Robert Gordon

Integrated surface water quality assessment of a rural watershed in Nova Scotia, Canada

Integrated water quality assessments that pertain not only to crop production systems but also public health at the watershed level are growing in popularity. The Thomas brook is a small (760 ha) tributary of the Cornwallis river located in the Annapolis Valley of Nova Scotia, Canada. The Annapolis valley is the most intensively managed agroecosystem in the province, characterized by both agricultural and residential land uses. The objective of this research was to: (i) quantify concentration and loading levels of nutrients (nitrogen and phosphorus) and total coliform bacteria in the surface waters and (ii) attempt to identify the primary sources of pollution within the Thomas brook. Five sampling stations were strategically stationed in the watershed based on the different land uses within the watershed. Water quality and stream flow were monitored at these monitoring stations during a three year period (May to November from 2001 to 2003). Water quality indicators monitored included total phosphorus (TP; 0.09 mg L-1), soluble reactive phosphorus (SRP; 0.09 mg L-1), nitrate-nitrogen (NO3 --N; 2.28 mg L-1), ammonium-nitrogen (NH4+ -N; 0.24 mg L-1) and E. coli (403 cfu 100ml-1). Results show that P concentrations were greatest in a section close to an adjacent dairy farm. The largest mass loadings of nitrogen to the stream were observed in the lower reaches of the watershed, which is surrounded by agricultural cropping systems. Whereas fecal coliform loading along stream reaches were affected by both livestock operations and residential dwellings. These findings support the suggestion that integrated water quality assessment is a key to develop management strategies that minimize health and environmental risks through the contamination of water.

Potential methane emission reductions for two manure treatment technologies

ABSTRACT The effect of two dairy manure treatments, solid–liquid separation (SLS) and anaerobic digestion (AD), on methane potential and the speed of production was evaluated. Assays were performed in the lab to measure methane (CH4) production over 202 d from dairy manure samples taken before and after each treatment. Compared to raw manure, CH4 emissions on a per-L basis were reduced 81% by SLS and 59% by AD, on average. The mean (SD) ultimate CH4 emission potential (B0) per kg of volatile solids (VS) was 247 (8) L CH4 kg−1 VS for raw manure, 221 (9) L CH4 kg−1 VS for separated liquid, and 160 (4) L CH4 kg−1 VS for anaerobic digestate. Thus, SLS reduced the B0 of the liquid fraction by 11% and AD reduced B0 by up to 35% compared to raw manure. Manure treatment affected the speed of CH4 production: SLS increased the CH4 production rate and thus separated liquid manure was the fastest to produce 90% of the ultimate CH4 production. Therefore, both the speed of degradation and B0 should be considered when assessing these techniques for farm-scale manure storages, because actual emission reductions will depend on storage conditions.

Dairy Manure Total Solid Levels Impact CH 4 Flux and Abundance of Methanogenic Archaeal Communities

Stored liquid dairy manures are methane (CH) emission hotspots because of the large amount of slurry volatile solids (VS) converted into CH by methanogens under anaerobic conditions. Our research has indicated that a reduction of total solids (TS) of slurries before storage can reduce CH emissions. In the current study, methanogen abundance was characterized in tanks with different CH emissions. Using mesoscale slurry storage facilities equipped for continuous gaseous emission monitoring, we stored dairy slurries having TS from 9.5 to 0.3% for up to 6 mo. Samples were taken after Day 30 and Day 120 of the storage (20 May-16 Nov. 2010) from the upper and bottom layers of the slurries. Methanogenic communities were studied by targeting the gene encoding the α subunit methyl-coenzyme M reductase (), which catalyzes the final step of methanogenesis. Interestingly, mean abundances of methanogens increased by ∼8 and 23% at the top and bottom sections, respectively, as slurry TS decreased from 9.5 to 0.3%. Cumulative CH emissions, however, decreased by ∼70% as slurry TS decreased from 9.5 to 0.3%. Nevertheless, compared with Day 30 of storage, mean abundances of methanogens were relatively higher at Day 120 (up to 19%), consistent with an increase in the cumulative CH emissions. Polymerase chain reaction denaturing gel electrophoresis analysis indicated a low methanogen diversity, with most bands sequenced closely related to the genus (>95% amino acid sequence similarity), the hydrogenotrophic methanogens. Results suggest that available carbon substrate and not methanogen abundance may be limiting cumulative CH emissions at reduced TS levels of dairy slurries.

Environmental Impacts of Mink Manure and Poultry Litter Stockpiling on Air Quality and Water Quality

The environmental impact of three manure stockpiling systems - uncovered poultry litter, covered poultry litter and uncovered mink manure - on surface and subsurface water quality and air quality was evaluated during a 592 day in situ field storage experiment. Surface runoff and subsurface leachate was analyzed to determine TKN, NH3-N, NO3-N, and TP concentrations and mass loadings. Surface runoff was the main transportation mechanism of P loss from the stockpiles with the majority lost during the two fall seasons. N losses from the poultry litter stockpiles were greatest during the initial 250 days of storage with most of the N lost to subsurface leaching. In mink stockpiles, however, the majority of N was lost in surface runoff. E. coli counts in runoff and leachate samples were highest during the first several rainfall events, with low levels detectable after 200 days. Peak NH3, N2O and CH4 fluxes were observed during the initial stages of stockpiling with the majority of total emissions released during the first 17, 125 and 45 days, respectively.

Odour Emissions Following Application of Hog Slurry to Grassland

Nuisance odours emanating from livestock operations are a major concern to the non-farming public. Several field experiments were conducted to evaluate the effect of management strategies and meteorological conditions on odour emissions from hog slurry applied to grass. Management strategies included slurry application rate, soil water status, slurry dilution with water and rainfall simulation shortly after field application. It was found that doubling (120,000 L ha-1) the application rate had no impact on odour emissions. Tripling (180,000 L ha-1) the application rate, however, increased emissions, relative to a conventional (60,000 L ha-1) application rate. Applying slurry to soil that received rainfall prior to application increased emissions in one of the experiments, compared to soil that did not receive water. On average, diluting slurry with water decreased emissions by only 11%. Meanwhile, rainfall immediately after application increased odour emissions by 17%. Odour fluxes increased with higher windspeed, net radiation and evapotranspiration. Odour emissions can therefore, be reduced by following proper application rates, but most importantly, by applying slurry during calm, cool days. However, such stable weather conditions may increase odour persistence due to lack of vertical mixing, reduced transfer rates and slow drying of the slurry.

Targeting Bacteria and Methanogens To Understand the Role of Residual Slurry as an Inoculant in Stored Liquid Dairy Manure

ABSTRACT Microbial communities in residual slurry left after removal of stored liquid dairy manure have been presumed to increase methane emission during new storage, but these microbes have not been studied. While actual manure storage tanks are filled gradually, pilot- and farm-scale studies on methane emissions from such systems often use a batch approach. In this study, six pilot-scale outdoor storage tanks with (10% and 20%) and without residual slurry were filled (gradually or in batch) with fresh dairy manure, and methane and methanogenic and bacterial communities were studied during 120 days of storage. Regardless of filling type, increased residual slurry levels resulted in higher abundance of methanogens and bacteria after 65 days of storage. However, stronger correlation between methanogen abundance and methane flux was observed in gradually filled tanks. Despite some variations in the diversity of methanogens or bacteria with the presence of residual slurry, core phylotypes were not impacted. In all samples, the phylum Firmicutes predominated (∼57 to 70%) bacteria: >90% were members of Clostridia. Methanocorpusculum dominated (∼57 to 88%) archaeal phylotypes, while Methanosarcina gradually increased with storage time. During peak flux of methane, Methanosarcina was the major player in methane production. The results suggest that increased levels of residual slurry have little impact on the dominant methanogenic or bacterial phylotypes, but large population sizes of these organisms may result in increased methane flux during the initial phases of storage. IMPORTANCE Methane is the major greenhouse gas emitted from stored liquid dairy manure. Residual slurry left after removal of stored manure from tanks has been implicated in increasing methane emissions in new storages, and well-adapted microbial communities in it are the drivers of the increase. Linking methane flux to the abundance, diversity, and activity of microbial communities in stored slurries with different levels of residual slurry can help to improve the mitigation strategy. Mesoscale and lab-scale studies conducted so far on methane flux from manure storage systems used batch-filled tanks, while the actual condition in many farms involves gradual filling. Hence, this study provides important information toward determining levels of residual slurry that result in significant reduction of well-adapted microbial communities prior to storage, thereby reducing methane emissions from manure storage tanks filled under farm conditions.

The Extent of Manure Removal from Storages and Its Impact on Gaseous Emissions

Manure remaining in storage due to incomplete removal is a source of microbial inoculum that may affect methane (CH), nitrous oxide (NO), and ammonia (NH) emissions during subsequent storage. Manure removal was studied by loading fresh manure into outdoor concrete tanks (10.6 m) that contained previously stored manure (inoculum) at six levels (0, 5, 10, 15, 20, and 25%, with 0% representing an empty tank). Emissions were continuously measured for 6-mo storage periods (warm and cold seasons) using flow-through chambers. Fluxes during the warm season (average manure temperature at 80 cm depth, = 17°C) were 25 times higher for CH, 20 times higher for NO, and 2.9 times higher for NH compared with the cold season ( = 4°C). Cumulative CH emissions increased linearly with the level of added inoculum in the cold season ( = 0.98). A similar linear increase was observed in the warm season from 0 to 20% inoculum ( = 0.91), after which a decrease in emissions was observed at 25%. Reducing inoculum from 15 to 5% reduced CH emissions by 26% in the warm season and 45% in the cold season. There was no clear effect of inoculum on NO and NH emissions, suggesting that complete manure storage emptying does not alter their emissions.

An Initial Assessment of a Wetland-Reservoir Drainage Water Treatment and Reuse System in Nova Scotia

Nutrient and pathogen export from agricultural drainage water is a major source of surface water quality degradation. Wetland-reservoir drainage water treatment and reuse systems have the potential to mitigate this pollution, as well as conserve water, improve crop yields, and increase bio-diversity. This study will assess the viability of this type of system in a colder climate. Specific objectives are to assess (i) system hydraulics and water balances; (ii) wetland treatment efficiencies; and (iii) reservoir water quality.

The Survival of E. coli in Agricultural Soil Treated With Dairy Manure

The survivability, persistence, and distribution of E. coli in soil raises serious water quality questions for rural communities. A field experiment to determine the effect of manure application timing (late spring or late summer) and manure application technique (surface broadcast or incorporated) on E. coli survival in soil was performed over two cropping seasons. Dairy manure was applied at a rate of 70 kg N/ha on 1 m2 plots in an agricultural field with a sandy loam soil. Soil samples were analyzed at weekly intervals for E. coli using a membrane filtration technique. Timing of manure application did influence survival as E. coli populations were higher when manure was applied in the late spring (June) as opposed to the late summer (August). Manure application technique also influenced the decline in organism populations, in that bacteria survived longer when the manure was surface broadcast versus when it was incorporated into the soil. Topsoil (to a 5 cm depth) was found to provide a more favorable environment for E. coli survival than subsoil (10-25 cm). Regrowth of E. coli populations was detected in some treated plots. The extended survival of E. coli and its ability to grow in soil emphasizes the need for appropriate farm manure management practices to minimize microbial contamination of surface and groundwater.

Sodium Persulfate and Potassium Permanganate Inhibit Methanogens and Methanogenesis in Stored Liquid Dairy Manure

Stored liquid dairy manure is a hotspot for methane (CH) emission, thus effective mitigation strategies are required. We assessed sodium persulfate (NaSO), potassium permanganate (KMnO), and sodium hypochlorite (NaOCl) for impacts on the abundance of microbial communities and CH production in liquid dairy manure. Liquid dairy manure treated with different rates (1, 3, 6, and 9 g or mL L slurry) of these chemicals or their combinations were incubated under anoxic conditions at 22.5 ± 1.3°C for 120 d. Untreated and sodium 2-bromoethanesulfonate (BES)-treated manures were included as negative and positive controls, respectively, whereas sulfuric acid (HSO)-treated manure was used as a reference. Quantitative real-time polymerase chain reaction was used to quantify the abundances of bacteria and methanogens on Days 0, 60, and 120. Headspace CH/CO ratios were used as a proxy to determine CH production. Unlike bacterial abundance, methanogen abundance and CH/CO ratios varied with treatments. Addition of 1 to 9 g L slurry of NaSO and KMnO reduced methanogen abundance (up to ∼28%) and peak CH/CO ratios (up to 92-fold). Except at the lowest rate, chemical combinations also reduced the abundance of methanogens (up to ∼17%) and CH/CO ratios (up to ninefold), although no impacts were observed when 3% NaOCl was used alone. With slurry acidification, the ratios reduced up to twofold, whereas methanogen abundance was unaffected. Results suggest that NaSO and KMnO may offer alternative options to reduce CH emission from stored liquid dairy manure, but this warrants further assessment at larger scales for environmental impacts and characteristics of the treated manure.