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The article presents a study on the characterization of phosphorus (P) sources in catchment basins. The importance of P sources identification is said to be crucial in preventing eutrophication that is primarily caused by agriculture-related activities. This study on watersheds analyzed samples of soil, stream, and various storm runoff sites such as field surface runoff and farm yards. The P concentration on streams and the mobilization of dissolved P are estimated using the environmental soil test to determine the potential for sediment and P transfer in runoff from agricultural land (DESPRAL). It concludes that Great Britain's Environmental Agency needs more than the England Catchment Sensitive Farming Delivery Initiative (ECSFDI) program to achieve good water quality in England.

Continuous pH, dissolved oxygen and temperature information for three sites on the upper portion of the River Kennet, a tributary of the Thames in southern England is presented. A thermodynamic model is developed which links this information to weekly water quality data allowing the estimation of dissolved carbon dioxide and calcite saturation levels within the river on a continuous basis. The results show a dynamic and variable system along the length of the river. Marked diurnal patterns are observed for pH, dissolved oxygen, dissolved carbon dioxide and calcite saturation and the highest fluctuations occur during the summer months. There is also a marked gradient downstream in average pH (7.5–8.0) and dissolved carbon dioxide (30–10 times atmospheric pressure). Dissolved oxygen levels average approximately 100% saturation across all sites, and the diurnal pattern occurring during the summer months declines downstream. The waters are permanently oversaturated with respect to calcite and the diurnal patterns of change are maximal during the summer months. The results are discussed in relation to: (a) the balance between photosynthesis and respiratory processes; (b) the relative interchanges between the sediment/plant interface with the water column; and (c) the rates of degassing of carbon dioxide and oxygen between the river surface and the atmosphere. [Copyright &y& Elsevier]

Soluble reactive phosphorus (SRP) concentrations in the River Thames, south east England, have significantly decreased from an annual maximum of 2100 μg l(-1) in 1997 to 344 in 2010, primarily due to the introduction of phosphorus (P) removal at sewage treatment works within the catchment. However, despite this improvement in water quality, phytoplankton biomass in the River Thames has greatly increased in recent years, with peak chlorophyll concentrations increasing from 87 μg l(-1) in the period 1997 to 2002, to 328 μg l(-1) in 2009. A series of within-river flume mesocosm experiments were performed to determine the effect of changing nutrient concentrations and light levels on periphyton biomass accrual. Nutrient enrichment experiments showed that phosphorus, nitrogen and silicon were not limiting or co-limiting periphyton growth in the Thames at the time of the experiment (August-September 2010). Decreasing ambient SRP concentration from 225 μg l(-1) to 173 μg l(-1) had no effect on periphyton biomass accrual rate or diatom assemblage. Phosphorus limitation became apparent at 83 μg SRP l(-1), at which point a 25% reduction in periphyton biomass was observed. Diatom assemblage significantly changed when the SRP concentration was reduced to 30 μg l(-1). Such stringent phosphorus targets are costly and difficult to achieve for the River Thames, due to the high population density and intensive agriculture within the Thames basin. Reducing light levels by shading reduced the periphyton accrual rate by 50%. Providing shading along the River Thames by planting riparian tree cover could be an effective measure to reduce the risk of excessive algal growth. If the ecology of the Thames is to reach the WFD's "good ecological status", then both SRP concentration reductions (probably to below 100 μg l(-1)) and increased shading will be required., (Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.)

Chlorophyll-a and nutrient concentrations were monitored at weekly intervals across 21 river sites throughout the River Thames basin, southern England, between 2009 and 2011. Despite a 90% decrease in soluble reactive phosphorus (SRP) concentration of the lower River Thames since the 1990s, very large phytoplankton blooms still occur. Chlorophyll concentrations were highest in the mid and lower River Thames and the larger tributaries. Lowest chlorophyll concentrations were observed in the smaller tributaries, despite some having very high phosphorus concentrations of over 300 μg l(-1). There was a strong positive correlation between river length and mean chlorophyll concentration (R(2)=0.82), and rivers connected to canals had ca. six times greater chlorophyll concentration than 'natural' rivers with similar phosphorus concentrations, indicating the importance that residence time has on determining phytoplankton biomass. Phosphorus concentration did have some influence, with phosphorus-enriched rivers having much larger phytoplankton blooms than nutrient-poor rivers of a similar length. Water quality improvements may now be capping chlorophyll peaks in the Rivers Thames and Kennet, due to SRP depletion during the spring/early summer phytoplankton bloom period. Dissolved reactive silicon was also depleted to potentially-limiting concentrations for diatom growth in the River Thames during these phytoplankton blooms, but nitrate remained in excess for all rivers throughout the study period. Other potential mitigation measures, such as increasing riparian shading and reducing residence times by removing impoundments may be needed, alongside phosphorus mitigation, to reduce the magnitude of phytoplankton blooms in the future., (Crown Copyright © 2012. Published by Elsevier B.V. All rights reserved.)

Variations in phosphorus (P) concentrations in an agriculturally impacted river draining a Chalk aquifer and an associated canal in the west of the Thames Basin, southern England are examined and linked to agricultural and sewage sources and within river/canal process controls. The study area comprises the River Dun, the adjacent River Kennet and the Kennet and Avon (K&A) Canal. Large seasonal variations are observed for soluble reactive phosphorus (SRP) and dissolved silicon (Si) with low concentrations in the spring and summer times when biological activity is high. The K&A Canal shows the largest SRP and Si concentration declines. This reflects high biological activity coupled with higher temperatures and higher water residence times. The extent of SRP removal is examined in relation to organic (uptake/release with phytoplankton growth/decay) and, to a lesser extent, inorganic (SRP coprecipitation with calcite) mechanisms. Boron (B) is used as a tracer of sewage sources. Agricultural inputs of both dissolved and particulate P (PP) can be important particularly under conditions where the catchment is wet and near surface/overland flow is important: sewage treatment works effluent and septic tank discharges to groundwater also probably provide a major component of the SRP occurring within the water column. The canal, and to a lesser extent the river, acts as sink for P in sewage effluent sources due to the high biological activity especially during the spring and summer. The aquifer probably acts as a major sink for agricultural and septic tank inputs of P.

The water quality of seven sites on the upper reaches of the River Kennet round the market town of Marlborough is described and related to the introduction of phosphorus treatment of effluent from Marlborough sewage treatment works (STW). The River Kennet is mainly groundwater-fed from a Cretaceous chalk aquifer and hence the river water is calcium- and bicarbonate-bearing and has a relatively constant composition of many major water quality determinants. In-stream biological activity gives rise to marked diurnal fluctuations in pH (of approx. 0.8 units). Dissolved carbon dioxide and dissolved oxygen also show marked diurnal fluctuations. Dissolved carbon dioxide varies from approximately 10 to 70 times atmospheric pressure, indicating net release of carbon dioxide and the dominance of heterotrophic (respiratory) processes over autotrophic processes (photosynthesis). Much of the excess carbon dioxide is probably associated with carbon dioxide laden groundwater inputs and the relatively short within-stream residence times ensures only limited degassing to the atmosphere. Diurnal fluctuations in dissolved oxygen vary from approximately 20% to 200% saturation. For both dissolved carbon dioxide and dissolved oxygen, the amplitude of fluctuations is much lower during the winter period, when biological activity is at its lowest. The concentrations of soluble reactive phosphorus (SRP), total phosphorus (TP) and boron increase markedly just downstream of the sewage works as a result of this point source input. These concentrations slowly decline further downstream as additional groundwater inputs dilute the effluent further. The introduction of chemical treatment of sewage effluent for phosphorus reduction at Marlborough STW resulted in a marked decrease in within-river SRP and TP concentrations to levels approximately the same as those upstream of the STW. A comparison of SRP and boron concentrations reveals a reduction in in-stream SRP concentrations by approximately 75% following effluent treatment. In terms of within-river processes controlling in-stream phosphorus concentrations, previous studies have indicated that one potentially important mechanism within calcium bicarbonate bearing rivers may be related to co-precipitation of phosphorus with calcium carbonate (calcite). The present study shows that the waters are oversaturated with respect to calcium carbonate, that no equilibrium conditions exist and that phosphorus removal has led to undetectable changes in calcium carbonate oversaturation. Hence, it is concluded that the primary changes in phosphorus levels within the river is directly associated with changing point source contributions from the STW and physical dilution within the river. However (1) the results relate to only the first year of study and subsequent differences may become apparent and (2) reactions between the water column and plant and bottom sediment interfaces may be important in regulating phosphorus fluxes within the river. The results presented in this paper mark a pilot phase of a longer-term initiative and this paper provides a background setting. The paper discusses the longer-term objectives and important gaps in knowledge of the system that requires further address.