Sediment Variables Research Articles

Control of hydrogen concentrations by microbial sulfate reduction in two contrasting anoxic coastal sediments

IntroductionMolecular hydrogen is produced by the fermentation of organic matter and consumed by organisms including hydrogenotrophic methanogens and sulfate reducers in anoxic marine sediment. The thermodynamic feasibility of these metabolisms depends strongly on organic matter reactivity and hydrogen concentrations; low organic matter reactivity and high hydrogen concentrations can inhibit fermentation so when organic matter is poor, fermenters might form syntrophies with methanogens and/or sulfate reducers who alleviate thermodynamic stress by keeping hydrogen concentrations low and tightly controlled. However, it is unclear how these metabolisms effect porewater hydrogen concentrations in natural marine sediments of different organic matter reactivities.MethodsWe measured aqueous concentrations of hydrogen, sulfate, methane, dissolved inorganic carbon, and sulfide with high-depth-resolution and 16S rRNA gene assays in sediment cores with low carbon reactivity in White Oak River (WOR) estuary, North Carolina, and those with high carbon reactivity in Cape Lookout Bight (CLB), North Carolina. We calculated the Gibbs energies of sulfate reduction and hydrogenotrophic methanogenesis.ResultsHydrogen concentrations were significantly higher in the sulfate reduction zone at CLB than WOR (mean: 0.716 vs. 0.437 nM H2) with highly contrasting hydrogen profiles. At WOR, hydrogen was extremely low and invariant (range: 0.41–0.52 nM H2) in the upper 15 cm. Deeper than 15 cm, hydrogen became more variable (range: 0.312–2.56 nM H2) and increased until methane production began at ~30 cm. At CLB, hydrogen was highly variable in the upper 15 cm (range: 0.08–2.18 nM H2). Ratios of inorganic carbon production to sulfate consumption show AOM drives sulfate reduction in WOR while degradation of organics drive sulfate reduction in CLB.DiscussionWe conclude more reactive organic matter increases hydrogen concentrations and their variability in anoxic marine sediments. In our AOM-dominated site, WOR, sulfate reducers have tight control on hydrogen via consortia with fermenters which leads to the lower observed variance due to interspecies hydrogen transfer. After sulfate depletion, hydrogen accumulates and becomes variable, supporting methanogenesis. This suggests that CLB’s more reactive organic matter allows fermentation to occur without tight metabolic coupling of fermenters to sulfate reducers, resulting in high and variable porewater hydrogen concentrations that prevent AOM from occurring through reverse hydrogenotrophic methanogenesis.

Methods for Quantifying Interactions Between Groundwater and Surface Water

Driven by the need for integrated management of groundwater (GW) and surface water (SW), quantification of GW–SW interactions and associated contaminant transport has become increasingly important. This is due to their substantial impact on water quantity and quality. In this review, we provide an overview of the methods developed over the past several decades to investigate GW–SW interactions. These methods include geophysical, hydrometric, and tracer techniques, as well as various modeling approaches. Different methods reveal valuable information on GW–SW interactions at different scales with their respective advantages and limitations. Interpreting data from these techniques can be challenging due to factors like scale effects, heterogeneous hydrogeological conditions, sediment variability, and complex spatiotemporal connections between GW and SW. To facilitate the selection of appropriate methods for specific sites, we discuss the strengths, weaknesses, and challenges of each technique, and we offer perspectives on knowledge gaps in the current science.

Precipitation variability and environmental change across late Quaternary glacial-interglacial cycles in lowland Central America: Insights from Lake Petén Itzá (Guatemala) sediments

Lowland Central America, a biodiversity hotspot in the northern Neotropics, is a region where the climate is influenced by the location and expansion-contraction of the Intertropical Convergence Zone (ITCZ) on seasonal to millennial timescales. Paleo-records from the Caribbean Sea and the eastern equatorial and subtropical Pacific Ocean illustrate the response of regional precipitation to fluctuations in global temperature, driven by glacial-interglacial cyclicity over the past 500 kyr. Here, we present a paleoclimate and paleoenvironment record from Lake Petén Itzá, lowland Guatemala, which spans the last ∼413 kyr. Sediment in the lake recorded lacustrine and terrestrial ecosystem responses to large-scale climate variability. Precipitation patterns during MIS11-9 (∼413-304 ka BP) align with the latitudinal position of the ITCZ, with superimposed effects from the strength of the Caribbean Low-Level Jet (CLLJ). A sediment hiatus, likely attributable to mass removal processes in the lake's shallower areas, spans the period from MIS8 (starting at 304 ka BP) to the end of MIS6 (at 149 ka BP). MIS6 was characterized by humid conditions, perhaps ascribable to a more southerly extension of cold fronts and intensification of the CLLJ. During MIS5, pronounced fluctuations among all sediment variables, accompanied by an abrupt decline in precipitation, may correspond with cold events inferred from North Atlantic Ocean sediment cores. Although discontinuous, the Lake Petén Itzá sediment record provides a window into late Quaternary climate and environmental change in lowland Central America.

Geotechnical Characterization of the Magdalena River Subsoil in Magangué, Colombia: A Study Using CPTu and SPT Tests

This study employs Cone Penetration Tests (CPTu) and Standard Penetration Tests (SPT) to analyze the geotechnical properties of the Magdalena River’s riverbed and banks. While these methods are standard in soil characterization, this research innovatively combines CPTu’s continuous profiling with SPT’s localized sampling to develop a nuanced stratigraphic model of the subsurface. This integrated approach provides a comprehensive view of the soil conditions, which is crucial for understanding sediment variability and stability along the riverbanks. The findings from this methodological integration enhance our ability to predict soil behavior under dynamic riverine conditions, offering valuable insights for erosion control and sustainable river management. The study underscores the practical benefits of synergizing traditional testing methods to address geotechnical challenges in river environments.

Early Pleistocene Orbital‐Scale Variability in Australian Northwest Shelf Sediments

AbstractPaleoclimate proxy records from regions sensitive to humidity/aridity extremes provide crucial insights into the natural forcing mechanisms underlying long‐term climate variability in broader regions. One such area is Northwest Australia, where the Australian monsoon impacts its northernmost fringes, which are bordered by the Great Sandy Desert inland. Marine sediments from the Australian Northwest Shelf record fluvial run‐off and eolian dust input during the wet and dry seasons, respectively. The location is therefore ideal for investigating long‐term variability in the Australian monsoon and Northwest Australian dust flux over orbital timescales. However, there are few continuous, high‐resolution paleoclimate records from this region spanning the early Pleistocene, when strong ice‐climate feedbacks of the late Pleistocene did not yet dominate global climate. Here, we present geochemical and environmental magnetic proxy records that reveal %CaCO3 and dust‐flux variability between 2.9 and 1.6 million years (Myr) ago from International Ocean Discovery Program Expedition 356 Site U1464 on the Australian Northwest Shelf. We establish a new, orbitally‐tuned chronology for Site U1464, primarily based on ∼400 thousand year (kyr) eccentricity cyclicity in %CaCO3, and observe strong obliquity variability (41 and 54 kyr periodicities) but almost no precession signal in the dust‐flux records. We propose that the 41 kyr cycle in Northwest Australian dust flux could be a linear response to East Asian winter monsoon intensity and/or the summer inter‐tropical insolation gradient (SITIG), whereas the 54 kyr cyclicity might be a non‐linear response to obliquity amplitude modulation via the SITIG effect on the cross‐equatorial atmospheric circulations.

Observing changes of fish community in a semi-arid subtropical coastal lagoon subject to ecological conservation

El Soldado is a semi-arid subtropical coastal lagoon subject to ecological conservation in the Gulf of California, where we reviewed the changes in the fish community structure before (1972; 1978–79; 1990–92) and after (cycle 1, 2018–2019; cycle 2, 2019–2020) the decree as a protected area, and we determined spatio-temporal changes between two consecutive annual cycles. We conducted monthly fish sampling cycles 1 and 2 with a small trawl net at three sites, where water and sediment variables were recorded, and drift macroalgae biomass was estimated. Results showed 99 fish species have been recorded in previous studies, and our study added 11 species. The fish assemblage (2018–2020) comprised 34 marine species and nine of them were dominant in both cycles. In general, higher fish abundance, richness, and diversity were observed in the cycle 1. Spatial changes, in both cycles, showed higher fish abundance, richness, and diversity in the innermost area of the lagoon, characterized by silty sediment and higher drift macroalgae biomass. Temporal changes showed higher fish abundance, richness, and diversity in summer-autumn during cycle 1, while during cycle 2, the higher values were in winter-autumn, mainly associated with seasonal variations in water temperature and the biogeographic affinity of fish species, but were also attributed to changes in the density of species classified as dominant. There was notable a drastic decrease of fish richness, diversity, and density during summer in cycle 2, which was attributed to be a warmer year. El Soldado fish community showed changes before and after the decree as a protected area, but also in the contiguous cycles. These changes include the addition of species, the prevalence of common species over 48 years, and the current dominant species that belong to indicator groups, which exhibit effectiveness in the conservation of this ecosystem.

The pulse of Yarlung Tsangpo River: Ultra-high-resolution insights into the flow and sediment

Traditional monitoring techniques of flow and sediment are inadequate for the sparsely populated, the rivers in the Qinghai-Tibetan Plateau region which are experiencing amplified climate change. Inspired by the Euchiloglanis fish, this study developed a unique self-contained hydrodynamic observation platform to withstand the high velocities of mountain rivers typically encountered in mountain rivers. The platform, equipped with sensors, was successfully deployed in the Yarlung Tsangpo River, collecting ultra-high-resolution data on flow and sediment over a period of nearly two months. Performance assessments showed that the median value of discharge per unit width measured and suspended sediment concentration by this system were basically consistent with those daily measurements from the hydrological station. Meanwhile, the superiority of the system was reflected in the more significant daily average change, especially at the flooding period. The data unveiled significant minute-level hydrological fluctuations and a complex interplay of factors affecting the river’s flow and sediment transport. A wavelet coherence analysis revealed asynchrony changes in short-period flow and sediment variables. Persistent short-period and coherent long-period signals are significantly displayed during flood events. The platform promises future applications, such as automated benthic observations and replacing traditional ’lead-line’ methods. Despite acknowledging system limitations of underwater attitude, burying tendency, and real-time data transmission capabilities, the study highlighted the crucial role of this system in understanding and managing river dynamics, particularly amid escalating environmental threats.

Chemometric heavy metal contamination in tropical Indian estuaries: Implications for source identification

The impact of urban and industrial effluents in the tropical Indian estuaries (Ariankuppam backwater and Chunnambar River), east coast of India have been investigated in the present study by determining the degree of heavy metals contamination of the estuarine sediments. A total of 30 surface sediment samples were collected from both estuaries and were analyzed for trace metals, grain size and organic matter. The granulometric analysis reveals that both the estuaries are predominated by silty sand to sandy silt. The significant amount of organic matter (OM) in the Ariankuppam estuary sediment is due to natural (mangroves) and anthropogenic (pollution) organic input. Pearson correlation analysis reveals that there was a strong negative correlation of sand fraction with other sediment variables (silt, clay, and organic matter) and heavy metals, whereas a positive correlation was observed between silt+clay, organic matter, and heavy metals. The significant positive correlation of Fe with Ni, Cu, Pb and Zn presents Fe-Mn oxyhydroxides are the main controlling factor of heavy metals in both estuarine sediments. Cluster analysis and PCA helped to discriminate the station groups along both estuaries according to their sediment components and heavy metals. This study also revealed that sediment grain size is a key factor influencing organic matter and heavy metal accumulation in surface sediments. The calculated pollution indices such as Contamination factor (CF), Geoaccumulation Index (Igeo) and Pollution Load Index (PLI) values indicate that both estuaries are moderate to highly contaminated by Co and low to moderately contaminated by Pb and Zn. Based on the factor analysis, it is presumed that river runoff and industrial and untreated domestic wastes from lands are responsible for increased heavy metal concentration in both estuaries. Increased levels of metal contamination along the Union Territory of Puducherry coastline may increase the risk of human exposure to metals through the consumption of seafood, making the need for tougher regulations on the discharge of metals into the environment even more important.

Upper Pleistocene in Mallorca: Sedimentary variability of littoral units in relation to different structural contexts

This comprehensive study explores the Upper Pleistocene geological history of Mallorca, employing a multidisciplinary approach that integrates previous findings with new insights. The research spans various coastal regions, focusing on four distinct study areas characterized by different geomorphological and structural contexts. The first structural context, exemplified by Port des Canonge, showcases a fold and thrust sedimentary succession, resulting in prominent cliffs with Jurassic and Triassic formations. The second context, observed in Caloscamps, features smoother reliefs and notable terrestrial sediment input. Meanwhile, the third context, represented by Punta de s’Avançada and Punta de n’Amer, exhibits cliffs carved on Upper Miocene tabular units devoid of terrestrial sediment input. The main objective is to provide a comprehensive understanding of the geological and sedimentological characteristics of the Upper Pleistocene units across the Mallorca coastal regions by investigating different study areas located along the west, north-west, north-east, and east coasts, in distinct geomorphological and geological contexts using sedimentological methodologies: stratigraphic analysis, X-ray diffraction analysis, microscopic techniques, and assessment of sediment color. Additionally, Optically Stimulated Luminescence (OSL) dating techniques are employed, providing a precise temporal framework spanning Marine Isotope Stage 6 (MIS 6) to Marine Isotope Stage 3 (MIS 3). The findings reveal the complex interplay of environmental factors, climatic variations, and geological evolution across Mallorca. Colluvial deposits and paleosols reflect climatic shifts. Alluvial fans and aeolianites highlight periods of intense sediment transport and deposition linked to climate fluctuations. Finally, to provide a comprehensive overview of the outcrops present on the island, a stratigraphic correlation of the mentioned areas was conducted. In conclusion, the study enhances our comprehension of the regional coastal dynamics, geological composition, and environmental history, providing invaluable contributions to the broader understanding of Pleistocene deposits.

Hydro-climatic extremes shift the hydrologic sensitivity regime in a cold basin

Escalating climate extreme events disrupt hydrological processes by affecting both water availability and sediment dynamics. However, the interconnection between hydrological variability and climatic extremes remains underexplored, particularly in cold regions under a changing climate. Here, we develop a yield-based dichotomy framework to examine the impact of shifted climatic extreme patterns on hydrological regimes in the Ishikari River Basin (IRB), Hokkaido, Japan, which is a crucial area for local agriculture and urban development. Utilizing a modified Soil and Water Assessment Tool (SWAT) integrated with downscaled CMIP6-GCM climate projections under Shared Socioeconomic Pathways (SSPs) scenarios, we identified significant annual variability in water and sediment yields associated with extreme climate events. Hot-dry conditions correlate with lower water and sediment yields, whereas increased cold extremes may result in higher sediment yields across the IRB. Our findings also indicate that hotter and drier patterns interact with hydrological processes, potentially establishing new hydrologic regimes and shifting climatic extremes-induced thresholds for yield classification within the IRB. Notably, under SSP585, both water availability and sediment transport are projected to intensify, increasing flood risks and exacerbating sedimentation challenges. Our study highlights the urgent need for adaptive water management strategies to address these anticipated changes in hydrological regimes in response to global climate change.

Response of streamflow and sediment variability to cascade dam development and climate change in the Sai Gon Dong Nai River basin

Response of streamflow and sediment variability to cascade dam development and climate change in the Sai Gon Dong Nai River basin

Geochemical and palynological characteristics of the Maykop sections in the north-west of the Shamakha-Gobustan region (Azerbaijan)

The article provides a comparative analysis of the results of complex palynological and geochemical studies of rocks from natural outcrops of Lagich, Angekharan and Agsu in the north-west of the Shamakhi-Gobustan region. A comparison of the distribution features of palynomorph species with the lithofacies variability of sediments made it possible to reveal the conditions of sedimentation during the formation of the described sections. In addition, the age of the units identified in the Maikop deposits in Lagich and Angekharan was clarified by analogy with the formations and horizons of similar ages in the Western and Central Ciscaucasia. The boundary of Eocene and Oligocene deposits in the Lagich section is assumed to be in the interval of 80–115 m. Late Eocene deposits occurring at the base of the section are apparently an analogue of the boundary deposits of the Beloglinskaya and Pshekhskaya formations of the Ciscaucasia. The presence of cold-water dinocysts of the species I.recurvus and calcareous nannofossils Coccolithus pelagicus in the boundary interval corresponds to the existing ideas about climate cooling at the end of the Eocene - beginning of the Oligocene. The formation of sediments in the upper intervals of the section probably occurred in more open marine conditions, relatively warm water, but with low levels of nutrients (nitrates). This interval of sediments with a characteristic phytoplankton complex can be correlated with the middle part of the Khadum horizon, an analogue of the Nizhny Morozkinsky subformation and, possibly, with the upper clayey part of the Polbinsky formation of Western and Central Ciscaucasia. The accumulation of the lower units of the studied part in the Angekharan, dated to the Early Oligocene, most likely occurred in a marine, shallower environment with possible short-term transgressive impulses. Overall, it is possible to suggest a proximal environment of high nutrient content in well-mixed waters within the inner neritic zone. An analogue of the deposits of this interval can be the Lower Morozkinsky Formation and the lower parts of the Upper Morozkinsky Formation of the Ciscaucasia. The significant increase in deflandroids in the upper part of the Angekharan section is similar to the changes noted during the transition to the zone of Deflandrea spinulosa f. Majkopica in the upper part of the Batalpashinskaya Formation of the late Oligocene in Ciscaucasia. The accumulation of sediments probably occurred in a marine basin with signs of stagnation in brackish, eutrophic environment, with a short-term supply of material from the photic zone. The conclusions about the peculiarities of changes in the depositional conditions in the study area are also confirmed by the results of geochemical studies. The deposits of the studied sections are represented by both terrestrial and aquatic types of organic matter (OM). Terrigenous OM was more typical in rocks from the Lagich and Agsu outcrops. The OM of rocks from the Lagich section varies from marginally mature to mature. In the Angekharan section the OM is thermally immature, as evidenced by the low Tmax values. Despite the small thickness of the Agsu outcrop, rock samples from this section contain kerogen of various stages of transformation from immature to mature. The carbon isotope composition (CIC) of Corg in sediments within the studied sections is in the δ13C range, characteristic of Oligocene sediments in the Paratethys. There is a higher enrichment of the 13C isotope in OM in sediments from the Agsu section.

Utilization of metal and radionuclide concentrations to assess the influence of shrimp farming on the geochemical characteristics of sediments.

This article assesses the environmental impacts of aquatic biota cultivation, focusing on shrimp farming in Brazil's Northeast, as this practice has proven to be one of the main sources of economic growth in the region. For this purpose, sediment samples were collected from areas impacted and not directly impacted by shrimp farming, and concentrations of key geochemical parameters such as salinity, various elements (K, P, Cu, Mn, Pb, Zn, Al, Ca, Fe, Mg, and Na), and natural radionuclides (K-40, Ra-226 and Ra-228) were compared using statistical tools. Element concentrations were determined using ICP-OES, and naturally occurring radionuclide concentrations were obtained through gamma spectrometry. Statistical tests, such as ANOVA and/or Mann-Whitney, cluster analysis, and principal component analysis, were applied to the results. Additionally, the ERICA Tool software was employed to estimate deleterious effects on both human and non-human biota. Descriptive statistics reveal variability in sediment parameters around shrimp farming. ANOVA and Mann-Whitney tests compare concentrations of shrimp farm sediment and not directly impacted sediment, showing non-significant differences for most elements. pH and salinity, crucial for shrimp health, exhibit higher values in shrimp farm sediment. Alkali and alkaline earth metals, including K and Na, show no significant differences. Factor and cluster analyses suggest that certain elements, mainly radionuclides, are influenced by sediment variability. Hazard indices for naturally occurring radionuclides indicate negligible risk to both human and non-human biota, reinforcing the absence of adverse effects from shrimp farming activities. This study provides a comprehensive analysis of the environmental impacts of shrimp farming, emphasizing the importance of monitoring geochemical parameters for coastal environmental management.

Effects of catchment land use on temperate mangrove forests

Human land use changes are threatening the integrity and health of coastal ecosystems worldwide. Intensified land use for anthropogenic purposes increases sedimentation rates, pollutants, and nutrient concentrations into adjacent coastal areas, often with detrimental effects on marine life and ecosystem functioning. However, how these factors interact to influence ecosystem health in mangrove forests is poorly understood. This study investigates the effects of catchment human land use on mangrove forest architecture and sedimentary attributes at a landscape-scale. Thirty sites were selected along a gradient of human land use within a narrow latitudinal range, to minimise the effects of varying climatic conditions. Land use was quantified using spatial analysis tools with existing land use databases (LCDB5). Twenty-six forest architectural and sedimentary variables were collected from each site. The results revealed a significant effect of human land use on ten out of 26 environmental variables.Eutrophication, characterised by changes in redox potential, pH, and sediment nutrient concentrations, was strongly associated with increasing human land use. The δ15N values of sediments and leaves also indicated increased anthropogenic nitrogen input. Furthermore, the study identified a positive correlation between human land use and tree density, indicating that increased nutrient delivery from catchments contributes to enhanced mangrove growth. Propagule and seedling densities were also positively correlated with human land use, suggesting potential recruitment success mechanisms. This research underpins the complex interactions between human land use and mangrove ecosystems, revealing changes in carbon dynamics, potential alterations in ecosystem services, and a need for holistic management approaches that consider the interconnectedness of species and their environment. These findings provide essential insights for regional ecosystem models, coastal management, and restoration strategies to address the impacts of human pressures on temperate mangrove forests, even in estuaries that may be relatively healthy.

Marine redox dynamics and biotic response to the mid-Silurian Ireviken Extinction Event in a mid-shelf setting

The early Silurian Llandovery–Wenlock boundary interval is marked by significant marine perturbations and biotic turnover, culminating in the Ireviken Extinction Event and the Early Sheinwoodian Carbon Isotope Excursion. Here, we apply multiple independent redox proxies to the early Wenlock Buttington section, which was deposited in a mid-shelf location in the Welsh Basin, UK. To account for the regional geochemical variability in marine sediments due to factors such as sediment provenance, we first define oxic baseline values for the Welsh Basin, utilizing deeper water, well-oxygenated intervals of late Llandovery age. Our approach documents unstable, oscillating redox conditions on the mid-shelf at Buttington. We suggest that these dynamic redox fluctuations are likely to relate to changes in the position of the chemocline or a migrating oxygen minimum zone. Benthic biota, such as trilobites, brachiopods, bivalves and gastropods, appear to have been relatively unaffected by fluctuating oxic-ferruginous conditions, but were more severely impacted by the development of euxinia, highlighting the inhibiting role of toxic sulfides. By contrast, the redox perturbations appear to have placed extreme stress on graptolites, causing many extinction losses regardless of the specific development of euxinia. Supplementary material: The geochemical data for the Buttington section is available at https://doi.org/10.6084/m9.figshare.c.7165009 Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system

Aquatic macroinvertebrate community colonisation and succession in macadamia orchard and communal area reservoirs: a case study of Luvuvhu River valley, South Africa

The demand for macadamia nut production worldwide has led to increased use of pesticides and chemicals for pest and disease control. Reservoirs in these macadamia farming sectors are at . The current study investigated macroinvertebrate colonisation and succession associated with two macadamia orchards and two communal area reservoirs. The potential effects of stressors from these land uses was tested for and compared using stone substrates over a 6-week period. Stone substrates from both reservoir types were abundantly colonised over time and the total macroinvertebrate taxa and abundance showed an increasing trend across the sampled weeks, with macadamia orchards having the highest number of macroinvertebrate taxa. Strong ecological succession was observed across reservoirs, with the initial succession of early colonisers – i.e., Chironominae (, Ostracoda (and Anax sp. (predator) within communal area reservoirs, and Chironominae, Ostracoda Radix natalensis (scrapers) in macadamia orchard reservoirs – followed by predatory colonisers such as Gyrinidae larvae, Trithemis sp. (macadamia orchard reservoirs), and Ranatra sp. (communal area reservoirs). Macroinvertebrate community structure differed significantly across sites and weeks, with no similarity being observed for communities across the different reservoirs. Redundancy analyses further highlighted 11 sediment chemistry variables (i.e., pH, resistivity, P, K, Na, Ca, Mg, Cu, B, Fe and S) which were significantly related to macroinvertebrate community structure. Thus, sediment variables were found to be better predictors of macroinvertebrate community structure in macadamia orchard reservoirs than communal area reservoirs. Consequently, we concluded that differences in colonisation ability among taxa and environmental stressors were important factors driving succession. These results add to the understanding of the macroinvertebrate colonisation processes and environmental stressors within agricultural landscapes, which can aid in the development of conservation management of freshwater ecosystems.

Impact of Fine Sediment on Benthic Macroinvertebrates Communities of Freshwater Ecosystem: A Review

The freshwater environment in Ethiopia is exposed to severe human influence because of fast population growth and other factors. Anthropogenic activities in developing countries such as river regulation and pollution have a potentially negative cumulative impact on water quantity and quality of the rivers and wetlands, hence negatively impacting benthic invertebrates and fishes. This review aims to identify the impacts of fine sediment on the community of benthic macroinvertebrates, and freshwater food webs, and to assess the response of benthic invertebrates to fine sediment pollution. Literature review was used as a methodology. Fine segment load on the freshwater ecosystem from both point and nonpoint sources may directly/indirectly alter the macroinvertebrate communities. Organic and inorganic contaminants as well as other sediment variables (sediment grain size, total organic carbon, nutrients, etc.) were affecting the community composition of benthic invertebrates. However, habitat features like the number of supplements or the silt grain measure clarify the variation in macroinvertebrate indices and metrics. The impact of metals and, to a lesser extent, organic contaminants may also be significant. Benthic macroinvertebrates are commonly used indicators of river ecological conditions that can be adversely affected by fine sediment loads. Sedimentation can change the suitability of the substrate for some taxa, increase macroinvertebrate drift, and affect respiration and feeding. To conclude, excessive fine sediment severely alters the structure and function of macroinvertebrates. At the regional and national levels, different governmental and non-governmental organizations, research institutions, and policy makers are recommended to take responsibility for reducing sediment discharge to the freshwater ecosystem by applying different conservation measures of benthic macroinvertebrates.

A 121‐ka record of Western Andean fluvial response to suborbital climate cycles recorded by rhythmic grain size variations of the Lima fluvial fan

AbstractA complete, fluvial stratigraphic record for the last glacial period of the Western Andes in Peru is not available due to preservation issues and spatial variability in sedimentation. Deposits are typically restricted to incomplete records of fluvial terraces or localised occurrences of alluvial fans and landslides. These landforms are thought to have formed under a regime of climate cyclicity controlling increases in precipitation. Because of the fragmented preservation of these deposits, as well as dating uncertainties, it remains unclear if orbital climate cycles, such as the precession cycle, or suborbital cycles, such as the wet Heinrich events, are driving Andean sedimentation. In this paper, we try to answer this question through a sedimentological–stratigraphical analysis of a much more complete sedimentary sequence than usually found in the region. We present the results of a grain size analysis of 5000 clasts and 13 new luminescence ages of a 52‐m‐long, stratigraphic section of the Lima fluvial fan in Peru. Bayesian age–depth modelling resulted in a robust chronostratigraphic framework and derived sedimentation rates. The stratigraphic record registered sedimentation from 121.7 ± 4 to ka. Three major sedimentation periods occurred between 121.7 to , 87 ± 1 to , and to ka. These periods registered various unconformities and coarsening–fining upward sequences which chronologically correlate to suborbital pluvial periods, recognised from speleothems and lake records, that drove fluvial deposition. They also correlate with the timing of other recognised sedimentation events throughout the Western Andes. Marine regression resulted in fan progradation and not in incision. The Lima fan stratigraphy represents therefore the most complete, last glacial fluvial record for the Peruvian Western Andes to date and it highlights the potential of fluvial fans as recorders of suborbital climate variability.

Water and sediment chemistry drivers of chlorophyll-a dynamics within a Ramsar declared floodplain pan wetland system.

Floodplain pans are hydrologically dynamic in nature and characterised by variables such as chlorophyll-a (chl-a), water, and sediment chemistry over their hydroperiods. The present study investigated the spatio-temporal variations in water and sediment physico-chemical, and chlorophyll-a concentration characteristics of six floodplain pans found in the Ramsar declared Makuleke wetlands, Kruger National Park, South Africa. The water and sediment physico-chemical variable values were generally elevated during the high-water period, whereas chlorophyll-a concentrations varied across pans and hydroperiod. Benthic chl-a concentration significantly varied across pans with concentrations ranging from 161 to 1036.2mg m2. The two-way ANOVA showed significant differences in benthic chl-a concentration among hydroperiods, and no significant differences were observed in pelagic chl-a across pans and hydroperiods. Generally, pelagic and benthic chl-a concentration increased as water and sediment chemistry variables increased. Furthermore, three sediment variables, i.e. pH, calcium, and magnesium, and water conductivity were found to be significant in structuring benthic chlorophyll-a dynamics in pans. However, none of the sediment and water variables had a significant effect on pelagic chl-a. Hydroperiod had a significant effect on influencing chl-a concentration, with high and low water level periods being characterised by low and high chl-a concentration, respectively. The n-MDS results showed strong overlaps in chl-a biomass among the Makuleke floodplain pans across hydroperiods. The increasing chl-a concentration in these floodplain pans due to potential bioturbation effects as a result of large mammals could potentially lead to eutrophication, which in turn could affect the system's primary productivity and aquatic biota. Therefore, it is important to establish a continuous monitoring programme on these pans to inform sound management decisions.

Bayesian integration of astrochronology and radioisotope geochronology

Abstract. Relating stratigraphic position to numerical time using age–depth models plays an important role in determining the rate and timing of geologic and environmental change throughout Earth history. Astrochronology uses the geologic record of astronomically derived oscillations in the rock record to measure the passage of time and has proven to be a valuable technique for developing age–depth models with high stratigraphic and temporal resolution. However, in the absence of anchoring dates, many astrochronologies float in numerical time. Anchoring these chronologies relies on radioisotope geochronology (e.g., U–Pb, 40Ar/39Ar), which produces high-precision (<±1 %), stratigraphically distributed point estimates of age. In this study, we present a new R package, astroBayes, for a Bayesian inversion of astrochronology and radioisotopic geochronology to derive age–depth models. Integrating both data types allows reduction in uncertainties related to interpolation between dated horizons and the resolution of subtle changes in sedimentation rate, especially when compared to existing Bayesian models that use a stochastic random walk to approximate sedimentation variability. The astroBayes inversion also incorporates prior information about sedimentation rate, superposition, and the presence or absence of major hiatuses. The resulting age–depth models preserve both the spatial resolution of floating astrochronologies and the accuracy as well as precision of modern radioisotopic geochronology. We test the astroBayes method using two synthetic datasets designed to mimic real-world stratigraphic sections. Model uncertainties are predominantly controlled by the precision of the radioisotopic dates and are relatively constant with depth while being significantly reduced relative to “dates-only” random walk models. Since the resulting age–depth models leverage both astrochronology and radioisotopic geochronology in a single statistical framework they can resolve ambiguities between the two chronometers. Finally, we present a case study of the Bridge Creek Limestone Member of the Greenhorn Formation where we refine the age of the Cenomanian–Turonian boundary, showing the strength of this approach when applied to deep-time chronostratigraphic questions.