Trends in nutrients

Abstract

The roles of nitrogen (N) and phosphorus (P) as key nutrients determining the trophic status of water bodies are examined, and evidence reviewed for trends in concentrations of N and P species which occur in freshwaters, primarily in northern temperate environments. Data are reported for water bodies undergoing eutrophication and acidification, especially water bodies receiving increased nitrogen inputs through the atmospheric deposition of nitrogen oxides (NO,). Nutrient loading on groundwaters and surface freshwaters is assessed with respect to causes and rates of change, relative rates of change for N and P, and implications of change for the future management of lakes. rivers and groundwaters. In particular, the nature and emphasis of studies for N species and P fractions in lakes versus rivers and groundwaters are contrasted. This review paper primarily focuses on results from North America and Europe, particularly for the UK where a wide range of data sets exists. Few nutrient loading data have been published on water bodies in less developed countries; however, some of the available data are presented to provide a global perspective. In general, N and P concentrations have increased dramatically (>20 times background concentrations) in many areas and causes vary considerably, ranging from urbanization to changes in agricultural practices. Phosphorus transformations generally operate over a longer time-scale than those of N, occur in fewer steps, and are strongly linked to the cycling of sediments (see Figure 2). Mechanisms of P transfer are relatively simple, involving assimilation and dissimilation by biota, immobilization through complexation and chelation, mobilization through the hydrolysis of bivalent and trivalent cations, and adsorption to sediments. Phosphorus does not undergo redox reactions within its cycle. Geochemical fluxes of P are 266 A. L. HEATHWAITE, P. J. JOHNES AND N. E. PETERS WATER m ATMOSPHERIC & bacterial decomposition HYDROSPHERIC y c / i s s i m i / a t i > SOIL BIOTA Organic \ assimilation/ e,g, SEDIMENTS (Fe3+, A13+) synthesis Kaolinite metal complexes nonmetal complexes (Fe3+, AP+) (Ca2+, MI-?+) nonmetal complexes orthophoshates (Ca'+. Mn2+) (H3P04 HzP04-orthophoshates HPO,~-, po43-) (H, PO, H, PO; HPO,~-. ~0~3 -I e.g. Kaolinite metal complexes \ Figure 2. Phosphorus cycle dependent on suspended sediment transport in water bodies and dust emissions to the atmosphere. The rate and magnitude of both fluxes are small. Newman (1995) suggests that phosphorus in the atmosphere from fine soil particles and the burning of plant material, coal and oil varies from 0.7 to 1.7 kgP ha-' yr-', with input rates showing marked spatial variations. Newman (1995) also suggests that P released through weaihering processes may produce yields from 0.05 to 1*0kgPha--' yr-', with rates reaching a high of 5 kg Pha-' yr-' in some locations. In the UK, several meres of the Shropshire glacial plain are considered to be naturally eutrophic as a result of weathering of deposits of P-rich minerals, such as ap...

Phosphorus fractionation in soil and sediments along a continuum from agricultural fields to nearshore lake sediments: Potential ecological impacts

“…Numerous studies have investigated the contribution of point and diffuse sources of P from source areas to stream channels (e.g., Sharpley et al, 1994;Heathwaite et al, 1996;Johnes and Hodgkinson, 1998;Haygarth and Jarvis, 1999). The impact of excess P on the freshwater aquatic systems has also been widely studied in its effects on biological growth and accumulation in stream and lake sediments (e.g., Bostrom et al, 1988;Hilton et al, 2006).…”

Stormflow Dynamics of Dissolved Organic Carbon and Total Dissolved Nitrogen in a Small Urban Watershed

“…(2) Biological and physical properties of soils control transformation, retention, and transport or removal of the constituents (Heathwaite et al 1996;Moore 1998). (3) Dominant hydrologic flowpaths through upper soil and litter layers to the stream determine contact time of the constituents with plant roots, the microbial community, and soil particles (Hedin et al 1998;Michalzik et al 2001).…”

Estimating nutrient production from human activities in subcatchments of the Red River, Manitoba

“…Note: * indicates significant at α = 0.1, ** indicates significant at α = 0.05. nutrients that are added to aquatic systems, a substantial proportion may be in forms that are not immediately available to aquatic biota (Heathwaite et al 1996;Reynolds and Davies 2001) or may be supplied when stream biological activity is minimal (e.g., during snowmelt).…”