R. Twilley
Louisiana State University, Oceanography and Coastal Sciences, Faculty Member
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Nutrient biogeochemistry associated with the early stages of soil development in deltaic floodplains has not been well defined. Such a model should follow classic patterns of soil nutrient pools described for alluvial ecosystems that are... more
Nutrient biogeochemistry associated with the early
stages of soil development in deltaic floodplains has
not been well defined. Such a model should follow
classic patterns of soil nutrient pools described for
alluvial ecosystems that are dominated by mineral
matter high in phosphorus and low in carbon and
nitrogen. A contrast with classic models of soil
development is the anthropogenically enriched
high nitrate conditions due to agricultural fertilization
in upstream watersheds. Here we determine
if short-term patterns of soil chemistry and dissolved
inorganic nutrient fluxes along the emerging
Wax Lake delta (WLD) chronosequence are
consistent with conceptual models of long-term
nutrient availability described for other ecosystems.
We add a low nitrate treatment more typical
of historic delta development to evaluate the
role of nitrate enrichment in determining the net
dinitrogen (N2) flux. Throughout the 35-year
chronosequence, soil nitrogen and organic matter
content significantly increased by an order of
magnitude, whereas phosphorus exhibited a less pronounced increase. Under ambient nitrate concentrations (>60 lM), mean net N2 fluxes (157.5 lmol N m-2 h-1) indicated greater rates of
gross denitrification than gross nitrogen fixation; however, under low nitrate concentrations (<2 lM), soils switched from net denitrification to net nitrogen fixation (-74.5 lmol N m-2 h-1).
As soils in the WLD aged, the subsequent increase in organic matter stimulated net N2, oxygen, nitrate, and nitrite fluxes producing greater fluxes in more mature soils. In conclusion, soil nitrogen and carbon accumulation along an emerging delta chronosequence largely coincide with classic patterns of soil development described for alluvial floodplains, and substrate age together with ambient nitrogen availability can be used to predict net N2 fluxes during early delta evolution.
stages of soil development in deltaic floodplains has
not been well defined. Such a model should follow
classic patterns of soil nutrient pools described for
alluvial ecosystems that are dominated by mineral
matter high in phosphorus and low in carbon and
nitrogen. A contrast with classic models of soil
development is the anthropogenically enriched
high nitrate conditions due to agricultural fertilization
in upstream watersheds. Here we determine
if short-term patterns of soil chemistry and dissolved
inorganic nutrient fluxes along the emerging
Wax Lake delta (WLD) chronosequence are
consistent with conceptual models of long-term
nutrient availability described for other ecosystems.
We add a low nitrate treatment more typical
of historic delta development to evaluate the
role of nitrate enrichment in determining the net
dinitrogen (N2) flux. Throughout the 35-year
chronosequence, soil nitrogen and organic matter
content significantly increased by an order of
magnitude, whereas phosphorus exhibited a less pronounced increase. Under ambient nitrate concentrations (>60 lM), mean net N2 fluxes (157.5 lmol N m-2 h-1) indicated greater rates of
gross denitrification than gross nitrogen fixation; however, under low nitrate concentrations (<2 lM), soils switched from net denitrification to net nitrogen fixation (-74.5 lmol N m-2 h-1).
As soils in the WLD aged, the subsequent increase in organic matter stimulated net N2, oxygen, nitrate, and nitrite fluxes producing greater fluxes in more mature soils. In conclusion, soil nitrogen and carbon accumulation along an emerging delta chronosequence largely coincide with classic patterns of soil development described for alluvial floodplains, and substrate age together with ambient nitrogen availability can be used to predict net N2 fluxes during early delta evolution.
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ABSTRACT: The growth, morphology, and chemical composition of Hydrilla verticillata, Myriophyllum spicatum, Potamogeton perfoliatus, and Vallisneria americana were compared among different salinity and light conditions. Plants were grown... more
ABSTRACT: The growth, morphology, and chemical composition of Hydrilla verticillata, Myriophyllum spicatum, Potamogeton perfoliatus, and Vallisneria americana were compared among different salinity and light conditions. Plants were grown in microcosms (1.2 m3) under ambient photoperiod adjusted to 50% and 8% of solar radiation. The culture solution in five pairs of tanks was gradually adjusted to salinities of 0, 2, 4, 6, and 12%ooW. ith the exception of H. verticillata, the aquatic macrophytes examined may be considered eurysaline species that are able to adapt to salinities one-third the strength of sea water. With increasing salinity, the inflorescence production
decreased in M. spicatum and P. perfoliatus, yet asexual reproduction in the latter species by underground buds
remained constant. Stem elongation increased in response to shading in M. spicatum, while shaded P. perfoliatus
had higher concentrations of chlorophyll a. In association with high epiphytic mass, chlorophyll a concentrations
in all species were greatest at 120oo. The concentration of sodium increased in all four species of aquatic macrophytes
examined here, indicating that these macrophytes did not possess mechanisms to exclude this ion. The nitrogen
content (Y) of the aquatic macrophytes tested increased significantly with higher sodium concentration (X), suggesting
that nitrogen may be utilized in osmoregulation (Y = X x 0.288 + 6.10, r2 = 0.71). The tolerance of V. americana and P. perfoliatus to salinity was greater in our study compared to other investigations. This may be associated with experimental methodology, whereby macrophytes were subjected to more gradual rather than abrupt changes in salinity. The two macrophytes best adapted to estuarine conditions in this study by exhibiting growth up to 12%oo including M. spicatum and V. americana, also exhibited a greater degree of response in morphology, tissue chemistry (including chlorophyll content and total nitrogen), and reproductive output in response to varying
salinity and light conditions.
decreased in M. spicatum and P. perfoliatus, yet asexual reproduction in the latter species by underground buds
remained constant. Stem elongation increased in response to shading in M. spicatum, while shaded P. perfoliatus
had higher concentrations of chlorophyll a. In association with high epiphytic mass, chlorophyll a concentrations
in all species were greatest at 120oo. The concentration of sodium increased in all four species of aquatic macrophytes
examined here, indicating that these macrophytes did not possess mechanisms to exclude this ion. The nitrogen
content (Y) of the aquatic macrophytes tested increased significantly with higher sodium concentration (X), suggesting
that nitrogen may be utilized in osmoregulation (Y = X x 0.288 + 6.10, r2 = 0.71). The tolerance of V. americana and P. perfoliatus to salinity was greater in our study compared to other investigations. This may be associated with experimental methodology, whereby macrophytes were subjected to more gradual rather than abrupt changes in salinity. The two macrophytes best adapted to estuarine conditions in this study by exhibiting growth up to 12%oo including M. spicatum and V. americana, also exhibited a greater degree of response in morphology, tissue chemistry (including chlorophyll content and total nitrogen), and reproductive output in response to varying
salinity and light conditions.
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—The development of ecosystem management plans to restore and rehabilitate natural resources requires an understanding of how specific ecological mechanisms regulate the structure and function of ecosystems. To achieve restoration goals,... more
—The development of ecosystem management plans to restore and rehabilitate natural resources requires an understanding of how specific ecological mechanisms regulate the structure and function of ecosystems. To achieve restoration goals, comprehensive plans and engineering designs must effectively change environmental drivers at the regional level to reduce stress conditions at the local environment that are responsible for ecosystem degradation. This document focuses on the Coastal Louisiana Ecosystem Assessment and Restoration (CLEAR) ecosystem forecasting framework and how it can be used to support the analysis of Louisiana's coastal restoration plans. Specifically, the framework is designed to (1) develop and incorporate conceptual ecological models that can be used to integrate ecological needs and opportunities with engineering designs, (2) utilize wetland loss rates to describe the most likely " future without " scenario for a variety of ecosystem attributes, (3) estimate broad ecosystem responses to restoration alternatives based on processes associated with succession of geomorphic and ecological systems, and (4) calculate ecological benefits for incorporation into decision support tools associated with large-scale geomorphic and hydrologic processes. This paper provides a brief overview of the spatial framework and modular design of the CLEAR ecosystem forecasting framework and describes in greater detail the evolution of the landscape change module, concepts for its refinement, and how it was utilized in evaluating a coastal restoration alternative proposed in the Coastal Protection and Restoration Authority Preliminary Draft Master Plan. Such projections by the CLEAR forecasting framework can evaluate processes and conditions that result in sustainable coastal ecosystems with habitat functions that support higher trophic levels.
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Absorption, translocation, and subsequent secretion of phosphorus by Nuplm Zuteum was studied under laboratory and field conditions. Laboratory studies showed that absorption rates (per gram dry weight of absorbing organ) differed with... more
Absorption, translocation, and subsequent secretion of phosphorus by Nuplm Zuteum was studied under laboratory and field conditions. Laboratory studies showed that absorption rates (per gram dry weight of absorbing organ) differed with the absorbing organ (roots > submersed leaves > floating leaves).
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Twilley, R.R., Blanton, L.R., Brinson, M.M. and Davis, G.J., 1985. Biomass production and nutrient cycling in aquatic macrophyte communities of the Chowan River, North Carolina. Aquat. Bot., 22 : 231-252. Net primary productivity (NPP) of... more
Twilley, R.R., Blanton, L.R., Brinson, M.M. and Davis, G.J., 1985. Biomass production and nutrient cycling in aquatic macrophyte communities of the Chowan River, North Carolina. Aquat. Bot., 22 : 231-252. Net primary productivity (NPP) of Nuphar luteum (L.) Sibth. & Smith and Justicia amer-icana (L.) Vahl was estimated for stands in the Chowan River, North Carolina. NPP of J. americana was estimated at 173 g dry wt. m-2 per growing season, based on the difference between maximum and minimum standing crops. For N. luteum, the great variation in bio-mass estimates and observed high mortality of floating leaves during the growing season resulted in an underestimate of net production using this approach. Estimates based on tagging experiments were 222 g dry wt. m-2 year-2 using annual turnover rates, compared to 234 g dry wt. m-2 year-1 using monthly rates. Nearly 92% of this net production was accounted for by above-ground structures, although they represented only 33% of the biomass at any one time. Nutrient distributions in both species differed spatially and seasonally for each plant structure, which suggests that accurate estimates of nutrient turnover would have been masked by whole plant analyses. Most notable, were high affinities of iron in below-ground structures and calcium and nitrogen in above-ground structures for both species. One-half the dry mass of above-ground structures was lost from mesh bags in only 7 days for N. luteum compared to 60 days for J. americana, indicating the high recycling potential of aquatic plant detritus. Nutrient immobilization during decomposition was minor except for calcium and magnesium in above-ground structures of J. ameri-cana. Highest nutrient turnover rates were for nitrogen and potassium at about 7.5 g m-2 year-~ in N. luteum and nutrient turnover rates for the floating-leaf macrophyte were higher than for the emergent macrophyte. Assuming that most of these nutrients originated from the sediments, these turnover rates represent significant fluxes of nutrients to the water column.
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Restoration of river deltas involves diverting sediment and water from major channels into adjoining drowned areas, where the sediment can build new land and provide a platform for regenerating wetland ecosystems. Except for local... more
Restoration of river deltas involves diverting sediment and water from major channels into adjoining drowned areas, where the sediment can build new land and provide a platform for regenerating wetland ecosystems. Except for local engineered structures at the points of diversion, restoration mainly relies on natural delta-building processes. Present understanding of such processes is sufficient to provide a basis for determining the feasibility of restoration projects through quantitative estimates of land-building rates and sustainable wetland area under different scenarios of sediment supply, subsidence, and sea-level rise. We are not yet to the point of being able to predict the evolution of a restored delta in detail. Predictions of delta evolution are based on field studies of active deltas, deltas in mine-tailings ponds, experimental deltas, and countless natural experiments contained in the stratigraphic record. These studies provide input for a variety of mechanistic delta models, ranging from radially averaged formulations to more detailed models that can resolve channels, topography, and ecosystem processes. Especially exciting areas for future research include understanding the mechanisms by which deltaic channel networks self-organize, grow, and distribute sediment and nutrients over the delta surface and coupling these to ecosystem processes, especially the interplay of topography, network geometry, and ecosystem dynamics.
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We discuss the mechanisms leading to nutrient limitation in tropical marine systems, with particular emphasis on nitrogen cycling in Caribbean ecosystems. We then explore how accelerated nutrient cycling from human activities is affecting... more
We discuss the mechanisms leading to nutrient limitation in tropical marine systems, with particular emphasis on nitrogen cycling in Caribbean ecosystems. We then explore how accelerated nutrient cycling from human activities is affecting these systems. Both nitrogen and phosphorus exert substantial influence on biological productivity and structure of tropical marine ecosystems. Offshore planktonic communities are largely nitrogen limited while nearshore ecosystems are largely phosphorus limited. For phosphorus, the ability of sediment to adsorb and store phosphorus is probably greater for tropical carbonate sediments than for most nearshore sediments in temperate coastal systems. However, the ability of tropical carbonate sediments to take up phosphorus can become saturated as phosphorus loading from human sources increases. The nature of the sediment, the mixing rate between nutrient-laden runoff waters and nutrient-poor oceanic waters and the degree of interaction of these water masses with the sediment will probably control the dynamics of this transition. Nearshore tropical marine ecosystems function differently from their temperate counterparts where coupled nitrification/denitrification serves as an important mechanism for nitrogen depuration. In contrast, nearshore tropical ecosystems are more susceptible to nitrogen loading as depurative capacity of the microbial communities is limited by the fragility of the nitrification link. At the same time, accumulation of organic matter in nearshore carbonate sediments appears to impair their capacity for phosphorus immobilization. In the absence of depurative mechanisms for either phosphorus or nitrogen, limitation for both these nutrients is alleviated and continued nutrient loading fuels the proliferation of nuisance algae.
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We discuss the mechanisms leading to nutrient limitation in tropical marine systems, with particular emphasis on nitrogen cycling in Caribbean ecosystems. We then explore how accelerated nutrient cycling from human activities is affecting... more
We discuss the mechanisms leading to nutrient limitation in tropical marine systems, with particular emphasis on nitrogen cycling in Caribbean ecosystems. We then explore how accelerated nutrient cycling from human activities is affecting these systems. Both nitrogen and phosphorus exert substantial influence on biological productivity and structure of tropical marine ecosystems. Offshore planktonic communities are largely nitrogen limited while nearshore ecosystems are largely phosphorus limited. For phosphorus, the ability of sediment to adsorb and store phosphorus is probably greater for tropical carbonate sediments than for most nearshore sediments in temperate coastal systems. However, the ability of tropical carbonate sediments to take up phosphorus can become saturated as phosphorus loading from human sources increases. The nature of the sediment, the mixing rate between nutrient-laden runoff waters and nutrient-poor oceanic waters and the degree of interaction of these water masses with the sediment will probably control the dynamics of this transition. Nearshore tropical marine ecosystems function differently from their temperate counterparts where coupled nitrification/denitrification serves as an important mechanism for nitrogen depuration. In contrast, nearshore tropical ecosystems are more susceptible to nitrogen loading as depurative capacity of the microbial communities is limited by the fragility of the nitrification link. At the same time, accumulation of organic matter in nearshore carbonate sediments appears to impair their capacity for phosphorus immobilization. In the absence of depurative mechanisms for either phosphorus or nitrogen, limitation for both these nutrients is alleviated and continued nutrient loading fuels the proliferation of nuisance algae.
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The rates of decomposition and nutrient regeneration were compared among six aquatic plants representing examples from phytoplankton (Chlorella sp.), macroalgae (Ulva lactuca), submersed vascular macrophytes (Myriophyllum spicatum,... more
The rates of decomposition and nutrient regeneration were compared among six aquatic plants representing examples from phytoplankton (Chlorella sp.), macroalgae
(Ulva lactuca), submersed vascular macrophytes (Myriophyllum spicatum, Potamogeton perfoliatus, and Ruppia maritima) and marsh grasses (Spartina alterniflora). These plants, which were obtained from the Choptank River estuary, Maryland, (except for Chlorella which was a laboratory culture) were placed in 1 mm mesh bags and incubated in aquaria with ambient water under dark, aerated, temperature controlled (20 + 3°C) conditions for 93 d. The rank in decomposition rates based on both decrease in original mass (decrease in chlorophyll a for Chlorella) and associated oxygen consumption was phytoplankton > macroalga > submersed macrophytes > emergent macrophyte, and rates were directly proportional to the initial nitrogen content of the plant tissues. Nitrogen content of all the plant tissues increased during decomposition, yet reductions of C:N ratios were only observed for those plants with initial C:N > 20. N:P ratios generally increased due to a much higher leaching for P (10-40% of initial P) compared with N (1 to 10% of original N). The leached P was equally distributed between dissolved inorganic and organic forms. Generally, the magnitude of P and N leaching rate was not related to respective initial nutrient concentrations of the plant, nor to the plant's structural integrity,(C:N ratio). Total N and P dissolved in the water column plus that in plant material,remaining in the mesh bags at the experiment's termination accounted for 7 to 48% of their original respective quantities for submersed macrophytes compared with 82-94% for Spartina.
(Ulva lactuca), submersed vascular macrophytes (Myriophyllum spicatum, Potamogeton perfoliatus, and Ruppia maritima) and marsh grasses (Spartina alterniflora). These plants, which were obtained from the Choptank River estuary, Maryland, (except for Chlorella which was a laboratory culture) were placed in 1 mm mesh bags and incubated in aquaria with ambient water under dark, aerated, temperature controlled (20 + 3°C) conditions for 93 d. The rank in decomposition rates based on both decrease in original mass (decrease in chlorophyll a for Chlorella) and associated oxygen consumption was phytoplankton > macroalga > submersed macrophytes > emergent macrophyte, and rates were directly proportional to the initial nitrogen content of the plant tissues. Nitrogen content of all the plant tissues increased during decomposition, yet reductions of C:N ratios were only observed for those plants with initial C:N > 20. N:P ratios generally increased due to a much higher leaching for P (10-40% of initial P) compared with N (1 to 10% of original N). The leached P was equally distributed between dissolved inorganic and organic forms. Generally, the magnitude of P and N leaching rate was not related to respective initial nutrient concentrations of the plant, nor to the plant's structural integrity,(C:N ratio). Total N and P dissolved in the water column plus that in plant material,remaining in the mesh bags at the experiment's termination accounted for 7 to 48% of their original respective quantities for submersed macrophytes compared with 82-94% for Spartina.
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Given the significance of natural and built assets of the Gulf of Mexico region, the three states of Alabama, Louisiana, and Mississippi, leveraged their unique partnerships, proximity, and significant prior investments in... more
Given the significance of natural and built assets of the Gulf of Mexico region, the three states of Alabama, Louisiana, and Mississippi, leveraged their unique partnerships, proximity, and significant prior investments in cyberinfras-tructure (CI) to develop the Northern Gulf Coastal Hazards Collaboratory (NG-CHC). This collaboratory was established to catalyze collaborative research
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Research Interests: Earth Sciences, Water quality, Hydrobiology, Biological Sciences, Seasonality, and 12 moreEnvironmental Sciences, Wetland, Surface Water, Water Temperature, Seasonal variation, Mangrove forest, Air Temperature, Dissolved Organic Carbon, Dissolved Oxygen, Organic carbon, Water Quality, and Soil Water
Research Interests: Geochemistry, Carbon, Biogeochemical cycles, Carbon Cycle, Endangered Species, and 20 moreGlobal change, Tides, Atmospheric sciences, Ecosystems, Exportation, Sediments, Nutrients, Sediment, Vegetation, Mangrove forest, Mineralization, Primary Production, Global Biogeochemical Cycles, Coastal Zone, Primary productivity, Organic carbon, Carbon Budget, Currents, Dissolved Inorganic Carbon, and Carbon Sink
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Research Interests: Earth Sciences, Hydrology, Water quality, Modeling, Biological Sciences, and 20 moreTides, Seasonality, Environmental Sciences, Flood, Evapotranspiration, Performance Model, Ground Water, Florida Everglades, Upwelling, Two-Dimensional Hydrodynamic Model, Intertidal Zone, Management Practice, Nutrient Loading, Water Quality, Water Flow, Overland Flow, Field Data, Wetland Restoration, Interannual Variability, and Water budget
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Research Interests: Cultural Policy, Science Policy, Ecological Economics, Water quality, Ecosystem management, and 23 moreCoastal Zone Management, Land Use Change, Seasonality, Environmental Sciences, Solar Energy, Environmental science and policy, Land Use, Negative Feedback, Conceptual Model, Economic Impact, Nitrogen, Data Collection, South America, Mangrove forest, Ecological Model, Environmental quality, Habitat Quality, Water Quality, Total Nitrogen, Pacific Coast, Residence Time, Simulation Model, and River Discharge
The authors summarize the main findings of the Florida Coastal Everglades Long-Term Ecological Research (FCE-LTER) program in the EMER, within the context of the Comprehensive Everglades Restoration Plan (CERP), to understand how regional... more
The authors summarize the main findings of the Florida Coastal Everglades Long-Term Ecological Research (FCE-LTER) program in the EMER, within the context of the Comprehensive Everglades Restoration Plan (CERP), to understand how regional processes, mediated by water flow, control population and ecosystem dynamics across the EMER landscape. Tree canopies with maximum height <3 m cover 49% of the EMER, particularly in the SE region. These scrub/dwarf mangroves are the result of a combination of low soil phosphorus (P < 59 μg P g dw−1) in the calcareous marl substrate and long hydroperiod. Phosphorus limits the EMER and its freshwater watersheds due to the lack of terrigenous sediment input and the phosphorus-limited nature of the freshwater Everglades. Reduced freshwater delivery over the past 50 years, combined with Everglades compartmentalization and a 10 cm rise in coastal sea level, has led to the landward transgression (∼1.5 km in 54 years) of the mangrove ecotone. Seasonal variation in freshwater input strongly controls the temporal variation of nitrogen and P exports (99%) from the Everglades to Florida Bay. Rapid changes in nutrient availability and vegetation distribution during the last 50 years show that future ecosystem restoration actions and land use decisions can exert a major influence, similar to sea level rise over the short term, on nutrient cycling and wetland productivity in the EMER.
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Assays of nitrogen fixation (acetylene reduction method) were performed on fresh leaf litter (yellow leaves recently fallen from the trees), aged leaf litter (brown leaves on the forest floor) of Rhizophora mangle, Avicennia germinans,... more
Assays of nitrogen fixation (acetylene reduction method) were performed on fresh leaf litter (yellow leaves recently fallen from the trees), aged leaf litter (brown leaves on the forest floor) of Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa; ...