately after impact. Convergence towards pre-impact production levels took ∼6 months. Many mangrove forests in peninsular Florida are subjected to multiple pruning events or other forms of repeated mechanical alteration by homeowners who seek to maintain a scenic vista of the Indian River Lagoon or other coastal waterway. The cumulative effect of stress induced by repeated impact is unknown at present.

Late Holocene erosional shoreface retreat within a silicilastic-to-carbonate transition zone, east central Florida, USA

ABSTRACT This study has reconstructed the late Holocene evolution of a section of the North American Atlantic coast barrier-island system in a siliciclastic-to-carbonate transition zone. A transgressive stratigraphy, analogous to that recognized beneath the siliciclastic barriers of the embayed Atlantic and Gulf coasts, was identified in the study area and generated by erosional shoreface retreat of the barrier island during Holocene sea-level rise. Vibracores from the backbarrier revealed the preservation of a thin (< 3.5 m) Holocene sediment succession consisting of muddy skeletal sand overlain by intercalations of clean skeletal sand and muddy skeletal sand capped by fibrous peat. In the foreshore, the fibrous peat is compressed and abruptly overlain by coarse shell hash grading upward into skeletal sand. The entire Holocene section rests unconformably upon a thin (< 0.25 m) quartz sand and featureless, gently seaward-dipping Pleistocene limestone surface. Sedimentologic, paleontologic, stratigraphic, and radiocarbon data suggest that this sequence is transgressive and was generated during erosional shoreface retreat of a wave-dominated, microtidal barrier-island system. The basal, muddy skeletal sand is interpreted to have been deposited in a shallow (3 m) backbarrier lagoon. These sediments were buried during overwash events that transported skeletal sand across the barrier and into the lagoon. Repeated overwash generated a shallowing-upward sequence capped by organic-rich tidal-wetland sediment. Radiocarbon dates suggest that wetland sedimentation started between 1200 and 1960 yr B.P. Landward retreat of the barrier is indicated by the foreshore unconformity (ravinement surface) that now truncates the fibrous peat. The preservation potential of the entire Holocene paralic section is probably low, given the lack of significant antecedent topographic relief and relatively slow rate of sea-level rise. The preservation potential should increase seaward, however, because the older paralic environments would have been subjected to faster sea-level rise.

Discussion of: Houston, J.R. and Dean, R.G., 2011. Sea-Level Acceleration Based on U.S. Tide Gauges and Extensions of Previous Global-Gauge Analyses. Journal of Coastal Research, 27(3), 409–417

In a recent article, Houston and Dean (2011) attempted to quantify acceleration in the rate of historical sea-level rise (SLR) by analyzing monthly averaged, long-term, tide-gauge records for 57 U.S. tide stations. The data were extracted from the Permanent Service for Mean Sea Level (PSMSL) at the National Oceanography Centre in Liverpool, U.K. The investigation involved the calculation of accelerations for each station for the period of record, plus accelerations for the 25 stations whose records extended back to 1930. The authors calculated decelerations, i.e., a slowing in the rate of SLR, for 16 of the 25 selected long-term gauge records. The authors stated that there is no evidence of acceleration in 20th century SLR, despite rising atmospheric temperatures. Therefore, they contended the accelerations forecasted to accompany continued warming are highly suspect. They concluded that researchers must now determine why global warming has not produced an acceleration in SLR. We believe the authors’ conclusions are erroneous for a variety of reasons, including those argued in the accompanying rebuttals. We will focus our criticism on three issues in the sections that follow.

Tuning Surface Water Management and Wetland Restoration Programs with Historic Sediment Accumulation Rates: Merritt Island National Wildlife Refuge, East-Central Florida, U.S.A

Abstract Previous research has demonstrated that reconnection of impounded wetlands to the Indian River Lagoon benefits estuarine fisheries and emergent ecosystems. However, no effort has yet been made to quantify the effects of managed surface water flow on patterns of sedimentation. Sedimentation patterns strongly influence wetland evolution, including the distribution of open water and emergent landscapes. Thus, the enumeration of sedimentation rates provides a basis for reconstructing the processes responsible for historic landscape change. These data also provide a basis for predicting landscape change that can accompany hydrologic reconnection of impounded wetlands to the Indian River Lagoon. In this investigation, conducted in the Merritt Island National Wildlife Refuge, Florida, we used cesium activity profiles to quantify rates of historic sediment accumulation at locations subject to managed (impounded) and unmanaged (natural) surface water hydrology. The data suggest impounded wetlands subject to historic submergence are now devoid of vegetation and experiencing substrate erosion in areas in which fetch is sufficient to induce wind-driven circulation. In unmanaged wetlands, surface elevations have kept pace with historic sea level rise solely through the in situ accumulation of organic matter. These observations suggest that hydrologic reconnection of impounded wetlands subject to persistent flooding throughout historic time will result in rapid and widespread submergence to water depths in excess of 10 to 20 cm. At these depths, most wetland plant taxa will not successfully recruit via seedling exchange. Hence, attempts to restore wetland areas analogous to those investigated during this study (i.e., Impoundment D) cannot be achieved simply by removing management structures that obstruct natural surface water flow. The wetland surface must either be (1) incrementally flooded to estuarine water level elevations slowly over time or (2) raised to the appropriate hydroperiod elevation before reconnection with suitable fill material. One possible source of fill is the Intracoastal Waterway, located within 2 km of the Merritt Island National Wildlife Refuge and intermittently dredged to maintain safe navigation.

Geologic evidence of net onshore sand transport throughout the Holocene marine transgression, southwest Florida

Abstract The Holocene sediment sequence within the Ten Thousand Islands area of southwest Florida consists of more than 3 m of marine shelly quartz sand which overlies a thin layer ( The specific mechanism responsible for onshore sand transport can only be speculated at the present time as climatic and wave data are essentially nonexistent for this remote area. However, net onshore sand transport implies that low steepness waves have mobilized a larger volume of sediment than waves of high steepness. Low steepness waves are generated under prevailing wave conditions and by the swell of distant tropical cyclones. High steepness waves are associated with winter cold fronts or the direct landfall of a tropical cyclone. Because wave heights average only 10 cm along this low energy coastline it is entirely possible that the swell of distant tropical cyclones is the principle mechanism by which sand is transported onshore and incorporated into the Holocene sediment sequence of the Ten Thousand Islands area.

Mud-bank destruction and the formation of a transgressive sand sheet, southwest Florida inner shelf

The Holocene sediment sequence immediately seaward of the Florida Bay mud-bank complex consists of a thin (<0.25 m) skeletal-sand sheet and skeletal-sand banks as much as 2.0 m thick. This is in marked contrast to the myriad carbonate mud banks within the bay. Sedimentologic, stratigraphic, and radiocarbon data suggest that the skeletal sands are partly the product of physical and biological degradation of precursor mud banks which existed at least 3500 yr B.P. During degradation of mud banks, most of the skeletal material is locally reworked, whereas mud is transported onshore (eastward) where it contributes to the buildup of younger constructional banks. Active mud-bank destruction is presently occurring in a transitional zone between the transgressive sand sheet and accretionary mud-bank complex. In this zone, bank stratigraphy consists of a lower mud-bank core and upper skeletal sand or entirely of skeletal sand. The sands diminish toward the interior of the bay, whereas the basal mud-bank facies disappears to the west. Continued sea-level rise at its present long-term rate of ∼4 cm/100 yr should be accompanied by a landward shift in the destructional zone and expansion of the transgressive sand sheet. Hence, it is hypothesized that much of the western Florida Bay mud-bank complex may ultimately be preserved as a thin skeletal-sand sheet and not as a muddy carbonate sequence as previously suggested. Paleoenvironmental reconstructions of Pliocene and Pleistocene transgressive sediment sequences from the south Florida peninsula support this hypothesis.

Florida, USA, Port Experience with Marpol Annex V

Abstract This study assesses the effectiveness of MARPOL Annex V regulations, hereafter referred to as the Annex, using observations of United States Department of Agriculture (USDA) personnel stationed at major Florida ports. the study was initiated at the request of the 1IOPS Marine Debris Workshop Steering Committee∗ and was designed to focus on Gulf and Caribbean experiences gained since the Annex became effective.