Primary Organic Sources Research Articles

Meiobenthos as food for farmed shrimps in the earthen ponds: Implications for sustainable feeding

Shrimp farming in earthen pond is one of the largest seafood growing industries among coastal mariculture, but it has faced environmental issues in recent years, e.g. overloading of supplementary feed cause deterioration of pond environments. In order to assess the impact of pond shrimp farming on the benthic environment, we investigated the changes in environmental variables and meiobenthic community structure during January to August in the earthen ponds rearing Marsupenaeus japonicus and Litopenaeus vannamei. Water and sediment samples were taken in January (before aquaculture), May (early stage) and August (late stage). We found sedimentary redox potential showed values below −150 mV in all ponds in the early and late rearing stages, indicating overall reduced and anoxic conditions. Sedimentary bulk organic matter (total nitrogen and organic carbon) accumulated along with the feeding addition during the rearing period. We found meiobenthic community structure to change over different rearing stages mainly because of an increase in nematode densities that was associated with shrimp farming activity in the studied ponds. We also investigated the functional roles of pond biota and supplementary feed by studying the benthic food web in these ponds by means of natural stable isotope ratios of carbon and nitrogen and fatty acid biomarkers in the early (May) and late (August) rearing stages. Pond biota (i.e. microalgae and meiobenthos) contributed abundantly to the diets of the two shrimp species. In the early stage, meiobenthos shared similar diets with shrimps (with both feeding on primary organic sources) and they could thus potentially compete for resources. At late rearing stages, meiobenthos represented however a functional link between primary producers and shrimps, serving as nutritional food sources for shrimp and providing them high amounts of polyunsaturated fatty acids (PUFAs). We found that the supplementary feed was not substantially consumed by the two shrimp species, which might pose an overfeeding threat to deteriorate the pond environment.

Primary and secondary organic aerosols in summer 2016 in Beijing

Abstract. To improve air quality, the Beijing government has employed several air pollution control measures since the 2008 Olympics. In order to investigate organic aerosol sources after the implementation of these measures, ambient fine particulate matter was collected at a regional site in Changping (CP) and an urban site at the Peking University Atmosphere Environment Monitoring Station (PKUERS) during the “Photochemical Smog in China” field campaign in summer 2016. Chemical mass balance (CMB) modeling and the tracer yield method were used to apportion primary and secondary organic sources. Our results showed that the particle concentration decreased significantly during the last few years. The apportioned primary and secondary sources explained 62.8 ± 18.3 and 80.9 ± 27.2 % of the measured OC at CP and PKUERS, respectively. Vehicular emissions served as the dominant source. Except for gasoline engine emissions, the contributions of all the other primary sources decreased. In addition, the anthropogenic SOC, i.e., toluene SOC, also decreased, implying that deducting primary emissions can reduce anthropogenic SOA. In contrast to the SOA from other regions in the world where biogenic SOA was dominant, anthropogenic SOA was the major contributor to SOA, implying that deducting anthropogenic VOC emissions is an efficient way to reduce SOA in Beijing. Back-trajectory cluster analysis results showed that high mass concentrations of OC were observed when the air mass was from the south. However, the contributions of different primary organic sources were similar, suggesting regional particle pollution. The ozone concentration and temperature correlated well with the SOA concentration. Different correlations between day and night samples suggested different SOA formation pathways. Significant enhancement of SOA with increasing particle water content and acidity was observed in our study, suggesting that aqueous-phase acid-catalyzed reactions may be the important SOA formation mechanism in summer in Beijing.

Food web of a subtropical tidal flat, Atlantic Southwestern: Temporal and spatial variability of the primary organic sources

Trophodynamic parameters have been used as input data for trophic models and are used as indicators to support ecosystem management decisions. To understand the ecosystems' trophic structure and functioning, it is important to identify the major primary carbon sources within a food web. This study aimed to investigate the spatial and temporal variability in isotopic composition of the basal sources of the food web of the Araçá Bay (23°49′S; 45°24′W) ecosystem. This site is a sheltered tidal flat and presents a sharp seasonal change in water temperature and salinity. Samples of 15 basal sources were analysed for δ13C (n = 187) and δ15N (n = 180) values and also for the C:N ratio, in January–March (austral summer) and June–July (austral winter) 2013, in the continental, intertidal (mangrove patches and soft and rocky bottoms) and sublittoral regions. The isotope values and C:N ratios were, in general, in the range of those available in previously published studies. C3 and C4 plants, green macroalgae and surface sediment organic matter (SSOM) did not present significant changes in the δ13C and δ15N values with time. For suspended particulate matter (SPM), microphytobenthos (MPB) and turf-forming algae, δ13C values were higher in the summer than in the winter; also in the summer, red macroalgae showed higher δ15N values. Spatial variability was investigated for SPM, SSOM and MPB. δ13C values were significantly higher for SSOM and MPB in the intertidal region than in the sublittoral but for SPM there was no difference among regions. Values of δ15N were higher for MPB in the intertidal region than in the sublittoral, and were higher for SPM in the sublittoral region than in the intertidal and continental regions. The δ13C associated to C:N values of SSOM indicated a coupling of the marine sublittoral region and the land organic matter of an adjacent island and the SPM δ15N variability pointed out a continental land-sea connection. Some mechanisms could explain the isotopic temporal and spatial shifts and sources of organic C in the study area: the seasonality of hydrodynamics and of phytoplankton size structures and biomass; the steady low concentration of nitrate and the episodic ammonia inputs; terrestrial runoff. Our results can contribute to the construction and understanding of a trophic model of the Araçá Bay ecosystem, and also for its management, considering the seasonal hydrodynamics, the coupling of marine sublittoral region in the São Sebastião channel and terrestrial organic matter from São Sebastião Island, as well as the continental land-sea connection. We suggest a monitoring program based on SPM, bottom detritus and Ulva fasciata, important primary organic sources for the Araçá Bay food web.

Isotopic analysis of wetland development in the American Southwest

The analysis of stable isotope and elemental fractions of organic material collected from San Bernardino Ciénega was used to understand the history of vegetation composition and climate change within this desert wetland. A 4000-yr record of sediment buildup, based on four 14C measurements, provides unique opportunities for the study of environmental conditions within an arid landscape and documents climate shifts from drier to wetter conditions in the late Holocene. δ13C, δ15N, and C:N values were measured from a 3.8 m deep sedimentary section to understand the dynamics of vegetation and hydrology in desert wetlands. Through this section we observe δ 13C and C:N values indicating a shift in the dominant source of organic matter within the section: prior to 850 cal. yr BP (below 60 cm), aquatic vascular plants and occasionally terrestrial vegetation were the primary organic sources, whereas freshwater algae were the dominant organic matter source above this level. These values indicate that while conditions remained arid at this locality, the amount of standing water on the ciénega has increased over time. These results document both climate change and vegetation evolution on the ecotone of the Sonoran and Chihuahuan deserts and demonstrate how the study of local sediment accumulation in ciénegas can provide critical information on changing conditions within arid environments.

δ 13C, δ 15N, carbon, nitrogen and phosphorus as indicators of plant ecophysiology and organic matter pathways in Everglades deep slough, Florida, USA

Historically, the Florida Everglades was characterized by a corrugated landscape of shorter hydroperiod, elevated sawgrass ( Cladium jamaicense) ridges and longer hydroperiod, deep water slough communities. Drainage and compartmentalization of the Everglades have fundamentally altered this pattern, and sawgrass ridge communities have expanded at the expense of deep water slough communities throughout much of the landscape. In this study we provide a simple isotopic and nutrient characterization of major components of the slough ecosystem to elucidate physiological and nutrient differences among species and to suggest pathways for organic matter decomposition that contribute to peat development in deep water sloughs. We examined carbon (C) and nitrogen (N) isotopes and C, N and phosphorus (P) concentrations of the floating-leaved macrophytes Nymphaea odorata and Nymphoides aquatica, the emergent macrophyte Eleocharis elongata, and the submerged species Utricularia foliosa and Utricularia purpurea, as well as soil and flocculent material from the southern Water Conservation Area 3-A. Flocculent material and soils had the highest N content (4.5 ± 0.2%) and U. foliosa and N. odorata had the highest P content (0.13 ± 0.01% to 0.12 ± 0.01%). The range for δ 15N average ± SE values was 5.81 ± 0.29‰ ( U. foliosa) to −1.84 ± 0.63‰ ( N. odorata), while the range for δ 13C values was −23.83 ± 0.12‰ ( N. odorata) to −29.28 ± 0.34‰ ( U. purpurea). Differences of up to 10‰ in C isotopic values of U. foliosa and N. odorata suggest fundamental physiological differences between these species. Along a degradation continuum, enrichment of 13C and 15N and extent of decomposition was negatively related to phosphorus concentrations. A two end-member 13C mixing model suggested that Utricularia species were the primary organic source for flocculent materials, whereas organic matter derived from root decomposition of N. odorata contributed to the progressively enriched δ 13C values found with depth in soils. These results illustrate the fundamentally important roles of Nymphaea and Utricularia species in ecosystem dynamics of deep water sloughs.

Accumulation of atmospheric and sedimentary PCBs and toxaphene in a Lake Michigan food web.

Seston, sediment, settling organic matter, and food web members were collected from Grand Traverse Bay, Lake Michigan, between April 1997 and September 1998 to examine PCB and toxaphene biomagnification. Stable isotopes of nitrogen and carbon were analyzed in samples and used to establish trophic structure of the food web and to determine the importance of atmospheric versus sedimentary sources in delivering PCBs to the food web. Nitrogen isotopes were confounded by multiple variables in this system, particularly seasonal variation, and did not display a simple pattern of enrichment among trophic levels. However, delta13C displayed little seasonal variation and was positively correlated with PCB concentrations among food web members (r2 = 0.69). Plots of delta13C vs PCBs separate food web members into three distinct groupings comprised of invertebrates, primary forage fish, and predatory fish. Stable isotope values of the primary organic sources indicate that the atmosphere, and not the sediment, is the most likely source of PCBs to the food web of Lake Michigan. Additionally, we suggest that seston may be important in delivering PCBs to pelagic food web members and species that receive a majority of their nutrition through pelagic sources. In contrast, settling particles are implicated in delivering PCBs to benthic organisms and Mysis relicta.

Effect of sulfate on anaerobic processes fed with dual substrates

Anaerobic reactors were operated in a semi-batch mode and fed with the dual substrates glucose (G) plus acetic acid (Ac) as primary organic sources to study the effect of sulfate on COD oxidation. With glucose, COD removal by methane formation was seriously inhibited, resulting in COD accumulation in the reactor. Although acetic acid can be consumed by some sulfate-reducing species, it was not a major substrate for sulfate reduction, but was largely responsible for methane formation in the anaerobic mixed culture used in this study. With dual substrates, extreme inhibition of methanogenesis did not occur as did with glucose alone. Instead, methanogens were found to work in harmony with acid formers as well as sulfate reducers to oxidise COD. Interestingly, from 12-hour monitoring, increased G/Ac COD ratios decreased COD removal rates as well as biogas production, but resulted in higher sulfate reduction. This suggests that there should be an optimal feed G/Ac COD ratio, for which removal of both organics could be maximised.

Effect of sulfate on anaerobic processes fed with dual substrates

Anaerobic reactors were operated in a semi-batch mode and fed with the dual substrates glucose (G) plus acetic acid (Ac) as primary organic sources to study the effect of sulfate on COD oxidation. With glucose, COD removal by methane formation was seriously inhibited, resulting in COD accumulation in the reactor. Although acetic acid can be consumed by some sulfate-reducing species, it was not a major substrate for sulfate reduction, but was largely responsible for methane formation in the anaerobic mixed culture used in this study. With dual substrates, extreme inhibition of methanogenesis did not occur as did with glucose alone. Instead, methanogens were found to work in harmony with acid formers as well as sulfate reducers to oxidise COD. Interestingly, from 12-hour monitoring, increased G/Ac COD ratios decreased COD removal rates as well as biogas production, but resulted in higher sulfate reduction. This suggests that there should be an optimal feed G/Ac COD ratio, for which removal of both organics could be maximised.