Notes: Abstract. The interactions of P with soils and sediments are examined in the context of transport processes from land, through rivers to estuaries and coastal waters. In soil erosion, selective size fractionation and preferential sorption to finer solids is crucial in the transport of P to water courses. Problems in quantifying the sorption affinity and equilibrium phosphate concentration (EPC) of mixtures of different soils and sediments are identified. Riverine transport of P by suspended solids is usually very important and examples of the changes in the amount and composition of particulate P (PP) concentration during storm events are discussed. Increased P content of solids during the first autumn storms, probably reflect the resuspension of accumulated stream bed-deposits. The fate of P in estuaries and their importance as possible long-term sinks of P are discussed. The relatively high concentrations of dissolved P associated with riverine inputs are to some extent buffered by the relatively high concentrations of suspended sediments resulting from tidal flows. Phosphorus may be released during transport to the sea due to decreases in the EPC, increases in salinity and release from bottom sediments as a result of low oxygen conditions.

Notes: SUMMARY. 1. An examination has been made of the water quality of a 50 km (Wigan to Litherland) length of the Leeds-Liverpool canal. Regular in situ measurements accompanied by sampling for laboratory analysis were made at seventeen stations over a 15-month period.2. Three principal contributory water types have been recognized, and the observations have allowed estimates to be made of their relative contributions to the total water flux in the lower reaches of the system. Linear flow rates (c. 0.6 km day−1 near Litherland) are consistent with previous reports.3. The combined field and laboratory measurements have been used to obtain estimates of the partial pressure of CO2 in the water (P co2), the degree of saturation of the water with respect to calcite (Ω) and the major ion speciation in the water. Because of the variable ionic compositions of the waters examined, these estimates were made using a program (WATEQ) which took account of ion-pairing.4. Diurnal and annual cycles with respect to pH, P co2 and ω occur, these being most marked in the lower parts of the study length when, for a large proportion of the spring and summer, P co2 was below the atmospheric level and noticeable supersaturation with respect to calcite occurred. In contrast, two of the contributory water types, the River Douglas input and the Creek, showed low pH and Ω values and high P co2 values throughout the year.

Notes: 1. The objectives of the present work were: (a) to evaluate the effects of the development and the presence of a photosynthetically active algal biofilm on chemical fluxes and processes at the sediment–water interface; (b) to measure the effects of the biofilm on chemical concentration gradients in the bulk sediment; and (c) to monitor pH and dissolved oxygen concentration in the biofilm, and through the sediment–water interface using microelectrodes.2. Two experiments were performed over a period of 8 weeks using a recirculating fluvarium channel containing river sediments with an exposed surface of 0.2 m2 and 20 dm3 of overlying solution. The first experiment was in darkness with minimal effects of a photosynthetically active biofilm. The second experiment in natural light produced a complex photosynthetic biofilm involving a succession of diatoms, green algae and cyanobacteria.3. The solution overlying the biofilm was monitored continuously for dissolved calcium, silicon, phosphorus, alkalinity and oxygen, as well as conductivity, temperature and pH. The surface of the sediment was also monitored for biological and physical changes as the biofilm developed. The overlying solution was analysed over a period of 48 h at 2-h intervals to examine the effects of a well-developed algal biofilm. At the end of the 48 h, pH and oxygen microelectrodes were used to measure gradients above and through the biofilm, and porewaters were analysed from sediments which had been longitudinally sectioned at a maximum depth resolution of 0.5 mm.4. Biofilm development had a large influence on the composition of the overlying solution and the development of vertical concentration gradients of solutes in the porewater. Once a diatom community was established, the concentration of dissolved silicon was low (〈 40 μm), with all the silicon diffusing from the underlying sediment being consumed in the biofilm (≈ 0.026 μmol m−2 s−1 at the end of the experiment).5. The concentrations of calcium, alkalinity and phosphorus in digested sediment increased near the sediment–water interface. X-ray diffraction analysis showed that calcite was formed at the surface. Estimation of the fluxes of alkalinity and calcium in the overlying solution were consistent with calcite formation during daylight and possible dissolution in darkness. The maximum precipitation flux of calcium was 0.87 μmol m−2 s−1 and the maximum net release flux was 0.89 μmol m−2 s−1.6. The net loss of soluble reactive phosphorus from the overlying solution measured over the intensive sampling period of 48 h is consistent with a coprecipitation mechanism and a surface density of phosphorus included in the lattice of calcite of 0.097 μmol m−2. Processes in the biofilm rather than diffusion from the sediment porewater control chemical fluxes of calcium, alkalinity and phosphorus from the sediment to the overlying water.