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Many landforms on Earth are profoundly influenced by biota. In particular, biota play a significant role in creating karst biogeomorphology, through biogenic CO2 accelerating calcite weathering. In this study, we explore the ecohydrologic feedback mechanisms that have created isolated depressional wetlands on exposed limestone bedrock in South Florida – Big Cypress National Preserve –as a case study for karst biogeomorphic processes giving rise to regularly patterned landscapes. Specifically, we are interested in: (1) whether cypress depressions on the landscape have reached (or will reach) equilibrium size; (2) if so, what feedback mechanisms stabilize the size of depressions; and (3) what distal interactions among depressions give rise to the even distribution of depressions in the landscape. We hypothesize three feedback mechanisms controlling the evolution of depressions and build a numerical model to evaluate the relative importance of each mechanism. We show that a soil cover feedback (i.e. a smaller fraction of CO2 reaches the bedrock surface for weathering as soil cover thickens) is the major feedback stabilizing depressions, followed by a biomass feedback (i.e. inhibited biomass growth with deepening standing water and extended inundation period as depressions expand in volume). Strong local positive feedback between the volume of depressions and rate of volume expansion and distal negative feedback between depressions competing for water likely lead to the regular patterning at the landscape scale. The individual depressions, however, are not yet in steady state but would be in ~0.2–0.4 million years. This represents the first study to demonstrate the decoupling of landscape-scale self-organization and the self-organization of its constituent agents. © 2018 John Wiley & Sons, Ltd. 相似文献
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Francis X. O’Beirn Peter B. Heffernan Randal L. Walker Michelle L. Jansen 《Estuaries and Coasts》1996,19(3):651-658
Young-of-the-year (YOY) oysters (Crassostrea virginica) in the Gulf of Mexico mature sexually and spawn in their first year. This study determined whether YOY oysters in the southeastern United States also mature and spawn in their first year. In 1991 and 1993, 300 YOY oysters were marked in May and 20–30 were sampled in subsequent months along with 20 adult controls. Two sites were chosen in 1991 (House Creek and Skidaway River) and one in 1993 (Skidaway River). At House Creek, YOY oysters were mature and spawned in September. YOY oysters at Skidaway spawned in October. Adult oysters did not appear to spawn in 1991. In 1993, the adult oysters spawned in August and September whereas, the YOY oysters spawned heavily in October. Oyster recruitment in coastal Georgia extends through October. The potential contribution of YOY oysters to this late season set is substantial, given that the YOY oysters are relatively large (≈4 cm) and are found in greater numbers than the adults. Oysters are capable of having two, if not more, generations within one year, prior to exposure of disease-causing organisms. Also, this particular reproductive strategy would increase the oysters suitability as a test subject in population genetic studies. 相似文献
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Adam C. Watts Danielle L. Watts Matthew J. Cohen James B. Heffernan Daniel L. McLaughlin Jonathan B. Martin David A. Kaplan Todd Z. Osborne Leda N. Kobziar 《地球表面变化过程与地形》2014,39(15):2027-2037
Patterned landscapes are often evidence of biotic control on geomorphic processes, emerging in response to coupled ecosystem processes acting at different spatial scales. Self‐reinforcing processes at local scales expand patches, while self‐inhibiting processes, operating at a distance, impose limits to expansion. In Big Cypress National Preserve (BICY) in southwest Florida, isolated forested wetland depressions (cypress domes) appear to be evenly distributed within a mosaic of short‐hydroperiod marshes and pine uplands. To test the hypothesis that the apparent patterning is regular, we characterized frequency distributions and spatial patterns of vegetation communities, surface and bedrock elevation, and soil properties (thickness and phosphorus content). Nearest neighbor distances indicate strongly significant wetland spatial overdispersion, and bedrock elevations exhibited periodic spatial autocorrelation; both observations are consistent with regular patterning. Bedrock elevations and soil P were clearly bimodal, suggesting strong positive feedbacks on wetland patch development. Soil‐surface elevations exhibited weaker bimodality, indicating smoothing of surface morphology by some combination of sediment transport, mineral reprecipitation, and organic matter production. Significant negative autocorrelation of bedrock elevations at scales similar to wetland spacing suggest the presence of distal negative feedbacks on patch expansion. These findings support the inference of regular patterning, and are consistent with the presence of local positive feedbacks among hydroperiod, vegetation productivity and bedrock dissolution. These processes are ultimately constrained by distal negative feedbacks, potentially induced by landscape scale limitations on the water volume required to enable this biogeomorphic mechanism. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Measurements were made of chlorophyll-a and phaeophytin-a in calcareous sediments along transects off the east coast of Florida (75–190 m) and the west coast of Grand Bahama Island (170–300 m). Solvent partitioning showed that chlorophyll-a concentrations never exceeded 0·1 mg m?2 at either location, most as degradation products. Total pigment concentrations (chlorophyll and phaeopigments) ranged from 0·18–1·83 mg m?2 in sediments off Grand Bahama Island and 2·50 to 20·65 mg m?2 off West Palm Beach. Pigments, expressed per gram dry weight of sediments, increased with depth across the Florida Continental Shelf. This is probably due to differences in sediment character between near-shore and off-shore sediments. 相似文献
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Ana García-García Daniel L. Orange Norman M. Maher Adam S. Heffernan Gary S. Fortier Andy Malone 《Marine and Petroleum Geology》2004,21(10):1255-1264
High-resolution seafloor and sub-surface data were acquired as part of a site survey in Iskenderun Bay, SE Turkey to characterize the geohazards at the location of the proposed drilling site. A 3 km×3 km geophysical study reveals a pockmark field which trends NE and NNE, similar to the trend of major fault systems in the area. The pockmarks, with an average diameter of 35 m, reach their highest density in the northern part of the detailed survey area, with 13 features/km2. Acoustic anomalies in the seismic records (acoustic turbidity, blanking, enhanced reflectors) below the proposed drilling site indicated potential shallow gas beneath it. The local seismic anomalies (amplitude and frequency) parallel to stratigraphy were assigned a low gas risk. As a result of the active neotectonics in the area, the pockmark field presented a potential hazard for drilling at the original location. The geohazard study resulted in moving the proposed drilling site eastward to an area of fewer pockmarks, less sub-surface seismic anomalies, and thus a location interpreted as a lower geohazard environment. 相似文献
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J. Stephen Hopkins Craig L. Browdy Richard D. Hamilton Joseph A. Heffernan 《Estuaries and Coasts》1995,18(1):116-123
Pond water in intensive shrimp ponds is typically high in nutrients, solids, and BOD and may have an adverse environmental impact when discharged to natural waters. As part of ongoing research to develop intensive production technologies that minimize the potential for environmental impact, a study investigated the effect of lowrate, coarse-grain sand filtration on the quality of effluent being discharged from an intensive shrimp pond receiving 5% d?1 water exchange. The effect of sand filtration on a recirculating no-exchange pond was also examined. For comparison, a third pond received no water exchange and no filtration. Sand filtration removed some particulate matter, but levels of dissolved and particulate organic and inorganic nutrients were changed little and were sometimes higher as the result of in situ decomposition. Low-rate sand filtration is not seen as a cost-effective method of increasing the carrying capacity of no-exchange shrimp ponds or drastically improving the effluent quality of ponds with water exchange. Compared to previous studies with decreased or no water exchange, the application of feed in these ponds was more stable with small portions fed at frequent intervals with a constant rate of 80 kg ha?1 d?1. These ponds, stocked with 40 m?2 juvenilePenaeus vannamei, had excellent survival and normal growth, resulting in productions levels approaching 7,000 kg ha?1 crop?1 without water exchange. This indicates that intensive shrimp farming may be possible in static no-exchange systems, thereby minimizing the potential impact of effluent as long as feed inputs do not overwhelm the assimilative capacity of the pond ecosystem. *** DIRECT SUPPORT *** A01BY069 00011 相似文献
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Our previous studies indicated that sea anemone microsomes contain cytochrome P450 (CYP) and have ethoxyresorufin O-dealkylation (EROD) activity. Other marine invertebrates have discrete organs which concentrate cytochromes P450, whereas cnidarians have evolved only to the tissue level of development. To examine the distribution of CYP in sea anemones, microsomes were prepared from the following tissue regions of two sea anemones, Anthopleura xanthogrammica: outer (heavy muscular wall), inner (imperfect and perfect mesentery, and retractor muscle), soft (digestive sac, gonads, and mesentery filaments), and tentacular (including algal/diatom symbiont). The cytochrome P450 content was distributed relatively evenly among the tissue regions. In contrast, the 418-nm CO-binding chromophore was approximately 10 times greater in the outer region than in any other region. Further, the 490-nm peak (which interferes with quantification of CYP in sea anemones) was greater in the outer region. In general, the EROD activity was comparable in the inner and soft regions and highest in the tentacles. However, the EROD results may have been complicated by the presence of the algal/diatom symbiont. 相似文献
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Fateme Yousefi Lalimi Marco Marani James Brendan Heffernan Andrea D'Alpaos A. Brad Murray 《地球表面变化过程与地形》2020,45(6):1456-1468
The formation and evolution of tidal platforms are controlled by the feedbacks between hydrodynamics, geomorphology, vegetation, and sediment transport. Previous work mainly addresses dynamics at the scale of individual marsh platforms. Here, we develop a process-based model to investigate salt marsh depositional/erosional dynamics and resilience to environmental change at the scale of tidal basins. We evaluate how inputs of water and sediment from river and ocean sources interact, how losses of sediment to the ocean depend on this interaction, and how erosional/depositional dynamics are coupled to these exchanges. Model experiments consider a wide range of watershed, basin, and oceanic characteristics, represented by river discharge and suspended sediment concentration, basin dimensions, tidal range, and ocean sediment concentration. In some scenarios, the vertical accretion of a tidal flat can be greater than the rate of sea level rise. Under these conditions, vertical depositional dynamics can lead to transitions between tidal flat and salt marsh equilibrium states. This type of transition occurs much more rapidly than transitions occurring through horizontal marsh expansion or retreat. In addition, our analyses reveal that river inputs can affect the existence and extent of marsh/tidal flat equilibria by both directly providing suspended sediment (favoring marshes) and by modulating water exchanges with the ocean, thereby indirectly affecting the ocean sediment input to the system (favoring either marshes or tidal flats depending on the ratio of the river and ocean water inputs and their sediment concentrations). The model proposed has the goal of clarifying the roles of the main dynamic processes at play, rather than of predicting the evolution of a particular tidal system. Our model results most directly reflect micro- and meso-tidal environments but also have implications for macro-tidal settings. The model-based analyses presented extend our theoretical understanding of marsh dynamics to a greater range of intertidal environments. © 2020 John Wiley & Sons, Ltd. 相似文献
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