Export Of Particulate Organic Matter Research Articles

High resolution profiles of vertical particulate organic matter export off Cape Blanc, Mauritania: Degradation processes and ballasting effects

Vertical carbon fluxes between the surface and 2500 m depth were estimated from in situ profiles of particle size distributions and abundances me/asured off Cape Blanc (Mauritania) related to deep ocean sediment traps. Vertical mass fluxes off Cape Blanc were significantly higher than recent global estimates in the open ocean. The aggregates off Cape Blanc contained high amounts of ballast material due to the presence of coccoliths and fine-grained dust from the Sahara desert, leading to a dominance of small and fast-settling aggregates. The largest changes in vertical fluxes were observed in the surface waters (<250 m), and, thus, showing this site to be the most important zone for aggregate formation and degradation. The degradation length scale ( L), i.e. the fractional degradation of aggregates per meter settled, was estimated from vertical fluxes derived from the particle size distribution through the water column. This was compared with fractional remineralization rate of aggregates per meter settled derived from direct ship-board measurements of sinking velocity and small-scale O 2 fluxes to aggregates measured by micro-sensors. Microbial respiration by attached bacteria alone could not explain the degradation of organic matter in the upper ocean. Instead, flux feeding from zooplankton organisms was indicated as the dominant degradation process of aggregated carbon in the surface ocean. Below the surface ocean, microbes became more important for the degradation as zooplankton was rare at these depths.

Nutrient supply to anticyclonic meso-scale eddies off western Australia estimated with artificial tracers released in a circulation model

The phytoplankton distribution off western Australia in the period from April to October is unique in that high biomass is generally associated with anticyclonic eddies and not with cyclonic eddies. As the western Australian region is oligotrophic this anomalous feature must be related to differing nutrient supply pathways to the surface mixed layer of cyclonic and anticyclonic eddies. A suite of modelled abiotic tracers suggests that cyclonic eddies are predominantly supplied by diapycnal processes that remain relatively weak until June–July, when they rapidly increase because of deepening surface mixed layers, which start to tap into the nutrient-replete waters below the euphotic zone. To the contrary, we find that anticyclonic eddies are predominantly supplied by injection of shelf waters, which carry elevated levels of inorganic nutrients and biomass. These injections start with the formation of the eddies in April–May, continue well into the austral winter and reach as far as several hundred kilometers offshore. The diapycnal supply of nutrients is suppressed in anticyclonic eddies since the injection of warm, low-salinity shelf waters delays the erosion of the density gradient at the base of the mixed layer. Our results are consistent with the observed seasonal cycles of chlorophyll a and observation of particulate organic matter export out of the surface mixed layer of an anticyclonic eddy in the region.

Trophic Transfers from Seagrass Meadows Subsidize Diverse Marine and Terrestrial Consumers

In many coastal locations, seagrass meadows are part of a greater seascape that includes both marine and terrestrial elements, each linked to the other via the foraging patterns of consumers (both predators and herbivores), and the passive drift of seagrass propagules, leaves, roots and rhizomes, and seagrass-associated macroalgal detritus. With seagrasses declining in many regions, the linkages between seagrass meadows and other habitats are being altered and diminished. Thus, it is timely to summarize what is known about the prevalence and magnitude of cross-habitat exchanges of seagrass-derived energy and materials, and to increase awareness of the importance of seagrasses to adjacent and even distant habitats. To do so we examined the literature on the extent and importance of exchanges of biomass between seagrass meadows and other habitats, both in the form of exported seagrass biomass as well as transfers of animal biomass via migration. Data were most abundant for Caribbean coral reefs and Australian beaches, and organisms for which there were quantitative estimates included Caribbean fishes and North American migratory waterfowl. Overall, data from the studies we reviewed clearly showed that seagrass ecosystems provide a large subsidy to both near and distant locations through the export of particulate organic matter and living plant and animal biomass. The consequences of continuing seagrass decline thus extend far beyond the areas where seagrasses grow.

Suspended sediments and organic matter in mountain headwaters of the Amazon River: Results from a 1-year time series study in the central Peruvian Andes

Few studies have examined the dynamics of sediments and suspended organic matter and their export from headwater basins in the Andes Mountains to the Amazon River, despite the fact that the Andes are the primary source of sediments to the lower Amazon basin. We measured river discharge as well as the concentration, δ 15N, δ 13C, %N, and %OC of coarse and fine suspended sediments (CSS and FSS) in the Chorobamba River, located in the central Andean Amazon of Peru. Samples were taken at least weekly over an entire year (July 2004–July 2005), with additional sampling during storms. Concentrations of particulate organic matter (POM) were generally low in the study river, with concentrations increasing by up to several orders of magnitude during episodic rain events. Because both overall flow volumes and POM concentrations increased under stormflow conditions, the export of POM was enhanced multiplicatively during these events. We estimated that a minimum of 80% of annual suspended sediment transfer occurred during only about 10 days of the year, also accounting for 74% of particulate organic carbon and 64% of particulate organic nitrogen transport. Significant differences occurred between seasons (wet and dry) for δ 13C of coarse and fine POM in the Chorobamba River, reflecting seasonal changes in organic matter sources. The time series data indicate that this Andean river exports approximately equal amounts of fine and coarse POM to the lower Amazon. The observation that the vast majority of sediments and associated OM exported from Andean rivers is mobilized during short, infrequent storm events and landslides has important implications for our understanding of Amazon geochemistry, especially in the face of incipient global change.

Changes of oceanographic characteristics and the state of pollution in the Izmit bay following the earthquake of 1999

The Izmit Bay is an elongated semi-enclosed bay in the Marmara Sea. It is being increasingly polluted by both domestic and industrial waste discharge since 1970’s. A monitoring program was conducted between 1999-2000 to document the state of pollution in the bay. This includes the effect of Marmara (Izmit) earthquake (magnitude 7.4) that occurred in August 1999. A stable two-layer ecosystem exists in the bay throughout the year due to continuous inflows of the saltier Mediterranean and brackish Black Sea waters to the Marmara basin. Therefore, the principal biochemical characteristics of the bay are governed by the two-layer flow system over the basin. Dissolved oxygen (DO) is generally at a saturated levels in the surface layer which is 10 to 15 m thick, but it is depleted to 60–70 µM in the lower layer, exhibiting a steep gradient in the sharp halocline. When the earthquake occurred, great loads of industrial wastes were released into the bay surface waters, which enhanced primary production in the upper layer and thus large export of particulate organic matter to lower layer and eventually to the bottom. Accordingly, DO was consumed and anoxic condition was established even in the upper layer/halocline interface, the halocline and bottom waters of the eastern and central bay. In this period, concurrent increases were observed in phosphate and ammonia contents at the halocline and in deep waters whilst the nitrate was almost consumed via denitrification processes in the anoxic water. Recently, the industrial C, N and P loads increased by as much as 8 fold within five years (1995–2000) whilst domestic inputs increased by 50%. Total organic matter discharged to the bay increased more than double within the last 15 years. Besides, most factories in the region release toxic wastes into the bay after only partial treatment.

Model complexity and performance: How far can we simplify?

Handling model complexity and reliability is a key area of research today. While complex models containing sufficient detail have become possible due to increased computing power, they often lead to too much uncertainty. On the other hand, very simple models often crudely oversimplify the real ecosystem and can not be used for management purposes. Starting from a complex and validated 1D pelagic ecosystem model of the Ligurian Sea (NW Mediterranean Sea), we derived simplified aggregated models in which either the unbalanced algal growth, the functional group diversity or the explicit description of the microbial loop was sacrificed. To overcome the problem of data availability with adequate spatial and temporal resolution, the outputs of the complex model are used as the baseline of perfect knowledge to calibrate the simplified models. Objective criteria of model performance were used to compare the simplified models’ results to the complex model output and to the available data at the DYFAMED station in the central Ligurian Sea. We show that even the simplest (NPZD) model is able to represent the global ecosystem features described by the complex model (e.g. primary and secondary productions, particulate organic matter export flux, etc.). However, a certain degree of sophistication in the formulation of some biogeochemical processes is required to produce realistic behaviors (e.g. the phytoplankton competition, the potential carbon or nitrogen limitation of the zooplankton ingestion, the model trophic closure, etc.). In general, a 9 state-variable model that has the functional group diversity removed, but which retains the bacterial loop and the unbalanced algal growth, performs best.

234Th, 210Pb, 210Po and stable Pb in the central equatorial Pacific: Tracers for particle cycling

Samples were collected during the 1992 US JGOFS EqPac Survey I and II cruises from 12°N to 12°S at 140°W in the central equatorial Pacific for water column profiles of dissolved, particulate and total 234Th, 210Pb and 210Po and total acid soluble stable Pb and sediment trap fluxes of 234Th, 210Pb and 210Po. Survey I occurred in February/March with moderate El Nino conditions while Survey II was conducted in September/October when there was a well developed cold-tongue. 234Th, 210Pb and 210Po are all particle reactive yet they partition differently between dissolved and particulate phases. Fractionation factors (the ratios of the distribution coefficients) show that the selectivity for suspended and sediment trap particles follows Th>Po>Pb. Scavenging residence times ( τ) for 234Th, 210Pb and 210Po ranged from 25 to 100 d, 3 to 8 years and 100 to 500 d, respectively. These particle reactive tracers have very different distributions in the water column, which reflect differences in their sources and sinks. The deficiency of 234Th relative to 238U was fairly uniformly distributed meridionally, though deficiencies were higher during Survey II when there was higher new production. Excess 210Pb relative to 226Ra was very asymmetrical with much higher excess values north of the equator. The distributions were similar for Surveys I and II. The deficiency of 210Po relative to 210Pb had a symmetrical distribution about the equator for both Survey I and II but the deficiencies were larger during Survey I when upwelling was smaller. Stable Pb was generally higher at the surface than at 250 m and there was no meridional trend from 12°N to 12°S. A mass balance for 210Pb was used to determine the atmospheric input of 210Pb. The average values for Surveys I and II were 0.12 and 0.32 dpm cm −2 year −1, respectively. There was no general increase in atmospheric input of 210Pb north of the equator but there was a strong maximum at 2–3°N during Survey I coincident with the location of the intertropical convergence zone (ITCZ), suggesting a large role for wet deposition. A mass balance for stable Pb was used to determine the atmospheric input of stable Pb. Results ranged from 110 to 140 pmol cm −2 year −1. This flux was low in the southern hemisphere and increased steadily north of the equator. We evaluated use of 210Po as a tracer for export of particulate organic matter during Survey I. Organic carbon and 210Po were highly correlated in suspended matter and sediment trap samples. Average values of organic carbon fluxes determined from the deficiencies of 210Po times the orgC/ 210Po ratio agreed well with those determined from the deficiencies of 234Th times the organic carbon/ 234Th ratio and 15N-new production, but had a much larger variability because of the more variable advection corrections.

Offshore export versus in situ fractionated mineralization: a 1-D model of the fate of the primary production of the Rías Baixas (Galicia, NW Spain)

A linked hydrodynamic mineralization model is described and used to evaluate offshelf fluxes and fractionated mineralization of particulate phytogenic materials in the coastal upwelling system of the Rías Baixas (NW Spain), under three different typical situations of the upwelling season. The simulations made indicate that the intensity of upwelling controls: (a) net community production (NCP); (b) particulate organic matter (POM) accumulation; (c) in situ mineralization; and (d) matter export in the ‘Rías Baixas.’ Under strong upwelling conditions, there is an important horizontal offshelf flux, having only a small mineralization effect on NCP; if weak upwelling conditions are simulated, POM export is dramatically reduced and in situ mineralization is significantly enhanced; finally, under average upwelling conditions, the offshelf export of POM is about one third of the POM accumulation inside the domain, evidencing its importance in the productivity enhancement of near-shore areas. According to our sensitivity tests, the net vertical velocity (water velocity plus sinking velocity) has a critical role in the C/N/P stoichiometry of POM.

Seasonal Patterns of Bacterial Abundance and Production in the Mississippi River Plume and Their Importance for the Fate of Enhanced Primary Production

Bacterial abundance and leucine incorporation were measured in the Mississippi/Atchafalaya River plume area during May 1992 and July 1993. Both parameters were highest at intermediate salinities during both season. The peak of bacterial leucine incorporation (∼2.5 nM h−1) and abundance was located at higher salinities in May 1992 than in July 1993. Leucine incorporation rates in surface waters decreased with increasing westward distance from the plume, whereas rates increased below the pycnocline with increasing westward distance. The high rates of bacterial activity in stratified bottom waters could potentially deplete oxygen within 3 to 50 days. The mean values for depth-integrated bacterial production were higher in May 1992 (787 mg C m−2 d−1) than in July 1993 (644 mg C m−2 d−1). The integrated values for bacterial production indicate that a variable proportion of the primary production is consumed by bacteria during spring and summer. Comparisons to the vertical export of POM and zooplankton grazing suggest that zooplankton grazing determines the amount of organic material available for bacterial mineralization in deeper layers. Depth-integrated gross bacterial production rates were highest in May 1992 when vertical export of particulate organic matter (POM) was also the greatest. The response of heterotrophic bacteria to increased organic matter input in the plume area during spring indicates that the microbes play a crucial role in the development of hypoxic conditions on the Louisiana shelf during early summer.

Regulation of vertical export of particulate organic matter from the euphotic zone by planktonic heterotrophs in eutrophicated aquatic environments

Different scenarios of remineralization response by planktonic heterotrophs on increasing primary production are presented. The consequences of these response patterns for the vertical export of particulate organic matter from the euphotic zone and productivity indexes are discussed. Reference is made to existing data and algorithms regarding primary production and vertical export of carbon from the euphotic zone. The response patterns of planktonic heterotrophs to increasing primary production most likely to be found in eutrophicated aquatic environments are indicated. The transport of particulate organic matter to depth in limnic as well as marine environments, as a fraction of a given rate of phytoplankton production, seems to depend on the structure and function of the prevailing planktonic food webs. It is suggested that herbivore control of suspended biomass along gradients of increasing nutrient supply results in decreasing carbon supply to bottom water and sediments. Carnivory probably reverses this trend, giving rise to increased carbon export. This conclusion has crucial consequences for investigating pelagic-benthic coupling, currently also a priority in eutrophication studies. Zooplankton orientated programmes will be a necessary component of future investigations of eutrophication in aquatic environments.

Long-term studies of the influence of invertebrate manipulations and drought on particulate organic matter export from headwater streams

Long-term studies of the influence of invertebrate manipulations and drought on particulate organic matter export from headwater streams

Particulate organic matter fluxes in a Tuamotu atoll lagoon (French Polynesia)

The standing stock and chemical composition of suspended particles (< 35 pm) were monitored in the lagoon of Tikehau Atoll from 1983 to 1987 and in surrounding oceanic waters (upper 250 m) during 4 cruises. Trapping rate of particulate material was measured between 1986 and 1987 and net export of particulate organic matter (POM) was roughly estimated using monthly average lagoon POM concentration and monthly average flow of water measured in the passage and the reef-flat spillways. Results showed that deep chlorophyll maxima in oceanic waters could reach 0.24 mg m-3 and were observed between 100 and 200 m even when ATP, POC, PON and POP concentrations were higher in the upper 100 m. POM concentration was homogeneous in the lagoon but varied considerably with time especially following 2 hurricanes in 1983. POM concentration was 30 to 40% higher in samples taken close to the bottom than in the water column. An oceanic station near the atoll was strongly influenced by the lagoonal discharge but POC export from the lagoon to the ocean represents only 6% of phytoplankton production. The POM content of Tikehau lagoon lies within the range recorded for coral reef areas and is made up of suspended particles 50 % of which are smaller than 5 pm. Their sedimentation (350 mg C m-' d-l) represents 80 'YO of phytoplankton production.

Still-water sinking velocity of fecal material from the pelagic tunicate Dolioletta gegenbauri

Results of recent models suggest that fecal pellet production by pelagic tunicates should have a major impact on the relative magnitude of export of particulate organic matter from the upper mixed layer of the ocean. However, little is known of the sinking velocities of feces from small salps and doliolids living in continental shelf waters This study was designed to determine the s inhng velocity of fecal pellets from Dolioletta gegenbauri under natural and amended food conditions, and to examine whether sinking behavior is best described by the Stokes or inertial formulations of the force balance equation. Still-water sinking velocity of pellets was determined in the laboratory at 20°C and 36.0 %S in a glass cylinder, and ranged from 59 to 405 m d-l Most of the feces produced by specimens fed only naturally occurring particles did not sink. About 70 % of the total variance of the logarithm of sinhng velocity of the pellets produced by specimens fed the amended diet was explained by a linear regression against the logarithm of pellet volume. These pellets sank more slowly than was expected based on sinking velocities of the pellets of copepods, euphausiids and salps. Also, the rate of increase of sinking velocity with increasing pellet size (which was a linear function of diameter) was lower than predicted by the Stokes equation (i.e. where sinking velocity of spherical particles diam.2), indicating that the pellets fell in an intermediate zone between the Stokes and inertial forms of the force balance equation.

Particulate Organic Matter Export from Three Headwater Streams: Discrete versus Continuous Measurements

Particulate organic matter (POM) export from three small headwater streams of the southern Appalachian Mountains was estimated using continuous and discrete (grab) measurement methods for 2 yr. Total annual POM export estimated from continuous measurements was always greater (28–68 kg ash-free dry mass (AFDM)) than estimates (8–44 kg AFDM) made from discrete measurements (i.e. POM concentration × total discharge). Continuous export samples were collected using a weir and gaging flume connected to a Coshocton proportional sampler designed to deliver 0.6% of discharge into a series of three settling barrels. The settling barrels removed a consistent proportion of POM (85–87%). The proportion of stream flow sampled by the Coshocton samplers was constant for each of the samplers (range 0.53–0.6%). The constant extraction efficiencies and proportional sampling of discharge allowed for the calculation of total export independent of discharge measurements (i.e. total export = amount in barrels ÷ extraction efficiency ÷ Coshocton percentage). The inability of the discrete method to adequately sample storm and bedload transport accounts for the underestimates of total annual export. This underestimation has important implications for studies which use discrete measurements to estimate POM export.

Tidal export of particulate organic matter from a Northern Australian mangrove system

Particulate carbon and nitrogen exports from a north Queensland mangrove system are estimated. Mangrove litter, flushed by tidal action at a rate of 10 kg C ha −1 day −1 , represents the major component of organic matter export. The net exchange of tidal-borne micro-particulate matter is difficult to estimate precisely. However, the net export rate attributable to this component is approximately 1·5 kg C ha −1 day −1 The nature of the microparticulate matter is described with particular reference to the variation of total organic carbon, adenosine triphosphate (ATP) and chlorophyll during a tidal cycle.