Potential Organic Matter Sources Research Articles

Determining Balanced Mixture Ratio of Palm Bagasse Compost to Improve Growth and Yield of Soybean

Soybean productivity in Indonesia was greatly affected by low soil fertility due to the excessive use of chemical fertilizers. Applying organic fertilizer or compost such as palm bagasse could be a potential source of organic matter to improve soil fertility and crop productivity. An effective compost should be rich in fiber and high C/N ratio. Therefore, compost is recommended to be mixed with other low C/N ratio materials to accelerate the composting and increase N content. This study was aimed to determine the mixture ratio of palm bagasse compost (PBC) with other materials, such as Azolla, Gliricidia leaves, tofu dreg waste. This study was conducted in Completely Randomized Block Design with two factors. The first factor was type of mixing ingredients such as Azolla, Gliricidia leaves, tofu dreg waste. The second factor was the dose (%) of PBC in combination with Urea (%), namely 0, 25, 50, 75, 100%. Each treatment was repeated in blocks. Results showed that the mixture of PBC with all organic N sources was promising to substitute Urea. Moreover, application of 100% PBC exhibited the highest soybean yield, suggesting that PBC could provide sufficient nutrients for soybean growth. This present study emphasized the potential of soybean production optimization with low dependence on chemical fertilizers, thus highlighting the potency of more sustainable soybean cultivation using organic fertilizer.

PENGARUH KOMPOS DAUN KEMIRI SUNAN (Reutealis trisperma (Blanco) Airy Shaw) TERHADAP KESUBURAN ENTISOL

Leaves of Reutealis trisperma (locally known as kemiri Sunan) are potential sources of organic matter and improve soil fertility, especially by increasing soil nutrient availability. This study aimed to analyze the impact of the application of compost using kemiri Sunan leaves as raw material on soil fertility, such as pH, total N and soil organic C. This study used a completely randomized design with six treatments and four replications. The treatments were without compost (control), compost 4 t ha-1, compost 8 t ha-1, compost 12 t ha-1, compost 16 t ha-1 and compost 20 t ha-1. This study used a PVC pipe with a diameter of 14 cm and a height of 60 cm for the composting process and using polybags for the soil incubation process. The leaves were mixed with EM4, molasses, and water in a ratio of 1:1:50; after mixing, all the ingredients were put into a tube, and observations were made. The soil was then mixed with compost according to the treatment dose of compost 0; 4; 8; 12; 16; 20 t ha-1, then added water until it reached field capacity and then put into a polybag and incubated for 30 days. Observations were made at 0, 15, and 30 days after incubation. The results of this study showed that the application of waste compost of kemiri Sunan leaves had a significantly increased soil pH, total N, and organic C. The best application of kemiri Sunan leaf compost was found at a dose of 20 t ha-1 .

Effect of Microbial Enriched Arecahusk Compost on Growth and Yield Attributes of Maize in Typic Rhodustalf of Southern Transitional Zone of Karnataka

ABSTRACT Currently, the majority of arecahusk waste is disposed of through combustion, leading to the loss of a potential source of organic matter and nutrient source. The value of arecanut waste as an organic material has not been fully realized so far. With this in view, an experiment was designed for arecanut husk composting at Agricultural and Horticultural Research Station, Bhavikere, during the kharif season and followed by a sequential cropping system consisting of maize followed by green gram in two consecutive years (2020–21 and 2021–22). The design includes 10 replicated treatments thrice in a fully randomized complete block design. Results indicated that application of 75% RDN with 25% RDN as Arecahusk Compost (AHC) and entire quantity of recommended dose of Farm Yard Manure (FYM) as AHC (based on N equivalent) increased the growth parameters like plant height (235.89, 265.63 cm), number of leaves (14.57, 16.61), and drymatter (394.67,428.22 g plant−1) over control which received 100% RDN and recommended dose of FYM (7.5 t/ha). Similar results were recorded for the yield attributes like cob length (20.88, 24.03 cm), cob girth (18.51, 19.86 cm), number of grains per row (37.79, 40.40), number of kernels per cob (597.14 and 608.67), root length (21.90 23.40 cm), root biomass (14.33, 15.61 q ha−1), grain yield (93.60, 95.67 q ha−1) and stover yield (110.66, 116.15 q ha−1) in both years. Growth and yield attributes were significantly correlated with grain and stover yields of maize (0.96*** to 1.00***). It was recorded 14.89% grain yield increase over control.

Dominance of autochthonous trophic base in northeast Asian stream food webs pre- and post-monsoon

Spatial and temporal variability in the trophic base of food webs is an inevitable ecological attribute in aquatic ecosystems with the role of aquatic and terrestrial sources varying from system to system. Despite high algal biomass, an apparent increase in terrestrial detritus during the East Asian summer monsoon would be expected to alter the dominant food web base from the pre- to post-monsoon period. The δ13C and δ15N values of common aquatic invertebrates and fish were compared with those of their potential sources of organic matter across the upstream channel and lacustrine habitats during the pre- and post-monsoon periods in the Se-oak Stream system of Korea. The purpose was to identify the variability in trophic structure (niche and diversity) at the community level and to quantify the contribution of terrestrial and aquatic carbon sources to the food web base. The δ13C and δ15N values of the major potential organic matter sources differentiated allochthonous leaf litter and riparian vegetation from autochthonous biofilm and seston, but with no significant spatial and temporal changes. The δ13C values of consumers fell within a narrower range than that of organic matter sources, consistent with the instream biofilm and seston values. However, the consumer δ15N values spanned a broad range, increasing from invertebrates to fish. The resultant niche overlaps of consumers in the isotopic niche space between seasons and locations, their narrower horizontal niche breadths compared to organic matter sources, and the isotope mixing-model estimates indicated that aquatic production was the primary source of organic matter supporting the aquatic food webs. Overall, the results revealed a consistent dominance of autochthonous trophic bases in both lotic and lentic food webs before and after the summer monsoon. Our findings, which highlight the trophic importance of aquatic algal production facilitated by anthropogenic nutrients in this shallow, low-turbidity, and well-illuminated stream food web, may provide insight into ecosystem processes that counteract potential terrestrial-aquatic links to influence food web dynamics based on natural nutrient sources in deep, highly turbid, or shaded stream counterparts.

Fingerprinting macrophyte Blue Carbon by pyrolysis-GC-compound specific isotope analysis (Py-CSIA).

There is a need for tools to determine the origin of organic matter (OM) in Blue Carbon Ecosystems (BCE) and marine sediments to (1) facilitate the implementation of Blue Carbon strategies into carbon accounting and crediting schemes and (2) decipher changes in ecosystem condition over decadal to millennial time scales and thus to understand and predict the stability of BCE in a changing world. Pyrolysis-GC-compound specific isotope analysis (Py-CSIA) is applied for the first time in marine environments and BCE research. We studied Australian mangrove, tidal marsh and seagrass sediments, in addition to potential sources of OM (Avicennia, Posidonia, Zostera, Sarcocornia, Ecklonia and Ulva species and seagrass epiphytes), to identify precursors of different biomacromolecule constituents (lignin, polysaccharides and aliphatic structures). Firstly, the link between bulk δ13C and δ13C reconstructed from compound-specific δ13C showed that the pyrolysis approach allows for the isotopic screening of a representative portion of the OM. Secondly, for all samples, the C isotope fingerprint of the carbohydrate products (plant polysaccharides) was the heaviest (13C enriched), followed by lignin and aliphatic products. The differences in δ13C among macromolecules and the overlap in δ13C among putative sources reflect the limitations of bulk δ13C analyses for deciphering OM provenance. Thirdly, phanerogams specimen had the heaviest carbohydrate and lignin, confirming that seagrass-derived lignocellulose can be traced based on δ13C. Consistent differences for individual compounds were identified between seagrasses and between Avicennia and Sarcocornia using Py-CSIA. Fourth, ecosystem shifts (colonization of seagrass habitats by mangrove) on millenary time scales, hypothesized in previous studies on the basis of bulk δ13C and Py-GC-MS, were confirmed by Py-CSIA. We conclude that Py-CSIA is useful in Blue Carbon research to decipher OM sources in marine sediments, identify ecosystem transitions in palaeoenvironmental records, and to understand the role of different OM compounds in Blue Carbon storage.

Distribution Characteristics, Source Analysis, and Pollution Evaluation of Organic Matter in Surface Sediments of Qingpu District, Yangtze River Delta Integration Demonstration Area

The surface sediments were collected from 25 sampling points in the Qingpu District of the Yangtze River Delta integration demonstration area, and the total organic carbon (TOC), total nitrogen (TN), organic carbon isotope (δ13C), and nitrogen isotope (δ15N) content in the samples were analyzed. The distribution characteristics and potential sources of organic matter in the surface sediments were discussed in detail, and the organic pollution index was also evaluated. The results showed that the ω(TOC) in the surface sediments of 31 sampling points in Qingpu District was 0.21%-3.55%, with an average value of 1.18%; ω(TN) ranged from 0.02% to 0.23%, with an average value of 0.09%. The δ13C ranged from -28.04‰ to -10.80 ‰, with an average of -22.28‰, and the δ15N ranged from 2.28‰ to 11.19‰, with an average of 5.76‰. The TOC content was significantly correlated with the TN content. Source analysis showed that the organic matter in the surface sediments of the study area was mainly affected by soil organic matter, sewage organic matter, and terrestrial plants. The calculation results of the contribution rate based on IsoSource software showed that the relative contribution rate of soil organic matter was relatively high (0.3%-96.8%), and domestic sewage had a certain contribution to the organic matter source of most sampling points. In addition, the selected end-member substances had certain differences in the contribution of organic matter sources in samples of different land use types. The evaluation index of organic pollution in the surface sediments of the study area ranged from 0.006-0.745, with an average value of 0.163, indicating that the organic pollution of the study area was considered lightly polluted. Among them, the pollution of sampling points around the Jinze Reservoir was more serious than that in other areas, indicating that there was a potential risk of eutrophication in this area, which requires certain attention.

Utilization of Tithonia diversifolia and sugarcane leaves to improve soil properties and plant growth on a sandy soil of Malang, East Java

A study on the addition of organic matter of different qualities was carried out to improve plant growth on a degraded sandy soil of Bambang Village, Wajak Malang, East Java. Two potential sources of organic matter in Bambang Village are Tithonia diversifolia and sugarcane leaves. This study aimed at elucidating the changes in some chemical properties of a degraded sandy soil of Malang, East Java, and nutrient uptake and growth of maize plants by applying mixtures of Tithonia diversifolia and sugarcane leaves of different quality. Treatments tested in this study were mixtures of Tithonia diversifolia leaves and sugarcane leaves at various proportions (%w/w), i.e. 100% Tithonia diversifolia leaves (T1), 100% sugarcane leaves (T2), 75% Tithonia diversifolia leaves + 25% sugarcane leaves (T3), 50% Tithonia diversifolia leaves + 50% sugarcane leaves (T4); without organic matters (T6), and control, without organic matter and inorganic fertilizers (T7). The results showed that the application of Tithonia diversifolia and sugarcane leaves affected soil pH, soil exchangeable bases, maize growth, and nutrients uptake. Nutrients taken up by maize plants significantly increased with the addition of Tithonia diversifolia leaves, either alone or in combination with sugarcane leaves. The application of 100% sugarcane leaves did not significantly affect maize growth and nutrient uptake.

Short-Term Effects of Biosolid Application on Two Mediterranean Agricultural Soils and Durum Wheat Yield

This study evaluated the effects of de-inking paper sludge (DPS) and sewage sludge (SS) application on soil properties, and durum wheat growth and yield. A pot experiment was performed on Calcaric cambisol (clCM) and Cromic Luvisol (coLV) soils. Three DPS rates (0, 30, and 60 Mg ha−1) were studied with and without nitrogen fertilizer (280 kg NH4NO3 ha−1). DPS was also mixed with SS at two rates (5 and 10 Mg ha−1) to highlight the benefits of organic nitrogen compared to mineral nitrogen. DPS improved total organic carbon and nitrogen, mineral nitrogen, and soils cation exchange capacity, the 30% rate provided the greatest improvement in both soils. DPS increased grain and root P, K, Ca, and Mg contents in both soils. It also increased wheat straw N, P, Mg, and Ca for the same soil compared to the control. Mixed DPS treatments with nitrogen fertilizer enhanced grain yield by up to 38% and increased root biomass in the studied soils. Thus, DPS is a potential source of organic matter and a liming agent for acid soils when appropriate supplemental fertilizer is provided.

Sources of organic matter in an atypical phytoplankton rich coral ecosystem, Marquesas Islands: composition and properties

The purpose of this work is to characterize several potential sources of organic matter (OM) in the Marquesas Islands, French Polynesia, and to understand how these sources contribute to OM pools. Stable isotope (δ 13 C and δ 15 N) and fatty acid (FA) compositions of OM potential sources (algal turf, benthic macroalgae, detrital terrestrial plants (DTP), phytoplankton) and OM pools (sediment (SOM) and particulate organic matter (POM)) were studied in coastal areas in Nuku Hiva Island. Isotope compositions of marine POM (δ 13 C = − 22.5 ± 0.8 ‰; δ 15 N = 12.1 ± 1.1 ‰) and SOM (δ 13 C = − 19.1 ± 0.9 ‰; δ 15 N = 14.4 ± 0.5 ‰) highlighted that OM sources at the base of the local food web had unusually high δ 15 N values. Potential FA markers of diatoms and/or cyanobacteria (20:5ω3 and 16:1ω7) were found in these two OM pools. In addition, coastal SOM also displayed FA markers of bacteria, macroalgae and terrestrial plants. For marine POM, potential macroalgae FA markers were recorded (18:2ω6 and 16:2ω4). The stable isotope mixing model highlighted the major contribution of phytoplankton to the coastal SOM (62%), followed by benthic macroalgae (32%), whereas marine POM was mainly composed of a mixture of algal turf and phytoplankton in similar averaged proportions (38%) but presenting wide variations. Our results as a whole strongly suggest that pelagic-benthic coupled processes drive the characteristics and properties of OM sources.

Microbial Origin of the Organic Matter Preserved in the Cayo Coco Lagoonal Network, Cuba

The southern part of the tropical Cayo Coco Island (Cuba) hosts a complex, highly evaporative and marine-fed lagoonal network. In the easternmost lagoon of this network, hypersaline conditions favour the development of complex sedimentary microbial ecosystems within the water column at the bottom water-sediment interface and on the shore. Some of these ecosystems are producing microbial mats and biofilms with variable mineralisation rates, depending on their location. Since the mineralisation of these microbial deposits is rare, the sedimentary record does not provide a direct window on the evolution of these ecosystems or their distribution through space and time. However, microbial deposits also produce copious amounts of organic matter, which may be used to decipher any microbial-related origin within the sedimentary record. Microbial mats and biofilms were identified as the potential source of organic material in addition to the surrounding mangrove, soils and suspended particulate matter (SPM). The origin and evolution of the sedimentary organic matter preserved within the lagoonal sediments has been analysed using geochemical parameters such as elemental (TOC, TN and [C/N]atomic ratio) and isotopic (δ13Corg and δ15NTN) signals on four sedimentary cores retrieved from different locations in the lagoon and compared with the geochemical signatures of the potential sources. Despite the high potential for organic matter accumulation in the studied lagoon, the TOC and TN downcore values in sediments that were analysed (i.e., micritic muds and bioclastic sands) remain very low compared to the sediment-water interface. The relative contributions of the different potential sources of organic matter were estimated using [C/N]atomic ratios and δ13Corg values. The δ15NTN signature was discarded as a source signature as it records synsedimentary, early diagenetic, secondary evolution of the nitrogen signal associated with OM remineralisation (i.e., denitrification). Finally, among the microbial deposits, the slime recognised in the permanently submersed zone of the waterbody appears to be the main contributor to the organic matter preserved within the sediments of the lagoon. SPM, mainly composed of microbial-rich particles, also contribute and cannot be ruled out as a source.

Isotopic evidence revealing spatial heterogeneity for source and composition of sedimentary organic matters in Taihu Lake, China

Abstract Tracing the formation processes of sedimentary organic matter (SOM) pools is crucial for understanding the carbon cycling of lake ecosystems, yet the source and composition of SOM, especially their spatial heterogeneity, in large and shallow lakes are still far from clear. In this study, SOM and its potential organic matter (OM) sources, including terrestrial particulate organic matter (POM), algae and aquatic macrophytes, were systematically investigated in Taihu Lake. We highlight the application of the end-member mixing model (EMM) based on Monte Carlo simulations of δ13C and δ15N ratios to more precisely depict the spatial heterogeneity for source and composition of SOM in such a large and shallow lake. The isotopically distinct signatures of SOM well displayed its sources obviously corresponded to the observed ecotypes of algae-type lakeshores, macrophyte-type lakeshore and groove in reed-belt. The results of EMM presented the higher proportion of terrestrial POM (46.8%–55.0%) than algae source (13.8%–23.4%) and macrophytes sources (20.0%–30.0%) in sediments from estuary and open water regions. The relative contribution proportions from three potential OM sources statistically correlated with relative contents of clay, silt and sand in sediments. The hydrodynamic force affected the grain size of sediments and drove the gradient distribution of SOM source contributions. These isotopic evidences revealed that aquatic macrophytes, algae bloom, inflow/outflow rivers and hydrodynamic changes could cause the spatial heterogeneity of SOM source and composition in large and shallow eutrophic lakes.

Enhanced microbial respiration due to carbon sequestration in pruning litter incorporated soil reduced the net carbon dioxide flux from atmosphere to tea ecosystem.

Tea (Camellia sinensis L.) bushes are periodically (at 3-4 year intervals) pruned (cut from top) to maintain vegetative growth stage and constant height. Plant residues (prunings litter) generated after pruning are generally left in the field as a potential source of organic matter in soil. Organic carbon (C) sequestration due to pruning litter incorporation is expected to increase microbial activity in soil. Being an evergreen plant, tea bushes assimilate atmospheric carbon dioxide (CO2 ) throughout the year; however, the relation between decomposition of pruning litters and net CO2 flux for tea plantation have not been studied before. The objective of this experiment was to evaluate the relation between organic C accumulation and microbial respiration in pruning litters incorporated soil and its subsequent effect on the net CO2 flux from the atmosphere to tea plantation. Tea bushes assimilated 1878.2-2371.2 kg CO2 ha-1 from the atmosphere within December to November; however, pruned bushes assimilated 1451.7-1840.8 kg CO2 ha-1 within the same period. Decomposition of pruning litters added organic matter in soil, which was mostly accumulated in larger soil aggregates having 2.0-0.25 mm size. Such organic matter accumulation significantly increased microbial respiration in those aggregates, which in turn increased the overall rate of CO2 emission from soil to the atmosphere. Decomposition of pruning litters leads to emission of 426.5-530.4 kg CO2 ha-1 from soil. Hence, pruned areas recorded relatively lower (16.0-27.4%) net CO2 flux from the atmosphere to tea ecosystem as compared to unpruned tea bushes. © 2019 Society of Chemical Industry.

Evaluating the contributions of different organic matter sources to urban river water during a storm event via optical indices and molecular composition

Dissolved organic matter (DOM) in river water dynamically changes with respect to its major sources during heavy rain events. However, there has been no established tool to estimate the relative contributions of different organic sources to river water DOM. In this study, the evolution in the contributions of ten different organic matter (OM) sources to storm water DOM was explored with a selected urban river, the Geumho River in South Korea, during storm events via an end-member mixing analysis (EMMA) based on fluorescence indices and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The OM source materials included treated effluent, road runoff, groundwater, topsoil, deep soil, leaves, reeds, riparian plants, attached algae, and suspended algae. The EMMA results provided quantitative estimates of the variations in the dominant OM sources with the progress of storms. Treated effluent was the prevailing source at the beginning period of the storm, while topsoil, leaves, riparian plants, and groundwater predominated during and after the peak period. The fluorescence indices-based evaluation was consistent with the statistical comparison of the molecular formulas derived from FT-ICR-MS conducted on the ten potential OM sources and the storm samples. The observed variations in the OM sources agreed with the typical characteristics of urban rivers in connection with anthropogenic inputs and the impact of surrounding impervious surfaces. This study demonstrates the application of intuitive and facile tools in estimating the relative impacts of OM sources in urban watersheds.

Carbon isotopic and biochemical fingerprints of sedimentary organic matter in lower Narmada and Tapi rivers, north-west coast of India

ABSTRACTSources of organic matter (OM) in lower Narmada and Tapi river-estuaries were examined using organic carbon to nitrogen ratio (Corg/N), stable carbon isotope ratio (δ13Corg) and lignin phenol biomarkers. The signature of lower Corg (av. 0.50%) and higher δ13Corg (av. –20.3‰) in Narmada and, higher Corg (av. 0.85%) and lower δ13Corg (av. –22.8‰) in Tapi highlight the difference in OM characteristics of both systems, nevertheless they flow adjacent to each other. The OM in Tapi was predominated by fresh plant tissues, as indicated by higher Λ8 = 1.2–3.2 mg/100 mg Corg, lower Ad/Alv = 0.22–0.46 and lower LPVI = 17–23. The plant OM present in the sediments of Narmada was previously degraded and mixed with soil. The OM contribution from algae was restricted to estuarine stations in both the rivers, which was ∼50% in Narmada and ∼35% in Tapi. The contribution of OM from fresh vascular plant was higher (20% to 63%) in Tapi than Narmada (2% to 35%). This study illustrated the benefits of using lignin phenols along with Corg/N and δ13Corg to identify the potential OM sources in two large river–estuary systems of India, which highlighted the complex interaction of natural and anthropogenic processes acted on the terrestrial OM compositions.

Does trophic level drive organic and metallic contamination in coral reef organisms?

Metallic and organic pollutants constitute a serious threat for coral reef ecosystems, potentially affecting a great number of species interacting within complex trophodynamic processes. Pesticides, PCBs and trace elements were measured on coral reef communities of three Pacific islands (Moorea, Wallis and New Caledonia) in relation with δ15N values, a proxy of trophic level. Several potential sources of organic matter, benthic invertebrates and fish belonging to various trophic strategies were sampled at each island. Wallis and New Caledonia displayed, respectively, the highest concentrations of pesticides and trace elements. In the three islands, most trace element concentrations (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and V) decreased when δ15N was rising (i.e. bioreduction), whereas Hg and Se biomagnified with increasing δ15N values. Only few trace elements in some islands did not show any significant trend in relation with δ15N (i.e., Ag in New Caledonia, Zn in Wallis and As plus Zn in Moorea). PCBs concentrations showed a significant bioreduction in New Caledonia and in Moorea, but a significant biomagnification in Wallis. Aldrin and heptachlor were the only pesticides to show a similar significant bioreduction in the three islands. Other pesticides, such as chlordecone, diazinon, endosulfan I and II, heptachlor-epoxide A and B, lindane and pp′-DDE displayed contrasted patterns (e.g. chlordecone significantly biomagnified in New Caledonia, significantly bioreduced in Wallis and did not displayed any significant trend in Moorea). Finally, for unclear reasons, Moorea displayed only negative significant correlations between δ15N and all pesticides (except pp′-DDT). Our results highlight that trophic level, here assessed through δ15N values, is a good predictor of metallic trace elements biomagnification or bioreduction in coral reef organisms. However, at large spatial scale, trophic level relevance to predict pesticides and PCBs biomagnification or bioreduction should be considered with caution and studied in close relation with local characteristics.

Organic matter sources for fish larvae and juveniles in a marine-estuarine interface (Mar Chiquita lagoon, Argentina)

The aim of this study was to analyze the organic matter (OM) origin in the nearshore and the surf zones adjacent to Mar Chiquita lagoon, in order to determine the importance of allochthonous estuarine detritus and in situ marine phytoplankton as carbon (C) sources for young fishes prior to entering the lagoon. Water samples from both the nearshore and the surf zones were collected for estimation of Chlorophyll a concentration, and δ13C and δ15N values of the particulate organic matter (POM). Isotopic composition of the zooplankton and fish larvae from both zones and fish juveniles from the surf zone were also estimated. The contribution of potential OM sources was quantified by Bayesian stable isotope mixing models (SIAR). SIAR models revealed that the POM composition in the coastal area close to Mar Chiquita lagoon comprised a mix of primary producers (terrestrial and marine). The cordgrass Spartina densiflora that develops in the saltmarshes bounding the lagoon, contributed most to the POM of the surf zone, being important as a C source for zooplankton from the same zone. Towards deeper waters (10–12 m, ~2.5 km offshore) with higher chlorophyll a concentrations, phytoplankton contributed most to the POM. Spartina densiflora was not relevant as a C source for larval and juvenile fishes. However, it was of importance to the group of primary consumers, which apparently sustain other zooplankton organisms that fish fed on. In this sense, the OM derived from S. densiflora and exported to the coastal area contributes to sustaining the prey for young fishes outside Mar Chiquita.

Pathways of organic matter in an estuarine mangrove trophic network assessed by carbon and nitrogen stable isotopes

Carbon and nitrogen stable isotopes were used to describe an estuarine mangrove food web in New Caledonia, SW Pacific. Isotopic values were measured for all components of the ecosystem, from various organic matter (OM) sources to predators. Primary producers showed δ13C values from −32.29‰ (Bruguiera gymnorhiza) to −24.67‰ (mouth particulate organic matter), whereas δ15N values ranged from 1.48‰ (Avicennia marina) to 10.17‰ (Eichomia crassipes). Two potential organic matter sources, i.e. the mangrove species and E. crassipes, appeared not to be directly used by consumers although were indirectly entering the food web through particulate and sedimentary organic matter pools (POM and SOM). Overall, invertebrates showed C-depleted and N-depleted values compared with fish, highlighting their lower trophic level. The highest trophic levels in this estuarine mangrove were represented by carangids (δ15N of 11.24‰ for Caranx sp. and 10.81‰ for Carangoides fulvoguttatus) and gerrids (δ15N of 10.42‰ for Gerres filamentosus). Two main pathways of organic matter were identified from sources of OM to end-members, i.e. from estuarine POM and SOM toward gerrids and from marine POM towards carangids. The food chain comprised three or four trophic levels, depending on the pathway of organic matter. The position of some consumer species within the reconstructed food web might imply that an important source of organic matter was probably missing, i.e. microphytobenthos. Despite an obvious connection, the role of river inputs as potential drivers of mangrove food web dynamics appeared important only during the wet season.

Growth Efficacy of Sorghum and Rice Amended with Dried Versus Composted Aquatic Vegetation

Aquatic vegetation is a potential source of organic matter and nutrients for crop production and soil sustainability. However, its high water content and presence of toxic compounds have been major deterrents for commercial application. This split-pot study evaluated the application of <em>Pistia stratiotes</em> (PS) (water lettuce) and <em>Lyngbya wollei</em> (LW) (filamentous cyanobacteria) to grow rice and sorghum. The aquatic vegetation was applied as dried and composted amendments on sandy (<3% organic matter) and muck (>80% organic matter) soils. A completely randomized split-pot design evaluated the effect of the amendments on root dry weight (RDW), shoot dry weight (SDW), and nutrient content of above ground biomass. The application of dried PS and LW on sandy soil produced larger and heavier sorghum shoots than those grown under composted treatments. Soil type was not a determinant factor of plant nutrient content: total Kjeldahl nitrogen, phosphorus, potassium and silicon. Shoot dry weight of rice grown on sandy soils was significantly greater than grown on muck soils using dried LW and composted LW treatments. The allelopathic effects of PS and LW were more pronounced on sandy soil compared to muck soil, indicating the potential application for using aquatic vegetation as a soil amendment on sandy soil in the future.

Identifying organic matter sources using isotopic ratios in a watershed impacted by intensive agricultural activities in Northeast China

Knowledge about the origin and variation of OM (organic matter) pools in a receiving river might provide a basis for addressing non-point sources of pollution resulting from intensive agricultural activity. In this study, an isotopic approach (δ13C, δ15N and C/N ratios) was used to identify potential OM sources and C and N cycle processes occurring in the Abujiao River watershed located in the Sanjiang Plain. A Bayesian model (stable isotope analysis in R, SIAR) was utilized to apportion the contributions of potential sources. In this watershed, isotopic ratios of δ13C ranged from −30.62‰ to −23.71‰ and from −28.22‰ to −23.98‰ in particulate organic matter (POM) and sedimentary organic matter (SOM), respectively. Slightly lower δ15N values (3.12±4.12‰ in POM; 3.7±2.42% in SOM) and C/N ratios (6.62±5.28 in POM; 10.73±6.58 in SOM) were found in SOM pools. Considerable spatio-temporal variability of the organic carbon and nitrogen isotopic ratios was present in the POM pool, which was controlled by storms and land use. The unusually low δ15N-POM values accompanied by high chlorophyll-a concentrations suggested that an isotopic fractionation effect caused by phytoplankton existed in the POM pool. However, isotopic characteristics indicated that the isotopic fractionation was absent in the SOM pool. SIAR modeling result showed that source contributions differed significantly among different sampling periods. During storms, ”soil OM” was the major source (accounting for 45.50%) in the POM pools. During other periods, effluent detritus and phytoplankton sources were predominant in the downstream region. Compared with POM, almost half of SOM came from terrestrial sources, and the effluent detritus and “soil OM” sources predominated in the SOM pool. This study suggested that assessment of behaviors and sources of OM could lead to the implementation of effective non-point source pollution reduction strategies and management practices for protecting water quality.

Benthic faunal assimilation pathways and depth-related changes in food-web structure across the Canadian Arctic

Climate changes in the Arctic are expected to decrease the currently tight pelagic–benthic coupling, yet large-scale, regional understanding of the origin of food for benthic organisms across both biological productivity and depth gradients is still missing. The organic matter assimilation pathways of benthic organisms, along with food-web structure, were investigated at shelf and slope locations spanning 2000km across the Canadian Arctic using stable carbon and nitrogen isotope analysis. Three potential food sources and over 75 benthic taxa belonging to four feeding guilds were analyzed, but the δ13C end-members for the benthic food-webs could not be clearly discerned. While spatial patterns of δ13C for pelagic particulate organic matter were linked to phytoplankton biomass at the time of sampling, sediment δ13C values reflected the relative composition of terrestrial and marine organic matter. On average, benthic primary consumers were enriched in 13C by 5 and 7‰ compared to the potential organic matter sources sampled in sediment and the water column, respectively. The δ13C discrepancy between identified sources of organic matter and benthic organisms suggests that an uncharacterized food source provided a significant carbon source to these animals. We propose that the 13C enrichment of benthic organisms may be largely caused by the assimilation of ice algae (which were not sampled in this study), particularly in regions of known high ice-algal standing stock such as Barrow Strait and Eclipse Sound. The δ15N values of bottom-water particulate organic matter and of benthic primary consumers increased with depth due to greater degradation of the settling organic material. The δ15N values of secondary consumers did not increase with depth, leading to a decrease of their trophic position compared with shallower regions and likely reflecting an increase in omnivory due to scarcity of prey at depth. This study emphasizes the potential importance of sea-ice algae as a carbon source for benthic communities in the Canadian Arctic and suggests that distinct food-web structures prevail over the shelf and slope.