Biochemical Composition Of Organic Matter Research Articles

Exoenzymatic activity and organic matter composition in sediments of the Northern Adriatic Sea: response to a river plume.

Exoenzymatic activities (aminopeptidase and b-glucosidase) and organic matter composition were investigated in June 1996 and February 1997 in the sediment of two areas of the Adriatic Sea differently influenced by the Po river. Protein, carbohydrate, and lipid concentrations were comparable to those reported in most productive systems. Sediment chlorophyll a and biopolymeric carbon concentrations in June were twice as high as in February, but highest exoenzymatic activities and organic matter turnover rates were observed in February (with aminopeptidase activities 10 times higher than in June). The accumulation of organic matter and lower protein and carbohydrate turnover rates observed in June were the result of a different biochemical composition of organic matter in the two sampling periods. In June, organic matter was characterized by a more refractory composition. The consequent reduction of available organic substrate was associated with a decrease in the exoenzymatic substrate affinity. Lower organic matter turnover rates were also observed in deeper sediment layers. In February, the freshwater plume was almost completely confined to the northern area, whereas in June it was extended to the southern area. The results suggest that river inputs influence the biochemical composition and distribution of the sediment organic matter and exoenzymatic activities in coastal marine sediments.

Can flooded organic matter from sediments predict mercury concentrations in zooplankton of a perturbed lake?

Mercury (Hg) and the composition of organic matter (OM) in sediments and large zooplankton (>190 μm) have been analysed in a perturbed lake (Lake 154) in northern Québec, Canada. We investigated whether methylmercury concentrations ([MeHg]) in flooded sediments can predict [MeHg] in zooplankton. [MeHg] at the uppermost sediment layers located immediately downstream of an inundated system (LA-40) are 10 times higher than at other sediment stations. Zooplankton organisms sampled downstream of LA-40 contain higher [MeHg] (183±50 ng g −1 dry wt.) than those of neighbouring natural lakes (66±37 ng g −1 dry wt.). OM in sediment and zooplankton samples has been characterised applying atomic carbon/nitrogen ratios (C/N) and stable carbon isotopic ratios (δ 13C). While C/N ratios in zooplankton from Lake 154 (5.6±0.4) do not differ from samples of natural lakes (5.7±0.1), δ 13C signatures are more depleted at stations close to the discharge of LA-40 (−33±0.4‰) with respect to zooplankton from unperturbed lakes (−30.6±0.7‰). Results of this tracer study suggest that the biochemical composition of OM in flooded sediments did not modify the biochemical composition of zooplankton and can therefore not predict [MeHg] in zooplankton.

Benthic Response to Mucilaginous Aggregates in the Northern Adriatic Sea: Biochemical Indicators of Eutrophication

In summer 1997, gelatinous aggregates appeared in the Adriatic Sea, covering large areas of the northern basin. This study deals with the comparison between the biochemical composition of the sedimentary organic matter in summer, 1996 (when no aggregates appeared), and in summer, 1997 (during the appearance of aggregates). the biochemical composition of organic matter in surface sediments (determined in terms of proteins, carbohydrates, lipids, phytopigments and nucleic acids) has been investigated in two areas along the coast of the NW-Adriatic Sea in order to characterize benthic processes during aggregate deposition on the sea floor. During mucilage accumulation, a significant increase of biochemical compounds was observed, and chlorophyll-a and carbohydrate concentrations doubled their concentrations. in contrast, protein concentrations decreased, so that overall biopolymeric carbon content (expressed as the sum of lipid, protein and carbohydrate carbon equivalents) did not display significant differences between sampling periods (1579.3 in June, 1996 1678.8 μgCg−1 and June, 1997). the protein to carbohydrate ratio decreased from 4.9 in June, 1996 to 1.8 in June, 1997. Mucilage production in June, 1997, modified significantly the biochemical composition of the sedimentary OM, thus affecting the potential availability of OM to benthic consumers. We hypothesise that the production of highly refractory composition of the sedimentary OM during mucilage accumulation might have an important biogeochemical implications.

A three-year time series of elemental and biochemical composition of organic matter in subtidal sandy sediments of the Ligurian Sea (northwestern Mediterranean)

Variations in organic matter composition and microphytobenthic biomass were examined in the surface sandy sediments at a water depth of 10 m in the Gulf of Marconi (NW Mediterranean Sea) over a three year period. Seasonal changes in elemental (organic C and total N) and biochemical (lipids, proteins, carbohydrates) composition of sediment organic matter as well as Chla were assessed in order to provide information about the origin and fate of sedimentary organic matter, the contribution of microphytobenthic biomass, seasonal and interannual variations of food quantity and quality, and factors related to food availability. Data obtained in this three-year study revealed that organic matter determined with a muffle furnace is clearly an overestimate of the organic content of the sediment and is thus of little significance for benthic ecologists studying community dynamics in relation to food availability. Labile organic matter, utilized to estimate the food potentially available for benthic consumers, accounted for only a small percentage (on average less than 10%) of total organic C. The highest labile fraction was observed in spring, whereas minima were recorded in winter. Analysis of elemental and biochemical composition of organic matter showed an inverse relationship between amount of organic matter and its potential availability to consumers; small quantities of high-quality organic matter were replaced by large quantities of refractory material. The labile portion was mostly microphytobenthic (65% of the labile carbon). Protein: carbohydrate ratios were low and confirmed the role of proteins as a potentially limiting factor for consumers. Significant differences in nutritional quality of the sediment organic matter were observed from year to year, changes due to the increase in specific labile compound content.

Labile organic matter and microbial biomasses in deep-sea sediments (Eastern Mediterranean Sea)

The distribution and the biochemical composition of organic matter were analysed in surface sediments (0–15 cm) of 22 continental and bathyal stations (110–2401 m; Ionian and Aegean Seas). Variations of labile organic matter (LOM), total organic matter (TOM), bacterial density and biomass were related to the benthic bacterial populations and to the environmental conditions. TOM was significantly correlated with water depth, but not with LOM, which was mostly composed of carbohydrates (89.6) followed by proteins and lipids (5.4 and 5.0.%). LOM ranged between 1.5 adn 2.7 mg g −1 sediment dry weight, declining in concentration from the sediment surface of 15 cm depth. Bacterial counts ranged betweem 0.16 and 9.42 × 10 8 cells g t-1 sediment dry weight. Bacterial density and biomasses in surface sediments (0–1 cm) were significantly correlated with carbohydrates and DNA concentrations. Although the overlying waters are oligotrophic and low concentrations of TOM are present, the relatively high percentage of LOM and bacterial density suggest that organic matter in deep-sea sediments of the Eastern Mediterranean Sea is not totally depleted of nutritional value.