Temporal variability in phosphorus transfers: classifying concentration–discharge event dynamics

Abstract

The importance of temporal variability in relationships between phosphorus (P) concentration (C p ) and discharge (Q) is linked to a simple means of classifying the circumstances of C p Q relationships in terms of functional types of response. New experimental data at the upstream interface of grassland soil and catchment systems at a range of scales (lysimeters to headwaters) in England and Australia are used to demonstrate the potential of such an approach. Three types of event are defined as Types 13, depending on whether the relative change in Q exceeds the relative change in C p (Type 1), whether C p and Q are positively inter-related (Type 2) and whether C p varies yet Q is unchanged (Type 3). The classification helps to characterise circumstances that can be explained mechanistically in relation to (i) the scale of the study (with a tendency towards Type 1 in small scale lysimeters), (ii) the form of P with a tendency for Type 1 for soluble (i.e., <0.45 mm P forms) and (iii) the sources of P with Type 3 dominant where P availability overrides transport controls. This simple framework provides a basis for development of a more complex and quantitative classification of C p Q relationships that can be developed further to contribute to future models of P transfer and delivery from slope to stream. Studies that evaluate the temporal dynamics of the transfer of P are currently grossly under-represented in comparison with models based on static/spatial factors.

Changing climate and nutrient transfers: Evidence from high temporal resolution concentration-flow dynamics in headwater catchments

“…Events were classified according to the relative dynamics of TP concentration (C P ) and discharge (Q), following the method of Haygarth et al (2004), into Type 1 (high Q, low C P ), Type 2 (high Q, high C P ) or Type 3 (low Q, high C P ) (Fig. 3).…”

Phosphorus in Surface Runoff from Calcareous Arable Soils of the Semiarid Western United States

“…Soil P accumulation clearly increases filterable reactive P concentrations in surface runoff, but it will be difficult to predict soil-test P concentrations above which this becomes an environmental concern. In particular, there are important scaling issues that remain to be resolved, because it is unclear how filterable reactive P concentrations measured in surface runoff in the field translate to catchment scales (Haygarth et al, 2004). "Change points" in soil P solubility offer a quantifiable and defensible threshold of environmental risk, but are potentially misleading because P concentrations in runoff from soils below the extractable soil P threshold may still threaten water quality.…”

Phosphorus Desorption Dynamics in Soil and the Link to a Dynamic Concept of Bioavailability

“…'Significant' inputs are defined as those that are of sufficient quantity to make an impact in the measured P concentration response in a chemo/hydrograph, determined at the given scale of focus (see Haygarth et al, 2004 for a discussion of how these may be 'measured'). These may be characterised in two theoretical extremes, the first being as spatially heterogeneous high intensity P input (e.g.…”