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.     

Effect of ditching operations on stream-water chemistry in a boreal forested catchment.

The effects of ditching of boreal forest land on stream-water quality and quantity was assessed by comparing, over a 4-year-period, the physicochemical properties of the water in two small streams (western Finland), one whose catchment was ditched for forestry halfway through the sampling period and another nearby (control) stream whose catchment was not ditched ('paired catchment method'). While the artificial drainage did not have any significant effect on the hydrograph, it resulted in an increase in the aquatic concentrations of Mn, Ca, Mg, suspended material and alkalinity, a decrease in the concentrations of TOC and H3O+, while for Al and Fe there was a change in control mechanisms. The concentration and control changes after ditching are related to changes in hydrological pathways and to the exposure of both organic (peat) and inorganic (mineral soil) layers on the ditch slopes.     

Use of continuous water quality records for hydrograph separation and to assess short-term variability and extremes in acidity and dissolved carbon dioxide for the River Dee, Scotland

A combination of continuous (15-min) pH, conductivity and temperature measurements and fortnightly spot-sampled water quality data were used to examine temporal variability and extremes in river water quality in an upland Scottish river: the River Dee at Mar Lodge. An empirical relationship was established for Gran-alkalinity by multiple regression against flow and conductivity for the fortnightly data. Applying this relationship to the continuous data, an estimate of continuous Gran-alkalinity was calculated. The continuous Gran-alkalinity record was used as (1) a conservative tracer in a simple two-component mixing model to determine the relative proportions of near-surface runoff and deeper groundwater contributing to stream flow; (2) to deconvolute the contribution of weathering and sea-salt contributions to stream conductivity; and (3) to calculate the excess partial pressure of carbon dioxide in stream water. The episodic variations in pH, weathering and sea-salt conductivity and excess partial pressures of carbon dioxide (EpCO2) associated with high flow events in the River Dee suggest that hydrological pathways play an important role in determining stream chemistry. The results of the hydrograph separation indicate that groundwater provides an important contribution to stream flow, and that there are large and hydrologically active stores of groundwater within the upper River Dee catchment. Sea-salts have an important influence on stream conductivity, particularly with the onset of storm runoff following summer drought periods. This suggests that sea-salts are concentrated in the upper soil horizons by dry deposition and/or evapotranspiration. EpCO2 behaves non-conservatively and shows marked diurnal variability under low-flow conditions during summer, inducing diurnal pH variations, and indicating the importance of within-river biological processes. This study emphasises the very intermittent nature of water quality extremes with stream spates and the diurnal nature of biologically-induced responses. Fortnightly sampling programmes do not capture the range of high flow extremes, and with sampling undertaken during the working day, biological extremes occurring at night are also missed, introducing bias. This study shows the value of continuous measurements for infilling aspects of these intermittent extremes. However, it is also noted that the relatively simple patterns of response observed from the continuous measurements may well belie a much more varied response at the sub-catchment and hillslope scales, as local chemical and hydrological heterogeneities do occur. Thus, the two-component mixing model used is, in practice, based on catchment integrated values for a range of soil water and groundwater endmembers.     

Modelling bacterial water quality in streams draining pastoral land

A model has been developed to predict concentrations of the faecal bacteria indicator E. coli in streams draining grazed hill-country in New Zealand. The long-term aim of the modelling is to assess effects of land management upon faecal contamination and, in the short term, to provide a framework for field-based research. A daily record of grazing livestock is used to estimate E. coli inputs to a catchment, and transport of bacteria to the stream network is simulated within surface and subsurface flows. Deposition of E. coli directly to streams is incorporated where cattle have access to them, and areas of permanent saturation ('seepage zones') are also represented. Bacteria are routed down the stream network and in-stream processes of deposition and entrainment are simulated. Die-off, both on land and in water, is simulated as a function of temperature and solar radiation. The model broadly reproduces observed E. coli concentrations in a hill-country catchment grazed by sheep and beef cattle, although uncertainty exists with a number of the processes represented. The model is sensitive to the distance over which surface runoff delivers bacteria to a stream and the amount of excretion direct to streams and onto seepage zones. Scenario analysis suggests that riparian buffer strips may improve bacterial water quality both by eliminating livestock defaecation in and near streams, and by trapping of bacteria by the riparian vegetation.     

Can sediment data be used to predict alkalinity and base cation chemistry of surface waters?

We hypothesise that stream sediment elemental composition can predict mean and minimum concentrations of alkalinity, Ca and Mg in the river water throughout a river network. We tested this hypothesis for the River Derwent catchment in North Yorkshire, England, by using 6 years of water chemistry data from the Environment Agency and a digital elevation model to flow path-weight British Geological Survey (BGS) sediment element concentration data. The predictive models for mean concentrations were excellent for Ca and alkalinity, but less good for Mg, and did not require land use data inputs as stream water sediment composition seems to reflect all aspects of the riparian zone soil system. Predictive model forms were linear. Attempts to predict minimum values for Ca and alkalinity also were less satisfactory. This probably is due to variations in hydrological response times to individual precipitation events across the catchment.     

Survival dynamics of fecal bacteria in ponds in agricultural watersheds of the Piedmont and Coastal Plain of Georgia

Animal agriculture in watersheds produces manure bacteria that may contaminate surface waters and put public health at risk. We measured fecal indicator bacteria (commensal Escherichia coli and fecal enterococci) and manure pathogens (Salmonella and E. coli 0157:H7), and physical-chemical parameters in pond inflow, within pond, pond outflow, and pond sediments in three ponds in agricultural watersheds. Bishop Pond with perennial inflow and outflow is located in the Piedmont, and Ponds A and C with ephemeral inflow and outflow in the Coastal Plain of Georgia. Bromide and chloride tracer experiments at Bishop Pond reflected a residence time much greater than that estimated by two models, and indicated that complete mixing within Bishop Pond was never obtained. The long residence time meant that fecal bacteria were exposed to solar UV-radiation and microbial predation. At Bishop Pond outflow concentrations of fecal indicator bacteria were significantly less than inflow concentrations; such was not observed at Ponds A and C. Both Salmonella and E. coli 0157:H7 were measured when concomitant concentrations of commensal E. coli were below the criterion for surface water impairment indicating problems with the effectiveness of indicator organisms. Bishop Pond improved down stream water quality; whereas, Ponds A and C with ephemeral inflow and outflow and possibly greater nutrient concentrations within the two ponds appeared to be less effective in improving down stream water quality.     

Effects of land use change on hydrological cycle from forest to upland field in a catchment,Japan

Understanding the effects of land use change on the hydrological cycle is very important for development of sustainable water resource in an upland field catchment. In this study, soil and hydrological properties in an upland field catchment, which was reclaimed partially from a forest catchment, were compared with another forest catchment. The soil properties of surface and subsurface layers were investigated in the two catchments. The soil was compacted and water-holding capacity of soil in the upland field catchment became smaller after the reclamation from forest to upland field, which decreased infiltration rate and water storage in the soil layers. We found that peak discharge and direct runoff in the upland field catchment increased compared with the forest catchment. Annual evapotranspiration from the upland field catchment tended to be lower due to the change in vegetation type and soil properties. Furthermore, a semi-distributed hydrological model was applied in the upland field catchment to understand the integrated effects of reclamation on the hydrological cycle. The model parameters, which were determined using a nonlinear optimization technique—the Shuffled Complex Evolution method (SCE), were compared between the two catchments. The Nash and Sutcliffe coefficient was used to evaluate the model performance. The simulated results indicated that evapotranspiration was decreased and change in discharge was more obvious in the surface layer. We considered that declined infiltration and water storage and increased peak discharge and direct runoff have a negative impact on water resources in the upland field catchment. This study will provide information for forest managers in planning and making decisions for land and water resource management.     

A model for predicting chloride concentrations in river water in a relatively unpolluted catchment in north-east Scotland

The River Dee is an oligotrophic soft water system, in the NE of Scotland, with a catchment area of approximately 2100 km2. The river rises in the Cairngorm Mountains and enters the North Sea at Aberdeen, approximately 140 km from its source. Water chemical quality data was collected every 2 weeks over 12 months for 59 sites distributed throughout the catchment. River water chloride concentrations increased significantly from west to east. In depth investigation of the relationship with distance from the coast revealed the significant difference in spatial distribution of river water chloride concentrations between upland and lowland/agricultural areas, suggesting the possible importance of agricultural practices to streamwater chloride concentrations. Thirty of the sample sites are independent and have been used to develop a simple model for prediction of streamwater Cl- concentration throughout the catchment. The model has been validated using data from the remaining sub-catchments. The model shows that mean Cl- concentration may be reliably predicted from distance from the coast and the percentage of improved grassland and arable land cover in each sub-catchment (r2 = 0.98). It is postulated that the land use effects may be partly due to the evolved link between landuse and catchment altitude characteristics, rather than just the direct effect of applied potassium chloride fertiliser on agricultural land. It was noted that there was insufficient forestry within the River Dee Catchment to reliably include % forest cover in the model.     

Linking land-use type and stream water quality using spatial data of fecal indicator bacteria and heavy metals in the Yeongsan river basin

This study reveals land-use factors that explain stream water quality during wet and dry weather conditions in a large river basin using two different linear models-multiple linear regression (MLR) models and constrained least squares (CLS) models. Six land-use types and three topographical parameters (size, slope, and permeability) of the watershed were incorporated into the models as explanatory variables. The suggested models were then demonstrated using a digitized elevation map in conjunction with the land-use and the measured concentration data for Escherichia coli (EC), Enterococci bacteria (ENT), and six heavy metal species collected monthly during 2007–2008 at 50 monitoring sites in the Yeongsan Watershed, Korea. The results showed that the MLR models can be a powerful tool for predicting the average concentrations of pollutants in stream water (the Nash-Sutcliffe (NS) model efficiency coefficients ranged from 0.67 to 0.95). On the other hand, the CLS models, with moderately good prediction performance (the NS coefficients ranged 0.28–0.85), were more suitable for quantifying contributions of respective land-uses to the stream water quality. The CLS models suggested that industrial and urban land-uses are major contributors to the stream concentrations of EC and ENT, whereas agricultural, industrial, and mining areas were significant sources of many heavy metal species. In addition, the slope, size, and permeability of the watershed were found to be important factors determining the extent of the contribution from each land-use type to the stream water quality. The models proposed in this paper can be considered useful tools for developing land cover guidelines and for prioritizing locations for implementing management practices to maintain stream water quality standard in a large river basin.     

Hydrology and the ecological quality of Scottish river ecosystems

Hydrology is a primary control on the ecological quality of river systems, through its influence on flow, channel geomorphology, water quality and habitat availability. Scottish rivers are widely perceived to be of high ecological quality, with abundant flow volumes and high water quality. However, historical and current river flow regulations, and land use change have altered the physical and chemical characteristics of Scottish rivers, with adverse consequences for aquatic biota. Baseline hydrological, geomorphological and water quality conditions in Scottish rivers are thus summarised. The impacts of river regulation and land use change on the hydrology, geomorphology and water quality of Scottish rivers are then discussed. Consequences of these changes for aquatic habitat are examined, with particular reference to the economically significant salmonid species (Salmo salar and Salmo trutta). Policy and management issues relating to the future ecological quality of Scottish rivers are reviewed. These include the impacts of climate change on ecological quality, the calculation and implementation of ecologically acceptable flows, and river restoration and best management practices within integrated catchment planning.     

Application of MIKE SHE modelling system to set up a detailed water balance computation

Estimation of total water balance is a substantial issue for watershed modelling in order to simulate the major components of the hydrological cycle to determine the stress of different anthropogenic activities on the available water resources within a catchment. In this context, the fully distributed physically based MIKE SHE modelling system was used to simulate the individual hydrological components of the total water balance for the Paya Indah Wetlands (PIW) watershed in the west of Peninsular Malaysia. Results reveal that the overall water balance is predominantly controlled by climate variables. Application of the model to the PIW watershed provides detailed estimation of the total water balance for a first‐order catchment in which actual evapotranspiration (ET) represents approximately 65 and 58%, while overland flow (OL) to the PIW lake system represents 12.38 and 12.3% of the total rainfall during the calibration and validation periods, respectively. The difference of the inflow and outflow was taken as storage in depth. Overall, the model gives a reasonable output of total error of less than 1% of the total rainfall, which in turn indicates that the interaction among components is satisfactorily sustained.     

Agriculture-induced increase in nitrate concentrations in stream waters of a large Mediterranean catchment over 25 years (1981–2005)

Anthropogenic activities influence past and present nitrate levels recorded in European stream waters, posing a threat to aquatic biota and human beings. Scarce information on temporal trends of nitrate concentration and its causes is available for Mediterranean catchments. This study presents the evolution of nitrate concentrations over 25 years in stream waters of the Ebro River Basin (Spain), a large Mediterranean catchment involving 85,566 km². Nitrate concentration increased with time in 46% of the 65 sites involved in the study. Agricultural cover of 30 hydrologically independent sub-catchments was the main land use related to nitrate concentration (R² = 0.69). Throughout the 25 year-period, the sites showing increased nitrate concentrations with time (trend sites) also presented an enhanced influence of agricultural cover on nitrate concentrations along the time frame of the study. As a result of these temporal changes, at the end of the studied period nitrate concentrations in stream waters responded similarly to agricultural cover in both trend and non-trend sites, showing non significant differences in the slope of the resultant regression models. At this time, agricultural cover explained 82% of the variability found in nitrate levels. If these trends remain unchanged, in 2015 many of the water bodies considered in this study would not comply with the requirements of the European Union Water Framework Directive (WFD). Therefore management decisions, mainly associated to agricultural practices, should be implemented as soon as possible at the catchment level to meet WFD objectives.     

Analysis of catchment evapotranspiration at different scales using bottom-up and top-down approaches

Physically-based hydrological models are used to predict catchment water balance through detailed simulation of hydrological processes at small temporal and spatial scales. However, annual catchment water balance can also be easily and simply predicted using lumped conceptual model. Comparison between physically-based hydrological models and lumped conceptual models can help us understand the dominant factors on catchment water balance at different scales. In this paper, a distributed physically-based hydrological model (i.e., bottom-up approach) and a simple water-energy balance model (i.e., top-down approach) are used to predict actual evapotranspiration in nine sub-catchments, and the whole basin of the Luan River in northern China. Both simulations give very close values of annual evapotranspiration and show the same complementary relationship between actual and potential evapotranspiration at annual time scale. From the analysis at different time scales through comparison of the top-down and the bottom-up methods, it is shown that the annual catchment evapotranspiration is controlled mainly by annual precipitation and potential evapotranspiration, and the variability of soil water and vegetation becomes more important at a smaller time scale in the study areas. It is also known that the relationship between potential and actual evapotranspiration shows a highly nonlinear relationship at the annual and catchment scale but can be simplified to a linear relationship at hourly temporal and hillslope scales, which is commonly used in the physically-based hydrological models.     

Water Quality and Management Strategies in London's Docklands

Regeneration and changes in land use in London's Docklands have resulted in new water quality requirements. Areas previously occupied by docks now form part of redevelopment projects which have made a feature of the water.
The paper describes a project to provide water that is aesthetically pleasing and of a quality suitable for water contact recreational activities.
An extensive programme of water sampling and analysis was carried out to gain an understanding of the processes affecting water quality, including the monitoring of algal growth. The river is the main source of nutrients in the docks, which results in large concentrations of algal biomass and bacterial contamination. The principal strategy is to limit light via artificial mixing systems supplemented by limiting the inflow of nutrients from the river.
The results from the water sampling programme have been used to build a 3D computer model with a supporting graphic information system to attain (a) qualitative evaluations of management and development options, and (b) short-term predictions of changes in water quality.     

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.     

Sustainable microbial water quality monitoring programme design using phage-lysis and multivariate techniques

Contamination of surface waters is a pervasive threat to human health, hence, the need to better understand the sources and spatio-temporal variations of contaminants within river catchments. River catchment managers are required to sustainably monitor and manage the quality of surface waters. Catchment managers therefore need cost-effective low-cost long-term sustainable water quality monitoring and management designs to proactively protect public health and aquatic ecosystems. Multivariate and phage-lysis techniques were used to investigate spatio-temporal variations of water quality, main polluting chemophysical and microbial parameters, faecal micro-organisms sources, and to establish ‘sentry’ sampling sites in the Ouse River catchment, southeast England, UK. 350 river water samples were analysed for fourteen chemophysical and microbial water quality parameters in conjunction with the novel human-specific phages of Bacteroides GB-124 (Bacteroides GB-124). Annual, autumn, spring, summer, and winter principal components (PCs) explained approximately 54%, 75%, 62%, 48%, and 60%, respectively, of the total variance present in the datasets. Significant loadings of Escherichia coli, intestinal enterococci, turbidity, and human-specific Bacteroides GB-124 were observed in all datasets. Cluster analysis successfully grouped sampling sites into five clusters. Importantly, multivariate and phage-lysis techniques were useful in determining the sources and spatial extent of water contamination in the catchment. Though human faecal contamination was significant during dry periods, the main source of contamination was non-human. Bacteroides GB-124 could potentially be used for catchment routine microbial water quality monitoring. For a cost-effective low-cost long-term sustainable water quality monitoring design, E. coli or intestinal enterococci, turbidity, and Bacteroides GB-124 should be monitored all-year round in this river catchment.     

Defining the sources of low-flow phosphorus transfers in complex catchments

Nutrient transfers from the land to rivers have the potential to cause persistent eutrophic impacts at low flows even though the transfers may constitute a minor percentage of total annual fluxes. In rural catchments, the contribution from agricultural soils during storm events can be particularly large and untangling the relative contributions from multiple sources that vary in time and space is especially problematic. In this study, the potential for domestic septic tank system pollution during low flows was investigated in 3 small catchments (3 to 5 km(2)) using an integrated series of methods. These included septic system surveys, continuous (10 min) total phosphorus (TP) monitoring at the outlet of each catchment, repeated low-flow water quality surveys in sub-catchments upstream of the catchment outlets and single day river-walk water quality surveys. A series of faecal matter and grey-water fingerprinting techniques were also employed. These included determining sterol ratios in stream sediments, monitoring the presence of proteins, E. coli and enterococci bacterial signatures and boron. The total density and density of poorly maintained septic systems mirrored the magnitude of frequent TP concentrations in the catchments although this relationship was less apparent in the nested sub-catchments. The exception was possibly related to the simple hydraulics in one particular catchment and indicated temporary effluent attenuation in the other catchments. Repeated low-flow and river-walk water quality surveys highlighted discrete areas and reaches where stepped changes in nutrient concentration occurred. Bio-chemical fingerprinting showed that between 7% and 27% of sediments were contaminated with human faecal material and correlation matrices indicated that, at least during low flows, P fractions were positively correlated with some markers of faecal and grey-water contamination.     

Predicting stream N and P concentrations from loads and catchment characteristics at regional scale: a concentration ratio method

We used a concentration ratio method to predict yearly and summer averages of stream total nitrogen, nitrate and total phosphorus concentrations at a regional scale. The ratio of the median daily concentration on the flow weighted annual concentration was used. This ratio characterizes the concentration dynamics of a catchment. We took advantage of the commonly used budget type models applied at a regional scale to relate concentrations to loads instead of directly to land uses, as has previously been done. The relationship was modeled with Boosted Regression Trees using catchment and stream characteristics along with loads and flows obtained from the SPARROW budget model. The ratio modeling approach was compared to a direct approach for concentration prediction, and also to a simple method where the mean ratio was used. The modeling performances of the ratio models were overall satisfying (r² of 49% to 78%), and a better choice than the two other methods tested. This ratio modeling approach is based on a steady state assumption and largely ignores temporal dynamics. As such, this modeling technique does not replace the more physically-based techniques, but allows for hybrid approaches for improved spatial interpolations. This method could be used to predict effectively the impact (at equilibrium) of land use change and management scenarios on water quality at a regional scale.     

Analysis of catchment evapotranspiration at different scales using bottom-up and top-down approaches

Physically-based hydrological models are used to predict catchment water balance through detailed simulation of hydrological processes at small temporal and spatial scales. However, annual catchment water balance can also be easily and simply predicted using lumped conceptual model. Comparison between physically-based hydrological models and lumped conceptual models can help us understand the dominant factors on catchment water balance at different scales. In this paper, a distributed physically-based hydrological model (i.e., bottom-up approach) and a simple water-energy balance model (i.e., top-down approach) are used to predict actual evapotranspiration in nine sub-catchments, and the whole basin of the Luan River in northern China. Both simulations give very close values of annual evapotranspiration and show the same complementary relationship between actual and potential evapotranspiration at annual time scale. From the analysis at different time scales through comparison of the top-down and the bottom-up methods, it is shown that the annual catchment evapotranspiration is controlled mainly by annual precipitation and potential evapotranspiration, and the variability of soil water and vegetation becomes more important at a smaller time scale in the study areas. It is also known that the relationship between potential and actual evapotranspiration shows a highly nonlinear relationship at the annual and catchment scale but can be simplified to a linear relationship at hourly temporal and hillslope scales, which is commonly used in the physically-based hydrological models.     

A comparison of SWAT, HSPF and SHETRAN/GOPC for modelling phosphorus export from three catchments in Ireland

Recent extensive water quality surveys in Ireland revealed that diffuse phosphorus (P) pollution originating from agricultural land and transported by runoff and subsurface flows is the primary cause of the deterioration of surface water quality. P transport from land to water can be described by mathematical models that vary in modelling approach, complexity and scale (plot, field and catchment). Here, three mathematical models (soil water and analysis tools (SWAT), hydrological simulation program-FORTRAN (HSPF) and système hydrologique Européen TRANsport (SHETRAN)/grid oriented phosphorus component (GOPC)) of diffuse P pollution have been tested in three Irish catchments to explore their suitability in Irish conditions for future use in implementing the European Water Framework Directive. After calibrating the models, their daily flows and total phosphorus (TP) exports are compared and assessed. The HSPF model was the best at simulating the mean daily discharge while SWAT gave the best calibration results for daily TP loads. Annual TP exports for the three models and for two empirical models were compared with measured data. No single model is consistently better in estimating the annual TP export for all three catchments.