Effect of watershed parameters on mercury distribution in different environmental compartments in the Mobile Alabama River Basin, USA

Total mercury (THg) and mono-methylmercury (MeHg) levels in water, sediment, and largemouth bass (LMB) (Micropterus salmoides) were investigated at 52 sites draining contrasting land use/land cover and habitat types within the Mobile Alabama River Basin (MARB). Aqueous THg was positively associated with iron-rich suspended particles and highest in catchments impacted by agriculture. Sediment THg was positively associated with sediment organic mater and iron content, with the highest levels observed in smaller catchments influenced by wetlands, followed by those impacted by agriculture or mixed forest, agriculture, and wetlands. The lowest sediment THg levels were observed in main river channels, except for reaches impacted by coal mining. Sediment MeHg levels were a positive function of sediment THg and organic matter and aqueous nutrient levels. The highest levels occurred in agricultural catchments and those impacted by elevated sulfate levels associated with coal mining. Aqueous MeHg concentrations in main river channels were as high as those in smaller catchments impacted by agriculture or wetlands, suggesting these areas were sources to rivers. Elevated Hg levels in some LMB were observed across all types of land use and land cover, but factors such as shallow water depth, larger wetland catchment surface area, low aqueous potassium levels, and higher Chl a concentrations were associated with higher Hg burdens, particularly in the Coastal Plain province. It is suggested that the observed large variability in LMB Hg burdens is linked to fish displacement by anglers, differences in food web structure, and sediment biogeochemistry, with surficial sediment iron oxides buffering the flux of MeHg from sediments to deeper water pelagic food webs.     

Retrieval of suspended particulate matter concentrations in the Danube River from Landsat ETM data

Alternations in river channel morphology result in a disturbed natural transport of suspended particulate matter (SPM). Suspended particulate matter serves as a transport medium for various pollutants, e.g. heavy metals. It is therefore important to understand how artificial obstructions alter the natural transport of suspended matter. Measurements of SPM in rivers are traditionally carried out during in situ sampling campaigns, which can provide only a limited view of the actual spatial distribution of suspended matter over large distances. Several authors have studied how space-borne remote sensing could be used for mapping of water quality in standing waters, but with only little attention paid to rivers. This paper describes the methodology how a Landsat ETM image was used to map the spatial patterns of SPM in the Slovak portion of the Danube River. Results of our investigation reveal that the Danube River in Slovakia exhibits gradual longitudinal decrease in concentrations of SPM. Based on a strong relationship between the Landsat near-infrared band (TM4) and field measurements, we developed a map of suspended particulate matter in the Danube River with a standard error (SE) of 2.92 mg/L. This study aims to show how archived satellite data and historical water quality data can be used for monitoring of SPM in large rivers. A methodology describing the minimum samples required for sufficiently accurate results is discussed in this paper also.     

Spatial and historical variation in sediment phosphorus fractions and mobility in a shallow lake

Temporal and spatial variation in sediment P composition and mobility were investigated in Loch Leven. Little change was observed in total sediment P (surface sediment at 4m depth), in comparison to a previous study (1990), despite significant reduction of external point sources of P. Labile P and residual P have both increased (0.007-0.039 mg PO(4)-P and 0.121-0.420 mg PO(4)-P per gram dry weight of sediment, respectively) since 1990. An analysis of P fractions, along a depth transect, indicated elevated labile P concentrations in shallow water sediment (<12 m overlying water depth). Regression analysis showed that spatial variability in reductant-adsorbed P was significantly related to sediment chlorophyll a concentration (R(2)=0.733, p<0.05). This may be linked to the production of oxygen, by benthic algae, resulting in the maintenance of an oxygenated layer at the sediment surface. Variation in labile P was best explained by overlying water temperature and equilibrium phosphate concentration (EPC0).     

The phosphorus content of fluvial sediment in rural and industrialized river basins

The phosphorus content of fluvial sediment (suspended sediment and the < 63 microm fraction of floodplain and channel bed sediment) has been examined in contrasting rural (moorland and agricultural) and industrialized catchments in Yorkshire, UK. The River Swale drains a rural catchment with no major urban and industrial areas, and the total phosphorus (TP) content of fluvial sediment is generally within the range 500-1,500 microg g(-1). There is little evidence of any major downstream increase in TP content. In contrast, fluvial sediment from the industrialized catchments of the Rivers Aire and Calder exhibits both higher levels of TP content and marked downstream increases, with values of TP content ranging from < 2,000 microg g(-1) in headwater areas upstream of the main urban and industrial areas, to values > 7,000 microg g(-1) at downstream sites. These elevated levels reflect P inputs from point sources, such as sewage treatment works (STWs) and combined sewer overflows. The influence of STWs is further demonstrated by the downstream increase in the inorganic P/organic P ratio from < 2 in the headwaters to > 4 in the lower reaches. Comparison of the P content of suspended sediment with that of the <63 microm fraction of potential source materials suggests that topsoil from upland moorland/pasture and from cultivated areas, and channel bank material are likely to be the main sources of particulate P (PP) in the River Swale and in the headwaters of the Rivers Aire and Calder. In the middle and lower reaches of the Rivers Aire and Calder, inputs associated with urban and industrial land uses, such as STWs, industrial effluents and street dust, are likely to represent the dominant sources of PP. During high flow events, such urban inputs may be diluted by inputs from moorland and agricultural land in the headwaters. Consequently, for all three rivers, there are inverse relationships between the TP content of suspended sediment and both discharge and suspended sediment concentration, reflecting changes in sediment and P sources during high flow events. Spatial variations in the P contents of the < 63 microm fraction of overbank floodplain deposits and channel bed sediment evidence a similar pattern as those for suspended sediment, with relatively low levels of TP in the River Swale and elevated levels in the middle and downstream reaches of the Rivers Aire and Calder. The PP concentrations associated with floodplain and channel bed sediment are, however, lower than equivalent values for suspended sediment, and this primarily reflects the differences in the particle size composition between the three types of sediments. Rates of floodplain deposition and the amounts of fine-grained sediment stored in the river channels are relatively high, and suggest that such environments may represent important sinks for PP. Based on the sediment samples collected from the study basins, a simple four-fold classification which relates the TP content of suspended sediment to upstream land use has been established. Both the range and the absolute values of TP content tend to increase with an increase in the level of urbanization and industrialization.     

Faecal indicator organism concentrations and catchment export coefficients in the UK

Characterisation of faecal indicator organism (FIO) concentrations and export coefficients for catchments with particular combinations of land use and under specific climatic regimes is critical in developing models to predict daily loads and apportion sources of the microbial parameters used to regulate water quality. Accordingly, this paper presents a synthesis of FIO concentration and export coefficient data for the summer bathing season, with some comparative winter data, for 205 river/stream sampling points widely distributed across mainland UK. In terms of both geometric mean (GM) FIO concentrations and export coefficients (expressed as cfu km(-2) h(-1)), the results reveal (1) statistically significant elevations at high flow compared with base flow, with concentrations typically increasing by more than an order of magnitude and export coefficients by about two orders; (2) significantly higher values in summer than in winter under high-flow conditions; and (3) extremely wide variability between the catchments (e.g. four orders of magnitude range for GM faecal coliform concentrations), which closely reflects land use-with urban areas and improved pastures identified as key FIO sources. Generally, these two most polluting land uses are concentrated in lowland areas where runoff (m3 km(-2) h(-1)) is low compared with upland areas, which in the UK are dominated by rough grazing and forestry. Consequently, contrasts in export coefficients between land use types are less than for FIO concentrations. The GMs reported for most land use categories are based on 13 sites and exhibit quite narrow confidence intervals. They may therefore be applied with some confidence to other catchments in the UK and similar geographical regions elsewhere. Examples are presented to illustrate how the results can be used to estimate daily summer base- and high-flow FIO loads for catchments with different land use types, and to assess the likely effectiveness of certain strategies for reducing FIO pollutant loadings in areas with extensive areas of lowland improved pasture.     

Land management as a factor controlling dissolved organic carbon release from upland peat soils 2: Changes in DOC productivity over four decades

Increasing DOC concentrations in surface waters have been observed across parts of Europe and North America over the past few decades. Most proposed explanations for these widespread trends invoke climate change or reductions in sulphate deposition. However, these factors do not seem apposite to explain either the fine-scale (within kilometres) or regional-scale spatial variation in DOC concentrations observed across the UK.We have reconstructed DOC concentrations and land use for one North Pennine and five South Pennine catchments (UK), located in three discrete areas, over the last four decades. Rainfall, temperature and sulphate deposition data, where available, were also collated and the potential influence of these factors on surface water DOC concentrations was assessed.Four of the six catchments examined showed highly significant (p < 0.001) increases (53-92%) in humic coloured DOC (hDOC) concentrations in drainage waters over the period 1990-2005. Changes in temperature and sulphate deposition may explain 20-30% of this trend in these four catchments. However, the rapid expansion of new moorland burn on blanket peat can explain a far greater degree (> 80%) of the change in hDOC. Far smaller increases in hDOC (10-18%) were identified for the two remaining catchments. These two sites experienced similar changes in sulphur deposition and temperature to those that had seen largest increases in DOC, but contained little or no moorland burn management on blanket peat.This study shows that regional-scale factors undoubtedly underlie some of the recent observed increases in drainage humic coloured DOC. However, changes in land management, in this case the extensive use of fire management on blanket peat, are a far more important driver of increased hDOC release from upland catchments in some parts of the UK. It suggests that the recent rapid increase in the use of burning on blanket peat moorland has implications for ecosystem services and carbon budgets.     

Developing environment-specific water quality guidelines for suspended particulate matter

It is generally well recognised that suspended particulate matter (SPM), from nano-scale particles to sand-sized sediments, can cause serious degradation of aquatic ecosystems. However, at present there is a poor understanding of the SPM conditions that water quality managers should aim to achieve in contrasting environments in order to support good ecological status. In this article, we analyse long-term SPM data collected from a wide range of reference-condition temperate environments in the UK (638 stream/river sites comprising 42 different ecosystem-types). One-way analysis of variance reveals that there is a statistically significant difference (p < 0.001) between the background SPM concentrations observed in contrasting ecosystems that are in reference condition (minimal anthropogenic disturbance). One of the 42 ecosystems studied had mean background concentrations of SPM in excess of the current European Union (EU) water quality guideline, despite being in reference condition. The implications of this finding are that the EU’s current blanket water quality guideline (25 mg L⁻¹ for all environments) is inappropriate for this specific ecosystem-type which will be non-compliant with the guideline regardless of the intensity of land-use. The other 41 ecosystems studied had mean concentrations below the current EU water quality guideline. However, this does not necessarily mean that the guideline is appropriate for these ecosystems, as previous research has demonstrated that detrimental impacts can be experienced by some freshwater organisms, of all trophic levels, when exposed to concentrations below 25 mg L⁻¹. Therefore, it is suggested here that it is likely that some ecosystems, particularly those with mean concentrations in the 0.00-5.99 mg L⁻¹ range, require much lower guideline values in order to be effectively protected. We propose a model for predicting environment-specific water quality guidelines for SPM. In order to develop this model, the 638 reference condition sites were first classified into one of five mean background SPM ranges (0.00-5.99, 6.00-11.99, 12.00-17.99, 18.00-23.99 and >24.00 mg L⁻¹). Stepwise Multiple Discriminant Analysis (MDA) of these ranges showed that a site’s SPM range can be predicted as a function of: mean annual air temperature, mean annual precipitation, mean altitude of upstream catchment, distance from source, slope to source, channel width and depth, the percentage of catchment area comprised of clay, chalk, and hard rock solid geology, and the percentage of the catchment area comprised of blown sand as the surface (drift) material. The MDA technique, with cross-validation (Wilks-Lambda 0.358, p 0.000), can predict the correct or the next closest SPM range of a site in 90% of cases. This technique can also predict SPM range membership in a probabilistic manner, allowing for an estimate of uncertainty to be made in the allocation of a site to an environment-specific SPM range.     

Faecal-indicator concentrations in waters draining lowland pastoral catchments in the UK: relationships with land use and farming practices

Faecal-indicator budget studies have shown marine bathing water quality at two small UK coastal resorts, Staithes and Newport, to be adversely affected by riverine inputs from lowland pastoral catchments (J. Chartered Inst. Water Environ. Mangt. 12 (1998) 414). The present paper reports on presumptive coliform (PC), presumptive Escherichia coli (PE) and presumptive streptococci (PS) concentrations at 43 sampling points on watercourses within these catchments, and on their relationship with land use and livestock-related management practices, such as grazing and slurry/manure applications. The results show > 10-fold elevations in geometric mean faecal-indicator concentrations under high-flow conditions, compared with low flow, with maximum high-flow geometric mean PC, PE and PS concentrations of 2.6 x 10(6), 1.8 x 10(6) and 4.4 x 10(5) cfu/100 ml, respectively. High-flow geometric mean concentrations exhibit highly significant positive correlations with land use/management variables associated with intensive livestock farming, both within the individual catchments and in the two combined. Additional factors, such as antecedent weather conditions and topography, contribute to inter-catchment variability in water quality. Although inputs from diffuse and point sources of pollution were not quantified, point sources (e.g. runoff from farm yards) seem likely to be significant. The findings suggest that it may be possible to develop generic statistical models to predict microbial water quality from land use and farm management data. They also provide indirect evidence that channel bed sediment 'stores' closely reflect land use within their catchments and that there is little die-off of organisms along watercourses.     

Bioremediation efficiency in the removal of dissolved inorganic nutrients by the red seaweed, Porphyra yezoensis, cultivated in the open sea

The bioremediation capability and efficiency of large-scale Porphyra cultivation in the removal of inorganic nitrogen and phosphorus from open sea area were studied. The study took place in 2002-2004, in a 300 ha nori farm along the Lusi coast, Qidong County, Jiangsu Province, China, where the valuable rhodophyte seaweed Porphyra yezoensis has been extensively cultivated. Nutrient concentrations were significantly reduced by the seaweed cultivation. During the non-cultivation period of P. yezoensis, the concentrations of NH4-N, NO2-N, NO3-N and PO4-P were 43-61, 1-3, 33-44 and 1-3 micromol L(-1), respectively. Within the Porphyra cultivation area, the average nutrient concentrations during the Porphyra cultivation season were 20.5, 1.1, 27.9 and 0.96 micromol L(-1) for NH4-N, NO2-N, NO3-N and PO4-P, respectively, significantly lower than in the non-cultivation season (p<0.05). Compared with the control area, Porphyra farming resulted in the reduction of NH4-N, NO2-N, NO3-N and PO4-P by 50-94%, 42-91%, 21-38% and 42-67%, respectively. Nitrogen and phosphorus contents in dry Porphyra thalli harvested from the Lusi coast averaged 6.3% and 1.0%, respectively. There were significant monthly variations in tissue nitrogen content (p<0.05) but not in tissue phosphorus content (p>0.05). The highest tissue nitrogen content, 7.65% in dry wt, was found in December and the lowest value, 4.85%, in dry wt, in April. The annual biomass production of P. yezoensis was about 800 kg dry wt ha(-1) at the Lusi Coast in 2003-2004. An average of 14708.5 kg of tissue nitrogen and 2373.5 kg of tissue phosphorus in P. yezoensis biomass were harvested annually from 300 ha of cultivation from Lusi coastal water. These results indicated that Porphyra efficiently removed excess nutrient from nearshore eutrophic coastal areas. Therefore, large-scale cultivation of P. yezoensis could alleviate eutrophication in coastal waters economically.     

Hydrological controls on nutrient concentrations and fluxes in agricultural catchments

Like many streams draining intensively farmed parts of lowland Scotland, water quality in the Newmills burn, Aberdeenshire, is characterized by relatively high nutrient levels; mean concentrations of NO3-N and NH3-N are 6.09 mg l(-1) and 0.28 mg l(-1), respectively, whilst average PO4-P concentrations reach 0.06 mg l(-1). Nutrient concentrations vary spatially and temporally with levels being highest under arable farming during the autumn and winter. Annual fluxes from the 14.5 km2 catchment are estimated at 25.67 and 1.26 kg ha(-1) a(-1) for NO3-N and NH3-N, respectively, and 0.26 kg ha(-1) a(-1) for PO4-P. Hydrological controls exert a strong influence on both nutrient concentrations and fluxes. Over short timescales nutrient concentrations and fluxes are greatest during storm events when P04-P and NH3-N are mobilized by overland flow in riparian areas, particularly where the soils have been compacted by livestock or farm machinery. Delivery of deeper soil water in subsurface storm flow, facilitated by agricultural under-drainage, provide large contributions of NO3-N on the recession limb of hydrological events. In contrast, groundwater inputs generally have lower NO3 concentrations implying that denitrification may be a pathway of N loss in the saturated zone. Approximately 75% of the N loss for the catchment occurs during the autumn and early winter when high flows dominate the hydrological regime. The close coupling of hydrological pathways and biogeochemical processes has major implications for catchment management strategies such as Nitrate Vulnerable Zones (NVZs) as it is likely that significant groundwater stores with long residence times will continue to cause N losses before water quality improvements become apparent.     

Evaluation of iron-phosphate as a source of internal lake phosphorus loadings

Biological, physical and chemical characteristics of the water column of a shallow (Zmax = 9.2 m), small (surface area 3.8 km2) residential and recreational lake near Prince George, British Columbia, indicated that the system was being loaded internally with phosphorus (P) from the sediments. The abundance of P released from the fine glaciolacustrine, and organic rich sediments was resulting in excess algal and weed growth. It was postulated that iron-phosphate reduction at redox potentials below approximately 200 mV and/or bacterially mediated orthophosphate (PO4-P) releases could be occurring. The development of an appropriate nutrient management strategy required that the process associated with the sediment P release be determined. The MINTEQA2 geochemical model was used to predict the release of orthophosphate (PO4-P) into the interstitial water with the assumption that P is present alternately as strengite, variscite and hydroxyapatite. The predicted release of PO4-P from these P containing minerals was compared to the concentration of PO4-P and total phosphorus (TP) in the overlying hypolimnion. In order to improve the accuracy of the model prediction, the proportion of the sediment present as iron-bound phosphate was estimated. A significant correlation between the observed hypolimnetic TP and interstitial PO4-P concentrations as predicted from iron-bound P dissolution (r2 = 0.59) was found. Total phosphorus release rates to the hypolimnion were also found to be strongly correlated to the iron-bound P component of the sediment (r2 = 0.88). Multivariate regression analyses showed significant relationships between hypolimnetic PO4-P and sediment iron-bound P, Eh, and interstitial Fe (r2 = 0.76). These results provided sufficient evidence to conclude that PO4-P in the system is predominantly bound to Fe-containing minerals and therefore could be managed using treatment techniques that address iron-bound phosphates.     

Characterisation of urban catchment suspended particulate matter (Auckland region, New Zealand); a comparison with non-urban SPM

Suspended particulate matter (SPM) is an important transport agent for metal contaminants in streams, particularly during high flow periods such as storm events. For highly contaminated urban catchments in the greater Auckland (New Zealand) area, trace metal partitioning between the dissolved phase and SPM was determined, and SPM characterised in terms of its Si, Al, Fe, Mn, Zn, Cu, Pb, TOC, TON and PO(4) concentrations, as well as particle size, abundance, type and surface area. This data was compared to similar data from representative non-urban catchments in the Auckland region, the Kaipara River and Waikato River catchments, to identify any significant differences in the SPM and its potential trace metal adsorption capacity. Trace metal partitioning was assessed by way of a distribution coefficient: K(D)=[Me(SPM)]/[Me(DISS)]. Auckland urban SPM comprises quartz, feldspars and clay minerals, with Fe-oxides and minor Mn-oxides. No particles of anthropogenic origin, other than glass shards, were observed. No change in urban SPM particle size or SSA was observed with seasonal change in temperature, but the nature of the SPM was observed to change with flow regime. The abundance of finer particles, SSA and Al content of the SPM increased under moderate flow conditions; however, Si/Al ratios remained constant, confirming the importance of aluminosilicate detrital minerals in surface run-off. The SPM Fe content was observed to decrease with increased flow and was attributed to dilution of SPM Fe-oxide of groundwater origin. The Kaipara River SPM was found to be mineralogically, chemically and biologically similar to the urban SPM. However, major differences between urban catchment SPM and SPM from the much larger (non-urban) Waikato River were observed, and attributed to a higher abundance of diatoms. The Fe content of the Waikato River SPM was consistently lower (<5%), and the Si/Al ratio and Mn content was higher. Such differences observed between urban and non-urban SPM did not appear to affect the partitioning of Zn and Cu; however, Pb in the Kaipara and Waikato Rivers was found to be more associated with the dissolved phase. This is likely to reflect higher particulate Pb inputs to urban systems.     

Riparian zone influence on stream water chemistry at different spatial scales: a GIS-based modelling approach, an example for the Dee, NE Scotland

A geographical information system (GIS-ARC/INFO) was used to collate existing spatial data sets on catchment characteristics to predict stream water quality using simple empirical models. The study, based on the river Dee catchment in NE Scotland, found that geological maps and associated geochemical information provided a suitable framework for predicting chemical parameters associated with acidification sensitivity (including alkalinity and base cation concentrations). In particular, it was found that in relatively undisturbed catchments, the parent material and geochemistry of the riparian zone, when combined with a simple hydrological flow path model, could be used to accurately predict stream water chemistry at a range of flows (Q95 to > Q5) and spatial scales (1-1000 km2). This probably reflects the importance of the riparian zone as an area where hydrological inputs to stream systems occur via flow paths in the soil and groundwater zones. Thus, evolution of drainage water chemistry appears to retain the geochemical characteristics of the riparian area as it enters the channel network. In more intensively managed catchments, riparian land use is a further influential factor, which can be incorporated into models to improve predictions for certain base cations. The utility in providing simple hydrochemical models, based on readily available data sets, to assist environmental managers in planning land use in catchment systems is discussed.     

Modelling sediment-microbial dynamics in the South Nation River, Ontario, Canada: Towards the prediction of aquatic and human health risk

Runoff from agricultural watersheds can carry a number of agricultural pollutants and pathogens; often associated with the sediment fraction. Deposition of this sediment can impact water quality and the ecology of the river, and the re-suspension of such sediment can become sources of contamination for reaches downstream. In this paper a modelling framework to predict sediment and associated microbial erosion, transport and deposition is proposed for the South Nation River, Ontario, Canada. The modelling framework is based on empirical relationships (deposition and re-suspension fluxes), derived from laboratory experiments in a rotating circular flume using sediment collected from the river bed. The bed shear stress governing the deposition and re-suspension processes in the stream was predicted using a one dimensional mobile boundary flow model called MOBED. Counts of live bacteria associated with the suspended and bed sediments were used in conjunction with measured suspended sediment concentration at an upstream section to allow for the estimation of sediment associated microbial erosion, transport and deposition within the modelled river reach. Results suggest that the South Nation River is dominated by deposition periods with erosion only occurring at flows above approximately 250 m³ s⁻¹ (above this threshold, all sediment (suspended and eroded) with associated bacteria are transported through the modelled reach). As microbes are often associated with sediments, and can survive for extended periods of time, the river bed is shown to be a possible source of pathogenic organisms for erosion and transport downstream during large storm events. It is clear that, shear levels, bacteria concentrations and suspended sediment are interrelated requiring that these parameters be studied together in order to understand aquatic microbial dynamics. It is important that any management strategies and operational assessments for the protection of human and aquatic health incorporate the sediment compartments (suspended and bed sediment) and the energy dynamics within the system in order to better predict the concentration of indicator organism.     

Factors influencing development of management strategies for the Abou Ali River in Lebanon II: seasonal and annual variation

The water quality of a river at any point reflects several major influences including but are not limited to climatic conditions and anthropogenic inputs. Assessing these influences is essential for managing land and water resources within a particular river catchment. The objectives of this study were to identify the causes of increasing or decreasing trends in the concentrations of various water quality parameters in the Abou Ali River in North Lebanon and to account for the consequential variations both annual and seasonal (low/high flow). The assessment was conducted at the end of the dry season in October 2002 and 2003 and the end of the wet season in March 2003 and 2004. Results established that dissolved oxygen levels were consistently higher at the end of the wet season. The concentrations of biochemical oxygen demand, ammonia nitrogen and ortho-phosphates did not exhibit a clear seasonal or annual variation. While the levels of total dissolved solids and nitrate nitrogen exhibited a decreasing trend in urban catchments, an increasing trend was observed in rural, agricultural and forested areas. The findings of this study reinforce the notion that management of point and non-point sources should be integrated as the combination of both sources connected with land use results in deleterious effects on water quality. The lack of good quality water hinders economic development and the potential for long term sustainability.     

River flow and associated transport of sediments and solutes through a highly urbanised catchment, Bradford, West Yorkshire

The hydrological characteristics of catchments become drastically modified in response to urbanisation. The total contributions and dynamics of runoff, suspended sediment and solutes may change significantly and have important implications downstream where they may affect flooding, instream ecological habitat, water quality and siltation of river channels and lakes. Although an appreciation of the likely hydrological changes is crucial for effective catchment management they are still poorly understood. In this paper we present data from a network of river monitoring stations throughout the heavily urbanised Bradford catchment, West Yorkshire. Sites are upstream, within and downstream of the highly urbanised central part of the catchment. Flow, turbidity (calibrated to suspended sediment concentration) and specific conductance (surrogate for solute concentration), logged at 15-min intervals, are presented for a 12-month period (June 2000 to June 2001). The total amounts and dynamics of flow, solute and suspended sediment transport were investigated. Estimated total flow and suspended sediment transport for the monitoring period were found to be high in response to the high total rainfall. Flow and sediment transport regimes were extremely 'flashy' throughout the catchment and became increasingly flashy in a downstream direction. Suspended sediment discharged from the Bradford subcatchment makes an important contribution to downstream sediment transport on the river Aire at Beal. Data suggest that the urbanised part of the Bradford catchment is extremely important in contributing solutes to the Beck (river). Although flow and sediment are also contributed to the Bradford Beck in the urbanised part of the catchment the data suggest that significant amounts may enter the combined sewer system and bypass the river. Understanding the spatial and temporal variations of flow and the transport of suspended sediment and solutes in rivers in urbanized subcatchments is crucial to their effective management and monitoring. Furthermore, this knowledge may be extremely important to the management and monitoring of downstream rivers in large scale mixed catchments.     

Particulate phosphorus bioavailability as a function of stream flow and land cover

Using total phosphorus concentrations to estimate eutrophication risk is problematic for management purposes, as only some forms of phosphorus are biologically available for phytoplankton growth. This study estimated the bioavailability of particulate phosphorus, in forested, urban, agricultural (i.e. dairy farm) and mixed land cover streams. Sixteen stream sites were sampled during base and storm flow conditions and the following parameters were determined: total suspended solids, total phosphorus, total dissolved phosphorus, particulate phosphorus, percent bioavailable particulate phosphorus (%BAPP), total bioavailable phosphorus and sediment particle size distribution. Algal assays with Pseudokirchneriella subcapitata were used to measure %BAPP. Percent BAPP averaged 17%, 26% and 24% for streams draining catchments with forested, mixed use and agricultural land cover, respectively, and %BAPP did not vary significantly between base and storm flow conditions in these stream types. In contrast, %BAPP averaged 73% in the urban streams during baseflows but declined to an average of only 19% during storms. Particle size distributions did not correlate with %BAPP in these samples. During storm events, particulate phosphorus concentrations increased in all streams by an average of 614% and total phosphorus increased by 200%, whereas total BAP (i.e. total dissolved phosphorus+%BAPP x particulate phosphorus) only increased by 72% because on average only 20% of the particulate phosphorus transported during these events was biologically available.     

pH对剩余污泥中氮、磷释放的影响

将pH分别控制在不同条件下(3.0、5.0、8.0、10.0和不调节),并测定各条件下剩余污泥溶出的NH4+-N和PO34--P浓度,考察了剩余污泥在水解酸化过程中pH对NH4+-N、PO43--P释放的影响。结果表明:对剩余污泥的pH进行调节,能够提高氨氮、正磷酸盐的释放量,且酸性环境下的NH4+-N和PO43--P释放量明显高于中性和碱性环境下的释放量。     

Phosphorus purification in a paddy field watershed using a circular irrigation system and the role of iron compounds

In a paddy field watershed using a circular irrigation system, it was clear that the watershed tended to purify phosphorus by an analysis on the mass balance of pollutants. A reasonable hypothesis was that the phosphorus precipitation with iron compounds in a river may affect the purification. To verify this, an investigation on phosphorus and iron in the river water and sediments were conducted. Total iron (T-Fe) concentration in the river ranged from 3 to 10 mg/L, and the concentration increased with the river flowing down, whereas dissolved iron (D-Fe) concentrations tended to decrease. The concentrations of total phosphorus (T-P) and phosphate phosphorus (PO4-P) also tended to decrease as the river flowing down. From the analysis of mass balance, the study watershed was considered to be a substantial iron source, having 307 and 206 kg/ha of annual outflow loads. In the sediment of the river, T-P ranged from 834 to 2440 microg/g, and most of the inorganic compound was Fe-P. In addition, The Bray No.2 phosphorus (441-1030 microg/g) was much higher than in paddy soils. Therefore, the sediment contained a large amount of phosphorus and was fertile. From the results of laboratory-based experiments, it can be said that iron compounds in the river were sufficient for the precipitation of phosphorus. Since the accumulated sediment in the river was conventionally dredged up and transported to adjacent paddy fields, it was considered to be that this operation played a significant role in phosphorus resource recycling.     

A comparison of nutrient sources and behaviour in two lowland subcatchments of the River Wye

Seasonal changes in concentrations and mass flow of dissolved silicon, orthophosphate and inorganic nitrogen were studied during 1978 in two lowland catchments of the R. Wye, the Frome and the Trothy, which are of similar drainage area but are subjected to different land use. In addition more intensive investigation of water quality changes were undertaken during storm events.Seasonal patterns of silicon concentrations were similar in the two rivers with major depletions in May and annual losses to diatoms were estimated to be equivalent to 5–12% of annual mass flow. Peak concentrations of orthophosphate were generally recorded during periods of low river flow in both rivers but concentrations were substantially greater in the Frome (mean, 0.42 mg l⁻¹) than the Trothy (mean, 0.19 mg l⁻¹), reflecting differences in population density. The principal form of inorganic nitrogen in both catchments was nitrate, but mean concentrations were considerably greater in the Frome (mean NO₃-N. 4.99 mg l⁻¹) than in the Trothy (mean NO₃-N. 2.93 mg l⁻¹) and seasonal variations were markedly different. Concentrations in the Frome increased during the summer months (maximum, 7 mg l⁻¹ whilst concentrations in the Trothy decreased during this period and this was reflected in positive and negative relationships between concentration and river flow respectively. Such differences in behaviour cannot be attributed to contributions from sewage and it is suggested that they may reflect differences in the proportion of groundwater contributing to river flow during the summer period and the nitrate content of that groundwater.Intensive sampling during storm events indicated that, overall, orthophosphate concentrations decreased and silicon and nitrate concentrations increased with increased flow, but there was considerable variation in solute behaviour during different events.