Catchment Sources Research Articles

Influences of the landscape pattern on riverine nitrogen exports derived from legacy sources in subtropical agricultural catchments

Changes in the landscape pattern can disturb legacy nitrogen (N) release by influencing hydrological and biogeochemical processes; thus, understanding the effects of landscape patterns on riverine N exports from legacy sources is critical for preparing water quality improvement strategies. In this study, an empirical statistical model that incorporates the net anthropogenic nitrogen input (NANI), runoff coefficient, and residential land area percentage was used to quantify the contribution of legacy sources to annual riverine ammonium nitrogen (NH4+–N), nitrate nitrogen (NO3−–N), and total nitrogen (TN) exports in eight adjacent agricultural catchments in subtropical southern China. The results indicated that annual riverine NH4+–N, NO3−–N, and TN exports from legacy sources ranged from 0.36–1.03, 3.09–4.89, and 3.94–6.79 kg ha−1 year−1, respectively, during the 2012–2017 period. Redundancy analysis (RDA) was used to analyze the interactions between legacy N release and landscape metrics at both the landscape and class levels. The RDA results suggested that higher dispersion, lower shape complexity, and greater heterogeneity in landscape patches can enhance the release of legacy N at the landscape level. In agricultural and residential areas, higher release of legacy N was associated with patches that are unfragmented and have a low shape complexity, whereas in woodland areas, the opposite was true. These analyses provide scientific support for preparing legacy N control strategies from the perspective of landscape ecology.

Approaches to herbicide (MCPA) pollution mitigation in drinking water source catchments using enhanced space and time monitoring

Freshwater occurrences of the selective acid herbicide 2-methyl-4-chloro-phenoxyacetic acid (MCPA) are an ongoing regulatory and financial issue for water utility industries as the number and magnitude of detections increase, particularly in surface water catchments. Assessments for mitigating pesticide pollution in catchments used as drinking water sources require a combination of catchment-based and water treatment solutions, but approaches are limited by a lack of empirical data. In this study, an enhanced spatial (11 locations) and temporal (7-hourly to daily sampling) monitoring approach was employed to address these issues in an exemplar surface water source catchment (384 km2). The spatial sampling revealed that MCPA was widespread, with occurrences above the 0.1 μg L−1 threshold for a single pesticide being highly positively correlated to sub-catchments with higher proportions of ‘Improved Grassland’ land use (r = 0.84). These data provide a strong foundation for targeting catchment-based mitigation solutions and also add to the debate on the ecosystems services provided by such catchments. Additionally, of the 999 temporal samples taken over 12 months from the catchment outlet, 25% were above the drinking water threshold of 0.1 μg L−1. This prevalence of high concentrations presents costly problems for source water treatment. Using these data, abstraction shutdowns were simulated for five scenarios using hydrometeorological data to explore the potential to avoid intake of high MCPA concentrations. The scenarios stopped abstraction for 4.2–9.3% of the April–October period and reduced intake of water containing over 0.1 μg L−1 of MCPA by 16–31%. This represents an important development for real-time proxy assessments for water abstraction in the absence of more direct pesticide monitoring data.

Sediment-routing controls on sandstone bulk petrographic composition and texture across an ancient shelf: Example from Cretaceous Western Interior Basin, Utah and Colorado, U.S.A.

ABSTRACTSediment-routing controls on sandstone texture and bulk petrography have been evaluated in linked alluvial–coastal–shelfal deposits of the Upper Cretaceous Castlegate Sandstone, Blackhawk Formation, Star Point Sandstone, and Mancos Shale (Western Interior Basin, Utah and Colorado, USA) using thin-section analysis of representative outcrop samples in the context of a high-resolution sequence stratigraphic and paleogeographic framework. The studied strata record deposition from two styles of sediment-routing system within an overfilled foredeep and contiguous intra-continental seaway. First, multiple transverse drainages supplied sand to fluvial, shoreline, and shelf segments of sediment-routing systems characterized by down-dip transport distances of 150–450 km and significant strike-oriented sediment transport along the shoreline. Second, the distal shoreline–shelf segment of an axially supplied sediment-routing system was characterized by sand transport for a distance of c. 300 km.Bulk petrographic composition indicates that transverse sediment-routing systems were sourced from catchments that supplied quartz-rich sand with a subordinate lithic component, while the large axial sediment-routing system was sourced from a catchment(s) supplying slightly more feldspathic sand. Thin-section measurements of mean grain size, sorting, skewness, and ratio of minimum-to-maximum diameter (a proxy for sphericity) are similar for sandstones deposited in fluvial, shoreline, and shelf segments of the transverse sediment-routing systems and in the shoreline–shelf segment of the axial sediment-routing systems, although hydrodynamic sorting is important in locally segregating grain-size populations within each segment. Further, textural analysis of detrital quartz, feldspar, and lithic sand-grain populations shows little evidence of relative change in mean grain size or apparent grain sphericity with downsystem distance, implying that sand-grain populations of different petrographic composition did not undergo significant differential mechanical breakdown during transport. Instead, the textural characteristics of these sand-grain populations are inferred to have been controlled mainly by bedrock lithology and recycling in source catchments. The textural signal of sediment-source areas then propagated downsystem in the sand fraction of detrital sediment supply. This inference is supported by the fine- to medium-grained, well- to very well-sorted character of all sandstone samples, consistent with recycling of sandstones and quartzites from the Sevier fold-and-thrust belt.

Middle–Late Triassic evolution of the Jameson Land Basin, East Greenland

AbstractThe Jameson Land Basin lies within the Greenland–Norway rift, to the south of Triassic basins on the Halten Bank and East Greenland shelf, and can therefore offer insights into the development of these less-well-documented offshore basins and the wider North Atlantic. This study focuses on the stratigraphic development of the Jameson Land Basin. Broad-scale stratigraphic logging is augmented with heavy mineral analysis that constrains the dominant source catchments during this period. A thickness of over 1.5 km of Middle–Late Triassic strata fill the Jameson Land Basin, predominantly comprising continental deposits laid down during arid to semi-arid climatic conditions. The basal Pingo Dal Group thickens westwards into the Stauning Alper Fault, forming a typical syn-rift succession. Thickness variations have also highlighted the presence of an intrabasinal high and an associated unconformity between the Pingo Dal Group and the overlying Gipsdalen Group, which provides the first direct evidence for Middle–Late Triassic rifting in East Greenland. Thickness variations in the overlying Gipsdalen Group are more subdued, and the Fleming Fjord Group, and its formations, display remarkably tabular geometries, with little evidence for significant lateral facies variance; this is suggestive of reduced topography and a more regional thermal subsidence signature. Provenance data indicate sediment sourcing from both the western and eastern basin margins during the deposition of the Pingo Dal Group, above which the western source area becomes dominant, alongside some axial input from the south.

Impact of Freeze-Thaw Cycles on Die-Off of E. coli and Intestinal Enterococci in Deer and Dairy Faeces: Implications for Landscape Contamination of Watercourses.

Characterising faecal indicator organism (FIO) survival in the environment is important for informing land management and minimising public health risk to downstream water users. However, key gaps in knowledge include understanding how wildlife contribute to catchment-wide FIO sources and how FIO survival is affected by low environmental temperatures. The aim of this study was to quantify E. coli and intestinal enterococci die-off in dairy cow versus red deer faecal sources exposed to repeated freeze–thaw cycles under controlled laboratory conditions. Survival of FIOs in water exposed to freeze–thaw was also investigated to help interpret survival responses. Both E. coli and intestinal enterococci were capable of surviving sub-freezing conditions with the faeces from both animals able to sustain relatively high FIO concentrations, as indicated by modelling, and observations revealing persistence in excess of 11 days and in some cases confirmed beyond 22 days. Die-off responses of deer-derived FIOs in both faeces and water exposed to low temperatures provide much needed information to enable better accounting of the varied catchment sources of faecal pollution and results from this study help constrain the parameterisation of die-off coefficients to better inform more integrated modelling and decision-making for microbial water quality management.

Agricultural land is the main source of stream sediments after conversion of an African montane forest

In many parts of Africa, soil erosion is an important problem, which is evident from high sediment yields in tropical montane streams. Previous studies in Kenya pointed to a large contribution from catchments cultivated by smallholder farmers. This led to the hypothesis that unpaved tracks and gullies are the main sediment sources in smallholder agriculture catchments of the highlands of Kenya. The aim of this study was to investigate the sediment sources with sediment fingerprinting to generate the knowledge base to improve land management and to reduce sediment yields. Four main sediment sources (agricultural land, unpaved tracks, gullies and channel banks) and suspended sediments were analysed for biogeochemical elements as potential tracers. To apportion the catchments target sediment to different sources, we applied the MixSIAR un-mixing modelling under a Bayesian framework. Surprisingly, the fingerprinting analysis showed that agricultural land accounted for 75% (95% confidence interval 63–86%) of the total sediment. Channel banks contributed 21% (8–32%), while the smallest contributions to sediment were generated by the unpaved tracks and gullies with 3% (0–12%) and 1% (0–4%), respectively. Erosion management strategies should target agricultural lands with an emphasis on disconnecting unpaved tracks form hillslope source areas to reduce sediment yields to Lake Victoria.

Revealing soil erosion characteristics using deposited sediment sources in a complex small catchment in the wind-water erosion crisscross region of the Chinese Loess Plateau

Sediment sources in catchments under the control of check dams in the wind-water erosion crisscross region are more complicated compared to other regions on the Chinese Loess Plateau. This is due to their general complexity, which mainly results from variation in soil, landform, vegetation, and erosion agents. Accordingly, we used the composite fingerprinting approach to trace sediment sources in a typical small catchment in this region. The aim was to reveal the erosion characteristics of the catchment throughout the trapping history of the check dam. Sediment sources were classified into three-source (paleosol, loess and sand) and four-source (paleosol-gully, loess-gully, slope bare of sand and slope covered by sand) groups on the basis of soil and landform types, respectively. Sediment sources throughout the whole trapping history of the check dam (1978–2010) could be classified into three stages according to variation in sedimentation rate. Results showed that depositional sediment in the check dam was primarily from gullies (averaging 80.1%), especially the paleosol-gully (>54.1%). The large contribution of gullies indicated that the main erosion agents were streamflow from rainstorm events and gravity. Coal mining also had a significant impact on contribution of sediment sources, especially for slopes. Since 1987, mining began to change the structure of hills in this region, leading to slope fissures, collapse, and landslides at junctions where gullies meet slopes, which increased the risk of slope erosion. This has caused an increase in sediment from slopes bare of sand distributed under condition of continues implementation of soil conservation measures, which converted sloping cropland into grassland or forest. Further studies are necessary to gain better insight into sediment transport and deposition within such complex environments, as well as to distinguish between the effects of multiple erosion agents.

Fingerprinting sediment sources in a typical karst catchment of southwest China

Due to the complex hydrogeological conditions in karst regions, it is difficult to measure sediment source contributions at a catchment scale directly. The objective of this study was to quantify the relative contributions of sediment sources and their temporal variability in a karst catchment in southwest China. Karst depressions can trap eroded sediment similar to a dam or reservoir and, thus, are representative and typical test beds for identifying sediment sources in karst regions. Three sediment cores were taken from a karst depression, 58 soil samples from three potential sediment sources were collected, and 18 soil properties were analyzed. The relative contributions of cropland, forestland, and fissure or crack soils were calculated using a multivariate mixing model. The fingerprinting results demonstrated that the cropland was the main sediment source in karst catchment. Specifically, according to the mean sediment contributions of the three deposited sediment cores, the sediment contribution from cropland topsoil was 69.3%, varying from 46.9% to 92.3%, and forestland soil and crack soil accounted for 8.6% and 22.1% of the sediment yield, and varying from 2.8% to 16.5% and 4.8%–36.6%, respectively. This result indicated that great attention should be paid when using only a single core to quantify sediment provenance. Due to the deposited sediment was generally disturbed as cropland in the karst depression, the area that has not been disturbed in recent decades in depression was more appropriate to trace sediment sources in karst catchment. To the best of our knowledge, this study was the first to quantify the contributions of sediment sources in the karst catchment of southwest China. This study provides valuable information and a preliminary reference for applying a composite fingerprinting technique to quantify sediment sources in karst catchments.

Particle-water interactions of bismuth under simulated estuarine conditions

Although the production and usage of bismuth (Bi) have been increasing, very little is known about the environmental behaviour of this heavy metal. In the present study, the particle-water interactions of Bi are examined under controlled conditions in which the metal is added as a tracer to estuarine sediment suspended in different, environmentally-relevant aqueous solutions. Adsorption isotherms were always linear over the Bi concentration range employed (up to 2000 μg L−1) and sediment-water distribution coefficients derived from isotherm gradients, KD (L kg−1), displayed an inverse dependence on pH in river water (and ranging from KD = 106,000 L kg−1 at pH 5.0 to KD = 17,700 L kg−1 at pH 9.0) that were consistent with the adsorption of hydroxo-complexes to the sediment surface. Higher adsorption in ultra-pure water of the same pH as river water and an order of magnitude increase in adsorption in seawater at pH 8.0 (KD = 1,530,000 L kg−1) and 0.7 M NaNO3 at pH 6.5 (KD = 4,290,000 L kg−1), however, required the presence of additional species or processes that are likely related to organic complexation of the metal. Thus, experiments conducted in mixtures of river water and seawater in the absence of sediment suggested that Bi may also be bound to colloidal organic molecules that undergo flocculation and salting out on estuarine mixing. Compared with other metals studied under similar conditions, Bi displays a high reactivity towards sediment particles and is, therefore, predicted to be retained in estuaries to a significant extent from catchment sources.

A Structural Equation Model of Success in Drinking Water Source Protection Programs

The management structures put in place for the protection of drinking water sources are multifaceted and include a range of government agencies, landholders and regulatory agencies. While source protection is widely practiced in the water industry, there is limited research on underlying constructs that support successful outcomes in drinking water source protection (DWSP) programs. This study builds on current research by further investigating the following proposed critical success factors (CSFs) for source protection: CSF1: policy and government agency support of source protection; CSF2: catchment condition information and risk monitoring; CSF3: support of operational field activities; and CSF4: response to water quality threats. This study uses structural equation modeling (SEM) to confirm the associations amongst the four CSFs. The results show that policy and government agency support for DWSP has a significant influence over how water service providers (WSPs) plan operational activities for risk management. This emphasizes the importance of the role policy and government agencies have in supporting DWSP. The relationships between the CSFs, which typically fall under the responsibility of WSPs, show that information on catchment condition influences operational activities for risk management, and these mediate the influence over response to water quality threats. The response to threats also showed a strong relationship with the function of monitoring catchment risk. The resulting SEM framework provides new insights into the underlying structures that influence outcomes in catchment management and source protection.

Mineral Magnetic and Geochemical Mapping of the Wular Lake Sediments, Kashmir Valley, NW Himalaya

This study presents major element geochemistry, mineral magnetism and textural analysis of lake-bottom sediments collected from the Wular Lake located in the Kashmir Valley (northwest Himalaya). Connected to the Jhelum River, Wular Lake basin occupies ~ 75% watershed area of the valley, covering ~ 10,196 km2, and makes it the major depo-centre for Kashmir Valley. The sediments represent dominant silt fraction with TiO2, MgO, Fe2O3 and MnO enrichment; and depletion of Na2O and P2O5 with reference to upper continental crust. The average CIA (64.17%) reflects moderate chemical weathering of the catchment source rocks. The mineral magnetic mapping identified distinct domains of restricted/reducing and well-ventilated/oxic conditions, illustrating spatial environmental variability within the lake-bottom environments. The geochemical and mineral magnetic mapping therefore provides a baseline reference for emerging climate and anthropogenic changes being experienced in the Kashmir Valley.

Utilising geochemical data for the identification and characterisation of mineral exploration sample media within cover sequence materials

A first pass workflow for placing cover sequence materials into four broad lithological groups using A–CNK–FM (Al2O3–CaO + Na2O + K2O–Fe2O3+MgO) and A–CN–K (Al2O3–CaO + Na2O–K2O) ternary diagrams in conjunction with the SiO2 vs Al2O3, Fe2O3 and CaO plus the Ca versus Sr XY diagrams has been derived from lithological logging and laboratory whole-rock geochemistry of 2346 samples. These lithological groups include siliciclastics (quartz sands and clays), weathered material, carbonate lithologies (marine limestone, pedogenic carbonate and compositions intermediate between the two end members) and ferruginous lithologies (including ferricrete and ferruginous sediments). Depositional, weathering and groundwater processes influence sample geochemistry during or after the formation of the material and will influence where the sample will plot on the geochemical diagrams used in this study. Geochemical data for discrete lithologies targeted during sampling (e.g. carbonate lithologies) clusters on diagrams used in the geochemical workflow, whereas data from targeted stratigraphic horizons (e.g. basement–cover interface) are more variable. The ability to characterise rock types that are texturally defined using the geochemical workflow is limited. For instance, the geochemistry of diamictite/conglomerate samples is dependent on the matrix versus clast content and composition as well as the source rock and catchment area. This workflow has the potential to be applied in a mineral exploration environment for rapid interpretation of real-time geochemical (e.g. portable XRF) data to gain an understanding of background geochemistry and geochemical signatures that may be related to underlying mineralisation. Key points A workflow for broad lithogeochemcial characterisation of cover sequence materials has been developed. Uses commonly collected major element plus strontium data acquired by laboratory or portable techniques. Categorises materials into siliciclastics, weathered material, carbonate lithologies and ferruginous lithologies. Applications include a mineral exploration environment for interpretation of large geochemical datasets to understand geology and mineralisation vectors.

Detrital zircon U-Pb geochronology of modern Andean rivers in Ecuador: Fingerprinting tectonic provinces and assessing downstream propagation of provenance signals

AbstractRecognizing detrital contributions from sediment source regions is fundamental to provenance studies of active and ancient orogenic settings. Detrital zircon U-Pb geochronology of unconsolidated sands from modern rivers that have source catchments with contrasting bedrock signatures provides insight into the fidelity of U-Pb age signatures in discriminating tectonic provenance and downstream propagation of environmental signals. We present 1705 new detrital zircon U-Pb ages for 15 samples of unconsolidated river sands from 12 modern rivers over a large spatial extent of Ecuador (∼1°N–5°S and ∼79°–77°W).Results show distinctive U-Pb age distributions with characteristic zircon age populations for various tectonic provinces along the Andean convergent margin, including the forearc, magmatic arc, and internal (hinterland) and external (foreland) segments of the fold-thrust belt. (1) Forearc and magmatic arc (Western Cordillera) river sands are characterized by Neogene–Quaternary age populations from magmatic sources. (2) Rivers in the hinterland (Eastern Cordillera) segment of the Andean fold-thrust belt have substantial populations of Proterozoic and Paleozoic ages, representing upper Paleozoic–Mesozoic sedimentary and metasedimentary rocks of ultimate cratonic origin. (3) River sands in the frontal fold-thrust belt (Subandean Zone to Oriente Basin) show distinctive bimodal Jurassic age populations, a secondary Triassic population, and subordinate Early Cretaceous ages representative of Mesozoic plutonic and metamorphic bedrock.Detrital zircon U-Pb results from a single regional watershed (Rio Pastaza) spanning the magmatic arc to foreland basin show drastic downstream variations, including the downstream loss of magmatic arc and hinterland signatures and abrupt introduction and dominance of selected sources within the fold-thrust belt. Disproportionate contributions from Mesozoic crystalline metamorphic rocks, which form high-elevation, high-relief areas subject to focused precipitation and active tectonic deformation, are likely the product of focused erosion and high volumes of local sediment input from the frontal fold-thrust belt, leading to dilution of upstream signatures from the hinterland and magmatic arc.

Using the sediment fingerprinting method to identify the sediment sources in small catchments with similar geological conditions

Traditional fingerprinting methods discriminate sediment sources based on differences in the source geological conditions or land use types. However, whether this method is effective if both the geological conditions and land use types are similar and the circumstances under which the method can be used remain unclear. To further understand the scope of applying the fingerprint identification method, this study selected the Wangjiagou catchment, which consists of subcatchments A and B, as the target. In this catchment, corn (Zea mays L.) was the species with the highest proportion in the dry land. Furthermore, the geological conditions in the catchment are consistent and, the soil is Eutric Regosol developed from the purple rock strata of the Jurassic system. A total of 85 source samples were collected in subcatchments A and B, and 11 sediment samples were collected at the outlets of the each of the subcatchments in the rainy season (from June to October). This research analyzed 48 geochemical elements as the potential fingerprint factors. In this case, the optimum composite fingerprint consisted of five individual properties (Zn, Ce, La, Li and Eu) in subcatchment, whereas four geochemical properties (Mn, La, Ni and Lu) passed the stepwise discriminant function analysis in subcatchment B. These properties exhibited discriminative powers of 100% in the respective subcatchments. The research results indicated the following: first, the multivariate mixing model can provide the contribution rates of each sediment source; second, the goodness of fit (GOF) of this model was greater than 95% in both subcatchments; and third, the sediment uncertainty of each source was within 5% in both subcatchment A and B. These findings indicate that the fingerprinting method can be used in areas with small differences in land use and geological conditions. The results show that great focus needs to paid to soil erosion on slope land in subcatchment A and mulberry fields in subcatchment B. In this area, high-impact human activities (i.e., extensive channel excavation and highly intense machine cultivation) have negated certain soil and water conservation measures. Therefore, in order to reduce soil erosion and ensure that the existing soil and water conservation measures are effective, farmers should implement rational channel management and no tillage or minimal tillage practices. Furthermore, to improve the fertilizer utilization rate of agro-ecosystems, deep fertilizer application and straw return technology should be promoted.

Magnesium isotopes reveal bedrock impacts on stream organisms

Magnesium is an essential element to aquatic organisms and understanding the origin of Mg is important for understanding their growth. Ultimately, Mg in streams is derived from the chemical weathering of bedrock in the catchment. In this study, we used Mg stable isotope ratios (δ26Mg) to test whether stream organisms reflect lithological sources in stream catchments. In November 2017 and May 2018, we sampled aquatic insects and small gobies from six temperate streams in the Lake Biwa area (central Japan). Three of these streams had up to 38% limestone in their catchment (limestone streams), and three streams lacked limestone (non-limestone streams). We hypothesised that stream organisms from limestone streams had significantly lower δ26Mg values compared to those of the same organisms from non-limestone streams. Aquatic insects from limestone streams had an average of 0.78‰ lower δ26Mg values than those of the same organisms from non-limestone streams, thereby indicating a lithological control on the δ26Mg of aquatic insects. Aquatic insects often showed an offset to higher δ26Mg values compared to those of stream water, thereby pointing to a 26Mg-enriched diet as an additional Mg source to water and/or Mg isotope fractionation during Mg accumulation. Instead, stream water was the main Mg source for small gobies, as their bones reflected the δ26Mg of water. We concluded that δ26Mg could trace Mg sources of aquatic organisms, and the same methodology can be applied to other metals.

Freshwater biodiversity conservation through source water protection: Quantifying the potential and addressing the challenges

Abstract Water insecurity is a defining feature of the Anthropocene, with degraded water quality and unreliable flows putting the well‐being of upstream and downstream communities, both human and aquatic, at risk. Within this context, the protection of drinking water at its source – ‘source water protection’ – is growing as a complementary water security solution to conventional built infrastructure, particularly but not only to address non‐point source pollution. An assessment of the likely source catchments of 4000 cities, supplying water to as many as 1.7 billion city dwellers, found that 85% of the total area of the catchments overlaps with freshwater ecoregions of high biodiversity value. Source water protection could contribute to conserving important freshwater biodiversity elements in these catchments, through activities such as land protection, restoration, and agricultural and ranching best‐management practices. Empirical evidence supporting the benefits of these types of activities to freshwater species and ecosystems is sparse, especially when considered at the scales required to achieve meaningful conservation objectives. This article explores the potential of source water protection to deliver freshwater conservation benefits, and solutions are proposed to address the challenges related to evidence gaps, trade‐offs, and financing. The broader opportunity for leveraging water security investments for biodiversity conservation, and the overall efficiencies that may accrue from optimizing for multiple benefits simultaneously, are discussed in the context of global frameworks such as the Sustainable Development Goals.

Fingerprinting changes in source contribution for evaluating soil response during an exceptional rainfall in Spanish pre-pyrenees

In the Mediterranean region, floods are expected to increase as a result of climate change and knowledge of soil erosion hot spots during exceptional rainfalls is required to support mitigation measures. This study quantifies the main sediment sources during an exceptional rainfall event in 2012 (235 mm) at the outlet of two catchments located in NE Spain. To this purpose, suspended sediments were collected during the flood event, complemented with entrapped sediments in mat taken one year after the event. We used fingerprinting methodology and applied the FingerPro unmixing model to estimate the contribution from main sources. The selected tracers clearly distinguished agricultural, rangeland, subsoil and channel banks as the four potential sources in both catchments. In the Vandunchil catchment, the 8 time-integrated suspended sediment samples revealed changes in source contribution during the 2-h sampling sequence. There were relatively high contributions from rangeland, agriculture and subsoil at the beginning of the sampling, representing 30, 40 and 35% of the total source contributions, respectively. Our records captured the delivery of pulses of eroded surface soil transported by runoff with direct connectivity to the stream. The sequence was followed by a sharp increase in channel bank contribution (up to 90%) in comparison to the other sources, reflecting streambank erosion and landslide occurrence, which manifested during the flood. In contrast, in the La Reina catchment, agricultural soils contributed the most (65%) and, together with subsoils (32%), were the main sources. These results reflect the effect of the higher connectivity and slope gradient of these cultivated fields of the La Reina catchment in comparison with those of the Vandunchil catchment.We discuss the possibility of using different properties, such as radionuclides, geochemistry and magnetic measurements, as tracers to distinguish between potential sources during an exceptional event in upland Mediterranean catchments. Our results support the use of fingerprinting techniques to determine variations in source contribution and sediment provenance during flood events, as extreme rainfalls are main drivers of sediment mobilization and key factors in changing landscapes. This is essential in identifying vulnerable hot spots, in which early-stage interventions are needed, and for helping policy makers with management of soil and water resources.

Salmon‐derived nutrient and organic matter fluxes from a coastal catchment in southeast Alaska

Abstract Salmon are important vectors for biogeochemical transport across ecosystem boundaries. Here we quantified salmon contributions to annual catchment fluxes of nutrients (N and P) and organic matter (C, N, and P) from a forested catchment in coastal southeast Alaska. Concentrations of ammonium and soluble reactive phosphorus increased by several orders of magnitude during spawning and were significantly correlated with spawning salmon densities. Nitrate concentrations increased modestly during spawning and were not significantly correlated with salmon densities. Salmon had a modest legacy effect on inorganic N and P as evidenced by elevated streamwater concentrations past the end of the spawning period. Dissolved organic carbon concentrations did not respond to the presence of salmon; however, concentrations of dissolved organic nitrogen and phosphorus showed a significant positive relationship to salmon densities. Changes in spectroscopic properties of the bulk streamwater dissolved organic matter pool indicated that streamwater dissolved organic matter became less aromatic and biolabile during spawning. On an annual basis, salmon were the dominant source of streamwater fluxes of inorganic nutrients, accounting for 92%, 65%, and 74% of annual streamwater fluxes of ammonium, nitrate, and soluble reactive phosphorus, respectively. In contrast, fluxes of organic matter were dominated by catchment sources with salmon accounting for <1% of the annual catchment flux of dissolved organic carbon and 12% and 15% of the annual fluxes of dissolved organic nitrogen and phosphorous respectively. These findings indicate that, in small coastal catchments, salmon can be a quantitatively important source of dissolved streamwater nutrients with implications for productivity in downstream estuarine ecosystems.

Water security in high mountain cities of the Andes under a growing population and climate change: A case study of La Paz and El Alto, Bolivia

Water resources in La Paz and El Alto, Bolivia strongly depend on runoff from mountain catchments in the Cordillera Real, Andes. The balance between the water available from the source catchments and the demand of the cities has become precarious during recent years because of an increasing population and the runoff variability caused by climate change. In this study, a first-order estimate of the future water supply and demand for the El Alto system, the most rapidly growing area in La Paz and El Alto, was obtained for the first time based on a demographic analysis and runoff projection, and effective measures for adapting to water shortage were examined. The water demand in 2036 is expected to increase by 15–53% compared to that of 2011, depending on the scenario for the water loss in the supply system and population estimates, while the projected water supply shows frequent reductions because of the climate variability and decreasing glacial meltwater. Thus, the water transfer from a neighboring system (the Achachicala system) will be indispensable to sustain the supply that cannot be covered by releases from Tuni Lake. Nevertheless, the El Alto system will likely face a serious water shortage after the mid-2020s for the most conservative scenario of demand increase, while large uncertainty was found for the balance of supply and demand, depending on the scenarios for population growth, improvement of water loss, and climate variability and trend. For supply side management, the extended diversion of runoff into Tuni Lake, water transfer from the Achachicala system, and transfer of runoff from the Taypichaca catchment will be effective in securing the water supply under various uncertain conditions.

Environmental Health Risk Assessment of Phthalic Acid Esters in Drinking Water Source Catchments of South China

Environmental Health Risk Assessment of Phthalic Acid Esters in Drinking Water Source Catchments of South China