Total Organic Carbon Loading Research Articles

Spatiotemporal patterns of water volume and total organic carbon concentration of agricultural reservoirs over South Korea

Lacking of available water quality data causes the limited understanding of the coupled dynamics of hydrologic and nutrient cycles in lakes and reservoirs and along river streams. This study conducts the rotated Principal Component Analysis (rPCA) of water volume and total organic carbon (TOC) concentration data from ∼2200 agricultural reservoirs in South Korea to extract the major modes of their spatiotemporal variability. Over 2020–2022, the total TOC load in the reservoirs ranges between 1,165 and 1,492 tons (289 and 360 Mtons of water storage volume; 3.54 and 4.60 mg/L of TOC concentration). The first rPCA mode is assoicated with a decreasing trend of water level (38 % of the explained variance) and increasing trend of TOC concentration (27 %) over the southern Korea region, where the TOC concentration increased during the 2022 drought. The second rPCA mode is associated with interannual variability of water level (25 %) and TOC concentration (18 %) over the central Korea region. This study found a marginal relationship between paddy field area and TOC concentration and their regime shift to high TOC concentration during the 2022 drought, which was a potential cause of the increased TOC concentration in 2022. This study provided observational evidence of interactions between water volume and TOC concentration during a severe drought, suggesting a possible shift of the role of agricultural reservoirs to carbon source.

Response of stream macroinvertebrate communities to forest harvesting in the Piedmont region of North Carolina

Forest disturbances have significant effects on water quality and quantity, river geomorphology, and the ecology of receiving waterbodies. Riparian forests provide numerous functions for aquatic communities including retaining fine sediments and nutrients, controlling water temperature, and providing food sources and habitat for aquatic organisms. Forestry Best Management Practices (BMPs) use riparian forests as buffers to mitigate potential sources of disturbance to aquatic ecosystems from forest management. The objective of this study was to quantify the impacts of timber harvest on stream macroinvertebrates in the Piedmont region. We assessed the changes in macroinvertebrate communities and identified their relationships with specific hydrologic and water quality parameters. We used a paired watershed approach to quantify the response of watershed hydrology and water quality to clearcut forest harvesting with the use of BMPs in the Hill Demonstration Forest and Umstead Research Farm in central North Carolina. We sampled macroinvertebrates and monitored water quality in the first-order streams, and surveyed vegetation within riparian zones one year preharvest (2010) and four years postharvest (2011–2014). We found more sensitive species (indicated by biotic index classifications), scrapers, and Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa from the harvested watershed than in the reference watershed at the Umstead Research Farm site. No differences were detected between the reference and treatment watersheds at the Hill Demonstration Forest site. More sensitive species were present in watersheds with the highest pine basal area and in-stream total organic carbon (TOC) loads. More scrapers were present in watersheds with low hardwood basal area, high stream flow, and more vines. EPT abundance was higher in watersheds with high stream flow, large pine trees, and thick leaf litter layer. EPT abundance was lower in watersheds with large hardwood trees and high TOC loads. Overall, sensitive species, scrapers, and EPT abundance were lower in the Umstead Research Farm reference watershed than in any other watershed. We conclude that, in contrast to similar studies in the region, clearcut harvesting with the use of BMPs did not cause detectable negative effects on macroinvertebrate communities. Moreover, water quality as determined by macroinvertebrates may even be improved in some cases following clearcutting. This study provides a better understanding of how macroinvertebrate communities in Piedmont streams change after harvesting and what watershed characteristics may be driving these changes. This information is useful in characterizing macroinvertebrates in headwaters in the Piedmont, and helps land managers protect aquatic resources across the region.

Biomethane production and microbial strategies corresponding to high organic loading treatment for molasses wastewater in an upflow anaerobic filter reactor.

Molasses wastewater contains high levels of organic compounds, cations, and anions, causing operational problems for anaerobic biological treatment. In this study, an upflow anaerobic filter (UAF) reactor was employed to establish a high organic loading treatment system for molasses wastewater and further investigated the microbial community dynamics in response to this stressful operation. The biogas production increased with an increase in total organic carbon (TOC) loading rate from 1.0 to 14g/L/day, and then it decreased with further TOC loading rate addition until 16g/L/day. The UAF reactor achieved a maximum biogas production of 6800mL/L/day with a TOC removal efficiency of 66.5% at a TOC loading rate of 14g/L/day. Further microbial analyses revealed that both the bacterial and archaeal communities developed multiple strategies to maintain stable operation of the reactor at high organic loading (e.g., Proteiniphilum and Defluviitoga maintained high abundances throughout the operation; Tissierella temporarily dominated the bacterial community at TOC loading rates of 8.0 to 14g/L/day; and multi-trophic Methanosarcina shifted as the dominant methanogen at the TOC loading rates of 8.0 to 16g/L/day). This study presents insights into a high organic loading molasses wastewater treatment system and the microbial flexibility in methane fermentation in response to process disturbances.

Application and evaluation of SWAT-C model to predict TOC loading in the Hwangryong River Watershed

Objectives : This study aims to assess the applicability of the SWAT-C water quality model recently developed to predict in-stream Total Organic Carbon (TOC) in a watershed within South Korea.Methods : The SWAT-C model was tested in the Hwangryong River Watershed. SWAT-C is an advanced version of Soil and Water Assessment Tool (SWAT) to simulate carbon cycling at the watershed scale. The model was simulated for 11 years (2010-2020) consisting of 2-year warm-up (2010-2011), 6-year calibration (2012-2017), and 3-year validation (2018-2020) periods. SWAT-C was calibrated and validated against monthly streamflow and TOC loads. The model performance was evaluated using NSE (Nash-Sutcliffe efficiency), KGE (Kling-Gupta efficiency), and PBIAS (percent bias) Simulated Dissolve Organic Carbon (DOC) and Particulate Organic Carbon (POC) loads were also presented to see the major caron type loaded to the downstream.Results and Discussion : The calibration results showed that SWAT-C could depict streamflow and TOC loads with acceptance model performances (NSE > 0.5, KGE > 0.5 and PBIAS =< 25%). Especially, the seasonal variations of TOC loads were well simulated by SWAT-C. The TOC load was predicted to increase in the summer season with high precipitation and slightly lower in the other seasons. This seasonal pattern is likely caused by frequent heavy rainfall events in summer.Conclusion : This study demonstrated that SWAT-C model is applicable in South Korea with sufficient prediction accuracy. Thus, SWAT-C would serve as an efficient tool to monitor TOC loads in South Korea.

Effects of organic carbon and sulfide on the anammox reaction in the anoxic column in the SRDAPN process for treating high-strength wastewater

Low energy consumption treatment of high-strength wastewater is crucial in controlling groundwater pollution and eutrophication in closed waterbodies. In this study, the sulfate reduction, denitrification/anammox, and partial nitrification (SRDAPN) process, which is an effective organic carbon and nitrogen removal process with low energy consumption for low strength wastewater, was applied to treat livestock wastewater with high COD and sulfate concentration, and microbial reaction and community were examined using an anaerobic–anoxic biological filter reactor that simulates circulation from an aerobic reactor. At a total organic carbon loading rate of 2.7–5.8 kgC/m3·day, sulfate reduction and methane production occurred simultaneously in the anaerobic column of the reactor. Specifically, sulfate reduction resulted in organic matter removal rates of 38 and 26% at ambient temperature and 25 °C, respectively. Furthermore, both heterotrophic and autotrophic denitrification occurred in the anoxic column, and when the organic loading rate in the anoxic reactor was below 0.2 kgC/m3·day, 33%–37% of ammonium and 33%–34% of nitrite were removed by the anammox reaction. Heterotrophic denitrification bacteria (Thauera, Comamonas, and Denitratisoma) and sulfur denitrification bacteria (Sulfurimonas denitrificans) grew in the lower and middle parts of the anoxic column, whereas anammox bacteria (2.5% of Candidatus Brocadia at ambient temperature and 9.4% of Candidatus Kuenenia at 25 °C) grew in the upper part of the anoxic column. These results indicate that the SRDAPN process based on sulfur cycle and anammox is useful for treatment of high strength wastewater with low energy consumption.

Diffuse nutrient export dynamics from accumulated litterfall in forested watersheds with remote sensing data coupled model

Nutrients exported from forest litterfall significantly contribute to the global cycling of elements and the water quality in watersheds. Simulating the watershed discharge load is challenging because of the combined effects of the decomposing litterfall and topographic heterogeneity. We quantified the contribution of diffuse nutrient export from forest litterfall in a low temperature watershed using artificial rainfall experiments and watershed territorial modeling with remote sensing data, and therefore, the critical spatial factors and corresponding nutrient export dynamics were identified. Rainfall intensity and terrain slope were found to be the key factors for nutrient export under different litterfall decomposition conditions. Based on the moderate resolution imaging spectroradiometer data and field observations, the temporal patterns of litterfall biomass of two types of dominant forests (broad-leaved and mixed) were interpreted. The spatial patterns of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) exports from watershed litterfall were simulated by coupling the observed discharge parameters under artificial rainfall conditions and watershed surface flow modeling with the hydrological characteristics of the forested areas. The average watershed TOC, TN, and TP loads exported from the litterfall were approximately 58.22, 7.89, and 0.37 kg ha−1 a−1, respectively. The exported loads of TOC, TN, and TP varied with the forest types, and the loads from the litterfall of deciduous broad-leaved forest were found to be ∼50–70% of loads from the litterfall of mixed forest. A comparison with similar studies worldwide also indicated that low temperature decreased the litterfall decomposition rate and diffuse nutrient export. This study indicated that litterfall nutrients were a key contributor to watershed water pollution, and their spatial discharge trend varied intensively with the terrestrial conditions. The modified simulation methods were found to accurately assess the cycling of nutrients from the forest litterfall on a watershed scale.

Self-generation of low ash carbon microspheres from the hydrothermal supernatant of anaerobic digestate: Formation insights and supercapacitor performance

This work provides the first observations of and insights into the self-generation of carbon microspheres from the supernatant after hydrothermal carbonization of anaerobic digestate has been completed and the hydrochar removed. Solid State NMR and XPS revealed that the carbon microspheres were comprised of decomposed fragments of proteins, carbohydrates and lignin. The carbon microspheres were significantly lower in ash content (3.1%), compared to the hydrothermal solid (41.2%) and precursor (25.2%) and their formation reduced the total organic carbon load of the supernatant. The low ash content allowed them to be easily activated, achieving a surface area of 1711.0 m2 g−1, compared to 51.4 m2 g−1 for the activated hydrothermal solid and 12.8 m2 g−1 for the activated precursor. The microcarbon spheres achieved a specific capacitance from cyclic voltammetry of 86 F g−1 at 100 mV s−1 to 176 F g−1 at 1 mV s−1, while the gravimetric capacitance was 42 F g−1 at 25 A g−1 and 140 F g−1 at 0.5 A g−1 in 0.5 M Li2SO4 and a 1.8V potential window. Overall, this study highlights the importance of exploring this new product and its valorisation potential for the hydrothermal carbonization of ash-rich precursors.

Coastal urbanization alters carbon cycling in Tokyo Bay

The carbon budget of Tokyo Bay, a highly urbanized coastal basin, was estimated using a box model that incorporated inorganic and organic carbon data over an annual cycle (2011–2012). The surface water represented net autotrophic system in which the annual net community production (NCP) was 19 × 1010 gC year−1. The annual loading of dissolved inorganic carbon and total organic carbon (TOC) from freshwater inputs was 11.2 × 1010 and 4.9 × 1010 gC year−1, respectively. The annual TOC sedimentation rate was 3.1 × 1010 gC year−1, similar to the annual air–sea CO2 uptake (5.0 × 1010 gC year−1). Although the NCP and TOC loading from freshwater inputs were respectively 3.0 and 2.7 times lower than those in the 1970s, the TOC sedimentation rate was similar. Therefore, a relatively high carbon efflux from Tokyo Bay likely occurred in the 1970s, including CO2 efflux to the atmosphere and/or export of labile organic carbon to the open ocean. The changes in carbon flow between the 1970s and 2011–2012 resulted from improved water quality due to increased sewage treatment facilities and improved sewage treatment efficiency in the catchment, which decreased the amount of labile organic carbon flowing into the bay.

Performance of a Woodchip Bioreactor for the Treatment of Nitrate-Laden Agricultural Drainage Water in Northeastern Germany

Reactive barriers, such as denitrifying bioreactors, have been identified as a clean-up option for nutrient-laden agriculture runoff. Here we tested a 20 m long, 3.75 m wide and 2.2 m deep woodchip bioreactor receiving tile drainage water from a 5.2 ha field site, aiming at testing the hydraulic functioning of a dual-inlet system and quantifying its impact on nutrient loads (nitrogen, reactive phosphorus, organic carbon) in a region with a drainage season taking place in the hydrological winter (November to April). The hydraulic conditions in the dual-inlet bioreactor system developed differently than expected; asymmetric flow rates led to long average hydraulic retention times and a highly dispersed residence time distribution, which was revealed by a bromide tracer test. With a nitrate load reduction of 51 to 90% over three drainage seasons, the woodchip bioreactor proved at the same time to be very effective under the winter conditions of northeastern Germany. The bioreactor turned from an orthophosphate source in the first year of operation into an orthophosphate sink in the second and third year, which was not expected because of anoxic conditions (favorable for denitrification) prevailing within the woodchips. Besides an efficient nutrient retention, the woodchip bioreactor contributed to the total organic carbon load of receiving waters, which impairs the overall positive role of bioreactors within intensively agriculturally used landscapes. We consider this promising low-maintenance biotechnology particularly suitable for single drainage pipes with high discharge and high nitrate concentrations.

Biotoxicity assessment of in-situ simulated stormwater runoff on typical urban roads in Shenzhen

In order to explore the biological toxicity of urban road stormwater runoff and hence ensure its reuse safety, we comprehensively analyze the toxicity level and the main influential factors of road stormwater runoff. By using <italic>Chlorella pyrenoidasa</italic> as a case study, we explore the toxicity adequacy as a parameter for the stormwater reuse safety assessment. We collect the in-situ simulated runoff samples from twelve typical urban roads in Shenzhen. The results show that deposited sediment load (TS) on urban road surface is not positively correlated with the heavy metal (HM) and total organic carbon (TOC) load attached to the surface. The toxicity of road rainwater runoff to <italic>Chlorella pyrenoidasa</italic> is not closely related to TS, HM and TOC loads. These results confirm that tranditional sponge city rainwater recycling approach for investigating stormwater quality based on particular pollutants is not appropriate. Instead, the combined toxicity given by all pollutants is a preferred option in terms of indicating whether the road stormwater can be reused safely in the process of sponge city construction. According to principal component analysis (PCA) results, industrial areas significantly contribute to the stormwater toxicity compared to other factors. Additionally, heavy metals could contribute more to the toxicity than organic matters. This implies that in sponge city construction, it is important to appropriately reuse stormwater with high toxicity based on the "fit for purposes" theory, as well as paying more attention to the removal of heavy metals.

Decreasing organic carbon bioreactivity in European rivers

Abstract European rivers experience increased loading of total organic carbon (TOC) from terrestrial sources due to factors involving changes in land use, climate and soil acidity. However, little is known about how increased TOC is linked to changes in the bioreactivity of organic matter in these rivers on a continental scale. We compiled paired measurements of TOC and biological oxygen demand in 5‐day 20°C dark incubations from 3,486 EU monitoring rivers. Assuming first‐order decay and a fixed respiratory quotient, annual average TOC and biological oxygen demand values were used to calculate 11,060 values of the decay coefficient k. The k decreased by two orders of magnitude as a power function of increasing TOC. This relationship could partly be explained by carbon quality, as the C:N ratio of the organic matter was the lowest in high‐reactivity low‐TOC rivers, and vice versa. A trend analysis showed that TOC increased by 18% from 1996 to 2012, while k decreased by as much as 50%. As a consequence, the biological oxygen demand in the water decreased over time in spite of the water browning trend (increased TOC). Together, these results suggest that reactivity is low near terrestrial hot spots for TOC export, and low during years with high terrestrial TOC loading, but increases in rivers with low TOC concentrations where internal processes in the water have high relative influence on bulk TOC quality. Thus, browning of European freshwaters is linked to strong decreases in TOC reactivity on a continental scale, suggesting that the impacts of browning on microbial water deoxygenation and greenhouse gas production are less severe than previously thought.

Hydro-climate and biogeochemical processes control watershed organic carbon inflows: Development of an in-stream organic carbon module coupled with a process-based hydrologic model

Dissolved organic carbon (DOC) in surface waters directly influences the speciation, transport, and fate of heavy metals, as well as the partitioning of organic contaminants. However, the lack of process-based watershed-scale models for simulating carbon cycling and transport has limited the effective watershed management to control organic carbon fluxes to source waters and throughout the river systems. Here, a process-based in-stream organic carbon (OC) module was developed, coupled with the physically process-based Soil and Water Assessment Tool (SWAT), and linked with its existing soil carbon module to simulate dynamics of both particulate organic carbon (POC) and DOC. The advanced model simulates a large spectrum of OC processes from landscapes to stream networks throughout the watersheds. In-stream organic carbon processes related to POC and DOC as state variables are modeled in the water column, and the transformations between different carbon species and interactions between OC with algae are considered. The module's ability to simulate total organic carbon (TOC) loads was assessed, and the monthly and seasonal variations were captured over 14 years. Simulations for TOC loads suggested that spring snowmelt and summer rainfall runoff events are the main driving forces behind TOC export in the watershed. The parameter sensitivity analysis and dynamic reaction rate simulated in the streams suggested that TOC dynamics in the study area are controlled by both landscape and in-stream processes. The spatiotemporal analysis of the simulated TOC load showed that 55.8% of total terrestrial OC exports into the streams are removed due to in-stream POC settling and DOC mineralization, confirming the necessity of integrating terrestrial and aquatic OC processes for process understanding and for modelling and management of water quality at the watershed scale. The developed OC module is a potentially effective tool for simulating the OC cycle at the watershed scale and can be applied further to water treatment plans and watershed management.

Multiple anthropogenic drivers behind upward trends in organic carbon concentrations in boreal rivers

Increases of riverine organic carbon concentrations have been observed across the northern hemisphere over the past few decades. These increases are the result of multiple environmental drivers, but the relative importance of the drivers is still unclear. We analyzed a dataset of >10 000 observations of riverine total organic carbon (TOC) concentrations and associated water chemistry and hydrological observations from 1993 to 2017. The observations span a ∼600 km north–south gradient from 30 individual river systems in Finland. Our data show significantly increasing TOC concentrations in 25 out of 30 systems, with an average increase from 12.0 to 15.1 mg l−1. The observed increase in riverine TOC concentrations led to an increase of 0.28 Mt in annual TOC load to the Baltic Sea from 1993 level to 2017 level. We analyzed the role of three putative environmental drivers of the observed TOC trends. Multiple regression analysis revealed that the most common driver was discharge, which alone explained TOC increases in 13 rivers, whereas pH and temperature were less important drivers (sole predictor in one and zero rivers, respectively). Different permutations of these three drivers were also found to be significant; the combination of discharge and pH being the most common (4 rivers). Land use was not in general linked with trends in TOC, except for the proportion of ditched land in the catchment, which was significantly correlated with increases in TOC concentration. Land use showed significant relationships with trends in discharge and pH. We also found that catchment characteristics are regulating the extent of these regional or global environmental changes causing the upward trends of riverine organic carbon.

Trametes versicolor immobilized on rotating biological contactors as alternative biological treatment for the removal of emerging concern micropollutants

White rot fungi have been studied for the removal of micropollutants of emerging concern from wastewater during the last decade. However, several issues need to be overcome for its plausible implementation at full-scale installations such as the addition of supplementary substrates, the partial re-inoculation of fresh fungi or the use of extended hydraulic retention times. This work proposes the immobilization of Trametes versicolor on rotating biological contactors at bench scale (flowrates of 10 L/d and reactor capacity of 10 L) for the treatment of different urban wastewater. This type of bioreactor achieved remarkable reductions of the total organic carbon loading of the wastewater (70–75%) in a wide range of C:N and C:P ratios with limited addition of supplementary substrates, non-refreshment of the fungal biomass and only 1-day of hydraulic retention. The addition of gallic acid as quinone-like mediator and quelated iron and manganese complexes increased the removal of pharmaceutical micropollutants mediated by the so-called advanced bio-oxidation process. The immobilization of Trametes versicolor on rotating biological contactors also showed a remarkable stabilization of the fungi during the continuous treatment of different urban wastewater under non-sterile conditions. Thus, this system is a sound alternative for biological urban wastewater treatment with pharmaceutical removal because overcome all the problems usually associated with the water treatment technologies based on white rot fungi that makes difficult the scaling-up of the process and its implementation in full scale wastewater treatment plants.

Analysis of factors affecting effluent TOC in publicly owned treatment works

Total organic carbon(TOC) was introduced as the water quality index of the rivers and lakes in 2013. This paper evaluated factors affecting effluent TOC concentrations and treated and discharged loads of existing publicly owned treatment works(POTWs). For selected POTWs with greater treatment capacity than 500㎥/day, factorial analysis was used to consider effects of kinds of biological treatment processes, inflow of other types of wastewater(industrial, livestock, landfill leachate wastewater, etc.) with domestic wastewater, sewer separation rate, and effluent discharging zones in which different effluent criteria applied. As a result, those factors did not show significant effect on effluent TOC concentration of POTWs in effluent discharging zone Ⅰ and Ⅱ. However, In effluent discharging zone Ⅲ and Ⅳ, kinds of biological treatment processes, the inclusion of other waste in influent of domestic wastewater, and the sewer separation rate were significant factors. The treated TOC load in POTWs was also not affected significantly by the variables set in this study. On the other hand, those three factors influenced significantly on the TOC load discharged to water bodies. The sum of factorial effects and the contribution rate of three factors to the discharged TOC load was 60.23 and 41%, 59.57 and 41%, and 42.04 and 18%, respectively.

Performance study on organic carbon, total nitrogen, suspended solids removal and biogas production in hybrid UASB reactor treating real slaughterhouse wastewater

The performance of slaughterhouse wastewater treatment was studied in Hybrid Upflow Anaerobic Sludge Blanket Reactor (HUASBR) consisting of polypropylene media as attached growth surface. During acclimation phase, the amount of real slaughterhouse wastewater was gradually increased, whereas the amount of synthetic wastewater was proportionally decreased in a mixed feed to the reactor. The batch performance was evaluated by feeding 1000 ml of raw slaughterhouse wastewater and observing consistent Chemical Oxygen Demand (COD) removal over a batch period of 72 h. After attaining maximum COD removal efficiency and maximum methane gas production, the reactor was operated under continuous mode with gradually increasing Total Organic Carbon (TOC) loading rate. The reactor showed steady increase in the TOC removal efficiency as well as incremental biogas production. In this study, TOC loading rate was varied in the range of (1.12–14.19)kg TOC/m3/d corresponding to decremental Hydraulic Retention Time (HRT) of (24–6) hours. The HUASBR enhanced the TOC removal efficiency in slaughterhouse wastewater up to maximum of 95.85% under the TOC loading rate of 6.97 kg TOC/m3/d for 10 h HRT. The TSS removal efficiency was observed to be in the range of (72–98) % throughout the study. Similarly, The TN removal was also recorded between (48–78) % out of all the continuous operations. The maximum methane gas production rate was observed as 61.5 L/d at 10 h HRT.

APLIKASI PROSES BIOLOGI ANAEROBIK PADA PENGOLAHAN AIR LIMBAH ORGANIK BERKONSENTRASI GARAM TINGGI “STUDI KASUS INDUSTRI UME BOSHI”

Anaerobic treatment of wastewater with high organic and salt content but low pH (TOC, 14 g/l; salt, 150 g/l; pH,2.7) generated during an “ume boshi” manufacturing process was investigated. Five-fold-diluted “ume boshi” effluent was treated by a draw-and-fill method at a volumetric TOC (total organic carbon) loading rate of 3.0 g/l/d with a TOC removal efficiency of 75%. Five-fold-diluted “ome boshi” effluent was also treated in an anaerobic fluidized-bed reactor (AFBR) at a maximum volumetric TOC loading rate of 3.0 g/l/d, which gave almost the same results as the draw-and-fill method. However, ten-fold-diluted “ome boshi” effluent could be treated in the AFBR at a maximum volumetric TOC loading rate of 11 g/l/d with a TOC removal efficiency of 85%. The methane content in the evolved gas was high, being 70%. The red pigment in the “ome boshi” effluent was completely decolorized by the anaerobic treatment. Key words :, Anaerobic fluidized-bed reactor, “Ume boshi”Co2+ and Ni2+ ions, decolorization

Complex patterns of catchment solute–discharge relationships for coastal plain rivers

AbstractRiverine solute versus discharge (C–Q) relationships provide information about the magnitude and dynamics of material fluxes from landscapes. We analysed long‐term patterns of C–Q relationships for 44 rivers in Florida across a suite of geogenic, nutrient, and organic solutes and investigated land cover, watershed size, and surficial geology as controls on these patterns. Solute concentrations generally exhibited far less variability than did discharge, with coherent solute‐specific behaviours repeated across watersheds. Geogenic solutes generally diluted with increasing discharge, whereas organic solutes generally enriched; patterns for nutrients were highly variable across watersheds, but on average exhibited chemostasis. Despite strong evidence of both geologic and land cover controls on solute flow‐weighted concentrations, these variables were poor predictors of C–Q slopes (β) or relative coefficients of variation (CVC:CVQ). CVC:CVQ generally increased with watershed size, and wetland area appeared to influence C–Q patterns for base cations and organic solutes. Perhaps most importantly, we observed significant slope breaks in C–Q association in approximately half of our observations, challenging the generality of using single power functions to describe catchment solute export patterns. For all solutes except phosphorus (P), C–Q slopes decreased above statistically identified breaks (slopes for P increased), with breaks consistently at or near median flow (i.e., 50% flow exceedance probability). This common pattern significantly impacts solute load estimates; failing to account for slope breaks overestimates nitrate and total organic carbon loads as much as 125% and underestimates P loads as much as 35%. In addition to challenging generic power‐law characterization of C–Q relationships for these coastal plain rivers, and exploring the load estimate consequences thereof, our study supports emerging insights about watershed hydrochemical behaviours across a wide array of solutes.

Spatial and temporal patterns of total organic carbon along the Vistula River course (Central Europe)

Various recent trends of river organic matter concentrations and flux have been presented for Northern Hemisphere. The catchment of the Vistula River has been a place of intensive economic transformation since the 1980s, which has been accompanied by increase of extreme weather and hydrological events. The patterns of total organic carbon (TOC) has not yet been studied on Vistula River, the largest Polish river, with a basin area of 194000 km2 and a mean annual flow exceeding 1000 m3s-1. Annual TOC concentrations in the river mouth decreased from 10.7 mgC dm−3 to 7 mgC dm−3 between years 2000–2014; however, during a 55-year period, the TOC decrease was estimated to be 45% as a result of a large scale reduction of waste supply to Polish rivers. The Vistula River annual mean TOC export (flow normalized) was 1.54 gC m−2 and significantly decreased, with a high inter-annual variations depending on hydrology. Gradual decreases of TOC flux were observed along the river continuum from headwaters to downstream. TOC export in wet years was 5 times higher than in dry years, indicating the important role of river flooding and droughts on TOC load to the southern Baltic Sea. Dam reservoir located on the lower part of the Vistula River course have had a large impact on the retention of terrestrial TOC load, reducing annual flux by approximately 20%.

Performance of Two Bioswales on Urban Runoff Management

This study evaluated the effectiveness of two bioswales eight years after construction in Davis, California. The treatment bioswale measured 9 m × 1 m × 1 m (L × W × D). Engineered soil mix (75% native lava rock and 25% loam soil) replaced the native loam soil. Four Red Tip Photinia (Photinia × fraseri Dress) trees and two Blueberry Muffin Hawthorn (Rhaphiolepis umbellata (Thunb.) Makino) shrubs were planted in the bioswale. Runoff flowed into the bioswale from an adjacent 171 m2 panel of turf grass. An identically sized control bioswale consisting of non-disturbed native soil was located adjacent to the treatment bioswale. Surface runoff quantity and quality were measured during three experiments with different pollutant loads. When compared to the control, the treatment bioswale reduced surface runoff by 99.4%, and reduced nitrogen, phosphate, and total organic carbon loading by 99.1%, 99.5%, and 99.4%, respectively. After eight years, tree growth characteristics were similar across both sites.