Elsevier

Journal of Hydrology

Volume 409, Issues 1–2, 28 October 2011, Pages 157-171
Journal of Hydrology

Subsurface transport of orthophosphate in five agricultural watersheds, USA

https://doi.org/10.1016/j.jhydrol.2011.08.014Get rights and content

Summary

Concentrations of dissolved orthophosphate (ortho P) in the unsaturated zone, groundwater, tile drains, and groundwater/stream water interfaces were assessed in five agricultural watersheds to determine the potential for subsurface transport. Concentrations of iron oxides were measured in the aquifer material and adsorption of ortho P on oxide surfaces was assessed by geochemical modeling. Attenuation of ortho P in these aquifers was attributed primarily to sorption onto iron oxides, and in one location onto clay minerals. Only one location showed a clear indication of phosphorus transport to a stream from groundwater discharge, although groundwater did contribute to the stream load elsewhere. Subsurface ortho P movement at a site in California resulted in a plume down gradient from orchards, which was attenuated by a 200 m thick riparian zone with natural vegetation. Iron oxides had an effect on phosphorus movement and concentrations at all locations, and groundwater chemistry, especially pH, exerted a major control on the amount of phosphorus adsorbed. Groundwater pH at a site in Maryland was below 5 and that resulted in complete sequestration of phosphorus and no movement toward the stream. Geochemical modeling indicated that as the surfaces approached saturation, groundwater concentrations of ortho P rise rapidly.

Highlights

► Phosphorus transport in groundwater was assessed at five agricultural watersheds. ► Phosphorus subsurface movement was controlled by sorption onto iron oxides or clays. ► Water chemistry and soil types affected phosphorus transport to the aquifers. ► Low pH conditions within an aquifer in Maryland prevented phosphorus transport. ► Geochemical modeling was used to assess adsorption.

Introduction

Nutrient transport (nitrogen and phosphorus compounds) from agricultural fields to surface and groundwater is one of the most serious environmental problems throughout the world (Salvia-Castellvi et al., 2005, National Research Council (NRC), 2005, Diaz et al., 2004). Eutrophication, or excessive growth of algae, of surface water bodies impairs their use for recreation and domestic consumption and limits their use by native biota. Where surface water is chlorinated and used for drinking water, increased levels of algae contribute to the formation of trihalomethanes and haloacetic acids (Scully et al., 1988; Oliver and Shindler, 1980), which have been shown to be both carcinogenic and mutagenic in laboratory toxicity studies (Boorman, 1999). Recently, Sprague and Lorenz (2009) reported an increase in total phosphorus concentrations in streams in the central United States between 1993 and 2003. The increase in total phosphorus was significantly correlated with an increase in fertilizer use. No significant change in total phosphorus was found in streams in the western or eastern United States.

In natural systems, phosphorus is mainly cycled through a plant-soil dynamic. However in agricultural systems, phosphorus is removed at harvest and must be replenished with either mineral fertilizer or manure. Soils may be over applied with respect to phosphorus because many management programs are tied to nitrogen control or crop needs and phosphorus management is not always considered (Sharpley et al., 2003). This issue is common in areas using manure, which typically has a N:P ratio lower than needed by most crops. Application of manure to meet N requirements often results in the application of P exceeding crop demand. Surface water contamination with phosphorus due to runoff from manured fields (Klausner et al., 1976, Hergert et al., 1981, Allen and Mallarino, 2008) and agriculture in general (Baker et al., 1975, Burwell et al., 1977, Sharpley and Syers, 1979, Vollenweider, 1968) is a well-studied topic.

It is known that phosphorus sorbs to soil particles. Phosphorus sorbs onto oxides of iron and aluminum (Hemwell, 1957, Zhang and Huang, 2007), clay minerals (Parfitt, 1978) and to calcium carbonate (Cole et al., 1953). It has been assumed that phosphorus transport to groundwater is negligible because of sorption and therefore earlier studies on phosphorus transport have been focused solely on surface water pathways (Baker et al., 1975, Burwell et al., 1977, Sharpley and Syers, 1979, Vollenweider, 1968). Attenuation of phosphorus movement and plant availability by interactions onto soil particles has been recognized by previous research (Gunjigake and Wada, 1981, Anderegg and Naylor, 1988, Parfitt, 1978). More recent studies (Devau et al., 2009), for example, have further refined understanding of various factors, such as soil pH, with respect to phosphorus mobility or plant availability and the importance of clay minerals, in addition to iron and aluminum oxides for controlling the distribution of phosphorus between soil and water.

It was hypothesized for this study that phosphorus movement in the unsaturated zone and along a groundwater flow path to a stream or tile drain would be different with location because of hydrological and chemical factors. Processes affecting the rate of water movement through the unsaturated zone are likely to be important for phosphorus transport as well as processes that affect sorption or dissolution. Chemical equilibrium may not be achieved in the unsaturated zone because of short residence times at some locations, if transport times are fast such as might occur because of preferential flow paths, and because of competition for sorption sites from competing ions. It was further hypothesized that groundwater processes affecting phosphorus would more likely be closer to equilibrium relative to the unsaturated zone as residence time increases and groundwater chemistry stabilizes allowing equilibrium conditions between the fluid and the solids. Groundwater/surface water interactions should also differ with location relative to the amount and direction of exchange of water across the streambed interface. Unsaturated zone, groundwater, and streambed materials and water chemistry are expected to affect the transport or immobilization of phosphorus. In a previous study at a set of five watersheds across a range of climatic and soil types within the United States, Domagalski et al. (2008a) showed that baseflow contributed more than 20% of the annual ortho P load in some of the streams of this study. Tesoriero et al. (2009) examined the baseflow index of some of the same streams, as this study, with a range of groundwater contributions to discharge. They found that the baseflow index was negatively correlated with in-stream ortho P concentrations at most sites. However, at sites dominated by baseflow or having favorable geochemical conditions (e.g. aquifers having low dissolved oxygen concentrations or lacking in iron and aluminum oxides, clay minerals, and calcium carbonate) groundwater contributions of ortho P to streams are important (Tesoriero et al., 2009). The purpose of this investigation was to examine the geochemical conditions and reactions affecting ortho P concentrations in the subsurface environmental compartments (unsaturated zone, groundwater, groundwater/surface water interface) of the five watersheds from the Domagalski et al. (2008a) and Tesoriero et al. (2009) studies. Geochemical modeling was used to determine the level of saturation of ortho P with respect to minerals and sorption onto iron oxides. The results of the modeling were used to interpret the subsurface ortho P concentrations and assess the potential for phosphorus transport along the groundwater flow paths.

Section snippets

Study areas

Five study areas were chosen in agricultural watersheds nested within larger basins that are being investigated by the US Geological Survey (USGS) NAWQA Program (US Geological Survey, 2010a) (Fig. 1). Specific characteristics of the aquifers, crop types, and phosphorus use for each study area are shown in Table 1.

Study areas were chosen from a previous investigation that included important agricultural systems and to cover a range of hydrologic settings using the hydrologic landscape concept (

Field methods

Unsaturated-zone monitoring locations were equipped with instrumentation to measure surficial soil temperature, soil heat flux, soil water matric potential and soil moisture at depth in order to estimate the flux of water out of the soil and the amount of water in the soil. Polyvinylchloride lysimeters with ceramic porous cups were installed at various depths to collect unsaturated zone water for chemical analysis by applied suction. The shallowest lysimeter was located just below the root zone

Phosphorus concentrations and water chemistry

Concentrations of ortho P for each hydrological compartment (unsaturated zone, groundwater, groundwater/surface water interface, streams, and tile drains (Indiana site only) are shown in Fig. 2, along with the US EPA criteria for total phosphorus in specific ecoregions (US Environmental Protection Agency, 2010). Concentrations of ortho P in rainfall were below the laboratory-reporting limit of 0.008 mg/L. Therefore rain was not considered a source of phosphorus to the soil.

Concentrations of

Summary and conclusion

Phosphorus can be transported below the root zone to the unsaturated zone and through an aquifer in agricultural settings. This study showed that under conditions where phosphorus is either not entirely taken up by plant tissue or where soil chemistry does not favor either precipitation or sorption, that sub-surface transport can result in elevated concentrations in groundwater or loadings to receiving streams. In this study, phosphorus transport to a stream was demonstrated most clearly at the

References (75)

  • N. Devau et al.

    Soil pH controls the environmental availability of phosphorus: experimental and mechanistic modeling approaches

    Appl. Geochem.

    (2009)
  • M. Salvia-Castellvi et al.

    Dissolved and particulate nutrient export from rural catchments: a case study from Luxembourg

    Sci. Total Environ.

    (2005)
  • B.L. Allen et al.

    Effect of liquid swine manure rate, incorporation, and timing of rainfall on phosphorus loss with surface runoff

    J. Environ. Qual.

    (2008)
  • American Public Health Association, 1998. Standard Methods for the Examination of Water and Wastewater, 20th ed....
  • J.C. Anderegg et al.

    Phosphorus and pH relationships in an acidic soil with surface and incorporated organic amendments

    Plant Soil

    (1988)
  • Y. Avnimelech

    Calcium–carbonate–phosphate surface complex in calcareous systems

    Nature

    (1980)
  • J.L. Baker et al.

    Nitrate, phosphorus, and sulfate in subsurface drainage water

    J. Environ. Qual.

    (1975)
  • Baker, N.T., Stone, W.W., Wilson, J.T., Meyer, M.T., 2006. Occurrence and Transport of Agricultural Chemicals in the...
  • G.A. Boorman

    Drinking water disinfection byproducts: review and approach to toxicity evaluation

    Environ. Health Perspect.

    (1999)
  • R.E. Burwell et al.

    Nitrogen and phosphorus movement from agricultural watersheds

    J. Soil Water Conserv.

    (1977)
  • E. Busenberg et al.

    Dating young groundwater with sulfur hexafluoride: natural and anthropogenic sources of sulfur hexafluoride

    Water Resour. Res.

    (2000)
  • P.D. Capel et al.

    National, holistic, watershed-scale approach to understand the sources, transport, and fate of agricultural chemicals

    J. Environ. Qual.

    (2008)
  • C.V. Cole et al.

    The nature of phosphate sorption by calcium carbonate

    Soil Sci. Soc. Am. J.

    (1953)
  • Diaz, R.J., Nestlerode, J., Diaz, M.L., 2004. A global perspective on the effects of eutrophication and hypoxia on...
  • J.L. Domagalski et al.

    Comparative study of transport processes of nitrogen, phosphorus, and herbicides to streams in five agricultural basins, USA

    J. Environ. Qual.

    (2008)
  • J.L. Domagalski et al.

    Influences of the unsaturated, saturated, and riparian zones on the transport of nitrate near the Merced River, California, USA

    Hydrol. J.

    (2008)
  • Dzombak, D.A., Morel, F.M.M., 1990. Surface Complexation Modeling—Hydrous Ferric Oxide. John Wiley, New York,...
  • G.N. Egwu et al.

    Phosphorus sorption isotherms and parameter estimates of soils of the savanna, and effect of soil properties on these parameters

    Electron. J. Environ., Agric. Food Chem.

    (2010)
  • H.I. Essaid et al.

    Using heat to characterize streambed water flux variability in four stream reaches

    J. Environ. Qual.

    (2008)
  • L.H. Fisher et al.

    Water movement within the unsaturated zone in four agricultural areas of the United States

    J. Environ. Qual.

    (2008)
  • Fishman, M.J., 1993. Methods of Analysis by the US Geological Survey National Water Quality Laboratory—Determination of...
  • Fishman, M.J., Friedman, L.C., 1989. Methods for Determination of Inorganic Substances in Water and Fluvial Sediments....
  • Fredrick, B.S., Linard, J.I., Carpenter, J.L., 2006. Environmental Setting of Maple Creek Watershed, Nebraska. US...
  • J.S. Freeman et al.

    The adsorption and precipitation of phosphate onto calcite

    Soil Sci.

    (1981)
  • C.T. Green et al.

    Limited occurrence of denitrification in four shallow aquifers in agricultural areas of the United States

    J. Environ. Qual.

    (2008)
  • Gronberg, J.M., Kratzer, C.R., 2006. Environmental Setting of the Lower Merced River Basin, California. US Geological...
  • N. Gunjigake et al.

    Effects of phosphorus concentration and pH on phosphate retention by active aluminum and iron of Ando soils

    Soil Sci.

    (1981)
  • Hancock, T.C., Brayton, M.J., 2006. Environmental Setting of the Morgan Creek Basin, Maryland, 2002–2004. US Geological...
  • T.C. Hancock et al.

    Pesticide fate and transport throughout unsaturated zones in five agricultural settings, USA

    J. Environ. Qual.

    (2008)
  • D. Hawke et al.

    Competitive adsorption of phosphate on goethite in marine electrolytes

    Environ. Sci. Technol.

    (1989)
  • G. Heckrath et al.

    Phosphorus leaching from soils containing different phosphorus concentrations in the Broadbalk experiment

    J. Environ. Qual.

    (1995)
  • Hemwell, J.B., 1957. The fixation of phosphorus by soils. In: Norman, A.G. (Ed.), Advances in Agronomy, vol. 9....
  • G.W. Hergert et al.

    Effects of dairy manure on phosphorus concentrations and losses in tile effluent

    J. Environ. Qual.

    (1981)
  • F.J. Hingston et al.

    Anion adsorption by goethite and gibbsite 2. Desorption of anions from hydrous oxide surfaces

    Soil Science

    (1974)
  • Y. Hochberg

    A sharper Bonferroni procedure for multiple tests of significance

    Biometrika

    (1988)
  • S.D. Klausner et al.

    Nitrogen and phosphorus losses from winter disposal of dairy manure

    J. Environ. Qual.

    (1976)
  • Lathrop, T.R., 2006. Environmental Setting of the Sugar Creek and Leary Weber Ditch Basins, Indiana, 2002–2004. US...
  • Cited by (68)

    View all citing articles on Scopus
    View full text