Rajan Tripathee - Academia.edu (original) (raw)
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Papers by Rajan Tripathee
Environmental Monitoring and Assessment, 2018
Biogeochemical processes in wetland soils are complex and are driven by a microbiological communi... more Biogeochemical processes in wetland soils are complex and are driven by a microbiological community that competes for resources and affects the soil chemistry. Depending on the availability of various electron acceptors, the high carbon input to wetland soils can make them important sources of methane production and emissions. There are two s i g n i f i c a n t p a t h w a y s f o r m e t h a n o g e n e s i s : acetoclastic and hydrogenotrophic methanogenesis. The hydrogenotrophic pathway is dependent on the availability of dissolved hydrogen gas (H 2), and there is significant competition for available H 2. This study presents simultaneous measurements of dissolved methane and H 2 over a 2-year period at three tidal marshes in the New Jersey Meadowlands. Methane reservoirs show a significant correlation with dissolved organic carbon, temperature, and methane emissions, whereas the H 2 concentrations measured with dialysis samplers do not show significant relationships with these field variables. Data presented in this study show that increased dissolved H 2 reservoirs in wetland soils correlate with decreased methane reservoirs, which is consistent with studies that have shown that elevated levels of H 2 inhibit methane production by inhibiting propionate fermentation, resulting in less acetate production and hence decreasing the contribution of acetoclastic methanogenesis to the overall production of methane.
Journal of Geophysical Research: Biogeosciences, 2014
Net ecosystem exchange (NEE) of tidal brackish wetlands in urban areas is largely unknown, albeit... more Net ecosystem exchange (NEE) of tidal brackish wetlands in urban areas is largely unknown, albeit it is an important ecosystem service. High carbon dioxide (CO 2) uptake of estuaries can potentially be achieved by creating conditions that foster CO 2 uptake and sequestration. Thus, this study sought to assess NEE in a mesohaline tidal urban wetland that has been restored and determine the biophysical drivers of NEE in order to investigate uptake strength and drivers thereof. Beginning in 2009, NEE was measured using the eddy covariance technique in a restored urban estuarine wetland. Maximum NEE rates observed were À30 μmol m À2 s À1 under high light conditions in the summer. Monthly mean NEE showed this ecosystem to be a CO 2 source in the winter, but a CO 2 sink in summer. Conditional Granger causality showed the influence of net radiation on half daily to biweekly timescales on NEE and the influence of water level at half daily time scales. The overall productivity of this wetland is within the expected range of tidal brackish marshes and it was a sink for atmospheric CO 2 in two out of the 3 years of this study and had a continued increase over the study period. Potential and actual carbon dioxide (CO 2) uptake strength, especially in urban areas and coastal wetlands remains unclear [Bridgham et al., 2006; Grimm et al., 2008; Pataki et al., 2006] as well as how CO 2 exchange will be affected by global environmental change [Bridgham et al., 2006]. In this context, management of wetlands that are known to be productive [Mitsch and Gosselink, 2007] could increase carbon (C) sequestration and potentially lead to C offset credits rendered [Hansen, 2009], and could also ameliorate sea level rise [Kirwan and Guntenspergen, 2010; Kirwan et al., 2010]. However, there are still significant knowledge gaps about the C sequestration potential of coastal wetlands and the effects of tidal salt marsh management on these C fluxes [Heilman et al., 1999; Zedler and Kercher, 2005]. In and around urban areas, previous land uses, current land management, air pollution, and the biophysical environment play an important role in determining the structure and function of wetland ecosystems and their respective C uptake strengths. Likewise, these anthropogenic factors may determine whether the wetlands will expand, contract, or remain stable [Keith et al., 2010]. Additional challenges include wastewater effluents [Hempel et al., 2008], elevated water temperatures from power plant water discharge [
Wetlands, 2014
Measurements of aboveground and belowground biomass allocations are important for characterizatio... more Measurements of aboveground and belowground biomass allocations are important for characterization of structure and function in marsh ecosystems as various processes such as carbon sequestration, gas transport, nutrient cycling, and ecosystem resilience are affected by these allocations. We measured aboveground and belowground biomass, root and rhizome characteristics, leaf area index (LAI), and carbon to nitrogen (C/N) ratio of various tissues of four tidal marsh species in New Jersey by harvesting biomass during peak growing season. The aboveground biomasses for Spartina patens, S. alterniflora, Phragmites australis, and Distichlis spicata were 2.3, 2.2, 1.7 and 1.2 kg m −2 , respectively. The ratio of belowground to aboveground biomass for S. alterniflora and D. spicata, harvested from a recently restored wetland were lower than in previous studies. LAI for S. alterniflora, D. spicata, P. australis, and S. patens were 8.4, 6.8, 4.8 and 3.7 m 2 m −2 , respectively. Diameter of rhizome and root, number of primary roots per node, root surface area to volume ratio, and C/N of various tissues varied with species. The measured above-and belowground biometric traits are crucial for a better understanding of carbon dynamics, and modeling greenhouse gas transport in marsh ecosystems.
In this study, we have been investigating an urban brownfield at Liberty State Park that has been... more In this study, we have been investigating an urban brownfield at Liberty State Park that has been abandoned approximately for 40 years. Natural colonization has taken place that allowed a pioneer forest to grow with primarily Betula populifera and Populus spec. Despite soil metal contamination this urban forest exhibits moderate annual productivity and serves as a carbon sink. Diameters at breast height (DBH, 1.35 m above ground) of all trees in a study plot were measured. Aboveground biomass equations were determined for both species through destructive sampling. Aboveground net primary production was about 770 gC m-2 a-1 in 2009. Canopy net assimilation (AnC) was modeled with the canopy conductance constrained assimilation (4CA) model using measured sapflux derived conductance and photosynthetic parameters measured with a LICOR 6400. Annual AnC in 2009 was approximately 1500 gC m-2 a-1 thus with a partitioning of biomass and respiration in the same range of most natural forest wit...
Journal of Geophysical Research: Biogeosciences, 2013
Estuarine and coastal wetlands exhibit high rates of carbon burial and storage in anaerobic sedim... more Estuarine and coastal wetlands exhibit high rates of carbon burial and storage in anaerobic sediments, but the extent to which carbon sequestration is offset by methane (CH 4) emissions from these ecosystems remains unclear. In this study we combine measurements of sediment-air CH 4 fluxes with monitoring of belowground CH 4 pools in a New Jersey tidal marsh in order to clarify mechanistic links between environmental drivers, subsurface dynamics, and atmospheric emissions. Measurements were conducted in an unvegetated mud flat and adjacent low marsh vegetated with Spartina alterniflora and Phragmites australis. Pore water measurements throughout the year revealed long-term CH 4 storage in mud flat sediments, leading to a seasonal lag in emissions that extended into winter months. CH 4 reservoirs and fluxes in vegetated sediments were well described by an empirical temperature-response model, while poor model agreement in unvegetated sediments was attributed to decouplings between production and flux due to storage processes. This study highlights the need to incorporate sediment gas exchange rates and pathways into biogeochemical process models.
Environmental Monitoring and Assessment, 2018
Biogeochemical processes in wetland soils are complex and are driven by a microbiological communi... more Biogeochemical processes in wetland soils are complex and are driven by a microbiological community that competes for resources and affects the soil chemistry. Depending on the availability of various electron acceptors, the high carbon input to wetland soils can make them important sources of methane production and emissions. There are two s i g n i f i c a n t p a t h w a y s f o r m e t h a n o g e n e s i s : acetoclastic and hydrogenotrophic methanogenesis. The hydrogenotrophic pathway is dependent on the availability of dissolved hydrogen gas (H 2), and there is significant competition for available H 2. This study presents simultaneous measurements of dissolved methane and H 2 over a 2-year period at three tidal marshes in the New Jersey Meadowlands. Methane reservoirs show a significant correlation with dissolved organic carbon, temperature, and methane emissions, whereas the H 2 concentrations measured with dialysis samplers do not show significant relationships with these field variables. Data presented in this study show that increased dissolved H 2 reservoirs in wetland soils correlate with decreased methane reservoirs, which is consistent with studies that have shown that elevated levels of H 2 inhibit methane production by inhibiting propionate fermentation, resulting in less acetate production and hence decreasing the contribution of acetoclastic methanogenesis to the overall production of methane.
Journal of Geophysical Research: Biogeosciences, 2014
Net ecosystem exchange (NEE) of tidal brackish wetlands in urban areas is largely unknown, albeit... more Net ecosystem exchange (NEE) of tidal brackish wetlands in urban areas is largely unknown, albeit it is an important ecosystem service. High carbon dioxide (CO 2) uptake of estuaries can potentially be achieved by creating conditions that foster CO 2 uptake and sequestration. Thus, this study sought to assess NEE in a mesohaline tidal urban wetland that has been restored and determine the biophysical drivers of NEE in order to investigate uptake strength and drivers thereof. Beginning in 2009, NEE was measured using the eddy covariance technique in a restored urban estuarine wetland. Maximum NEE rates observed were À30 μmol m À2 s À1 under high light conditions in the summer. Monthly mean NEE showed this ecosystem to be a CO 2 source in the winter, but a CO 2 sink in summer. Conditional Granger causality showed the influence of net radiation on half daily to biweekly timescales on NEE and the influence of water level at half daily time scales. The overall productivity of this wetland is within the expected range of tidal brackish marshes and it was a sink for atmospheric CO 2 in two out of the 3 years of this study and had a continued increase over the study period. Potential and actual carbon dioxide (CO 2) uptake strength, especially in urban areas and coastal wetlands remains unclear [Bridgham et al., 2006; Grimm et al., 2008; Pataki et al., 2006] as well as how CO 2 exchange will be affected by global environmental change [Bridgham et al., 2006]. In this context, management of wetlands that are known to be productive [Mitsch and Gosselink, 2007] could increase carbon (C) sequestration and potentially lead to C offset credits rendered [Hansen, 2009], and could also ameliorate sea level rise [Kirwan and Guntenspergen, 2010; Kirwan et al., 2010]. However, there are still significant knowledge gaps about the C sequestration potential of coastal wetlands and the effects of tidal salt marsh management on these C fluxes [Heilman et al., 1999; Zedler and Kercher, 2005]. In and around urban areas, previous land uses, current land management, air pollution, and the biophysical environment play an important role in determining the structure and function of wetland ecosystems and their respective C uptake strengths. Likewise, these anthropogenic factors may determine whether the wetlands will expand, contract, or remain stable [Keith et al., 2010]. Additional challenges include wastewater effluents [Hempel et al., 2008], elevated water temperatures from power plant water discharge [
Wetlands, 2014
Measurements of aboveground and belowground biomass allocations are important for characterizatio... more Measurements of aboveground and belowground biomass allocations are important for characterization of structure and function in marsh ecosystems as various processes such as carbon sequestration, gas transport, nutrient cycling, and ecosystem resilience are affected by these allocations. We measured aboveground and belowground biomass, root and rhizome characteristics, leaf area index (LAI), and carbon to nitrogen (C/N) ratio of various tissues of four tidal marsh species in New Jersey by harvesting biomass during peak growing season. The aboveground biomasses for Spartina patens, S. alterniflora, Phragmites australis, and Distichlis spicata were 2.3, 2.2, 1.7 and 1.2 kg m −2 , respectively. The ratio of belowground to aboveground biomass for S. alterniflora and D. spicata, harvested from a recently restored wetland were lower than in previous studies. LAI for S. alterniflora, D. spicata, P. australis, and S. patens were 8.4, 6.8, 4.8 and 3.7 m 2 m −2 , respectively. Diameter of rhizome and root, number of primary roots per node, root surface area to volume ratio, and C/N of various tissues varied with species. The measured above-and belowground biometric traits are crucial for a better understanding of carbon dynamics, and modeling greenhouse gas transport in marsh ecosystems.
In this study, we have been investigating an urban brownfield at Liberty State Park that has been... more In this study, we have been investigating an urban brownfield at Liberty State Park that has been abandoned approximately for 40 years. Natural colonization has taken place that allowed a pioneer forest to grow with primarily Betula populifera and Populus spec. Despite soil metal contamination this urban forest exhibits moderate annual productivity and serves as a carbon sink. Diameters at breast height (DBH, 1.35 m above ground) of all trees in a study plot were measured. Aboveground biomass equations were determined for both species through destructive sampling. Aboveground net primary production was about 770 gC m-2 a-1 in 2009. Canopy net assimilation (AnC) was modeled with the canopy conductance constrained assimilation (4CA) model using measured sapflux derived conductance and photosynthetic parameters measured with a LICOR 6400. Annual AnC in 2009 was approximately 1500 gC m-2 a-1 thus with a partitioning of biomass and respiration in the same range of most natural forest wit...
Journal of Geophysical Research: Biogeosciences, 2013
Estuarine and coastal wetlands exhibit high rates of carbon burial and storage in anaerobic sedim... more Estuarine and coastal wetlands exhibit high rates of carbon burial and storage in anaerobic sediments, but the extent to which carbon sequestration is offset by methane (CH 4) emissions from these ecosystems remains unclear. In this study we combine measurements of sediment-air CH 4 fluxes with monitoring of belowground CH 4 pools in a New Jersey tidal marsh in order to clarify mechanistic links between environmental drivers, subsurface dynamics, and atmospheric emissions. Measurements were conducted in an unvegetated mud flat and adjacent low marsh vegetated with Spartina alterniflora and Phragmites australis. Pore water measurements throughout the year revealed long-term CH 4 storage in mud flat sediments, leading to a seasonal lag in emissions that extended into winter months. CH 4 reservoirs and fluxes in vegetated sediments were well described by an empirical temperature-response model, while poor model agreement in unvegetated sediments was attributed to decouplings between production and flux due to storage processes. This study highlights the need to incorporate sediment gas exchange rates and pathways into biogeochemical process models.