The impact of ditch blocking on the hydrological functioning of blanket peatlands

Ditch blocking in blanket peatlands is common as part of peatland restoration. The effects of ditch blocking on flow regimes and nearby water tables were examined in a field trial. After an initial 6‐month monitoring period, eight ditches had peat dams installed 10 m apart along their entire length (dammed), four of these ditches were also partially infilled through bank reprofiling (reprofiled). Four ditches were left open with no dams or reprofiling (open). These 12 ditches and the surrounding peat were monitored for 4 more years. An initial five‐fold reduction in discharge occurred in the dammed and the reprofiled ditches with the displaced water being diverted to overland flow and pathways away from the ditches. However, there was a gradual change over time in ditch flow regime in subsequent years, with the overall volume of water leaving the dammed and the reprofiled ditches increasing per unit of rainfall to around twice that which occurred in the first year after blocking. Hence, monitoring for greater than one year is important for understanding hydrological impacts of peatland restoration. Overland flow and flow in the upper ~4 cm of peat was common and occurred in the inter‐ditch areas for over half of the time after ditch blocking. There was strong evidence that topographic boundaries of small ditch catchments, despite being defined using a high‐resolution Light Detection And Ranging‐based terrain model, were not always equivalent to actual catchment areas. Hence, caution is needed when upscaling area‐based fluxes, such as aquatic carbon fluxes, from smaller scale studies including those using ditches and small streams. The effect of ditch blocking on local water tables was spatially highly variable but small overall (time‐weighted mean effect <2 cm). Practitioners seeking to raise water tables through peatland restoration should first be informed either by prior measurement of water tables or by spatial modelling to show whether the peatland already has shallow water tables or whether there are locations that could potentially undergo large water‐table recoveries.     

Fluvial carbon flux from headwater peatland streams: significance of particulate carbon flux

The extensive blanket peatlands of the UK uplands account for almost half of total national terrestrial carbon storage. However, much of the blanket peat is severely eroded so that the contemporary role of the peatland system in carbon sequestration is compromised by losses of organic carbon in dissolved (DOC) and particulate (POC) form in the fluvial system. This paper presents the first detailed assessment of dissolved and organic carbon losses from a severely eroded headwater peatland (River Ashop, South Pennines, UK). Total annual fluvial organic carbon losses range from 29–106 Mg C km,^‐2 decreasing from the headwaters to the main catchment outlet. In contrast to less eroded systems fluvial organic carbon flux is dominated by POC. POC:DOC ratios decrease from values of 4 in the headwaters to close to unity at the catchment outlet. These results demonstrate the importance of eroding headwater sites as sources of POC to the fluvial system. Comparison with a range of catchment characteristics reveals that drainage density is the best predictor of POC:DOC but there is scatter in the relation in the headwaters. Steep declines in specific POC yield from headwater catchments are consistent with storage of POC within the fluvial system. Key to the significance of fluvial carbon flux in greenhouse gas budgets is understanding the fate of fluvial carbon. Further work on the fate of POC and the role of floodplains in fluvial carbon cycling is urgently required. Copyright © 2012 John Wiley & Sons, Ltd.     

DOC budgets of drained peat catchments: implications for DOC production in peat soils

The blocking of drainage ditches in peat has been proposed as a possible mitigation strategy for the widely observed increases in dissolved organic carbon (DOC) concentrations from northern peatlands. This study tested the hypothesis that drain‐blocking could lead to lower DOC concentrations by measuring the DOC export from a series of small peat‐covered catchments over a period of 2 years. Six catchments were chosen: two were pristine that had never been drained; three where drains had been blocked (one in 1995, and two in 2003); and a control peat drain catchment where the drain was left unblocked throughout the study. In the case where drains were blocked as part of thus study, the drains were observed for 2 months before blocking and 2 years after blocking. The results show that: (i) high concentrations of DOC can come from water ponded in the drain; (ii) the DOC export (flux of DOC per area of catchment) from the six study catchments shows a high degree of positive correlation with both catchment size and water yield; (iii) distinctly lower DOC export with water yield was observed for the catchments containing higher‐order channels (>27 500 m²) as opposed to single drain catchments (>7500 m²); (iv) drain‐blocking resulted in a statistically significant decrease in DOC export (average was 39%) but the effect upon DOC concentration explained only 1% of the variance in the data. The results suggest that drain blocking works by decreasing the flow from the drain, not by changing the production of DOC in the peat. The change in export with catchment size implies a considerable removal of DOC from large catchments. Copyright © 2009 John Wiley & Sons, Ltd.     

Spectrophotometric properties of surface water dissolved organic matter in an afforested upland peat catchment

Many upland catchments in the UK have undergone afforestation; their characteristic waterlogged soils require extensive pre‐plantation ground drainage to allow tree establishment. In peatland areas this can result in very highly coloured runoff and enhanced dissolved organic matter (DOM) export in rivers of naturally high concentrations. In 1966, the Coalburn Experimental Catchment, northern England, was established to investigate the impact of afforestation on an upland peat catchment. Here we report the variations in DOM spectrophotometric properties of streamflow in the catchment at canopy closure, especially with respect to potential carbon sources within the artificial drainage ditches. Drainage ditches are characterized by water that has higher absorption coefficients and which is more highly coloured than in the catchment tributaries. Ditched, afforested areas produce more highly‐coloured runoff waters that are more fluorescent and absorbent normalized to carbon concentration compared to ditches in open moorland. Ditches that had been experimentally re‐excavated have organic matter of different spectrophotometric character, with higher dissolved organic carbon concentration and less aromatic or lower molecular weight material. It is hypothesized that this is due to the exposure of bare peat faces within and adjacent to the ditches that are more susceptible to drying compared to vegetated areas. The large extent of this drainage network acts as both a rapid transport network increasing hydrological connectivity and a pool for the storage of DOM, which is of different spectrophotometric character under low flow conditions, depending on management conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Variability of particulate (SS,POC) and dissolved (DOC,NO3) matter during storm events in the Alegria agricultural watershed

The temporal variability of suspended sediment, nitrates (NO₃) and dissolved (DOC) and particulate organic carbon concentrations was analysed in the Alegria agricultural watershed over a 2‐year period. Nine storm events were studied, including an exhaustive analysis of hydrometeorological conditions, quantification of fluxes, and concentration‐discharge hysteresis loop characterization. The overall aim was to study the variability in these components during storm events and determine the mechanisms (flow paths) affecting the trajectories, from the source to the stream. The forms, rotational patterns and trends of hysteretic loops were investigated, and relationships between hysteresis features and hydrological parameters were studied. The results revealed clear differences between particulate (suspended sediment, particulate organic carbon) and dissolved (DOC, NO₃) matter transport responses. Movement of the particulate matter was attributed to surface water, as reflected in clockwise hysteresis loops, whereas dissolved matter showed, in general, counterclockwise hysteresis loops, indicating a time delay in the arrival of solutes to the stream. This could be related to subsurface flow paths for DOC and a groundwater source for NO₃. Copyright © 2013 John Wiley & Sons, Ltd.     

Release of dissolved organic carbon from upland peat

This study examines the release of dissolved organic carbon (DOC) from upland peat during the period of the autumn flushing. Hydroclimatic conditions were monitored in conjunction with measurements of absorbance and the E4/E6 ratio of the stream draining an 11·4 km² upland peat catchment in northern England. During two months of monitoring the effects of 67 separate rainfall events were examined showing that:

• The peat behaves hydrologically as if it were a two end‐member system consisting of old, interevent, and new, event, water. Runoff is initiated by percolation excess of new water at the acrotelm–catotelm interface.
• The discharge of dissolved organic matter behaves like a three end‐member system with the between‐event water being low in DOC and storm events being characterized by two types of water. Initial runoff being characterized by new water rich in DOC that gives way to new water depleted in DOC. This transition can be ascribed to the runoff progressing from throughflow within the acrotelm progressing to saturation‐excess overland flow.
• Depletion of DOC during storm events is accompanied by a change in the character of the DOC as the E4/E6 ratio changes. This suggests that the decrease in DOC during events is the result of exhaustion of reserves rather than changes in the flowpaths being utilized by runoff.
• The amount of carbon released in any event is critically dependent upon the time between events during which oxidation processes generate a reservoir of available carbon. Production of available carbon in the catchment is as high as 4·5 g C per day per m³ of peat, suggesting a turnover rate of peat of the order of 42 years. Copyright © 2002 John Wiley & Sons, Ltd.

     

Fluvial organic carbon composition and concentration variability within a peatland catchment—Implications for carbon cycling and water treatment

Fluvial organic carbon (OC) transformations are an important component of carbon cycling and greenhouse gas production in inland waters resulting in considerable recent interest in the fate of fluvial OC exported from carbon rich soils such as peatlands. Additionally, peatland catchments are important drinking water collection areas, where high OC concentrations in runoff have water treatment implications. This analysis presents the results from a year‐round intensive study within a water treatment catchment draining an area of peatland, considering carbon transformations along a continuum from headwater river, through a storage reservoir and pipe, to a water treatment works. The study uses a unique combination of methods (colourmetric, ultrafiltration, and ¹⁴C radiocarbon dating) to assess catchment wide changes in fluvial carbon composition (colour, size, and age) alongside concentration measures. The results indicate clear patterns of carbon transformations in the river and reservoir and dissolved low molecular weight coloured carbon to be most subject to change, with both loss and replacement within the catchment residence time. Although the evidence suggests dissolved OC (DOC) gains are from particulate OC breakdown, the mechanisms of DOC loss are less certain and may represent greenhouse gas losses or conversions to particulate OC. The transformations presented here appear to have minimal impact on the amount of harder to treat (<10 kDa) dissolved carbon, although they do have implications for total DOC loading to water treatment works. This paper shows that peatland fluvial systems are not passive receptors of particulate and dissolved organic carbon but locations where carbon is actively cycled, with implications for the understanding of carbon cycling and water treatment in peatland catchments.     

A distributed TOPMODEL for modelling impacts of land‐cover change on river flow in upland peatland catchments

There is global concern about headwater management and associated impacts on river flow. In many wet temperate zones peatlands can be found covering headwater catchments. In the UK there is major concern about how environmental change, driven by human interventions, has altered the surface cover of headwater blanket peatlands. However, the impact of such land‐cover changes on river flow is poorly understood. In particular, there is poor understanding of the impacts of different spatial configurations of bare peat or well‐vegetated, restored peat on river flow peaks in upland catchments. In this paper, a physically based, distributed and continuous catchment hydrological model was developed to explore such impacts. The original TOPMODEL, with its process representation being suitable for blanket peat catchments, was utilized as a prototype acting as the basis for the new model. The equations were downscaled from the catchment level to the cell level. The runoff produced by each cell is divided into subsurface flow and saturation‐excess overland flow before an overland flow calculation takes place. A new overland flow module with a set of detailed stochastic algorithms representing overland flow routing and re‐infiltration mechanisms was created to simulate saturation‐excess overland flow movement. The new model was tested in the Trout Beck catchment of the North Pennines of England and found to work well in this catchment. The influence of land cover on surface roughness could be explicitly represented in the model and the model was found to be sensitive to land cover. Copyright © 2014 John Wiley & Sons, Ltd.     

Fluvial transport of suspended sediment and organic carbon during flood events in a large agricultural catchment in southwest France

Water draining from a large agricultural catchment of 1 110 km² in southwest France was sampled over an 18‐month period to determine the temporal variability in suspended sediment (SS) and dissolved (DOC) and particulate organic carbon (POC) transport during flood events, with quantification of fluxes and controlling factors, and to analyze the relationships between discharge and SS, DOC and POC. A total of 15 flood events were analyzed, providing extensive data on SS, POC and DOC during floods. There was high variability in SS, POC and DOC transport during different seasonal floods, with SS varying by event from 513 to 41 750 t; POC from 12 to 748 t and DOC from 9 to 218 t. Overall, 76 and 62% of total fluxes of POC and DOC occurred within 22% of the study period. POC and DOC export from the Save catchment amounted to 3090 t and 1240 t, equivalent to 1·8 t km^?2 y^?1 and 0·7 t km^?2 y^?1, respectively. Statistical analyses showed that total precipitation, flood discharge and total water yield were the major factors controlling SS, POC and DOC transport from the catchment. The relationships between SS, POC and DOC and discharge over temporal flood events resulted in different hysteresis patterns, which were used to deduce dissolved and particulate origins. In both clockwise and anticlockwise hysteresis, POC mainly followed the same patterns as discharge and SS. The DOC‐discharge relationship was mainly characterized by alternating clockwise and anticlockwise hysteresis due to dilution effects of water originating from different sources in the whole catchment. Copyright © 2011 John Wiley & Sons, Ltd.     

Towards understanding organic matter fluxes and reactivity in surface waters: Filtering impact on DOC and POC degradation

Peatlands cover a very small area of the Earth, but store globally significant quantities of carbon and export disproportionate quantities of fluvial organic carbon, especially when the peatlands are degraded or disturbed. Peatland headwater catchments with high concentrations of dissolved and particulate organic carbon (DOC and POC) provide an opportunity to investigate the possibility of competing effects that could lead to enhanced or diminished turnover of DOC in the presence of POC. Both POC and DOC can be degraded by light and microbes, producing smaller molecules and releasing CO₂ and CH₄ to the atmosphere, and POC can inhibit light penetration, stabilize DOC by providing adsorption sites and providing surfaces for microbes to interact with DOC. However, the majority of peatland fluvial carbon studies are conducted using filtered water samples, and measure only the DOC concentration, so the impact of the particulate organic matter (POM) on in-stream processing of organic carbon is relatively unknown. It is therefore possible that studies have underestimated carbon transformations in rivers as they have not considered the interaction of the particulate material on the dissolved concentrations; there could be higher losses than previously estimated, increasing the contribution of peatland headwaters to GHG emissions. In this study, we assessed if the current approach of DOC degradation studies accurately represent the impact of POM on DOC degradation, by quantifying DOC production from POM, and therefore POC, over time in water with manipulated POM concentrations. Both filtered and unfiltered water lost 60% of the DOC over 70 hours, whereas the treatment with additional POM lost only 35%. The results showed that filtering does not significantly impact the DOC degradation rates; however, when the POC concentration was doubled, there was a significant reduction in DOC degradation, suggesting that filtering would still be necessary to get accurate rates of DOC transformations in waters with high POC concentrations.     

Fluvial carbon export and CO2 efflux in representative nested headwater catchments of the eastern La Plata River Basin

This study involved a baseline evaluation of fluvial carbon export and degas rates in three nested rural catchments (1 to 80 km²) in Taboão, a representative experimental catchment of the Upper Uruguay River Basin. Analyses of the carbon content in stream waters and the catchment carbon yield were based on 4‐year monthly in situ data and statistical modeling using the United States Geological Survey load estimator model. We also estimated p CO₂ and degas fluxes using carbonate equilibrium and gas‐exchange formulas. Our results indicated that the water was consistently p CO₂ saturated (~90% of the cases) and that the steep terrain favors high gas evasion rates. The mean calculated fluvial export was 5.4 tC·km^?2·year^?1 with inorganic carbon dominating (dissolved inorganic carbon:dissolved organic carbon ratio >4), and degas rates (~40 tC km^?2·year^?1) were nearly sevenfold higher than the downstream export. The homogeneous land use in this nested catchment system results in similar water‐quality characteristics, and therefore, export rates are expected to be closely related to the rainfall–runoff relationships at each scale. Although the sampling campaigns did not fully reproduce storm‐event conditions and related effects such as flushing or dilution of in‐stream carbon, our results indicated a potential link between dissolved inorganic carbon and slower hydrological pathways related to subsurface water storage and movement.     

EXPORTS OF ORGANIC CARBON IN BRITISH RIVERS

This study provides the first detailed estimate of riverine organic carbon fluxes in British rivers, as well as highlighting major gaps in organic carbon data in national archives. Existing data on organic carbon and suspended solids concentrations collected between 1989 and 1993, during routine monitoring by the River Purification Boards (RPBs) in Scotland and the National River Authorities (NRAs) in England and Wales, were used with annual mean flows to estimate fluxes of dissolved and particulate organic carbon (DOC and POC) in British rivers. Riverine DOC exports during 1993 varied from 7·7–103·5 kg ha⁻¹ year⁻¹, with a median flux of 31·9 kg ha⁻¹ year⁻¹ in the 85 rivers for which data were available. There was a trend for DOC fluxes to increase from the south and east to the north and west. A predictive model based on mean soil carbon storage in 17 catchments, together with regional precipitation totals, explained 94% of the variation in the riverine DOC exports in 1993. This model was used to predict riverine DOC fluxes in regions where no organic carbon data were available. Calculated and predicted fluxes were combined to produce an estimate for exports of DOC to tidal waters in British rivers during 1993 of 0·68±0·07 Mt. Of this total, rivers in Scotland accounted for 53%, England 38% and Wales 9%. Scottish blanket peats would appear to be the largest single source of DOC exports in British rivers. An additional 0·20 Mt of organic carbon were estimated to have been exported in particulate form in 1993, approximately two–thirds of which was contributed by English rivers. It is suggested that riverine losses of organic carbon have the potential to affect the long-term dynamics of terrestrial organic carbon pools in Britain and that rivers may regulate increases in soil carbon pools brought about by climate change. © 1997 by John Wiley & Sons, Ltd.     

Organic carbon transport in the Songhua River,NE China: Influence of land use

Carbon transported by rivers is an important component of the global carbon cycle. Here, we report on organic carbon transport along the third largest river in China, the Songhua River, and its major tributaries. Water samples were collected seasonally or more frequently to determine dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations and C/N and stable carbon isotopic ratios. Principal component analysis and multiple regression analysis of these data, in combination with hydrological records for the past 50 years, were used to determine the major factors influencing the riverine carbon fluxes. Results indicate that the organic carbon in the Songhua River basin is derived mainly from terrestrial sources. In the 2008–2009 hydrological year, the mean concentrations of DOC and POC were 5.87 and 2.36 mg/L, and the estimated fluxes of the DOC and POC were 0.30 and 0.14 t·km^?2·year^?1, respectively. The riverine POC and DOC concentrations were higher in subcatchments with more cropland, but the area‐specific fluxes were lower, owing to decreased discharge. We found that hydrological characteristics and land‐use type (whether forest or cropland) were the most important factors influencing carbon transport in this system. Agricultural activity, particularly irrigation, is the principal cause of changes in water discharge and carbon export. Over the last 50 years, the conversion of forest to cropland has reduced riverine carbon exports mainly through an associated decrease in discharge following increased extraction of water for irrigation.     

Controls on fluvial carbon efflux from eroding peatland catchments

Global peatlands store an unparalleled proportion of total global organic carbon but it is vulnerable to erosion into fluvial systems. Fluvial networks are being recognized as areas of carbon transformation, with eroded particulate organic carbon processed to dissolved organic carbon and CO₂. Existing studies indicate biodegradation and photodegradation as key processes controlling the transformation of organic carbon in fluvial systems, with initial concentrations of dissolved organic carbon (DOC) identified as a control on the rate of carbon mineralization. This study manipulates temperature and incident light intensity to investigate carbon mineralization rates in laboratory simulations of peatland sediment transport into fluvial systems. By directly measuring gaseous CO₂ emissions from sampled stream water, the relationship of temperature and light intensity with carbon efflux is identified. In simulations where sediment (as particulate organic matter, POM) is absent, temperature is consistently the dominant factor influencing carbon efflux rates. This influence is independent of the initial DOC concentration of the water sample. In simulations where POM was added, representing a peatland river receiving eroded terrestrial sediment, initial DOC concentration predicts 79% of the variation in total gaseous carbon efflux whereas temperature and light intensity predict 12% and 3%, respectively. When sampled stream water's mineralization rates in the presence of added POM are analysed independently, removing DOC as a model variable, the dominant variable affecting CO₂ efflux is opposite for each sample. This study presents novel data suggesting peatland erosion introduces further complexity to dynamic stream systems where rates of carbon transformation processes and the influence of specific environmental variables are interdependent. Anthropogenic climate change is identified as a leading risk factor perpetuating peatland erosion; therefore, understanding the fate of terrestrial sediment in rivers and further quantifying the benefits of protecting peatland soils will be of increasing importance to carbon budgeting and ecosystem function studies.     

Heat as a tracer to estimate dissolved organic carbon flux from a restored wetland

Heat was used as a natural tracer to characterize shallow ground water flow beneath a complex wetland system. Hydrogeologic data were combined with measured vertical temperature profiles to constrain a series of two-dimensional, transient simulations of ground water flow and heat transport using the model code SUTRA (Voss 1990). The measured seasonal temperature signal reached depths of 2.7 m beneath the pond. Hydraulic conductivity was varied in each of the layers in the model in a systematic manual calibration of the two-dimensional model to obtain the best fit to the measured temperature and hydraulic head. Results of a series of representative best-fit simulations represent a range in hydraulic conductivity values that had the best agreement between simulated and observed temperatures and that resulted in simulated pond seepage values within 1 order of magnitude of pond seepage estimated from the water budget. Resulting estimates of ground water discharge to an adjacent agricultural drainage ditch were used to estimate potential dissolved organic carbon (DOC) loads resulting from the restored wetland. Estimated DOC loads ranged from 45 to 1340 g C/(m2 year), which is higher than estimated DOC loads from surface water. In spite of the complexity in characterizing ground water flow in peat soils, using heat as a tracer provided a constrained estimate of subsurface flow from the pond to the agricultural drainage ditch.     

Groundwater flushing of solutes at wetland and hillslope positions during storm events in a small glaciated catchment in western New York,USA

While the role of groundwater in flushing of solutes has long been recognized, few studies have explicitly studied the within‐event changes in groundwater chemistry. We compared the changes in groundwater chemistry during storm events for a wetland and hillslope position in a small (1·5 ha) glaciated, forested catchment in western New York. Flushing responses for dissolved organic carbon (DOC) and nitrogen (DON), nitrate (NO₃) and sulfate (SO₄) in wetland and hillslope groundwaters were also compared against the corresponding responses in stream water. Eight storm events with varying intensity, amount, and antecedent moisture conditions were evaluated. Solute flushing patterns for wetland and hillslope groundwaters differed dramatically. While DOC concentrations in wetland groundwater followed a dilution trend, corresponding values for hillslope groundwater showed a slight increase. Concentrations for NO₃ in wetland groundwater were below detection limits, but hillslope groundwaters displayed high NO₃ concentrations with a pronounced increase during storm events. Flushing responses at all positions were also influenced by the size of the event and the time between events. We attributed the differences in flushing to the differences in hydrologic flow paths and biogeochemical conditions. Flushing of the wetland did appear to influence storm‐event stream chemistry but the same could not be said for hillslope groundwaters. This suggests that while a variety of flushing responses may be observed in a catchment, only a subset of these responses affect the discharge chemistry at the catchment outlet. Copyright © 2009 John Wiley & Sons, Ltd.     

Interactions and connectivity between runoff generation processes of different spatial scales

Monitoring runoff generation processes in the field is a prerequisite for developing conceptual hydrological models and theories. At the same time, our perception of hydrological processes strongly depends on the spatial and temporal scale of observation. Therefore, the aim of this study is to investigate interactions between runoff generation processes of different spatial scales (plot scale, hillslope scale, and headwater scale). Different runoff generation processes of three hillslopes with similar topography, geology and soil properties, but differences in vegetation cover (grassland, coniferous forest, and mixed forest) within a small v‐shaped headwater were measured: water table dynamics in wells with high spatial and temporal resolution, subsurface flow (SSF) of three 10 m wide trenches at the bottom of the hillslopes subdivided into two trench sections each, overland flow at the plot scale, and catchment runoff. Bachmair et al. ( 2012 ) found a high spatial variability of water table dynamics at the plot scale. In this study, we investigate the representativity of SSF observations at the plot scale versus the hillslope scale and vice versa, and the linkage between hillslope dynamics (SSF and overland flow) and streamflow. Distinct differences in total SSF within each 10 m wide trench confirm the high spatial variability of the water table dynamics. The representativity of plot scale observations for hillslope scale SSF strongly depends on whether or not wells capture spatially variable flowpaths. At the grassland hillslope, subsurface flowpaths are not captured by our relatively densely spaced wells (3 m), despite a similar trench flow response to the coniferous forest hillslope. Regarding the linkage between hillslope dynamics and catchment runoff, we found an intermediate to high correlation between streamflow and hillslope hydrological dynamics (trench flow and overland flow), which highlights the importance of hillslope processes in this small watershed. Although the total contribution of SSF to total event catchment runoff is rather small, the contribution during peak flow is moderate to substantial. Additionally, there is process synchronicity between spatially discontiguous measurement points across scales, potentially indicating subsurface flowpath connectivity. Our findings stress the need for (i) a combination of observations at different spatial scales, and (ii) a consideration of the high spatial variability of SSF at the plot and hillslope scale when designing monitoring networks and assessing hydrological connectivity. Copyright © 2013 John Wiley & Sons, Ltd.     

Using hydrogeochemical signatures of stream water to assess pathways for rainfall events: towards a predictive model

Thanks to its simple division into agricultural and forestry land use, the Corbeira catchment (Galicia, Spain) is used as a case study to build a predictive model using hydrogeochemical signatures. Stream data acquired under recessional flow conditions over a one year period were obtained from a sampling station near the downstream end of the catchment, and using principal component analysis, it is shown that some of the analytical parameters are covariant, and some are negatively correlated. These findings support inferences about the pathways of rainfall in the catchment. Specific signatures may be associated with the dominant hydrological source, either surface runoff or subsurface waters: additionally, the dominant land use in that part of the catchment, where the flow originated, can also be predicted. The dominant runoff shows a strong covariance between suspended solids (SS) and particulate phosphorus (PP), with a clear negative correlation with pH. Dissolved organic carbon (DOC) data are associated with this covariant set when these compounds are available in the soils in question. Dissolved phosphorus, total organic nitrogen and dissolved nitrates are also associated with the same covariant set when the runoff flows through areas of extensive agricultural use. The SS ? PP covariance is less significant at lower flows. Typical base flow regimes show a significant covariance between salinity and pH, with a marked negative correlation with SS ? PP set, confirming the dominance of subsurface waters in the baseflow, as expected. Seasonally divergent DOC ? SS behaviour proves to be a useful tracer for rainfall regimes. The DOC trend shows a sinusoidal annual variation in amplitude, determined by the rainfall regime. As a result, flow from the catchment is dominated by surface water whenever there is synchronicity between the peaks of DOC and SS. Copyright © 2013 John Wiley & Sons, Ltd.     

Organic carbon fluxes from the upper Yangtze basin: an example of the Longchuanjiang River,China

To investigate the effects of anthropogenic activity, namely, land use change and reservoir construction, on particulate organic carbon (POC) transport, we collected monthly water samples during September 2007 to August 2009 from the Longchuanjiang River to understand seasonal variations in the concentrations of organic carbon species and their sources and the yield of organic and inorganic carbon from the catchment in the Upper Yangtze basin. The contents of riverine POC, total organic carbon and total suspended sediment (TSS) changed synchronously with water discharge, whereas the contents of dissolved organic carbon had a small variation. The POC concentration in the suspended sediment decreased non‐linearly with increasing TSS concentration. Higher molar C/N ratio of particulate organic matter (average 77) revealed that POC was dominated by terrestrially derived organic matter in the high flows and urban wastewaters in the low flows. The TSS transported by this river was 2.7 × 10⁵ t/yr in 2008. The specific fluxes of total organic carbon and dissolved inorganic carbon (DIC) were 5.6 and 6 t/km²/yr, respectively, with more than 90% in the high flow period. A high carbon yield in the catchment of the upper Yangtze was due to human‐induced land use alterations and urban wastes. Consistent with most rivers in the monsoon climate regions, the dissolved organic carbon–POC ratio of the export flux was low (0.41). Twenty‐two percent (0.9 t/km²/yr) of POC out of 4 t/km²/yr was from autochthonous production and 78% (3.1 t/km²/yr) from allochthonous production. The annual sediment load and hence the organic carbon flux have been affected by environmental alterations of physical, chemical and hydrological conditions in the past 50 years, demonstrating the impacts of human disturbances on the global and local carbon cycling. Finally, we addressed that organic carbon flux should be reassessed using adequate samples (i.e. at least two times in low‐flow month, four times in high‐flow month and one time per day during the flood period), daily water discharge and sediment loads and appropriate estimate method. Copyright © 2011 John Wiley & Sons, Ltd.