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Emission refers to the rate at which gases or particulates are being released into ambient air. Air emissions from poultry farm consist of dust, particulate matter, odors, endotoxins, methane, H2S, CO2, and nitrogenous compounds such as NH3. However, NH3 emissions and N deposition can be a major source of pollution in pig and poultry farm (Bouwman et al., 1997; Hutchings et al., 2001).
In the UK, 80% of NH3 emissions came from livestock manure and N fertilizers (Sutton et al., 1995; Asman, 1990). These gases is normally transferred by wet or dry deposition to terrestrial plants and its surrounding (Asman & van Jaarsveld, 1991). In the Europe, NH3 emissions have increased by more than 50% over the last few decades (Sutton et al., 1995; McCrory & Hobbs, 2001). 80% of the yearly emissions came from intensification of livestock production (Pain et al., 1998), with 90% out of it came from animal wastes and fertilizers (Buijsman et al. (1998). In Netherlands, 85% of the total NH3 emissions originates from livestock farming (Koerkamp et al., 1998). While in Germany, 70-90% of the total NH3 emissions originated from animal livestock (Flaig and Mohr, 1996).
NH3 is a colourless gas, lighter than air and has a pungent order. The pungent gas is released during the breakdown of the urea, excreted by pig and poultry farm. According to Koerkamp (1994) and Sutton et al. (19998), this reactive gas deposited and absorbed by land and water surfaces, usually close to where it was emitted (dry deposition) . In some case, some ammonia may reach higher levels in the atmosphere and be blown long distances before being deposited in rainfall (wet deposition). The greatest concentrations of ammonium-N in rain are found in the south and east of the UK where there are also reported to have a large number of extensive livestock farm.
Besides that, NH3 is highly water-soluble and this gases is classified as particulate precursor - readily reacts with other substances in the atmosphere to form ammonium and other substances. A substances comprised of ammonia and ammonium are called reduced nitrogen, NHx. NH3 is emitted from the liquid as gas by a process volatilization. Animal waste are excrete as uric acid and then be broken down to urea (Figure 2.1). During this process, ammonia are released by volatilization. Livestock manures are known to be the major sources of ammonia emission. Ammonia emissions is increased by the use of N in fertilizers or high protein diet in animal feeds. If the N is not metabolized into animal protein, the amount of N in dung and urine will also increased.
Figure 2.1: Ammonia flows in the atmosphere, adapted from (http://www.defra.gov.uk/environment/quality/air/airquality/publications/ammonia/documents/ammonia-in-uk.pdf) showing the movement of NH3 through wet and dry deposition.
Effects of NH3 and other N gaseous to ecosystem community
NH3 and NH4 deposition in UK is currently above critical load of N in many parts of UK including the upland and lowland heath, upland bog, semi-natural grassland and some woodlands. Over the last 20 years, many studies have been conducted to give an evidence of reverse impact of N deposition (Wilson and Pitcairn, 1988; Fangmeier et al., 1994; Sutton et al., 1995; Pain et al., 1998). An area of high NH3 emissions has been reported to alter or change species composition and ultimately changing the community ecosystem (Sutton et al., 1993; Bobbink et al., 1996; Van Dobben & Ter Braak, 1998; Ruoss, 1999; Wolseley & James, 2002).
Apart from offensive odour emanating from husbandry unit, substantial amount of NH3 also causes excessive nitrogen input (eutrophication) and acidification (Phillips & Pain, 1998; Koerkamp et al., 1998; Wathes, 1998; Erisman et al., 2003).
N deposition are known to caused subtle changes of plant species. In an area where plant species are adapted to limited N, increasing N-deposition caused the native plant to be outnumbered to those that requires higher concentration of NH3. Eutrophication increased the growth of plants thriving on a limited N supply . At the same time, species that cannot cope well with increasing N are replaced by N-loving species. Some studies has shown an appearance of non-native species in semi-natural ecosystems. For example, some parts of heathland have been taken over by grass when N deposition increases. The loss of moss-dominated heathland are also reported to be reduced due to an increase of N. In terms of conservation, this situation may lead to loss of probably important species. According to Barkman (1958) and Brodo (1968), ecological succession can also be reversed due to NH3 pollution.
The domination of N-loving species (nitrophytes) at the expense of acidophytes or original vegetation (Pitcairn et al., 1991; Sutton et al., 1993; Woodin & Farmer, 1993) was more apparent on acid-bark trees, where nitrophytes were reported to be absent or very rare. N deposition also triggered plant sensitivity to stresses such as frost, drought and insect damage. Thus this will also contribute to reduced stability of plant species.
Besides eutrophication, NH3 emissions also contribute to acidification of soil and surface waters. NH3 was deposited on soil, oxidized to nitrate and increases soil acidity. Acidification begin when nitrogen and sulphur oxide compounds (NOx SOx) are converted to nitric and sulfuric acid. These are substances in acid rain formation. NH3 neutralized sulfuric acid and turned the droplet to ammonium bisulphate. However, this process only happen if NH3 concentration is less than twice of the sulfuric acid. If NH3 concentration is greater than twice the sulfuric acid level, it will react with other acid vapors (Patterson & Adrizal, 2005).
Since excess ammonia lead to serious environmental impacts, many European countries such as the UK, Denmark, Sweeden and Germany have passed a regulations limiting the level of NH3 emission from livestock houses (Sommer et al., 2009). Under Gothenburg Protocol, participated countries are committed to bring NH3 emissions within national ceilings (Angus et al., 2006). Sensitive area (within 300 m from source) are classified according to their critical load and are not permitted to increase their NH3 emissions when there are any changes in production (Sommer et al., 2009).
Besides NH3, other N-gaseous emitted from pig and poultry farm are NOx and N2O. Eventhough the impact of NH3 well documented, the effect of other gases should also be taken into consideration. NOx are known to trigger ozone promotion and acid rain which caused the death or decline of forest in many parts of Europe. While N2O are the factor which contribute to ozone depletion (Williams et al., 1992; Saggar et al., 2004). N2O emissions are significantly contribute by solid manure heaps and N fertilizers (Bouwman, 1990; Williams et al., 1992; Chadwick et al., 1999; Jacobson et al., 2003).
N2O naturally exists in the atmosphere at a very low concentrations, about 310ppb. However, because N2O has 150 years of lifetime thus it lingers longer and the effects could be 300 two tomes higher than of CO2 (Watson et al., 1996). Besides that, excess NH3 which settle on the soil also contributing to the increase of N2O emissions (Bouwman (1990; Williams et al., 1992; Granli & Bùckman; 1994). Williams et al., (1992) in his study, concluded that N2O emissions was associated more to denitrification than that of nitrification. Even so, the prevalence of these two processes as the dominant source of N2O production can be switched very rapidly, depending on soil properties, drainage in soil, climatic properties and level of organic content (Groffman, 1991; Saggar et al., 2004).
2.1.2 Effects of N-deposition to lower plants
NH3 is an important source for lower plants such as algae, lichen and bryophytes (Hansen et al., 1997; Downing & Rigler, 1984). Lower plants such as epiphytic terrestrial algae, lichen and bryophytes which do not have waxy cuticle or stomata are more prone to NH3 intake in the surrounding compared to higher plants (Reiners & Olson, 1984). The uptake of NH3 by lower plants are enhanced by moisture and dew on the plants itself (ApSimon et al., 1987). There are several studies reporting the effect of NH3 emissions to the vegetation of lichen (Barkman 1969; Hawksworth & Rose 1970; Nimis et al., 1990; Søchting, 1995; Krupa, 2003; Wolseley et al., 2006) and bryophytes (Beltman et a., 1995; Kooijman & Bakker, 1995; Pitcairn et al., 1995; Paulissen, 2004). However, to the best of our knowledge, there are no published report on the effects of ammonia emissions to epiphytic terrestrial algae.
Nitrogen and phosphorus have been determined as primary limiting nutrients to algal growth (Schindler, 1971). Suppressed supply of N caused a decline in algal growth but at the same time, an excess NH3 can also affect the density and diversity of algae (Mangas-Ramirez et al., 2002). Besides NH3, NOx which is responsible for the formation of acid rain, also contribute to algal growth. When there is an excessive supply of NOx, trees lose flowers and fruits before budding. Eutrophication in water body due to excess N will contribute to algal bloom. This phenomenon rapidly depletes oxygen in water bodies and caused death to large number of algae. Algal bloom caused by eutrophication have been prove lethal or toxic to algae (Handy & Poxton, 1993).
The current study postulated that :
N-deposition played an important role in determining species diversity, that N will promote the survival of nitrophytes species and suppress acidophytes species.
NH3 emitted from N source (livestock farm) as dry deposition are deposited locally and therefore reduced in concentration at a very close distance from the livestock farm.
2.1.5 Aims and objectives
The aim of this study are as follows :
To asses the relation between distances from N source (pig and poultry farm) to algal density.
To determine which pollutant has the most effect on algal density.
To investigate whether either one or more N-gaseous play their effect on the growth of epiphytic algae.
The examine the role of aspect and bark pH in affecting algal density.
To access the effect of pollutants to bark pH.
2.2 Materials and Methods
2.2.1 Site Descriptions
This study has been conducted at a rural area in 200 acres farm located on the western side of the Windsor Great Park in Berkshire, south east England (Figure 2.2). The farm which is situated at the edge of an intensely farmed irrigated region, has been developed since 1790s where extended farming and construction of farm has taken place (www.pastscape.org. English Heritage monument records). It was used as a dairy unit then and only after April 1997, the farm was converted to a pig and poultry farm. This farm is consisting of approximately 100 sows, 200 piglets, 650 growers and 1200 chickens. These intensive livestock farms emit strong smells of ammonia.
The area is semi-arid with minimum mean annual temperature of 17.8 0C maximum of 23.5 0C. Mean annual rainfall for this area is 12.4 mm. Four sites along South-Westerly wind direction were selected along a transect at 5 m, 35 m, 150 m downwind and 400 m upwind as a control site. In each site, 3 Quercus robur (oak trees) trees were selected for biomonitoring.
Figure 2.2 : Location showing the pig and poultry farm and 3 sites following the south westerly wind direction. A= 5 m, B= 35 m, C= 150 m (downwind sites), D= 400 m (upwind as a control site).
N Gaseous Monitoring
N gaseous monitoring was carried out to monitor the concentrations of NH3, NOx, NO2 and NO using open-ended passive diffusion tube samplers supplied by Gradko UK. Tube samplers were first introduced by Palmes (Palmes et al, 1976) and have been widely used for many studies (Bower at al., 1991; Campbell, 1988; Campbell et al., 1994; Batty, 2003). The tubes were designed for passively monitoring airborne gases and molecules. They consist of an acrylic tube and two closely fitted caps and small steel meshes between the tube and the cap. Three replicate samplers were placed at each monitoring sites, at 1.5m above ground flora. The samplers were left on the sites for 3 weeks.
The sampler contained filters impregnated with phosphoric acid which absorbs gas-phase NH3 as NH4, that can be easily measured spectrophotometrically by the indophenol blue method (Allen, 1989). The mean concentration of NH3 during the exposure period was calculated using the exposure time and ammonium content (Andersen et al., 2006). Detection limit of NH3 analysis was 0.149 µg NH4. The level of NH3 were later obtained from ion chromatography with reference to a calibration curve derived from the analysis of standard ammonium solutions for NH3.
The mesh discs which detect NO2 were soaked in 50%v/v triethanolamine (TEA)/acetone solution as an absorbent. Nitrogen dioxide and its derivatives were analysed using UV spectrophotometry. The concentrations of nitrite ions absorbed by the mesh were quantitatively determined by UV/visible spectrophotometry with reference to a calibration curves derived from the analysis of standard nitrite solutions. Limit of detection for NOx and NO2 is 2.71 ppb and 0.10 ppb respectively.
2.2.3. Systematic Algal Collection
Systematic algae collection was carried out along line transect through the woodland adjacent to the pig and poultry farm, following the south westerly prevailing wind direction. One control site at 400m upwind from the farm building and three sites at the downwind direction has been set up. The downwind sites were at 5 m, 35 m and 150 m from the pig and poultry farm. Three Quercus robur at each site were placed with 15 x 15 cm quadrat, at 1.5 m above the ground, in line with passive samplers. The quadrat were placed at 1300 SE, 2100 SW and 3100 NW.
Algae within each quadrat were collected by brushing the quadrat surface with a wetted cotton bud and then steeping it in a 20 cm specimen tube containing 40 ml distilled water. Some algae were quite difficult to remove and a scalpel was then used to scrape the algae from the bark of the tree. All samples were stored in a refrigerator at 1-4°C to prevent post-sampling growth. After vigorous shaking, 10 µl of the algal suspension was pipetted onto a microscope slide. A Brunel digital light microscope at 400 x magnification was used to aid identification and for counting of algal cells. Scope Image Advance software was used to aid in image capturing.
An estimation of density was made by multiplying the total number of cells in 10 µl, to that in 40 ml, to provide an estimate of algal density in one 225 cm2 quadrat. Species identifications followed John et al., (2003); Milow & Aishah (2006); López-Bautista et al. (2006) and database for the world's algal listings (www.algaebase.org). Photomicrographs of the algae were taken to facilitate identification. Some 'difficult' species were sent to Dr Fabio Rindi (National University of Galway) and Prof David John (Natural History Museum) for further discussion and confirmation.
Bark pH analysis
Bark samples were collected beneath the quadrat used for algal collection. Bark samples were collected at 1m height from the base of the tree. Method for bark pH followed Kricke (2002) where 0.5 g of the surface tree bark were ground and soaked in vials with 10 ml deionized water. The vials were shaken vigorously and left for 30 minutes, shaken in an automatic shaker for another 20 minutes. Bark pH was measured with a Mettler Toledo MP 230 pH meter.
2.2.5 Data Analysis and Statistics
Data were analysed using SPSS, MINITAB and R statistical software. Samples were tested for equal variance using Anderson-Darling normality test. The relationships between different variables were explored using Pearson's correlation coefficient and linear regression. ANOVA and t-test were used in many cases. Tukey's Pairwise Comparison was used to test for differences between each sites. Non normally distributed data was analysed using Friedman test which was using ranking order, to investigate the role of aspect in affecting algal growth.
2.3.1 The relation between distances from source and algal density
Algal density is negatively correlated with distances from the farm (Pearson correlation coefficient, R = - 0.783, r = 88%, p = 0.003). Algae in the quadrat showed an obvious differences in terms of algal density across distance (Figure 2.3). In this study, data showed a significant increase of algae nearer to the farm (1-way ANOVA, F3,8 = 29.54, p = 0.001). Number of algae are significantly higher nearer the source at 5m and 35m compared to other sites.
Figure 2.3 : Variation in algal density per ml across distances from the source (farm). The values are the means ± SE bars. Value with different letter indicates significant differences at p < 0.05. Data shows a clear reduction of algae at 150 m from the source. Algal density at this site are almost on the same scale as in the control site (400 m upwind).
Comparing between distances, the highest density of algae was recorded at 5 m from the farm with 3166 ±160 cells/ml. This was followed by a site at 35 m from the source with 2001 ± 397 cells/ml. Further away from the farm at 150 m, algal density were reduced drastically to 332 ± 287 cells/ml. As expected, the control site which was located 400 m upwind from the farm showed the lowest number of algae at 194 ± 87.9 cells/ml.
Tukey's pairwise comparison was run to test between sites. It showed that at 5m and 35m from the farm, no significant different has been found between these two sites. The same situation were found between site at 150 m and the control site. Thus, data was pointing to the point that sites located nearer to the source were found to be significantly higher to the ones located further away from the farm. All data has been tested for normality and were found to be of normally distributed, using Anderson-Darling Normality Test.
2.3.2 Pollutant Concentrations Emitted from the Farm
NH3 showed a clear reduction in terms of concentrations as the distances increasing (Figure 2.4a). NH3 concentrations were negatively correlated with distance from the farm and this is the only pollutant which showed a clear reduction in terms of concentrations. At 5 m, NH3 concentrations was at 18.34 ± 1.38 µgm-3. The concentrations continue to decrease quite drastically at 35 m to 9.72 ± 1.69 µgm-3. At only 150 m from the farm, the NH3 concentrations was almost reaching the background data at 5.10 ± 1.78 µgm-3. NH3 concentrations at the control site, which was located at 400 m upwind was 3.74 ± 1.11 µgm-3.
Other atmospheric pollutants such as nitrogen dioxide, nitrogen oxide and nitric oxide fluctuates within distances but showed no obvious pattern (Figure 2.4b-d).
Figure 2.4 : Variations of Algal Density as a Function of Atmospheric Pollutants Across Distance From the Farm.
a) Ammonia b) Nitrogen dioxide c) Nitrogen oxide d) Nitric oxide
2. 3.3 The relation between algal density and pollutant concentrations
Out of four pollutants tested in this study, only NH3 and NOx were found to have a significant correlation with algal density (Figure 2.5a and 2.5c). NH3 was found to have a strong positive correlation with algal density (p<0.001, r = 0.912). NO2, while showing a significant correlation, only showed a mild positive correlation to algal density (p<0.05, r = 0.631). Both NO2 and NO were not significantly correlated to algal density (Figure 2.5b and 2.5d).
Figure 2.5 : Correlations between algal density and atmospheric pollutants.
a) Ammonia b) Nitrogen dioxide c) Nitrogen oxide d) Nitric oxide
2.3.4 The Role of Pollutants in Affecting the Bark pH
Bark pH was positively correlated with NH3 concentrations (R=0.768, p=0.004) and negatively correlated with distance from the pig and poultry farm (1-way ANOVA, F3,8 = 13.35, p = 0.002). Bark pH ranged from 6.12 - 6.18 at 5 m and 35 m and then reduced to 4.3 - 4.5 at sites away from the farm (Figure 2.6).
Tukey's pairwise comparison showed that there are no significant difference between bark pH at 5 m and 35 m. Both of these sites were located close to the farm. Similarly, sites further away from the farm namely site at 150 m and control site, also showed no significant different between the two.
Figure 2.6 : Variations of bark pH in relation to distance. The values are the means ± SE bars. Value with different letter indicates significant differences at p < 0.05.
In terms of a relation between bark pH and pollutant concentrations, NH3 showed a positive correlation while NOx showed a negative correlation (Figure 2.7a and 2.7c). NH3 was found to have a strong relation with bark pH (p<0.05, r = 0.768). At the highest concentrations of ammonia, bark pH reached up to almost pH 6.6. When the NH3 concentration was at the lowest concentration, bark pH tended to be more acidic, going as low as pH 4.0 (Figure 2.7a).
On the other hand, NOx showed a mild negative correlation with bark pH (p<0.05, r = -0.587). Bark pH were more acidic at higher concentrations of NOx as compared to lower concentrations (Figure 2.7c). NO2 and NO showed no significant correlation with bark pH (Figure 2.7b and 2.7d).
Figure 2.7 : Correlation between bark pH and atmospheric pollutants.
a) Ammonia b) Nitrogen dioxide c) Nitrogen oxide d) Nitric oxide
The role of Aspect in Affecting Algal Density
The ranking order of algal density in relation to aspects is 2100 SW > 1300 SE > 3100 NW. Algal density were highest at 2100 SW with 1445 ± 377 cells/ml and lowest at 3100 NW with 1383 ± 384 cells/ml (Figure 2.8). Total number of algae in the quadrat at 1300 SE was 1442 ± 430 cell/ ml. Eventhough there are differences in terms of algal density between aspects, the difference was not statistically significant. Thus, this particular study showed that aspect does not affect algal density (p=0.779, S=0.50). Data were analysed using Friedman Test for non-parametric data.
Figure 2.8 : Variations of algal density in relation to aspects.
2.4.1 Algal Density Within Close Proximity of Pollutant Source
Algal density were found to be higher in number, closer to the source of pollutants (Figure 2.3). A strong positive correlation between NH3 and algal density explains the relation between these two entity (p<0.001, r = 0.912). As concentrations of NH3 increases, algal density were also increasing (Figure 2.5a). There are 72 % reduction at 150 m from the source, and 80 % at 400 m from the source. Fowler et al., (1998) reported a reduction of 98% in the first 200 m from the source and Pitcairn et al. (2002) reported a sharp decrease in the first 200 m and 95% reduction at 650 m from the source. The number of algae were highest when the NH3 concentrations were at its peak as dissolved inorganic nitrogen such as ammonia, nitrate and nitrite usually affecting the distribution, productivity, and abundance of algae (Ryther and Dunstan, 1971; Nelson et al., 2003; Thornber et al., 2008; Pinon-Gimate (2009). Increased levels of N with decreasing distance from the pig and poultry farm (Figure 2a) is in agreement with Kauppi (1980), Pitcairn et al., (1998), Søchting (1995), Ruoss (1999) and Vingiani (2004). Higher N concentrations frequently increase the rate of agal growth (Doering et al., 1995; Harlin, 1995; Taylor et al., 1999; Thornber et al., 2008). The background data at 400 m upwind is 3.74 µgm-3. This is in perfect agreement with a work carried out in Netherlands by Buijsman et al., (1998) where mean concentrations in background data ranged from 2-4 µgm-3. This is almost similar to regions with agricultural activities in the UK, Austria and Switzerland. Sutton et al., (2001), Löflund et al., (2002) and Thoni et al., (2004) however reported a lower annual mean NH3 concentrations of <1 µgm-3 in regions without agricultural activity.
This data explained the mono-species of algae found on trees surrounding the farm. The hypothesis is Desmococcus sp. is nitrophytic species and because NH3 concentrations are high, other algal species could not continue to survive or have a less adaptation thus reducing in number. Eventually, Desmococcus sp. outgrown other algal species due to high NH3 concentrations.
Unsurprisingly, there are no other species of algae in the quadrat but the nitrogen-loving algae, Desmococcus olivaceus. High NH3 resulting in nitrophytic species was also suggested by van Herk (1999). Pitcairn et al. (1998) who speculate that an area with high nitrogen deposition will result in nitrogen-tolerant species and lack of N sensitive species. Also, they observed that species composition within 50-300 m of the emission source is adversely affected. Most of the species found within close vicinity of the source are 'weed species' and species number is reduced. Desmococcus olivaceus which is known as nitrophilous species were abundant within close proximity to the poultry and pig farm. According to Sparrius (1970), nitrophilous epiphytes are positively correlated with NH3 and at the same time, decreases acidophilus epiphytes.
In present study, NH3 concentrations close to the farm was 18 times higher than the critical level (1µgm-3). Critical level is defined as the concentration in the atmosphere above which direct adverse effects on receptors such as plants, ecosystems or materials, may occur according to present knowledge (Posthumus, 1988). Compared to other nitrogenous gaseous, NH3 is the main source of dry deposition of atmospheric pollutants within close vicinity to husbandry unit (van Herk, 2003; Frati et al., 2008).
NH3 concentrations at the closest station to the source (5 m) was highest compared to other stations (35 m, 150 m, control site) at 18.34 ± 1.38 µgm-3. In line with the theory, number of algae at this station were found to be the highest at this point with 3166 ±160 cells/ml (Figure 2.4a). As NH3 was reduced to 9.72 ± 1.69 µgm-3, algal density also decreases to 2001 ± 397 cells/ml. No significant different between algae at these two distances (5 m and 35 m). However, a significant result has been found between stations close to the source (5 m and 35 m) and further away from the source (150 m and control). This result showed that at a distance below 35 m, NH3 concentrations are still significantly higher and thus contributing to the overall algal density within these distances.
Since NH3 distribute very quickly into the air within a short distance, algal density were found to decrease accordingly. Fowler et al. (1998) and Sommer (2009) also observed the same pattern where NH3 concentrations decline sharply at increasing distances from the pollutant source. Observation made by Fowler et al. (1998) showed that 60% of NH3 emitted from the farm was deposited within 50 m and was closed to background NH3 concentrations at only 276 m from the source. This is in agreement with the work carried out by Skiba et al. (2006) where they observed an increase of NH3 concentrations up to 40 times, nearer the source as opposed to the background site.
At 150 m from the farm, algal density were significantly lower than at 5 m and 35 m (Figure 2.3). With NH3 concentrations dropped to 5.10 ± 1.78 µgm-3, algal density was decreasing to 332 ± 287 cells/ml (Figure 2.4a). Interestingly, algal density at 5 m and 35 m showed no significant difference with the algae collected at the control site. Located 400 m upwind from the farm, with no or little effect of NH3, algae at the control site were only 194 ± 87.9 cells/ml (Figure 2.3). It showed that at only 150 m from the source, there are only a little effect of NH3 in affecting the growth of algae. This finding is in line with a research conducted by Sommer et al. (2009) which concluded that at 150-200 m from the pollutant source, the farm was only marginally affected by NH3 emitted from the chicken farm.
Apart from NH3, other N-deposited gaseous emitted from the farm only showed a mild fluctuation between the distances (Figure 2.4b-d). No apparent pattern were observed for NO2, NOX and NO. These gaseous were also found not to have any significant relation to the number of algae, except for NOx (Figure 2.5c). Though only showing a mild positive correlation (p<0.05, r = 0.631), the effect of NOx is thought to have an effect on algal density. According to Sutton et al. (1993), areas of high deposition has faced a change in vegetation due to increased deposition. Eutrophic plant species was found to increase at the expense of oligotrophic species.
2.4.2 Effects of Bark pH and Aspect in Affecting the Algal Density
Pollutant concentrations especially of NH3 are believed to play a role in determining the bark pH (van Herk, 2003). In this study, pH ranged from 4.3 to 6.2. Barkman (1958) reported in his work that typical pH range for Quercus sp. is between 3.7-5. Van Herk (2001) reported a slightly different pH range, from 3.7-4.4 in forest environment, 3.8-5.0 in urban areas and 5.6-6.4 in intense agricultural areas. As the NH3 concentrations increased, the pH also increased (Figure 2.7a). Closer to the farm where NH3 concentrations was highest, bark pH was at the highest as well. Moving further away from the farm where NH3 concentrations was the lowest, value of bark pH was also at the lowest point (Figure 2.6).
Higher density of algae closer to the farm are as a result of the pH. Higher pH provide better environment for algal growth. Green algae normally grow better at a higher pH. Moss (1973) stated that green algae Desmidium swartzii would not survive when pH is less than 4. Long exposure of NH3 promotes nitrophilus species of lichens and this were mainly due to rising bark pH, especially within 2-3km from the pollutant source (van Herk, 2001; van Herk et al., 2003). Due to alkaline properties in NH3, the pH increased and ultimately helped in shifting the species composition (van Herk, 2001).
The growth of lichen and bryophytes are known to be affected by aspect or orientation (Plitt & Pessin 1924; Barkman 1958). This is due to the fact that orientation will affect amount of light received by lichens and bryophytes. Also, aspects are affecting humidity, which known to favour the growth (Ferris-Kaan, 1995; Ferris and Carter, 2000). However, Buckley et al., (1997) stated that light intensity does not necessarily have strong influences on vegetation.
In northern temperate areas, lichen are usually higher on the northern side of trees where the area are shielded from direct sunlight thus receiving less intensity of light (Barkman, 1958; Brodo, 1973; Stubbs, 1989; Ferris & Carter, 2000). In current study, higher number of algae were on the southwest side of the tree. The same conclusion was derived by work from Gómez, (1985). According to Barkman (1958) and Rubiano (1988), lichen coverage are higher when it is protected by local wind. In this case, eventhough southwest area of the tree has direct effect of the wind, the number of algae are higher due to higher NH3 concentrations brought about by the wind.
According to Hylander (2005) who studied the effect of aspects on bryophytes in boreal forest, there was a significant effect between bryophtes on the north and south. He concluded that the north-facing bryophytes have less percentage of bryophytes declination compared to the south-facing bryophytes.
In this study, algae at different angle of the tree showed no significant different with the aspects (Figure 2.8). Eventhough there were a higher number of algae at 2100 SW compared to other aspects, the difference were not statistically significant. This hypothesis is that the sampling site is the homogenous type, thus permitting almost the same amount of light and shades between trees regardless of their location. Marques et al. (2004) also reported that lichen transplanted facing the wind and shielded from the wind do not differ and thus concluded that orientation do not play a significant role in their study.
This study are following the patterns of many other studies carried out at livestock farm over the past two decades, evaluating the involvement and effect of atmospheric pollutants from livestock farm to the adjacent area. The hypotheses that N-deposition played an important role in determining species diversity was proved to be correct from the results presented from this current work. N deposition was found to aid a healthy growth of Desmococcus olivaceus, the only dominant algal species available in the sites. The existing of only one dominant species of epiphytic algae on Quercus robur within close proximity of the farm might pointing us to the right direction - that high N deposition are contributing to nitrophytes species and may alter community ecosystem. It is believed that other algal species could not tolerate high N and had been suppressed by N thriving species such as D. olivaceus. In other words, high N content in the atmosphere and the surface triggered the survival of nitrophytes species and suppressed acidophytes species.
As the number of algae decreased are positively correlated with the distance from the farm, NH3 has been treated as the main pollutant which affecting the algae. Although other gaseous such as NOx also showing a positive correlation but the effect of NH3 are very significant that we could almost regarded NH3 as the major factor affecting the number of algae in this area.
In terms of conservation effort, attention should be paid to an area of high N to prevent further loss to algal species which could not thrive in an area of high N. This step will also prevent community change within close proximity of pig and poultry farm.