Nicholas J K Howden

Sustainable Phosphorus Management and the Need for a Long-Term Perspective: The Legacy Hypothesis

Perspective: The Legacy Hypothesis Philip M. Haygarth,*,† Helen P. Jarvie,‡ Steve M. Powers, Andrew N. Sharpley, James J. Elser, Jianbo Shen, Heidi M. Peterson, Neng-Iong Chan, Nicholas J. K. Howden, Tim Burt, Fred Worrall, Fusuo Zhang, and Xuejun Liu †Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, U.K. ‡Centre for Ecology and Hydrology, OX10 8BB, Wallingford, Oxfordshire, U.K. University of Notre Dame, Environmental Change Initiative, South Bend, Indiana 46617, United States Division of Agriculture, University of Arkansas, Fayetteville, Arkansas 72701, United States School of Life Sciences, Arizona State University, Tempe, Arizona 85287, United States Center for Resources, Environment and Food Security, China Agricultural University, Key Laboratory of Plant-Soil Interactions, Ministry of Education, Beijing 100193, P. R. China Minnesota Department of Agriculture, Pesticides and Fertilizer Management Division, Saint Paul, Minnesota 55155, United States University of Bristol, Queen’s School of Engineering, BS8 1TH, Bristol, U.K. Durham University, Department of Geography, DH1 3LE, Durham, U.K. Durham University, Department of Earth Sciences, DH1 3LE, Durham, U.K.

Nitrate pollution in intensively farmed regions: What are the prospects for sustaining high‐quality groundwater?

[1] Widespread pollution of groundwater by nutrients due to 20th century agricultural intensification has been of major concern in the developed world for several decades. This paper considers the River Thames catchment (UK), where water-quality monitoring at Hampton (just upstream of London) has produced continuous records for nitrate for the last 140 years, the longest continuous record of water chemistry anywhere in the world. For the same period, data are available to characterize changes in both land use and land management at an annual scale. A modeling approach is used that combines two elements: an estimate of nitrate available for leaching due to land use and land management; and, an algorithm to route this leachable nitrate through to surface or groundwaters. Prior to agricultural intensification at the start of World War II, annual average inputs were around 50 kg ha−1, and river concentrations were stable at 1 to 2 mg l−1, suggesting in-stream denitrification capable of removing 35 (±15) kt N yr−1. Postintensification data suggest an accumulation of 100 (±40) kt N yr−1 in the catchment, most of which is stored in the aquifer. This build up of reactive N species within the catchments means that restoration of surface nitrate concentrations typical of the preintensification period would require massive basin-wide changes in land use and management that would compromise food security and take decades to be effective. Policy solutions need to embrace long-term management strategies as an urgent priority.

Nitrate in United Kingdom Rivers: Policy and Its Outcomes Since 1970

Modern conventional farming provides Western Europe and North America with reliable, high quality, and relatively cheap supplies of food and fiber, increasingly viewed as a potential source of fuel. One of the costs is continued widespread pollution of rivers and groundwater-predominantly by nutrients. In 1970, in both the United States and UK, farming was focused on maximizing yield and management practices were rapidly modernizing. Little attention was paid to the external impacts of farming. In 2010, diffuse pollution from agriculture is being seriously addressed by both voluntary and statutory means in an attempt to balance environmental costs with the continued benefits of agricultural production. In this paper we consider long-term changes in the concentration and flux of nitrate in five rural UK rivers to demonstrate the impact of agricultural intensification and subsequent policies to reduce diffuse pollution on river water quality between 1970 and 2010.

Farming for Water Quality: Balancing Food Security and Nitrate Pollution in UK River Basins

Widespread pollution of groundwater by nutrients is an externality of modern intensive agriculture. Rising nitrate concentrations in freshwater have been of concern throughout the developed world for several decades. Initial worries focused on human health but more recently nitrates role in eutrophication has also become a cause for concern. Because the impact on water quality often comes decades after land use change, the challenge for science is to produce an integrated model of catchment hydrology and quality applicable to the long time-scales involved and that can cope with the complexity of connectivity among land, aquifer, and river. This article discusses the balance between food production, and therefore food security, and protection of water resources. We use recent results from a catchment-scale model of the River Thames in the United Kingdom to demonstrate that the response time of catchments can be on the order of decades, given the delays induced by groundwater flow through aquifers. Historically, the main drivers for changes in N fluxes were massive land use change associated with wartime plowing of permanent pastures and postwar modernization and intensification of agriculture, leading to the current quasi-steady state of N-dependent but leaky agriculture. It is clear that restoration of water quality to mid-twentieth-century levels would require very severe changes in land use and land management, significantly affecting UK food supply and security. Moreover, the potential timescales for recovery are well beyond those of normal political cycles. Failure to act will mean a continued high level of nitrogen transfer to rivers, estuaries, and oceans, with potentially serious ecological implications, and continued emissions greenhouse gases to the atmosphere. Notwithstanding improved efficiency of agronomic methods, the situation is unlikely to change significantly without radical shifts in legislation or farm economics.

The flux of dissolved nitrogen from the UK – Evaluating the role of soils and land use

Fluvial dissolved nitrogen (dissolved organic nitrogen [DON], nitrate and ammonium) fluxes from the terrestrial biosphere of the UK to surrounding oceans are explained on the basis of combined predictions of soil to water transfer and in-stream loss. The flux of different nitrogen species from land to surface waters is estimated using an export coefficient model employing catchment soil, land use and hydroclimatic characteristics, fitted to flux estimates derived from the Harmonised Monitoring Scheme between 2001 and 2007 for 169 UK catchments. In-stream losses of DON, nitrate and ammonium were estimated using a transit time filter in the fluvial network. Comparisons of modelled land to water N flux (2125 ktonnes N yr(-1)) with estimates of N fluxes to estuarine and ocean systems at the tidal limit (791 ktonnes N yr(-1)) suggest that significant in-channel N losses occur. These in transit losses are equivalent to up to 55 kg N ha(-1) yr(-1).

Quantifying landscape-level methane fluxes in subarctic Finland using a multiscale approach

Abstract Quantifying landscape‐scale methane (CH 4) fluxes from boreal and arctic regions, and determining how they are controlled, is critical for predicting the magnitude of any CH 4 emission feedback to climate change. Furthermore, there remains uncertainty regarding the relative importance of small areas of strong methanogenic activity, vs. larger areas with net CH 4 uptake, in controlling landscape‐level fluxes. We measured CH 4 fluxes from multiple microtopographical subunits (sedge‐dominated lawns, interhummocks and hummocks) within an aapa mire in subarctic Finland, as well as in drier ecosystems present in the wider landscape, lichen heath and mountain birch forest. An intercomparison was carried out between fluxes measured using static chambers, up‐scaled using a high‐resolution landcover map derived from aerial photography and eddy covariance. Strong agreement was observed between the two methodologies, with emission rates greatest in lawns. CH 4 fluxes from lawns were strongly related to seasonal fluctuations in temperature, but their floating nature meant that water‐table depth was not a key factor in controlling CH 4 release. In contrast, chamber measurements identified net CH 4 uptake in birch forest soils. An intercomparison between the aerial photography and satellite remote sensing demonstrated that quantifying the distribution of the key CH 4 emitting and consuming plant communities was possible from satellite, allowing fluxes to be scaled up to a 100 km2 area. For the full growing season (May to October), ~ 1.1–1.4 g CH 4 m−2 was released across the 100 km2 area. This was based on up‐scaled lawn emissions of 1.2–1.5 g CH 4 m−2, vs. an up‐scaled uptake of 0.07–0.15 g CH 4 m−2 by the wider landscape. Given the strong temperature sensitivity of the dominant lawn fluxes, and the fact that lawns are unlikely to dry out, climate warming may substantially increase CH 4 emissions in northern Finland, and in aapa mire regions in general.

Phosphate stable oxygen isotope variability within a temperate agricultural soil

In this study, we conduct a spatial analysis of soil total phosphorus (TP), acid extractable phosphate (PO4) and the stable oxygen (O) isotope ratio within the PO4 molecule (δ18OPO4) from an intensively managed agricultural grassland site. Total P in the soil was found to range from 736 to 1952 mg P kg− 1, of which between 12 and 48% was extractable using a 1 M HCl (HClPO4) solution with the two variables exhibiting a strong positive correlation. The δ18OPO4 of the extracted PO4 ranged from 17.0 to 21.6‰ with a mean of 18.8‰ (± 0.8). While the spatial variability of Total P has been researched at various scales, this is the first study to assess the variability of soil δ18OPO4 at a field-scale resolution. We investigate whether or not δ18OPO4 variability has any significant relationship with: (i) itself with respect to spatial autocorrelation effects; and (ii) HClPO4, elevation and slope - both globally and locally. Results indicate that δ18OPO4 was not spatially autocorrelated; and that δ18OPO4 was only weakly related to HClPO4, elevation and slope, when considering the study field as a whole. Interestingly, the latter relationships appear to vary in strength locally. In particular, the δ18OPO4 to HClPO4 relationship may depend on the underlying soil class and/or on different field managements that had operated across an historical north-south field division of the study field, a division that had been removed four years prior to this study.

Human impact on long-term organic carbon export to rivers

Anthropogenic landscape alterations have increased global carbon transported by rivers to oceans since pre-industrial times. Few suitable observational datasets exist to distinguish different drivers of carbon increase, given that alterations only reveal their impact on fluvial dissolved organic carbon (DOC) over long time periods. We use the worlds longest record of DOC concentrations (130 years) to identify key drivers of DOC change in the Thames basin (UK). We show that 90% of the long-term rise in fluvial DOC is explained by increased urbanization, which released to the river 671 ktonnes C over the entire period. This source of carbon is linked to rising population, due to increased sewage effluent. Soil disturbance from land-use change explained shorter-term fluvial responses. The largest land-use disturbance was during the Second World War, when almost half the grassland area in the catchment was converted into arable land, which released 45 ktonnes C from soils to the river. Carbon that had built up in soils over decades was released to the river in only a few years. Our work suggests widespread population growth may have a greater influence on fluvial DOC trends than previously thought.

Analysis of Nitrate Concentrations Using Nonlinear Time Series Models

Analysis of Nitrate Concentrations Using Nonlinear Time Series Models This study examines two long-term time series of nitrate-nitrogen concentrations from the River Ouse and Stour situated in the Eastern England. The time series of monthly averages were decomposed into trend, seasonal and cyclical components and residuals to create a simple additive model. Residuals were then modelled by linear time series models represented by models of the ARMA (autoregressive moving average) class and nonlinear time series models with multiple regimes represented by SETAR (self-exciting threshold autoregressive) and MSW (Markov switching) models. The analysis showed that, based on the minimal value of residual sum of squares (RSS) of one-step ahead forecast in both datasets, SETAR and MSW models described the time series better than models ARMA. However, the relative improvement of SETAR models against ARMA models was low ranging between 1% and 4% with the exception of the three-regime model for the River Stour where the improvement was 48.9%. In comparison, the relative improvement of MSW models was between 44.6% and 52.5 for two-regime and from 60.4% to 75% for three-regime models. However, the visual assessment of models plotted against original datasets showed that despite a high value of RSS, some ARMA models could describe the analyzed time series better than AR (autoregressive), MA (moving average) and SETAR models with lower values of RSS. In both datasets MSW models provided a very good visual fit describing most of the extreme values. The results of this work could be used as a base for construction of other time series models used to describe or predict nitrate-nitrogen concentrations. Analýza Koncentrácií Dusičnanov Pomocou Nelineárnych Modelov Časových Radov. Štúdia sa zaoberá analýzou dlhých časových radov koncentrácií dusičnanového dusíka v rieke Ouse a Stour vo Východnom Anglicku. Časové rady priemerných mesačných koncentrácií dusičnanov boli rozložené na trendovú, sezónnu a cyklickú zložku a reziduá pripočítané k sebe a tvoriace jednoduchý aditívny model. Reziduá boli ďalej modelované zložitejŠími lineárnymi modelmi reprezentovanými modelmi triedy ARMA a nelineárnymi viacrežimovými modelmi SETAR a MSW. Výsledky analýzy ukázali, že na základe minimálnej hodnoty sumy Štvorcov reziduí (SSR) jednokrokovej predpovede, v oboch prípadoch SETAR aj MSW modely opísali časové rady lepŠie ako modely triedy ARMA. Vo väčŠine prípadov relatívne zlepŠenie modelov SETAR oproti jednoduchým AR(1) modelom bolo malé v rozmedzí od 1 do 4 % s výnimkou trojrežimového modelu pre rieku Stour, kde to bolo až 48,9 %. Naopak, relatívne zlepŠenie modelov MSW oproti AR(1) modelom bolo v rozmedzí 44,6 až 52,5 % pre dvojrežimové a 60,4 až 75 % pre trojrežimové modely. Vizuálne posúdenie jednotlivých modelov vŠak ukázalo, že napriek vysokým hodnotám SSR, niektoré ARMA modely dokázali lepŠie opísať dané časové rady ako modely AR, MA a SETAR s nižŠími hodnotami SSR. V oboch prípadoch MSW modely dokázali dostatočne dobre opísať aj extrémne hodnoty oboch časových radov. Výsledky práce môžu byť použité pri tvorbe iných opisných alebo predpovedných modelov koncentrácie dusičnanového dusíka vo vodách.

The stable oxygen isotope ratio of resin extractable phosphate derived from fresh cattle faeces.

Rationale Phosphorus losses from agriculture pose an environmental threat to watercourses. A new approach using the stable oxygen isotope ratio of oxygen in phosphate (δ18OPO4 value) may help elucidate some phosphorus sources and cycling. Accurately determined and isotopically distinct source values are essential for this process. The δ18OPO4 values of animal wastes have, up to now, received little attention. Methods Phosphate (PO4) was extracted from cattle faeces using anion resins and the contribution of microbial PO4 was assessed. The δ18OPO4 value of the extracted PO4 was measured by precipitating silver phosphate and subsequent analysis on a thermal conversion elemental analyser at 1400°C, with the resultant carbon monoxide being mixed with a helium carrier gas passed through a gas chromatography (GC) column into a mass spectrometer. Faecal water oxygen isotope ratios (δ18OH2O values) were determined on a dual‐inlet mass spectrometer through a process of headspace carbon dioxide equilibration with water samples. Results Microbiological results indicated that much of the extracted PO4 was not derived directly from the gut fauna lysed during the extraction of PO4 from the faeces. Assuming that the faecal δ18OH2O values represented cattle body water, the predicted pyrophosphatase equilibrium δ18OPO4 (Eδ18OPO4) values ranged between +17.9 and +19.9‰, while using groundwater δ18OH2O values gave a range of +13.1 to +14.0‰. The faecal δ18OPO4 values ranged between +13.2 and +15.3‰. Conclusions The fresh faecal δ18OPO4 values were equivalent to those reported elsewhere for agricultural animal slurry. However, they were different from the Eδ18OPO4 value calculated from the faecal δ18OH2O value. Our results indicate that slurry PO4 is, in the main, derived from animal faeces although an explanation for the observed value range could not be determined.