Nutrient Inputs Research Articles

Improving ecosystem health in highly altered river basins: a generalized framework and its application to the Mississippi-Atchafalaya River Basin.

Continued large-scale public investment in declining ecosystems depends on demonstrations of "success". While the public conception of "success" often focuses on restoration to a pre-disturbance condition, the scientific community is more likely to measure success in terms of improved ecosystem health. Using a combination of literature review, workshops and expert solicitation we propose a generalized framework to improve ecosystem health in highly altered river basins by reducing ecosystem stressors, enhancing ecosystem processes and increasing ecosystem resilience. We illustrate the use of this framework in the Mississippi-Atchafalaya River Basin (MARB) of the central United States (U.S.), by (i) identifying key stressors related to human activities, and (ii) creating a conceptual ecosystem model relating those stressors to effects on ecosystem structure and processes. As a result of our analysis, we identify a set of landscape-level indicators of ecosystem health, emphasizing leading indicators of stressor removal (e.g., reduced anthropogenic nutrient inputs), increased ecosystem function (e.g., increased water storage in the landscape) and increased resilience (e.g., changes in the percentage of perennial vegetative cover). We suggest that by including these indicators, along with lagging indicators such as direct measurements of water quality, stakeholders will be better able to assess the effectiveness of management actions. For example, if both leading and lagging indicators show improvement over time, then management actions are on track to attain desired ecosystem condition. If, however, leading indicators are not improving or even declining, then fundamental challenges to ecosystem health remain to be addressed and failure to address these will ultimately lead to declines in lagging indicators such as water quality. Although our model and indicators are specific to the MARB, we believe that the generalized framework and the process of model and indicator development will be valuable in an array of altered river basins.

A comprehensive analysis of submarine groundwater discharge and nutrient fluxes in the Bohai Sea, China

Groundwater discharge and associated nutrient fluxes in the Bohai Sea, China has attracted great attention, but most studies lacked high spatial resolution for the whole sea. As the largest semi-enclosed sea in China, the Bohai Sea is confronted with strong environmental pollution problems such as eutrophication induced by terrestrial nutrient inputs. However, the role of SGD has not been evaluated well for the whole Bohai Sea. In this study, stable isotopes (hydrogen and oxygen), radioactive isotope (228Ra), salinity, and temperature were combined to trace the diluted seawater. Mass balances of 228Ra, oxygen isotope, and salinity were used to quantify SGD and nutrient fluxes to the Bohai Sea. The estimated submarine fresh groundwater discharge (SFGD) and SGD to the Bohai Sea were (6.0 ± 0.5) × 109 and (2.7 ± 1.6) × 1011 m3 a−1, respectively. SFGD represents 10 % to 11 % of the total river discharge and SGD is about 2 to 8 folds of the total river discharge to the sea. Moreover, SGD derived dissolved nutrients to the Bohai Sea were (4.8 ± 4.0) × 1010 mol a−1 for dissolved inorganic nitrogen, (1.9 ± 1.7) × 1010 mol a−1 for dissolved inorganic phosphorus, and (6.7 ± 5.5) × 1010 mol a−1 for silicon. These nutrient inputs were about 10 to 20 folds of the total riverine inputs. Overall, this study underscores the importance of evaluating SGD to better understand the terrestrial imported nutrients in regional scale.

Activity and community structure of nitrifiers and denitrifiers in nitrogen-polluted rivers along a latitudinal gradient

Nitrogen (N) cycling in rivers is particularly active and dynamic due to excess nutrient inputs worldwide. However, the multidimensional spatial patterns of the activity and community structure of N-cycling microorganisms in rivers remain unclear, limiting our understanding of river ecological functions, especially N removal capacity. Here, we measured the nitrification and denitrification rates and identified nitrifying and denitrifying microorganisms using high-throughput sequencing of archaeal amoA, bacterial amoA, nirK, and nirS genes in channel sediments, riparian rhizosphere soils, and riparian bulk soils of 30 N-polluted rivers across China. Results showed that in the lateral dimension, nitrification rates in sediments did not differ significantly from those in rhizosphere and bulk soils, but denitrification rates were higher in sediments than in bulk soils. However, the archaeal amoA gene abundance in sediments was considerably lower than that in rhizosphere and bulk soils, and bacterial amoA gene abundance in sediments was greater than that in rhizosphere soils. In the vertical dimension, both nitrification and denitrification rates in riparian bulk soils decreased with soil depth, and topsoils harbored more nitrifying and denitrifying microbes than subsoils. Denitrification but not nitrification rates increased with latitude and altitude but decreased with increasing mean annual temperature and precipitation. Overall, these results provide new insights into the multidimensional spatial patterns of river N cycling at a large scale, which is crucial to evaluating the N removal function of global rivers.

The connection between Submarine Groundwater Discharge and seawater quality: The threat of treated wastewater injected into coastal aquifers

Submarine Groundwater Discharge (SGD) delivers nutrients to the coastal sea triggering phytoplankton blooms, eutrophication, and can also serve as a pathway for contaminants. Wastewater treatment plants (WWTP) including injection wells in coastal areas influence coastal aquifers and might impact the composition and magnitude of SGD fluxes. In tourist areas, wastewater treatment may be less efficient and larger in volume during high seasons, potentially impacting nutrient fluxes from SGD and exacerbating environmental impacts. This study analyzes the nutrient transfer from treated wastewater injection in karstic aquifers to the coastal sea via SGD, considering the impacts of tourism seasonality. This study is conducted in Cala Deià, a small cove in the Balearic Islands, a Mediterranean tourist destination. The findings suggest that the seasonality of tourism, leading to variations in the volume of wastewater treated in the WWTP, influences the dynamics of the coastal aquifer. This leads to increased SGD water and nutrient fluxes to the sea in summer, i.e. the peak tourist season. The measured DIN, DIP, and DSi inventories in the cove are much larger in August than in April (3, 10, and 1.5 times higher, respectively) due to higher input of nutrients in summer due to SGD impacted by the WWTP. These elevated nutrient flows can support algal blooms in the cove, compromising water quality for local swimmers and tourists. Indeed, in August, shoreline stations exhibited eutrophic Chl-a concentrations, with peaks reaching approximately 4 mg Chl-a L−1. These elevated levels suggest the presence of an algal bloom during the survey. The anthropogenic origin of SGD-driven nutrients is traced in seawater and seagrass meadows, as evidenced by high ∂15N signatures indicative of polluted areas. Thus, the high pressure exerted on coastal areas by tourism activities increased the magnitude of SGD nutrient fluxes, thereby threatening coastal ecosystems and the services they provide.

Vicuña antipredator diel movement drives spatial nutrient subsidies in a high Andean ecosystem.

Large animals could be important drivers of spatial nutrient subsidies when they ingest resources in some habitats and release them in others, even moving nutrients against elevational gradients. In high Andean deserts, vicuñas (Vicugna vicugna) move daily between nutrient-rich wet meadows, where there is abundant water and forage but high risk of predation by pumas (Puma concolor), and nutrient-poor open plains with lower risk of predation. In all habitats, vicuñas defecate and urinate in communal latrines. We investigated how these latrines impacted soil and plant nutrient concentrations across three habitats in the Andean ecosystem (meadows, plains, and canyons) and used stable isotope analysis to explore the source of fecal nutrients in latrines. Latrine soils had higher concentrations of nitrogen, carbon, and other nutrients than did nonlatrine soils across all habitats. These inputs corresponded with an increase in plant quality (lower C:N) at latrine sites in plains and canyons, but not in meadows. Stable isotope mixing models suggest that ~7% of nutrients in plains latrines originated from vegetation in meadows, which is disproportionately higher than the relative proportion of meadow habitat (2.6%) in the study area. In contrast, ~68% of nutrients in meadow latrines appear to originate from plains and canyon vegetation, though these habitats made up nearly 98% of the study area. Vicuña diel movements thus appear to concentrate nutrients in latrines within habitats and to drive cross-habitat nutrient subsidies, with disproportionate transport from low-lying, nutrient-rich meadows to more elevated, nutrient-poor plains. When these results are scaled up to the landscape scale, the amount of nitrogen and phosphorus subsidized in soil at plains latrines was of the same order of magnitude as estimates of annual atmospheric nitrogen and phosphorus deposition for this region (albeit far more localized and patchy). Thus, vicuña-mediated nutrient redistribution and deposition appears to be an important process impacting ecosystem functioning in arid Andean environments, on par with other major inputs of nutrients to the system.

Quantifying the contribution of methane diffusion and ebullition from agricultural ditches

Agricultural ditches are significant methane (CH4) sources since substantial nutrient inputs stimulate CH4 production and emission. However, few studies have quantified the role of diffusion and ebullition pathways in total CH4 emission from agricultural ditches. This study measured the spatiotemporal variations of diffusive and ebullitive CH4 fluxes from a multi-level ditch system in a typical temperate agriculture area, and assessed their contributions to the total CH4 emission. Results illustrated that the mean annual CH4 flux in the ditch system reached 1475.1 mg m−2 d−1, among which 1376.7 mg m−2 d−1 was emitted via diffusion and 98.5 mg m−2 d−1 via ebullition. Both diffusive and ebullitive fluxes varied significantly across different types of ditches and seasons, with diffusion dominating CH4 emission in middle-size ditches and ebullition dominating in large-size ditches. Diffusion was primarily driven by large nutrient inputs from adjacent farmlands, while hydrological factors like water temperature and depth controlled ebullition. Overall, CH4 emission accounted for 86 % of the global warming potential across the ditch system, with 81 % attributed to diffusion and 5 % to ebullition. This study highlights the importance of agricultural ditches as hotspots for CH4 emissions, particularly the dominant role of the diffusion pathway.

Water quality drives the reconfiguration of riverine planktonic microbial food webs

The food web is a cycle of matter and energy within river ecosystems. River environmental changes resulting from human activities are increasingly threatening the composition and diversity of global aquatic organisms and the multi-trophic networks. How multiple environmental factors influence food web patterns among multi-trophic microbial communities in rivers remains largely unknown. Using water quality evaluation and meta-omics techniques, we investigated the composition, structure and interaction characteristics, and drivers of food webs of microorganisms (archaea, bacteria, fungi, protists, metazoa, viridiplantae and viruses) at multiple trophic levels in different water quality environments (Classes II, III, and IV). First, water quality deterioration led to significant changes in the composition of the microbial community at multiple trophic levels, which were represented by the enrichment of Euryarchaeota in the archaeal community, the increase of r-strategists in the bacterial community, and the increase of the proportion of predators in the protist community. Second, deteriorating water quality resulted in a significant reduction in the dissimilarity of community structure (homogenization of community structure in Class III and IV waters). Of the symbiotic, parasitic, and predatory networks, the community networks in Class II water all showed the most stable symbiotic, parasitic, and predatory correlations (higher levels of modularity in the networks). In Class III and IV waters, nutrient inputs have led to increased reciprocal symbiosis and decreased competition between communities, which may have the risk of a positive feedback loop driving a system collapse. Finally, inputs of phosphorus and organic matter could be the main drivers of changes in the planktonic microbial food web in the Fen River. Overall, the results indicated the potential ecological risks of exogenous nutrient inputs, which were important for aquatic ecosystem conservation.

An environmental flow to an ephemeral creek increases the input of carbon and nutrients to a downstream receiving river

Although intermittent and ephemeral rivers lack surface flow for part of the year, they provide vital refuges for biota in otherwise dry semi-arid and arid landscapes. The hydrology of many such rivers has been altered due to river regulation and climate change. Environmental flows can be delivered to address the negative impacts of regulated flows, however there is limited knowledge of how dry ephemeral ecosystems respond following environmental flows. This study examined changes in water quality of the ephemeral Thule Creek in the southern Murray-Darling Basin, Australia, following delivery of environmental water from an irrigation canal. We also examined how the environmental flow influenced water quality of Wakool River that receives inflows from Thule Creek. Six sites in Thule Creek, three in Wakool River, and one in Yarraman irrigation channel (source water) were monitored for dissolved organic carbon (DOC), nutrients and dissolved oxygen (DO) once per week over 15 weeks from October 2019 to January 2020. The environmental flow resulted in high DOC concentrations (4.4–76 mg/L). Although low DO levels at sites in Thule Creek were recorded on some dates below the threshold for fish stress (< 4 mg/L) there were no fish kills observed during the environmental flow. The carbon-rich and nutrient-rich water (DOC >10 mg/L, total phosphorus up to 94 μg/L, total nitrogen up to 1,125 μg/L) was detected in the Wakool River downstream of Thule Creek confluence compared to the Wakool River upstream of Thule Creek confluence (DOC 6.6 mg/L, total phosphorus up to 64 μg/L, total nitrogen up to 805 μg/L) during the period when the environmental flow in Thule Creek was connected with the Wakool River. This research provides an example of how irrigation canal networks can be used to deliver environmental water to an ephemeral river to maintain refuges and contribute to the productivity of a receiving river further downstream. Careful management of the timing, volume and duration of environmental flows in arid or semi-arid landscapes is needed to avoid the development of poor water quality during, or following, the delivery of environmental water.

How nutrient retention and TN:TP ratios depend on ecosystem state in thousands of Chinese lakes

Worldwide, anthropogenic activities threaten surface water quality by aggravating eutrophication and increasing total nitrogen to total phosphorus (TN:TP) ratios. In hydrologically connected systems, water quality management may benefit from in-ecosystem nutrient retention by preventing nutrient transport to downstream systems. However, nutrient retention may also alter TN:TP ratios with unforeseen consequences for downstream water quality. Here, we aim to increase understanding of how nutrient retention may influence nutrient transport to downstream systems to improve long-term water quality management. We analyzed lake ecosystem state, in-lake nutrient retention, and nutrient transport (ratios) for 3482 Chinese lakes using the lake process-based ecosystem model PCLake+. We compared a low climate change and sustainability-, and a high climate change and economy-focused scenario for 2050 against 2012. In both scenarios, the effect of nutrient input reduction outweighs that of temperature rise, resulting in more lakes with good ecological water quality (i.e., macrophyte-dominated) than in 2012. Generally, the sustainability-focused scenario shows a more promising future for water quality than the economy-focused scenario. Nevertheless, most lakes remain phytoplankton-dominated. The shift to more macrophyte-dominated lakes in 2050 is accompanied by higher nutrient retention fractions and less nutrient transport to downstream waterbodies. In-lake nutrient retention also alters the water's TN:TP ratio, depending on the inflow TN:TP ratio and the ecosystem state. In 2050 higher TN:TP ratios are expected in the outflows of lakes than in 2012, especially for the sustainability-focused scenario with strong TP loading reduction. However, the downstream impact of increased TN:TP ratios depends on actual nutrient loadings and the limiting nutrient in the receiving system. We conclude that nutrient input reductions, improved water quality, higher in-lake nutrient retention fractions, and lower nutrient transport to downstream waterbodies go hand in hand. Therefore, water quality management could benefit even more from nutrient pollution reduction than one would expect at first sight.

Dynamic changes of net anthropogenic nitrogen/phosphorus input and its riverine export in the Beijing's subcenter

AbstractDue to human activities, the overabundance of regional nitrogen/phosphorus (N/P) has a huge impact on ecological environment worldwide. It is necessary to comprehensively understand the human‐induced N/P input and spatiotemporal variations of nutrients in a river. As the adjustment to the spatial structure of Beijing, the Beijing's subcenter is an important strategic position in promoting the coordinated development of Beijing–Tianjin–Hebei. In this study, the dynamic changes of ammonia nitrogen (NH3‐N) and total phosphorus (TP) from 2012 to 2022 were analyzed, then the net anthropogenic N input (NANI) and net anthropogenic P input (NAPI) was estimated in the Beijing's subcenter. The results showed that both NH3‐N and TP had an overall downward trend with a three‐stage pattern. The NANI and NAPI declined from 5.68 × 104 and 0.95 × 104 to 0.78 × 104 and 0.15 × 104 kg km−2 per year, respectively. The chemical fertilizers input accounted for the largest part at 53–81% of NANI and 49–80% of NAPI. There were high values of N and P input in the southeast of Tongzhou, and the fluxes of N and P were positively correlated with the input of anthropogenic N and P in the Chaobai River Basin (Tongzhou District) and the Beiyun River Basin (Tongzhou District). This study would provide the foundation for setting priorities and enacting more targeted N/P management strategies in the Beijing's subcenter.

Biogenic element driving mechanism in the occurrence of Chinese coastal eco-environmental disasters and regulation for ecological environment health.

In recent decades, China's coastal ecological environment has undergone significant changes under multiple pressures such as climate change and high intensity of human activities. The occurrence and scale of harmful algal blooms represented by the red tide and the green tide are increasing rapidly. Moreover, environmental problems such as hypoxia and acidification in seawater have become increasingly prominent. It is urgent to find out the occurrence mechanism and prevention measures of marine eco-environmental disasters. Therefore, we explained the connotation of the concept of "marine eco-environmental disaster" for the first time, and systematically interpreted the biogenic element driving mechanisms in the occurrence of eco-environmental disasters in China nearshore area in the aspects of exogenous input of nutrients, the mineralization and decomposition of marine organic matters and nutrient regeneration, as well as the abnormal nutrient structure in offshore waters. We pointed out that the drastic increases of terrigenous nutrient discharge caused by enhancing human activities, together with the complex biogeochemical cycle process after biogenic elements entering the sea, led to the frequent occurrence of coastal eco-environmental disasters. On this basis, combined with the latest research progress in this field, we put forward the regulatory schemes for coastal ecological environment health based on the controlling of seawater biogenic element. That is, based on land-sea integration strategy, the reduction of land-source pollutants, especially inorganic nitrogen from land, coastal zone and into the sea, and the normalization of nutrient structure in coastal seawater through artificial regulation technology, are the key points to reduce and control the occurrence of disasters and improve the quality of the coastal ecosystems.

Assessing long-term diatom changes in sub-Arctic ponds receiving high fluxes of seabird nutrients.

Algal bioindicators, such as diatoms, often show subdued responses to eutrophication in Arctic lakes because climate-related changes (e.g., ice cover) tend to be the overriding factors influencing assemblage composition. Here, we examined how sub-Arctic ponds historically receiving high nutrient inputs from nesting seabirds have responded to recent climate change. We present diatom data obtained from 12 sediment cores in seaduck-affected ponds located on islands through Hudson Strait, Canada. All study cores show consistently elevated values of sedimentary ẟ15N, an established proxy for tracking marine-derived nutrients, indicating seabirds have been present on these islands for at least the duration of the sediment records (~100 to 400 years). We document diverse epiphytic diatom assemblages to the base of all sediment cores, which is in marked contrast to seabird-free Arctic ponds-these oligotrophic sites typically record epilithic diatom flora prior to recent warming. Diatoms are likely responding indirectly to seabird nutrients via habitat as nutrients promote the growth of mosses supporting epiphytic diatom communities. This masks the typical diatom response to increased warming in the Arctic, which also results in habitat changes and the growth of mosses around the pond edges. Changes in sedimentary chlorophyll a were not consistently synchronous with large changes in ẟ15N values, suggesting that primary production in ponds is not responding linearly to changes in seabird-derived nitrogen. Across all ponds, we recorded shifts in diatom epiphytic assemblages (e.g., increases in % relative abundance of many Nitzschia species) that often align with increases in chlorophyll a. The changes in diatoms and chlorophyll a, although variable, are most likely driven by climate change as they are generally consistent with longer ice-free conditions and growing seasons. Together, our results show that to effectively use diatoms in animal population reconstructions across the sub-Arctic and Arctic, a strong understanding of eutrophication and climate change, based on supplementary proxies, is also required.

Lower Jurassic (Pliensbachian–Toarcian) marine paleoenvironment in Western Europe: sedimentology, geochemistry and organic petrology of the wells Mainzholzen and Wickensen, Hils Syncline, Lower Saxony Basin

AbstractOver the past few decades, Toarcian (Early Jurassic) black shale deposits of NW Europe have been extensively studied, and the possible global and regional mechanisms for their regional variation have been discussed. In this context, the black shales of the Northwest German Basin are still sparsely studied with regard to their palaeo-depositional history. This study aims to understand the connection between regional and global influences on the widespread Early Toarcian oceanic anoxic event by examining two wells covering the Upper Pliensbachian to Upper Toarcian sediments in the Northwestern German Basin. The core intervals were analysed using a multidisciplinary approach, including geochemistry, biostratigraphy and organic petrography. Marine palaeoenvironmental changes were reconstructed, and sediment sequences were stratigraphically classified to allow a supra-regional stratigraphic correlation. The results reveal complex interactions between sea level changes, climate warming, basin confinement, and Tethys–Arctic connectivity resulting in the Toarcian black shale deposition. Upper Pliensbachian sediments were deposited under terrigenous influence, shallow water depths, and predominantly oxic bottom water conditions. The deposition of black shale is characterized by algal organic material input and anoxic bottom water conditions. Strong correlations between water stratification, anoxia, and bioproductivity suggest that global warming and intensification of monsoonal rainfall, continental weathering, and increasing freshwater and nutrient inputs were the main factors controlling the formation of black shales. Prolonged deposition of OM-rich sediments in the NWGB may be related to intensified monsoonal precipitation in northern Europe and enhanced Tethys–Arctic connectivity at the serpentinum–bifrons transition. Graphical Abstract

Evaluation of essential and trace metals/metalloids distribution and probable human health risk implications from branded liquid and powder milks available in Dhaka City, Bangladesh.

The processed forms of milk, branded liquid, and power milk available in Dhaka city, the capital of Bangladesh, were investigated for essential and trace metal/metalloids regarding nutritional and human health risk aspects. For this, the potential nutritional contribution, estimated daily intake (EDI) and non-carcinogenic risk for six different life stages with male and female categories, as well as the carcinogenic risk for children and adults of both genders, were addressed. In total, 46 branded liquid and powder milk samples were considered for this analysis employing atomic absorption spectroscopy. The concentration of essential elements showed the trends of K > Ca > Na > Mg > Fe > Zn > Mn > Cu and K > Ca > Na > Mg > Fe > Cu > Mn > Zn for liquid and powder milk samples, respectively, but the potentially hazardous one showed the same trends (Cr > Pb > Hg > As > Cd) for both items. Except for Cr, Hg, and Fe, the elemental compositions of both milk categories differed considerably (< 0.05). Compared to the threshold values for milk samples (liquid and powder), Fe (19% and 27%), Mn (100% and 63%), Cu (0% and 23%), Zn (94% and 0%), Pb (25% and 13%), and Cr (0% and 3%) showed above the permissible limits. The nutrient input was the highest for Ca (27.2% and 18.7%), followed by Mg, K, and Na. The EDI of studied elements was within the daily permissible limit in both the milk category (except age group (≤ 3) and the female category). The non-carcinogenic risk assessment showed that the age groups ≤ 3 for liquid milk and ≤ 3 and 3 < X ≤ 14 with female categories for powder milk exceeded the threshold level (> 1) in the case of Cr, Cd, As, Zn, and Mn. The probable carcinogenic risks indicated an unacceptable risk level (< 1.00E-04) for the ingestion of Cr through powder milk samples for children in male and female categories. Finally, it believes that green cow farming practices and green milk processing technology, as well as continuous monitoring of toxic metals, can limit the ultimate risk worldwide.

Monitoring network optimization and impact of fish farming upon water quality in the Três Marias Hydroelectric Reservoir, Brazil.

Hydroelectric power is the main source of electrical energy in Brazil. Electrical energy providers have the duty to monitor water quality in reservoirs to preserve water quality and support best management practices that enable multiple wateruses, including fish production. In this context, the objectives of this study were (i) to perform a historical evaluation of water quality in Três Marias Reservoir, (ii) to present an optimization of the water quality monitoring network, and (iii) to evaluate the evolution and impact of fish farming upon surface water quality by using secondary data measured in situ and remote sensing. A systematic approach was applied to analyze historical water quality data. Principal component analysis (PCA) and cluster analysis (CA) were applied to identify the most important parameters and monitoring points. Images obtained from Sentinel 2 were treated by contrast to quantify simple and weighted densities of fish farming activities in the region while regression analysis was performed to verify correlations between these densities and water quality parameters. Results showed that the pH and total suspended solids were the most important parameters for characterizing water quality, especially near tributaries, and that monitoring points could be grouped into three clusters (upstream, central, and downstream regions) with distinct water quality conditions. The PCA indicated that there is no redundance among parameters nor monitoring stations and that areas near tributaries must be prioritized for monitoring as these are important sources of suspended solids. Remote sensing images showed thatthearea occupied by fish farms has increased in the reservoir from 2016 to 2022and the methodology used for this purpose in this study may be applied to other bodies of water. Chlorophyll-a showed a direct relationship with the density of fish farms indicating a possible influence of nutrient input to the reservoir by this activity. These results provide valuable information to support decision-making related to water management in the reservoir.

Tracing the geochemical imprints of Maastrichtian black shales in southern Tethys, Egypt: Assessing hydrocarbon source potential and environmental signatures

This study conducted comprehensive bulk and molecular geochemical analyses, as well as elemental investigations, on seventeen black shale samples collected from the Upper Cretaceous sediments on the western margin of the Red Sea. The primary objective is to assess the hydrocarbon generation potential, maturity, source input, biodegradation levels, and depositional environment characteristics within the Lower Maastrichtian interval near the Safaga area. Lower Maastrichtian black shales demonstrate very good to excellent source rock generative potential based on pyrolysis data. The prevalent kerogen type in the older black shale at the Heweitat mine is Type II, whereas within the younger units at the Queih mine, it predominantly exhibits Type II/III kerogen. These Maastrichtian black shales remain thermally immature, as evidenced by vitrinite reflectance (VRr < 0.5%), pyrolysis data, and biomarker proxies.The studied black shales show that the organic matter input comprises bacterial and algal biomass with minor terrigenous contributions. Additionally, there is no evidence of significant biodegradation in the studied samples based on molecular fossils data. Microscopic analysis and various bulk and molecular characteristics, in conjunction with major and trace element profiles, collectively indicate a marine depositional environment with oxygen-deficient bottom water conditions during source rock deposition. The presence of isorenieratene and aryl isoprenoids suggests persistent and episodic photic zone anoxia during the Maastrichtian period. Elevated nutrient inputs and paleobioproductivity were recorded in the older black shale at the Heweitat mine compared to the younger one at the Queih mine. Paleoproductivity and oxygen depletion emerge as pivotal factors influencing the accumulation and preservation of organic matter within the black shales. These findings provide valuable insights into the environmental conditions prevailing during the deposition of Maastrichtian sediments in the Eastern Desert.

A benthic foraminifera perspective of the Late Miocene-Early Pliocene Biogenic Bloom at ODP Site 1085 (Southeast Atlantic Ocean)

The Late Miocene-Early Pliocene Biogenic Bloom (ca. 9.0–3.5 Ma) was a phase of high marine biological productivity documented globally at multiple ocean sites, related to an increase in nutrient input and/or a significant reorganization of nutrients in the oceans. Here, we studied the Biogenic Bloom at Ocean Drilling Program (ODP) Site 1085 in the Southeast Atlantic Ocean, additionally providing an updated age model based on calcareous nannofossil biostratigraphy. During the event, we identified four intervals characterised by distinct benthic foraminiferal assemblages, suggesting changes in paleoenvironmental/paleoceanographic conditions. The Biogenic Bloom extends from 8.1 to 3.0 Ma at Site 1085, as detected by different proxies such as linear sedimentation rates, carbonate mass accumulation rates, benthic foraminiferal indices and assemblage data. The inferred paleoenvironmental changes allowed us to differentiate four intervals within the Biogenic Bloom. From 8.1 to 5.2 Ma and from 3.8 to 3.0 Ma, the high benthic foraminiferal accumulation rates (BFARs) and the abundance of phytodetritus-exploiting taxa point to highly seasonal phytoplankton blooms. Between 5.2 and 4.8 Ma, we document short-term fluctuations between well‑oxygenated conditions with transient input of phytodetritus and phases of low oxygen eutrophic conditions. Between 4.8 and 3.8 Ma, a decrease in opportunistic species and an increase in eutrophic taxa likely suggest a switch to a higher food supply to the seafloor. Our data shows that the onset of the Biogenic Bloom was synchronous with other global well-dated records and its end appears to align with other Atlantic records. Lastly, our findings support the hypothesis that the Biogenic Bloom was not a single productivity event, but a complex event made up of several short-lived, high-productivity regimes with different driving forces.

Phosphorus forms and adsorption properties of paddy field soils and potential risk to Indawgyi Lake, Myanmar

The largest freshwater and oligotrophic lake in northern Myanmar, called Indawgyi Lake, is at potential risk of eutrophication due to the phosphorus (P) export from nearby paddy fields. In this study, the P status of the soil of paddy fields and its potential mobility to the lake water to cause eutrophication have been evaluated. The Indawgyi Lake is the third largest lake in Asia and became a UNESCO biosphere reserve in June 2017 for its outstanding contribution to providing habitat for threatened birds and aquatic species. Although many other sources, e.g. high tourist interest, loss of natural forest areas, the gathering of pilgrims and lack of proper wastewater treatment plants are contributing to the P nutrients input to the lake, the increase of paddy fields around the lake area and use of synthetic fertiliser which exports to the lake is considered to the primary source of P export to the lake. In this study, the soil P was examined with different P extracted methods and P export to the lake was calculated. The extracted P differed in order and magnitude with different methods, and the order was increased in accordance with CaCl2 < DL-P < Olsen-P < BD-P < HCL-P < TP and for iron, it was HCl-Fe < TFe. All extracted Olsen-P was below 10 mg kg−1, which is below the critical level (30–172 mg kg−1) for P loss. On the other hand, the soil has a high P sorption capacity, and the maximum sorption capacity among the soil samples that were done with the Langmuir equation is 0.790 mg g−1. Our findings suggested that paddy fields are not contributing to the eutrophication of the lake at present. However, comparing the historical map around the lake area from 1944 to 2017, it has been found that the area of paddy fields around the lake has increased almost three-fold from 1944 to 2017. As a result of increasing paddy fields and synthetic fertiliser use, we can say that P export from paddy fields can cause severe eutrophication to the lake in the near future.

Fresh and saline groundwater nutrient inputs and their impacts on the nutrient budgets in a human-effected bay

Submarine groundwater discharge (SGD) can be highly enriched in nutrients, especially in bays with strong human activity, but has often been overlooked in coastal nutrient budgets. This study investigated the impact of both fresh and saline SGD on nutrient budgets in Sanmen Bay, China, a region heavily influenced by human activities. Based on the 224Ra mass balance model, the total SGD flux was estimated to be (1.1 ± 0.1) × 108 m3 d−1 (13.9 ± 0.5 cm d−1). Additionally, a water-salt mass balance model revealed that fresh SGD flux accounted for ~9.0 % of the total SGD flux. The results highlight the significance of fresh SGD as a freshwater source, contributing to 35.9 % of the total dissolved inorganic phosphorus (DIP) flux via SGD. Considering all nutrient sources and sinks in the Sanmen Bay, SGD was identified as the primary source of nutrients in Sanmen Bay, contributing 53.9 % and 11.9 % of the total dissolved inorganic nitrogen (DIN) and DIP input, respectively. Furthermore, the discharge of industrial/domestic sewage and mariculture wastewater also posed a potential threat to nutrient levels in the bay. Thus, initiatives such as reasonable control of culture species and scale, strengthening wastewater discharge and SGD management are crucial for maintaining the ecological environment of the Sanmen Bay.

Assessment of Soil Fertility Status in Selected Fields under Maize Production in Kongwa District, Dodoma Region, Tanzania

This study was conducted in the Kongwa District to assess the fertility status of soils of the selected fields under maize production to understand fertility variability among soils and recommend appropriate fertilizer rates. The study involved randomly selected 24 maize fields. Composite soil samples were collected in these fields at 0–20 cm deep and characterized for soil fertility status. Results indicated that 48% of the soils were sandy clay loam and 26% were sandy loam. The remaining fields had clay or loamy sand textural classes. The soil pH ranged from extremely acidic (3.52) to moderately alkaline (7.7), organic carbon ranged from very low to medium (0.19-1.60%) and total N were very low to low (0.01-0.15%). Also, results indicated that 42% of soils had P deficiency and 16.7% had inadequate S levels. In addition, 45.8% of the soils had inadequate exchangeable K and exchangeable Mg levels ranged from very low to high (0.29-4.06 cmol(+) kg-1). Exchangeable Ca was low to very high (1.06 to 10.04 cmol(+) kg-1) with favourable base saturation for crop production. The CEC ranged from very low (2.62 cmol(+) kg-1) to medium (18.9 cmol(+) kg-1). Extractable micronutrients such as Cu, Fe, and Mn were adequate but Zn was inadequate in 58% of the soils. Categorizing nutrient status in soils of the study area showed that fertility is poor regarding N, P, K, Zn, Mg, and Ca. Hence, the studied soils need external nutrient inputs and proper management to optimize crop production.