Phosphorus export from catchments: a global view

Abstract

We reviewed global P export and its controlling factors from 685 world rivers. We used available continuous (runoff, rainfall, catchment area, % land use, and population density) and discrete (runoff type, soil type, biome, dominant land use, dominant type of forest, occurrence of stagnant water bodies in catchment, and Gross Product per Capita [GPC]) variables to predict export of P fractions. P export (kg P km 22 y 21 ) spanned 6 orders of magnitude worldwide. The distribution of all fractions of P export (total P [TP], soluble reactive P [SRP], and nonSRP [dissolved organic and particle-bound P]) was right skewed. Export of nonSRP had the highest coefficient of variability, and nonSRP was the dominant part of export. The available environmental variables predicted global P export fairly well (R 2 = 0.73) if total N export was included in calculations. The unexplained variance in P export might be attributed to noise in the data set, inaccuracy of measurements of environmental variables at fine scales, lack of quantitative data on anthropogenic P sources, insufficient knowledge of P behavior in catchment soils, and nonlinearity of controlling processes. P exports were highly variable among catchment types, and runoff and population density were the predictors shared by most models. P export appeared to be controlled by different sets of environmental variables in different types of catchments. Quasi-empirical, mechanistic models of P export performed better than did empirical models. Our mechanistic understanding of P export could be improved by refining current analytical methods to obtain fast and reliable values of all P fractions in aquatic ecosystems and by incorporating better and more detailed data on catchment features, anthropogenic sources of P, and instream variables in a mechanistic modelling framework.

Effects of climatic change on stream water quality in Spain

“…They may include the balance between extreme and normal events (i.e. storm-vs baseflow; Butturini et al 2006), catchment effects (land use and its effects on evapotranspiration and runoff; Alvarez-Cobelas et al 2005) and in-stream processes (denitrification, mineralization, burial;Alvarez-Cobelas et al 2008, 2009). We recommend that future studies consider local scale processes in addition to the pure climatic effects to gain better pictures of ecological responses to changing climates.…”

“…The IPCC report (Kundzewicz et al 2007), which deals with climatic change effects on inland water quality, is not particularly focused on streams, even though these systems are important providers of ecosystem services that support human activities in many ways (Fischlin et al 2007). Recent studies that cover nutrient export rates from catchments on a worldwide basis show the importance of climatic settings (arid vs temperate areas) on nutrient dynamics (Alvarez-Cobelas et al 2008, 2009). While results from these studies provide insight on how stream biogeochemistry in temperate areas might approximate conditions of dryland streams, the responses of climatic influences on water quality in arid areas can not be benchmarked from a spatial perspective and would require a reconstruction of temporal trends to assess the magnitudes of change over time (Jansons and Butina 1998;Ozaki et al 2003).…”

Estimation of phosphorus export from a Mediterranean agricultural catchment with scarce data

“…In other European agricultural catchments of similar size, a release of 0.1-4.7 kg ha -1 year -1 was found (Kronvang et al 2007). In a study including 685 catchments worldwide, by far the majority of catchments had annual exports 0-1 kg ha -1 year -1 , but values of up to 50 kg ha -1 year -1 were reported (Alvarez-Cobelas et al 2009). Thus, the estimated long-term TP release of this study (0.58 kg ha -1 year -1 ) can be classified as below average for this region, and much below the highest worldwide values.…”

Spatial and temporal dynamics of biogeochemical processes in the Fraser River, Canada : a coupled organic-inorganic perspective

“…Our measurements may exclude significant inputs of N and P from fertilizer and manure runoff and sewage and stormwater overflow, sources which rival or dwarf natural fluxes in many other rivers (Howarth et al, 1996;Boyer et al, 2006;Shen and Liu, 2008;Alvarez-Cobelas et al, 2009)…”