Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment-sea... more Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment-seawater nitrogen flux, an important driver of pelagic productivity. To investigate how this perturbation affects the fluxes of NO X − (nitrite/nitrate), NH 4 + and O 2 , we incubated estuarine sand and subtidal silt in recirculating seawater with a CO 2-adjusted pH of 8.1 and 7.9. During a 41-day incubation, the seawater kept at pH 8.1 lost 97% of its NO X − content but the seawater kept at pH 7.9 lost only 18%. Excess CO 2 increased benthic photosynthesis. In the silt, this was accompanied by a reversal of the initial NO X − efflux into influx. The estuarine sand sustained its initial NO X − influx but, by the end of the incubation, released more NH 4 + at pH 7.9 than at pH 8.1. We hypothesise that these effects share a common cause; excess CO 2 increased the growth of benthic microalgae and so nutrient competition with ammonia oxidising bacteria (AOB). In the silt, diatoms likely outcompeted AOB for NH 4 + and photosynthesis increased the dark/light fluctuations in the pore water oxygenation inhibiting nitrification and coupled nitrification/denitrification. If this is correct, then excess CO 2 may lead to retention of inorganic nitrogen adding to the pressures of increasing coastal eutrophication. Ocean acidification, a consequence of the absorption of atmospheric carbon dioxide, is expected to accelerate over the upcoming century, altering marine biota and associated ecosystem processes 1-3. Our ability to predict the functioning of the future high-CO 2 ocean, however, is still in its infancy 1,4,5. For the coastal ocean, such prediction is complicated by natural and anthropogenic phenomena rendering the seawater carbonate chemistry variable at timescales from seconds to years (reviewed by Waldbusser & Salisbury 6 , Mostofa et al. 3). Current research thus distinguishes between carbonate weather-the short-term variability in the seawater pH-pCO 2 system-and carbonate climate, the longer-term shift in the baseline pH-pCO 2 system 6. The latter may alter environmental conditions for microorganisms in coastal sediment that drive the remineralisation of organic matter and associated biogeochemical cycles 7. Given that benthic remineralisation provides 30-80% of the inorganic nutrients required by pelagic primary production 8-10 , ocean acidification-driven alterations of benthic nutrient cycles could have implications for coastal ecosystem functioning. The nitrogen cycle may be altered more than any other nutrient cycle in response to CO 2 enrichment (reviewed by Hutchins et al. 5). For example, studies have revealed evidence for CO 2-induced changes in the sediment-seawater inorganic nitrogen flux 11,12 , increased nitrogen fixation due to enhanced growth of diazotrophic cyanobacteria 13-15 , and inhibition of nitrification 7. Other studies, however, found no effects of CO 2 enrichment on benthic nitrification 16 and denitrification 17. Unravelling the mechanisms behind CO 2-induced changes in benthic nitrogen cycling is challenging because the microbial activity that drives nitrogen transformations is modulated by macrobenthic infauna reworking particles and ventilating burrows 11,18-26. In coastal waters where sunlight penetrates to the seabed, another complication exists: excess CO 2 may increase the photosynthesis of benthic microalgae 27,28 altering the activity of nitrogen transforming microbes and associated sediment-seawater inorganic nitrogen flux. Two mechanisms have been proposed; (1) benthic microalgae may outcompete ammonia-oxidizing microorganisms in the uptake of ammonia 29,30 , and (2) enhanced benthic O 2 evolution may inhibit dissimilatory nitrate reduction 29-33. Although
Ecosystem feedback to ocean acidification in a cohesive photosynthetic sediment 2 Ecosystem feedb... more Ecosystem feedback to ocean acidification in a cohesive photosynthetic sediment 2 Ecosystem feedbacks in response to ocean acidification can amplify or diminish the diel pH oscillations that characterize productive coastal waters. We report that benthic microalgae generate such oscillations in the porewater of cohesive sediment and ask how carbonation (acidification) of the overlying seawater alters these in the absence and presence of biogenic calcite. To do so, we placed a 1-mm layer of ground oyster shells (Treatment) or sand (Control) onto intact sediment cores free of large dwelling fauna, and then gradually increased the pCO2 in the seawater above half of the Treatment and Control cores from 472 to 1216 μatm (pH 8.0 to 7.6, CO2:HCO3from 4.8 to 9.6 x 10-4). Vertical porewater [O2] and [H + ] microprofiles measured 16 d later showed that this carbonation had decreased O2 penetration in all cores, indicating a metabolic response. In carbonated seawater: (1) sediment biogeochemical processes added and removed more H + to and from the porewater in darkness and light, respectively, than in ambient seawater increasing the amplitude of the dark-light porewater [H + ] oscillations, and (2) the dissolution of calcite decreased the porewater [H + ] below that in overlying seawater, reversing the dark sediment-seawater H + flux and decreasing the amplitude of diel [H + ] oscillations. This dissolution did not, however, counter the negative effect of carbonation on sediment O2 penetration. We hypothesise that the latter effect and the observed enhanced acidification of the sediment porewater were caused by an ecosystem feedback: a CO2-induced increase in the microbial reoxidation of reduced solutes with O2.
Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment-sea... more Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment-seawater nitrogen flux, an important driver of pelagic productivity. To investigate how this perturbation affects the fluxes of NO (nitrite/nitrate), NH and O, we incubated estuarine sand and subtidal silt in recirculating seawater with a CO-adjusted pH of 8.1 and 7.9. During a 41-day incubation, the seawater kept at pH 8.1 lost 97% of its NO content but the seawater kept at pH 7.9 lost only 18%. Excess CO increased benthic photosynthesis. In the silt, this was accompanied by a reversal of the initial NO efflux into influx. The estuarine sand sustained its initial NO influx but, by the end of the incubation, released more NH at pH 7.9 than at pH 8.1. We hypothesise that these effects share a common cause; excess CO increased the growth of benthic microalgae and so nutrient competition with ammonia oxidising bacteria (AOB). In the silt, diatoms likely outcompeted AOB for NH and photosynthesi...
Plans to exploit an offshore source of iron sand in South Taranaki Bight (STB), New Zealand, caus... more Plans to exploit an offshore source of iron sand in South Taranaki Bight (STB), New Zealand, caused concerns that such exploitation may expose benthic and pelagic biota to elevated trace metal concentrations. We conducted dilute-acid extractions and standard elutriate tests to investigate the potential of this exploitation to (1) create a new seafloor with elevated trace metal content, (2) mobilise trace metals during iron sand extraction and, (3) enrich the returning process seawater, which feeds iron sand through mills, with trace metals. We found that recruits of freshly uncovered sediment may encounter higher-than-natural concentrations of cadmium, nickel and chromium (but not of copper, lead, and zinc) and propose to investigate the bioavailability of these metals. Elutriate test with raw and milled iron sand revealed that, for nickel and copper, dilution of the process seawater may be required to meet the local water quality guideline. We argue that this dilution can be achieved by adjustment of the mass and seawater balance of the offshore extraction process.
Growing numbers and increased stocking of marine mussel farms make reliable techniques for enviro... more Growing numbers and increased stocking of marine mussel farms make reliable techniques for environmental effect assessment a priority. Previously, we showed how the color intensity of soft sediment could be used to estimate its acid volatile sulfide (AVS) content, a product of the anaerobic microbial degradation of organic matter deposits. We then proposed to include assessments of the AVS farm footprint in marine farm monitoring, in particular, to investigate temporal changes in the extent of the seafloor area of elevated sediment AVS content. Such assessment requires accurate detection of the AVS footprint boundary. Here, we demonstrate how to detect this boundary with analyses of sediment color intensity. We analyzed 182 sediment profile images taken along three transects leading from approximately 50 m inside to 200 m outside a long-line mussel farm in New Zealand and found that the mean sediment color intensity inside the farm boundary was almost one third lower than that of th...
We investigated the sediment-seawater solute flux at five sites in the polluted Avon-Heathcote Es... more We investigated the sediment-seawater solute flux at five sites in the polluted Avon-Heathcote Estuary, New Zealand, to provide a point of comparison for future studies of the effects of the closure of a major wastewater outfall into the estuary. Sediments collected in winters 2007 and 2008, and summer 2008, ranked consistently in organic matter content. Microelectrode profiling and sediment-core incubations revealed (1) a dominant role of microphytes in regulating solute flux causing significant differences in the dark and light sediment O₂ consumption (R(d), R(l)), total sediment O₂ utilisation (TOU(d), TOU(l)), and inorganic nutrient flux, (2) consistent ranking of sites in solute flux, and (3) a clear solute-flux signature of the wastewater effluent. Sediment near the wastewater outfall exhibited the highest absolute R and TOU(,) the lowest ratio R(l)/R(d,) the highest dark efflux of dissolved reactive phosphorus and ammonium, and the highest dark and light uptake of nitrate+nitrite.
Periodic disturbance of surface sediment is a natural feature of marine environments. Following e... more Periodic disturbance of surface sediment is a natural feature of marine environments. Following exposure to oxygenated seawater, the disturbed sediment oxidises leading to the recovery of its surface chemistry. Despite its importance for the ecology of the sediment-water interface, the dynamics of this recovery is not well known. We studied the effects of disturbance depth and seawater flow speed on the oxidation of estuarine cohesive sediment in a laboratory flume with microelectrodes. We removed surface sediment to 2 depths (5 and 50 mm) and then observed changes in sediment O 2 distribution and consumption over 1 h under conditions of slow and fast flow (3.5 and 7.5 cm s-1). Measurements were repeated 1 d later. The consumption of O 2 in the treated sediments reached a 'quasi stable state' within 7 h (50 mm depth) and 16 h (5 mm depth) characterised by very slow changes due to slow oxidation of reduced solids. Faster flow increased the rate at which sediment from 50 mm depth oxidised but not that of the sediment from 5 mm depth. After 20 to 24 h, sediments disturbed to 50 and 5 mm depths still differed in O 2 distribution and consumption, both from each other and from the pre-treatment sediment. Differences in the response of pore water O 2 distribution to an abrupt increase in flow speed (3.5 to 7.5 cm s-1) were also still evident at this time. Our measurements confirmed the results of previous theoretical analyses in that they indicate that the duration of the recovery of the surface sediment chemistry from disturbance and the chemical properties of the recovering sediment are controlled by the kinetics of solute and solid oxidation. Oxidation of reduced solids in disturbed sediment can result in a characteristic chemical signature at the sediment surface that lasts in the order of at least days.
Nearshore zones experience increased sedimentation due to coastal development and enhanced loads ... more Nearshore zones experience increased sedimentation due to coastal development and enhanced loads of fine terrestrial sediment (hereafter, TS) in river waters. Deposition of TS can alter seabed biogeochemical processes but the effects on benthic ecosystem functioning are unknown. The results of a past experiment with defaunated, intertidal sediment suggest that a decrease in the oxygenation of this sediment by a thin (mm) TS deposit causes substrate rejection (refusal to bury) by post-settlement juvenile recruits of the tellinid bivalve Macomona liliana. We further examined this behaviour, asking if such deposits negatively affect burial when applied to intertidal sediment that is oxygenated by bioturbation (C) or depleted of dead and living organic matter (D). We observed recruits on the surface of four treatments: C, D, and the same sediments to which we added a 1.7-1.9 mm layer of TS (CTS, DTS). The TS deposit decreased the oxygenation and the pH of the underlying intertidal sediment (CTS) confirming previous results, but significantly increased but not decreased the probability of burial, irrespectively of treatment. Juveniles more likely buried into C than into D. The mechanism that caused previously observed substrate rejection by post-settlement juvenile M. liliana remains unclear but our results suggest that contact of the recruits with the TS deposit does not cause substrate rejection. We now hypothesise that conditioning of sediment by bioturbation can mediate negative effects of TS deposits on the recruits' burial behaviour.
O 2 plays a key role in early sedimentary diagenetic processes, but the effect of most macrofauna... more O 2 plays a key role in early sedimentary diagenetic processes, but the effect of most macrofaunal species on the pathways and rates of supply of O 2 into the seabed are not well known. We investigated the effect of the ophiuroid Amphiura filiformis, one of the dominant macrobenthic species on soft bottoms in the northeast Atlantic, at depths of ϳ15-100 m, in a laboratory environment. We determined how the presence of the ophiuroid changed the total O 2 uptake of macrofauna-free sediment by combining measurements from a microcosm approach and an approach that uses microelectrodes and a flushed aquarium. We suggest that natural populations of A. filiformis can account for 80% of the total flux of O 2 into the soft bottom. At least 67% of this portion is due to the diffusion of O 2 across additional sediment-water interfaces excavated by the brittle star.
Kay Vopel1*, Alexis Marshall2, Shelly Brandt2, Adam Hartland3, Charles K. Lee3, S. Craig Cary2, 3... more Kay Vopel1*, Alexis Marshall2, Shelly Brandt2, Adam Hartland3, Charles K. Lee3, S. Craig Cary2, 3 Conrad A. Pilditch2 4 1School of Science, Auckland University of Technology, Private Bag 92006, Auckland, New Zealand 5 2School of Science, University of Waikato, Private Bag 3105, Hamilton, New Zealand 6 3Environmental Research Institute, School of Science, University of Waikato, Private Bag 3105, 7 Hamilton, New Zealand 8 9
We investigated emergence of marine benthic harpacticoid and cyclopoid copepods from subtidal sed... more We investigated emergence of marine benthic harpacticoid and cyclopoid copepods from subtidal sediment into the bottom water. Previous studies that used traps in the field found that copepods emerged from the sediment within 2 h of dusk. We examined emergence in 20-min sampling periods over 13 h from 1200 to 0100 h in a laboratory flume under conditions of constant flow speed. The light intensity was adjusted to field conditions every 20 min. We observed a peak in emergence during the 20-min sampling period after the onset of darkness, greatly increasing the accuracy with which the timing of emergence is known. This result will help to set the stage for studies of emergence cues.
Deep-sea Research Part Ii-topical Studies in Oceanography, 2001
The nematode assemblages of experimentally impacted and adjacent sediments in abyssal depths of t... more The nematode assemblages of experimentally impacted and adjacent sediments in abyssal depths of the eastern equatorial Pacific were investigated 7 years after a physical disturbance. A total of 3048 nematodes belonging to 68 genera and 26 families were identified. The nematode fauna at both disturbed and control sites was dominated by specimens belonging to the genera Acantholaimus, Chromadorita, Thalassomonhystera, Desmoscolex, Halalaimus and Diplopeltula. These genera contribute to about 55% and 50% of total nematode fauna in the disturbed and control sites, respectively. The mean relative abundance of the dominant genus Acantholaimus amounted to about 20%. Generic diversity, evenness and richness at the undisturbed sites do not significantly differ from the corresponding median values at the disturbed sites. Mean k-dominance curves show differences in community structure between treatments. Ordination of square- and fourth-root-transformed family abundances revealed groupings of ...
Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment-sea... more Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment-seawater nitrogen flux, an important driver of pelagic productivity. To investigate how this perturbation affects the fluxes of NO X − (nitrite/nitrate), NH 4 + and O 2 , we incubated estuarine sand and subtidal silt in recirculating seawater with a CO 2-adjusted pH of 8.1 and 7.9. During a 41-day incubation, the seawater kept at pH 8.1 lost 97% of its NO X − content but the seawater kept at pH 7.9 lost only 18%. Excess CO 2 increased benthic photosynthesis. In the silt, this was accompanied by a reversal of the initial NO X − efflux into influx. The estuarine sand sustained its initial NO X − influx but, by the end of the incubation, released more NH 4 + at pH 7.9 than at pH 8.1. We hypothesise that these effects share a common cause; excess CO 2 increased the growth of benthic microalgae and so nutrient competition with ammonia oxidising bacteria (AOB). In the silt, diatoms likely outcompeted AOB for NH 4 + and photosynthesis increased the dark/light fluctuations in the pore water oxygenation inhibiting nitrification and coupled nitrification/denitrification. If this is correct, then excess CO 2 may lead to retention of inorganic nitrogen adding to the pressures of increasing coastal eutrophication. Ocean acidification, a consequence of the absorption of atmospheric carbon dioxide, is expected to accelerate over the upcoming century, altering marine biota and associated ecosystem processes 1-3. Our ability to predict the functioning of the future high-CO 2 ocean, however, is still in its infancy 1,4,5. For the coastal ocean, such prediction is complicated by natural and anthropogenic phenomena rendering the seawater carbonate chemistry variable at timescales from seconds to years (reviewed by Waldbusser & Salisbury 6 , Mostofa et al. 3). Current research thus distinguishes between carbonate weather-the short-term variability in the seawater pH-pCO 2 system-and carbonate climate, the longer-term shift in the baseline pH-pCO 2 system 6. The latter may alter environmental conditions for microorganisms in coastal sediment that drive the remineralisation of organic matter and associated biogeochemical cycles 7. Given that benthic remineralisation provides 30-80% of the inorganic nutrients required by pelagic primary production 8-10 , ocean acidification-driven alterations of benthic nutrient cycles could have implications for coastal ecosystem functioning. The nitrogen cycle may be altered more than any other nutrient cycle in response to CO 2 enrichment (reviewed by Hutchins et al. 5). For example, studies have revealed evidence for CO 2-induced changes in the sediment-seawater inorganic nitrogen flux 11,12 , increased nitrogen fixation due to enhanced growth of diazotrophic cyanobacteria 13-15 , and inhibition of nitrification 7. Other studies, however, found no effects of CO 2 enrichment on benthic nitrification 16 and denitrification 17. Unravelling the mechanisms behind CO 2-induced changes in benthic nitrogen cycling is challenging because the microbial activity that drives nitrogen transformations is modulated by macrobenthic infauna reworking particles and ventilating burrows 11,18-26. In coastal waters where sunlight penetrates to the seabed, another complication exists: excess CO 2 may increase the photosynthesis of benthic microalgae 27,28 altering the activity of nitrogen transforming microbes and associated sediment-seawater inorganic nitrogen flux. Two mechanisms have been proposed; (1) benthic microalgae may outcompete ammonia-oxidizing microorganisms in the uptake of ammonia 29,30 , and (2) enhanced benthic O 2 evolution may inhibit dissimilatory nitrate reduction 29-33. Although
Ecosystem feedback to ocean acidification in a cohesive photosynthetic sediment 2 Ecosystem feedb... more Ecosystem feedback to ocean acidification in a cohesive photosynthetic sediment 2 Ecosystem feedbacks in response to ocean acidification can amplify or diminish the diel pH oscillations that characterize productive coastal waters. We report that benthic microalgae generate such oscillations in the porewater of cohesive sediment and ask how carbonation (acidification) of the overlying seawater alters these in the absence and presence of biogenic calcite. To do so, we placed a 1-mm layer of ground oyster shells (Treatment) or sand (Control) onto intact sediment cores free of large dwelling fauna, and then gradually increased the pCO2 in the seawater above half of the Treatment and Control cores from 472 to 1216 μatm (pH 8.0 to 7.6, CO2:HCO3from 4.8 to 9.6 x 10-4). Vertical porewater [O2] and [H + ] microprofiles measured 16 d later showed that this carbonation had decreased O2 penetration in all cores, indicating a metabolic response. In carbonated seawater: (1) sediment biogeochemical processes added and removed more H + to and from the porewater in darkness and light, respectively, than in ambient seawater increasing the amplitude of the dark-light porewater [H + ] oscillations, and (2) the dissolution of calcite decreased the porewater [H + ] below that in overlying seawater, reversing the dark sediment-seawater H + flux and decreasing the amplitude of diel [H + ] oscillations. This dissolution did not, however, counter the negative effect of carbonation on sediment O2 penetration. We hypothesise that the latter effect and the observed enhanced acidification of the sediment porewater were caused by an ecosystem feedback: a CO2-induced increase in the microbial reoxidation of reduced solutes with O2.
Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment-sea... more Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment-seawater nitrogen flux, an important driver of pelagic productivity. To investigate how this perturbation affects the fluxes of NO (nitrite/nitrate), NH and O, we incubated estuarine sand and subtidal silt in recirculating seawater with a CO-adjusted pH of 8.1 and 7.9. During a 41-day incubation, the seawater kept at pH 8.1 lost 97% of its NO content but the seawater kept at pH 7.9 lost only 18%. Excess CO increased benthic photosynthesis. In the silt, this was accompanied by a reversal of the initial NO efflux into influx. The estuarine sand sustained its initial NO influx but, by the end of the incubation, released more NH at pH 7.9 than at pH 8.1. We hypothesise that these effects share a common cause; excess CO increased the growth of benthic microalgae and so nutrient competition with ammonia oxidising bacteria (AOB). In the silt, diatoms likely outcompeted AOB for NH and photosynthesi...
Plans to exploit an offshore source of iron sand in South Taranaki Bight (STB), New Zealand, caus... more Plans to exploit an offshore source of iron sand in South Taranaki Bight (STB), New Zealand, caused concerns that such exploitation may expose benthic and pelagic biota to elevated trace metal concentrations. We conducted dilute-acid extractions and standard elutriate tests to investigate the potential of this exploitation to (1) create a new seafloor with elevated trace metal content, (2) mobilise trace metals during iron sand extraction and, (3) enrich the returning process seawater, which feeds iron sand through mills, with trace metals. We found that recruits of freshly uncovered sediment may encounter higher-than-natural concentrations of cadmium, nickel and chromium (but not of copper, lead, and zinc) and propose to investigate the bioavailability of these metals. Elutriate test with raw and milled iron sand revealed that, for nickel and copper, dilution of the process seawater may be required to meet the local water quality guideline. We argue that this dilution can be achieved by adjustment of the mass and seawater balance of the offshore extraction process.
Growing numbers and increased stocking of marine mussel farms make reliable techniques for enviro... more Growing numbers and increased stocking of marine mussel farms make reliable techniques for environmental effect assessment a priority. Previously, we showed how the color intensity of soft sediment could be used to estimate its acid volatile sulfide (AVS) content, a product of the anaerobic microbial degradation of organic matter deposits. We then proposed to include assessments of the AVS farm footprint in marine farm monitoring, in particular, to investigate temporal changes in the extent of the seafloor area of elevated sediment AVS content. Such assessment requires accurate detection of the AVS footprint boundary. Here, we demonstrate how to detect this boundary with analyses of sediment color intensity. We analyzed 182 sediment profile images taken along three transects leading from approximately 50 m inside to 200 m outside a long-line mussel farm in New Zealand and found that the mean sediment color intensity inside the farm boundary was almost one third lower than that of th...
We investigated the sediment-seawater solute flux at five sites in the polluted Avon-Heathcote Es... more We investigated the sediment-seawater solute flux at five sites in the polluted Avon-Heathcote Estuary, New Zealand, to provide a point of comparison for future studies of the effects of the closure of a major wastewater outfall into the estuary. Sediments collected in winters 2007 and 2008, and summer 2008, ranked consistently in organic matter content. Microelectrode profiling and sediment-core incubations revealed (1) a dominant role of microphytes in regulating solute flux causing significant differences in the dark and light sediment O₂ consumption (R(d), R(l)), total sediment O₂ utilisation (TOU(d), TOU(l)), and inorganic nutrient flux, (2) consistent ranking of sites in solute flux, and (3) a clear solute-flux signature of the wastewater effluent. Sediment near the wastewater outfall exhibited the highest absolute R and TOU(,) the lowest ratio R(l)/R(d,) the highest dark efflux of dissolved reactive phosphorus and ammonium, and the highest dark and light uptake of nitrate+nitrite.
Periodic disturbance of surface sediment is a natural feature of marine environments. Following e... more Periodic disturbance of surface sediment is a natural feature of marine environments. Following exposure to oxygenated seawater, the disturbed sediment oxidises leading to the recovery of its surface chemistry. Despite its importance for the ecology of the sediment-water interface, the dynamics of this recovery is not well known. We studied the effects of disturbance depth and seawater flow speed on the oxidation of estuarine cohesive sediment in a laboratory flume with microelectrodes. We removed surface sediment to 2 depths (5 and 50 mm) and then observed changes in sediment O 2 distribution and consumption over 1 h under conditions of slow and fast flow (3.5 and 7.5 cm s-1). Measurements were repeated 1 d later. The consumption of O 2 in the treated sediments reached a 'quasi stable state' within 7 h (50 mm depth) and 16 h (5 mm depth) characterised by very slow changes due to slow oxidation of reduced solids. Faster flow increased the rate at which sediment from 50 mm depth oxidised but not that of the sediment from 5 mm depth. After 20 to 24 h, sediments disturbed to 50 and 5 mm depths still differed in O 2 distribution and consumption, both from each other and from the pre-treatment sediment. Differences in the response of pore water O 2 distribution to an abrupt increase in flow speed (3.5 to 7.5 cm s-1) were also still evident at this time. Our measurements confirmed the results of previous theoretical analyses in that they indicate that the duration of the recovery of the surface sediment chemistry from disturbance and the chemical properties of the recovering sediment are controlled by the kinetics of solute and solid oxidation. Oxidation of reduced solids in disturbed sediment can result in a characteristic chemical signature at the sediment surface that lasts in the order of at least days.
Nearshore zones experience increased sedimentation due to coastal development and enhanced loads ... more Nearshore zones experience increased sedimentation due to coastal development and enhanced loads of fine terrestrial sediment (hereafter, TS) in river waters. Deposition of TS can alter seabed biogeochemical processes but the effects on benthic ecosystem functioning are unknown. The results of a past experiment with defaunated, intertidal sediment suggest that a decrease in the oxygenation of this sediment by a thin (mm) TS deposit causes substrate rejection (refusal to bury) by post-settlement juvenile recruits of the tellinid bivalve Macomona liliana. We further examined this behaviour, asking if such deposits negatively affect burial when applied to intertidal sediment that is oxygenated by bioturbation (C) or depleted of dead and living organic matter (D). We observed recruits on the surface of four treatments: C, D, and the same sediments to which we added a 1.7-1.9 mm layer of TS (CTS, DTS). The TS deposit decreased the oxygenation and the pH of the underlying intertidal sediment (CTS) confirming previous results, but significantly increased but not decreased the probability of burial, irrespectively of treatment. Juveniles more likely buried into C than into D. The mechanism that caused previously observed substrate rejection by post-settlement juvenile M. liliana remains unclear but our results suggest that contact of the recruits with the TS deposit does not cause substrate rejection. We now hypothesise that conditioning of sediment by bioturbation can mediate negative effects of TS deposits on the recruits' burial behaviour.
O 2 plays a key role in early sedimentary diagenetic processes, but the effect of most macrofauna... more O 2 plays a key role in early sedimentary diagenetic processes, but the effect of most macrofaunal species on the pathways and rates of supply of O 2 into the seabed are not well known. We investigated the effect of the ophiuroid Amphiura filiformis, one of the dominant macrobenthic species on soft bottoms in the northeast Atlantic, at depths of ϳ15-100 m, in a laboratory environment. We determined how the presence of the ophiuroid changed the total O 2 uptake of macrofauna-free sediment by combining measurements from a microcosm approach and an approach that uses microelectrodes and a flushed aquarium. We suggest that natural populations of A. filiformis can account for 80% of the total flux of O 2 into the soft bottom. At least 67% of this portion is due to the diffusion of O 2 across additional sediment-water interfaces excavated by the brittle star.
Kay Vopel1*, Alexis Marshall2, Shelly Brandt2, Adam Hartland3, Charles K. Lee3, S. Craig Cary2, 3... more Kay Vopel1*, Alexis Marshall2, Shelly Brandt2, Adam Hartland3, Charles K. Lee3, S. Craig Cary2, 3 Conrad A. Pilditch2 4 1School of Science, Auckland University of Technology, Private Bag 92006, Auckland, New Zealand 5 2School of Science, University of Waikato, Private Bag 3105, Hamilton, New Zealand 6 3Environmental Research Institute, School of Science, University of Waikato, Private Bag 3105, 7 Hamilton, New Zealand 8 9
We investigated emergence of marine benthic harpacticoid and cyclopoid copepods from subtidal sed... more We investigated emergence of marine benthic harpacticoid and cyclopoid copepods from subtidal sediment into the bottom water. Previous studies that used traps in the field found that copepods emerged from the sediment within 2 h of dusk. We examined emergence in 20-min sampling periods over 13 h from 1200 to 0100 h in a laboratory flume under conditions of constant flow speed. The light intensity was adjusted to field conditions every 20 min. We observed a peak in emergence during the 20-min sampling period after the onset of darkness, greatly increasing the accuracy with which the timing of emergence is known. This result will help to set the stage for studies of emergence cues.
Deep-sea Research Part Ii-topical Studies in Oceanography, 2001
The nematode assemblages of experimentally impacted and adjacent sediments in abyssal depths of t... more The nematode assemblages of experimentally impacted and adjacent sediments in abyssal depths of the eastern equatorial Pacific were investigated 7 years after a physical disturbance. A total of 3048 nematodes belonging to 68 genera and 26 families were identified. The nematode fauna at both disturbed and control sites was dominated by specimens belonging to the genera Acantholaimus, Chromadorita, Thalassomonhystera, Desmoscolex, Halalaimus and Diplopeltula. These genera contribute to about 55% and 50% of total nematode fauna in the disturbed and control sites, respectively. The mean relative abundance of the dominant genus Acantholaimus amounted to about 20%. Generic diversity, evenness and richness at the undisturbed sites do not significantly differ from the corresponding median values at the disturbed sites. Mean k-dominance curves show differences in community structure between treatments. Ordination of square- and fourth-root-transformed family abundances revealed groupings of ...
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