Helen P. Jarvie

Delivery and cycling of phosphorus in rivers: A review

Phosphorus (P) supply (concentration and flux) is an important driver for biological activity in flowing waters and needs to be managed to avoid eutrophication impacts associated with urbanisation and agricultural intensification. This paper examines the role of in-stream retention and cycling in regulating river P concentrations in order to better understand the links between P sources and their ecological impacts. In terms of their composition (solubility and concentration), patterns of delivery (mode and timing) and therefore ecological relevance, P sources entering rivers are best grouped into wastewater discharges > runoff from impervious surfaces (roads, farmyards) > runoff from pervious surfaces (forestry, cultivated land and pasture). The localized impacts of soluble P discharges during ecologically sensitive periods can be distinguished from the downstream impacts associated with particulate P discharges under high flows due to the different processes by which these sources are retained, transformed and assimilated within the river channel. The range of physico-chemical processes involved in P cycling and the variable importance of these processes in different river environments according to stream size, stream geomorphology and anthropogenic pressures are summarised. It is concluded that the capacity to retain (process) P within the river channel, and hence regulate the downstream delivery of P without stressing the aquatic communities present, is considerable, especially in headwaters. To help achieve good water quality, there is scope to better manage this ecosystem service through regulation of P supply whilst optimising in-stream P retention according to subsidy-stress theory. Further research is needed to develop in-stream management options for maximising P subsidies and to demonstrate that regulation of downstream P delivery will reduce the incidence of eutrophication in connected waterbodies.

Phosphorus legacy: overcoming the effects of past management practices to mitigate future water quality impairment

The water quality response to implementation of conservation measures across watersheds has been slower and smaller than expected. This has led many to question the efficacy of these measures and to call for stricter land and nutrient management strategies. In many cases, this limited response has been due to the legacies of past management activities, where sinks and stores of P along the land-freshwater continuum mask the effects of reductions in edge-of-field losses of P. Accounting for legacy P along this continuum is important to correctly apportion sources and to develop successful watershed remediation. In this study, we examined the drivers of legacy P at the watershed scale, specifically in relation to the physical cascades and biogeochemical spirals of P along the continuum from soils to rivers and lakes and via surface and subsurface flow pathways. Terrestrial P legacies encompass prior nutrient and land management activities that have built up soil P to levels that exceed crop requirements and modified the connectivity between terrestrial P sources and fluvial transport. River and lake P legacies encompass a range of processes that control retention and remobilization of P, and these are linked to water and sediment residence times. We provide case studies that highlight the major processes and varying timescales across which legacy P continues to contribute P to receiving waters and undermine restoration efforts, and we discuss how these P legacies could be managed in future conservation programs.

Major ion concentrations and the inorganic carbon chemistry of the Humber rivers

Measurements of major ion concentrations in the main rivers draining into the Humber estuary show two dominant spatial patterns, related to anthropogenic sources from catchments draining urban/industrial areas and background weathering sources from the rural catchments. Most major ions exhibit dilution effects with flow, with higher concentrations at baseflow compared with stormflow conditions. This suggests a predominance of point (effluent) and/or groundwater (weathering) sources of major ions. An exception is NO3−, which exhibits higher concentrations under stormflow conditions in certain rural catchments, suggesting diffuse (catchment) sources, possibly derived from agricultural runoff. Inter-ion relationships were used for endmember mixing analysis to identify whether or not components were exhibiting conservative behaviour within the river. The dominant relationship between major ions is a straight line between baseflow and stormflow endmembers, indicative of conservative mixing processes. The chemical mixing patterns appear to be controlled by hydrology and the existence of distinct inter-ion ratios between baseflow and stormflow endmembers. In terms of the inorganic carbon system, HCO3− is the major component of dissolved inorganic carbon (DIC), with dissolved CO2 (H2CO30 and CO2(aq)) representing approximately 10% and CO32− less than 1% of DIC. All river waters are oversaturated with respect to CO2, with excess partial pressures of carbon dioxide (EpCO2) typically between 5 and 20 times atmospheric partial pressure. The elevated levels of EpCO2 in the river water are sufficient to decouple the relationship between pH and alkalinity. EpCO2 is related to microbial production of CO2 by breakdown of organic carbon and the availability of nutrients (particularly NO3−) and is generally highest in the rivers draining urban and industrial catchments, together with the Derwent which receives high rates of agricultural runoff. EpCO2 and pH do not exhibit simple mixing relationships and both determinands are inherently non-conservative in behaviour. These results provide important background information on which to base more detailed process studies and modelling work. The results imply that most of the major ions can be modelled using simple mixing relationships. In contrast the non-conservative behaviour of EpCO2 and pH may require more thorough process evaluation for modelling the in-stream carbon system.

The British river of the future: How climate change and human activity might affect two contrasting river ecosystems in England

The possible effects of changing climate on a southern and a north-eastern English river (the Thames and the Yorkshire Ouse, respectively) were examined in relation to water and ecological quality throughout the food web. The CLASSIC hydrological model, driven by output from the Hadley Centre climate model (HadCM3), based on IPCC low and high CO(2) emission scenarios for 2080 were used as the basis for the analysis. Compared to current conditions, the CLASSIC model predicted lower flows for both rivers, in all seasons except winter. Such an outcome would lead to longer residence times (by up to a month in the Thames), with nutrient, organic and biological contaminant concentrations elevated by 70-100% pro-rata, assuming sewage treatment effectiveness remains unchanged. Greater opportunities for phytoplankton growth will arise, and this may be significant in the Thames. Warmer winters and milder springs will favour riverine birds and increase the recruitment of many coarse fish species. However, warm, slow-flowing, shallower water would increase the incidence of fish diseases. These changing conditions would make southern UK rivers in general a less favourable habitat for some species of fish, such as the Atlantic salmon (Salmo salar). Accidental or deliberate, introductions of alien macrophytes and fish may change the range of species in the rivers. In some areas, it is possible that a concurrence of different pressures may give rise to the temporary loss of ecosystem services, such as providing acceptable quality water for humans and industry. An increasing demand for water in southern England due to an expanding population, a possibly reduced flow due to climate change, together with the Water Framework Directive obligation to maintain water quality, will put extreme pressure on river ecosystems, such as the Thames.

Trace element inter-relationships for the Humber rivers: inferences for hydrological and chemical controls

Abstract Data on a wide range of trace elements, determined by multi-element procedures based on inductively coupled plasma emission and mass spectrometry, are presented for the major rivers entering the Humber estuary. The average trace element chemistry varies significantly across the region with a clear divide between the southern and northern rivers. This pattern is related to lead-zinc-barium mineralisation and flood plain sediment contamination from historic mining activity, and to historic and current industry and urbanisation to the south. For the industrial/urban rivers, most dissolved components dilute with flow; this pattern is most clearly seen for those components with little acid available particulate (AAP) fractions. In the rural/mineralised areas, dissolved components show more variable flow patterns. AAP fractions and dissolved components with significant associated AAP fractions usually increase with flow in all rivers. The different trace elements show multi-linear relationships with one another. These are much tighter than the links between dissolved and AAP components of the same element. Two main groups of closely associated elements emerge, but these groups are different on northern and southern rivers. The first group corresponds to elements which dilute with flow and this group includes significantly more trace elements to the south where industrial and urban inputs dominate. For this group, within-river chemical processes do not seem to be operative as linear relationships with each of the trace elements of the group and chloride are observed: chloride is chemically conserved within river systems and is predominantly found in the point source effluent discharges. The second group corresponds to those determinands which increase with increasing flow for both dissolved and AAP fractions and they have a high AAP fraction: relationships show much more scatter for this group. Links between dissolved and particulate fractions for this second group are weak and are not well described by empirical partition coefficient relationships which are commonly used in environmental modelling studies. Rather, AAP fractions are much more closely linked with suspended solid concentrations than the dissolved component. The reasons for the contrasting behaviour between the two groups probably reflects the inability of 0.45 μm filtration (47 mm diameter cellulose nitrate Whatman sterile filters in this case) to remove all colloidal sized materials. Thus, for this second group, at high flows, when suspended sediments are at their highest, there is the greatest potential for acid available enrich micro-particulates to pass through the filters. This features provides a fundamental schism for environmental research for this second and wide ranging group: process based water suspended-sediment interaction modelling requires a clear separation between truly dissolved and truly particulate fractions; water industry based environmental sampling and management strategies, as well as legislative water consent controls, are based on a 0.45 μM separation. The results point to the importance of contributing sources and hydrological controls in determining dissolved and AAP concentrations in the Humber rivers. The role of within-river chemical controls is much less clear-cut and may well be of second order importance.

Phosphorus sources, speciation and dynamics in the lowland eutrophic River Kennet, UK.

This paper examines the behaviour of phosphorus (P) in a lowland chalk (Cretaceous-age) stream, the upper River Kennet in southern England, which has been subject to P remediation by tertiary treatment at the major sewage treatment works in the area. The effects of treatment are examined in relation to boron, a conservative tracer of sewage effluent and in terms of the relative contributions of soluble reactive phosphorus (SRP) loads from point and diffuse sources, and in-stream SRP loads. These results indicate a baseline reduction in in-stream SRP concentrations immediately following P-treatment of approximately 72%. Subsequent high flows result in a greater contribution of diffuse inputs and increases in SRP levels relative to the initial post-treatment period. The dynamics of SRP and particulate phosphorus (PP) are examined under a wide range of river flow conditions. Given the flashy nature of near-surface runoff in the River Kennet, sub-weekly (daily automated) sampling was used to examine the dynamics in SRP and PP concentrations in response to storm events. Simple empirical models linking weekly SRP concentrations with flow were developed. The empirical models were successfully applied to the daily data, to partition TP measurements and provide an estimate of daily SRP and PP concentrations. Mass balance studies were used to examine net gains and losses along the experimental river reach and indicate large net losses (up to 60%) during the extreme low flows and high SRP concentrations prior to P-treatment, which may be linked to extensive epiphytic growth. Phosphorus dynamics and response to P-treatment are discussed in relation to hydrological controls in permeable chalk catchments and wider implications for eutrophication management are examined.

Water Quality Remediation Faces Unprecedented Challenges from “Legacy Phosphorus”

“Legacy Phosphorus” Helen P. Jarvie,†,* Andrew N. Sharpley,‡ Bryan Spears, Anthony R. Buda, Linda May, and Peter J. A. Kleinman †Centre for Ecology and Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, U.K. ‡Department of Crop, Soil and Environmental Sciences, Division of Agriculture, University of Arkansas, Fayetteville, Arkansas, United States Centre for Ecology and Hydrology, Bush Estate, Penicuik, Midlothian, U.K. Agricultural Research Service, Pasture Systems and Watershed Management Research Unit, U.S. Department of Agriculture, University Park, Pennsylvania, United States

Modelling of phosphorus inputs to rivers from diffuse and point sources.

The difference in timing of point and diffuse phosphorus (P) delivery to a river produces clear differences in the P concentration-flow relationship. Point inputs decrease in concentration with increasing river flow, due to dilution of a relatively constant input, whereas diffuse (non-point) load usually increases with river flow. This study developed a simple model, based on this fundamental difference, which allowed point and diffuse inputs to be quantified by modelling their contribution to river P concentration as a power-law function of flow. The relationships between total phosphorus (TP) concentration and river flow were investigated for three contrasting UK river catchments; the Swale (Yorkshire), the Frome (Dorset) and the Avon (Warwickshire). A load apportionment model was fitted to this empirical data to give estimates of point and diffuse load inputs at each monitoring site, at high temporal resolution. The model produced TP source apportionments that were similar to those derived from an export coefficient approach. For many diffuse-dominated sites within this study (with up to 75% of the annual TP load derived from diffuse sources), the model showed that reductions of point inputs would be most effective in order to reduce eutrophication risk, due to point source dominance during the plant and algae growing period. This modelling approach should provide simple, robust and rapid TP source apportionment from most concentration-flow datasets. It does not require GIS, information on land use, catchment size, population or livestock density, and could provide a valuable and versatile tool to catchment managers for determining suitable river mitigation options.

The geography of the Humber catchment

Abstract The geography of the Humber catchment is described in relation to the varied geology, relief, resources, industrial structure and location, agriculture and population distribution. The review of catchment characteristics is set within an historical perpective, with an evaluation of current and possible future trends in agriculture, population, industry and possible implications for river water quality.

The LOIS river monitoring network: strategy and implementation

Abstract The large-scale, highly integrated, multidisciplinary nature of the LOIS rivers programme mean that certain measurements were common to many LOIS research projects (including water discharge, suspended sediment concentrations, pH, conductivity) or depended upon routine weekly or flood-related sampling (eg. for nutrients, metals and organics). This paper describes the underlying strategy which led to the design of the major observational programme in LOIS rivers and provides information on siting of sample points, field sampling methods, instrumentation and associated chemical analyses. There was a need for field measurements to reflect the full range of river flows and to identify critical points for measurement of flux from, and within, the large-scale study river basins. Tests of manual sampling runs against the time series of river flows indicate good representation of both low to moderate flows and extreme flood events in the LOIS rivers field data. Field and analytical methods for sampling the wide range of chemical determinands (major and minor elements, trace metals, nutrients, inorganic and organic carbon and micro-organic pollutants) are outlined. The first LOIS chemical harmonisation assessment, designed to investigate the comparability and accuracy of the chemical and analytical techniques used by the LOIS community is also reported.