Phosphorus losses from land to water will be impacted by climate change and land management for food production, with detrimental impacts on aquatic ecosystems. Here we use a unique combination of ...methods to evaluate the impact of projected climate change on future phosphorus transfers, and to assess what scale of agricultural change would be needed to mitigate these transfers. We combine novel high-frequency phosphorus flux data from three representative catchments across the UK, a new high-spatial resolution climate model, uncertainty estimates from an ensemble of future climate simulations, two phosphorus transfer models of contrasting complexity and a simplified representation of the potential intensification of agriculture based on expert elicitation from land managers. We show that the effect of climate change on average winter phosphorus loads (predicted increase up to 30% by 2050s) will be limited only by large-scale agricultural changes (e.g., 20-80% reduction in phosphorus inputs).The impact of climate change on phosphorus (P) loss from land to water is unclear. Here, the authors use P flux data, climate simulations and P transfer models to show that only large scale agricultural change will limit the effect of climate change on average winter P loads in three catchments across the UK.
Increased fluxes of reactive nitrogen (Nr), often associated with N fertilizer use in agriculture, have resulted in negative environmental consequences, including eutrophication, which cost billions ...of dollars per year globally. To address this, best management practices (BMPs) to reduce Nr loading to the environment have been introduced in many locations. However, improvements in water quality associated with BMP implementation have not always been realised over expected timescales. There is a now a significant body of scientific evidence showing that the dynamics of legacy Nr storage and associated time lags invalidate the assumptions of many models used by policymakers for decision making regarding Nr BMPs. Building on this evidence, we believe that the concepts of legacy Nr storage dynamics and time lags need to be included in these models. We believe the biogeochemical research community could play a more proactive role in advocating for this change through both awareness raising and direct collaboration with policymakers to develop improved datasets and models. We anticipate that this will result in more realistic expectations of timescales for water quality improvements associated with BMPs. Given the need for multi-nutrient policy responses to tackle challenges such as eutrophication, integration of N stores will have the further benefit of aligning both researchers and policymakers in the N community with the phosphorus and carbon communities, where estimation of stores is more widespread. Ultimately, we anticipate that integrating legacy Nr storage dynamics and time lags into policy frameworks will better meet the needs of human and environmental health.
•Nitrogen (N) pollution from agriculture has negative environmental impacts.•Environmental benefits of initiatives to reduce N loads not always detectable.•N storage dynamics and time lag invalidate steady state models often used in policy.•Researchers should advocate for integrating N stores and time lags into policy.•Quantifying N storage aligns with phosphorus and carbon cycling research.
In northern peatlands, near‐saturated surface conditions promote valuable ecosystem services such as carbon storage and drinking water provision. Peat saturated hydraulic conductivity (Ksat) plays an ...important role in maintaining wet surface conditions by moderating drainage and evapotranspiration. Peat Ksat can exhibit intense spatial variability in three dimensions and can change rapidly in response to disturbance. The development of skillful predictive equations for peat Ksat and other hydraulic properties, akin to mineral soil pedotransfer functions, remains a subject of ongoing research. We report a meta‐analysis of 2,507 northern peat samples, from which we developed linear models that predict peat Ksat from other variables, including depth, dry bulk density, von Post score (degree of humification), and categorical information such as surface microform type and peatland trophic type (e.g., bog and fen). Peat Ksat decreases strongly with increasing depth, dry bulk density, and humification; and increases along the trophic gradient from bog to fen peat. Dry bulk density and humification are particularly important predictors and increase model skill greatly; our best model, which includes these variables, has a cross‐validated r2 of 0.75 and little bias. A second model that includes humification but omits dry bulk density, intended for rapid field estimations of Ksat, also performs well (cross‐validated r2 = 0.64). Two additional models that omit several predictors perform less well (cross‐validated r2 ∼ 0.5), and exhibit greater bias, but allow Ksat to be estimated from less comprehensive data. Our models allow improved estimation of peat Ksat from simpler, cheaper measurements.
Key Points
We report skillful statistical models to estimate saturated hydraulic conductivity in northern peats from simpler measurements
Peat dry bulk density and humification (von Post score) are particularly powerful predictors
Our models represent an improvement over existing pedotransfer functions for peat saturated hydraulic conductivity
Improving stream water quality in agricultural landscapes is an ecological priority and a legislative duty for many governments. Ecosystem health can be effectively characterised by organisms ...sensitive to water quality changes such as diatoms, single-celled algae that are a ubiquitous component of stream benthos. Diatoms respond within daily timescales to variables including light, temperature, nutrient availability and flow conditions that result from weather and land use characteristics. However, little consideration has been given to the ecological dynamics of diatoms through repeated seasonal cycles when assessing trajectories of stream function, even in catchments actively managed to reduce human pressures. Here, six years of monthly diatom samples from three independent streams, each receiving differing levels of diffuse agricultural pollution, reveal robust and repeated seasonal variation. Predicted seasonal changes in climate-related variables and anticipated ecological impacts must be fully captured in future ecological and water quality assessments, if the apparent resistance of stream ecosystems to pollution mitigation measures is to be better understood.
Accurate quantification of sources of phosphorus (P) entering the environment is essential for the management of aquatic ecosystems. P fluxes from mains water leakage (MWL-P) have recently been ...identified as a potentially significant source of P in urbanised catchments. However, both the temporal dynamics of this flux and the potential future significance relative to P fluxes from wastewater treatment works (WWT-P) remain poorly constrained. Using the River Thames catchment in England as an exemplar, we present the first quantification of both the seasonal dynamics of current MWL-P fluxes and future flux scenarios to 2040, relative to WWT-P loads and to P loads exported from the catchment. The magnitude of the MWL-P flux shows a strong seasonal signal, with pipe burst and leakage events resulting in peak P fluxes in winter (December, January, February) that are >150% of fluxes in either spring (March, April, May) or autumn (September, October, November). We estimate that MWL-P is equivalent to up to 20% of WWT-P during peak leakage events. Winter rainfall events control temporal variation in both WWT-P and riverine P fluxes which consequently masks any signal in riverine P fluxes associated with MWL-P. The annual average ratio of MWL-P flux to WWT-P flux is predicted to increase from 15 to 38% between 2015 and 2040, associated with large increases in P removal at wastewater treatment works by 2040 relative to modest reductions in mains water leakage. However, further research is required to understand the fate of MWL-P in the environment. Future P research and management programmes should more fully consider MWL-P and its seasonal dynamics, alongside the likely impacts of this source of P on water quality.
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•Seasonality + scenarios in P fluxes from mains water leakage (MWL-P) quantified.•MWL-P compared to wastewater P flux (WWT-P) and catchment P export.•Winter burst MWL-P > 150% of spring/autumn flux, equal to up to 20% of winter WWT-P.•MWL-P/WWT-P ratio predicted to increase to 38% by 2040 due to WWT P removal.•MWL-P flux and seasonality should be considered in future P research and management.
Quantifying temporal and spatial variation of soil phosphorus (P) input, output and balance across Chinese arable land is necessary for better P management strategies. Here, we address this challenge ...using a soil P budget to analyse the soil P balance in arable land across the whole of China, for the period 1980–2012. Results indicated that the total P input to soil increased from 22.5 kg P/ha in 1980 to 79.1 kg P/ha in 2012. However, the total P output from soil only increased from 17.9 kg P/ha in 1980 to 36.9 kg P/ha in 2012. Therefore, the average net soil P surplus in China increased from 4.6 kg P/ha in 1980 to 42.1 kg P/ha in 2012. Our research found great variation in soil P balances across different regions. Soil P balance varied between regions with the order of southeast (SE) > north central (NC) and the middle and lower reaches of Yangtze River (MLYR) > southwest (SW) > northwest (NW) > northeast (NE). Phosphorus that has accumulated in agricultural soil across China could theoretically meet crop P demands for approximately 4.8–12.0 yrs, depending on the bioavailability of P stored in soils. Increasing the return rates of manure and straw could substantially reduce the demand for fertilizer‐P. This paper represents a basis for more targeted, regionally informed P fertilizer recommendations in Chinese soils.
Headwater streams are an important feature of the landscape, with their diversity in structure and associated ecological function providing a potential natural buffer against downstream nutrient ...export. Phytobenthic communities, dominated in many headwaters by diatoms, must respond to physical and chemical parameters that can vary in magnitude within hours, whereas the ecological regeneration times are much longer. How diatom communities develop in the fluctuating, dynamic environments characteristic of headwaters is poorly understood. Deployment of near-continuous monitoring technology in sub-catchments of the River Eden, NW England, provides the opportunity for measurement of temporal variability in stream discharge and nutrient resource supply to benthic communities, as represented by monthly diatom samples collected over two years. Our data suggest that the diatom communities and the derived Trophic Diatom Index, best reflect stream discharge conditions over the preceding 18-21 days and Total Phosphorus concentrations over a wider antecedent window of 7-21 days. This is one of the first quantitative assessments of long-term diatom community development in response to continuously-measured stream nutrient concentration and discharge fluctuations. The data reveal the sensitivity of these headwater communities to mean conditions prior to sampling, with flow as the dominant variable. With sufficient understanding of the role of antecedent conditions, these methods can be used to inform interpretation of monitoring data, including those collected under the European Water Framework Directive and related mitigation efforts.
Headwater streams are an important feature of the landscape, with their diversity in chlorophyll-a and community structure a function of mean antecedent conditions.
A classification scheme for pollutant natural attenuation potential at the groundwater–surface water interface is presented, and its predictive power for explaining baseflow river nitrate ...concentration investigated. Both the classification scheme and statistical analysis are undertaken at Water Framework Directive surface water body scale for England and Wales, in baseflow conditions when relative groundwater contribution to rivers is greatest. The results of multiple regression analyses demonstrate statistically significant relationships between the classification of natural attenuation potential, its component properties, and baseflow river nitrate concentration. Natural attenuation at the groundwater–surface water interface is shown to be a significant control on observed river nitrate concentrations, albeit less influential than land-use descriptors. The results indicate that natural attenuation processes have a measurable impact on baseflow river chemistry at surface water body scale, and that consideration of natural attenuation processes at the groundwater–surface water interface would improve regional and catchment-scale risk prediction, and could help in the design of more sustainable catchment management strategies.
The movement of nitrate through the vadose zone has major implications for environmental and human health. This issue is particularly prevalent in karst terrain where agricultural activity, thin ...soils and dual permeability compound the problem of high nitrate loading to the overlying ecosystem. However, a paucity of records which document vadose zone nitrate concentrations prior to the 21st century render legacy nitrate dynamics, source attribution and baseline conditions to be poorly parameterised. Speleothems growing within karst cave settings may provide an opportunity to obtain records of vadose zone nitrate contamination which extend throughout the anthropogenic era. Here, we use dual isotope analysis of δ15NNO3 and δ18ONO3 in a contemporary study at Cueva-cubío del Llanío, N. Spain, designed to examine the transformation of nitrate between surface to cave environment, taking account of biogeochemical transformation, karst hydrology and partitioning as controls on the delivery of nitrate to the speleothem record. Concentrations of nitrate within speleothem calcite are low (measured range of 0.05 mM to 0.37 mM) due to partitioning (DNO3) across the dripwater-calcite interface. Values of δ15NNO3 extracted from cave waters in Cueva-cubío del Llanío (range +2.0 to +7.0‰) are shown to be excellent indicators of nitrate source and demonstrate no fractionation during incorporation into speleothem carbonate (range of δ15NNO3 in speleothem carbonate +1.6‰ to +6.4‰). Values of δ18ONO3 contained within cave waters (range −2.5‰ to +6.0‰) and speleothem carbonate (range +12.3‰ to +32.3‰) reflect a mixed signal of source, biogeochemical processing and hydrological pathway, providing critical insight into the behaviour of the karst aquifer. Contemporary systematics at Cueva-cubío del Llanío therefore confirm speleothem carbonate contains an excellent record of vadose zone nitrate. Analysis of nitrate contained within speleothem carbonate from other regions confirms the ubiquitous nature of partitioning across the water‑carbonate interface and the use of speleothem nitrate isotopes for recording surface ecosystem processes and vadose zone behaviour. Application of these principles to dated speleothem records should provide critical timeseries of nitrate loading, enabling understanding and remediation against the presence of vadose zone legacy nitrate.
Summary
Using industrial by‐products (IBPs) in conjunction with vegetated buffer strips (VBSs) has the potential to be a cost‐effective strategy for tackling phosphorus (P) export from agricultural ...land. Using an integrated mesocosm approach, we examined the effect of surface application of IBPs within VBSs on the removal of P fractions in surface and sub‐surface flow. Artificial run‐off was applied to VBSs (1.2 m long × 0.4 m wide, and 5% slope) that were amended with either 20 t ha−1 of Al‐based water treatment residual (Al‐WTR) or 20 t ha−1 of ochre, or remained as unamended controls. To explore the persistence of the effects of amendment over multiple run‐off events, two 30‐minute artificial run‐off events (3 litre minute−1) were applied to the mesocosms over a period of five days. When compared with inflow concentrations, the unamended VBSs reduced total P (37–54%) and particulate P (61–64%) concentrations in surface run‐off, but increased soluble reactive P (SRP) (5–9%) and total dissolved P concentrations (4–8%). Enhancing VBSs with IBPs improved retention of soluble P fractions in surface run‐off, for example, 61–62 and 15–19% of the SRP in the inflow was retained in VBSs amended with Al‐WTR and ochre, respectively. Surface application of either ochre or Al‐WTR also reduced the concentrations of soluble P fractions in sub‐surface flow. The magnitude of these effects depended on inflow P concentrations. Unlike Al‐WTR, the effectiveness of ochre gradually declined over the duration of each run‐off event because of erosion of ochre by run‐off.
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