Nutrient Saturation Research Articles

Multiple antibiotic resistance and herbicide catabolic profiles of bacteria isolated from Lake Villarrica surface sediments (Chile)

Antibiotics and herbicides are contaminants of emerging concern in aquatic environments. Lake Villarrica is a relevant freshwater body in Chile and was recently designated a ‘saturated nutrient zone’. Here, we investigated the occurrence of multiple antibiotic resistance (MAR) and herbicide catabolic profiles among bacteria present in the surface sediments of Lake Villarrica. The occurrence of antibiotic-resistant genes (ARGs; blaTEM, catA and tetM) and herbicide-catabolic genes (HCGs; phnJ and atzA) was investigated by qPCR. Subsequently, the presence of culturable bacteria with multiple resistance to amoxicillin (AMX), chloramphenicol (CHL) and oxytetracycline (OXT) was studied. Forty-six culturable MAR (AMX + CHL + OXT) strains were isolated and characterized with respect to their resistance to 11 antibiotics by using a disc diffusion assay and testing their ability to use herbicides as a nutrient source. qPCR analyses revealed that ARGs and HCGs were present in all sediment samples (101 to 103 gene copies g−1), with significant (P ≤ 0.05) higher values in sites near Villarrica city and cattle pastures. The plate method was used to recover MAR isolates from sediment (103–106 CFU g−1), and most of the 46 isolates also showed resistance to oxacillin (100%), cefotaxime (83%), erythromycin (96%) and vancomycin (93%). Additionally, 54 and 57% of the MAR isolates were able to grow on agar supplemented (50 mg L−1) with atrazine and glyphosate as nutrient sources, respectively. Most of the MAR isolates were taxonomically close to Pseudomonas (76.1%) and Pantoea (17.4%), particularly those isolated from urbanized sites (Pucón city). This study shows the presence of MAR bacteria with herbicide catabolic activity in sediments, which is valuable for conservation strategies and risk assessments of Lake Villarrica. However, major integrative studies on sediments as reservoirs or on the fate of MAR strains and traces of antibiotics and herbicides as a result of anthropic pressure are still needed.

Nutrient leaching potential along a time series of forest water reclamation facilities in northern Idaho

Forest water reclamation is a decades-old practice of repurposing municipal reclaimed water using land application on forests to filter nutrients and increase wood production. However, long-term application may lead to nutrient saturation, leaching, and potential impairment of ground and surface water quality. We studied long-term effects of reclaimed water application on nutrient leaching potential in a four-decade time series of forest water reclamation facilities in northern Idaho. Our approach compared reclaimed water treated plots with untreated control plots at each of the forest water reclamation facilities. We measured soil nitrifier abundance and net nitrification rates and used tension lysimeters to sample soil matrix water and drain gauges to sample from a combination of matrix and preferential flow paths. We determined nutrient leaching as the product of soil water nutrient concentrations and model-estimated drainage flux. There was more than 450-fold increase in nitrifier abundance and a 1000-fold increase in net nitrification rates in treated plots compared with control plots at long-established facilities, indicating greater nitrate production with increased cumulative inputs. There were no differences in soil water ammonium, phosphate, and dissolved organic nitrogen concentrations between control and effluent treatments in tension lysimeter samples. However, concurrent with increased nitrifier abundance and net nitrification, nitrate concentration below the rooting zone was 2 to 4-fold higher and nitrate leaching was 4 to 10-fold higher in effluent treated plots, particularly at facilities that have been in operation for over two decades. Thus, net nitrification and nitrifier abundance assays are likely indicators of nitrate leaching potential. Inorganic nutrient concentrations in drain gauge samples were 2 to 11-fold higher than lysimeter samples, suggesting nutrient losses occurred predominantly through preferential flow paths. Nitrate was vulnerable to leaching during the wet season under saturated flow conditions. Although nitrogen saturation is a concern that should be mitigated at long-established facilities, these forest water reclamation facilities were able to maintain average soil water nitrate concentrations to less than 2 mg L−1, so that nitrogen and phosphorous are effectively filtered to below safe water standards.

The morphophysiological and yield characteristics of biquinho amarelo pepper in response to bovine rumen residue and chicken litter in soil are dose dependent

In response to the growing demand for environmentally sustainable agricultural practices that enhance production efficiency, this study aimed to determine the optimal application rates of bovine rumen content (CBR) and chicken litter (CCL) as organic composts. Conducted in a controlled greenhouse environment, the research assessed the effects of various doses of these composts on soil chemical and microbiological properties and on the growth and productivity of yellow biquinho pepper (Capsicum chinense Jacq.). The results of this study confirm that organic composts improve soil health and increase the growth and productivity of yellow biquinho pepper. However, while CBR consistently enhances plant growth across a range of doses, CCL shows a dose-dependent response, with the highest fruit production achieved at an application rate of 73.92 Mg ha−1. Although this dose of CCL is beneficial for increasing yield, it also marks a threshold beyond which further increases may lead to negative effects such as nutrient saturation or salt accumulation, potentially resulting in soil toxicity. The study supports the use of CBR and CCL as effective soil conditioners and emphasizes the need to identify the optimal compost dose to efficiently harness the benefits of organic composts in sustainable agricultural practices.

Exploring long-term trends in microcystin toxin values associated with persistent harmful algal blooms in Grand Lake St Marys

High external nutrient loads from agricultural runoff have led to persistent and highly toxic algal blooms in Grand Lake St Marys (GLSM) for decades. These pervasive blooms are concurrent with long-term (2009 – 2021) toxin and environmental monitoring, providing a robust weekly dataset for modeling microcystins. Median weekly microcystin concentrations (23.2 µg/L) routinely exceeded World Health Organization recreational limits (20 µg/L) for the study period (ranged 0.03 - 185.0 µg/L). Here, we used a Bayesian hierarchical dynamic linear model to hindcast weekly microcystin toxins using external nutrient loads from tributary data as well as internal lake nutrient and physicochemical concentrations. Overall, lake TN was the biggest driver of microcystin concentration in GLSM. Likewise, TN:TP was a strong negative driver of microcystin (i.e. low N:P ratios align with lower total microcystins), suggesting that N availability directly impacts toxins. External nutrient loading was positively related to microcystin during winter and spring; however, there was no relationship detected between toxin and external loading during summer or fall (particulate phosphorus exhibited the strongest signal but all external nutrients were unsurprisingly correlated). This lack of direct correlation on a weekly timescale between external loads and cyanobacterial toxins during the summer months likely results from nutrient saturation and reflects the importance of internal loading for bloom maintenance as supported by the correlation between in-lake TN and microcystin. Thus, management goals to reduce the highest biomass and toxins in the summer should focus on reduction of winter and spring external nutrient loads. Supporting this, both 2010 and 2021 had lower rain in the first half of the year (winter/spring), resulting in less loading, and experienced smaller/later low toxicity blooms. This suggests that, although internal nutrient loads are important for bloom maintenance, reduced external loads are an effective management strategy even in nutrient saturated systems such as GLSM.

Environmental stress level to model tumor cell growth and survival.

Survival of living tumor cells underlies many influences such as nutrient saturation, oxygen level, drug concentrations or mechanical forces. Data-supported mathematical modeling can be a powerful tool to get a better understanding of cell behavior in different settings. However, under consideration of numerous environmental factors mathematical modeling can get challenging. We present an approach to model the separate influences of each environmental quantity on the cells in a collective manner by introducing the "environmental stress level". It is an immeasurable auxiliary variable, which quantifies to what extent viable cells would get in a stressed state, if exposed to certain conditions. A high stress level can inhibit cell growth, promote cell death and influence cell movement. As a proof of concept, we compare two systems of ordinary differential equations, which model tumor cell dynamics under various nutrient saturations respectively with and without considering an environmental stress level. Particle-based Bayesian inversion methods are used to quantify uncertainties and calibrate unknown model parameters with time resolved measurements of in vitro populations of liver cancer cells. The calibration results of both models are compared and the quality of fit is quantified. While predictions of both models show good agreement with the data, there is indication that the model considering the stress level yields a better fitting. The proposed modeling approach offers a flexible and extendable framework for considering systems with additional environmental factors affecting the cell dynamics.

Application of Freeze Concentration Technologies to Valorize Nutrient-Rich Effluents Generated from the Anaerobic Digestion of Agro-Industrial Wastes

The production of biogas through anaerobic digestion implies the generation of 90–95% of digested raw material, namely digestate. A nutrient-rich stream is generally applied to cropland to enhance yields, due to its high abundance of nutrients. Nevertheless, the intensive digestate farming brings about nutrient saturation and groundwater contamination. The application of downstream emerging technologies that focus on the recovery of nutrients from digestate have been studied, yet freeze concentration technology (FC) has never been considered for this purpose. This study evaluates the performance of FC technology applied to concentrate nitrogen (N), phosphorus (P) and potassium (K) from an effluent of a reverse osmosis unit that is treating the digestate of agro-industrial waste effluents. For this aim, two lab-scale methodological approaches were investigated, namely, progressive FC (PFC) and suspension FC (SFC), set through the utilization of different FC configurations. The concentrates obtained in both FC methods agreed with the regulations for fertilizers in terms of nutrients and metals content; meanwhile, the diluted fraction can be delivered as water for irrigation in high-density livestock areas. The application of FC solves the transportation cost side effect of livestock waste on the one hand, and soil contamination with nutrient on the other hand.

Grazing Induced Shifts in Phytoplankton Cell Size Explain the Community Response to Nutrient Supply.

Phytoplankton cell size is important for a multitude of functional traits such as growth rates, storage capabilities, and resistance to grazing. Because these response traits are correlated, selective effects on mean community cell size of one environmental factor should impact the ability of phytoplankton to cope with other factors. Here, we experimentally apply expectations on the functional importance of phytoplankton cell size to the community level. We used a natural marine plankton community, and first altered the community’s cell size structure by exposing it to six different grazer densities. The size-shifted communities were then treated with a saturated nutrient pulse to test how the changes in community size structure influenced the mean community growth rate in the short-term (day 1–3) and nutrient storage capacity in the postbloom phase. Copepod grazing reduced the medium-sized phytoplankton and increased the share of the smallest (<10 µm3) and the largest (>100,000 µm3). Communities composed of on average small cells grew faster in response to the nutrient pulse, and thus confirmed the previously suggested growth advantage of small cells for the community level. In contrast, larger phytoplankton showed better storage capabilities, reflected in a slower post-bloom decline of communities that were on average composed of larger cells. Our findings underline that the easily measurable mean cell size of a taxonomically complex phytoplankton community can be used as an indicator trait to predict phytoplankton responses to sequential environmental changes.

Nutrient saturation of crop monocultures and agroforestry indicated by nutrient response efficiency

Efficient use of nutrients is a key requisite for a sustainable intensification of agriculture in order to meet the increasing global crop demand while minimizing deleterious environmental impacts. Agroforestry systems exhibit tree–crop interactions, which potentially contribute to nutrient-efficient agro-ecosystems. Our goal was to determine whether the conversion from cropland monocultures to alley-cropping agroforestry increases nutrient response efficiency (NRE), the ability of plants to convert available nutrients into biomass. We found that crop yield, plant-available nutrients and NRE were comparable between agroforestry and monocultures, but the trees in agroforestry had high NRE, contributing to nutrient retention of the agroforestry systems as a whole. The unimodal relationship of the crops’ NRE with plant-available nutrients suggests that NRE values were beyond optimum in both agroforestry and monoculture indicating nutrient saturation. This indicates that fertilizer inputs can be reduced (or optimized) without sacrificing crop yield or profit. Based on the NRE curves, we assessed that a reduction of plant-available N by 50% would lead to a decrease in crop yield by 17% and a concomitant increase in N response efficiency by 67%, whereas a similar reduction of plant-available P would lead to a decrease in crop yield by 8% with an increase in P response efficiency by 83%. An optimized fertilization to achieve such lower levels of plant-available nutrients will have beneficial effects on nutrient retention and redistribution. Optimizing fertilizer input will make alley-cropping agroforestry a productive and profitable agro-ecosystem that contributes to an ecologically sustainable agriculture.

Nutrient limitation of phytoplankton in Chesapeake Bay: Development of an empirical approach for water-quality management

Understanding the temporal and spatial roles of nutrient limitation on phytoplankton growth is necessary for developing successful management strategies. Chesapeake Bay has well-documented seasonal and spatial variations in nutrient limitation, but it remains unknown whether these patterns of nutrient limitation have changed in response to nutrient management efforts. We analyzed historical data from nutrient bioassay experiments (1992–2002) and data from long-term, fixed-site water-quality monitoring program (1990–2017) to develop empirical approaches for predicting nutrient limitation in the surface waters of the mainstem Bay. Results from classification and regression trees (CART) matched the seasonal and spatial patterns of bioassay-based nutrient limitation in the 1992–2002 period much better than two simpler, non-statistical approaches. An ensemble approach of three selected CART models satisfactorily reproduced the bioassay-based results (classification rate = 99%). This empirical approach can be used to characterize nutrient limitation from long-term water-quality monitoring data on much broader geographic and temporal scales than would be feasible using bioassays, providing a new tool for informing water-quality management. Results from our application of the approach to 21 tidal monitoring stations for the period of 2007–2017 showed modest changes in nutrient limitation patterns, with expanded areas of nitrogen-limitation and contracted areas of nutrient saturation (i.e., not limited by nitrogen or phosphorus). These changes imply that long-term reductions in nitrogen load have led to expanded areas with nutrient-limited phytoplankton growth in the Bay, reflecting long-term water-quality improvements in the context of nutrient enrichment. However, nutrient limitation patterns remain unchanged in the majority of the mainstem, suggesting that nutrient loads should be further reduced to achieve a less nutrient-saturated ecosystem.

Predicting Nutrient Incontinence in the Anthropocene at Watershed Scales

Quantifying nutrient attenuation at watershed scales requires long-term water chemistry data, water discharge, and detailed nutrient input chronicles. Consequently, nutrient attenuation estimates are largely limited to long-term research areas or modeling studies, constraining understanding of the ecological characteristics controlling nutrient attenuation and complicating efforts to protect or restore water quality in developed and developing regions. Here, we combined long-term data and a broad suite of biogeochemical parameters from 49 watersheds in northwestern France to test how well instantaneous measurements can predict nitrogen (N) and phosphorus (P) attenuation at watershed scales. We evaluated 13 biogeochemical and 12 hydrological proxies of hydrological flowpaths, residence time, and biogeochemical transformation. Across the 49 watersheds, nutrient attenuation ranged from 88 to −2% for N and 99-96% for P. The strongest biogeochemical proxies of N attenuation were NO − 3 isotopes, rare earth elements (REEs), radon, and turbidity, together explaining 75% of observed variation. For P attenuation, REEs, NO − 3 isotopes, molecular weight of dissolved organic matter, and radon were the strongest proxies, but only explained 27% of observed variation. However, a single hydrological parameter-annual runoff-explained 91% of N attenuation and the relative abundance of schist bedrock explained 56% of P attenuation. We discuss how runoff both controls and reflects watershed hydrology, biogeochemistry, and nutrient attenuation. For example, runoff was correlated with long-term decreases in nutrient concentration, demonstrating how leakier watersheds recover more quickly from nutrient saturation. Given the immense fertilization capacity of modern society, we propose that eutrophication can only be solved by reducing nutrient inputs, though hydrochemical proxies can provide valuable information on where to carry out essential food production activities.

Ex vivo biophysical characterization of a hydrogel-based artificial vitreous substitute.

PurposeTo characterize the biophysical properties of an artificial vitreous body substitute (VBS), which consists of a biocompatible, cross-linked, hyaluronic acid (HA)-based hydrogel, by analysing the VBS’s influence on intraocular pressure (IOP) and retinal integrity in distinct ex vivo eye models in order to evaluate the its potential for in vivo biocompatibility testing.MethodsPig eyes were obtained immediately postmortem, and VBS was injected after core-vitrectomy. IOP was followed for 24 h (n = 5). VBS influence on retinal integrity was investigated using isolated bovine retinas superfused with an oxygen saturated nutrient solution. An electroretinogram (ERG) was recorded on explanted bovine retinae using silver/silver chloride electrodes; after application of VBS for 2 min, a washout period of 70 min was employed. The percentage of a-and b-wave reduction at the end of the washout phase was compared to baseline values (n = 5). Data were calculated throughout as the mean and the standard deviation. qRT-PCR (Bax/Bcl–2-ratio, GFAP- and PGP9.5-levels) or western blot analysis was used to test for toxicity of Princess Volume after 24 h (and β-3 tubulin with GAPDH as a control gene). Significance was estimated by Student´s t-test; p ≤0.05 was considered to be statistically significant.ResultsThe IOP increased non-significantly by 10% after 24 h. Short-term biocompatibility testing using isolated superfused bovine retinas showed neither significant reductions of the b-wave nor the a-wave amplitudes (b-wave reduction 14.2%, p>0.05; a-wave reduction 23.9%, p>0.05). qRT-PCR and western blot analysis did not reveal significant toxicity after 24 h.ConclusionsThe manufactured HA-based hydrogel showed highly favourable biophysical characteristics in the explored ex vivo models, justifying in vivo studies enabling the assessment of biocompatibility.

Influence of dual nitrogen and phosphorus additions on nutrient uptake and saturation kinetics in a forested headwater stream

AbstractNitrogen (N) and phosphorus (P) can limit autotrophic and heterotrophic metabolism in lotic ecosystems, yet most studies that evaluate biotic responses to colimitation focus on patch-scale ...

Light effects on phytoplankton morphometric traits influence nutrient utilization ability

Light and nutrients are essential resources for phytoplankton growth and considered to shape the size structure and other morphometric traits (surface:volume ratio, deviation from spherical shape) of phytoplankton communities. If morphometric traits influence the growth and resource use, shifts by one of the two factors should influence the capability to utilize the other factor. We performed a two-step experiment, where a natural phytoplankton community was first exposed to three different light levels (supposed to be limiting, saturating and slightly inhibiting for the majority of species) and grown until stationary phase. Then, the pre-conditioned communities were split into two nutrient treatments (control and saturating nutrient pulse) and again grown until stationary phase under the medium light intensity. During the experimental light phase, community mean cell-size increased with light, but surface:volume ratio and deviation from spherical shape decreased. Moreover, in response to the following nutrient pulse, the low light pre-conditioned communities showed the highest initial growth rates in response to the nutrient pulse. The high light pre-conditioned communities showed the highest conversion of the nutrient pulse into biomass during the stationary phase. These results demonstrate how the imprint of one environmental factor on trait distribution influences the ability to cope with another.

Uptake kinetics and storage capacity of dissolved inorganic phosphorus and corresponding N:P dynamics in Ulva lactuca (Chlorophyta).

Dissolved inorganic phosphorus (DIP) is an essential macronutrient for maintaining metabolism and growth in autotrophs. Little is known about DIP uptake kinetics and internal P-storage capacity in seaweeds, such as Ulva lactuca (Chlorophyta). Ulva lactuca is a promising candidate for biofiltration purposes and mass commercial cultivation. We exposed U.lactuca to a wide range of DIP concentrations (1-50μmol·L-1 ) and a nonlimiting concentration of dissolved inorganic nitrogen (DIN; 5,000μmol·L-1 ) under fully controlled laboratory conditions in a "pulse-and-chase" assay over 10d. Uptake kinetics were standardized per surface area of U.lactuca fronds. Two phases of responses to DIP-pulses were measured: (i) a surge uptake (VS ) of 0.67±0.10μmol·cm-2 ·d-1 and (ii) a steady state uptake (VM ) of 0.07±0.03μmol·cm-2 ·d-1 . Mean internal storage capacity (ISCP ) of 0.73± 0.13μmol·cm-2 was calculated for DIP. DIP uptake did not affect DIN uptake. Parameters of DIN uptake were also calculated: VS =12.54± 1.90μmol·cm-2 ·d-1 , VM =2.26±0.86μmol· cm-2 ·d-1 , and ISCN =22.90±6.99μmol·cm-2 . Combining ISC and VM values of P and N, nutrient storage capacity of U.lactuca was estimated to be sufficient for ~10d. Both P and N storage capacities were filled within 2d when exposed to saturating nutrient concentrations, and uptake rates declined thereafter at 90% for DIP and at 80% for DIN. Our results contribute to understanding the ecological aspects of nutrient uptake kinetics in U.lactuca and quantitatively evaluating its potential for bioremediation and/or biomass production for food, feed, and energy.

Linking Biomass Productivity to Genotype-Specific Nutrient Cycling Strategies in Mature Hybrid Poplars Planted Along an Environmental Gradient

This study used three hybrid poplar (Populus × spp.) clones (13 years old) with different parentages planted in three abandoned farmland sites along a regional gradient of elevation and soil fertility in southern Québec (Canada). We evaluated the effects of plantation site and clone on nutrient concentrations in green foliage and leaf litter, on leaf litter mass remaining, on soil properties and on biomass yield. Green foliage and leaf litter nutrient concentrations, and litter decomposition, are under strong genetic and environmental control in hybrid poplars. Clone-specific correlation patterns between green foliage and leaf litter nutrient concentrations were observed, as well as between soil nutrient availability and foliage or leaf litter nutrient concentrations. Despite the wide variations in soil nutrient availability and elevation between sites, only the clone effect was significant on biomass yield. An increase in N and P resorption proficiency with declining soil NO3 and P availability, observed in all clones, could explain stable yields of each clone across sites. The most productive clones (DN × M-915508 and M × B-915311) were more proficient at resorbing N, P and K, while the least productive clone (D × N-131) had the highest N, P and K concentrations in green foliage and in litter. The ability of clone M × B-915311 to maintain high litter Ca and Mg concentrations on sites with soil characterised by lower pH, lower base saturation and lower nutrient availability (NO3, P, Ca and Mg) may also be linked to its high and stable productivity. Differences in litter quality between clones did not yield significant differences in soil properties or in litter mass remaining after 2 years. However, short-term decay trajectories varied between clones. As litter mass remaining was strongly correlated to elevation, the plantation site significantly affected leaf litter mass remaining, which ranged from 4.5 to 35.5% between sites after 2 years.

Estimating uncertainty in ambient and saturation nutrient uptake metrics from nutrient pulse releases in stream ecosystems

AbstractNutrient spiraling is an important ecosystem process characterizing nutrient transport and uptake in streams. Various nutrient addition methods are used to estimate uptake metrics; however, uncertainty in the metrics is not often evaluated. A method was developed to quantify uncertainty in ambient and saturation nutrient uptake metrics estimated from saturating pulse nutrient additions (Tracer Additions for Spiraling Curve Characterization; TASCC). Using a Monte Carlo (MC) approach, the 95% confidence interval (CI) was estimated for ambient uptake lengths (Sw‐amb) and maximum areal uptake rates (Umax) based on 100,000 datasets generated from each of four nitrogen and five phosphorous TASCC experiments conducted seasonally in a forest stream in eastern Tennessee, U.S.A. Uncertainty estimates from the MC approach were compared to the CIs estimated from ordinary least squares (OLS) and non‐linear least squares (NLS) models used to calculate Sw‐amb and Umax, respectively, from the TASCC method. The CIs for Sw‐amb and Umax were large, but were not consistently larger using the MC method. Despite the large CIs, significant differences (based on non‐overlapping CIs) in nutrient metrics among seasons were found with more significant differences using the OLS/NLS vs. the MC method. We suggest that the MC approach is a robust way to estimate uncertainty, as the calculation of Sw‐amb and Umax violates assumptions of OLS/NLS while the MC approach is free of these assumptions. The MC approach can be applied to other ecosystem metrics that are calculated from multiple parameters, providing a more robust estimate of these metrics and their associated uncertainties.

Physiological Responses of Two Epiphytic Bryophytes to Nitrogen, Phosphorus and Sulfur Addition in a Subtropical Montane Cloud Forest.

Atmospheric depositions pose significant threats to biodiversity and ecosystem function. However, the underlying physiological mechanisms are not well understood, and few studies have considered the combined effects and interactions of multiple pollutants. This in situ study explored the physiological responses of two epiphytic bryophytes to combined addition of nitrogen, phosphorus and sulfur. We investigated the electrical conductivity (EC), total chlorophyll concentration (Chl), nutrient stoichiometry and chlorophyll fluorescence signals in a subtropical montane cloud forest in south-west China. The results showed that enhanced fertilizer additions imposed detrimental effects on bryophytes, and the combined enrichment of simulated fertilization exerted limited synergistic effects in their natural environments. On the whole, EC, Chl, the effective quantum yield of photosystem II (ΦPSII) and photochemical quenching (qP) were the more reliable indicators of increased artificial fertilization. However, conclusions on nutrient stoichiometry should be drawn cautiously concerning the saturation uptake and nutrient interactions in bryophytes. Finally, we discuss the limitations of prevailing fertilization experiments and emphasize the importance of long-term data available for future investigations.

Plant species response to variation in soil nutrient saturation gradients in Zaraninge Forest, Tanzania

AbstractZaraninge is a former forest reserve which is now included as part of the Saadani National Park in Bagamoyo District Coast Region. The influence of soil mineral nutrients (N, P, K, Mg and Na) on the pattern of plant species distributions was determined, and transect method was used for data collection. Plant species composition and abundance followed variation in soil nutrient gradients within Zaraninge Forest. Canonical correspondence analysis of soil and plant data showed that calcium, magnesium and phosphorus were the mineral nutrients that significantly influenced the distribution plant species (P &lt; 0.05) while other nutrients had no significant effects. Data from this study provide evidence of the existing variation in soil nutrient saturation gradients to which plant species distribution responds within the forest. A successful conservation of Zaraninge Forest biodiversity requires protecting the soil which is the necessary habitat for the plant species.

Effects of experimental nutrient loading on phosphorus uptake by biofilms: evidence for nutrient saturation in mid-Atlantic streams

AbstractBiofilms generally account for the majority of P assimilation in streams. However, relatively few direct measurements have been made that link nutrient loadings to biofilm assimilation. We measured P uptake rates for natural benthic biofilms sampled from 8 streams situated along a productivity gradient in the mid-Atlantic region, where point-source nutrient loadings were applied with an in situ enrichment system (ISES). ISES consisted of vials spiked with increasing concentrations of P with and without N. Short-term radiotracer (H333PO4) experiments were conducted to measure P uptake by biofilms growing on the surface of the vials collected from the streams. The relationship between P uptake and P loading in each stream was explained using simple linear regression. In all streams, P uptake rates declined with increased experimental P loading and as a function of stream productivity. Biofilms had significantly higher uptake rates overall in low- vs high-productivity streams (1.29 and 0.84 log10[nmo...

Heterozoan carbonates from the equatorial rocky reefs of the Galápagos Archipelago

AbstractStrongly influenced by seasonal and interannual (i.e. El Niño‐Southern Oscillation) upwelling, the equatorial setting of the Galápagos Archipelago is divided into well‐defined temperature, nutrient and calcium carbonate saturation (Ωaragonite) regions. To understand the relationship between oceanographic properties and sediment grain associations, grain size, carbonate content and components from sea floor surface samples were analysed, representing the main geographical regions of the Galápagos Archipelago. The shallow‐water rocky reefs of the Galápagos Archipelago are characterized by mixed carbonate–siliciclastic slightly gravelly sands. Despite minor differences in carbonate content, major differences exist in the distribution and composition of key carbonate producing biota.Halimedais absent and benthic foraminifera occur in extremely low abundance. The western side of the Galápagos Archipelago is strongly influenced by nutrient‐rich, low‐Ωaragonite, subtropical water, which generates a heterozoan carbonate biofacies in a tropical realm resembling cold‐water counterparts (i.e. serpulid, echinoderm, gastropod, barnacle and bryozoan‐rich facies). The Central East region is composed of a transitional‐heterozoan biofacies. Biofacies observed in the northern region have an increased occurrence of tropical corals, albeit with a minor overall contribution to the carbonate components. Although the temperature gradient would allow for a broader distribution of photozoan biofacies, the increased nutrient concentration and related reduced light penetration from the upwelled waters favour heterozoan carbonate factories, mimicking cool‐water, deeper or higher latitude environments. The recent sedimentary record of the Galápagos Archipelago presents a range of tropical heterozoan carbonate communities, responding to more than simply latitude or temperature but a much more complex mixture of physical, evolutionary and geological processes.