Lowland Agricultural Catchment Research Articles

A model for quantifying the effectiveness of leaky barriers as a flood mitigation intervention in an agricultural landscape

AbstractLeaky barriers have become an important mitigation option within natural flood management to reduce downstream flood risk. Modelling is a key tool to aid in the design of leaky barrier installations for flood mitigation, but there is limited evidence about the accuracy of model representations of the system. Here, the hydrological model SWAT was combined with a water routing model that simulates multiple leaky barriers as permeable sluice gates. Storage behind individual barriers was quantified using barrier dimensions and LIDAR topography. The model was applied to a series of 27 leaky barriers installed as part of a long‐term manipulation experiment into a 11‐km2 intensive lowland agricultural catchment in Leicestershire, England. Evaluation of the model against flow data collected before and after leaky barrier installation and time‐lapse photography taken across storm events at individual barriers demonstrated robust model performance (Nash‐Sutcliffe efficiency and R2 across 19 validation events were 0.84 ± 0.14 and 0.91 ± 0.08, respectively). Empirical and modelling data were then combined to demonstrate that the 17,700 m3 of water storage provided by the 27 leaky barriers reduced peak flows at the catchment outlet by 22 ± 6% and delayed the peak in flow by up to 5 h for 11 storm events recorded after all barriers had been installed. The volume of storage utilised prior to the flood event was a key factor influencing the reduction in peak flow, and a sensitivity analysis indicated that barriers should be permeable to accelerate drain‐down of the barrier and help to mitigate risk from multiple storm events occurring in sequence.

The Impact of Various Types of Cultivation on Stream Water Quality in Central Poland

Agricultural practices have a significant impact on stream water quality in rural landscapes; however, there is still little empirical evidence of how different types of cultivation alter the hydrochemistry of running water. Thus, the current study explored the spatial dynamics of selected ion concentrations and their land cover dependence in lowland agricultural catchments. From November 2021 to October 2022, water samples were collected from 30 sites located across small tributaries of the rivers Bzura, Pilica, and Radomka for chemical analysis of their NO3, NO2, NH4, Ca, Mg, K, Na, As, Ba, Sr, and V concentrations. The results indicated a clear spatial heterogeneity of water quality, related to lithology and dominant land cover evaluated with the CORINE Land Cover 2018 dataset. Overall, sites representing agricultural land promoted increased concentrations of major and trace elements, while those with pepper cultivation were additionally contaminated with NO3 and NO2. The correlation performance for nitrogen compounds was the highest for narrower buffer zones, which was not documented for major and trace elements, which were linked more strongly with land cover at larger scales. Such new insights into the water quality dynamics of lowland agricultural catchments, being a simultaneous reflection of lithology, agricultural practices, and several municipal impacts, have significant implications for appropriate water management in rural landscapes.

Spatial and seasonal variability of sub–daily water temperature dynamics in the lowland agricultural catchment of the Wkra River

Spatial and seasonal variability of sub–daily water temperature dynamics in the lowland agricultural catchment of the Wkra River

Hydroclimatic variability and riparian wetland restoration control the hydrology and nutrient fluxes in a lowland agricultural catchment

Climate change and riparian management are major drivers of hydrological change, with important implications for nutrient fluxes in lowland streams. However, the coupling of hydrological and nutrient dynamics is complex due to time-variant flow paths, interacting biogeochemical processes and variation in land use, fertilization levels and management measures. Here, we assessed the long-term (30 year) changes in climate, discharge, groundwater levels and stream water quality in a mixed land use catchment (Demnitzer Mill Creek catchment, DMC) in northern Germany. The catchment was subject to wetland restoration and subsequent beaver (Castor fiber) recolonization over the last 15 years. Climatic variability is the primary driver of the hydrological regime, with discharge and groundwater variations closely coupled to increases in annual air temperature and fluctuations of annual rainfall. Over the past 8 years, stream flows have been greatly reduced during a prolonged drought period. Meanwhile, beaver dams have also moderated flow regimes and facilitated groundwater recharge. In terms of water quality regimes, the concentration-discharge (C-Q) relationship for nitrate (NO3-N) and soluble reactive phosphate (SRP) showed positive and negative chemodynamic behavior respectively, whilst dissolved organic carbon (DOC) exhibited chemostatic behavior. These differences were dictated by the intrinsic properties of each solute in terms of contrasting catchment storage and immobilization processes. Moreover, the changing hydrological conditions regulated such patterns and strengthened the C-Q relationships for nutrients during the drought. As an integrated result of drought and wetland restoration, nutrient concentrations and fluxes in stream water have been reduced in recent years. Headwater catchments like DMC, where much of the hydrochemical signature of larger, downstream river networks are generated, are critical observatories for integrating understanding of the linkages between water quality and land management in an era of climate change.

Physicochemical drivers of managed river and agricultural drainage channel macroinvertebrate communities

AbstractArtificial channels are common features in lowland agricultural catchments, and are a potentially significant habitat for aquatic species. Recent studies have suggested communities in managed rivers and artificial channels are broadly similar, but with some compositional differences. However, because relatively few studies have considered how artificial channels may contribute to supporting aquatic communities, their physicochemical condition and suitability for aquatic fauna remain poorly characterised. Therefore, this study explores the role of physicochemical variables in driving macroinvertebrate community differences between intensively managed rivers and artificial channels in a highly arable catchment. Aquatic macroinvertebrates were sampled in intensively managed rivers and artificial channels. Physicochemical water quality variables were also recorded, and used to identify macroinvertebrate community responses. Both intensively managed rivers and artificial channels had spatiotemporally stable communities, with no significant differences in richness, abundance, effective diversity or Berger–Parker dominance detected between sampling months or channel types. Macroinvertebrate composition in intensively managed rivers and artificial channels was significantly different, and driven by the relative abundance of taxa present, not the number of taxa unique to each channel type. Compositional differences between intensively managed rivers and artificial channels were partially driven by conductivity, dissolved oxygen and temperature. Identifying remaining sources of compositional variance may support tailored management strategies that accentuate compositional differences between rivers and artificial channels, increasing overall diversity in intensively farmed arable catchments.

Land Cover Effects on Selected Nutrient Compounds in Small Lowland Agricultural Catchments

The influence of landscape on nutrient dynamics in rivers constitutes an important research issue because of its significance with regard to water and land management. In the current study spatial and temporal variability of N-NO3 and P-PO4 concentrations and their landscape dependence was documented in the Świder River catchment in central Poland. From April 2019 to March 2020, water samples were collected from fourteen streams in the monthly timescale and the concentrations of N-NO3 and P-PO4 were correlated with land cover metrics based on the Corine Land Cover 2018 and Sentinel 2 Global Land Cover datasets. It was documented that agricultural lands and forests have a clear seasonal impact on N-NO3 concentrations, whereas the effect of meadows was weak and its direction was dependent on the dataset. The application of buffer zones metrics increased the correlation performance, whereas Euclidean distance scaling improved correlation mainly for forest datasets. The concentration of P-PO4 was not significantly related with land cover metrics, as their dynamics were driven mainly by hydrological conditions. The obtained results provided a new insight into landscape–water quality relationships in lowland agricultural landscape, with a special focus on evaluating the predictive performance of different land cover metrics and datasets.

Quantifying hydro-sedimentary transfers in a lowland tile-drained agricultural catchment

Soil erosion, runoff and sediment connectivity are strongly impacted by anthropogenic features in lowland agricultural catchments. Among these landscape features, the role played by tile drainage on water and sediment transfers and hillslope-to-river connectivity in drained catchments remains poorly understood. This study quantified water and sediment transfers in a tile drained catchment of central France by combining high frequency rainfall, discharge and sediment concentration measurements at the outlet of a set of 10 tile drained plots (34 ha) and at the medium-sized (120 km2) catchment scale. Over the monitoring period, including a dry and a wet year compared to average conditions (one year with 112% of the mean annual rainfall and one year with 64% of the mean annual rainfall), 36 rainfall-flood events were recorded and analyzed. The high frequency analysis of water and sediment transfers in tile-drained plots showed a high seasonal variability and the occurrence of two transfer pathways in the soil column including the slow drainage of saturated soils and the occurrence of preferential flow pathways through the soil column. Indeed, 13 of the 36 recorded flood events showed hydrographs with two components, reflecting these two pathways: slow transfers in the soil columns and fast transfers through soil macropores and/or cracks. Indeed, at the beginning of the flood event, a high-magnitude peak overlaid on the hydrograph. On average, this fast peak contributed 15% of the water and sediment fluxes. The sediment dynamics in tile drains was suggested to depend on sediment storage and exhaustion processes occurring in the tile drain network.

The influence of substrate type on macroinvertebrate assemblages within agricultural drainage ditches

Artificial drainage ditches are common features in lowland agricultural catchments that support a wide range of ecosystem services at the landscape scale. Current paradigms in river management suggest activities that increase habitat heterogeneity and complexity resulting in more diverse floral and faunal assemblages; however, it is not known if the same principles apply to artificial drainage ditch systems. We examined the effects of four artificial substrates, representing increasing habitat complexity and heterogeneity (bricks, gravel, netting and vegetation), on macroinvertebrate community structure within artificial drainage ditches. Each substrate type supported a distinct macroinvertebrate community highlighting the importance of habitat heterogeneity in maintaining macroinvertebrate assemblages. Each substrate type also displayed differing degrees of community heterogeneity, with gravel communities being most variable and artificial vegetation being the least. In addition, several macroinvertebrate diversity metrics increased along the gradient of artificial substrate complexity, although these differences were not statistically significant. We conclude that habitat management practices that increase habitat complexity are likely to enhance macroinvertebrate community heterogeneity within artificial drainage channels regardless of previous management activities.

Disruptions and re-establishment of the calcium-bicarbonate equilibrium in freshwaters

During recent decades, increasing anthropogenic activities have affected natural ionic composition, including the strongest and most common relationship between ionic concentrations in the majority of natural global freshwaters, i.e., the Ca2+-ANC (acid neutralizing capacity) equilibrium. Using long-term monitoring data and MAGIC modelling, we evaluated effects of major present environmental stressors (synthetic fertilizers, liming, acidic deposition, forest disturbances, and climate change) on the Ca2+-ANC equilibrium. We evaluated the effects for three different types of terrestrial ecosystems, a circumneutral lowland agricultural catchment, two acid sensitive mountain forest catchments differing in forest health, and one acid sensitive alpine catchment. All catchments are in a region with the world-largest changes in fertilizing rates and acidic deposition in the 20th century, with increasing impacts until the late 1980s, and their subsequent abrupt, dramatic decreases. These strong changes resulted in a substantial disruption, followed by continuing re-establishment of the Ca2+-ANC relationship in all study waters. The shape of the disruption and the following re-establishment of its new value were dependent on the intensity, duration, and combination of stressors, as well as on catchment characteristics (bedrock composition, soil amount and composition, vegetation status, and hydrology). We conclude that a new equilibrium may deviate from its natural value due to the (1) legacy of fertilizing, acidic deposition and liming, affecting the soil Ca2+ pools, (2) forest disturbances and management practices, and (3) climate change.

Water Table Dynamics Control Carbon Losses from the Destabilization of Soil Organic Matter in a Small, Lowland Agricultural Catchment

The biogeochemistry of soil organic matter (SOM) is driven by a combination of stabilization and destabilization mechanisms. Among the various ways in which SOM is lost, soil moisture controls the leaching of dissolved organic and inorganic carbon (DOC and DIC) and CO2 fluxes (FCO2). The aim of this study was to investigate the impact of naturally occurring water table dynamics on the couplings between these three types of C losses. The DIC and DOC concentrations in the soil solutions and the FCO2 values at the soil surface were collected fortnightly over a nine-month period at four sampling points located along two topographic transects characterized by different water table dynamics. The water table depth, soil temperature and water-filled pore space (WFPS) were monitored at each site. Linear and nonlinear regressions were used to explore the couplings between C losses, WFPS and soil temperature. The dynamics of the water table seem to drive DOC solubilization, diffusion, and export mechanisms in addition to microbial processes and the equilibrium between DIC and CO2. The main descriptors of this water table dynamic were the residence time, return time and number of oscillations of the water table. Considering both transects, FCO2 was positively correlated with DOC, which highlights the importance of substrate accessibility for SOM mineralization. This paper emphasizes the importance of the water table dynamic for the coupling between SOM carbon losses.

Catchment-scale influences on riverine organic matter in southern New Zealand

Riverine particulate organic matter (POM) is a critical vector for nutrient cycling of carbon at both regional and global scales. POM and suspended sediment (SS) are transported concomitantly through rivers, and their concentrations change in association to landscape transformations and natural fluctuations. The proportion of POM to SS mobilised in rivers under base flow is an important component of carbon flux to oceans, and is a useful metric for understanding hillslope–river coupling and hydraulic connectivity. We quantified POM during base flow conditions in southern New Zealand to assess the role of different catchment characteristics that control the spatial variability of organic matter in the fluvial environment. The proportion of POM to total suspended material (TSM) can be <5%, or much higher at 50–80% across southern New Zealand, with the highest concentrations associated with lowland agricultural catchments. Particulate organic carbon yields were estimated to be between 0.04 and 2.7 t km−2 a−1 discharged into the Pacific Ocean. The POM% responds to both intrinsic and extrinsic catchment characteristics, affecting the availability of organic material and mechanisms for transport including vegetation cover, topographic controls, and hydrological controls. Across southern New Zealand it is evident that riverine organic matter is spatially organised and connected to broader hillslope processes, albeit difficult to predict at the catchment scale.

Riparian wetland rehabilitation and beaver re-colonization impacts on hydrological processes and water quality in a lowland agricultural catchment

Quantifying the catchment water balance and the characterization of its water quality changes are effective tools for establishing the response of catchments to shifting land management practices. Here we assess long-term hydrological partitioning and stream water chemistry over a 30-year period in a rural mixed land use catchment in northern Germany undergoing riparian wetlands and widespread re-colonization by beavers (Castor fiber) along the river network. We used long-term spatially distributed stream discharge, groundwater levels and surface water quality data with a simple monthly water balance model, changes in the variability in discharge measurements, and statistical analysis of spatio-temporal changes in stream water quality to assess long-term changes. Water balance estimates indicated high proportions of evapotranspiration loss (~90% of total precipitation) and relatively low groundwater recharge (<5% of total precipitation) prior to riparian rehabilitation in 2000. Increasing groundwater levels from 2000 to 2017 and the relatively linear nature of the catchment storage – discharge relationship, indicate a gradual increase in groundwater recharge (buts still <10% of total precipitation). Wetland rehabilitation, greatly enhanced by increasing beaver populations, resulted in longer water transit times in the stream network, less linear storage-discharge relationship and a loss of daily stream variability, increased DOC concentrations, isotopic evaporative enrichment downstream, and moderated stream temperatures. There was limited long-term water quality improvements from wetland rehabilitation on either nitrate or total phosphorus concentrations, with unchanged seasonal summer and winter peak concentrations for phosphorus and nitrate, respectively. This likely reflects the long-term legacy of fertilizer use on nutrient reservoirs in the catchment's soils, aquifers, and stream network. These long-term changes in hydrology and stream chemistry resulting from riparian rehabilitation and changes in agricultural management practices provide invaluable insights into catchment functioning and an evidence base for future planning in relation to long-term climatic changes.

Hydro‐sedimentary Dynamics of a Drained Agricultural Headwater Catchment: A Nested Monitoring Approach

Core Ideas Discharge and sediment concentrations were measured in a drained catchment. The impact of tile drainage at the catchment scale was analyzed with a nested approach. The major part of sediment fluxes occurred during winter floods. Sediment transfer in the tile drain was episodic although significant. Soil erosion and sediment transfer are extensive in lowland agricultural catchments. In these environments, high‐frequency datasets of both water discharge and suspended sediment concentrations are often lacking. In particular, the impact of tile drainage networks on sediment fluxes in these catchments is poorly understood. Our research quantified sediment fluxes between 2013 and 2016 at five nested stations including a tile drain outlet across a small (25‐km2) agricultural catchment (located in the Loire River basin, France) representative of lowland cultivated environments of the middle part of this basin. Sediment fluxes varied from 1 to 38 t km−2 yr−1 across the monitored subcatchments. Most of sediment fluxes (79 ± 9%) were measured during flood events (n = 44), mostly occurring in winter (75%) and spring (20%). Seasonality controlled most of the variations of sediment fluxes. Sediment transfers in tile drains occurred episodically. Flows were measured during 11.4% of the monitoring time. A mean time lag of 80 min was recorded between the peak discharge at the drain outlet and the downstream river station. At the event scale, sediment fluxes exported from the tile drain varied between 1.1 × 10−4 and 2.5 t km−2 and remained of the same order of magnitude as those measured at the downstream river station, although the latter were on average 53% lower. Results suggest significant storage of sediment material in the river channel and its export during the most intense flood events. Our research emphasizes the need for continuous monitoring of water and sediment transfers in agricultural catchments equipped with tile drains.

Landform transformation and long-term sediment budget for a Chernozem-dominated lowland agricultural catchment

Abstract The loess hilly lands of the South-West Foreland of the West Carpathians are characterized by favorable climatic conditions, smooth topography, fertile soils and a long settlement history. For the first time, we document changes to human-induced landforms in a small zero-order dry valley (0.28 km2) with Calcic Chernozem soils and develop a long-term sediment budget. The original surface was reconstructed based on interpreting records of erosion and deposition from 185 soil cores and six valley cross-sections. The topography inherited from the Pleistocene was transformed through lowering of hillslope ridges and convexities, along with infilling of shallow depressions within the original valley bottom. On convex-convex landforms had an average net erosion of − 0.32 ± 0.01 m, while average net accumulation in the valley bottom was estimated at 0.20 ± 0.01 m. The correlation between change in soil profile depth with profile curvature (− 0.51, p < 0.01) was stronger than with slope (− 0.42, p < 0.01). The sediment budget was calculated using the Average Per Unit (APU) approach. When slope classes were used in calculating net soil loss from catchments was 143·103 Mg·km− 2, whereas 154·103 Mg·km− 2 was estimated when morphometric forms of hillslopes were used instead. Both values are < 60% of estimates for similar loess catchments in Central and Western Europe. Prior to 1949, the landscape structure was characterized by small and narrow fields and vegetative field barriers that limited water and aeolian sediment fluxes in the direction of the thalweg and main wind directions. The landscape structure favoured the low-intensity tillage, erosion and accumulation within fields, and short-distance sheet and rill erosion on hillslopes. The land-use changes in the 1950′s caused removal of barriers for water and aeolian sediment transport, and changed the direction of sediment fluxes of tillage erosion. Past landscape structures should thus be considered when establishing and interpreting sediment budgets for lowland agricultural catchments.

Nitrous oxide emissions from streams in a Swedish agricultural catchment

Excess nitrogen fertiliser in agricultural soils might be leached to streams and converted to the greenhouse gas nitrous oxide (N2O). To assess the importance of N2O emissions from agricultural streams, concentration dynamics and emissions N2O emissions in streams were investigated in a 32km2 lowland agricultural catchment located in Sweden. Dissolved N2O concentration was measured at nine occasions between December 2014 and August 2015 at nine stream stations. The stream stations represented sub-catchments with different land use characteristics with agricultural land use ranging from 0 to 63% of the area. Stream N2O percentage saturation ranged 40–2701% and showed large spatial and temporal variations. Statistical analysis using mixed models revealed that N2O concentration was significantly linked to nitrate concentration in the stream water, to the percentage arable land in the sub-catchments as well as to the stream water discharge. Using two empirical equations to estimate the N2O emissions showed that streams were generally a source of N2O to the atmosphere (mean 108 and 175μgNm−2h−1 with first and second equation). The catchment scale estimate of N2O stream emissions was compared to the estimate obtained using IPCC guidelines linking N fertilisation inputs and leaching to N2O emissions. The comparison suggested that N2O stream emission calculated using the IPCC methodology might be underestimated. A coarse estimate suggests that N2O stream emissions represent about 4% of the total N2O emissions from N-fertiliser at the catchment scale. Hence while streams covered only 0.1% of the catchment area they were of disproportionate importance as a source of N2O to the atmosphere.

Can channel banks be the dominant source of fine sediment in a UK river?: an example using 137Cs to interpret sediment yield and sediment source

AbstractCultivated fields have been shown to be the dominant sources of sediment in almost all investigated UK catchments, typically contributing 85 to 95% of sediment inputs. As a result, most catchment management strategies are directed towards mitigating these sediment inputs. However, in many regions of the UK such as the Nene basin there is a paucity of sediment provenance data. This study used the caesium‐137 (137Cs) inventories of lake and floodplain cores as well as the 137Cs activities of present day sediment to determine sediment provenance. Sediment yields were also reconstructed in a small lake catchment.Low 137Cs inventories were present in the lake and floodplain cores in comparison to the reference inventory and inventories in cores from other UK catchments. Caesium‐137 activities in the present day sediments were low; falling close to those found in the channel bank catchment samples. It was estimated that 60 to 100% of the sediment in the Nene originated from channel banks.Pre‐1963 sediment yields were approximately 11.2 t km−2 yr−1 and post‐1963 was approximately 11.9 t km−2 yr−1. The lack of increased sediment yield post‐1963 and low sediment yield is unusual for a UK catchment (where a yield of 28 to 51 t km−2 yr−1 is typical for a lowland agricultural catchment), but is explained by the low predicted contribution of sediment from agricultural topsoils. The high channel bank contribution is likely caused by the river being starved of sediment from topsoils, increasing its capacity to entrain bank material.The good agreement between the results derived using cores and recently transported sediments, highlight the reliability of 137Cs when tracing sediment sources. However, care should be taken to assess the potential impacts of sediment particle size, sediment focusing in lakes and the possible remobilization of 137Cs from sedimentary deposits. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Quantifying sediment sources in a lowland agricultural catchment pond using 137Cs activities and radiogenic 87Sr/86Sr ratios

Soil erosion often supplies high sediment loads to rivers, degrading water quality and contributing to the siltation of reservoirs and lowland river channels. These impacts are exacerbated in agricultural catchments where modifications in land management and agricultural practices were shown to accelerate sediment supply. In this study, sediment sources were identified with a novel tracing approach combining cesium (137Cs) and strontium isotopes (87Sr/86Sr) in the Louroux pond, at the outlet of a lowland cultivated catchment (24km2, Loire River basin, France) representative of drained agricultural areas of Northwestern Europe.Surface soil (n=36) and subsurface channel bank (n=17) samples were collected to characterize potential sources. Deposited sediment (n=41) was sampled across the entire surface of the pond to examine spatial variation in sediment deposits. In addition, a 1.10m sediment core was sampled in the middle of the pond to reconstruct source variations throughout time. 137Cs was used to discriminate between surface and subsurface sources, whereas 87Sr/86Sr ratios discriminated between lithological sources. A distribution modeling approach quantified the relative contribution of these sources to the sampled sediment.Results indicate that surface sources contributed to the majority of pond (μ 82%, σ 1%) and core (μ 88%, σ 2%) sediment with elevated subsurface contributions modeled near specific sites close to the banks of the Louroux pond. Contributions of the lithological sources were well mixed in surface sediment across the pond (i.e., carbonate sediment contribution, μ 48%, σ 1% and non-carbonate sediment contribution, μ 52%, σ 3%) although there were significant variations of these source contributions modeled for the sediment core between 1955 and 2013. These fluctuations reflect both the progressive implementation of land consolidation schemes in the catchment and the eutrophication of the pond.This original sediment fingerprinting study demonstrates the potential of combining radionuclide and strontium isotopic geochemistry measurements to quantify sediment sources in cultivated catchments.

Surface runoff in flat terrain: How field topography and runoff generating processes control hydrological connectivity

Summary In flat lowland agricultural catchments in temperate climate zones with highly permeable sandy soils, surface runoff is a rare process with a large impact on the redistribution of sediments and solutes and stream water quality. We examine hydrological data obtained on two field sites in the Netherlands for a period of 1.5 years to give an integrated narrative of surface runoff in this type of catchment. In the monitoring period, seven surface runoff events were observed with a magnitude of 9.8–975 L runoff. Four of these events were classified as saturation excess events, due to a shallow water table. Three of the events occurred under infiltration excess conditions due to rainfall in combination with snowmelt. Though the microtopography of the fields was quite different, they were identical in terms of topographical indicators. Therefore, we analyzed the dynamics of hydrological connectivity on these fields with a numerical model that takes into account routing variability through microtopography and calculated simplified hydrographs and Relative Surface Connection functions from the results. The connectivity dynamics of the fields were different as quantified by these indicators. We found that the dynamics of hydrological connectivity in this low-angle terrain are not just a function of the soil surface meso- and microtopography, but also of the type of surface runoff generating process. This is an important factor to consider when using connectivity functions as an upscaling tool in catchment scale modeling.

Quantifying the dominant sources of sediment in a drained lowland agricultural catchment: The application of a thorium-based particle size correction in sediment fingerprinting

Soil erosion is one of the main factors influencing land degradation and water quality at the global scale. Identifying the main sediment sources is therefore essential for the implementation of appropriate soil erosion mitigation measures. Accordingly, caesium-137 (137Cs) concentrations were used to determine the relative contribution of surface and subsurface erosion sources in a lowland drained catchment in France. As 137Cs concentrations are often dependent on particle size, specific surface area (SSA) and novel thorium (Th) based particle size corrections were applied. Surface and subsurface samples were collected to characterize the radionuclide properties of potential sources. Sediment samples were collected during one hydrological year and a sediment core was sampled to represent sediment accumulated over a longer temporal period. Additionally, sediment from tile drains was sampled to determine the radionuclide properties of sediment exported from the drainage network. A distribution modelling approach was used to quantify the relative sediment contributions from surface and subsurface sources. The results highlight a substantial enrichment in fine particles and associated 137Cs concentrations between the sources and the sediment. The application of both correction factors reduced this difference, with the Th correction providing a more accurate comparison of source and sediment samples than the SSA correction. Modelling results clearly indicate the dominance of surface sources during the flood events and in the sediment core. Sediment exported from the drainage network was modelled to originate predominantly from surface sources. This study demonstrates the potential of Th to correct for 137Cs particle size enrichment. More importantly, this research indicates that drainage networks may significantly increase the connectivity of surface sources to stream networks. Managing sediment transferred through drainage networks may reduce the deleterious effects of suspended sediment loads on riverine systems in similar lowland drained agricultural catchments.

Heavy Rainfall Impacts on Trihalomethane Formation in Contrasting Northwestern European Potable Waters.

There is emerging concern over the impact of extreme events such as heavy rainfall on the quality of water entering the drinking water supply from aboveground sources, as such events are expected to increase in magnitude and frequency in response to climate change. We compared the impact of rainfall events on streamwater quality in four contrasting upland (peatland and mineral soil) and lowland agricultural catchments used to supply drinking water in France (Brittany) and the United Kingdom (North Wales) by analyzing water samples collected before, during, and after specific events. At all four streams, heavy rainfall led to a considerable rise in organic matter concentration ranging from 48 to 158%. Dissolved organic carbon (DOC) quality, as determined using specific ultraviolet absorbance, changed consistently at all sites during rainfall events, with a greater proportion of aromatic and higher molecular weight compounds following the onset of rainfall. However, the change in DOC quality and quantity did not significantly alter the trihalomethane formation potential. We observed small increases in trihalomethane (THM) generation only at the Welsh peatland and agricultural sites and a small decrease at the Brittany agricultural site. The proportion of brominated THMs in chlorinated waters was positively correlated with bromide/DOC ratio in raw waters for all sites and hydrological conditions. These results provide a first indication of the potential implications for surface-based drinking water resources resulting from expected future increases in rainfall event intensity and extension of dry periods with climate changes.