Behzad Mortazavi

University of Alabama | UA · Department of Biological Sciences

Burrowing animals can profoundly affect the biological structure and ecosystem functions of their environments. For instance, burrowing crabs increase sediment deposition and facilitate sediment homogenization and turnover, with potential impacts to sediment biogeochemistry. However, the relative importance of burrowing crabs on sediment dynamics c...

Coastal salt marshes provide valuable ecosystem services but are subjected to multiple concomitant stressors that may impact their ability to provide those services. Global climate change has led to the poleward expansion of mangroves into salt marshes on each continent where mangroves and marshes co-occur. In the northern Gulf of Mexico, warming w...

Coastal marshes provide valuable ecosystem services including the removal of excess nitrogen (N) prior to reaching coastal waters. Crude oil contamination can disrupt N cycling processes, and while the impacts of crude oil on marsh structure and function are well studied, less is known about the effects of different oil components. The objective of...

Widespread degradation and destruction of coastal wetlands over the last century have spurred on the practice of creating salt marshes to mitigate losses of wetland area and ecosystem function. Constructed marshes can quickly recover plant biomass, but biogeochemical functions, such as the recovery of nitrogen removal capacity through denitrificati...

Quantifying and characterizing groundwater flow and discharge from barrier islands to coastal waters is crucial for assessing freshwater resources and contaminant transport to the ocean. In this study, we examined the groundwater hydrological response, discharge, and associated nutrient fluxes in Dauphin Island, a barrier island located in the nort...

Human-made stormwater control systems are biogeochemical hotspots, but construction and management may result in homogenization of their ecosystem structure. Roadside ditches are a ubiquitous part of the landscape, yet few studies have quantified their biogeochemical potential. We conducted a study to determine (a) nitrate (NO3⁻) removal potential...

Human activities have led to 1–2% of coastal wetlands lost per year globally, with subsequent losses in ecosystem services such as nutrient filtering and carbon sequestration. Wetland construction is used to mitigate losses of marsh cover and services resulting from human impacts in coastal areas. Though marsh structure can recover relatively quick...

Coastal salt marshes are some of the most productive ecosystems on Earth, providing numerous services such as soil carbon storage, flood protection and nutrient filtering, several of which are mediated by the sediment microbiome associated with marsh vegetation. Here, nutrient filtering (nitrate removal through denitrification) was examined by dete...

Wetlands are endangered ecosystems that provide vital habitats for flora and fauna worldwide. They serve as water and carbon storage units regulating the global climate and water cycle, and act as natural barriers against storm-surge among other benefits. Long-term analyses are crucial to identify wetland cover change and support wetland protection...

Human activities have decreased global salt marsh surface area with a subsequent loss in the ecosystem functions they provide. The creation of marshes in terrestrial systems has been used to mitigate this loss in marsh cover. Although these constructed marshes may rapidly recover ecosystem structure, biogeochemical processes may be slow to recover....

Coastal salt marshes are some of the most productive ecosystems on Earth, providing numerous services such as soil carbon storage, flood protection and nutrient filtering, several of which are mediated by the sediment microbiome associated with marsh vegetation. Here, nutrient filtering (nitrate removal through denitrification) was examined by dete...

Salt marsh biogeochemical processes are regulated by ecosystem structure (e.g. plant community composition). However, plant-specific responses to stressors such as elevated nutrient inputs can have differing impacts on nitrogen (N) removal and carbon (C) sequestration. We conducted a field manipulation to investigate the impact of elevated nutrient...

Functional traits define an organism in terms of how the organism interacts with its environment and determine the influence the organism has on dynamic ecosystem processes, such as biogeochemical nutrient cycling. Freshwater mussels (Bivalvia: Unionidae) form hotspots of biogeochemical activity in benthic environments by alleviating nutrient limit...

Benthic macrofauna play important roles in coastal ecosystems through their impact on nutrient cycling and by serving as an mportant trophic link. This study investigated the influence of environmental stressors on macrofaunal community abundance, biomass and diversity and evaluated impacts of those benthic organisms on nutrient fluxes and denitrif...

Anthropogenic pressures, such as diking, construction of dams, and oil spills negatively impact coastal marshes creating growing pressure to preserve and to restore salt marshes due to their critical role in permanently removing nitrate runoff through denitrification as well as other ecosystem services they provide. This study determined denitrific...

Marine oil spills are catastrophic events that cause massive damage to ecosystems at all trophic levels. While most of the research has focused on carbon‐degrading microorganisms, the potential impacts of hydrocarbons on microbes responsible for nitrification have received far less attention. Nitrifiers are sensitive to hydrocarbon toxicity: ammoni...

The eutrophication of estuaries results from increasing anthropogenic nutrient inputs to coastal waters. Ecosystem recovery from eutrophication is partly dependent on the ability of a system to assimilate or remove nutrients, and denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are important pathways for nitrogen (N) removal o...

Salt marshes play a key role in removing excess anthropogenic nitrogen (N) loads to nearshore marine ecosystems through sediment microbial processes such as denitrification. However, in the Gulf of Mexico the loss of marsh vegetation due to human-driven disturbances such as sea level rise and oil spills can potentially reduce marsh capacity for N r...

In this study the impact of hydrocarbons on nitrogen cycling in intertidal sediments from a barrier island in the north central Gulf of Mexico was investigated. Initial total petroleum hydrocarbon (TPH) concentrations of the sediments averaged 49 ± 27 mg kg−1 in June and 75 ± 48 mg kg−1 in November. Following the addition of crude oil, TPH concentr...

Altered nutrient cycles and consumer populations are among the top anthropogenic influences on ecosystems. However, studies on the simultaneous impacts of human-driven environmental alterations on ecosystem functions, and the overall change in system multifunctionality are scarce. We used estuarine tidal flats to study the effects of changes in her...

Alabama Center for Ecological Resilience (ACER) GRIIDC Metadata

Premise of the study: The cold season in the Arctic extends over 8 to 9 mo, yet little is known about vascular plant physiology during this period. Evergreen species photosynthesize under the snow, implying that they are exchanging water with the atmosphere. However, liquid water available for plant uptake may be limited at this time. The study ob...

We investigated different types of biostimulation practices to enhance degradation of weathered conventional diesel fuel in sandy beach sediments from coastal Alabama. Biodegradation rates were measured following the addition of either inorganic nutrients, or organic matter derived from either plant material (Spartina alterniflora) or fish tissue (...

A great effort has been made to identify factors that regulate community structure and their consequences on ecosystem functions. Nutrients and herbivores are now well known drivers of plant species abundances and assemblages, and their effects on ecosystem functions through changes in biodiversity have been recently explored mostly on artificial p...

To quantify the effect of oysters on sediment N cycling, oyster-free cages and cages with adult or juvenile oysters [Crassostrea virginica (Gmelin, 1791)] were suspended above the sediments at two sites in Mobile Bay, Alabama, located in the northern Gulf of Mexico. While hydrogen sulfide (HS–) was below detection limits at Site 2, HS– exceeded 500...

Sediments have an important role in nutrient dynamics by providing sites for denitrification, which, in conjunction with nitrogen (N) fixation and other processes such as dissimilatory nitrate reduction to ammonium (DNRA), can regulate ecosystem N availability. Little Lagoon, Alabama, USA, is affected by anthropogenic perturbations and has N inputs...

Carbon gas fluxes in tidal marshes vary spatially and temporally because of vegetation cover, subsurface biogeochemical processes, and environmental forcing. The objective of this study was to examine how ecosystem carbon gas exchange changes along an estuarine salinity gradient. We measured carbon dioxide (CO2) and methane (CH4) gas fluxes from th...

ABSTRACT: Benthic processes in estuarine systems can alleviate nutrient over-enrichment by removing nitrogen (N) via denitrification, or further intensify eutrophication by supplying N back to the water column. The main objectives of this study were to (1) examine the magnitude and seasonality of benthic fluxes and denitrification, and (2) determin...

This study investigated potential nitrogen fixation, net nitrification, and denitrification responses to short-term crude oil exposure that simulated oil exposure in Juncus roemerianus salt marsh sediments previously impacted following the Deepwater Horizon accident. Temperature as well as crude oil amount and type affected the nitrogen cycling rat...

Ecological theory argues that the controls over ecosystem processes are structured hierarchically, with broader-scale drivers acting as constraints over the interactions and dynamics at nested levels of organization. In river ecosystems, these interactions may arise from broadscale variation in channel form that directly shapes benthic habitat stru...

Methane is an effective greenhouse gas but has a short residence time in the atmosphere, and therefore, reductions in emissions can alleviate its greenhouse gas warming effect within a decadal time frame. Continuous and high temporal resolution measurements of methane concentrations and carbon isotopic ratios (δ(13)CH4) can inform on mechanisms of...

Estuaries located in the northern Gulf of Mexico are expected to experience reduced river discharge due to increasing demand for freshwater and predicted periods of declining precipitation. Changes in freshwater and nutrient input might impact estuarine higher trophic level productivity through changes in phytoplankton quantity and quality. Phytopl...

Deciduous plants in the Arctic are increasing in abundance due to warming trends, and this increase will likely contribute to changes in regional carbon dynamics. One of the dominant deciduous-shrub genera, Salix, is highly susceptible to leaf galls, but the influence of arthropod herbivores on plant-level carbon uptake in the Arctic remains poorly...

Arctic tundra plant communities are subject to a short growing season that is the primary period in which carbon is sequestered for growth and survival. This period is often characterized by 24-h photoperiods for several months a year. To compensate for the short growing season tundra plants may extend their carbon uptake capacity on a diurnal basi...

Coastal salt marshes are highly sensitive wetland ecosystems that can sustain long-term impacts from anthropogenic events such as oil spills. In this study, we examined the microbial communities of a Gulf of Mexico coastal salt marsh during and after the influx of petroleum hydrocarbons following the Deepwater Horizon oil spill. Total hydrocarbon c...

The rates of crude oil degradation by the extant microorganisms in intertidal sediments from a northern Gulf of Mexico beach were determined. The enhancement in crude oil degradation by amending the microbial communities with marine organic matter was also examined. Replicate mesocosm treatments consisted of: (i) controls (intertidal sand), (ii) sa...

Forest ecosystems experience various disturbances that can affect belowground carbon cycling to different degrees. Here, we investigate if successive annual foliar scorching events will result in a large and rapid decline in soil CO2 efflux, similar to that observed in girdling studies. Using the fire-adapted longleaf pine (Pinus palustris Mill.) t...

Background / Purpose: The purpose of this project was to determine the indirect N removal (i.e. denitrification) from an estuary where oyster restoration projects were implemented. Main conclusion: Sediment redox conditions (hydrogen sulfide) are the main control on whether or not denitrification can occur, regardless of oyster treatment.

Background/Question/Methods Carbon fluxes in tidal marshes vary spatially and temporally due to vegetation cover, subsurface biogeochemical processes, and tidal inundation. Methane (CH4) emissions, in particular, have been shown to vary widely with changing salinity and vegetative species composition. The objective of this study is to use measure...

Background/Question/Methods The increase in abundance of arctic deciduous plants such as dwarf birch (Betula nana) and willows (Salix sp.) is coincident with warming trends and will likely contribute to changes in regional carbon dynamics. However the influence of herbivores, particularly specialist herbivores such as gall-inducing arthropods, on...

Background/Question/Methods The increasing temperatures in the Arctic are contributing to changes in regional carbon dynamics. This increase in temperature will potentially influence the allocation of newly assimilated photosynthates into metabolic pools (sugars, lipids) by the vegetation. The study was conducted in arctic tundra near Toolik Lake,...

Background/Question/Methods Saltwater marsh carbon dynamics are affected by topography, geomorphology, hydro-edaphic conditions, vegetation composition, and other biotic and abiotic variables. Our primary objective is to examine ecosystem carbon dynamics in Spartina alterniflora (C4) and Juncus roemerianus (C3) dominated marshes along the Mississ...

Functional gene normalized signal intensities detected by GeoChip. (XLSX)

Total number of bacterial OTUs detected by PhyloChip in Inlet and Marsh sediments in all phyla. (PDF)

Total bacterial OTUs detected by PhyloChip for all samples. Positive fraction and normalized fluorescence intensity values are reported. (XLSX)

Following the Deepwater Horizon explosion and crude oil contamination of a marsh ecosystem in AL in June 2010, hydrocarbon-degrader microbial abundances of aerobic alkane, total hydrocarbon, and polycyclic aromatic hydrocarbon (PAH) degraders were enumerated seasonally. Surface sediment samples were collected in October and December of 2010 and in...

We measured the delta C-13 of assimilated carbon (foliage organic matter (delta C-OM), soluble carbohydrates (delta C-SC), and waxes (delta C-W)) and respiratory carbon (foliage (delta C-FR), soil (delta C-SR) and ecosystem (CO2)-C-13 (delta C-ER)) for two years at adjacent ecosystems in the southeastern U.S.: a regenerated 32 m tall mature Pinus p...

In the present study, microbial community responses to exposure to unweathered Macondo Well crude oil and conventional diesel in a sandy beach environment were determined. Biodegradation was assessed in mesocosm experiments with differing fuel amounts (2,000 and 4,000 mg/kg) and with or without inorganic nutrient amendment. Carbon dioxide productio...

Benthic oxygen, dinitrogen, and nutrient fluxes (NH 4+, NO 3−, and PO 43−) were measured monthly during a 1-year period at two locations in Weeks Bay, a shallow (1.4 m) and eutrophic estuary in Alabama. Gross primary productivity (GPP), ecosystem respiration (R), and net ecosystem metabolism were determined from high-frequency dissolved oxygen meas...

Background/Question/Methods Soil CO2 efflux, the combination of belowground autotrophic and heterotrophic respiration, is the largest terrestrial source of carbon dioxide (CO2) to the atmosphere, yet the mechanistic controls of this important flux are currently under debate. Until recently, the dynamics and controls of the heterotrophic component...

We measured the 13C of assimilated carbon [foliage organic matter (deltaCOM), leaf soluble carbohydrates ((deltaCSC), and leaf waxes ((deltaCW)] and respiratory carbon [foliage (deltaCF), soil (deltaCS) and ecosystem respired CO2 (deltaCR)] over a two-year period at two sites in central Florida that are typical of Southeastern US coastal plain pine...

Background/Question/Methods Mercury (Hg) has been identified as a pollutant that poses a human health risk for people consuming contaminated seafood. The EPA has set a value of 0.1 g/kg body weight/day for safe exposure to this neurotoxin. Mercury enters the food web at the microbial level and is methylated and then biomagnified, through ingestion,...

Background/Question/Methods Theory and experimental data concerning habitat-related ecophysiological traits suggest carbon allocation strategy depends on resources availability. Species tend to shift from a conservation strategy in a resource-limited environment to a production strategy in rich environment. In high latitudes, global warming tends t...

Background/Question/Methods We examined benthic nitrogen fluxes monthly over a one year period at two locations, Mid Bay and Magnolia River, in Weeks Bay, AL NERR site. Weeks Bay is a shallow sub-estuary of Mobile Bay, with an average depth of 1.5 m, and high inputs of nitrogen (N) supported by a predominately agricultural watershed. The objectiv...

Bacterioplankton abundance and chlorophyll concentration and the factors that control them (temperature, nutrient concentrations, and rates of growth, grazing, and export) were studied in Apalachicola Bay, FL, during two summers with contrasting river discharge. A reduction in river discharge from the summer of 2003 (S03) to the summer of 2004 (S04...

Improved global estimates of terrestrial photosynthesis and respiration are critical for predicting the rate of change in atmospheric CO(2). The oxygen isotopic composition of atmospheric CO(2) can be used to estimate these fluxes because oxygen isotopic exchange between CO(2) and water creates distinct isotopic flux signatures. The enzyme carbonic...

Isotopic labelling experiments were conducted to assess relationships among (13)C of recently assimilated carbon (deltaC(A)), foliage respiration (deltaC(F)), soluble carbohydrate (deltaC(SC)), leaf waxes (deltaC(LW)) and bulk organic matter (deltaC(OM)). Slash pine, sweetgum and maize were grown under (13)C depleted CO(2) to label biomass and then...

The δ13C of slash pine foliage dark-respired CO2 (δ13CF) was measured at temperatures ranging from 6.6° to 30°C. The δ13CF was 13C-enriched initially after dark by as much as 9‰ and declined toward an asymptotic value after a few hours in the dark. Maximum enrichment in δ13CF occurred at the lowest temperatures and the decline in δ13CF toward the a...

The δ13C of pine needle CO2 evolved in darkness (δ13Cr) for slash pine trees (Pinus elliottii) was determined by placing recently collected pine needles in darkness and collecting respired CO2 over a short time period (< 15 min). δ13Cr measurements were made over several 24 h periods to test the hypothesis that significant variation in δ13Cr would...

Temporal variability in the (13)C of foliage (delta(13)C(F)), soil (delta(13)C(S)) and ecosystem (delta(13)C(R)) respired CO(2) was contrasted between a 17.2-m tall evenly aged loblolly pine forest and a 35-m tall unevenly aged mature second growth mixed broadleaf deciduous forest in North Carolina, USA, over a 2-year period. The two forests are lo...