Production Of New Organic Matter Research Articles

Mitigation of Eutrophication and Hypoxia through Oyster Aquaculture: An Ecosystem Model Evaluation off the Pearl River Estuary.

Shellfish aquaculture has been proposed to abate eutrophication because it can remove nutrients via shellfish filter-feeding. Using a three-dimensional physical-biogeochemical model, we investigate how effective oyster aquaculture can alleviate eutrophication-driven hypoxia off the Pearl River Estuary. Results show that oysters reduce sediment oxygen consumption and thus hypoxia, by reducing both particulate organic matter directly and regenerated nutrients that support new production of organic matter. The hypoxia reduction is largest when oysters are farmed within the upper water of the low-oxygen zone, and the reduction increases with increasing oyster density although oyster growth becomes slower due to food limitation. When oysters are farmed upstream of the hypoxic zone, the farming-induced hypoxia reduction is small and it declines with increasing oyster density because the nutrients released from the farm can increase downstream organic matter production. An oyster farming area of 10 to 200 km2 yields a hypoxic volume reduction of 10% to 78%, equaling the impact of reducing 10% to 60% of river nutrient input. Our results demonstrate that oyster aquaculture can mitigate eutrophication and hypoxia, but its effectiveness depends on the farming location, areal size, and oyster density, and optimal designs must take into account the circulation and biogeochemical characteristics of the specific ecosystem.

New production across the shelf-edge in the northeastern North Sea during the stratified summer period

Abstract New production of organic matter from photosynthesis based on “new” nitrate transported into the illuminated surface layer fuels temperate ecosystems during periods of stratification when surface waters are nutrient limited. Published observations from the northeastern North Sea show a large spatial heterogeneity in vertical nitrate fluxes and suggest shelf edge mixing may be the major source for new production here during the stratified summer season. In the current study, we further investigate these empirical findings with a numerical model, where physical transports and mixing are evaluated against observations of temperature, salinity, nutrients and dissipation of turbulent kinetic energy. The relatively shallow central North Sea is separated from the deep Norwegian trench by a strong shelf edge current. This shelf edge frontal zone is characterized by a vertical separation of the surface and benthic boundary layers by an intermediate layer exhibiting low turbulence. A new nitrate assimilation model, driven by light and nitrate availability, is developed and applied for quantifying the potential for, and distribution of, new production in the area. New production in the frontal zone above the shelf edge is located in a narrow high productive (~100 mg C m−2 day−1) band. This is in qualitative accordance with observations. The model results also suggest, however, that new production of similar magnitude occurs above the deep Norwegian trench, where a shallow nutricline in combination with mesoscale eddy activity leads to increased transport of nitrate to the surface layer. Increased new production along the shelf edge could potentially impact ecosystem structure and may explain the relatively high species richness and fishing activity recorded in this part of the North Sea.

Variations of the Organic Matter Composition in the Sea Surface Microlayer: A Comparison between Open Ocean, Coastal, and Upwelling Sites Off the Peruvian Coast.

The sea surface microlayer (SML) is the thin boundary layer between the ocean and the atmosphere, making it important for air-sea exchange processes. However, little is known about what controls organic matter composition in the SML. In particular, there are only few studies available on the differences of the SML of various oceanic systems. Here, we compared the organic matter and neuston species composition in the SML and the underlying water (ULW) at 11 stations with varying distance from the coast in the Peruvian upwelling regime, a system with high emissions of climate relevant trace gases, such as N2O and CO2. In the open ocean, organic carbon, and amino acids were highly enriched in the SML compared to the ULW. The enrichment decreased at the coastal stations and vanished in the upwelling regime. At the same time, the degradation of organic matter increased from the open ocean to the upwelling stations. This suggests that in the open ocean, upward transport processes or new production of organic matter within the SML are faster than degradation processes. Phytoplankton was generally not enriched in the SML, one group though, the Trichodesmium-like TrL (possibly containing Trichodesmium), were enriched in the open ocean but not in the upwelling region indicating that they find a favorable habitat in the open ocean SML. Our data show that the SML is a distinct habitat; its composition is more similar among different systems than between SML and ULW of a single station. Generally the enrichment of organic matter is assumed to be reduced when encountering low primary production and high wind speeds. However, our study shows the highest enrichments of organic matter in the open ocean which had the lowest primary production and the highest wind speeds.

Modeling organic carbon burial during sea level rise with reference to the Cretaceous

After three decades of research on the correlation between sea level and various proxies, there has been very little quantification of the first‐order influence of sea level change on nutrient inventory, marine productivity, and burial of organic carbon. We present a model aimed at quantifying the burial of organic carbon as a function of sea level rise. The biogeochemical model explicitly considers the mean surface area distribution of the Earth as a function of elevation. Also included is dissolved inorganic phosphate (DIP) liberated from coastal sediments during transgression. We quantify how sea level rise of magnitudes inferred for the mid‐Cretaceous influences the phosphorus cycle and burial of organic carbon. The burial efficiency is greater on the shelf. Therefore, in the model, the larger shelf area under high sea level results in more efficient burial of marine organic carbon for a given DIP concentration and associated new production of organic matter (NP). With a Late Cretaceous model shelf area the residence time of DIP decreases by 60% relative to the present‐day reference. Thus, in the final steady state, DIP and NP in the open ocean are reduced compared to today when the biologically reactive phosphorus (Preac) fluxes to the ocean from land are held constant. The lower new production reduces the oxygen demand for respiration and results in a significant oxygenation of the global ocean. Finally, the global organic carbon burial decreases by 30% relative to today in the model. This decrease results from feedbacks between the flux of organic carbon to the seafloor and the ratio of organic carbon to Preac in buried sediments. In contrast, during sea level rise, coastal erosion may increase the Preac flux to the ocean by up to ∼20% relative to today and cause a temporary increase in DIP concentration in the ocean. The resulting increase in organic carbon burial is equivalent to a carbon isotope event of +0.5 to 1‰. Larger carbon isotope events can be triggered by sea level rise only when the ocean is sufficiently close to anoxia in the oxygen minimum zone just prior to the sea level rise.

Water, salt, and nutrient exchanges in San Francisco Bay

We constructed water, salt, and nutrient budgets for San Francisco Bay and used them to analyze the net biogeochemical performance of the bay. The bay was subdivided into three sectors, North, Central, and South Bay, with the Central Bay serving as a proxy for the oceanic end member. Separate budgets were constructed for the wet (October—March) and dry (April—October) seasons of each year for 6 yr (1990–1995). This period of record contained 2 yr of above normal runoff (1993, 1995) and 4 yr of below average runoff. Effluent from sewage treatment plants accounts for approximately 50% of the nutrient loading to the bay in winter and 80% of the summer loading. Both arms of the bay were apparently net heterotrophic during the winter, with this signal being strongest during the wet winters of 1993 and 1995. We conclude that overall the bay is slightly net autotrophic (production of new organic matter in the bay by plant growth exceeds respiratory demands); however, this varies seasonally (strongest in summer) and is complicated by the possibility of significant abiotic P adsorption in the North Bay.

New vs. export production on the continental shelf

Abstract The uptake of atmospheric CO 2 by the oceans via the biological pump and the sustainability of fish catch are driven by new production of organic matter and its export into deep waters or its consumption by organisms of higher tropic level. The f -ratio based on 15 N measurements of discrete samples for continental shelf waters is around 0.4. However, the system-level constraints imposed by mass balance indicate that this f -ratio may be too high. Specifically, it is more than twice as the value determined on the basis of net export of organic carbon. Such a discrepancy is caused by the fact that, unlike the open-ocean system where remineralized nutrients below the euphotic zone do not return easily, the remineralized nutrients on the shelf reenter the euphotic zone quickly. Since new production based on direct 15 N measurements on the shelf actually utilizes nutrients remineralized on the shelf as well, the value is higher than the net export of organic carbon sustained on external sources of nutrients. It is the net export of carbon, however, that sequesters CO 2 and sustains productivity on the shelf.

Non‐Redfield C:N ratio of transparent exopolymeric particles in the northwestern Mediterranean Sea

The stoichiometric model of Redfield, which describes the elemental composition of marine organic matter, is generally used to link the production of new organic matter to the uptake of nitrate. The Redfield C:N molar ratio of 6.6 is a well‐established value for particulate organic matter produced in surface waters. Yet recent studies have shown that the inorganic C:N uptake ratio during nitrate‐limiting conditions is >14. This non‐Redfield behavior during the production of new organic matter suggests that a large standing stock of organic matter, rich in carbon, should accumulate in the euphotic zone from the spring bloom to late summer. This hypothetical pool of carbon‐rich organic matter and the pool of transparent exopolymeric particles (TEP) exhibit similar seasonal distributions, which suggests that TEP may indeed be this carbon‐rich pool. For this scheme to work, TEP should have a high C:N ratio. TEP distribution from an open‐ocean site in the northwestern Mediterranean Sea (DYFAMED) was monitored, and TEP C:N ratio was measured from TEP produced in the laboratory by bubbling dissolved organic matter collected in the field. We found that the TEP pool increases during the summer season and that the C:N ratio of TEP produced from naturally occurring dissolved organic matter, is well in excess of the Redfield ratio with an overall average C:N molar ratio of ~20. As a result, the production of TEP could be the main pathway of carbon overconsumption required of oligotrophic, nitratelimiting waters, and, thus, TEP may represent an important intermediary pool in the ocean carbon cycle.

The upwelling of nutrients in the central Skagerrak

Measurements of inorganic nutrients during four expeditions to the Skagerrak, within the SKAGEX programme in 1990 and 1991, form the basis for estimation of the magnitude of potential new primary production caused by upwelling of nutrients in the central part of Skagerrak. Calculations have been made using available transport and upwelling data given in the literature together with the concentrations of nitrogenous nutrients (nitrite, nitrate and ammonia), phosphate and silicate in the lower part of the pycnocline in the upwelling area. The potential new production of organic matter due to upwelling is estimated at 6.15 × 10 6 t C year −1 based on a vegetative period of 8 months. This corresponds to 190 gC m −2 year −1 if distributed over the entire Skagerrak area. A possible contribution to diatom production from the upwelling of silicate is estimated to be 2.09 × 10 6 t C year −1, which corresponds to 64 gC m −2 year −1.

Degradation of Organic Substances in Reservoirs

Due to the retention of water in an impoundment, the degradation of easily decomposable organic substances expressed as BOD (“self- purification”) is higher in a reservoir compared to a similar stretch of flowing river. For the same reason, the production of new organic matter by phytoplankton (PP) is also enhanced after impoundment. Data on reservoirs with theoretical retention time (RT) in the range of 1 - 535 days showed that PP reached 9 - 99% of the total input (TI) expressed as BOD (TI = PP + BOD load by inflows). The share of PP increases with increasing RT, decreases with increasing mean depth and depends on the quality of inflows. During 10 years' period, the relation of BOD and PP to bacterial and algal respiration has been examined in a temperate, dimictic, canyon-shaped reservoir. Total budget showed that BOD decrease fluctuated between 70 to 88% of TI, irrespective of the increasing PP during the whole period.

The production of dissolved organic matter in the sea, as related to the primary gross production of organic matter

An attempt is made to establish the relation between the mean annual primary gross production and the production of dissolved organic matter in the sea. An unexpectedly high proportion was found to exist between the formation of dissolved organic substances and the production of new organic matter by photosynthesis. This adds an argument, based on data, to the existing reasons for being careful in the use of the word primary gross production of fresh organic matter, whether this should mean fixation of CO 2 in particulate organic matter or in the dissolved stage.