Su R.,University of Southern Mississippi |
Kuehn K.A.,University of Southern Mississippi |
Phipps S.W.,Weeks Bay National Estuarine Research Reserve
Freshwater Biology | Year: 2015
Despite the well-known occurrence of 'standing-dead' emergent plant litter in freshwater marshes, the role of fungi in its decomposition is poorly known. Here, we quantified the growth and biomass dynamics of fungi associated with standing-dead Typha domingensis leaves, estimated the contribution of fungi to carbon flow during decomposition and assessed their contribution to nutrient (nitrogen and phosphorus) cycling. In a subtropical freshwater marsh, standing leaves of T. domingensis were sampled in August while living (green) and then monthly during leaf senescence and standing-dead decomposition for 1 year. Leaf samples were analysed for mass loss, fungal biomass (ergosterol), rates of fungal production (14C-acetate incorporation) and microbial respiration (CO2 evolution), and for litter chitin (glucosamine), carbon, N and P concentrations. Losses in T. domingensis leaf carbon (37%) occurred during senescence and standing decomposition. During this time, increases in ergosterol and chitin concentrations were observed in the standing litter, indicating the rapid colonisation of decaying Typha leaves by fungi. Estimated fungal biomass (from ergosterol) reached a maximum of 37 mg C g-1 detrital C. Over the entire study period, estimated cumulative fungal production in standing Typha litter was 39 mg C g-1 initial detrital C, indicating that 11% of leaf C was converted to fungal C. The corresponding estimate of cumulative microbial respiration was 136 mg C g-1 initial detrital C, indicating that 37% of Typha leaf litter C was mineralised by microorganisms (bacteria and fungi) during decomposition. Fungi also immobilised up to c.27% and c.55% of the total detrital N and P, respectively. Fungi play an important role in the cycling of C and nutrients in freshwater marshes, and this should be integrated into current models that describe major biogeochemical pathways. © 2015 John Wiley & Sons Ltd.
Cebrian J.,Dauphin Island Sea Laboratory |
Cebrian J.,University of South Alabama |
Stutes A.L.,Dauphin Island Sea Laboratory |
Stutes A.L.,University of South Alabama |
And 7 more authors.
Revista de Biologia Tropical | Year: 2012
The olive snail (Neritina reclivata) is ubiquitous in tropical and sub-tropical systems of the Gulf of Mexico, however its impacts on sediment microalgae have been little studied. Many coastal systems around the world are being eutrophied due to human activities, and seemingly they will continue to be eutrophied to a further extent in the future. Exploring the single and combined impacts of further nutrient enrichment and grazing by the olive snail on sediment microalgae in such eutrophic systems is an important question for our understanding and management of these systems. Here we examine the effects of short-term nutrient enrichment and grazing by the olive snail N. reclivata on sediment microalgal biomass and composition in a shallow eutrophic estuary (Weeks Bay, Alabama, USA) of the Northern Gulf of Mexico. For this, we performed a series of factorial experiments adding or not nutrients and removing or not the snail, for a total of four treatments in each experiment: ambient grazing, ambient nutrients; ambient grazing, increased nutrients; no grazing, ambient nutrients; and no grazing, increased nutrients. We did not find any significant impact of nutrient addition in any of the eight short-term (i.e. four days) experiments carried out. Impacts by the snail were minor; we only found a decrease in biomass due to snail grazing in one of the eight experiments, and no impacts on microalgal (i.e. diatom) composition. High ambient nutrient concentrations in the sediment porewater and low snail abundances on the sediment could explain these findings. Our results suggest that ephemeral, short-term nutrient pulses into eutrophic coastal systems of the Northern Gulf of Mexico, such as Weeks Bay (Alabama, USA), should not greatly affect the abundance of sediment microalgae, even though those pulses occur in well-lit areas. The results further suggest the snail N. reclivata is not a major control of sediment microalgal populations in the subtidal sedimentary areas studied. Our findings contrast with the results of past work in sediments with well-lit and nutrient poor conditions, or sediments with high densities of other snail grazers. In conjunction this and other investigations indicate that the response of sediment microalgae to nutrient enrichment and modified grazer abundance depends to a large extent on the initial levels of nutrient availability and grazing before the system is altered.
Miller M.M.,University of South Alabama |
Phipps S.W.,Weeks Bay National Estuarine Research Reserve |
Major C.S.,University of South Alabama |
Major K.M.,University of South Alabama
Estuaries and Coasts | Year: 2011
This study was designed to investigate non-point source nutrient pollution and its influences on submerged aquatic plant community structure and biological invasion in the Weeks Bay National Estuarine Research Reserve (WBNERR). A monthly vegetation survey was conducted to document plant abundance and changes in community structure; physicochemical data and water samples were collected on a bi-monthly basis to monitor environmental conditions (i.e.,pH, salinity, dissolved oxygen, light intensity, and attenuation) and water column nutrient (NO2 -/NO3 - and NH4 +) and chlorophyll a concentrations. A total of seven submerged aquatic species were identified at the WBNERR with the occurrence of only one non-native species (Hydrilla verticillata). Statistical analyses suggest that water column nitrogen concentrations along with variations in dissolved oxygen (0.6-11.5 mg L-1), light attenuation, pH (5.6-8.6), and temperature (11-33°C) play key roles in determining the aquatic plant abundance and distribution in the WBNERR. © 2011 Coastal and Estuarine Research Federation.
Canion A.,Dauphin Island Sea Laboratory |
MacIntyre H.L.,Dauphin Island Sea Laboratory |
Phipps S.,Weeks Bay National Estuarine Research Reserve
Estuarine, Coastal and Shelf Science | Year: 2013
The inputs of primary productivity models may be highly variable on short timescales (hourly to daily) in turbid estuaries, but modeling of productivity in these environments is often implemented with data collected over longer timescales. Daily, seasonal, and spatial variability in primary productivity model parameters: chlorophyll a concentration (Chla), the downwelling light attenuation coefficient (kd), and photosynthesis-irradiance response parameters (Pmchl, αChl) were characterized in Weeks Bay, a nitrogen-impacted shallow estuary in the northern Gulf of Mexico. Variability in primary productivity model parameters in response to environmental forcing, nutrients, and microalgal taxonomic marker pigments were analysed in monthly and short-term datasets. Microalgal biomass (as Chla) was strongly related to total phosphorus concentration on seasonal scales. Hourly data support wind-driven resuspension as a major source of short-term variability in Chla and light attenuation (kd). The empirical relationship between areal primary productivity and a combined variable of biomass and light attenuation showed that variability in the photosynthesis-irradiance response contributed little to the overall variability in primary productivity, and Chla alone could account for 53-86% of the variability in primary productivity. Efforts to model productivity in similar shallow systems with highly variable microalgal biomass may benefit the most by investing resources in improving spatial and temporal resolution of chlorophyll a measurements before increasing the complexity of models used in productivity modeling. © 2013 Elsevier Ltd.
Caffrey J.M.,University of West Florida |
Murrell M.C.,U.S. Environmental Protection Agency |
Amacker K.S.,University of West Florida |
Harper J.W.,Apalachicola Bay National Estuarine Research Reserve |
And 3 more authors.
Estuaries and Coasts | Year: 2014
Measurements of primary production and respiration provide fundamental information about the trophic status of aquatic ecosystems, yet such measurements are logistically difficult and expensive to sustain as part of long-term monitoring programs. However, ecosystem metabolism parameters can be inferred from high frequency water quality data collections using autonomous logging instruments. For this study, we analyzed such time series datasets from three Gulf of Mexico estuaries: Grand Bay, MS; Weeks Bay, AL; and Apalachicola Bay, FL. Data were acquired from NOAA's National Estuarine Research Reserve System Wide Monitoring Program and used to calculate gross primary production (GPP), ecosystem respiration (ER), and net ecosystem metabolism (NEM) using Odum's open water method. The three systems represent a diversity of estuaries typical of the Gulf of Mexico region, varying by as much as two orders of magnitude in key physical characteristics, such as estuarine area, watershed area, freshwater flow, and nutrient loading. In all three systems, GPP and ER displayed strong seasonality, peaking in summer and being lowest during winter. Peak rates of GPP and ER exceeded 200 mmol O2 m-2 day-1 in all three estuaries. To our knowledge, this is the first study examining long-term trends in rates of GPP, ER, and NEM in estuaries. Variability in metabolism tended to be small among sites within each estuary. Nitrogen loading was highest in Weeks Bay, almost two times greater than that in Apalachicola Bay and 35 times greater than to Grand Bay. These differences in nitrogen loading were reflected in average annual GPP rates, which ranged from 825 g C m-2 year-1 in Weeks Bay to 401 g C m-2 year-1 for Apalachicola Bay and 377 g C m-2 year-1 in Grand Bay. Despite the strong inter-annual patterns in freshwater flow and salinity, variability in metabolic rates was low, perhaps reflecting shifts in the relative importance of benthic and phytoplankton productivity, during different flow regimes. The advantage of the open water method is that it uses readily available and cost-effective sonde monitoring technology to estimate these fundamental estuarine processes, thus providing a potential means for examining long-term trends in net carbon balance. It also provides a historical benchmark for comparison to ongoing and future monitoring focused on documenting the effect of human activities on the coastal zone. © 2013 The Author(s).