High Primary Productivity Research Articles

The challenge of estimating kelp production in a turbid marine environment.

Coastal kelp forests produce substantial marine carbon due to high annual net primary production (NPP) rates, but upscaling of NPP estimates over time and space remains difficult. We investigated the impact of variable underwater photosynthetically active radiation (PAR) and photosynthetic parameters on photosynthetic oxygen production of Laminaria hyperborea, the dominant NE-Atlantic kelp species, throughout summer 2014. Collection depth of kelp had no effect on chlorophyll a content, pointing to a high photoacclimation potential of L. hyperborea towards incident light. However, chlorophyll a and photosynthesis versus irradiance parameters differed significantly along the blade gradient when normalized to fresh mass, potentially introducing large uncertainties in NPP upscaling to whole thalli. Therefore, we recommend a normalization to kelp tissue area, which is stable over the blade gradient. Continuous PAR measurements revealed a highly variable underwater light climate at our study site (Helgoland, North Sea) in summer 2014, reflected by PAR attenuation coefficients (Kd ) between 0.28 and 0.87 m-1 . Our data highlight the importance of continuous underwater light measurements or representative average values using a weighted Kd to account for large PAR variability in NPP calculations. Strong winds in August increased turbidity, resulting in a negative carbon balance at depths >3-4m over several weeks, considerably impacting kelp productivity. Estimated daily summer NPP over all four depths was 1.48 ± 0.97 g C · m-2 seafloor · d-1 for the Helgolandic kelp forest, which is in the range of other kelp forests along European coastlines.

Multiple Factors Driving Carbonate System in Subtropical Coral Community Environments along Dapeng Peninsula, South China Sea

Coral reef ecosystems have extremely high primary productivity and play an important role in the marine carbon cycle. However, due to the high carbon metabolism efficiency of coral communities, little is known about the carbon sink–source properties of coral reefs. In November 2022, in situ field investigations coupled with incubation experiments were conducted in typical subtropical coral reef waters, i.e., Yangmeikeng Sea Area (Area I) and Dalu Bay (Area Ⅱ), to explore the dynamics of the carbonate system and its controlling factors. The results revealed that the carbonate parameters had high variability, comprehensively forced by various physical and biochemical processes. Overall, Areas I and Ⅱ were net sinks of atmospheric CO2, with net uptake fluxes of 1.66 ± 0.40 and 0.99 ± 0.08 mmol C m−2 day−1, respectively. The aragonite saturation state (ΩA), 3.04–3.87, was within the range adequate for growth of tropical shallow-water scleractinian corals. Inorganic carbon budget results indicated that photosynthesis and microbial respiration were the main factors affecting the dynamics of carbonate systems in the whole study area. However, focusing on the reef areas, coral metabolism was also a key factor affecting the carbonate system in seawater (especially in Area I) and its contribution accounted for 28.9–153.3% of the microbial respiration. This study highlighted that metabolism of coral communities could significantly affect the seawater carbonate system, which is of great significance in the context of the current process of ocean acidification.

Holocene sedimentary sequences from Nachvak and Saglek Fjords (Northern Labrador) as a record of deglaciation of the Torngat Mountains and Hudson Bay

Constraining the final retreat of the Laurentide Ice Sheet offers the best opportunities to understand the impacts of glacial retreat on landscapes and sedimentary processes, and their relation to oceanography and climate variations in Eastern North America. In Northern Labrador, an area that lacks chronological constraints on terrestrial data, investigating deglacial dynamics is also important as meltwater pulses may affect the deepwater formation that takes place in the Labrador Sea. In this paper, we investigate the deglacial sedimentary sequences from Nachvak and Saglek Fjords located in the Torngat Mountains of Northern Labrador. Sub-bottom profiles reveal that both fjords contain a deglacial sequence thicker than 100 m, including important mass-movement deposits reaching thicknesses of 40 m. These events were possibly triggered by glacio-isostatically induced earthquakes during the Younger Dryas and the Early Holocene. Estimations based on well-dated gravity cores sampled in both fjords suggest a deglaciation before the Younger Dryas for the Nachvak Outer Basin, but only 2000 yr later for the equivalent basin in Saglek Fjord. Such asynchronous retreat is explained by the presence of Saglek Bay acting as a buffer zone against oceanic forcing at the entrance of Saglek Fjord. In the sediment cores, high concentrations of detrital carbonates and an equivalent of the Hudson-Strait red bed are correlated with major deglacial events occurring between 9.2 and 8.1 cal ka BP in the Hudson Bay area. A progressive postglacial transition began around 8.0 cal ka BP with a decrease of detrital carbonate inputs and an increasing influence of North Atlantic waters. This transition ended abruptly with a regional major environmental change around 6.3 cal ka BP after the end of the Laurentide Ice Sheet melting. Magnetic properties reflecting enhanced bottom oxygen consumption reveal a high primary productivity from 6.3 to 3.8 cal ka BP in Saglek and Nachvak main basins, and probably a stronger water stratification. Overall, these results indicate that the deglacial and postglacial sedimentary dynamics of Nachvak and Saglek Fjords was influenced by (1) massive mass-movement deposits possibly generated by earthquakes, (2) sediment export by deglacial processes from both the local and the Hudson Bay areas and (3) the influence of Labrador Sea waters.

Low content of highly reactive iron in sediments from Prydz Bay and the adjacent Southern Ocean: Controlling factors and implications for sedimentary organic carbon preservation

Examining iron (Fe) speciation in marine sediments is critical to understand Fe and carbon biogeochemical cycling in polar regions. In this study, we investigated the speciation of Fe in sediments from Prydz Bay and the adjacent Southern Ocean, and examined the factors controlling Fe speciation and its relationship with total organic carbon (TOC). Our results reveal that unreactive silicate Fe (FeU) is the dominant pool of total Fe (FeT), followed by poorly reactive sheet silicate Fe (FePRS), reducible crystalline Fe oxides (Feox2), easily reducible amorphous/poorly crystalline Fe oxides (Feox1), and magnetite (Femag), with carbonate-associated ferrous Fe (Fecarb) being the smallest pool. The highly reactive Fe (FeHR)/FeT ratios (0.13 ± 0.06) in our study area are among the lowest end-member globally, primarily due to weak bedrock weathering and slow glacier melting. The Feox1/FeT ratios are similar to those in continental shelf and marginal seas containing highly weathered materials, while the Feox2/FeT ratios are significantly lower. This result implicates that low temperature inhibits the aging of iceberg melting-sourced Feox1 potentially, and accordingly the regulation of weathering on the FeHR/FeT ratio is mainly reflected in Feox2/FeT ratio. There are no significant correlations between TOC and FeHR, Fecarb, Feox1 or Feox2 in the research region. Four distinct patterns of TOC/FeHR ratio can be discerned by summarizing the global data set: (a) high TOC/FeHR ratios (> 2.5) are likely the result of high marine primary productivity and low chemically weathered source materials; (b) low TOC/FeHR ratios (< 0.6) are caused by high rates of FeHR inputs and OC remineralization; (c) mid-range TOC/FeHR ratios (0.6 – 2.5) typical of most river particulates and marginal sea sediments indicate the same FeHR and OC sources and/or interactions between each other; (d) both low TOC and FeHR content is the result of low marine primary productivity and weak chemical weathering. Our findings provide new insights into the relationship between FeHR and TOC in polar sediments.

Carbon Biogeochemistry of the Estuaries Adjoining the Indian Sundarbans Mangrove Ecosystem: A Review.

The present study reviewed the carbon-biogeochemistry-related observations concerning CO2 and CH4 dynamics in the estuaries adjoining the Indian Sundarbans mangrove ecosystem. The review focused on the partial pressure of CO2 and CH4 [pCO2(water) and pCH4(water)] and air-water CO2 and CH4 fluxes and their physical, biogeochemical, and hydrological drivers. The riverine-freshwater-rich Hooghly estuary has always exhibited higher CO2 emissions than the marine-water-dominated Sundarbans estuaries. The mangrove sediment porewater and recirculated groundwater were rich in pCO2(water) and pCH4(water), enhancing their load in the adjacent estuaries. Freshwater-seawater admixing, photosynthetically active radiation, primary productivity, and porewater/groundwater input were the principal factors that regulated pCO2(water) and pCH4(water) and their fluxes. Higher chlorophyll-a concentrations, indicating higher primary production, led to the furnishing of more organic substrates that underwent anaerobic degradation to produce CH4 in the water column. The northern Bay of Bengal seawater had a high carbonate buffering capacity that reduced the pCO2(water) and water-to-air CO2 fluxes in the Sundarbans estuaries. Several authors traced the degradation of organic matter to DIC, mainly following the denitrification pathway (and pathways between aerobic respiration and carbonate dissolution). Overall, this review collated the significant findings on the carbon biogeochemistry of Sundarbans estuaries and discussed the areas that require attention in the future.

Riverine and submarine groundwater nutrients fuel high primary production in a tropical bay

River discharge has long been recognized as a major source of nutrients supporting high primary production (PP) in Bandon Bay, while submarine groundwater discharge (SGD) and atmospheric deposition have largely been overlooked. In this study, we evaluated contributions of nutrients via river, SGD and atmospheric deposition, and their roles on PP in the bay. Contribution of nutrients from the three sources during different time of the year was estimated. Nutrients supply from Tapi-Phumduang River accounted for two-fold the amount from SGD while very little supply was from atmospheric deposition. Significant seasonal difference in silicate and dissolved inorganic nitrogen were observed in river water. Dissolved phosphorous in river water was mainly (80 % to 90 %) of DOP in both seasons. For the bay water, DIP in wet season was two-fold higher than in dry season while dissolved organic phosphorus (DOP) was only one half of those measured in dry season. In SGD, dissolved nitrogen was mostly inorganic (with 99 % as NH4+), while dissolved phosphorous was predominantly (DOP). In general, Tapi River is the most important source of nitrogen (NO3−, NO2−, and DON), contributing >70 % of all considered sources, especially in wet season, while SGD is a major source for DSi, NH4+ and phosphorus, contributing 50 % to 90 % of all considered sources. To this end, Tapi River and SGD deliver a large quantity of nutrients and support high PP in the bay (337 to 553 mg-C m−2 day−1).

Monastic Agrifood Products in Greece: Trends and perspectives

In recent years, many monasteries throughout Greece using high quality primary production are able, either via traditional ways and new technology applications to produce outstanding boutique final products for the consumer, usually sold in urban niche conventional, and/or e-markets. The aim of the present original research is to examine the main purchasing trends of monastic agri-food products by a sample of 112 consumers in Northern Greece, as well as to investigate their views on the market prospects of these products. The research findings showed that consumers bought monastic agri-food products on the account of their high quality and because they sought authentic, traditional taste. In addition, the majority of study participants expressed the belief that the demand for monastic agri-food products will increase significantly in the near future.

Modeling carbon export mediated by biofouled microplastics in the Mediterranean Sea

AbstractMarine microplastics can be colonized by biofouling microbial organisms, leading to a decrease in microplastics' buoyancy. The sinking of biofouled microplastics could therefore represent a novel carbon export pathway within the ocean carbon cycle. Here, we model how microplastics are biofouled by diatoms, their consequent vertical motion due to buoyancy changes, and the interactions between particle‐attached diatoms and carbon pools within the water column. We initialize our Lagrangian framework with biogeochemical data from NEMO‐MEDUSA‐2.0 and estimate the amount of organic carbon exported below 100 m depth starting from different surface concentrations of 1‐mm microplastics. We focus on the Mediterranean Sea that is characterized by some of the world's highest microplastics concentrations and is a hotspot for biogeochemical changes induced by rising atmospheric carbon dioxide levels. Our results show that the carbon export caused by sinking biofouled microplastics is proportional to the concentration of microplastics in the sea surface layer, at least at modeled concentrations. We estimate that, while current concentrations of microplastics can modify the natural biological carbon export by < 1%, future concentrations projected under business‐as‐usual pollution scenarios may lead to carbon exports up to 5% larger than the baseline (1998–2012) by 2050. Areas characterized by high primary productivity, that is, the Western and Central Mediterranean, are those where microplastics‐mediated carbon export results to be the highest. While highlighting the potential and quantitatively limited occurrence of this phenomenon in the Mediterranean Sea, our results call for further investigation of a microplastics‐related carbon export pathway in the global ocean.

Dominance of land-derived organic matter in highly productive Bandon Bay, Thailand

Bandon Bay is Thailand's productive area for mariculture of many economically important species including oysters and clams. High primary productivity in this shallow bay leads to organic matter (OM) production in the water column and its export to underlying sediments and adjacent areas. However, the understanding of the source and fate of OM in Bandon Bay is still scarce. To address this knowledge gap, we investigated organic carbon (OC) and total nitrogen (TN) elemental contents, C/N elemental ratios, and stable carbon (δ13C) and nitrogen isotopic (δ15N) compositions in surface sediments, sediment cores, and suspended particulate matter (SPM) collected from Bandon Bay and surrounding river systems during the wet season in 2019. δ13C values in bay sediments indicate a major contribution of from terrigenous sources. During low tide, river-associated high-δ15N input of SPM from freshwater phytoplankton input to the bay was evident. The OM source apportionment was further made using a four-end-member mixing model showing more than 70% of sediment organic matter to be of terrestrial origin (freshwater phytoplankton and land soils) most likely brought to the bay via Tapi-Phumduang River. In addition, tidal cycles, and prevailing circulation in the bay cause mixing of OM in the bay with marine OM from the Gulf of Thailand. All these processes work together to bring about dispersal, dilution, and transformation of OM in Bandon Bay, which maintain high organic content in the sediment and supply nutrients essential for high shellfish production in Bandon Bay.

Factors that shape large‐scale gradients in clonality

AbstractAimMany plant species reproduce clonally. However, ecologists still have much to learn about the factors that shape large‐scale patterns in plant clonal growth and reproduction, especially in the southern hemisphere. We addressed this knowledge gap by quantifying relationships between reproductive mode and a suite of plant characteristics and environmental variables.LocationAustralia.TaxonSpermatophytes.MethodsWe used data for 914,456 species‐site combinations (including 4116 unique species) in Australia to quantify the bivariate relationships between the probability of species having clonal reproduction and four plant characteristics and 16 environmental variables, using phylogenetic logistic regressions. We also compared the relative effects across plant characteristics and environmental variables groups through principal component analysis and phylogenetic logistic regressions.ResultsThe probability of species having clonal reproduction was much more strongly related to plant characteristics than to environmental variables. Short, herbaceous plants and monocots were more likely to have clonal reproduction and were more common in environments with low temperatures, low solar radiation, high moisture availability, high net primary productivity (NPP) and high soil organic carbon and nitrogen contents. Tall, woody plants and eudicots tended to have only sexual reproduction, and were more common in dry and soil impoverished environments.Main conclusionsOur results advance the understanding of the factors that shape large‐scale patterns in plant reproduction strategy. For example, the fact that clonality is more common in shorter, herbaceous species suggests that clonality can be added to the suite of traits that align species on the fast‐slow continuum. The fact that clonal reproduction is more tightly correlated with moisture availability, NPP and soil nutrients than climatic extremes and variations suggests that clonal reproduction may be better understood as a strategy for population expansion in resource abundant sites than as a strategy for reproductive assurance under environmental stress.

Patterns and determinants of plant‐derived lignin phenols in coastal wetlands: Implications for organic C accumulation

Abstract As a major plant‐derived soil organic carbon (SOC) component, lignin phenols are unique biomarkers that reflect biogeochemical characteristics under different vegetation compositions and climatic zones in coastal wetlands. However, the latitudinal patterns of plant‐derived lignin phenols to SOC and their link with the stability and controlling mechanisms remain poorly understood. A total of 156 soil samples from 39 sites along a 5000 km coastal transect, were taken to explore the effects of biological and environmental controls on the patterns of lignin phenols. Lignin phenols had contents ranging from 1.91 to 83.3 mg g−1 OC, and a positive correlation was detected in grass‐dominated salt marsh, but a weakly negative correlation in mangrove. Positive correlations between SOC or lignin content and C/V or S/V (the cinnamyl‐ or syringyl‐to‐vanillyl) ratios were found, while overall negative correlations between SOC or lignin content and (Ad/Al)V or (Ad/Al)S (the acid‐to‐aldehyde of vanillyl or syringyl units) ratios were detected, respectively, which confirmed the validity of these lignin biomarker degradation parameters. Our findings revealed that plant C inputs and monomer ratios directly influenced the capacity of lignin phenols in soils. Lignin content and stabilization was mainly controlled by soil properties (i.e. pH, EC sand/clay). Mean annual temperature (MAT) influenced the patterns of lignin phenols both directly by increasing decomposition and indirectly by changing the vegetation and soil biogeochemistry (i.e. microbial substrate availability). Coastal wetlands are characterized by high primary productivity and C burial rate, yet plant‐derived lignin phenols are not as much as we thought compared to microbial residues C. Precise identification and quantification of the origin, decomposition, and determinants of lignin phenols help us understand their contribution to C sequestration and its response to climate and environmental changes. Read the free Plain Language Summary for this article on the Journal blog.

Dissolved Organic Carbon Dynamics Variability from Ponds Draining Different Landscapes in a Typical Agricultural Watershed

Dissolved organic carbon (DOC) in inland waters (rivers, reservoirs, lakes, and small ponds) plays a significant role in the global carbon cycle and affects global climate change. In addition, DOC is also a vital indicator of the water environment due to its multiple physical, chemical, and ecological roles. Lakes and ponds of small sizes are abundant on a global and regional scale, and a large increase in ponds is expected with global agricultural land expansion. However, the DOC characteristics of ponds in agricultural watersheds are still unclear, posing a challenge to better understanding the carbon cycle of inland waters. In this study, we explored the DOC variability and their influencing factors in ponds draining different landscapes in a typical agricultural watershed to address the issue. The field measurements over a year showed the DOC concentration varied among ponds draining different landscapes. Specifically, the mean DOC concentrations in the natural pond, sewage pond, aquaculture pond, and irrigation pond were (6.17 ± 1.49) mg/L, (12.08 ± 2.92) mg/L, (9.36 ± 2.92) mg/L, and (8.91 ± 2.71) mg/L, respectively. Meanwhile, monthly measurements found the DOC varied across sampling dates. The DOC variability was positively correlated with nutrients, primary production, and precipitation, suggesting anthropogenic loadings, an internal production rate, and hydrological regime that regulated the substantial variability of DOC in these ponds at the watershed scale. Further, large pollutant discharge and high primary production led to peak DOC occurring in the sewage pond. Our results implied that more attention should be paid to ponds in agricultural watersheds to better understand the roles of inland waters in the global carbon cycle.

High functional diversity of avian breeders of the mammoth steppe during the last glacial maximum

The largest continuous ecosystem was presented by the mammoth steppe during the Pleistocene, which exhibited high primary productivity and plant diversities creating a diverse set of habitats. This work is the first investigation where I aimed to analyse the functional diversity of bird species predicted to breed at the Last Glacial Maximum (LGM) within the Eurasian part of the mammoth steppe, in comparison to present-day metrics calculated for the same spatial region. To do so, I performed Species Distribution modelling of the breeding ranges of birds distributed in Eurasia and projected the breeding ranges backward to the LGM. Next, I computed functional diversity metrics with and without phylogenetic control for both LGM and present timescales and analysed relationships among functional diversity metrics calculated for the LGM and modern times.I found that i) although the total number of species of birds at the LGM is far less than during present conditions within the same zone, species richness values are predicted to be similar; ii) the distribution ranges of birds breeding within the mammoth steppe zone are governed by annual mean temperature, temperature seasonality, minimum temperature of the coldest month and the mean temperature of the wettest quarter; iii) with the exception of function richness, all descriptors of functional diversity showed significantly higher values during the LGM than those calculated for the present; iv) the observed correlation between co-occurrence and phylogenetic distance was found to be significant during present timescales but showed non-significant relationships on LGM timescales; v) all descriptors of phylogenetic species diversity differed significantly between present and LGM timescales.

Latitudinal transition of epipelagic mesozooplankton in the northwestern Pacific in winter

The northwestern Pacific (NWP) is a hotspot of marine biodiversity study, and zooplankton is a crucial secondary producer in the marine ecosystem. It is of utmost importance to do extensive study on the distribution of zooplankton community in the NWP. The distribution of epipelagic zooplankton community in the 143–146°E section between the equator and 36°N in winter was examined in this study. The findings indicated that the Kuroshio extension, the North Pacific Subtropical Gyre, the North Equatorial Current and the North Equatorial Countercurrent were the four main ocean currents in the NWP that regulated the latitudinal transition of epipelagic mesozooplankton and split the sample section into four station groups. The key factors influencing zooplankton's geographic distribution were temperature, primary productivity, and current movement. In general, as latitude increased, zooplankton abundance and biomass first decreased and subsequently flourished in the NWP. Diversity indexes and indicator species also revealed the difference across the communities in four station groups. The body length of zooplankton declined gradually from north to south under the combined influence of temperature and primary production, with the minimum in the oligotrophic subtropical zone and a sub-peak in the high primary production area near the equator. Additionally, the abundance of zooplankton was higher in the winter than in the summer due to seasonal fluctuations in the properties of the ocean currents. This study elucidated the control effects of ocean currents on the latitudinal distribution of zooplankton, supplemented records of the geographic distribution and body length characteristics of zooplankton communities in the NWP, and provided the basis for further research on the ecological role of zooplankton communities and the global changes of marine ecosystems.

Using a demographic model to project the long‐term effects of fire management on tree biomass in Australian savannas

AbstractTropical savannas are characterized by high primary productivity and high fire frequency, such that much of the carbon captured by vegetation is rapidly returned to the atmosphere. Hence, there have been suggestions that management‐driven reductions in savanna fire frequency and/or severity could significantly reduce greenhouse gas emissions and sequester carbon in tree biomass. However, a key knowledge gap is the extent to which savanna tree biomass will respond to modest shifts in fire regimes due to plausible, large‐scale management interventions. Here, we: (1) characterize relationships between the frequency and severity of fires and key demographic rates of savanna trees, based on long‐term observations in vegetation monitoring plots across northern Australia; (2) use these relationships to develop a process‐explicit demographic model describing the effects of fire on savanna tree populations; and (3) use the demographic model to address the question: to what extent is it feasible, through the strategic application of prescribed burning, to increase tree biomass in Australian tropical savannas? Our long‐term tree monitoring dataset included observations of 12,344 tagged trees in 236 plots, monitored for between 3 and 24 years. Analysis of this dataset showed that frequent high‐severity fires significantly reduced savanna tree recruitment, survival, and growth. Our demographic model suggested that: (1) despite the negative effects of frequent high‐severity fires on demographic rates, savanna tree biomass appears to be suppressed by only a relatively small amount by contemporary fire regimes, characterized by a mix of low‐ to high‐severity fires; and (2) plausible, management‐driven reductions in the frequency of high‐severity fires are likely to lead to increases in tree biomass of about 11.0 t DM ha−1 (95% CI: −1.2–20.8) over a century. Accounting for this increase in carbon storage could generate significant carbon credits, worth, on average, three times those generated annually by current greenhouse gas (methane and nitrous oxide) abatement projects, and has the potential to significantly increase the economic viability of fire/carbon projects, thereby promoting ecologically sustainable management of tropical savannas in Australia and elsewhere. This growing industry has the potential to bring much‐needed economic activity to savanna landscapes, without compromising important natural and cultural values.

Seasonal constraints on the burial of organic carbon in the eutrophic Lake Taihu

Eutrophication alters the function of lake ecosystems through phytoplankton blooms and is a major contributor to organic carbon (OC) burial in lakes worldwide. Although Lake Taihu is notable for its severe eutrophication yet low OC burial, why cyanobacteria-derived OC is ineffectively buried in the lake is unknown. Because seasonal hydrological and ecological dynamics in eutrophic lacustrine ecosystems would significantly modify the preservation and degradation behaviors of OC, seasonal variations in paired particulate samples from both the water column and surface sediment are critical in evaluating cyanobacteria-derived OC burial. In this study, we present the steroid results of water and sediments collected from Meiliang Bay in Lake Taihu across cyanobacteria-bloom and decay seasons (from May 2018 to June 2019) to investigate constraints on the seasonal burial of autochthonous and allochthonous OC. The results indicate that cyanobacteria contribute a considerable amount of OC to the water body in the cyanobacterial bloom season, while terrestrial OC becomes the main contributor during the cyanobacterial decay season. Although OC degradation occurs throughout the water column, substantially more OC degradation was observed at the water-sediment interface. The extensive degradation of OC in the bloom season eventually reverses the seasonal distribution characteristics of particulate OC in the water column, leading to less accumulation of OC under the background of higher cyanobacteria-derived OC input. The combined effect of OC bioavailability, temperature, oxygen exposure, and more importantly microorganism activities, accounts for much higher OC degradation rates in the bloom season. Similar phenomena were observed in subtropical shallow lakes with high primary productivity, suggesting that eutrophication might have a limited influence on OC burial when compared to other factors related to OC degradation.

Complex pattern of environmental changes and organic matter preservation in the NE Ordos lacustrine depositional system (China) during the T-OAE (Early Jurassic)

The lower Toarcian black shale and mudstone succession of the Anya section in the northeastern Ordos Basin records a climatically controlled evolution of the lacustrine system during the negative carbon isotope excursion (NCIE) of the Toarcian oceanic anoxic event (T-OAE; ca. 183 Ma). In the Anya section, petrography integrated with climate proxies (Sr/Cu and Rb/Sr) and weathering indices (weathering index of Parker, chemical index of weathering and plagioclase index of alteration), suggests that a warm-humid climate with sporadic semihumid-semiarid intervals developed during the early Toarcian and was coincident with strong chemical weathering. Sr/Ba and S/TOC ratios suggest that the Anya section's rocks were generally deposited in freshwater. Four phases (phases A, B, C and D) in lake evolution are distinguished from the variation in petrographical and geochemical proxies providing clues about the drivers of environmental change and organic matter accumulation in the lacustrine basin. Phases A and C have a high preservation of organic matter derived from lake plankton (Type II-III kerogens), were characterized by anoxia, and coincided with high primary productivity. On the contrary, phases B and D indicate a low primary productivity and suboxic-oxic conditions, with a lower organic matter content of predominantly higher land plant origin (Type III kerogen). The accumulation of organic matter was mainly controlled by changes in primary productivity and redox conditions that were tightly linked to the local sedimentary evolution of the Ordos Basin and to global and regional climate. During the early Toarcian NCIE, the accumulation of organic-poor sediment and terrestrial organic matter may have been driven by enhanced seasonality, superimposing on local lake level changes. As a consequence, the peak of the T-OAE carbon cycle perturbation does not coincide with lacustrine black shale deposition and/or peak anoxia in this continental depositional system. This emphasizes the significance of local or regional environmental change on the carbon sequestration within lacustrine systems.

Geochemical characteristics of shales from the first member of Qingshankou Formation in Gulong Sag, Songliao Basin, China: Implication for mechanism of organic matter enrichment

Commercial oil production from the first member of the Qinshankou Formation in the Songliao Basin, China has proven it can be a promising target for shale oil recovery. However, geochemical characteristics and the mechanism of organic matter (OM) enrichment in this layer remain unknown. Herein, a large number of samples collected from the first member were analyzed through a combination of organic and inorganic geochemical methods. Results show, bedding oil shale and laminated shale are prominent facies in this member. Moreover, this member mainly consists of type-I and –II kerogen at highly thermal mature stage, belonging to good to excellent source rock. Overall, this member has been deposited in the semi-humid to humid and warm paleoclimate, fresh to brackish water mass, and dysoxic to anoxic conditions. This member is enriched in P2O5, indicating the high primary productivity. Moreover, lack of relation between P2O5, with Al2O3 and Fe2O3 concentrations, suggests that the contribution of terrigenous detritus influx and the effect of Fe cycle for P enrichment in sediments can be disregarded. The terrigenous detritus influx, rapid sedimentation rate and marine transgression were found to be detrimental to the OM enrichment. Moreover, more serious oxygen deficiency in water mass along with slightly lower sedimentation rate, made the lower part of this member to yield better preservation conditions and weaker dilution effect, which resulted in the formation of OM with better quality and higher abundance. Collectively preservation conditions were found to be significant for the OM enrichment.

Climate fluctuations during the Ordovician-Silurian transition period in South China: Implications for paleoenvironmental evolution and organic matter enrichment

The Ordovician-Silurian (OS) transition witnessed dramatic tectonic, climatic, marine, and biological coevolution, during which organic-rich black shale was widely deposited and is considered an important source rock. However, the potential links between the differential enrichment pattern of organic matter and climate fluctuations and paleoenvironmental evolution during this period are still unclear. In this paper, the Late Ordovician-early Silurian black shale in a JieLong (JL) section in South China was identified by graptolitic fossils, total organic carbon (TOC) content, X-ray diffraction (XRD), scanning electron microscopy (SEM) and geochemical analysis. The results show that the provenances of sedimentary rocks are all granodiorite-like. According to the variations in the TOC content and geochemical indicators, four layers are delineated. Under warm and humid climatic conditions, sea level rise and unstable seasonal upwelling led to Unit 1 organic matter enrichment controlled by high primary productivity, anoxic conditions and effective smectite production. Unit 2 organic matter burial was controlled by cold, arid and oxic environmental conditions, but primary productivity was still relatively high. After the end of the glacial period, warm and humid climatic conditions and rapid transgression were the main factors affecting the burial of organic matter in Unit 3. Under hot and humid climate conditions, higher terrigenous detrital inputs and unfavourable preservation environments, the dilution of organic matter in Unit 4 was accelerated. The corrected chemical index of alteration (CIAcorr) values show that the study area experienced a climate change of alternating cold and warm conditions in response to the climate fluctuation during the glacial-interglacial period. The CIAcorr value is negatively correlated with the TOC content, while the generation of available clay minerals (smectite) in warm and humid climates is usually consistent with the enhanced burial flux of organic matter, supporting the important role of climate fluctuations in the accumulation of organic matter. Finally, a comparison of the data from the present study with geochemical data from different profiles in South China reveals the role of climatic fluctuations during the OS transition in controlling paleoenvironmental evolution and organic matter enrichment, while such a heterogeneous factor is usually associated with global or regional geological events. Our study highlights this differential enrichment mechanism as a combined response of multiple factors and provides important implications for glacial-interglacial organic matter enrichment mechanisms.

Response of fish stocks in Lake Victoria to enforcement of the ban on illegal fishing: Are there lessons for management?

Most small-scale inland fisheries in the Global South prohibit fishing gear with smaller meshes than is legally permitted. Nonetheless, in most instances, this is not strictly enforced. But starting in 2017, Uganda and Tanzania ramped up enforcement on Lake Victoria. We used time series hydro-acoustic data to determine whether the strict enforcement achieved the management goal of increased biomass (t) of commercial species and an increase in the biomass of big Nile perch (>50 cm). The biomass for 2018–2021 (under strict enforcement) was expected to be greater than in 2007–2017 (prior to strict enforcement). The biomass of key species fluctuated annually, but no spatial or temporal differences in biomass associated with strict enforcement were evident. Similarly, the biomass of big Nile perch did not increase. Our findings suggest that mesh sizes may have limited influence on fish biomass dynamics in Lake Victoria, and that high primary productivity of the lake, high turnover rates of fish species, and limited compliance by fishers likely counteract the effects of high fishing effort on biomass and size structure of fish. Therefore, the high cost of strict top-down enforcement and the societal cost of lost lives, jobs, and livelihoods may not be justified.