Effects of wind farm construction on concentrations and fluxes of dissolved organic carbon and suspended sediment from peat catchments at Braes of Doune, central Scotland

This paper assesses the impacts of disturbance associated with the construction of a wind farm on fluxes of dissolved organic carbon (DOC) and suspended sediment from a blanket peat catchment in central Scotland during the period immediately following completion of construction. Six streams draining the site were sampled on six dates from October 2006, when construction was completed, and an additional three control streams to the west of the site were sampled on the same dates. Turbidity and stage were recorded semi-continuously in the two largest streams (one disturbed and one control), which were also sampled during storm events. Absorbance (400 nm) and DOC concentrations were determined on all samples, and suspended sediment was determined on the event samples. Absorbance and DOC were closely correlated in both the disturbed and undisturbed streams, with slightly greater absorbance per unit DOC in the disturbed streams. DOC concentrations in disturbed tributaries were always greater than those in undisturbed streams, with mean differences ranging from 2 to around 5 mg L-1. DOC and stage were positively correlated during events with maximum concentrations in excess of 30 mg L-1 at peak flow. Suspended sediment concentrations were markedly elevated in the disturbed stream with maximum concentrations at peak flow some 4-5 times greater than in the control. The colour of the sediment suggested that it was highly organic in nature at peak flow, and suspended particulate organic carbon represented a further loss of C from the site. Using flow-weighted mean DOC concentrations calculated for the storms monitored in autumn 2007, dissolved carbon losses can be estimated for the catchments of the disturbed and control streams. From these data the additional DOC loss related to disturbance associated with the wind farm is estimated at 5 g m-2

Determining Sources of Dissolved Organic Carbon and Nutrients in an Urban Basin Using Novel and Traditional Methods

Water quality in urban ecosystems is sensitive to localized disturbances potentially affecting those mechanisms which influence nutrient cycles. The Carters Creek Basin has been reported to have elevated concentrations of dissolved organic carbon (DOC). In combination with high terrestrial nutrient export from non-point sources and point source effluent discharge, this has been suggested to contribute to E.Coli recovery and regrowth. Spatial identification of loading “hot-spots” or locations of elevated nutrient concentrations of non-point, terrestrial sources may provide critical information necessary for appropriate mitigation efforts and watershed management. This study used traditional and novel methods for source tracking nutrients and dissolved organic carbon in small urban and rural watersheds in Brazos County, Texas. A nested watershed approach allowed identification of problem areas of nutrient loading. A novel cost-effective technique using diffuse reflectance near-infrared spectroscopy was used to identify sources of DOC. Monthly stream sampling was conducted at 12 sites from 2012 to 2013. Impacts of human activity on landscape features determining source pathways for nutrient retention, transport, and conversion were identified in this study. Higher nitrate-N (0.12-22.8 mg L-1), orthophosphate-P (0.11-3.60mgL-1), and DOC concentrations (18.6-68.1 mg L-1) were found across the watershed than in 2007. Factors such as increased erosion, sodic soil dispersion, land use, and flow conditions wereidentified as possible causes for increased carbon (C), nitrogen (N) and phosphorus (P) observed in the basin. This study supported the use of near-infrared spectroscopy to elucidate watershed sources of carbon. The major sources of DOC into the Carter Creek basin watersheds were leachate from soil and turfgrass. Rural subwatersheds had less complicated source signatures than their urban counterparts. Urban impervious runoff signatures also clustered with stream water signatures, especially during high flow in October and September. These results indicate that specific vegetation such as turfgrass used for landscapes in urban watersheds coupled with sodic irrigation may alter traditional nitrogen, phosphorus and carbon cycling in urbanizing watersheds. Spatial source tracking will enable efficient pollution mitigation and protect water quality as a result of this study

Sub-daily rates of degradation of fluvial carbon from a peat headwater stream

In-stream processing of allochthonous dissolved organic carbon (DOC) and particulate organic carbon (POC) in peat-sourced headwaters has been shown to be a significant part of the terrestrial carbon cycle, through photo- and bio-degradation, with both DOC and POC converted to carbon dioxide (CO2). This study reports a series of 70-h, in situ experiments investigating rates of degradation in unfiltered surface water from a headwater stream in the River Tees, North Pennines, UK. Half the samples were exposed to the normal day/night cycle (ambient); half were continuously dark. The study found that the DOC concentration of samples in the ambient treatment declined by 64 % over the 70 h, compared with 6 % decline for the samples kept in the dark. For POC, the loss in the ambient treatment was 13 %. The average initial rate of loss of DOC in the ambient treatment during the first day of the experiment was 3.36 mg C/l/h, and the average rate of photo-induced loss over the whole 70 h was 1.25 mg C/l/h. Scaling up these losses, the estimate of total organic carbon loss from UK rivers to the atmosphere is 9.4 Tg CO2/year which would be 0.94 % of the global estimate of CO2 emissions from streams and rivers from the 2013 IPCC report. Initial rate kinetics in the light were as high as 3rd order, but the study showed that no single rate law could describe the whole diurnal degradation cycle and that separate rate laws were required for night and day processes. The comparison of dark and ambient treatment processes showed no evidence of photo-stimulated bacterial degradation

Freshwater umbrella - the effects of nitrogen deposition & climate change on freshwaters in the UK

In upland areas of the UK located away from direct human disturbance through agriculture, industrial activities and urban pollution, atmospheric pollution poses one of the major threats to the chemical and biological quality of lakes and streams. One of the most important groups of pollutants is nitrogen (N) compounds, including oxidised forms of N called NOx, generated mainly by fossil fuel combustion especially in motor vehicles, and reduced forms of N (ammonia gas or dissolved ammonium compounds) generated mainly from agricultural activities and livestock. These nitrogen compounds may dissolve in rain or soilwater to form acids, or may be taken up as nutrients by plants and soil microbes in upland catchments, and then subsequently released in acid form associated with nitrate leaching at a later date. It is well established that nitrate leaching contributes to acidification of upland waters, with damage to aquatic ecosystems including plants, invertebrates and fish. However it has recently been suggested that nitrate leaching may also be associated with nutrient enrichment of upland waters that contain biological communities adapted to very low nutrient levels

Upland streamwater nitrate dynamics across decadal to sub-daily timescales: a case study of Plynlimon, Wales

Streamwater nitrate dynamics in the River Hafren, Plynlimon, mid-Wales were investigated over decadal to sub-daily timescales using a range of statistical techniques. Long-term data were derived from weekly grab samples (1984–2010) and high-frequency data from 7-hourly samples (2007–2009) both measured at two sites: a headwater stream draining moorland and a downstream site below plantation forest. This study is one of the first to analyse upland streamwater nitrate dynamics across such a wide range of timescales and report on the principal mechanisms identified. The data analysis provided no clear evidence that the long-term decline in streamwater nitrate concentrations was related to a decline in atmospheric deposition alone, because nitrogen deposition first increased and then decreased during the study period. Increased streamwater temperature and denitrification may also have contributed to the decline in stream nitrate concentrations, the former through increased N uptake rates and the latter resultant from increased dissolved organic carbon concentrations. Strong seasonal cycles, with concentration minimums in the summer, were driven by seasonal flow minimums and seasonal biological activity enhancing nitrate uptake. Complex diurnal dynamics were observed, with seasonal changes in phase and amplitude of the cycling, and the diurnal dynamics were variable along the river. At the moorland site, a regular daily cycle, with minimum concentrations in the early afternoon, corresponding with peak air temperatures, indicated the importance of instream biological processing. At the downstream site, the diurnal dynamics were a composite signal, resultant from advection, dispersion and nitrate processing in the soils of the lower catchment. The diurnal streamwater nitrate dynamics were also affected by drought conditions. Enhanced diurnal cycling in Spring 2007 was attributed to increased nitrate availability in the post-drought period as well as low flow rates and high temperatures over this period. The combination of high-frequency short-term measurements and long-term monitoring provides a powerful tool for increasing understanding of the controls of element fluxes and concentrations in surface waters

Source, production and export of dissolved organic carbon and nitrogen

The purpose of this research was to quantify the major sources of dissolved organic carbon (DOC) and nitrogen (DON) in forest soils and ascertain mechanisms for their production and export to surface waters. To quantify the source of DOC we made use of the on-going litter manipulation study (DIRT) at Harvard Forest, Massachusetts. The organic horizon supplies 74% of DOC to bulk soil solution, 12% is supplied by leaf litter, and 13% from root exudate and decay. In plots with no inputs, DON concentrations were 9% higher than the control plots. When either roots or litter were excluded, DON concentrations increased by 17% and 12% respectively. Both DON and DOC concentrations were significantly related to fungal biomass (R2 = 0.99 and 0.90; p \u3c 0.01). We investigated the mechanisms of DOC and DON production and their relationship with CO2 and soil C:N ratio and the effect of chronic carbon and nitrogen manipulation on these relationships. DOC was significantly related to soil respiration in the hardwood plots (R2 = 0.61; p \u3c 0.05), chronic carbon and nitrogen manipulation did not affect this relationship. In the coniferous control plots, the relationship between DOC and soil respiration was strong and significant (R2 = 0.93 p \u3c 0.05) but nitrogen fertilization affected the relationship. DOC was significantly related to soil C:N among forest type and treatment suggesting that the overall mechanisms of DOC production are unaffected by either carbon or nitrogen manipulation. We examined the effect of cold and warm temperature on the relationships between DOC, DON soil respiration and soil C:N in a laboratory controlled study. Temperature had no significant effect on the relationships between DOC and soil C:N, DOC and DON, DON and soil C:N but a significant temperature effect was apparent between both DOC and DON and soil respiration. We used mean biome soil C:N ratio and mean biome DOC export to derive an empirical model (R2 = 0.99 p \u3c 0.001). The model predicted DOC export from contrasting forest types to within 4.5% of their observed exports. We estimated global annual riverine DOC export to be between 0.41--0.48 Pg yr-1

Sources and Fates of Dissolved Organic Carbon in Rural and Urban Watersheds in Brazos County, Texas

The Bryan/College Station (B/CS) region has been reported to have elevated concentrations of dissolved organic carbon (DOC) in surface water. Increased DOC concentrations are worrisome as DOC has been shown to be an energy source for the recovery and regrowth of E. coli and many watersheds are impaired by high bacteria levels. To examine the sources and fates of DOC in rural and urban regions to better understand DOC movement though the environment, seven watersheds were studied. To investigate source, streams were analyzed using diffuse reflectance near infrared spectroscopy (DR-NIR) and carbon isotopes. Fate of DOC was determined through monthly streams samples, gathered between March 2011 and February 2012, which were incubated for biodegradable DOC (BDOC). Soil in the region was sampled based on land use categories. Soil was analyzed for DOC and BDOC as well as DOC adsorption, the other major fate of DOC. Above ground vegetation was sampled in conjunction with soil and analyzed for BDOC. Data indicated that fecal matter from cliff swallows provided considerable organic material to streams in the B/CS region as shown through DR-NIR. Carbon isotope values in streams ranged from -23.5 +/- 0.7% to -26.8 +/- 0.5%. Stream spectra may be able to predict carbon isotope values in streams (Adj. R2 = 0.88). Mean annual stream DOC concentrations ranged from 11 +/- 3 mg/L to 31 +/- 12 mg/L, which represents a significant decrease in DOC between 2007 and 2011. Concurrent increases in pH and conductivity were also recorded. The decrease in DOC and the increases in pH and conductivity may be due to impacts of high sodium irrigation tap water. Biodegradable DOC was low in streams, which is likely due to DOC being present in streams in refractory forms that are resistant to microbial breakdown. Soil chemistry, including soil adsorption, was greatly influenced by sodium. The elevated adsorption coefficients and release values seen in highly developed and urban open areas can be attributed to frequent exposure to high sodium irrigation water. The results indicate that sodium is a major driver of DOC in the system. Sound management decisions concerning irrigation water chemistry and urban development might eventually emerge to protect water quality as a result of this research

Dynamics of dissolved organic matter composition in Scottish rivers and headwater streams – resolving environmental and biogeochemical process interactions

Dissolved organic matter (DOM) has a wide range of chemical structures that give it a multifunctional role in the natural environment. Although the role of DOM in aquatic ecosystems has been the focus of previous work, a comprehensive understanding of the compositional behaviour of DOM under different environmental processes is still incomplete. New field-based geochemistry data is presented from a two-year study (03/2017- 03/2019) in Scottish headwaters and a 9-month study in large Scottish rivers. This research shows that the DOM mobilisation follows seasonality with enhanced exports of DOM during winter months compared to the summer. At a larger spatial scale, the seasonal trend is overprinted by the catchments soil type. Size-Exclusion Chromatography combined with high-resolution time series of DOM variables reveal that precipitation events preferentially mobilise humics from the surrounding soils, while humics concentration decline during low flow conditions. Furthermore, the data show that non-UV absorbing (“invisible”) low molecular weight (LMW) neutrals (iDOM) contribute up to 50 % to the total DOM pool in headwaters, especially during low flow conditions, and on average 13 % to the DOM in larger river systems. The source of iDOM was found to be the topsoil of peatland and peaty podzols. Consequently, more labile OM can be leached from soils into the aquatic environment in the future through disturbed soils promoting instream microbial growth and act as a nutrient source for aquatic plants

Recovery responses of acidified Finnish lakes under declining acid deposition

The present work provides a regional-scale assessment of the changes in acidifying deposition in Finland over the past 30 years and the current pattern in the recovery of acid-sensitive lakes from acidification in relation to changes in sulphate deposition. This information is needed for documenting the ecosystem benefits of costly emission reduction policies and further actions in air pollution policy. The development of sulphate deposition in Finland reflects that of European SO2 emissions. Before the 1990s, reductions in sulphur emissions in Europe had been relatively small and sulphate deposition showed no consistent trends. Due to emission reduction measures that were then taken, sulphate deposition started to clearly decline from the late 1980s. The bulk deposition of sulphate has declined 40-60% in most parts of the country during 1990-2003. The decline in sulphate deposition exceeded the decline of base cation deposition, which resulted in a decrease in acidity and acidifying potential of deposition over the 1990s. Nitrogen deposition also decreased since the late 1980s, but less than that of sulphate, and levelling off during the 1990s. Sulphate concentrations in all types of lakes throughout Finland have declined from the early 1990s. The relative decrease in lake sulphate concentrations (average 40-50%) during 1990-2003 was rather similar to the decline in sulphate deposition, indicating a direct response to the reduction in deposition. There are presently no indications of elevated nitrate concentrations in forested headwater lakes. Base cation concentrations are still declining in many lakes, especially in south Finland, but to a lesser extent than sulphate allowing buffering capacity (alkalinity) to increase. The recovery has been strongest in lakes in which sulphate has been the major acidifying agent, and recovery has been the strongest and most consistent in lakes in south Finland. The recovery of lakes in central Finland and north Finland is not as widespread and strong as observed in south. Many catchments, particularly in central Finland, have a high proportion of peatlands and therefore high TOC concentrations, and runoff-induced surges of organic acids have been an important confounding factor suppressing the recovery of pH and alkalinity in these lakes. Chemical recovery is progressing even in the most acidified lakes, but the buffering capacity of many lakes is still low and still sensitive to acidic input. Chemical recovery is resulting in biological recovery with populations of acid-sensitive fish species increasing. Increasing TOC concentrations are indicated in small forest lakes in Finland, which appear to be related to decreasing sulphate deposition and improved acid-base status of the soil. A new challenge is climate change with potential trends in temperature, precipitation and runoff, which are expected to affect future chemical and biological recovery from acidification. The potential impact of mobilization and leaching of organic acids may become particularly important in Finnish conditions. Long-term environmental monitoring has evidently shown the success of international emission abatement strategies. The importance and value of integrated monitoring approach including physical, chemical and biological variables is clearly indicated, and continuous environmental monitoring is needed as a scientific basis for further actions in air pollution policy. The effect of climate change will increase data requirements, and should be taken into account when assessing long-term surface water quality and developing future monitoring networks, due to more complex processes involved