Porewater Ammonium Concentrations Research Articles

Effects of Microtopography on Hydrology, Physicochemistry, and Vegetation in a Tidal Swamp of the Hudson River

Hudson River freshwater tidal swamps have dynamic flooding and oxygenation regimes due to daily tidal flushing. Microtopography, small scale differences in elevation, adds even more complexity to inundation patterns and may have important implications for nutrient flow and wetland plant communities. The objective of this study was to determine if differences in inundation between microtopographic features were sufficient to alter physical, chemical, and biological attributes. Microtopography significantly affected flooding duration and redox conditions. Hummocks had lower concentrations of soluble phosphate in their porewater probably due to differing depths of iron oxidation. Hummocks also had lower porewater ammonium concentrations which could be explained by higher plant uptake of nitrogen on hummocks or less ammonium being nitrified and subsequently denitrified in hollows due to lack of oxygen. Decomposition rates were slower in hollows perhaps due to lack of oxygen due to flooding or differing decomposer communities. Fewer herbaceous plant species were found in hollows compared to hummocks perhaps because of hollow’s anoxic soils. Microtopography affects freshwater tidal swamp ecosystem function by affecting oxygen penetration, nutrient availability, rates of decomposition, and herbaceous plant species distributions.

Wetland response to sedimentation and nitrogen loading: diversification and inhibition of nitrogen‐fixing microbes

Anthropogenic inputs of nutrients and sediment simultaneously impact coastal ecosystems, such as wetlands, especially during storms. Independent and combined effects of sediment and ammonium nitrate loading on nitrogen fixation rates and diversity of microbes that fix nitrogen (diazotrophs) were tested via field manipulations in Spartina foliosa and unvegetated zones at Tijuana Estuary (California, USA). This estuary is subject to episodic nitrogen enrichment and sedimentation associated with rain-driven flooding and slope instabilities, the latter of which may worsen as the Triple Border Fence is constructed along the U.S.-Mexico border. Responses of diazotrophs were assessed over 17 days using acetylene reduction assays and genetic fingerprinting (terminal restriction fragment length polymorphism [T-RFLP]) of nifH, which codes for dinitrogenase reductase. Sulfate-reducing bacteria performed approximately 70% of nitrogen fixation in Spartina foliosa rhizospheres in the absence of nitrogen loading, based on sodium molybdate inhibitions in the laboratory. Following nutrient additions, richness (number of T-RFs [terminal restriction fragments]) and evenness (relative T-RF fluorescence) of diazotrophs in surface sediments increased, but nitrogen fixation rates decreased significantly within 17 days. These responses illustrate, within a microbial community, conformance to a more general ecological pattern of high function among assemblages of low diversity. Diazotroph community composition (T-RF profiles) and rhizosphere diversity were not affected. Pore water ammonium concentrations were higher and more persistent for 17 days in plots receiving sediment additions (1 cm deep), suggesting that recovery of diazotroph functions may be delayed by the combination of sediment and nutrient inputs. Nitrogen fixation constitutes a mechanism for rapid transfer of fixed N to S. foliosa roots and a variety of primary consumers (within 3 and 8 days, respectively), as determined via 15N2 enrichment studies with in situ microcosms of intact marsh sediment. Thus, long-term declines in nitrogen fixation rates in response to increasingly frequent nutrient loading and sedimentation may potentially alter nitrogen sources for vascular plants as well as trophic pathways in wetland ecosystems.

Isotopic composition of dissolved inorganic nitrogen in high mountain lakes: variation with altitude in the Pyrenees

Abstract. Nitrogen deposition in remote areas has increased, but the effect on ecosystems is still poorly understood. For aquatic systems, knowledge of the main processes driving the observed variation is limited, as is knowledge of how changes in nitrogen supply affect lake biogeochemical and food web processes. Differences in dissolved inorganic nitrogen (DIN) between lakes cannot be understood without considering catchment characteristics. In mountains, catchment features (e.g., thermal conditions, land cover) vary considerably with elevation. The isotopic composition of nitrogen (δ15N) is increasingly used to study aquatic ecosystem dynamics. Here we explore the variability of δ15N in DIN in high mountain lakes and show that environmental conditions that change with altitude can affect the isotopic ratio. We measured ammonium and nitrate δ15N values in atmospheric deposition, epilimnetic water, deep chlorophyll maximum water (DCMW) and sediment pore water (SPW) from eight mountain lakes in the Pyrenees, both above and below the treeline. Lakes showed relatively uniform δ15N-NH4+ values in SPW (2.2±1.6‰), with no variation corresponding to catchment or lake characteristics. We suggest that organic matter diagenesis under similar sediment conditions is responsible for the low variation between the lakes. In the water column, the range of δ15N values was larger for ammonium (−9.4‰ to 7.4‰) than for nitrate (−11.4‰ to −3.4‰), as a result of higher variation both between and within lakes (epilimnetic vs. DCM water). For both compounds part of the difference correlated with altitude or catchment features (e.g., scree proportion). Based on concentration, chemical and isotopic tendencies, we suggest that patterns arise from the distinct relative contributions of two types of water flow paths to the lakes: one from snowpack melting, with little soil interaction; and another highly influenced by soil conditions. The snow-type flow path contributes low DIN concentrations depleted in 15N, whereas the soil-type flow path contributes high nitrate concentrations with higher δ15N. The proportion of these two types of source correlates with average catchment features when there is extensive snow cover during spring and early summer and probably becomes more dependent on local characteristics around the lake as summer advances. Lake depth and pore water ammonium concentrations, among other features, introduce secondary variation. In the context of nitrogen deposition studies, lakes with higher snow-type influence will probably register changes in N deposition and pollution sources better, whereas lakes with higher soil-type influence may reflect long-term effects of vegetation and soil dynamics.

Wetland response to sedimentation and nitrogen loading: diversification and inhibition of nitrogen-fixing microbes

Anthropogenic inputs of nutrients and sediment simultaneously impact coastal ecosystems, such as wetlands, especially during storms. Independent and combined effects of sediment and ammonium nitrate loading on nitrogen fixation rates and diversity of microbes that fix nitrogen (diazotrophs) were tested via field manipulations in Spartina foliosa and unvegetated zones at Tijuana Estuary (California, USA). This estuary is subject to episodic nitrogen enrichment and sedimentation associated with rain-driven flooding and slope instabilities, the latter of which may worsen as the Triple Border Fence is constructed along the U.S.–Mexico border. Responses of diazotrophs were assessed over 17 days using acetylene reduction assays and genetic fingerprinting (terminal restriction fragment length polymorphism [T-RFLP]) of nifH, which codes for dinitrogenase reductase. Sulfate-reducing bacteria performed ~70% of nitrogen fixation in Spartina foliosa rhizospheres in the absence of nitrogen loading, based on sodium molybdate inhibitions in the laboratory. Following nutrient additions, richness (number of T-RFs [terminal restriction fragments]) and evenness (relative T-RF fluorescence) of diazotrophs in surface sediments increased, but nitrogen fixation rates decreased significantly within 17 days. These responses illustrate, within a microbial community, conformance to a more general ecological pattern of high function among assemblages of low diversity. Diazotroph community composition (T-RF profiles) and rhizosphere diversity were not affected. Pore water ammonium concentrations were higher and more persistent for 17 days in plots receiving sediment additions (1 cm deep), suggesting that recovery of diazotroph functions may be delayed by the combination of sediment and nutrient inputs. Nitrogen fixation constitutes a mechanism for rapid transfer of fixed N to S. foliosa roots and a variety of primary consumers (within 3 and 8 days, respectively), as determined via 15N2 enrichment studies with in situ microcosms of intact marsh sediment. Thus, long-term declines in nitrogen fixation rates in response to increasingly frequent nutrient loading and sedimentation may potentially alter nitrogen sources for vascular plants as well as trophic pathways in wetland ecosystems.

Benthic fluxes of nitrogen and phosphorus at southern bluefin tuna Thunnus maccoyii sea-cages

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 390:251-263 (2009) - DOI: https://doi.org/10.3354/meps08186 Benthic fluxes of nitrogen and phosphorus at southern bluefin tuna Thunnus maccoyii sea-cages P. R. Lauer1,2,3,4,*, M. Fernandes1,3, P. G. Fairweather2,3, J. Tanner1,3, A. Cheshire1,3,5 1South Australian Research & Development Institute, Aquatic Sciences, PO Box 120, Henley Beach, South Australia 5022, Australia 2Flinders University of South Australia, GPO Box 2100, Adelaide, South Australia 5001, Australia 3Aquafin Cooperative Research Centre, PO Box 120, Henley Beach, South Australia 5022, Australia 4Present address: Primary Industries and Resources South Australia, Aquaculture Division, GPO Box 1625, Adelaide, South Australia 5001, Australia 5Present address: SMU Pty Ltd, 24 Winding Way, Belair, South Australia 5052, Australia *Email: peter.lauer@sa.gov.au ABSTRACT: To assess the effects of southern bluefin tuna farming on benthic nutrient cycling, we measured sedimentation rates, porewater nutrients, sedimentary total nitrogen (N) and phosphorus (P) content, and benthic fluxes at 2 tuna sea-cages and associated control (non-farm) sites in South Australia over the course of a farming season. Sedimentation rates exceeded 40 g dry weight m–2 d–1 only at the sea-cage sites, and porewater concentrations of ammonium and phosphate were up to 10 and 100 times that measured at control sites, respectively. The highest ammonium and phosphate fluxes from the sediments into the water column were recorded at sea-cage sites (9962 and 2177 µmol m–2 h–1, respectively) towards the end of the season, and these were in excess of 10 times those recorded at control sites in any month. The annual average of the sediment fluxes associated with southern bluefin tuna farming produced over 7 and 40 times the daily requirements of N and P, respectively, for calculated primary productivity. The high sedimentation rates, porewater concentrations and benthic flux rates recorded at sea-cages at the end of the farming season were not observed 4 mo after the southern bluefin tuna were harvested. These data show that sedimentation rates and sediment geochemistry respond rapidly to farming activities. The risks associated with farming southern bluefin tuna include enrichment of pelagic nutrients from benthic fluxes that can lead to increased primary production. Thus continuation of site fallowing on an annual basis is strongly recommended. Sustainability of the coastal ecosystem supporting southern bluefin tuna farming must consider the regional consequences from these inputs of N and P, occurring not only through increased sedimentation but also direct nutrient availability in the water column. KEY WORDS: Aquaculture environments · Nutrients · Sedimentation · Sea-cage farming · South Australia Full text in pdf format PreviousNextCite this article as: Lauer PR, Fernandes M, Fairweather PG, Tanner J, Cheshire A (2009) Benthic fluxes of nitrogen and phosphorus at southern bluefin tuna Thunnus maccoyii sea-cages. Mar Ecol Prog Ser 390:251-263. https://doi.org/10.3354/meps08186 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 390. Online publication date: September 18, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Unusually negative nitrogen isotopic compositions (δ<sup>15</sup>N) of mangroves and lichens in an oligotrophic, microbially-influenced ecosystem

Abstract. Extremes in δ15N values in mangrove tissues and lichens (range =+4 to −22‰) were measured from a mangrove forest ecosystem located on Twin Cays, offshore islands in Belize, Central America. The N isotopic compositions and concentrations of NH4+/NH3 in porewater, rainwater, and atmospheric ammonia, and the δ15N of lichens, mangrove leaves, roots, stems, and wood were examined to study the biogeochemical processes important for establishing these unusual N isotopic ratios. Dwarfed Rhizophora mangle trees had the most negative δ15N, whereas fringing Rhizophora trees, the most positive δ15N values. Porewater ammonium concentrations had little relationship to N isotopic fractionation in mangrove tissues. In dwarfed mangroves, the δ15N of fine and coarse roots were 6–9‰ more positive than leaf tissue from the same tree, indicating different sources of N for root and leaf tissues. When P was added to dwarfed mangrove trees without added N, δ15N increased within one year from −12‰ to −2‰, approaching the δ15N of porewater ammonium (δ15N=+4‰). Isotopically depleted ammonia in the atmosphere (δ15N=−19‰) and in rainwater (δ15N=−10‰) were found on Twin Cays. We propose that foliar uptake of these atmospheric sources by P-stressed, dwarfed mangrove trees and lichens can explain their very negative δ15N values. In environments where P is limiting for growth, uptake of atmospheric N by Rhizophora mangle may be an important adaptive strategy.

Physiological responses of the seagrass Posidonia oceanica to elevated organic matter content in sediments: An experimental assessment

Here we studied the effects of adding organic carbon and nutrients to sediment on the physiology and survival of the seagrass Posidonia oceanica in a field experiment in the Medes Islands (NE Spain). Nine randomly selected plots were established at a depth of 10 m; three were enriched with organic carbon (OM treatment), three with organic carbon and nutrients (OMN treatment), and three were kept as controls (CON). The experiment was performed over 5 months and sampling of plants and sediments was done in March, May and July 2002. Sediment sulfide pools and pore water ammonium concentrations increased significantly in OM and OMN plots, both treatments showing increased reducing conditions in the sediment. Plants in these two treatments showed higher mortality and lower biomass compared to plants from CON plots. The greatest effects on seagrass occurred in the OMN plots, indicating a synergistic effect of organic carbon and nutrient additions. Treatments had significant effects on plant nitrogen (N) and phosphorous (P) metabolism, shown by an increase in free amino acid (FAA) content, a change in FAA composition and a lack of increase in N and P tissue content. Treated plants showed higher g-aminobutyric acid (GABA) and malate concentrations and lower concentrations of non-structural carbohydrates compared to CON, indicating that anaerobic respiration in below-ground tissues occurred. Several of the physiological changes shown by P. oceanica can be interpreted as adaptations to anoxia exposure. However, the increased mortality in treated plots demonstrates that this seagrass does not tolerate highly reduced sediments.

Effect of Sediment Manipulation on the Biogeochemistry of Experimental Sediment Systems

Abstract Before biological or biogeochemical experimentation, sediments are often manipulated and defaunated with the use of many different approaches and only modest consideration of treatment effects on sediment biogeochemistry and fluxes. Mesocosm experiments require large quantities of sediment and no standard protocol to defaunate and equilibrate muddy sediments before initiation of experiments has been determined. Using fine-grained sediments, we examined a number of treatments: (1) intact with macroinfauna; (2) intact, macroinfauna individually removed; (3) homogenized surface sediment with macrofauna; (4) homogenized deep sediment without macroinfauna; and (5) intact deep sediment without macroinfauna. In weekly batch core flux incubations, we measured dissolved oxygen, dinitrogen gas, ammonium (NH4+), nitrate plus nitrite (NO3− + NO2−), silicate (Si), and soluble reactive phosphorus (SRP) fluxes over a 5-week period. In addition, we determined porewater ammonium concentrations over time. Differen...

The effect of mouth opening on the biomass and community structure of microphytobenthos in a small oligotrophic estuary

The relationship between microphytobenthic biomass, community structure and physico-chemical conditions was studied in the Van Stadens Estuary, South Africa. Quarterly sampling was conducted in 2003. Temporal variation in community structure was explained by the percentage contribution of very fine sand in the sediment and by porewater ammonium concentrations. Microphytobenthic biomass showed strong negative correlations with water column salinity and sediment redox potential, and a positive correlation with water column soluble reactive phosphorus concentration. Temporal variation in mouth condition, sediment structure and nutrient availability changed biomass and community structure but there was little spatial variability. During the quarterly sampling of this study, microphytobenthic biomass was higher during open mouth conditions (1.43 ± 0.14–3.64 ± 0.94 μg g −1 sediment) than under closed conditions (0.25 ± 0.08–1.88 ± 0.22 μg g −1 sediment). The estuary was sampled weekly immediately following a mouth breaching event, physico-chemical conditions and microphytobenthic biomass were measured. Biomass did not decrease following mouth breaching and ranged between 0.25 ± 0.02 and 0.56 ± 0.10 μg g −1 sediment. This is contrary to other studies on South African intermittently open estuaries and indicates the importance of site specific data and detailed descriptions of the opening event.

Nitrogen cycling in the sediments of Santa Barbara basin and Eastern Subtropical North Pacific: Nitrogen isotopes, diagenesis and possible chemosymbiosis between two lithotrophs (Thioploca and Anammox)—“riding on a glider”

Abstract This article presents data on the isotopic composition of pore water ammonium and N org in the anoxic sediments of the Santa Barbara Basin and the Eastern Subtropical North Pacific (ESNP) region. Ammonium δ 15 N behaves differently in the two regions, reflecting variability in bacterial processes of sedimentary nitrogen cycling. In Santa Barbara Basin, stoichiometry of TCO 2 and NH 4 + production defined by pore water chemistry indicates that the only reaction influencing pore water ammonium concentration in these sediments appears to be organic matter decomposition. Pore water ammonium was found to be 1–3‰ heavier than decomposing organic matter. In contrast, the upper 15–30 cm of ESNP pore waters have ammonium with δ 15 N that is more than 10‰ heavier than decomposing organic matter. At greater depth, the δ 15 N of deeper pore waters approaches that of decomposing organic matter. Mass balance calculations indicate that the observed isotopic enrichment is not due to the preferential loss of isotopically enriched organic matter. Pore water profiles show that the zone with heavy isotopes is characterized by a TCO 2 /NH 4 + inputs ratio of 4 or less. We attribute this to the presence of Thioploca bacteria, who transport NO 3 − to depth and reduce it to NH 4 + while oxidizing sulfide. Based on pore water stoichiometry, and reaction–diffusion modeling of pore water isotopic composition we propose that the 15 N-enriched ammonium is produced as the result of chemosymbiosis between Thioploca and Anammox-like bacteria in these sediments. Our work provides the new insights into benthic microbial ecology, and the role of coupled individual metabolic pathways in sedimentary nitrogen cycling. In Santa Barbara Basin, factors which contribute to the isotopic fractionation of 1–3‰ between pore water ammonium and solid N org were also considered. In this sediments, ∼23% of the rain of organic nitrogen is lost to diagenesis, therefore, the isotopic effect of degradation on the residual N org is estimated to be small, − 0.7‰. The most likely cause of fractionation is preferential degradation of an isotopically heavier, more labile marine fraction relative to an isotopically lighter, more refractory terrestrial component of the organic matter, but other possibilities cannot be ruled out. When corrected for the observed fractionation, it appears that the δ 15 N of these sediments may represent non-steady state conditions.

Disturbance and recruitment: a test of solute and substrate specificity using Mercenaria mercenaria and Capitella sp. 1

Disturbances alter sediment surface chemistry, and this alteration promotes rejection of habitats by new benthic recruits. To date, the specific compound(s) affecting the rejection response have not been identified, but model predictions and experimental evidence suggest that oxygen and ammonium concentrations are informative. We evaluated the recruitment response of the oppor- tunistic polychaete Capitella sp. 1 to disturbed, undisturbed and recovering sediments, with parallel measures of oxygen concentration at the sediment surface. Results suggest that Capitella sp. 1 avoid disturbed sediments, but the behavior was not consistent with surface oxygen concentration. We also manipulated porewater ammonium concentration and examined the recruitment responses of Mer- cenaria mercenaria and Capitella sp. 1 to experimentally altered, as well as naturally disturbed, sur- faces. Results suggest that M. mercenaria avoid disturbed habitats, regardless of ammonium concen- tration; however, Capitella sp. 1 responses were consistent with avoidance of high ammonium environments. Finally, we tested a prediction of our disturbance recovery model: that chemical signals associated with disturbance, and responses of recruits, vary as a function of the diagenetic regime. As predicted, chemical concentrations were more dramatically changed in disturbed muds relative to disturbed sands. Capitella sp. 1 rejected disturbed mud surfaces having high ammonium/low oxygen but accepted habitats having low ammonium and high oxygen, including undisturbed mud and sand surfaces, and disturbed sand surfaces. M. mercenaria rejected disturbed sediments regardless of ammonium or oxygen concentration, or sediment type. Our findings con- firm that small-scale geochemical processes that are widespread in sedimentary habitats affect recruitment decisions.

Interactions between Methane Oxidation and Nitrification in Coastal Sediments

Galveston Bay sediments exhibit substantial spatial and seasonal variability in rates of nitrification and aerobic methane oxidation. We examined the biogeochemical and microbiological controls on these processes using aerobic enrichment slurries. Potential aerobic methane and ammonia oxidation rates from unamended control slurries were compared to rates in slurries amended with methane, ammonium, or methane + ammonium. Bacterial community composition was monitored using denaturing gradient gel electrophoresis (DGGE) analysis of PCR amplified ribosomal and functional gene DNA. Potential methane and ammonia oxidation rates increased over time in sediments amended with methane and ammonium, respectively. The highest potential methane oxidation rates occurred in treatments receiving both ammonium and methane suggesting that methanotrophs in the enrichment cultures were nitrogen limited. The highest ammonia oxidation rates occurred in treatments amended with ammonium only. Treatments receiving both ammonium and methane exhibited ammonia oxidation rates and porewater ammonium concentrations similar to those measured in the unamended control suggesting that methanotrophs may have inhibited ammonia oxidation by sequestering available ammonia. Sequence analysis revealed a decrease in general bacterial community diversity over time and a shift in ammonia-oxidizing bacterial composition corresponding with methane availability. However, methanotroph community composition similarities between treatments with different relative methane oxidation rates suggest that changes in physiological activity, as well as shifts in community composition, contributed to the observed patterns in potential rates.

Evidence for density-dependent effects of infauna on sediment biogeochemistry and benthic–pelagic coupling in nearshore systems

We report results of a laboratory experiment that examines the effect of density-dependent interactions among infauna on organism–sediment–seawater relationships. The experiment includes a time series documentation of feeding behavior of the deposit- and suspension-feeding bivalve Macoma balthica, concurrent with measures of sediment biogeochemical processes that are affected by different feeding modes. We hypothesized that feeding behavior and emigration rates might shift with increasing density, and that these shifts would have cascading effects on benthic primary productivity, sediment–seawater exchanges, and porewater concentrations of ammonium and silicate. Macoma individuals were maintained in aquaria at three different densities (46, 230, and 460 individuals m −2) that fall within their natural abundances in the Chesapeake Bay. Individuals fed mostly on suspended material throughout the experiment, resorting to deposit feeding behavior only at the highest densities. Disturbances on the sediment surface during deposit feeding periods were not sufficient to impact benthic primary productivity and the associated interception effect of microalgae on sediment–seawater exchanges, as seen in previous studies. However, the bivalves impacted sediment fluxes directly through bioturbational activity, and these effects showed significant density interactions. For ammonium, fluxes ranged from 1.3 to 3.7 mmol m −2 d −1 and generally did not increase as a function of increasing Macoma density. Rather, highest fluxes generally were observed in intermediate density treatments. For silicate, a different trend was observed. Fluxes tended to parallel density, and ranged from 6.4 to 13.5 mmol m −2 d −1, however, the relationship was not linear. These observations suggest that as infaunal density shifts, so does the balance of ammonium to silicate efflux. Thus, benthic population structure may impact water column processes not only through enhancing the flux, but also through alteration of elemental ratios. Experiments that uncover the strength of these interactions, and models that blend the actions of individuals, populations, and material components, would greatly enhance our understanding of the geochemistry of organism–sediment relations.

Effects of Phragmites australis removal on marsh nutrient cycling

In the northeast US removal of exotic and invasive plant species is a common wetland restoration activity and the invasive common reed (Phragmites australis) is often the target of control efforts. We examined effects of reed removal on sediment nutrient pools and denitrification potential in a tidal freshwater marsh on the Connecticut River. In the first year after herbicide application and cutting of a reed stand, porewater ammonium concentrations in the removal area were about 4× higher relative to extant reed or cattail. Denitrification potentials were 50% lower than in a reference stand of reed. Denitrification activity had “recovered” by the second growing season after reed removal but porewater ammonium continued to accumulate. By the third growing season following reed removal, plant regrowth had occurred over approximately half the experimental plot and porewater ammonium had declined to pre-manipulation levels. Sediment organic content, moisture and porewater phosphate showed no significant response to reed removal over the four-year course of this study. Reed removal allowed regrowth of a more diverse plant community thereby achieving one of the goals of this restoration effort but patterns in ammonium accumulation and denitrification suggest a reduction in the capacity of this site to act as a sink for nitrogen.

Macrofauna and nutrient cycling in the Swan River Estuary, Western Australia: experimental results

AbstractThis study investigated the effect of benthic macrofauna on nutrient fluxes. The influence of the macrofauna on nutrients released from the sediments was investigated experimentally in the laboratory using sediment cores from the Swan–Canning Estuary. Excretion rates of common benthic species were also measured to quantify the role of the macrofauna in estuarine nutrient cycling.The presence of macrofauna increased the release of phosphate and ammonium into the water column but decreased the release, or resulted in uptake, of nitrate by the sediments. There were no significant differences in porewater concentrations of ammonium, nitrate or phosphate between treatments with and without macrofauna. The macrofauna clearly had an important role in nutrient fluxes, as nutrient release differed between cores with and without fauna, and nutrient fluxes were significantly correlated with increased faunal biomass.Other factors, such as season and dissolved oxygen concentrations, influenced the concentration of nutrients released. Ammonium was released into the overlying water column at higher rates in winter than summer, while nitrate was released at higher rates in summer than winter. Aeration did not have a significant effect on nutrient fluxes, however there was a significant increase in filterable reactive phosphorus, and decrease in nitrate, in the porewater of cores which were not aerated.Benthic species excreted phosphate, nitrate and ammonium, with ammonium present in the largest amounts. Comparison of excretion rates to the amount of nutrients released into the water column in the core experiments revealed that excretion could account for 30% of the phosphate and >200% of the ammonium measured in the water column.Clearly the benthic macrofauna have a significant role with respect to benthic nutrient fluxes within the Swan–Canning Estuary, with benthic regeneration of nutrients estimated to equal external loading of nutrients. However, further work is required to more precisely define the influence of seasonality, dissolved oxygen, microbial activity and sediment characteristics on nutrient fluxes. Copyright © 2001 John Wiley & Sons, Ltd.

Leakage of ammonium, urea, and dissolved organic nitrogen and carbon from eelgrass Zostera marina roots and rhizomes during sediment handling

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 16:303-307 (1999) - doi:10.3354/ame016303 Leakage of ammonium, urea, and dissolved organic nitrogen and carbon from eelgrass Zostera marina roots and rhizomes during sediment handling Jens W. Hansen*, Bente Aa. Lomstein Department of Microbial Ecology, Institute of Biological Sciences, University of Aarhus, Building 540, Ny Munkegade, DK-8000 Aarhus C, Denmark *Present address: National Environmental Research Institute, Vejlsøvej 25, DK-8600 Silkeborg, Denmark. E-mail: jwh@dmu.dk ABSTRACT: The leakage of urea, ammonium, dissolved organic nitrogen, and dissolved organic carbon from Zostera marina root-rhizomes during different porewater extractions was examined. In addition, the concentrations of these compounds were measured in root-rhizomes to estimate the potential leakage from root-rhizomes during sediment handling. The concentrations of ammonium, urea, and dissolved organic nitrogen in root-rhizomes were 22 to 51 times higher than the respective average porewater concentrations within the upper 5 cm of the sediment. Up to 70% of the compounds in question leaked from root-rhizomes during sediment handling, with a resultant, up to 8-fold, increase in the respective porewater concentrations. The porewater concentrations of ammonium, urea, and dissolved organic nitrogen and carbon were on average overestimated by a factor of 2 within the upper 5 cm of the sediment due to leakage from root-rhizomes. Thus, it is recommended that roots and rhizomes are removed from the sediment before porewater extraction by conventional methods. KEY WORDS: Zostera marina · Roots · Rhizomes · Sediment · Porewater · Leakage · Nitrogen · Carbon Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 16, No. 3. Publication date: February 24, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.

Distribution of estuarine benthic diatom species along salinity and nutrient gradients

Changes in relative abundance of estuarine epipelic microalgae along an estuarine gradient were investigated, and population densities of different species along a small-scale nutrient gradient generated by a sewage treatment outfall and in laboratory mesocosms enriched with ammonium were also studied. The relative abundance of certain species of epipelic diatoms was related to location along the estuarine salinity and nutrient gradient: Navicula gregaria and N. phyllepta were abundant at oligo- and mesohaline sites respectively, and Pleurosigma angulatum and Plagiotropis vitrea were abundant at polyhaline sites. On a smaller spatial scale, though there were no significant patterns in microalgal biomass in relation to nutrient enrichment, there were significant differences in the population densities of different epipelic species along a multivariate nutrient gradient (decreasing concentrations of ammonium, nitrite, silicate, organic content, and increasing salinity and pore-water nitrate concentrations) away from a sewage outfall along a saltmarsh creek. The diatoms Nitzschia sigma and Gyrosigma limosum and the cyanobacteria Oscillatoria limosa and O. princeps had significantly higher population densities near the outfall, and Navicula phyllepta, N. pargemina, Nitzschia frustulum, Cylindrotheca signata and Pleurosigma angulatum were significantly more abundant at the seaward end of the gradient. In laboratory tidal mesocosms, sediment cores from along the gradient had their pore-water ammonium concentrations increased to 380–450 μM NH4 +. After 26 days, the population densities of Gyrosigma fasciola, G. littorale, P. angulatum, N. phyllepta, Cylindrotheca signata, C. closterium and Niztschia apiculata were significantly reduced, while those of G. limosum, N. sigma, Scolioneis tumida and O. limosa were unaffected, or were significantly higher compared with control cores. Laboratory manipulations of ammonium concentrations supported the observed field distributions, indicating that epipelic species do have different trophic preferences and ammonium concentration may be a significant factor in determining estuarine species composition of epipelic algae.

Experimental Studies of Caribbean Seagrass Bed Development

Processes important in the development of subtidal seagrass beds composed of Thalassia testudinum, Syringodium filiforme, Halodule wrightii, and many rhizophytic algal species were examined in situ for 52 mo in a coral reef lagoon on St. Croix, United States Virgin Islands. The study emphasized the early stages of development of the seagrass beds and the role played by colonizing rhizophytic algae. I tested the hypotheses that nutrient accumulation in the sediments limits seagrass recolonization, and that rhizophytic algae facilitate sediment nutrient accumulation by stabilizing the sediments and adding organic matter from rapidly decomposing thalli. Vegetation was removed from 0.25— and 1—m2 plots in 3 m of water. Plot treatments consisted of: (1) no further manipulation, (2) adding nitrogen plus phosphorus fertilizer to the sediments, (3) removing colonizing rhizophytic algae to minimize algal effects (e.g., sediment stabilization, organic input), and (4) removing colonizing algae and adding "plastic algae" to stabilize sediments without organic input. Plant densities, sediment grain size, redox potential, inorganic nitrogen concentrations in porewaters, and ammonium production rates were measured over time in all plots, including undisturbed controls. All recolonization occurred through vegetative propagation. The sequence of plant recolonization was unaffected by the treatments, corresponding instead to life history characteristics and nutrient requirements of the species involved. Rhizophytic algae invaded the plots within a few months, followed by the seagrass Syringodium, then Thalassia. The seagrass Halodule was insignificant in the recolonization. Densities of rhizophytic algae and Syringodium declined when the density of Thalassia reached 200 leaf shoots/m2. The rates of increase in seagrass leaf shoot densities and biomass were greatest in the fertilized plots, supporting the nutrient limitation hypothesis. Rhizophytic algae facilitated seagrass recolonization; seagrass densities, biomass, and porewater ammonium concentrations were lowest in plots where algae were removed. Sediment ammonium concentrations decreased when Thalassia became dominant. Ammonium production in the sediments increased as the plant community developed. The nitrogen required for Syringodium productivity was met easily by ammonium production, assuming no competition from Thalassia. In contrast, Thalassia accounted for >93% of the nitrogen required for total seagrass productivity, and ammonium production could supply up to 45% of this requirement. At the end of the experiment (52 mo), Thalassia density and ammonium production rates in the sediments were lower than in the surrounding undisturbed seagrass bed. The experiment provides evidence for a resource—ratio model where the rate of succession is controlled by a sediment nutrient supply that increases over time. The sequence of colonization is determined by relative rates of vegetative propagation by stolons and rhizomes across the sediment surface, which are inversely correlated with whole plant productivity and thus with requirements for nutrients. Algal colonizers tolerate low nutrients by having low productivities. The climax species Thalassia is a competitive species effective at exploiting the sediment nutrient resource. Co—existence, rather than replacement, of species occurs, despite a relatively benign disturbance regime.

Sediment ammonium availability and eelgrass (Zostera marina) growth

The interaction of sediment ammonium (NH 4 + ) availability and eelgrass (Zostera marina L.) growth, biomass and photosynthesis was investigated using controlled environment and in-situ manipulations of pore water ammonium concentrations. Sediment diffusers were used to create pore water diffusion gradients to fertilize and deplete ammonium levels in sediments with intact eelgrass rhizospheres. Between October, 1982 and September, 1983 controlled environment experiments using plants from shallow (1.3 m) and deep (5.5 m) stations in a Great Harbor, Woods Hole, Massachusetts, USA eelgrass meadow along with in-situ experiments at these stations provided a range of sediment ammonium concentrations between 0.1 and 10 mM (adsorbed+interstitial NH 4 + ). The results of the in-situ experiments indicate that nitrogen limitation of eelgrass growth does not occur in the Great Harbor eelgrass meadow. A comparison of NH 4 + regeneration rates and eelgrass nitrogen requirements indicates an excess of nitrogen supply over demand and provides an explanation for the lack of response to the manipulations. Results of controlled environment experiments combined with in-situ results suggest that sediment ammonium pool concentrations above approximately 100 μmol NH 4 + per liter of sediment (interstitial only) saturate the growth response of Zostera marina.

Benthic nutrient regeneration processes in different sediment types of Kiel Bight

Abstract Long-term investigations of pore-water ammonium concentrations and sediment oxygen uptake were carried out in three different sediment types along a slope in Kiel Bight. The inverse relation between mineralization rates and ammonium concentrations at the three stations is explained by the differences in the role of various mechanisms transporting nutrients out of the sediments. Direct water exchange due to turbulent or density driven processes, bioturbation and pumping activity of benthic macrofauna and molecular diffusion are involved to various extents in nutrient fluxes out of the sediments studied. The role of different sediment types in the interaction with the pelagic system is discussed in a conceptual framework of pelagic system functioning in Kiel Bight.