No-till management for agronomic crop production is recognized as an effective practice to regain a portion of soil organic matter lost following decades of cultivation. Increasing soil organic matter sequesters C, conserves organic N and concomitantly improves soil quality. Objectives of this research were to: i) quantify C sequestration rate and N conservation with duration of continuous no-till; ii) measure C stratification with continuous no-till as an indicator of soil quality; and iii) evaluate the Illinois soil N test (ISNT) for its value to predict fertilizer N needs of corn in Virginia. Objectives i and ii were achieved by collecting soil samples from 63 production fields in the Virginia Coastal Plain that were managed using continuous no-till from 0 to 14 yrs. No-till management resulted in sequestration of 0.308 ± 0.280 Mg C ha⁻¹ y⁻¹ and conservation of 22.2 ± 21.2 kg N ha⁻¹ yr⁻¹ (0-15 cm). The C stratification ratio (0-2.5 cm: 7.5-15 cm) increased with increasing duration of continuous no-till (0.133 ± 0.056 yr⁻¹) due to the accumulation of organic matter at the soil surface indicating improved soil quality with continuous no-till management. Objective iii was addressed by conducting 29 on-farm fertilizer N response trials in major corn producing areas of Virginia with the duration of continuous no-till management ranging from 0 to 25 yrs. The ISNT values were significantly related to yield without fertilizer N (r² = 0.57; p<0.001) and relative yield (r² = 0.64; p<0.0001). We also found that the ISNT extracted a relatively consistent percentage of total soil N (16.3 ± 0.73 %) suggesting it is a poor indicator of labile N. Total soil N values did almost as well as the ISNT in predicting yield without fertilizer N (r² = 0.53; p = 0.0002), and equally well predicting relative yield (r² = 0.64; p<0.0001). Results do not suggest the ISNT is useful for measuring mineralizalbe N or improving fertilizer N recommendations in Virginia cropping systems. / Ph. D.

The EPA Lead and Copper Rule set Action Limits for lead and copper concentrations in potable water, but accelerated corrosion of lead in potable water systems due to a galvanic connection to copper remains a significant health risk to consumers. In addition to elevated lead release due to galvanic corrosion of lead-tin solder and leaded brass fixtures, partial lead service line replacements with copper pipe present long-term health concerns. Prior research has demonstrated that the effects of galvanic corrosion can be controlled by water chemistry, and the interplay between alkalinity, natural organic matter (NOM), and orthophosphate (added as corrosion inhibitor) may have a significant influence on corrosion of common lead plumbing materials. Results of bench-scale experiments demonstrate that in some waters galvanic corrosion can multiply lead release from lead pipe by up to 60 times, but other waters curtail the galvanic current and alleviate the effects of galvanic corrosion. Measurements of pH at the lead surface demonstrate that a corrosive micro-environment forms during stagnation in which the local pH drops to 3.0 or lower, demonstrating that the worst-case scenario for galvanic corrosion of lead occurs during long stagnation periods. In addition to water chemistry, flow pattern also has an impact on galvanic corrosion of lead. Conventional wisdom regarding lead release indicates that continuous flow results in the greatest mass of lead release, but reports of anomalously high lead concentrations after long periods of stagnation point to the contrary. In this experiment, continuous flow of chlorinated water through a Pb-Cu galvanic couple promoted Pb(IV) formation and resulted in potential reversal that caused lead pipe to become cathodic to copper and minimized lead release to water. In contrast, intermittent flow resulted in sustained galvanic attack, and a mass balance of Pb release indicated that a greater total mass of lead was released with intermittent flow. These results have important implications for assessing lead risk at the tap, especially considering long stagnation periods at facilities such as schools and increasing efforts for water conservation. Elevated copper release in potable water can cause aesthetic problems and mild health concerns and often occurs in new plumbing systems prior to the formation of a protective scale layer on the pipe surface. While solubility in new copper pipes tends to be controlled by an amorphous solid of high solubility, over time, the natural copper aging process results in the formation of a protective scale of much lower solubility, but the transition can be inhibited in waters with high levels of NOM. Experiments demonstrated that GAC treatment to remove NOM accelerates the aging process to a protective scale that provides a long-term reduction in copper release even after GAC treatment is terminated. Therefore, compared to pH adjustment and orthophosphate addition, which must be continued perpetually, GAC treatment may be a more holistically pleasing method of copper corrosion control. This approach could be useful in the commissioning of new buildings to facilitate rapid aging and avoid potential long-term copper corrosion problems. / Master of Science

Agricultural activities have significant impacts on global biogeochemical cycles, particularly carbon and nitrogen. Conventional row-crop agriculture accelerates the decomposition of soil organic matter, contributing to atmospheric carbon and declining soil fertility. Planting perennial warm season grasses is a useful management alternative to row crop agriculture because these species have been shown to be effective at increasing soil carbon storage and retaining nitrogen. The objectives of this research were to examine how converting row crops to a native perennial warm season grass (Panicum virgatum L., common name switchgrass) influences the recovery of soil organic matter fractions and nitrogen retention within an agricultural watershed in the Shenandoah Valley of Virginia. Soil samples were analyzed for total carbon and nitrogen, three particulate organic matter fractions, root biomass, mineralizable carbon and nitrogen pools, and microbial biomass. Surprisingly, I observed significant declines in bulk soil organic matter and surface particulate organic matter pools following switchgrass establishment. There were no differences in mineralizable carbon and microbial biomass pools between row crop and switchgrass soils, but labile carbon pools and nitrogen immobilization increased as switchgrass stands matured. These results are potentially due to switchgrass litter inputs stimulating microbial communities and accelerating the decomposition of recalcitrant soil organic matter, leading to declines in soil organic carbon stocks. The results from this study will be used to understand the environmental and economic benefits of implementing switchgrass plantings in agricultural watershed as a means to mitigate agriculturally-induced effects on carbon storage and nitrogen retention in soils. / Master of Science

Concern over rising atmospheric CO2 due to fossil fuel combustion has intensified research into carbon-neutral energy and fuel production. Therefore, bioenergy production has expanded during the last decade, increasing demand for forest-based bioenergy feedstocks. Millions of acres of privately and industrially owned pine plantations exist across the southeastern US, representing a vast area of land that could be utilized to produce bioenergy without significant land-use change or diversion of agricultural resources from food production. Furthermore, loblolly pine (Pinus taeda L.) plantations offer the unique opportunity to utilize space between rows of planted trees to grow an herbaceous bioenergy crop, such as switchgrass (Panicum virgatum L.). This novel forest management regime has the potential to provide positive environmental and economic services, but hinges in part on impacts to soil carbon (C) and nitrogen (N) cycling, availability of belowground resources, and potential negative impacts of competition between pine and switchgrass on plant productivity. Three specific objectives were addressed in this study: 1) compare different bioenergy management regimes in regards to temporal dynamics of N cycling and availability following forest establishment (see Chapter 2); 2) determine the impact of loblolly pine and switchgrass intercropping on microbial N cycling processes (see Chapter 3); and 3) evaluate chemical and physical mechanisms of soil organic matter (SOM) stabilization and test their sensitivity to pine-switchgrass intercropping (see Chapter 4). The study site was located in the Lower Coastal Plain physiographic province in Lenoir County, North Carolina, USA (35-12'59'' N; 077-26'13'' W). Soils were mapped as Pantego (fine‐loamy, siliceous, semiactive, thermic Umbric Paleaquults) or Rains (fine‐loamy, siliceous, semiactive, thermic Typic Paleaquults) soil series, both of which are very poorly drained. However, previous site management in the late 1960’s and early 1970’s included installation of ditches to lower the water table and reduce saturation at the soil surface. Additionally, bedding of soil in rows was used to raise root systems of planted loblolly pine seedlings above the water table, increase soil aeration, and reduce competition. Space between bedded rows of pine trees was referred to as the interbed. Results from Chapter 2 showed that switchgrass significantly reduced interbed soil NH4 + and NO3 - concentrations by 39% and 60%, respectively, over the course of the timeframe (30 months) of this study. Surprisingly, in beds of the pine-switchgrass treatment significant increases in NO3 - concentration were measured from July - December 2011. From Chapter 3, gross N mineralization rates ranged from 0.18 - 4.7 µg N g -1 soil d-1 , while gross nitrification rates ranged from 0.02 - 0.47 µg N g-1 soil d-1 . At the 0-5 cm depth in switchgrass interbeds, gross N mineralization was reduced from April to November potentially reflecting microbial C limitations due to reduced soil C concentrations. At the 0-5 cm depth in beds of the pine-switchgrass treatment, gross N mineralization rates were elevated by 1.29 µg N iii g -1 soil d-1 in November and 1.02 µg N g-1 soil d-1 in February on average corresponding to a 305% and 193% increase, respectively. From Chapter 4, total C content in beds and interbeds ranged from 15 to 88 Mg C ha-1 and was reduced by 27% in beds of the pine-switchgrass treatment. Average C concentration for aggregate fractions was significantly lower in beds of the pine-switchgrass treatment at 0-5, 15- 30, and 30-45 cm depths, amounting to ~23%, ~28%, and ~34% reduction, respectively. Values of δ 13C for the >2000 µm aggregate size fraction at the 0-5 cm depth were diluted, corresponding to estimates of 13 - 25% of the >2000 µm C pool comprised of new pine-derived C. For SOM fractionated by density, elevated C concentrations were found in the occluded light fractions in both beds and interbeds of the pine-switchgrass treatment. Enriched δ13C in occluded light fractions led to estimates of 2.5 - 12.5% of this C fraction comprised of new switchgrass-derived C. In the free light fraction, new pine-derived C accounted for 15% and 9% of C at the 5-15 and 15-30 cm depth, respectively. Three overarching conclusions were generated from my research: 1) switchgrass grown between loblolly pine trees effectively utilized excess soil NH4 + and NO3 - when N availability was high following harvesting of a mature plantation proceeded by establishment of a second rotation of loblolly pine (see Chapter 2); 2) gross N mineralization rates were reduced under switchgrass during the growing season when soil C availability was low, but were elevated under switchgrass and adjacent loblolly pines when switchgrass was dormant and C availability was likely higher (see Chapter 3); and 3) SOM stabilized by physical or chemical mechanisms responded differently to pine-switchgrass intercropping, with losses in aggregate-stabilized C and gains in occluded, mineral-stabilized C. Furthermore, losses of aggregate C was associated with a significant reduction in total soil C in beds of the pine-switchgrass treatment. Results from 13C mass balance suggested incorporation of switchgrass-derived C into occluded light fractions of beds and interbeds. Finally, incorporation of new pine-derived C into the >2000 µm aggregate size fraction and free light fraction indicate pine inputs of particulate organic matter into these SOM fractions in beds of the pine-switchgrass treatment (see Chapter 4). I hypothesize that loblolly pines have increased root growth in beds in response to competition with switchgrass for N in the interbed, thereby alleviating seasonal microbial C limitations and stimulating microbial N cycling processes and increasing plant-available N. Overall, this research suggests that soil C and N cycling in pine plantations is altered by intercropping of pine and switchgrass. Through a mechanistic understanding of how C and N are cycled in forests and the impact of various forest management regimes on soil C and N cycling, effective management strategies can be implemented to utilize forests for intensive biomass production while limiting loss of soil C and N, and in some cases even enhancing soil C and N retention. Future research initiatives should seek to unravel the complex belowground interactions between roots of different plant species and soil microbial communities competing for limiting resources. Understanding how these interactions drive soil C storage, N cycling and availability, and forest productivity will ultimately improve resource utilization in these managed ecosystems as well as our basic understanding of how natural and managed ecosystems function. / Ph. D.

As anthropogenic nutrient loads threaten the health of the Chesapeake Bay, lotic processes throughout its headwaters may buffer increased nitrogen inputs by converting them to stable forms, ultimately through denitrification to N2 gas. However, the temporal environmental factors controlling baseflow nitrogen retention are poorly understood, particularly temperature, shading, and dissolved organic matter dynamics. This study therefore attempts to elucidate the effects of these environmental variables on nitrogen cycling within the Fair Hill Natural Resources Management Area (Fair Hill), a forested watershed within the Piedmont physiographic province of the Chesapeake Bay. As expected, groundwater and allochthonous organic matter inputs set the foundation for lotic biogeochemistry at Fair Hill, creating a nutrient-limited, heterotrophic reach. Within this setting, three temporal "hot-moments" of in-stream nutrient processing were observed: the release of ammonium and phosphate during the warm - but shaded - growing season; nitrate uptake during autumnal leaf-fall; and a unique spike of nitrate uptake and respiration-induced degradation of labile organic matter during a drought. Consequently, the baseflow capacity of this headwater stream to buffer nutrient exports to the Chesapeake Bay constantly varies throughout the year in response to light availability, temperature, and in-stream organic matter dynamics. / Master of Science / Throughout the Chesapeake Bay watershed, ecological processes known as nitrogen retention can naturally remove nitrogen pollution from small streams (a.k.a. headwater streams), and hence the Chesapeake Bay watershed. However, in-stream nitrogen retention varies throughout the year due to seasonal changes in temperature, shading (as leaves grow in the spring or fall off in the fall), and the amount and type of organic matter in the stream. This study examines how these three variables (temperature, shading, and dissolved organic matter dynamics) affect nitrogen retention in a headwater, forested stream within the Fair Hill Natural Resources Management Area (Fair Hill) located in the Piedmont region of the Chesapeake Bay watershed. As expected, groundwater and organic matter inputs set the foundation for in-stream conditions at Fair Hill, creating an environment with low concentrations of nitrate and phosphate (thus causing the stream to be nutrient-limited), while also creating a heterotrophic environment, which is an environment where more oxygen is consumed by microbes than produced by algae and plants. Additionally, three seasonal patterns regarding in-stream nutrient dynamics were observed at Fair Hill. Firstly, in-stream ammonium and phosphate concentrations increased during the warm - but shaded - growing season. Secondly, in-stream nitrate concentrations decreased when leaves fell in the fall. Thirdly, during a drought, in-stream nitrate removal increased while in-stream organic matter became more degraded. Consequently, in-stream nutrient retention at Fair Hill varies constantly throughout the year in response to light availability, temperature, and in-stream organic matter dynamics.

Yes / Characterising the organic and microbial matrix of water are key issues in ensuring a safe potable water supply. Current techniques only confirm water quality retrospectively via laboratory analysis of discrete samples. Whilst such analysis is required for regulatory purposes, it would be highly beneficial to monitor water quality in-situ in real time, enabling rapid water quality assessment and facilitating proactive management of water supply systems. A novel LED-based instrument, detecting fluorescence peaks C and T (surrogates for organic and microbial matter, respectively), was constructed and performance assessed. Results from over 200 samples taken from source waters through to customer tap from three UK water companies are presented. Excellent correlation was observed between the new device and a research grade spectrophotometer (r2 = 0.98 and 0.77 for peak C and peak T respectively), demonstrating the potential of providing a low cost, portable alternative fluorimeter. The peak C/TOC correlation was very good (r 2 = 0.75) at low TOC levels found in drinking water. However, correlations between peak T and regulatory measures of microbial matter (2 day/3 day heterotrophic plate counts (HPC), E. coli, and total coliforms) were poor, due to the specific nature of these regulatory measures and the general measure of peak T. A more promising correlation was obtained between peak T and total bacteria using flow cytometry. Assessment of the fluorescence of four individual bacteria isolated from drinking water was also considered and excellent correlations found with peak T (Sphingobium sp. (r 2 = 0.83); Methylobacterium sp. (r 2 = 1.0); Rhodococcus sp. (r 2 = 0.86); Xenophilus sp. (r 2 = 0.96)). It is notable that each of the bacteria studied exhibited different levels of fluorescence as a function of their number. The scope for LED based instrumentation for insitu, real time assessment of the organic and microbial matrix of potable water is clearly demonstrated. / The research reported here was sponsored by the Engineering and Physical Sciences Research Council under grants EP/I001379/1, EP/I001468/1 and EP/I029346/1.

In order to delineate the potential sources and to understand the main controls on the biogeochemical cycling of dissolved and particulate organic matter (DOM, POM) and dissolved inorganic nitrogen (DIN) during estuarine mixing, comprehensive seasonal geochemical and isotopic and surveys across the freshwater-tidal interface were carried out in the Tyne and Tweed Estuaries, NE UK. This study provided a contrast between a relatively pristine system (Tweed) with one that is heavily influenced by anthropogenic activity (Tyne). Geochemical and isotopic (13C, 14C and 15N) analyses demonstrated the predominance of terrigenous organic matter in both these estuaries, with elevated river discharges leading to enhanced terrestrial loading. High pCO2 values in the Tyne (summer) and Tweed (winter) suggested that a significant fraction of this terrestrially-derived organic matter (both DOM and POM pools) is relatively labile and can potentially undergo significant mineralization during estuarine mixing. In both estuaries in situ processing of DIN was relatively minor, with mixing between different sources being the main factor in controlling the distribution of nitrate and ammonium across the salinity gradient. However, anthropogenic ammonium discharges in the Tyne were found to have an enormous direct and indirect impact on estuarine nitrogen cycling. Large, concave removals of terrigenous high molecular weight (HMW) DOC caused by flocculation, biodegradation, and/or photochemical oxidation were associated with a non-conservative 13C-enrichment in d13C signatures. Radiocarbon dates showed an export of young (modern) HMW DOC and old (100-1000s of years), terrigenous POC to the North Sea. 14C-enriched values in coastal North Sea HMW DOC were attributed to anthropogenic discharges originating from within the coastal North Sea environment. In the Tweed, seasonal changes in soil characteristics resulted in an older age for POM during the summer. In the Tyne, decreases in POC% with increasing salinity sometimes coincided with an increase in POC age. This was attributed to mixing with older sediment and to the possible preferential loss of the younger, more labile POC fraction during mineralization. This study has shown that land use patterns, sewage inputs, and freshwater flushing time are the main influences in determining the behaviour and origin of organic matter and DIN entering the coastal North Sea in these two systems.

No description available.

This dissertation thesis focuses on the removability of algal organic matter (AOM) by coagulation during water treatment and also on the influence of AOM on the coagulation of other substances present in source water. Special emphasis is put on the description of coagulation mechanisms. The effectiveness of AOM removal by coagulation was investigated by coagulation tests performed with optimized doses of coagulants (aluminium or ferric sulphate) under different pH values. Peptides and proteins contained in cellular organic matter of cyanobacterium Microcystis aeruginosa were used in the experiments since they have been previously reported to disturb the coagulation process. Moreover, peptides and proteins underwent coagulation experiments together with kaolin particles, representing clay particles in turbid waters, in both the presence and absence of coagulants to investigate the effect of AOM on the coagulation of turbid waters. To enable the description of coagulation mechanisms, AOM were characterised in terms of charge, functional groups, molecular weight and ability to form dissolved complexes with coagulant metals. The experimental results demonstrated that the removability of peptides and proteins is greatly dependent on pH value and on the properties of the involved particles or molecules....

<p>Nedbrytning av organiskt material är en nyckelfaktor som påverkar omvandlingar av de många grundämnen som utgör eller är associerade till just organiskt material. En stor del av nedbrytningen av akvatiskt organiskt material (OM) sker i gränsskiktet mellan sediment och vatten. Eftersom så många biogeokemiska cykler styrs av nedbrytningen av OM är det viktigt att ha kunskap om processer och påverkansfaktorer både på mikro- och makronivå. Mineraliseringshastigheten av OM är en vanligt förekommande mätparameter, men vanligtvis inkluderar mätningarna inte de naturliga processer som kan påverka nedbrytnings-hastigheterna, t.ex. fysiska krafter.</p><p>Syftet med den här studien är att studera mineraliseringshastigheten av det OM som finns naturligt i ytsediment i söt- och brackvatten när det utsätts för fysiska krafter som orsakar förändringar i redox-förhållanden, resuspension eller advektivt porvattenflöde. Fem</p><p>laborativa experiment har utförts för att belysa syftet:</p><p>Åldrat ytsediment från en sötvattens å utsattes för olika redox förhållanden där oxisk respiration, sulfatreduktion respektive metanogenes gynnades. Resultaten visade ingen skillnad i mineraliseringshastighet beroende på behandling. Detta motsäger studier utförda i marina miljöer, där anoxiska förhållanden ger en lägre mineraliseringshastighet än oxiska.</p><p>Vidare gjordes två studier på brackvattensediment där effekten av resuspension var i centrum. Den ena studien fokuserade på frekvens och varaktighet av resuspensionstiderna, den andra på olika typer av sediment. Studierna visade att väldigt korta resuspensionstider med upp till 48 timmars stillhet mellan varje resuspension ökade mineraliseringstakten med fem gånger jämfört med diffusivt utbyte, och mer än dubblerades i jämförelse med kontinuerlig resuspension eller resuspension i långa perioder. Resuspensionen under kort tid var troligen gynnande då resuspension fysiskt stör bildningen av stabila bakteriesamhällen. Mineraliseringshastigheterna i sediment som domineras av väldigt fin, fin eller medium sand visade lika hastigheter, medan grov sand visade en signifikant lägre mineraliseringshastighet. Likheterna mellan de tre första sedimenttyperna kan dock ha påverkats av tillgång på lättnedbrytbart OM då sediment och vatten hämtades in under en algblomning.</p><p>Till sist studerades effekten på mineraliseringshastigheten av advektivt porvattenflöde. Detta gjordes på åldrat sediment dels från en sötvattensbäck dels från en brackvattenstrand. Inget av de två sedimenttyperna visade någon skillnad i mineraliseringshastighet i jämförelse med diffusivt styrda system. Det är i motsats till tidigare marina studier, men är i linje med den första studien, där mineraliseringshastigheten var oberoende av redox-förhållande.</p><p>Den generella slutsatsen från den här studien är nödvändigheten att studera samma aspekter i olika typer av akvatiska system, eftersom responsen verkar vara annorlunda beroende på system, t.ex. söt- brack- och saltvatten. Faktorer som kan förklara de här skillnaderna finns ännu inte, vilket gör att småskaliga studier och modeller blir viktiga verktyg för att utreda detta.</p> / <p>Organic matter mineralisation is a key parameter that affects most other element transformations associated with organic matter. A substantial part of aquatic organic matter (OM) mineralisation takes place at the interface between sediment and water. Understanding OM mineralisation is important at both the micro and macro scales, since it drives many biogeochemical cycles. OM mineralisation rates are widely measured, but generally not all the natural factors possibly affecting the rates, such as physical forcing, are considered.</p><p>This thesis examines the mineralisation rates of indigenous OM in fresh and brackish surface sediments, subjected to different physical forces inducing changed redox conditions, resuspension, and advective pore water flow. Five experiments were performed to this end.</p><p>Aged surface sediment from a freshwater river was subjected to different redox conditions favouring oxic respiration, sulphate reduction, and methanogenesis, respectively. Results indicated no difference in mineralisation rate irrespective of treatment. This contradicts what has been found in marine environments, where anoxic mineralisation rates are lower than oxic ones.</p><p>Further, two studies of resuspension of brackish sediments were performed, one addressing the impact of the frequency and duration of the resuspension events, and the other addressing the impact of resuspension on different types of sediments. The studies found that very brief resuspension events followed by calm periods of up to 48 h increased mineralisation rates by five times compared to diffusion, and more than doubled the rate compared to continuous or long-term resuspension. The short-term events were possibly favoured because resuspension physically disturbs the arrangement of a stable bacteria community. Mineralisation rates on sediments dominated by very fine, fine, or medium-grained sand were the same, while coarse sand displayed a significantly lower rate. The similar rates of the three first sediment types could stem from access to labile OM, due to an ongoing algae bloom when the sediment and water samples were collected.</p><p>Finally, the effect of advective pore water flow on aged sediment from one fresh and one brackish sediment was studied. Neither of the sediments displayed a mineralisation rate different from those occurring in incubations in which only diffusive exchange occurred. This contradicts the findings of previous marine studies, but is in line with the first study, which did not detect different mineralisation rates irrespective of redox conditions.</p><p>The general conclusion is that it is necessary to study the same physical forces in different aquatic environments, since responses appear to differ, for example, between freshwater, brackish, and marine environments. Factors explaining these differences have not yet been expressed, making small-scale studies and modelling a challenge for future research.</p>