R. Twilley | Louisiana State University (original) (raw)
Papers by R. Twilley
Innovation in Aging, Jun 30, 2017
The Activities-specific Balance Confidence scale (ABC-6) is advantageous in busy clinical or rese... more The Activities-specific Balance Confidence scale (ABC-6) is advantageous in busy clinical or research settings as it can be administered in significantly less time than the original 16-item ABC scale (ABC-16). The purpose of this study was to examine the convergent, discriminant and concurrent validity of the ABC-6 in older adults with diabetes mellitus (DM) with and without diagnosed diabetic peripheral neuropathy (DPN). Thirty older adults (aged ≥65) were age-and sex-matched in 3-groups: 10 with DM (DM-group), 10 with diagnosed DPN (DPN-group), and 10 without DM (noDMgroup). Balance confidence was quantified with the ABC-16 which includes the six items of the ABC-6. Potential correlates were evaluated in physical and psychological domains. Our results indicated the ABC-6 and ABC-16 balance confidence scores were strongly correlated (r=0.969, p<0.001; convergent validity). The ABC-6 revealed significant differences in balance confidence between the noDM-and DM-groups (p<0.001; discriminant validity) whereas the ABC-16 did not (p>0.05). The ABC-6 was moderately but significantly correlated with physical activity level (r=0.528, p=0.017), mobility (r=-0.520, p=0.027), balance (r=0.633, p=0.003) and depressive symptoms (r=-0.515, p=0.020) in the DM study-groups (concurrent validity). In conclusion, the ABC-6 and ABC-16 had excellent convergent validity and both ABC-scales had similar concurrent validity. However, the ABC-6 was more sensitive to detect subtle differences in balance confidence in older adults with diabetes without diagnosed DPN than the ABC-16. Overall the ABC-6 is a valid assessment tool that may provide a means for early detection of balance and mobility-related declines in older adults with DM without diagnosed DPN.
Nutrient biogeochemistry associated with the early stages of soil development in deltaic floodpla... 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.
ABSTRACT: The growth, morphology, and chemical composition of Hydrilla verticillata, Myriophyllum... 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.
—The development of ecosystem management plans to restore and rehabilitate natural resources requ... 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.
Absorption, translocation, and subsequent secretion of phosphorus by Nuplm Zuteum was studied und... 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).
Twilley, R.R., Blanton, L.R., Brinson, M.M. and Davis, G.J., 1985. Biomass production and nutrien... 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.
American Fisheries …, 2008
The development of ecosystem management plans to restore and rehabilitate natural resources requi... 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.
Woody debris is abundant in hurricane-impacted forests. With a major hurricane affecting South Fl... more Woody debris is abundant in hurricane-impacted forests. With a major hurricane affecting South Florida mangroves approximately every 20 yr, carbon storage and nutrient retention may be influenced greatly by woody debris dynamics. In addition, woody debris can influence seedling regeneration in mangrove swamps by trapping propagules and enhancing seedling growth potential. Here, we report on line-intercept woody debris surveys conducted in mangrove wetlands of South Florida 9-10 yr after the passage of Hurricane Andrew. The total volume of woody debris for all sites combined was estimated at 67 m 3 /ha and varied from 13 to 181 m 3 /ha depending upon differences in forest height, proximity to the storm, and maximum estimated wind velocities. Large volumes of woody debris were found in the eyewall region of the hurricane, with a volume of 132 m 3 /ha and a projected woody debris biomass of approximately 36 t/ha. Approximately half of the woody debris biomass averaged across all sites was associated as small twigs and branches (fine woody debris), since coarse woody debris >7.5 cm felled during Hurricane Andrew was fairly well decomposed. Much of the small debris is likely to be associated with post-hurricane forest dynamics. Hurricanes are responsible for large amounts of damage to mangrove ecosystems, and components of associated downed wood may provide a relative index of disturbance for mangrove forests. Here, we suggest that a fine:coarse woody debris ratio ≤0.5 is suggestive of a recent disturbance in mangrove wetlands, although additional research is needed to corroborate such findings.
International Journal of Forestry Research, 2013
Rhizophora mangle and Laguncularia racemosa cooccur along many intertidal floodplains in the Neot... more Rhizophora mangle and Laguncularia racemosa cooccur along many intertidal floodplains in the Neotropics. Their patterns of dominance shift along various gradients, coincident with salinity, soil fertility, and tidal flooding. We used leaf gas exchange metrics to investigate the strategies of these two species in mixed culture to simulate competition under different salinity concentrations and hydroperiods. Semidiurnal tidal and permanent flooding hydroperiods at two constant salinity regimes (10 g L −1 and 40 g L −1 ) were simulated over 10 months. Assimilation ( ), stomatal conductance ( ), intercellular CO 2 concentration ( ), instantaneous photosynthetic water use efficiency (PWUE), and photosynthetic nitrogen use efficiency (PNUE) were determined at the leaf level for both species over two time periods. Rhizophora mangle had significantly higher PWUE than did L. racemosa seedlings at low salinities; however, L. racemosa had higher PNUE and and, accordingly, had greater intercellular CO 2 (calculated) during measurements. Both species maintained similar capacities for A at 10 and 40 g L −1 salinity and during both permanent and tidal hydroperiod treatments. Hydroperiod alone had no detectable effect on leaf gas exchange. However, PWUE increased and PNUE decreased for both species at 40 g L −1 salinity compared to 10 g L −1 . At 40 g L −1 salinity, PNUE was higher for L. racemosa than R. mangle with tidal flooding. These treatments indicated that salinity influences gas exchange efficiency, might affect how gases are apportioned intercellularly, and accentuates different strategies for distributing leaf nitrogen to photosynthesis for these two species while growing competitively.
Restoration of river deltas involves diverting sediment and water from major channels into adjoin... 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.
Biogeochemistry, 1999
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.
Biogeochemistry, 1999
We discuss the mechanisms leading to nutrient limitation in tropical marine systems, with particu... 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.
Biogeochemistry, 1999
We discuss the mechanisms leading to nutrient limitation in tropical marine systems, with particu... 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.
Hydrobiologia, 1998
Seasonal and spatial patterns of aquatic primary production were compared in a tidal creek (Ester... more Seasonal and spatial patterns of aquatic primary production were compared in a tidal creek (Estero Pargo) bordered by mangroves and open waters of Terminos Lagoon, Mexico. Comparisions were made during a 17-month period in 1990-91 that spanned dry, rainy, and storm or 'Norte' seasons. Annual net primary productivity was 478 g C m −2 yr −1 in the lagoon and 285 g C m −2 yr −1 in the tidal creek. In some months, there were significant differences in primary production between the two sites. In both areas, the highest productivity occurred in summer at the start of the rainy season (June 1991), and the lowest production occurred during the dry season from February to May. Aquatic primary production was lower during the dry season of 1991 in comparison to 1990, possibly related to unusually low precipitation during 1991. Seasonal changes in water column productivity were correlated to variations in light and precipitation. The effect of runoff from mangrove forests was assessed by serial additions of surface water from a fringe forest to bottle incubations of lagoon water. Small additions of mangrove water stimulated primary production in lagoon waters during all seasons. The net productivity was extremely sensitive to aliquot volume; small amounts (0.3 and 1.7% of total volume) were stimulatory, increasing rates by > 50% in 7 of 12 experiments. The greatest effect occurred in September, 1990, when productivity tripled after an amendment with 1 ml (0.3% by volume) of mangrove water. Additions greater than 3% of total volume generally led to reduction in net productivity probably due to the inhibitory effect of humic substances. In many tropical systems, tidal exchange of estuarine waters with mangrove forests is likely to be important to enhancing water column productivity by exporting organic nutrients and other growth-enhancing substances to the estuary.
Biogeochemistry, 1999
Published data and analyses from temperate and tropical aquatic systems are used to summarize kno... more Published data and analyses from temperate and tropical aquatic systems are used to summarize knowledge about the potential impact of land-use alteration on the nitrogen biogeochemistry of tropical aquatic ecosystems, identify important patterns and recommend key needs for research. The tropical N-cycle is traced from pre-disturbance conditions through the phases of disturbance, highlighting major differences between tropical and temperate systems that might influence development strategies in the tropics. Analyses suggest that tropical freshwaters are more frequently N-limited than temperate zones, while tropical marine systems may show more frequent P limitation. These analyses indicate that disturbances to pristine tropical lands will lead to greatly increased primary production in freshwaters and large changes in tropical freshwater communities. Increased freshwater nutrient flux will also lead to an expansion of the high production, N-and light-limited zones around river deltas, a switch from P-to N-limitation in calcareous marine systems, with large changes in the community composition of fragile mangrove and reef systems. Key information gaps are highlighted, including data on mechanisms of nutrient transport and atmospheric deposition in the tropics, nutrient and material retention capacities of tropical impoundments, and N/P coupling and stoichiometric impacts of nutrient supplies on tropical aquatic communities. The current base of biogeochemical data suggests that alterations in the N-cycle will have greater impacts on tropical aquatic ecosystems than those already observed in the temperate zone.
Estuaries and Coasts, 2011
Salinity, water temperature, and chlorophyll a (chl-a) biomass were used as performance measures ... more Salinity, water temperature, and chlorophyll a (chl-a) biomass were used as performance measures in the period 1999-2001 to evaluate the effect of a hydrological rehabilitation project in the Ciénaga Grande de Santa Marta (CGSM)-Pajarales lagoon complex, Colombia where freshwater diversions were initiated in 1995 and completed in 1998. The objective of this study was to evaluate how diversions of freshwater into previously hypersaline (>80) environments changed the spatial and temporal distribution of environmental characteristics. Following the diversion, 19 surveys and transects using a flow-through system were surveyed in the CGSM-Pajarales complex to continuously measure selected water quality parameters. Geostatistical analysis indicates that hydrology and salinity regimes and water circulation patterns in the CGSM lagoon are largely controlled by freshwater discharge from the Fundacion, Aracataca, and Sevilla Rivers. Residence times in the CGSM lagoon were similar before (15.5±3.8 days) and E. Barry Moser is deceased.
Innovation in Aging, Jun 30, 2017
The Activities-specific Balance Confidence scale (ABC-6) is advantageous in busy clinical or rese... more The Activities-specific Balance Confidence scale (ABC-6) is advantageous in busy clinical or research settings as it can be administered in significantly less time than the original 16-item ABC scale (ABC-16). The purpose of this study was to examine the convergent, discriminant and concurrent validity of the ABC-6 in older adults with diabetes mellitus (DM) with and without diagnosed diabetic peripheral neuropathy (DPN). Thirty older adults (aged ≥65) were age-and sex-matched in 3-groups: 10 with DM (DM-group), 10 with diagnosed DPN (DPN-group), and 10 without DM (noDMgroup). Balance confidence was quantified with the ABC-16 which includes the six items of the ABC-6. Potential correlates were evaluated in physical and psychological domains. Our results indicated the ABC-6 and ABC-16 balance confidence scores were strongly correlated (r=0.969, p<0.001; convergent validity). The ABC-6 revealed significant differences in balance confidence between the noDM-and DM-groups (p<0.001; discriminant validity) whereas the ABC-16 did not (p>0.05). The ABC-6 was moderately but significantly correlated with physical activity level (r=0.528, p=0.017), mobility (r=-0.520, p=0.027), balance (r=0.633, p=0.003) and depressive symptoms (r=-0.515, p=0.020) in the DM study-groups (concurrent validity). In conclusion, the ABC-6 and ABC-16 had excellent convergent validity and both ABC-scales had similar concurrent validity. However, the ABC-6 was more sensitive to detect subtle differences in balance confidence in older adults with diabetes without diagnosed DPN than the ABC-16. Overall the ABC-6 is a valid assessment tool that may provide a means for early detection of balance and mobility-related declines in older adults with DM without diagnosed DPN.
Nutrient biogeochemistry associated with the early stages of soil development in deltaic floodpla... 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.
ABSTRACT: The growth, morphology, and chemical composition of Hydrilla verticillata, Myriophyllum... 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.
—The development of ecosystem management plans to restore and rehabilitate natural resources requ... 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.
Absorption, translocation, and subsequent secretion of phosphorus by Nuplm Zuteum was studied und... 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).
Twilley, R.R., Blanton, L.R., Brinson, M.M. and Davis, G.J., 1985. Biomass production and nutrien... 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.
American Fisheries …, 2008
The development of ecosystem management plans to restore and rehabilitate natural resources requi... 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.
Woody debris is abundant in hurricane-impacted forests. With a major hurricane affecting South Fl... more Woody debris is abundant in hurricane-impacted forests. With a major hurricane affecting South Florida mangroves approximately every 20 yr, carbon storage and nutrient retention may be influenced greatly by woody debris dynamics. In addition, woody debris can influence seedling regeneration in mangrove swamps by trapping propagules and enhancing seedling growth potential. Here, we report on line-intercept woody debris surveys conducted in mangrove wetlands of South Florida 9-10 yr after the passage of Hurricane Andrew. The total volume of woody debris for all sites combined was estimated at 67 m 3 /ha and varied from 13 to 181 m 3 /ha depending upon differences in forest height, proximity to the storm, and maximum estimated wind velocities. Large volumes of woody debris were found in the eyewall region of the hurricane, with a volume of 132 m 3 /ha and a projected woody debris biomass of approximately 36 t/ha. Approximately half of the woody debris biomass averaged across all sites was associated as small twigs and branches (fine woody debris), since coarse woody debris >7.5 cm felled during Hurricane Andrew was fairly well decomposed. Much of the small debris is likely to be associated with post-hurricane forest dynamics. Hurricanes are responsible for large amounts of damage to mangrove ecosystems, and components of associated downed wood may provide a relative index of disturbance for mangrove forests. Here, we suggest that a fine:coarse woody debris ratio ≤0.5 is suggestive of a recent disturbance in mangrove wetlands, although additional research is needed to corroborate such findings.
International Journal of Forestry Research, 2013
Rhizophora mangle and Laguncularia racemosa cooccur along many intertidal floodplains in the Neot... more Rhizophora mangle and Laguncularia racemosa cooccur along many intertidal floodplains in the Neotropics. Their patterns of dominance shift along various gradients, coincident with salinity, soil fertility, and tidal flooding. We used leaf gas exchange metrics to investigate the strategies of these two species in mixed culture to simulate competition under different salinity concentrations and hydroperiods. Semidiurnal tidal and permanent flooding hydroperiods at two constant salinity regimes (10 g L −1 and 40 g L −1 ) were simulated over 10 months. Assimilation ( ), stomatal conductance ( ), intercellular CO 2 concentration ( ), instantaneous photosynthetic water use efficiency (PWUE), and photosynthetic nitrogen use efficiency (PNUE) were determined at the leaf level for both species over two time periods. Rhizophora mangle had significantly higher PWUE than did L. racemosa seedlings at low salinities; however, L. racemosa had higher PNUE and and, accordingly, had greater intercellular CO 2 (calculated) during measurements. Both species maintained similar capacities for A at 10 and 40 g L −1 salinity and during both permanent and tidal hydroperiod treatments. Hydroperiod alone had no detectable effect on leaf gas exchange. However, PWUE increased and PNUE decreased for both species at 40 g L −1 salinity compared to 10 g L −1 . At 40 g L −1 salinity, PNUE was higher for L. racemosa than R. mangle with tidal flooding. These treatments indicated that salinity influences gas exchange efficiency, might affect how gases are apportioned intercellularly, and accentuates different strategies for distributing leaf nitrogen to photosynthesis for these two species while growing competitively.
Restoration of river deltas involves diverting sediment and water from major channels into adjoin... 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.
Biogeochemistry, 1999
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.
Biogeochemistry, 1999
We discuss the mechanisms leading to nutrient limitation in tropical marine systems, with particu... 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.
Biogeochemistry, 1999
We discuss the mechanisms leading to nutrient limitation in tropical marine systems, with particu... 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.
Hydrobiologia, 1998
Seasonal and spatial patterns of aquatic primary production were compared in a tidal creek (Ester... more Seasonal and spatial patterns of aquatic primary production were compared in a tidal creek (Estero Pargo) bordered by mangroves and open waters of Terminos Lagoon, Mexico. Comparisions were made during a 17-month period in 1990-91 that spanned dry, rainy, and storm or 'Norte' seasons. Annual net primary productivity was 478 g C m −2 yr −1 in the lagoon and 285 g C m −2 yr −1 in the tidal creek. In some months, there were significant differences in primary production between the two sites. In both areas, the highest productivity occurred in summer at the start of the rainy season (June 1991), and the lowest production occurred during the dry season from February to May. Aquatic primary production was lower during the dry season of 1991 in comparison to 1990, possibly related to unusually low precipitation during 1991. Seasonal changes in water column productivity were correlated to variations in light and precipitation. The effect of runoff from mangrove forests was assessed by serial additions of surface water from a fringe forest to bottle incubations of lagoon water. Small additions of mangrove water stimulated primary production in lagoon waters during all seasons. The net productivity was extremely sensitive to aliquot volume; small amounts (0.3 and 1.7% of total volume) were stimulatory, increasing rates by > 50% in 7 of 12 experiments. The greatest effect occurred in September, 1990, when productivity tripled after an amendment with 1 ml (0.3% by volume) of mangrove water. Additions greater than 3% of total volume generally led to reduction in net productivity probably due to the inhibitory effect of humic substances. In many tropical systems, tidal exchange of estuarine waters with mangrove forests is likely to be important to enhancing water column productivity by exporting organic nutrients and other growth-enhancing substances to the estuary.
Biogeochemistry, 1999
Published data and analyses from temperate and tropical aquatic systems are used to summarize kno... more Published data and analyses from temperate and tropical aquatic systems are used to summarize knowledge about the potential impact of land-use alteration on the nitrogen biogeochemistry of tropical aquatic ecosystems, identify important patterns and recommend key needs for research. The tropical N-cycle is traced from pre-disturbance conditions through the phases of disturbance, highlighting major differences between tropical and temperate systems that might influence development strategies in the tropics. Analyses suggest that tropical freshwaters are more frequently N-limited than temperate zones, while tropical marine systems may show more frequent P limitation. These analyses indicate that disturbances to pristine tropical lands will lead to greatly increased primary production in freshwaters and large changes in tropical freshwater communities. Increased freshwater nutrient flux will also lead to an expansion of the high production, N-and light-limited zones around river deltas, a switch from P-to N-limitation in calcareous marine systems, with large changes in the community composition of fragile mangrove and reef systems. Key information gaps are highlighted, including data on mechanisms of nutrient transport and atmospheric deposition in the tropics, nutrient and material retention capacities of tropical impoundments, and N/P coupling and stoichiometric impacts of nutrient supplies on tropical aquatic communities. The current base of biogeochemical data suggests that alterations in the N-cycle will have greater impacts on tropical aquatic ecosystems than those already observed in the temperate zone.
Estuaries and Coasts, 2011
Salinity, water temperature, and chlorophyll a (chl-a) biomass were used as performance measures ... more Salinity, water temperature, and chlorophyll a (chl-a) biomass were used as performance measures in the period 1999-2001 to evaluate the effect of a hydrological rehabilitation project in the Ciénaga Grande de Santa Marta (CGSM)-Pajarales lagoon complex, Colombia where freshwater diversions were initiated in 1995 and completed in 1998. The objective of this study was to evaluate how diversions of freshwater into previously hypersaline (>80) environments changed the spatial and temporal distribution of environmental characteristics. Following the diversion, 19 surveys and transects using a flow-through system were surveyed in the CGSM-Pajarales complex to continuously measure selected water quality parameters. Geostatistical analysis indicates that hydrology and salinity regimes and water circulation patterns in the CGSM lagoon are largely controlled by freshwater discharge from the Fundacion, Aracataca, and Sevilla Rivers. Residence times in the CGSM lagoon were similar before (15.5±3.8 days) and E. Barry Moser is deceased.