Reactive Phosphorus Research Articles

Exploring polyphosphates in soil: presence, extractability, and contribution to microbial biomass phosphorus

Polyphosphates (Poly-P) are known to fulfil several important physiological functions. Many microorganisms can accumulate large amounts of Poly-P in their biomass. Regardless of these facts, systematic research on Poly-P in soil is missing, probably due to the absence of any method of direct Poly-P quantification. In this study, we attempted to unequivocally prove the presence of Poly-P in the biomass of soil microorganisms and quantify their extractability and contribution to microbial biomass phosphorus. To do so, we combined several approaches that can indicate Poly-P presence in soil microbial biomass indirectly, i.e. growth of soil inoculum on media without phosphorus, associated with measurement of changes in the microbial biomass stoichiometry, and the colour of the microbial suspension stained by the Neisser method. All soil microbial communities exhibited growth on media without phosphorus. As the growth on this media depleted Poly-P content, the biomass carbon to phosphorus and nitrogen to phosphorus ratio increased and the colour of the microbial suspension stained by the Neisser method changed predictively. The associated Poly-P addition experiment indicated that the recovery of added Poly-P from soil in form of soluble reactive phosphorus in sodium bicarbonate extract may reach up to 93% mainly due to abiotic depolymerization. Using a simple stoichiometric model applied to measured data, we calculated that the Poly-P content of microbial biomass in our soils may be up to 45 or 70% of total microbial biomass phosphorus depending on the assumptions applied regarding parameter values. We discuss the magnitude of error associated with the measurement of soil microbial phosphorus due to the high extractability of Poly-P.

Denitrifying bioreactors and dissolved phosphorus: Net source or sink?

Understanding the world through a lens of phosphorus (P), as Dr. Andrew Sharpley aimed to do, adds a deeper dimension for water quality work in the heavily tile-drained US Midwest where nitrate is often the nutrient of biggest concern. Denitrifying woodchip bioreactors reduce nitrate pollution in drainage water, but dissolved phosphorus leached from the organic fill is a possible pollution tradeoff. Recent work by Dr. Sharpley and others defined such tradeoffs as strategic decisions in which a negative outcome is accepted with prior knowledge of the risk. In this vein, we assessed 23 site-years from full-size bioreactors in Illinois to determine if bioreactors were a net dissolved reactive phosphorus (DRP) source and, if so, to determine flow-related correlation agents (1904 sample events; 10 bioreactors). DRP was removed across the bioreactors in 15 of 23 site-years. The 23 site-years provided a median annual DRP removal efficiency of 12% and a median annual DRP removal rate of 7.1mg DRP/m3 bioreactor per day, but the ranges of all removal metrics overlapped zero. The highest daily bioreactor DRP removal rates occurred with high inflow concentrations and under low hydraulic retention times (i.e., under higher loading). Dr. Sharpley was one of the first to explore losses of DRP in subsurface drainage and performed decades of useful applied studies that inspired approaches to management of P loss on both drained and undrained land. We seek to honor this legacy with this practical study of the DRP benefits and tradeoffs of denitrifying bioreactors.

Unconventionally microspheric quasi-solid electrolyte interface approach for durable and highly reactive phosphorus for lithium-ion storage

Solid electrolyte interface (SEI) film is the most important separation layer between nonaqueous electrolytes and anodes to protect anode from corrosion and maintain continuous ionic diffusion tunnels. However, SEI film, especially for high-capacity anode materials, is still confined to continuous and stable ionic conductive layer despite the conventional SEI film is intrinsically poor to resist against the drastic volumetric changes of active centers. Herein, an unconventional spheric quasi-SEI film is thus strategically configured on cost-effective red phosphorus electrode materials by moderate phosphorylation combined with pore-forming process. Microstructure adjustment from solid microspheres structure to hollowed core–shell spheres is visibly taken place on this amazing spheric quasi-SEI film during the stabilization. Benefiting from the highly activated surface with weakened PP bond strength and the strengthened binding force between phosphorus and binders, the optimized phosphorus anode presents an outstanding long-term durability with a high discharge capacity of 1126.4 mAh/g over 400 cycles at 200 mA g−1 even at a high phosphorus load ratio of 70 wt%. This revolutionary configuration of quasi-SEI film provides high-capacity anode materials subject to large volumetric changes an unconventional approach from dependence on conductive framework/matrix.

Predicting river phytoplankton blooms and community succession using ecological niche modeling

AbstractExcessive phytoplankton concentrations in rivers can result in the loss of plant and invertebrate communities, and threaten drinking water supplies. Whilst the physicochemical controls on algal blooms have been identified previously, how these factors combine to control the initiation, size, and cessation of blooms in rivers is not well understood. We applied flow cytometry to quantify diatom, chlorophyte, and cyanobacterial group abundances in the River Thames (UK) at weekly intervals from 2011 to 2022, alongside physicochemical data. A niche modeling approach was used to identify thresholds in water temperature, flow, solar radiation, and soluble reactive phosphorus (SRP) concentrations required to produce periods of phytoplankton growth, with blooms only occurring when all thresholds were met. The thresholds derived from the 2011 to 2018 dataset were applied to a test data set (2019–2022), which predicted the timing and duration of blooms at accuracies of > 80%. Diatoms and nano‐chlorophyte blooms were initiated by flow and water temperature, and usually terminated due to temperature and flow going out of the threshold range, or SRP and Si becoming limiting. Cyanobacterial bloom dynamics were primarily controlled by water temperature and solar radiation. This simple methodology provides a key understanding of phytoplankton community succession and inter‐annual variation and can be applied to any river with similar water quality and phytoplankton data. It provides early warnings of algal and cyanobacterial bloom timings, which support future catchment management decisions to safeguard water resources, and provides a basis for modeling changing phytoplankton bloom risk due to future climate change.

Temporal and spatial variations and driving factors of phytoplankton in Yongjiang River estuary

To explore the temporal and spatial variations in phytoplankton community in small estuaries, we collected surface water samples from Yongjiang River estuary during wet, normal, and dry seasons and determined the main driving factors of phytoplankton community. A total of 358 species belonging to nine phyla and 123 genera were identified in all seasons. During wet, normal, and dry seasons, species number was 276, 154 and 151, and the abundance was (170.45±225.43)×103, (51.92±30.28)×103 and (31.65±12.79)×103 cells·L-1, respectively. Diatoms dominated the phytoplankton community, and the main dominant species were Cyclotella meneghiniana, Skeletonema costatum, and Paralia sulcata. Shannon diversity and Pielou evenness indices decreased from inside mouth to outside mouth in wet season, but there was no obvious spatial difference in normal season or dry season. Results of non-metric multidimensional scaling analysis and analysis of similarities showed that phytoplankton community composition differed significantly among different regions (inside, at and outside mouth) and different seasons. In wet season, phytoplankton abundance was significantly positively correlated with temperature, dissolved inorganic nitrogen, and dissolved reactive phosphorus, but significantly negatively correlated with salinity. In normal season, phytoplankton abundance was significantly negatively correlated with temperature. In dry season, it was not significantly correlated with environmental factors. Results of redundancy analysis showed that temperature, salinity, ammonium and dissolved reactive phosphorus explained the variations in phytoplankton community by 19.5%, 11.9%, 9.4% and 8.2%, respectively. These results revealed high dominance of diatoms and the main driving factors (temperature, salinity and nutrients) of phytoplankton community in Yongjiang River estuary.

Release of phosphorus and metal(loid)s from manured soils to floodwater during a laboratory simulation of snowmelt flooding.

Phosphorus (P) and metal accumulation in manured agricultural soils and subsequent losses to waterways have been extensively studied; however, the magnitudes and the factors governing their losses during spring snowmelt flooding are less known. We examined the P and metal release from long-term manured soil to floodwater under simulated snowmelt flooding with recent manure additions. Intact soil columns collected from field plots located in Randolph, Southern Manitoba, 2 weeks after liquid swine manure treatments (surface-applied, injected, or control with no recent manure addition) were flooded and incubated for 8 weeks at 4± 1°C to simulate snowmelt conditions. Floodwater (syringe filtered through 0.45µm) and soil porewater (extracted using Rhizon-Mom samplers) samples were periodically extracted and analyzed for dissolved reactive phosphorus (DRP), pH, zinc (Zn), manganese (Mn), iron (Fe), magnesium (Mg), calcium (Ca), and arsenic (As). Mean floodwater DRP concentrations (mg L-1) for manure injected (2.0±0.26), surface-applied (2.6±0.26), and control (2.2±0.26) treatments did not differ significantly. Despite manure application, DRP loss to floodwater did not significantly increase compared to the control, possibly due to the elevated residual soil P at this site from the long-term manure use. At the end of simulated flooding, the DRP concentrations increased by 1.5-fold and 5-fold in porewater and floodwater, respectively. Metal(loid) concentrations were not affected by manure treatments in general, except for Zn and Mg on certain days. Unlike DRP, where porewater and floodwater concentrations increased with time, metalloid concentration in porewater and floodwater did not show consistent trends with flooding time.

Control of phosphorus release from sediment by iron/aluminum co-modified zeolite: efficiency, mechanism, and response of microbial communities in sediment.

The efficiency of iron/aluminum co-modified zeolite (FeAl-Z) covering and amendment for controlling the internal loading of phosphorus (P) from sediment to the overlying water (OW) and its controlling mechanism were explored. The response of the composition of sedimentary microbial communities in sediment and their function to the FeAl-Z capping and amendment was also examined. FeAl-Z showed good removal performance for phosphate in aqueous solution. The maximum phosphate adsorption quantity for FeAl-Z at pH 7 attained 11.2mg P/g. The release of sediment endogenous phosphorus to OW can be successfully restrained by the FeAl-Z covering and amendment, and the suppression ability of FeAl-Z covering was stronger than that of FeAl-Z amendment. Under the capping or amendment condition, FeAl-Z can effectively inactivate the labile phosphorus measured by diffusion gradient in thin film (DGT-LP) in the overlying water and surface sediment. The added FeAl-Z transformed redox-sensitive phosphorus (BD-P) to metal oxide-bound phosphorus (NaOH-IP) and residual phosphorus (Res-P) in sediment, which increased the stability of inorganic phosphorus in the sediment. The passivation of soluble reactive phosphorus (SRP) and DGT-LP in the surface sediment by FeAl-Z significantly contributed to the inhibition of sediment endogenous phosphorus release to OW by the FeAl-Z capping, and the passivation of SRP, DGT-LP and mobile phosphorus in the surface sediment played a pivotal role in the control of sediment internal phosphorus release by the FeAl-Z amendment. The FeAl-Z amendment and capping did not increase the liberation risk of Fe from sediment, and the microorganisms in the sediments under the conditions of FeAl-Z amendment and covering still can perform good ecological functions. Results of this research demonstrate that FeAl-Z capping has high application potential in the control of phosphorus transfer from sediment to OW.

Sediment microbial fuel cell coupled floating treatment wetland for enhancing non-reactive phosphorus removal

The presence of non-reactive phosphorus (NRP) in environmental waters presents a potential risk of eutrophication and poses challenges for the removal of all phosphorus (P) fractions. This study presents the first investigation on the removal performance and mechanism of three model NRP compounds, sodium tripolyphosphate (STPP), adenosine 5′-monophosphate (AMP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), in the sediment microbial fuel cell-floating treatment wetland (SMFC-FTW). Coupling SMFC with plants proved to be effective at removing NRP via electrochemical oxidation and plant uptake, particularly the challenging-to-degrade phosphonates that contain C–P bonds. Compared with the control group, the removal efficiencies of the model NRP in SMFC were observed to increase by 11.9%–20.8%. SMFC promoted the conversion of NRP to soluble reactive phosphorus (sRP) and the transfer of P to sediment. Furthermore, the electrochemical process enhanced both plant growth and P uptake, and increased P assimilation by 72.6%. The presence of plants in the bioelectrochemical system influenced the occurrence and fate of P by efficiently assimilating sRP and supporting microbial transformation of NRP. Consequently, plants enhanced the removal efficiencies of all P fractions in the overlying water. This study demonstrated that SMFC-FTW is a promising technology to remove various NRP species in environmental waters.

Evaluation of water quality and trophic status in relation to seasonal water mixing in a highland Lake Ardibo, Ethiopia.

The aim of the present study was to evaluate the spatio-temporal variability of various physical and chemical parameters of water quality and to determine the trophic state of Lake Ardibo. Water samples were collected from October 2020 to September 2021 at three sampling stations in four different seasons. A total of 14 physico-chemical parameters, such as water temperature, pH, dissolved oxygen (DO), electrical conductivity, turbidity, alkalinity, Secchi-depth, nitrate, ammonia, silicon dioxide, soluble reactive phosphorus, total phosphorus, chloride, and fluoride were measured using standard methods. The results demonstrated that temporal variation existed throughout the study period. Except for turbidity, the water quality of the lake varied significantly within the four seasons (ANOVA, p < 0.05). DO levels decreased significantly during the dry season following water mixing events. Chlorophyll-a measurements showed significant seasonal differences ranging from 0.58 μg L-1 in the main-rainy season to 8.44 μg L-1 in the post-rainy period, indicating moderate algal biomass production. The overall category of Lake Ardibo was found to be under a mesotrophic state with medium biological productivity. A holistic lake basin approach management is suggested to maintain water quality and ecological processes and to improve the lake ecosystem services.

Phosphorus starvation response genes and function coupling: A mechanism to regulate phosphorus availability in a subtropical estuary

Phosphorus (P) plays an important role in regulating primary production in estuarine environments. However, knowledge of the P-functional gene composition of microbial communities and the mechanisms of microbial adaptation to changes in available P in estuaries remain limited. This study coupling 16 s rDNA and metagenomics sequencing was conducted to reveal the relationship between P cycling functional genes, microbial interactions, and P availability in the Jiulong River Estuary. The results showed that the relative abundance of P cycling functions genes was highest in winter, and lowest in summer. Spatially, the total relative abundance of P cycling functions genes was higher in the riverward than that in the seaward. P cycling functional microbial interactions and P cycling gene coupling were strongest in summer and in the seaward. Changes in both temperature and salinity had significant direct and indirect effects on P cycling function, and the influence of salinity on P cycling function was greater than that on the microbial community in the estuary. Salinity had significant direct negative effects on inorganic P-solubilization (IP), organic P-mineralization (OP), and P uptake and transport functions (PT). Whereas, salinity had a significant positive effect on P-starvation response regulation (PR) function. Thus, salinity and microbial communities regulate the soluble reactive phosphate concentrations in estuarine environments by strengthening internal coupling among P cycling functions, promoting PR function, and facilitating PT gene expression. PR is the most important predictors, PR, PT, and PR-PT together explained 38.56 % of the overall soluble reactive phosphorus (SRP) variation. Over 66 % of the explained SRP variations can be predicted by the PR, PT, and PR-PT functional genes. This finding improves the knowledge base of the microbial processes for P cycling and provides a foundation for eutrophication management strategies in the estuary.

Nutrient supplementation changes chemical composition of soil organic matter density fractions in desert steppe soil in northern China

The influence of reactive nitrogen (N) and phosphorus (P) supplementation on ecosystem dynamics of soil organic matter (SOM) shows extensive variations. The underlying mechanisms of regulation of the chemical composition and dynamics of different SOM density fractions (DFs) in aggregates in a desert steppe by N and P supplementation are unclear. Here, the chemical composition and organic carbon (C) and N dynamics of various SOM DFs under N and P addition were assessed. Surface soil samples taken at 0–10 cm depth were obtained from 4-year (2017–2021) experiments under four conditions, namely N treatment, P treatment, combined N and P treatment (NP), and no nutrient supplementation (CK), in a desert steppe located in northern China. Nutrient supplementation significantly increased (P < 0.05) SOM content by 8.89–35.4%; however, the total N content remained constant. N addition mainly increased SOM content in the macroaggregates (>0.25 mm), while P enhanced SOM in microaggregates (0.25–0.053 mm) and silt-clay (<0.053 mm). The fine particulate organic matter (fPOM) proportion was increased significantly (P < 0.05) by 18.4% and 16.4% in macro- and microaggregates under N addition, respectively; P addition mainly enhanced mineral-associated SOM (mSOM) proportion in aggregates. N supplementation remarkably enhanced (P < 0.05) fPOM’s organic C content by 27.3% and 32.0%, and N content by 40.9% and 145.7% in macro- and microaggregates, respectively. Single N and P addition promoted the enrichment of labile and resistant organic components in light fraction (LF), respectively. N promoted the enrichment of stable organic components in the mSOM of microaggregates. Nutrient inputs drive mSOM formation through the interaction of carboxyl-C and mineral surface. Based on a stronger δ13C and δ15N signal, N addition enhanced SOM decomposition in aggregates. Nutrient supplementation promoted SOM accumulation through the formation of more stable old C in POM and silt-clay. Our findings suggest that SOM accumulation in desert steppe probably increases following nutrient addition, but the mechanism is different through which N or P enrichment affects soil dynamics and chemical composition of SOM DFs in desert steppe.

Prediction of microbial activity and abundance using interpretable machine learning models in the hyporheic zone of effluent-dominated receiving rivers

Serving as a vital linkage between surface water and groundwater, the hyporheic zone (HZ) plays a fundamental role in improving water quality and maintaining ecological security. In arid or semi-arid areas, effluent discharge from wastewater treatment facilities could occupy a predominant proportion of the total base flow of receiving rivers. Nonetheless the relationship between microbial activity, abundance and environmental factors in the HZ of effluent-receiving rivers appear to be rarely addressed. In this study, a spatiotemporal field study was performed in two representative effluent-dominated receiving rivers in Xi'an, China. Land use data, physical and chemical water quality parameters of surface and subsurface water were used as predictive variables, while the microbial respiratory electron transport system activity (ETSA), the Chao1 and Shannon index of total microbial community, as well as the Chao1 and Shannon index of denitrifying bacteria community were used as response variables, while ETSA was used as response variables indicating ecological processes and Shannon and Chao1 were utilized as parameters indicating microbial diversity. Two machine learning models were utilized to provide evidence-based information on how environmental factors interact and drive microbial activity and abundance in the HZ at variable depths. The models with Chao1 and Shannon as response variables exhibited excellent predictive performances (R2: 0.754–0.81 and 0.783–0.839). Dissolved organic nitrogen (DON) was the most important factor affecting the microbial functions, and an obvious threshold value of ∼2 mg/L was observed. Credible predictions of models with Chao1 and Shannon index of denitrifying bacteria community as response variables were detected (R2: 0.484–0.624 and 0.567–0.638), with soluble reactive phosphorus (SRP) being the key influencing factor. Fe (Ⅱ) was favorable in predicting denitrifying bacteria community. The ESTA model highlighted the importance of total nitrogen in the ecological health monitoring in HZ. These findings provide novel insights in predicting microbial activity and abundance in highly-impacted areas such as the HZ of effluent-dominated receiving rivers.

Submerged macrophyte root oxygen release reduces sediment oxygen demand: A positive feedback loop in shallow lakes

Shallow lakes have two stable ecological states, macrophyte dominated or algal dominated. The macrophyte dominated state is the more desired state as it generally has clearer water that is safe for contact recreation. Whereas the algal dominated state is considered degraded, resulting from high anthropogenic nutrient inputs, with turbid water that is often unsafe for contact recreation. These ecological states are somewhat resilient due to in-lake feedback loops that maintain or enhance conditions for the dominate primary producer. For the macrophyte dominated state, many of these feedback loops are theoretically plant density dependent, but rarely has the plant density required to initiate these feedback loops been identified. Here we illustrate the plant density dependence of a previously unstudied feedback loop present in the macrophyte dominated state. Increased densities of Isoëtes kirkii were able to reduce sediment oxygen demand through their root oxygen releases. This reduction in sediment oxygen demand occurred at 32 plants m−2 in a garden soil and 63 plants m−2 in the sediment of a hypo-eutrophic lake, a disparity likely due to the higher initial sediment oxygen demand present in the lake sediments. In a shallow lake, plants present in the hypolimnion will reduce sediment oxygen demand, increasing the amount of time required before anoxic conditions are created and the resulting release of dissolved reactive phosphorus. This will likely decrease the potential for subsequent algal blooms and the associated shading of submerged macrophytes, thus maintaining in-lake conditions that favour macrophytes.

Hydrodynamics and phosphorus loading in an urbanized river channel influences response to future managed change: Insights from advection-dispersion modelling

There is a need to understand what makes certain targeted measures for in-river phosphorus load reduction more effective than others. Therefore, this paper investigates multiple development scenarios in a small lowland polluted river draining an urban area (The Cut, Bracknell, UK), using an advection-dispersion model (ADModel-P). A comparative analysis is presented whereby changes in concentrations and fluxes of soluble reactive phosphorus (SRP) and organic phosphorus (OP) have been attributed to specific transformations (mineralization, sedimentation, resuspension, adsorption-desorption, and algal uptake) and correlated to controlling factors. Under present day conditions the river stretch is a net source of SRP (10.4 % increase in mean concentration) implying a release of previously accumulated material. Scenarios with the greatest impact are those based on managed reduction of phosphorus load in sources (e.g., 20 % increase in afforestation causes an in-river SRP and OP reduction of 1.3 % to 12.6 %) followed by scenarios involving changes in water temperature (e.g., 1 °C decrease leads to in-river SRP reduction around 3.1 %). Measures involving increased river residence time show the lowest effects (e.g., 16 % decrease in velocity results in under 0.02 % in-river SRP and OP reduction). For better understanding downstream persistence of phosphorus pollution and the effectiveness of mitigation measures the research demonstrates the importance of establishing when and where reaches are net adsorbers or desorbers, and whether sedimentation or resuspension is important.

Relative prevalence of top-down versus bottom-up control in planktonic ecosystem under eutrophication and climate change: A comparative study of typical bay and estuary

Eutrophication and climate change may affect the top-down versus bottom-up controls in aquatic ecosystems. However, the relative prevalence of the two controls in planktonic ecosystems along the eutrophication and climate gradients has rarely been addressed. Here, using the field surveys of 17 years in a typical bay and estuary, we test two opposite patterns of trophic control dominance and their response to regional temporal eutrophication and climate fluctuations. It was found that trophic control of planktonic ecosystems fluctuated between the dominance of top-down and bottom-up controls on time scales in both the bay and estuary studied. The relative prevalence of these two controls in both ecosystems was significantly driven directly by regional dissolved inorganic nitrogen but, for the estuary, also by the nonlinear effects of regional sea surface temperature. In terms of indirect pathways, community relationships (synchrony and grazing pressure) in the bay are driven by both regional dissolved inorganic nitrogen - soluble reactive phosphorus ratio and sea surface temperature, but this drive did not continue to be transmitted to the trophic control. Conversely, trophic control in estuary was directly related to grazing pressure and indirectly related to synchrony. These findings support the view that eutrophication and climate drive the relative prevalence of top-down versus bottom-up controls at ecosystem and temporal scales in planktonic ecosystems, which has important implications for predicting the potential impacts of anthropogenic and environmental perturbations on the structure and function of marine ecosystems.

Internal phosphorus loading alters nutrient limitation and contributes to cyanobacterial blooms in a polymictic lake

Clear Lake, a medium-sized hypereutrophic, polymictic lake in northern California, has had recurring harmful cyanobacteria blooms (HCBs) for over a century despite reductions in external phosphorus (P) loadings. Internal P loading can alter nutrient availability and limitation supporting HCBs but is rarely quantified or compared with external loads. We have quantified external P loads from 2019 to 2021 for the three main tributaries (accounting for 46% of the flow) and internal loadings using two methods: a P mass balance and modeled release rates of soluble reactive phosphorus from oxic and anoxic sediments. In addition, we combined high-frequency in situ measurements of water temperature and dissolved oxygen, discrete grab sampling for nutrient chemistry, and remote sensing to explore the potential drivers of the observed variability and provide a comprehensive view of the spatiotemporal dynamics of HCBs. By understanding the relative contribution of external and internal nutrient loadings and the relationship between environmental parameters and HCBs, interannual bloom variability can be better predicted. Comparative estimates of external and internal phosphorus loading indicate that internal sources accounted for 70–95% of the total P input into the system during the study period. Contrary to other lakes, the intensity of the summer bloom season was correlated to the timing and duration of anoxia rather than the magnitude of spring runoff. Internally released P shifted the system from phosphorus to nitrogen limitation during the summer, potentially favoring the proliferation of nitrogen-fixing cyanobacteria.

Seasonal changes of prokaryotic microbial community structure in Zhangjiayan Reservoir and its response to environmental factors

As a typical sub-deep reservoir in the upper reaches of the Yangtze River in the southwest region, Zhangjiayan Reservoir is also an important source of drinking water. Exploring the role of microorganisms in the material cycle of water bodies is of great significance for preventing the exacerbation of eutrophication in the reservoir. In this study, water samples from the overlying water of five points in the reservoir were collected four times in spring (April), summer (July), autumn (November), and winter (January) of 2022–2023 using a gas-tight water sampler. Physicochemical factors were measured, and the microbial community structure was analyzed by high-throughput MiSeq sequencing of the V3–V4 hypervariable region of 16S rRNA gene in order to explore the relationship between physicochemical factors and microbial community structure and the dominant microbial populations that affect eutrophication of the reservoir. The following results were obtained through analysis. Among the 20 overlying water samples from Zhangjiayan Reservoir, a total of 66 phyla, 202 classes, 499 orders, 835 families, 1716 genera, and 27,904 ASVs of the bacterial domain were detected. The phyla Proteobacteria and Actinobacteria were dominant in the microbial community of the overlying water in Zhangjiayan Reservoir. At the genus level, hgcI_clade and Actinobacteria had the highest abundance and was the dominant population. The microbial community in the water of Zhangjiayan Reservoir has a high level of diversity. The diversity index ranked by numerical order was winter > autumn > summer > spring. Significant differences were found in the composition and structure of the microbial community between the spring/summer and autumn/winter seasons (p < 0.05). Total phosphorus, dissolved total phosphorus, soluble reactive phosphorus, and dissolved oxygen have a significant impact on the composition and structure of the microbial community (p < 0.01). The bacterial community in the overlying water of Zhangjiayan Reservoir showed a mainly positive correlation. Sphingomonas, Brevundimonas, and Blastomonas were the central populations of the bacterial community in the overlying water of Zhangjiayan Reservoir. This study indicates that environmental factors, such as phosphorus and other nutrients, have a significant impact on the formation of the microbial community structure in different seasons. Sphingomonas, Brevundimonas, and Blastomonas are key populations that may have a significant impact on eutrophication in Zhangjiayan Reservoir.

Physiographic Environment Classification: a Controlling Factor Classification of Landscape Susceptibility to Waterborne Contaminant Loss

Spatial variation in the landscape factors climate, geomorphology, and lithology cause significant differences in water quality issues even when land use pressures are similar. The Physiographic Environment Classification (PEC) classifies landscapes based on their susceptibility to the loss of water quality contaminants. The classification is informed by a conceptual model of the landscape factors that control the hydrochemical maturity of water discharged to streams. In New Zealand, a case study using climatic, topographic, and geological data classified the country into six, 36, and 320 classes at Levels 1 (Climate), 1–2 (Climate + Geomorphology), and 1–3 (Climate + Geomorphology + Lithology), respectively. Variance partitioning analysis applied to New Zealand’s national surface water monitoring network (n = 810 stations) assessed the contributions of PEC classes and land use on the spatial variation of water quality contaminants. Compared to land use, PEC explained 0.6× the variation in Nitrate Nitrite Nitrogen (NNN), 1.0× in Total Kjeldahl Nitrogen (TKN), 1.8× in Dissolved Reactive Phosphorus (DRP), 2.3× in Particulate Phosphorus (PP), 2.6× in E. coli, and 4.3× in Turbidity (TURB). Land use explained more variation in riverine NNN, while landscape factors explained more variation in DRP, PP, E. coli, and TURB. Overall, PEC accounted for 2.1× more variation in riverine contaminant concentrations than land use. The differences in contaminant concentrations between PEC classes (p < 0.05), after adjusting for land use, were consistent with the conceptual model of hydrochemical maturation. PEC elucidates underlying causes of contaminant loss susceptibility and can inform targeted land management across multiple scales.

Spring applied phosphorus loss with cover crops in no-till terraced field

Cover crops (CC) can improve phosphorus (P) cycling by reducing water related P losses and contributing to P nutrition of a rotational crop. This is particularly important in claypan soils with freeze-thaw cycles in early spring in the Midwest U.S. This 4-year study (2019–2022) examined the impact of CC monoculture and mix of CC species on P losses from a fertilizer application, and determined the P balance in soil compared to no cover crop (noCC). The CC mix consisted of wheat (Triticum aestivum L.), radish (Raphanus raphanistrum subsp. Sativus), and turnip (Brassica rapa subsp. Rapa) (3xCCmix) in 2019 and 2021 before corn, and cereal rye (Secale cereale L.) was planted as monoculture before soybean in 2020 and 2022. The 3xCCmix had no effect on total phosphorus (TP) and dissolved reactive phosphorus (PO4–P) concentration or load in 2019 and 2021. Cereal rye reduced TP and PO4–P load 70% and 73%, respectively, compared to noCC. The variation in soil moisture, temperature, and net precipitation from fertilizer application until CC termination affected available soil P pools due to variability in CC species P uptake, residue decomposition, and P loss in surface water runoff. Overall, the P budget calculations showed cereal rye had 2.4 kg ha−1 greater P uptake compared to the 3xCCmix species which also reduced P loss in water and had greater differences in soil P status compared to noCC. This study highlights the benefit of CCs in reducing P loss in surface runoff and immobilizing P through plant uptake. However, these effects were minimal with 3xCCmix species and variability in crop residue decomposition from different CC species could affect overall P-soil balance.

A perceptual approach to address complex water management issues in lowland permeable catchments

Water quality management is a pressing global concern, and an increasingly complex issue due to climate and land-use change, legacy pollution, and the persistent release of well-known and emerging contaminants from diffuse and point sources. The increasing availability of high-frequency monitoring data is leading existing, often heuristic approaches, to be judged inadequate. Water managers frequently rely on simple qualitative and/or quantitative approaches for decision-making, but a lack of tangible improvement in freshwater quality outcomes is demanding new and innovative approaches that rely more on physical process understanding, rather than precedent. In this study, we drew upon local geological, hydrogeological, and hydrological data to infer a high-level perceptual model of surface/groundwater interactions in a chalk stream in Dorset, UK. We used the perceptual model to interrogate spatial and temporal trends in historical water quality data and to construct reach-scale nutrient mass balances. Through novel representation with Sankey diagrams, the perceptual model highlighted the relative importance of different hydrological features. Surface/groundwater interactions were found to occur predominantly by spring flow. We demonstrate that river flow accretion was dominated by the Chalk aquifer despite only occupying ca. 15 % of the surface bedrock area, and that spring sources, whilst vital to dilute treated sewage inputs in baseflow conditions, were also major sources of legacy nitrate. Nutrient mass balances showed that sewage treatment works contributed ca. 13 % to soluble reactive phosphorus load, with groundwater accounting for ca. 48 %. Thus, a determinand often associated with point-source pollution was shown to be diffuse dominated in this river. The study demonstrated how a multi-disciplinary approach to water management, based on a comprehensive perceptual modelling approach, could identify hitherto unknown sources and relative contributors to freshwater pollution and allow flow and load apportionment studies to provide useful decision-support to manage nutrient pollution. The novel application of perceptual modelling tools, such as the Sankey diagram, allows different source attributions to be presented in an accessible manner, and can be readily transferred to other study areas.