Nutrient Enrichment Research Articles

Distribution characteristics of soil crusts under two kinds of aerial seeding plants in the northeastern margin of Tengger Desert

In order to explore the effects of two plants on the spatial distribution and nutrient distribution of crusts in different directions and distances after 30 years of aerial seeding, as well as the relationship between crust thickness and nutrient content, this paper takes the aerial seeding afforestation area in the northeastern margin of Tengger Desert as the research area, and the crusts under the plants of Hedysarum scoparium and Calligonum mongolicum as the research objects. The distribution of crust thickness and nutrients was analyzed, and the relationship between them was constructed. The thickness of the crust of H. scoparium and C. mongolicum was the largest in the southeast direction and the smallest in the northwest direction. With increasing distance from the plant, it shows a significant decreasing trend. The crust thickness of H. scoparium was higher than that of C. mongolicum. The nutrient indexes in the southeast direction of the crust of H. scoparium and C. mongolicum were significantly higher than those in the northwest direction; With the increase of the distance from the root of the plant, the nutrient content showed a significant decreasing trend. The contents of organic matter and available nitrogen in the crust of C. mongolicum were higher than those of H. scoparium, and the contents of available potassium and available phosphorus were lower than those of H. scoparium. The trend of nutrient enrichment rate of the crusts of the two plants was consistent with the trend of nutrient distribution. There was a significant positive correlation between the crust thickness and nutrients in the four directions under C. mongolicum. There was a significant positive correlation between the crust thickness and nutrients in the southwest direction under H. scoparium. The changes of available nitrogen, available phosphorus, available potassium and organic matter content in the crust under H. scoparium can explain 52.5% of the change of its thickness. The changes of available nitrogen, available phosphorus, available potassium and organic matter content in the crust under C. mongolicum can explain 78.5% of the change of its thickness. After 30 years of aerial seeding in Tengger Desert, the thickness and nutrients of the crust in the southeast direction of H. scoparium and C. mongolicum were significantly higher than those in the northwest direction and showed a decreasing trend with the increase of distance from the root of the plant. There was a positive correlation between crust nutrient and thickness.

Groundwater Quality Assessment: A Case of Urban Population Demography and Nutrient Enrichment in Ibadan, Southwestern Nigeria

Groundwater Quality Assessment: A Case of Urban Population Demography and Nutrient Enrichment in Ibadan, Southwestern Nigeria

Unprecedented Harmful algal bloom in the UK and Ireland’s largest lake associated with gastrointestinal bacteria, microcystins and anabaenopeptins presenting an environmental and public health risk

Harmful Algal Blooms (HABs) are outbreaks of aquatic toxic microalgae emerging as a global problem driven by nutrient enrichment, global climate change and invasive species. We uniquely describe a HAB of unprecedented duration, extent and magnitude during 2023 in Lough Neagh; the UK and Ireland’s largest freshwater lake, using an unparalleled combination of satellite imagery, nutrient analysis, 16S rRNA gene sequencing and cyanotoxin profiling. The causative agent Microcystis aeruginosa accounted for over a third of DNA in water samples though common bacterioplankton species also bloomed. Water phosphate levels were hypertrophic and drove local algal biomass. The HAB pervaded the entire ecosystem with algal mats accumulating around jetties, marinas and lock gates. Over 80 % of bacterial DNA isolated from algal mat samples consisted of species associated with wildfowl or livestock faeces and human-effluent wastewater including 13 potential pathogens that can cause serious human illness including: E. coli, Salmonella, Enterobacter and Clostridium among others. Ten microcystins, nodularin and two anabaenopeptin toxins were confirmed as present (with a further microcystin and four anabaenopeptins suspected), with MC-RR and -LR in high concentrations at some locations (1,137–18,493 μg/L) with MC-LR exceeding World Health Organisation (WHO) recreational exposure guidelines in all algal mats sampled. This is the first detection of anabaenopeptins in any waterbody on the island of Ireland. Notwithstanding the ecological impacts, this HAB represented an environmental and public health risk, curtailing recreational activities in-and-around the lake and damaging local businesses. Reducing agricultural runoff and discharge from human-effluent wastewater treatment to manage nutrient loading, and the public health risk, should be the top priority of stakeholders, especially government. Key recommendations include Nature-based Solutions that avoid conflict with the productivity and profitability of the farming sector enhancing sustainability. We hope this stimulates real-world action to resolve the problems besetting this internationally important ecosystem.

The interaction between warming and enrichment accelerates food-web simplification in freshwater systems.

Nutrient enrichment and climate warming threaten freshwater systems. Metabolic theory and the paradox of enrichment predict that both stressors independently can lead to simpler food-webs having fewer nodes, shorter food-chains and lower connectance, but cancel each other's effects when simultaneously present. Yet, these theoretical predictions remain untested in complex natural systems. We inferred the food-web structure of 256 lakes and 373 streams from standardized fish community samplings in France. Contrary to theoretical predictions, we found that warming shortens fish food-chain length and that this effect was magnified in enriched streams and lakes. Additionally, lakes experiencing enrichment exhibit lower connectance in their fish food-webs. Our study suggests that warming and enrichment interact to magnify food-web simplification in nature, raising further concerns about the fate of freshwater systems as climate change effects will dramatically increase in the coming decades.

Nutrient enrichment and herbivory alter carbon balance in temperate seagrass communities

Large nutrient levels and herbivory stress, particularly when acting together, drive a variety of responses in seagrass communities that ultimately may weaken their carbon balance. An in situ three-months experiment was carried out in two contrasting seasons to address the effects of two levels of nutrient load and three levels of artificial clipping on Cymodocea nodosa plants. Nutrient enrichment shifted the community from autotrophic to heterotrophic and reduced DOC fluxes in winter, whereas enhanced community carbon metabolism and DOC fluxes in summer. Herbivory stress decreased the net primary production in both seasons, whereas net DOC release increased in winter but decreased in summer. A reduction of seagrass food-web structure was observed under both disturbances evidencing impacts on the seagrass ecosystems services by altering the carbon transfer process and the loss of superficial OC, which may finally weaken the blue carbon storage capacity of these communities.

Concurrent nitrogen and phosphorus enrichment increases ecosystem carbon use efficiency in an alpine grassland

Ecosystem carbon use efficiency (CUEe) is a crucial indicator for assessing the capacity of ecosystems to sequester atmospheric carbon (C). However, it remains unclear how nitrogen (N) and phosphorus (P) influence CUEe and how climatic factors regulate CUEe. Here, a four-year manipulative experiment was conducted in a semi-arid alpine grassland ecosystem to explore the response of CUEe to N and P additions with fluctuating interannual precipitation. Our study revealed that the N and P combination synergistically improved CUEe; the single additions of N or P did not affect CUEe. The variation in CUEe was correlated to a larger in net ecosystem CO2 exchange (NEE) relative to gross ecosystem productivity (GEP). Similarly, the combination of N and P significantly increased aboveground biomass, whereas addition alone did not. Under the combined addition of N and P, a significant decrease in species diversity led to decreases in CUEe. Moreover, precipitation indirectly increased CUEe by increasing NEE. Our findings underscore the co-limitation of N and P resources for CUEe in the alpine grassland ecosystem and identify community structure and climate factors as key drivers of CUEe variations following nutrient enrichment.

Chromophoric dissolved organic matter traces seasonally changing coastal processes in a river-influenced region of the western Bay of Bengal.

The optical characteristics of colored dissolved organic matter (CDOM) serve as a convenient tool for evaluating coastal processes, e.g., river runoff, anthropogenic inputs, primary production, and bacterial/photochemical processes. We conducted a study on the seasonal and spatial variability of absorbance and fluorescence characteristics of CDOM and nutrients in the coastal waters near the Gauthami estuary of River Godavari, the largest peninsular river of India, for a year. The surface aCDOM(350) showed a significant inverse relation with salinity in the coastal region, indicating a conservative mixing of marine and terrestrial end members. The aCDOM(350) was not conservative in the offshore (100m isobath) waters due to enrichment by secondary sources. Seasonal variability in optical properties indicated diverse sources for CDOM, as revealed by principal component analysis. The excitation-emission matrix (EEM) spectra followed by parallel factor analysis (EEM-PARAFAC) revealed four distinct fluorophores. The tyrosine (B) fluorophore showed a predominant increase in the post-monsoon season (October to January), while tryptophan (T) was relatively more enriched, coincident with nutrient enrichment and transparency increase during the early monsoon phase (July). The biological index (BIX), which reflects recent photosynthetic activity, also displayed relatively higher values during the early monsoon. The humic fluorophores A and M, and humification index (HIX) were relatively enriched during the later phase of monsoon (July-October). HIX was > 4 in a few samples of the offshore region (100-m isobath) and indicated a probable contamination from drill-mud (bentonite) used in hydrocarbon exploration. During the monsoon, the relationship between T and B with CDOM was not evident due to the masking of B fluorescence in intact protein. However, during the post-monsoon (POM) and pre-monsoon (PRM) periods, this masking effect was not observed, likely due to protein degradation via bacterial and photochemical processes, respectively. Temporal variability in nutrients indicated that high ammonium levels were produced during POM (OM bacterial degradation), and high nitrite levels were observed during PRM (due to primary production). This study provides foundational insights into the use of CDOM for understanding the impact of diverse environmental, river discharge, and anthropogenic factors on coastal ecosystems.

Impact of Nutrient Enrichment on Community Structure and Co-Occurrence Networks of Coral Symbiotic Microbiota in Duncanopsammia peltata: Zooxanthellae, Bacteria, and Archaea.

Symbiotic microorganisms in reef-building corals, including algae, bacteria, archaea, fungi, and viruses, play critical roles in the adaptation of coral hosts to adverse environmental conditions. However, their adaptation and functional relationships in nutrient-rich environments have yet to be fully explored. This study investigated Duncanopsammia peltata and the surrounding seawater and sediments from protected and non-protected areas in the summer and winter in Dongshan Bay. High-throughput sequencing was used to characterize community changes, co-occurrence patterns, and factors influencing symbiotic coral microorganisms (zooxanthellae, bacteria, and archaea) in different environments. The results showed that nutrient enrichment in the protected and non-protected areas was the greatest in December, followed by the non-protected area in August. In contrast, the August protected area had the lowest nutrient enrichment. Significant differences were found in the composition of the bacterial and archaeal communities in seawater and sediments from different regions. Among the coral symbiotic microorganisms, the main dominant species of zooxanthellae is the C1 subspecies (42.22-56.35%). The dominant phyla of bacteria were Proteobacteria, Cyanobacteria, Firmicutes, and Bacteroidota. Only in the August protected area did a large number (41.98%) of SAR324_cladeMarine_group_B exist. The August protected and non-protected areas and December protected and non-protected areas contained beneficial bacteria as biomarkers. They were Nisaea, Spiroplasma, Endozoicomonas, and Bacillus. No pathogenic bacteria appeared in the protected area in August. The dominant phylum in Archaea was Crenarchaeota. These symbiotic coral microorganisms' relative abundances and compositions vary with environmental changes. The enrichment of dissolved inorganic nitrogen in environmental media is a key factor affecting the composition of coral microbial communities. Co-occurrence analysis showed that nutrient enrichment under anthropogenic disturbances enhanced the interactions between coral symbiotic microorganisms. These findings improve our understanding of the adaptations of coral holobionts to various nutritional environments.

Effect of Fertilizer With Potassium Humate and the Method of Addition to the Growth and Yield of Red Cabbage

Background: The application of potassium humate has been recognized for its potential to enhance plant growth and yield due to its nutrient enrichment properties. Specific Background: Despite extensive research on various fertilizers, the specific effects of potassium humate on red cabbage (Ruby King cultivar) growth and yield, especially concerning the method of application, remain underexplored. Knowledge Gap: Limited studies have addressed the comparative impact of foliar spraying versus soil addition of potassium humate on cabbage vegetative growth and yield characteristics. Aims: This study aimed to evaluate the effects of different concentrations of potassium humate (0, 50, 100, 150 g.l-1) and application methods (foliar spraying and soil addition) on the growth and yield of red cabbage. Results: A randomized complete block design (RCBD) with three replications was implemented during the 2022-2023 agricultural season. Significant improvements in vegetative growth and yield were observed with the highest concentration (150 g.l-1) of foliar spraying. Key vegetative and yield parameters, such as plant height, stem length, number of leaves, leaf chlorophyll content, average head weight, and total yield, were positively influenced. Novelty: This study uniquely highlights the superior efficacy of foliar spraying with potassium humate at 150 g.l-1 over soil addition, providing insights into optimizing fertilization strategies for red cabbage. Implications: The findings advocate for the use of potassium humate, particularly via foliar spraying, as a beneficial organic fertilizer to enhance red cabbage growth and yield. This practice could lead to improved agricultural productivity and better tolerance of plants to environmental stresses, supporting sustainable agriculture initiatives. Highlights: Superior Growth: Foliar spraying with 150 g.l-1 potassium humate boosts growth. Yield Increase: Highest humate concentration yields maximum red cabbage. Effective Strategy: Foliar spraying outperforms soil addition for fertilization. Keywords: Potassium humate, foliar spraying, red cabbage, vegetative growth, yield enhancement

Functional traits of exotic submerged macrophytes mediate diversity-invasibility relationship in freshwater communities under eutrophication

Plant diversity may respond differently in terms of whether it can drive plant invasions in freshwater ecosystem. Linkages and interactions between diversity and invasibility have not been clearly resolved, and it is unclear how nutrient enrichment (e.g., eutrophication) will affect this relationship. As a key predictor of plant growth, the ability of functional traits to mediate trade-offs in the diversity-invasibility relationship is unknown. Here, we conducted a series of experiments to determine the role of exotic plant functional traits in the diversity-invasibility relationship of submerged macrophyte communities under eutrophication. We selected common native and exotic submerged macrophytes in the subtropics to construct different diverse submerged macrophyte communities to simulate invasion. Meanwhile, to test the adaptability and importance of functional traits, we experimentally verified the differences in functional traits between exotic and native species. Our results showed a positive correlation between native plant diversity and community invasibility. Moreover, the invader's performance was predominantly determined by functional traits of exotic species, such as plant biomass and tissue nutrients, which were significantly altered by species diversity. Furthermore, our results suggested that functional traits contribute significantly more to the invasiveness of exotic submerged macrophytes than the other factors to which they are subjected. Plant functional traits can mediate the diversity–invasibility relationship because of the higher intrinsic dominance of exotic submerged macrophyte species. In summary, our study revealed diversity-invasibility relationship in submerged macrophyte communities and highlighted functional traits as key drivers of invasion of high-risk exotic submerged macrophyte species. Although previous studies have elucidated the importance of functional trait studies for plant invasions, our study provides the only current evidence demonstrating the important role of invaders' functional traits in mediating the diversity-invasibility relationship. This novel perspective offers valuable insights into the management and control of invasive aquatic plants.

Forest zone and root compartments outweigh long-term nutrient enrichment in structuring arid mangrove root microbiomes

Forest zone and root compartments outweigh long-term nutrient enrichment in structuring arid mangrove root microbiomes

Enrichment of nutrients from anaerobically digested centrate minimizing microplastics content using a combination of membrane processes

Centrifuge effluent, or centrate, is a liquid stream generated in the sludge line of wastewater treatment plants in the sludge dewatering process. Nutrients are solubilized in the anaerobic digestion of the sludge, mainly in the form of ammonium-nitrogen and phosphates. Thus, when the dewatering of the digested sludge is performed (usually by centrifugation), a sludge liquor stream enriched in nutrients is generated. However, it also contains microparticles, including microplastics, since most of the microparticles from the wastewater are transferred to the sludge treatment line in wastewater treatment plants. In this work, microplastics in centrate have been analyzed (counted and identified), and membrane technologies (ultrafiltration and forward osmosis) have been applied to concentrate nutrients and to obtain a microplastic-free stream for further nutrient recovery. Two alternative configurations have been compared, changing the application order of these processes. The results showed that obtaining a stream with a concentration higher than 6000 mg/L of ammonium has been possible by using ammonium sulfate (150 g/L) as a draw solution in the forward osmosis process. On the other hand, as a consequence of the ultrafiltration application, microparticles were concentrated in the reject stream up to 800 microparticles/L. At the same time, the permeate presents a lower concentration of microplastics without reducing the concentration of the nutrients. In this way, this pioneering study enables the production of a nutrient-enriched stream with reduced microplastic concentrations, that could be applied to the agricultural soil as biofertilizer.

Diversity of carbon cycle-linked phyllosphere microorganisms: A key driver of CO2 flux in macrophyte-dominated aquatic systems

Planktonic microorganisms have been recognized as important components in biogeochemical cycling in lakes. However, research into the impact of phyllosphere microorganisms, particularly those involved in carbon cycling, on CO2 fluxes in macrophyte-dominated lakes within the context of global environmental changes remains scarce. Here, by employing high-throughput sequencing techniques, we experimentally tested how nutrient enrichment, top-down effects of fish and increases in dissolved organic carbon (DOC) affect CO2 exchange flux at the water-air interface by altering the community structure and functioning of phyllosphere bacteria on macrophytes. We found that our mesocosm ecosystems exhibited a net absorption of CO2, but nutrient enrichment significantly decreased the absorption ability. Mantel tests and multiple regression modeling also showed that eutrophication-associated parameters (total nitrogen, total phosphorus and ammonium nitrogen), pH, and extinction coefficient were the key drivers influencing abundance of phyllosphere functional microorganisms. In addition, these experimental treatments significantly altered the composition, diversity and co-occurrence networks of carbon cycling-associated phyllosphere microorganisms, which impacted the CO2 flux. Structural equation models and linear regression further showed that the Shannon Index of phyllosphere functional microorganisms related to carbon cycling (rather than plant volume inhabited - PVI) had a significant positive impact on CO2 fixation. This means that environmental changes—especially eutrophication—may hinder carbon sequestration by decreasing the diversity of phyllosphere microorganisms rather than reducing the abundance of submerged macrophytes. This study increases our understanding of carbon cycling processes in aquatic environments from a management perspective by emphasizing the importance of protecting the diversity of phyllosphere microorganisms in macrophyte-dominated lakes.

DYNAMICS OF A TRI-TROPHIC LEVEL MODEL WITH EXCESS FOOD NUTRIENT CONTENT AND INTRAGUILD PREDATION STRUCTURE

The dynamics of consumers can be affected by both nutrient-deficient food (low phosphorus (P) to carbon (C) ratio) and nutrient-excessive (high P:C) food, which is known as the stoichiometric knife-edge phenomenon. In this study, aiming to illustrate the responses of herbivores and omnivores to food with excessive P content, we present and analyze a tri-trophic level stoichiometric knife-edge model incorporating the intraguild predation structure. The model dynamics are theoretically examined, including the boundedness and positivity of solutions, the existence and stability of boundary equilibria, and the existence of positive equilibria. Numerical simulations show that the model has complex dynamics, encompassing chaotic-like oscillations, multiple types of bifurcations, long transients, and regime shifts. Moderate P levels facilitate the coexistence of the three species, whereas both lower and higher P levels result in the extinction of herbivores and omnivores. Specifically, the energy enrichment paradox occurs at low P levels. In contrast, the nutrient enrichment paradox occurs at high P levels, both of which are detrimental to the survival of herbivores and omnivores. Furthermore, the high-intensity predation of producers by omnivores helps to restrain the occurrence of chaotic dynamics. These findings contribute to a deeper understanding of the mechanisms of multi-species coexistence.

Hydrothermal carbonisation of manure-derived digestates: Chemical properties and heavy metals distribution in end-products

Hydrothermal carbonisation (HTC) presents a promising method for converting high-moisture biomass into hydrochars, which can serve as valuable sources of carbon and nutrients for soil applications. However, there is a lack of comprehensive understanding regarding the characterisation and potential environmental risks of hydrochars with respect to different feedstock types and operating conditions especially when compared to those obtained from dry pyrolysis. This research aims to investigate the chemical properties and re-partitioning of Ni, Cd, Cr and Pb in the HTC-treated mono-and co-digestates derived from the anaerobic digestion of pig manure and ensiled maize. Hydrochars were produced from homogeneous digestate slurries, where manure was derived from a unique source separation facility, and maize was collected from a contaminated land, both containing potentially higher concentrations of heavy metals (HMs) compared to typical feedstock. The hypothesis states that HTC would further reduce the potential availability of these metals, enhancing the quality of the end-products as bio-based fertilisers or soil improvers. The derived hydrochars were analysed for their composition and HMs extractability. Higher yields were observed for both digestates at lower temperatures and shorter residence times, whereas the total nitrogen and carbon content showed an opposite trend. The composition of the digestates and the HTC operating parameters influenced the enrichment of nutrients and release of the HMs from the hydrochars, enabling their classification as potential solid organic fertilisers according to the Fertilising Products Regulation (EU) 2019/1009. Notably, the HTC treatment at 200–220 °C for 4 h resulted in the highest immobilization of Ni, Cd, Cr, and Pb in both digestates. This treatment strategy effectively reduced the ecological risk index of these products, thereby mitigating potential environmental impacts associated with the HMs contamination.

Bottom water quality plasticity in the northern gulf of Mexico hypoxic zone

The growth of the now ubiquitous hypoxic zones found throughout the global coastal ocean are primarily a consequence of nutrient enrichment in surface waters increasing organic production that sinks into bottom waters where oxygen is depleted faster than it is replenished. Hypoxic zones may increase or decline in number because of future climate changes. Here we summarize the summertime variations of dissolved inorganic silicate (DSi), phosphate (DIP), nitrogen (DIN; nitrate + nitrite and ammonium) and ammonium concentrations in the bottom waters of the northern Gulf of Mexico continental shelf from 1985 to 2022. The concentrations of all three are strongly correlated to oxygen concentrations, but not in the same way. At zero oxygen concentration, the annual concentrations of DSi, DIP, and ammonium changed over 38 years at a rate of 1.6 % y−1, 2.0 % y−1 and -1.7 % y−1, respectively. However, the nitrate + nitrite concentrations at zero oxygen concentrations did not change over the same interval. The silicate efflux from anoxic sediments is directly related to warming temperatures and is co-related to phosphate concentrations. The bottom water DSi:DIN molar ratios increased over three decades as DIN:DIP molar ratios decreased, suggesting strong nitrogen limitation compared to silicate and phosphate, and reveal significant plasticity in regeneration rates in the bottom waters that may be dependent on changes in the surface waters. Hypoxia and food web models based on a stationary equipoise of these amounts and ratios in surface and bottom waters will likely be deficient as coastal waters warm, acidification increases, and river water quality changes. Data refreshment and improved understanding of food web changes and warming futures are recommended.

Microplastic pollution and nutrient enrichment shift the diet of freshwater macroinvertebrates

Microplastic pollution poses a global threat to freshwater ecosystems, with laboratory experiments indicating potential toxic impacts through chemical toxicity, physical abrasion, and false satiation. Bioplastics have emerged as a potential greener alternative to traditional oil-based plastics. Yet, their environmental effects remain unclear, particularly at scales relevant to the natural environment. Additionally, the interactive impacts of microplastics with other environmental stressors, such as nutrient enrichment, are poorly understood and rarely studied. Under natural conditions organisms might be able to mitigate the toxic effects of microplastics by shifting their diet, but this ability may be compromised by other stressors. This study combines an outdoor mesocosm experiment and stable isotope analysis to determine changes in the trophic niches of three freshwater invertebrate species exposed to conventional (HDPE) and bio-based biodegradable (PLA) microplastics at two concentrations, both independently and combined with nutrient enrichment. Exposure to microplastics altered the isotopic niches of two of the invertebrate species, with nutrient enrichment mediating this effect. Moreover, the effects of microplastics were consistent regardless of their type or concentration. Under enriched conditions, two of the species exposed to microplastics shifted to a specialised diet compared with controls, whereas little difference was observed between the isotopic niches of those exposed to microplastic and controls under ambient nutrient conditions. Additionally, PLA was estimated to support 24 % of the diet of one species, highlighting the potential assimilation of bioplastics by biota and possible implications. Overall, these findings suggest that the toxic effects of microplastics suggested from laboratory studies might not manifest under real-world conditions. However, this study does demonstrate that subtle sublethal effects occur even at environmentally realistic microplastic concentrations. The crucial role of nutrient enrichment in mediating microplastic effects underscores the importance of considering microplastic pollution in the context of other environmental stressors.

Benthic diatom diversity in microtidal mangrove estuaries

Mangrove habitats support taxonomically diverse benthic communities, yet their effects on microphytobenthos remain understudied. This study investigated the benthic diatom community structure of 17 microtidal mangrove estuaries situated along the east coast of South Africa. High sediment organic content (≤ 18.1 %) and clay fraction (≤ 17.5 %) measured in the Avicennia marina and Rhizophora mucronata habitats favoured diverse communities (H′ > 3) and the presence of unique benthic diatom species such as Gyrosigma balticum. The habitat complexity and stabilisation provided by the mangrove forests served as microrefugia for colonisation of benthic diatoms. Taxa displayed a broad range of nutrient tolerance, with some nutrient tolerant species (e.g., Halamphora acutiuscula, Navicula clausii, Navicula gregaria, and Navicula radiosa) dominating the communities in the Mbashe and Mnyameni estuaries. The presence of these nutrient tolerant taxa in relatively pristine systems serves as an early warning for possible anthropogenic nutrient enrichment.

Arbuscular mycorrhizal communities respond to nutrient enrichment and plant invasion in phosphorus‐limited eucalypt woodlands

Abstract Arbuscular mycorrhizal fungi (AMF) facilitate ecosystem functioning through provision of plant hosts with phosphorus (P), especially where soil P is limiting. Changes in soil nutrient regimes are expected to impact AMF, but the direction of the impact may depend on context. We predicted that nitrogen (N)‐only enrichment promotes plant invasions and exacerbates their P limitation, increasing the utility of AMF and promoting AMF diversity. We expected that enrichment with N, P and other nutrients similarly promotes plant invasions, but decreases the benefit and diversity of AMF because P is readily available for both native and exotic plants. We tested these hypotheses in eucalypt woodlands of south‐western Australia, that occur on soils naturally low in P. We evaluated AMF communities within three modified ground‐layer states representing different types of nutrient enrichment and associated plant invasions. We compared these modified states to near‐natural reference woodlands. AMF richness varied across ground‐layer states. The moderately invaded/N‐enriched state showed the highest AMF richness, while the highly invaded/NP‐enriched state showed the lowest AMF richness. The reference state and the weakly invaded/enriched state were intermediate. AMF richness and colonisation were higher in roots of exotic than native plant species. AMF community composition differed among ground‐layer states, with the highly invaded/NP‐enriched state being most distinct. Distinctions among states were often driven by family‐level patterns. Reference and moderately invaded/N‐enriched states each supported distinct groups of zero‐radius operational taxonomic units (zOTUs) in Acaulosporaceae, Gigasporaceae and Glomeraceae, whereas Gigasporaceae and Glomeraceae were nearly absent from the highly invaded/NP‐enriched state. Further, Diversisporaceae and Glomeraceae were most diverse in the moderately invaded/N‐enriched state. Synthesis. Both the nature of soil nutrient enrichment and plant provenance matter for AMF. N‐only enrichment of low‐P soils increased AMF richness, likely due to the introduction of AMF‐dependent exotic plant species and exacerbation of their P limitation. In contrast, multi‐nutrient enrichment, decreased AMF richness potentially due to a decrease in host dependence on AMF, regardless of host provenance. The changes in AMF community composition with nutrient enrichment and plant invasion warrant further research into predicting the functional implications of these changes.

The Bonney Coast upwelling: How physical processes shape the feeding behaviour of blue whales

This study employs a fully coupled physical-biological model to explore the oceanic dynamics and phytoplankton production in one of Australia’s most prominent coastal upwelling systems, the Bonney Coast Upwelling, that has barely been studied before. The study focusses on how physical processes provide two different food sources for blue whales (Balaenoptera musculus), namely, krill (treated as nonbuoyant particles) and zooplankton, both feeding on phytoplankton. While plankton grows in the euphotic zone in response to nutrient enrichment on time scales of weeks, krill can only be transported into the region via ambient currents. Findings of this study suggest that phytoplankton blooms appear slowly in the main upwelling plume on timescales of 4-8 weeks. Dynamical influences from incoming coastal Kelvin waves significantly weaken or strengthen this classical upwelling plume and its plankton productivity. On the other hand, the upwelling-favourable wind induces a continuous coastal current that also extends eastward past the Bonney Coast. This current operates to transport and distribute krill (that cannot swim horizontally) westward along the shelf, which explains the apparent conundrum why blue whales also feed on the upstream side of the upwelling plume. The author postulates that the variability of both plankton production and the intensity of the upwelling flow (passing krill swarms along the shelf) control the feeding locations of blue whales and other baleen whales on Australia’s southern shelves.