PHOSPHORUS LOADING FROM URBAN STORMWATER RUNOFF AS A FACTOR IN LAKE EUTROPHICATION .1. THEORETICAL CONSIDERATIONS AND QUALITATIVE ASPECTS

A theoretical fractionation of urban runoff phosphorus (P) according to its chemical mobility and potential biological impact is presented and the P fractions feasible for routine analysis established. Urban runoff P from two separate storm sewer systems draining residential areas in the Lake Wingra basin (Madison, Wis.) was characterized in detail. Flow-weighted mean concentrations of dissolved inorganic P [P(i)] for individual runoff events ranged from 0.10 to 2.11 mg P/liter and generally comprized ≥79% of the total dissolved P [P(t)], allowing optimization of routine P characterization by the determination of dissolved P(i) [or dissolved P(t)] and total P. Flow-weighted mean concentrations of total particulate P [P(t)] ranged from 0.14 to 2.37 mg P/liter. However, while the composition of the particulate P(t) at the lower concentration was widely variable, at the higher concentrations particulate P(t) was constituted mainly of organic P [P(o)]. Flow-weighted mean concentrations of dissolved P(i) were more consistently correlated at a significant level with particulate P(t) and particulate P(o) than with particulate P(i). The higher concentrations of dissolved and particulate P were associated with leaf and elm fruit fall, in the fall and spring, respectively, and with longer dry periods immediately before runoff events. A significant proportion (35 to 50%) of the particulate P(t) occurring during the first flush and high flow phases of runoff events would remain suspended in the lake photic zone for several days. The upper limit for potentially available P in urban runoff can be given by dissolved P(i) [or dissolved P(t)] plus 0.25 x particulate P(t), for the watersheds studied.; A theoretical fractionation of urban runoff phosphorus (P) according to its chemical mobility and potential biological impact is presented and the P fractions feasible for routine analysis established. urban runoff P from two separate storm sewer systems draining residential areas in the Lake Wingra basin (Madison, Wis. ) was characterized in detail. Higher concentrations of dissolved and particulate P were associated with leaf and elm fruit fall, in the fall and spring, respectively, and with longer dry periods immediately before runoff events. A significant proportion (35 to 50%) of the particulate total P occurring during the first flush and high flow phases of runoff events would remain suspended in the lake photic zone for several days. An expression is given for calculating the upper limit for potentially available P in urban runoff.