Macrophyte and periphyton dynamics in a UK Cretaceous chalk stream: the River Kennet,a tributary of the Thames

An initial study to observe the seasonal trends and to determine the factors influencing macrophyte and periphyton growth patterns was undertaken on a representative reach of the River Kennet (UK) over a 2-year period (1998–2000). Maximum average macrophyte and average periphyton dry matter biomass recorded during the growing season were 200 and 21 g m⁻², respectively. The relationships between macrophyte and periphyton percentage cover and biomass data with physico-chemical variables were investigated. Regression analysis indicated that of the parameters measured, flow, and in the case of the dominant Ranunculus spp., solar radiation, were best able to predict macrophyte biomass and cover. The periphytic biomass within the reach was low, possibly as a result of relatively high flows and low phosphorus concentrations following the introduction of effluent treatment at the sewage works immediately upstream of the reach. Periphytic biomass was poorly correlated with the physical variables measured. This indicates that biomass is regulated by complex interactions between the physical and chemical factors, such as flow, solar radiation and phosphorus concentration. These interrelationships require further investigation.     

On modelling the impacts of phosphorus stripping at sewage works on in-stream phosphorus and macrophyte/epiphyte dynamics: a case study for the River Kennet

A new model of in-stream phosphorus and macrophyte dynamics, ‘The Kennet model’, was applied to a reach of the River Kennet, southern England. The reach, which is 1.5 km long, is immediately downstream of Marlborough sewage treatment works, where phosphorus reduction by tertiary effluent treatment began in September 1997. The model is used to simulate the flow, water chemistry and macrophyte biomass within the reach, both before and after phosphorus removal from the effluent. Monte Carlo experiments coupled with a general sensitivity analysis indicate that the model offers a feasible explanation for the salient aspects of the system behaviour. Model simulations indicate that epiphyte smothering is an important limitation to macrophyte growth, and that higher stream and pore water soluble reactive phosphorus (SRP) concentrations allow the earlier onset of growth for the epiphytes and macrophytes, respectively. Higher flow conditions are shown to reduce the simulated peak epiphyte biomass; though at present, the effect of flow on the macrophyte biomass is unclear. Another simulation result suggests that phosphorus will not be released from the bed sediments in this reach following phosphorus removal from the effluent.     

Effects of a diesel spill on freshwater macroinvertebrates in two urban watercourses,Wiltshire, UK

The impacts of a spill of approximately 9800 L of diesel on a small stream and the River Ray (near Swindon, Wiltshire, UK) were examined using kick-net sampling of freshwater macroinvertebrate families at impacted and reference sites. Initial impacts (10 days after the spill) 50 m downstream of the spill were severe, with only 9% survival of individuals (excluding oligochaete worms) and 56% survival of invertebrate families. The percentage survival of macroinvertebrates increased progressing downstream from the spill, with no detectable impacts beyond approximately 4 km downstream. The crustacean families Asellidae and Gammaridae were particularly sensitive to the diesel spill. The recovery of the macroinvertebrate community was assessed 13.5 months after the spill. At this time, recovery was almost complete, with only minor impacts at the sites closest to the spill. The use of live laboratory sorting of samples from impacted sites provided essential information on the impacts of the diesel spill.     

Long-term trends in water quality and their impact on macroinvertebrate assemblages in eutrophic lowland rivers

Long-term trends in water quality in eutrophic lowland rivers in eastern England were investigated and their impact on macroinvertebrate assemblages studied. Dissolved oxygen (DO) declined significantly in eight rivers in Essex and Suffolk over 40 years to 1998. Chloride concentrations significantly increased during the same period in most rivers. Total oxidized nitrogen and soluble reactive phosphorus increased until the 1980s, then began to decline. Biotic scores (Lincoln Quality Index) generally increased over 14 years to 1998 and there were significant positive relationships between biotic scores and several nutrients. Invertebrate families and environmental variables sampled over the eight rivers in a dry year (1997) and a wet year (1998) were subjected to multivariate analysis. River stretches were grouped according to substrate requirements of indicator invertebrates. In the dry year, those river stretches behind mills or immediately downstream of sewage treatment works (STW) were grouped. In the wet year, there was only one separate group, comprising sites downstream of STWs. Nutrients, DO and low flows have a much greater influence on water quality, and hence invertebrate assemblages, during drought years than during wet years.     

Heavy metal bioaccumulation and macroinvertebrate community changes in a Mediterranean stream affected by acid mine drainage and an accidental spill (Guadiamar River, SW Spain)

In the 1998 Aznalcóllar mining accident, 5 million cubic meters of toxic waste were spilled into the Guadiamar River (SW Spain). This paper describes the likely effects of metal pollution on the macroinvertebrate community in the first 15 km of the river adjacent to the mine, 2 years after the spill. The contents of Zn, Cu, Pb, As, Cd, Tl, and Sb in water, sediment, and in the caddisfly Hydropsyche were analysed, together with some physico-chemical parameters. From the results of physico-chemical and community parameters, the studied area was divided into three sections: the first section contained upstream control stations, not affected by current mining activities, and with a diverse macroinvertebrate community structure (mean number of families = 19); the second section, close to the mine, was severely polluted, with more than 50 mg l(-1) of Zn or 1.6 mg l(-1) of Cu in water, a pH of nearly 4, and a very diminished macroinvertebrate community (three families); in the last section, 6-15 km downstream from the mine, the water quality improved, metal concentrations decreased, pH reached neutrality and the macroinvertebrate community comprised eight families. We also determined metal concentrations in the larvae of Hydropsyche and found increases of 3- to 35-fold (for Cu and Cd, respectively) compared to control sites. As far as we are aware, these values are the highest concentrations so far detected in this caddisfly anywhere in the world. Different patterns of metal and pH tolerance were identified in macroinvertebrates. Most of the species were intolerant to present pollution levels and were only present in control sites. Others were tolerant to metal pollution but not to low pH and were present in the main river downstream of the mine, while a very few species managed to live in the most polluted section, with very low pH and high metal concentrations.     

Sewage effluent clean-up reduces phosphorus but not phytoplankton in lowland chalk stream (River Kennet, UK) impacted by water mixing from adjacent canal

Information is provided on phosphorus in the River Kennet and the adjacent Kennet and Avon Canal in southern England to assess their interactions and the changes following phosphorus reductions in sewage treatment work (STW) effluent inputs.A step reduction in soluble reactive phosphorus (SRP) concentration within the effluent (5 to 13 fold) was observed from several STWs discharging to the river in the mid-2000s. This translated to over halving of SRP concentrations within the lower Kennet. Lower Kennet SRP concentrations change from being highest under base-flow to highest under storm-flow conditions. This represented a major shift from direct effluent inputs to a within-catchment source dominated system characteristic of the upper part to the catchment. Average SRP concentrations in the lower Kennet reduced over time towards the target for good water quality. Critically, there was no corresponding reduction in chlorophyll-a concentration, the waters remaining eutrophic when set against standards for lakes.Following the up gradient input of the main water and SRP source (Wilton Water), SRP concentrations in the canal reduced down gradient to below detection limits at times near its junction with the Kennet downstream. However, chlorophyll concentrations in the canal were in an order of magnitude higher than in the river. This probably resulted from long water residence times and higher temperatures promoting progressive algal and suspended sediment generations that consumed SRP. The canal acted as a point source for sediment, algae and total phosphorus to the river especially during the summer months when boat traffic disturbed the canal's bottom sediments and the locks were being regularly opened. The short-term dynamics of this transfer was complex. For the canal and the supply source at Wilton Water, conditions remained hypertrophic when set against standards for lakes even when SRP concentrations were extremely low.     

Responses of aquatic organisms to metal pollution in a lowland river in Flanders: a comparison of diatoms and macroinvertebrates

The role of macroinvertebrates and diatoms as indicator for metal pollution was investigated by assessing both biota along a metal gradient in the Belgian river the Dommel. Macroinvertebrates and diatoms were sampled in summer and winter and physical-chemical characteristics of the water were measured at four different sample periods and related to sediment characteristics. Although metal concentrations, except cadmium, in the water nowhere exceeded water quality standards, high metal concentrations were measured in the sediment, indicating historical contamination of the Dommel. At the sites that were situated downstream of the pollution source, high levels of conductivity and chloride were measured in the water. Redundancy Analysis (RDA) indicated pH, phosphate and zinc as the significant environmental variables explaining each respectively 7.7%, 11.6% and 22.6% of the macroinvertebrate community composition. Two clusters could be separated, with Gammarus pulex, Leptocerus interruptus, Baetis rhodani and Cloeon dipterum associated with low zinc concentrations and Tubificidae, Asellus aquaticus, Erpobdella sp. and Chironomus thummi-plumosus associated with higher zinc concentrations. Ammonium (10.6%), conductivity (16.5%), chloride (11.4%) and zinc (5.9%) turned out to be significant variables explaining the diatom community structure. Based on physical-chemical differences and species composition, three different groups could be separated. With this Tabellaria flocculosa and Fragilaria capucina var. rumpens were associated with low metal concentrations, Gomphonema parvulum and Nitzschia palea with elevated concentrations and Eolimna minima and Sellaphora seminulum with high zinc concentrations. In conclusion, the diatom community best reflected the metal gradient. With regard to water quality indices, those based on macroinvertebrates best followed the metal pollution gradient and were most strongly correlated with physical-chemical variables of water and sediment. This study indicated that to assess the effect of metal pollution in lowland rivers, the combined use of macroinvertebrates and diatoms is more appropriate than the use of both biota separately.     

Back-pumping of agricultural runoff into a large shallow lake and concurrent changes in the macroinvertebrate assemblage

Macroinvertebrates were monitored during the summer of 2001 at two paired reference and impact sites, to assess potential effects of agricultural runoff, which was back-pumped upstream into Lake Okeechobee, USA. Monitoring was conducted prior to back-pumping (Pre, April-May), during back-pumping (BP, June-September) and during the following year (Post, April-September, 2002, impact sites only). Prior to back-pumping, the macroinvertebrate communities at both impact sites differed from those at their respective reference sites. During back-pumping, differences in the macroinvertebrate communities were slightly less pronounced among the eastern pair of sites but were more pronounced at the western sites than they were prior to back-pumping. There also were marginal differences in the macroinvertebrate communities at both impact sites between the Pre and BP periods, while very little change was observed in the communities among the same periods at both reference sites. For the Post-Pre and Post-BP period comparisons, there were clear differences between the macroinvertebrate communities at the western impact site, while less pronounced differences were observed at the eastern impact site. This suggests that the Post back-pumping assemblage did not return to that observed prior to back-pumping activity. During BP, several water-quality variables appeared to be different among each of the paired sites and the correlation between water-quality variables and macroinvertebrate community structure was strong at the western sites but weaker at the eastern sites. This suggests that a combination of abiotic variables may have been influencing the community structure at the western sites while back-pumping was occurring. Macroinvertebrates at all sites reflected poor water quality, but more taxonomic changes during back-pumping were observed at the impact sites than at the reference sites. It is not known if these taxonomic changes resulted in impacts among the macroinvertebrate community or to higher-trophic-level predators such as fish. If lake restoration activities result in a shift to a less pollution-tolerant macroinvertebrate community, and the anticipated reduction in future back-pumping activity does not occur, the macroinvertebrate community may return to one that is dominated by pollution-tolerant taxa in affected portions of the lake.     

Effect of dumping and cleaning activities on the aquatic ecosystems of the Guadiamar River following a toxic flood

The main aim of the study was to document the recovery of the aquatic ecosystem after the release of toxic mining waste in the Guadiamar River Basin (Sevilla, SW Spain) in April 1998. Samples of water, plankton, periphyton and macroinvertebrates were taken once a month at nine sampling stations (six affected by the toxic release and three for control). Water hardness and pH recovered in a few weeks and did not change significantly thereafter in the river or in the marsh stations. Only the Agrio River (the tributary that received the initial waste dump) had a low pH (3-5) throughout the study period. High ammonia contents (up to 300 microM) were measured at two sampling stations due to sewage and oil mill pollution. Eutrophication was also common at most of the stations, including one reference site. The planktonic community did not differ substantially between reference and affected stations. On all occasions the small phytoplankton and zooplankton (rotifers) were dominant. Compared with the reference station, chlorophyll a in the riverine area increased, especially in the sewage-affected stations, while in the marsh area, no significant differences were found between affected and reference stations. After 6 months of cleaning operations, in November 1998 the macroinvertebrate community of the river was composed mainly of species of short life cycles typical of ponds (Heteroptera, Coleoptera and Odonata), while typical riverine species found at the upstream control station had not recolonized the river due to the transformation of the river into a series of artificial ponds constructed as sediment traps. An analysis of variance showed significantly higher values (P < 0.05) for all heavy metals analysed (Zn, Cu, Pb, As, Cd, Sb, Tl) in plankton and macroinvertebrate communities from impacted sites. Values found in invertebrates were highly variable, with a mean concentration of the most abundant metals, Zn and Cu, between two and three times those found in unpolluted areas. Values for As were up to five times higher while Pb, Sb and Tl showed up to 10-fold increases. At the affected stations, the metal concentrations found in biofilms, plankton and particulate material were more than five times greater than those in invertebrates. The slow recovery of the aquatic ecosystem clearly reflected the impact of the metal discharge and the subsequent cleaning activities following the mine spill, as well as the sewage inputs at two of the stations studied.     

Assessing land-use effects on water quality, in-stream habitat, riparian ecosystems and biodiversity in Patagonian northwest streams

Changes in land-use practices have affected the integrity and quality of water resources worldwide. In Patagonia there is a strong concern about the ecological status of surface waters because these changes are rapidly occurring in the region. To test the hypothesis that greater intensity of land-use will have negative effects on water quality, stream habitat and biodiversity we assessed benthic macroinvertebrates, riparian/littoral invertebrates, fish and birds from the riparian corridor and environmental variables of 15 rivers (Patagonia) subjected to a gradient of land-use practices (non-managed native forest, managed native forest, pine plantations, pasture, urbanization). A total of 158 macroinvertebrate taxa, 105 riparian/littoral invertebrate taxa, 5 fish species, 34 bird species, and 15 aquatic plant species, were recorded considering all sites. Urban land-use produced the most significant changes in streams including physical features, conductivity, nutrients, habitat condition, riparian quality and invertebrate metrics. Pasture and managed native forest sites appeared in an intermediate situation. The highest values of fish and bird abundance and diversity were observed at disturbed sites; this might be explained by the opportunistic behavior displayed by these communities which let them take advantage of increased trophic resources in these environments. As expected, non-managed native forest sites showed the highest integrity of ecological conditions and also great biodiversity of benthic communities. Macroinvertebrate metrics that reflected good water quality were positively related to forest land cover and negatively related to urban and pasture land cover. However, by offering stream edge areas, pasture sites still supported rich communities of riparian/littoral invertebrates, increasing overall biodiversity. Macroinvertebrates were good indicators of land-use impact and water quality conditions and resulted useful tools to early alert of disturbances in streams. Fish and birds having a greater ability of dispersion and capacity to move quickly from disturbances would reflect changes at a higher scale.     

An integrated modelling and multicriteria analysis approach to managing nitrate diffuse pollution: 2. A case study for a chalk catchment in England

The site-specific land use optimisation methodology, suggested by the authors in the first part of this two-part paper, has been applied to the River Kennet catchment at Marlborough, Wiltshire, UK, for a case study. The Marlborough catchment (143 km(2)) is an agriculture-dominated rural area over a deep chalk aquifer that is vulnerable to nitrate pollution from agricultural diffuse sources. For evaluation purposes, the catchment was discretised into a network of 1 kmx1 km grid cells. For each of the arable-land grid cells, seven land use alternatives (four arable-land alternatives and three grassland alternatives) were evaluated for their environmental and economic potential. For environmental evaluation, nitrate leaching rates of land use alternatives were estimated using SHETRAN simulations and groundwater pollution potential was evaluated using the DRASTIC index. For economic evaluation, economic gross margins were estimated using a simple agronomic model based on nitrogen response functions and agricultural land classification grades. In order to see whether the site-specific optimisation is efficient at the catchment scale, land use optimisation was carried out for four optimisation schemes (i.e. using four sets of criterion weights). Consequently, four land use scenarios were generated and the site-specifically optimised land use scenario was evaluated as the best compromise solution between long term nitrate pollution and agronomy at the catchment scale.     

Habitat quality–physicochemical water quality–littoral macroinvertebrate community nexus in Lugo Lake (Ethiopia): Priorities for sustainable water resources management

The integration of water quality characteristics with habplot-based habitat quality assessment score (HabQA) has received little attention in ecological quality assessment studies. This study investigated the macroinvertebrate community structure in relation with lake habitat quality and physicochemical water quality variables in Lugo Lake (Ethiopia). Twelve sampling sites (eight agricultural and four recreational) were included. The variation among macroinvertebrates data was significantly explained by HabQA score and soluble reactive phosphorus. The study revealed the greater importance of habitat quality characteristics in comparison with the other conventional physicochemical characteristics on macroinvertebrate community structure. We strongly recommend the use of HabQA system while studying macroinvertebrate community structure for a deeper understanding of the environmental functioning of tropical lakes. The results suggested the need to apply integrated and sustainable protection and management of the lake catchment (including wetlands) to enhance the ecological integrity and hence biodiversity of lakes.     

Long term variation in water colour from Yorkshire catchments.

Water colour is a problem in the upland water-gathering grounds of the UK. It has shown considerable variation over recent years and this needs to be put into the longer-term context. In order to do this, factors to convert water colour measured in absorbance units per metre (Au/m) to Hazen units are presented for ten sites in the Yorkshire region using data from August 1997 to June 1998. The conversion factors are site-specific and there is some evidence that they may show seasonal variation. There is also a short-term upward trend in the conversion factor for a number of catchments, which may be related to their recovery following the 1995 drought. Time series of water colour in Hazen from 1980 to 1998 are shown for selected sites. The seasonal variation in colour levels is disrupted at all sites during and following drought periods, notably 1990-1992 and 1995-1998 and, in the case of two sites with long-term colour measurements, the 1975-1976 drought. These periods are followed by enhanced levels of colour and, since the end of the 1995 drought, unprecedented high values have been recorded at some catchments.     

Eutrophication downstream from small reservoirs in mountain rivers of Central Spain

In this research we examined the hypothesis that upper reaches of rivers and streams can experience eutrophication as a consequence of deep releases from dams. Field studies were conducted in four mountain rivers (Tormes, Riaza, Eresma and Miraflores Rivers) of Central Spain. The watersheds of these rivers are underlain by siliceous rocks. A small deep-release storage reservoir is found in the upper reaches of each river. Two sampling sites, upstream and downstream from the reservoir, were established in stony riffles of each impounded river. Significant (P < 0.01) increases in conductivity and nutrient (NO3-N, NH4-N, PO4-P) concentrations downstream from the reservoirs were measured. Significant (P < 0.01) increases in periphyton chlorophyll a and ash-free dry biomass were also quantified at downstream sites. Significant (P < 0.01) correlation coefficients indicated that phosphate would play a more important role as the limiting nutrient for periphyton. Relative abundances of macroinvertebrate scrapers and collector-gatherers increased downstream from the reservoirs. Furthermore, taxon dominance, total density and total biomass of macroinvertebrates tended to be higher at downstream sites than at upstream sites. In contrast, taxon diversity and relative abundance of macroinvertebrate shredders decreased downstream from the reservoirs. It is concluded that small deep-release storage reservoirs, located in upper reaches of siliceous rivers, can act as nutrient sources, causing eutrophication downstream. Nutrients would ultimately come from land/forest runoff. The fact that terrestrial vegetation was not completely removed before filling reservoirs could also contribute to the eutrophication process.     

Factors Governing Macrophyte Status in Hampshire Chalk Streams: Implications for Catchment Management

Severe droughts in the late 1980s and 1990s have highlighted the fragility of many aquatic environments in southern England; in particular, declining river flows may be having an adverse affect on macrophytes in the chalk-fed streams of the Rivers Test and Itchen. Detailed macrophyte survey data which were collected from representative sites in both rivers during 1991–1995 are interpreted in the context of changing hydroclimatic, water quality and in-stream channel conditions. Multivariate statistical analyses support the assertion that river flow is the most significant parameter governing observed changes in macrophyte cover. During low flow years, filamentous algae have increased at most sites to the detriment of Ranunculus spp. These findings have catchment-management implications which should be addressed if the long-term integrity of such aquatic ecosystems is to be safeguarded.     

An experimental investigation of subsurface ground temperature in Texas: a complete study

This paper describes the results of experimental studies conducted in Houston, Texas from June 1997 to May 1998 to determine seasonal variations of subsurface ground temperature. The results indicate that the average ambient temperature is 89.31°F (31.84°C) in summer (June–October), and 63.93°F (17.74°C) in winter (November–February). The ground temperature at depths greater than 10 feet remains relatively constant through the year. At a depth of 10 feet (3.04 m), the average ground temperature is 75.12°F (23.96°C) in summer and 75.87°F (24.37°C) in winter. The observed temperature differential between the ambient and the ground temperature at 10 feet is 8–17°F (4.4–9.4°C). The temperature differential suggests that there is potential for pre-heating and pre-cooling the ambient air used in conditioning commercial and institutional buildings. The least square fit equations to project average monthly subsurface ground temperatures are presented.     

Spatial heterogeneity and air pollution removal by an urban forest

Estimates of air pollution removal by the urban forest have mostly been based on mean values of forest structure variables for an entire city. However, the urban forest is not uniformly distributed across a city because of biophysical and social factors. Consequently, air pollution removal function by urban vegetation should vary because of this spatial heterogeneity. This paper presents a different approach to evaluate how the spatial heterogeneity of the urban forest influences air pollution removal at the socioeconomic subregion scale. Air pollution removal for July 1997 to June 1998 and July 2000 to June 2001 were estimated using measured urban forest structure data from three socioeconomic subregions in Santiago, Chile. Dry deposition was estimated using hourly climate, mixing height, and pollutant concentration data. Pollution removal rates among the three socioeconomic subregions were different because of heterogeneous urban forest structure and pollution concentrations. Air pollution removal per square meter of tree cover was greatest in the low socioeconomic subregion. Pollution removal during 1997–1998 was different from 2000 to 2001 due to pollution concentration differences. Seasonal air quality improvement also differed among the subregions. Results can be used to design management alternatives at finer administrative scales such as districts and neighborhoods that maximize the pollution removal rates by the urban forest in a subregion. Policies that affect the functionality of urban forest structure must consider spatial heterogeneity and scale when making region-wide recommendations. Similarly, when modeling the functionality of the urban forest, models must capture this spatial heterogeneity for inter-city comparisons.     

Implementation of artificial neural networks (ANNs) to analysis of inter-taxa communities of benthic microorganisms and macroinvertebrates in a polluted stream

This study was performed to gain an understanding of the structural and functional relationships between inter-taxa communities (macroinvertebrates as consumers, and microbes as decomposers or preys for the invertebrates) in a polluted stream using artificial neural networks techniques. Sediment samples, carrying microorganisms (eubacteria) and macroinvertebrates, were seasonally collected from similar habitats in streams with different levels of pollution. Microbial community taxa and densities were determined using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and 16S rDNA sequence analysis techniques. The identity and density of macroinvertebrates were concurrently determined. In general, differences were observed on grouping by self-organizing map (SOM) in polluted, clean and recovering sites based on the microbial densities, while the community patterns were partly dependent on the sampling period. A Spearman rank order correlation analysis revealed correlations of several eubacterial species with those of macroinvertebrates: a negative correlation was observed between Acidovorax sp. (from polluted sites) and Gammaridae (mostly from the clean site), while Herbaspirillum sp. and Janthinobacterium sp. appeared to have positive correlations with some macroinvertebrate species. The population dynamics of the tolerant texa, Tubificidae and Chironomidae, appeared to be related with changes in the densities of Acidovorax sp. This study revealed community relationships between macroinvertebrates and microorganisms, reflecting the connectivity between the two communities via the food chain. A further physio-ecological and symbiological study on the invertebrate-microorganism relationships will be required to understand the degradation and utilization of detritus in aquatic ecosystems as well as to elucidate the roles of the inter-taxa in the recovery of polluted aquatic environments.     

Establishing hydroecological relationships to manage the impacts of groundwater abstraction

Despite the pressing environmental, economic and social issues surrounding water abstraction, scientific methods for managing its ecological impacts remain in their infancy. In this paper, we demonstrate statistically significant relationships between in‐stream ecological condition using macroinvertebrates and the hydrological effect of groundwater abstraction on surface water flows in streams originating from Permo‐Triassic sandstone aquifers in the English midlands. Ecological condition was most strongly correlated to the effect of abstraction on medium‐low flows (Q₇₅) compared with effects at other flows, water quality, habitat or seasonal effects. Ecological impacts occurred when the effect of abstraction on Q₇₅ flows exceeded 60%. The same relationships were shown among individual macroinvertebrate taxa, validating the biological responses. The hydroecological model has provided a scientific basis for making local decisions on investigation sites and has helped to focus resources to areas at risk of not meeting Good Ecological Status under the Water Framework Directive because of abstraction.     

Physico-chemical controls on phosphorus cycling in two lowland streams. Part 1 -- the water column

This paper investigates phosphorus (P) transport and transformation dynamics in two contrasting sub-catchments of the River Kennet, England. Samples were collected daily under baseflow and hourly under stormflow conditions using autosamplers for 2 years and analysed for a range of determinands (full P fractionation, suspended sediment (SS), cations, pH, alkalinity, temperature and oxygen). Concentrations of SRP, SUP, PP and SS were higher in the flashy River Enborne (means of 0.186, 0.071, 0.101 and 34 mg l(-1), respectively) than the groundwater-fed River Lambourn (0.079, 0.057, 0.028 and 9 mg l(-1), respectively). A seasonal trend in the daily P dataset was evident, with lower concentrations during intermediate flows and the spring (caused by a dilution effect and macrophyte uptake) than during baseflow conditions. However, in the hourly P dataset, highest concentrations were observed during storm events in the autumn and winter (reflecting higher scour with increased capacity to entrain particles). Storm events were more significant in contributing to the total P load in the River Enborne than the River Lambourn, especially during August to October, when dry antecedent conditions were observed in the catchment. Re-suspension of P-rich sediment that accumulated within the channel during summer low flows might account for these observations. It is suggested that a P-calcite co-precipitation mechanism was operating during summer in the River Lambourn, while adsorption by metal oxyhydroxide groups was an important mechanism controlling P fractionation in the River Enborne. The influence of flow conditions and channel storage/release mechanisms on P dynamics in these two lowland rivers is assessed.