Evaluation of Anthropogenic Carbon Dioxide (CO2) Concentrations along River Nworie, Imo State, Nigeria

The importance of wetlands along rivers (flood plains) as sink or source of CO2 gas has always been overlooked. In the face of climate change floods along river, experience nutrient loading from flood waters, and tend to release CO2 in significant amounts. The present study therefore examines two climatic factors as these relate to CO2 concentrations along river Nworie and compared with control. Reconnaissance study with land use namely bridge, road construction, busy junction and waste dumpsite were designated sampling points while the control was an area with very little anthropogenic disturbance. CO2 concentrations were measured three times daily, for seven weeks and weekly average was recorded using CO2 analyzer AZ77535. Temperature and relative humidity were measured concurrently as CO2 concentrations. Results showed that CO2 concentrations ranged from 500 ± 7.35 to 579 ± 4.18 ppm with average value of 575.5 ± 2.76 ppm which was higher than control (470.71 ± 15.43 ppm). Temperature was lowest at point B and D (30.70oC) and showed an average ranged of 33.03 ± 0.76 to 38.35 ± 1.65oC> Control (29 ± 0.82oC). Relative humidity (RH) was generally low at all points with an average of 56.18 ± 1.18 to 68.98 ± 1.43% <control (66.70 ± 6.37%). Standard deviations were low for all parameters signifying good results with all parameters showing 0.5% to 10.3% variability. All relationships between CO2/temperature and CO2/RH were positive and better described as exponential relationship. Anthropohenic impact estimate were very high with respect to control point which ranged 103.88% to 127 Nigeria 25%. The high estimate obtained suggested that the many activities experienced along the river is causing high temperature and thus high CO2 concentrations. However, a bigger study with more study sites is required to elucidate more accurate distributions of emissions and their source regions for tracking the changes associated with anthropogenic activities and emission mitigation policies. Citation: Wirnkor VA, Ebere EC, Ngozi VE (2018) Evaluation of Anthropogenic Carbon Dioxide (CO2) Concentrations along River Nworie, Imo State, Nigeria. Environ Pollut Climate Change 2: 159. 10.4172/2573-458X.1000159


Introduction
The worldwide concern with global climate has highlighted the challenges faced by both industrialized and developing countries on the issue of increasing greenhouse gas emissions. These gases are chlorofluorocarbons (CFC), carbon dioxide (CO 2 ), methane (CH 4 ), and nitrogen oxides (NO x ) which absorbs the radiation in the earth atmospheric system. Excess of these gases often affect the environment causing global warming [1]. While the greenhouse effect has been beneficial to maintain global temperatures compatible to human life, recent increases in average temperatures due to human activities are causing great alarm.
Of all greenhouse gases responsible for global warming, CO 2 is of major concern. Atmospheric CO 2 is produced naturally from volcanic out gassing, the combination of organic matter and the respiration processes of living anaerobic organisms [2] and artificially from combustion of various fossil fuels and deforestation etc. The artificial sources of CO 2 emissions are generally thought to be responsible for global warming causing increase in atmospheric CO 2 by about 43 % since the beginning of the age of industrialization. In 2016, the Earth's atmosphere CO 2 concentration is averagely 402 parts per million (by volume) which continues to increase [3].
The concentrations of carbon dioxide in the atmosphere as well as climatic parameters such as temperature and relative humidity fluctuate slightly with the seasons and on regional basis. This is evident in some studies conducted from different areas of the world [4][5][6][7][8][9][10][11], in sub-Saharan West Africa [12][13][14][15] and Nigeria has been reviewed [16][17][18]. The predictions of global future climate change rely mostly on the ability to quantify fluxes of greenhouse gases, especially CO 2 , at regional scales. However, micronutrients along river banks are equally influenced by greenhouse gases and so the current project is important.
The aim of the study is to determine the dry season variation of atmospheric carbon dioxide along River Nworie, Owerri Municipal, Imo state, Nigeria. Since oceans with land sequesters about half of the anthropogenic emissions of atmospheric CO 2 [16][17][18][19]. Wetlands along many rivers have not been characterized for greenhouse gases emissions or absorption; hence the current research contributes to information on this subject. Also, measurements over the wetland are very helpful for understanding emissions growth as well as verifying the mitigation policies.

Study area
Nworie River is a first order stream that runs about 5 km course across Owerri metropolis in Imo State before emptying into Otamiri

Method of data analysis
Data analysis was done using Microsoft excel 2007 and values of all the results from the sampling points was recorded as calculated mean values of ambient temperature, relative humidity and air CO 2 concentrations for morning, afternoon and evening hours. The standard deviation (SD) was determined and co-efficient of variation (CV %) was used to determine variation in the concentration of CO 2 between samplings points using equation 1.
Anthropogenicity was estimated according to [23] given in equation 2. It is the ratio actual carbon dioxide concentration to reference concentrations expressed in percentage. This estimates the impact of human activities on ambient concentration of carbon dioxide along river Nworie.

Measured CO concentration APn
Reference CO concentration = × The control data were used as the reference concentrations.

Results and Discussion
The results for variability and basic descriptive statistical summary for temperature, relative humidity and ambient CO 2 concentration obtained at various points of the river for seven weeks during November and December 2016 is presented in Table  The trend for CO 2 concentrations for the sampling points and control is presented in Figure 2. The concentration of atmospheric River. It is about 9.2 km long. Imo state is situated in the southern rain forest vegetation belt of Nigeria, it has between latitude 5 o and longitude 7 o 34 o E. It has an annual rainfall of about 1700-2500 mm. The climate of the study area follows a tropical pattern with the rainy season lasting between seven and eight months between April and October with interruption in August and dry season running through November to March. Average humidity of 80%-85% occurs during the rainy season. Temperature is similar all over the state, with maximum values ranging from 280 o C to 350 o C and minimum values from 190 o C to 240 o C.

Control point
The control is a land area that is saturated with water from the rainy season. The area experiences no anthropogenic disturbance and located around Bishop's Court, Owerri which is more than 7 km away from river Nworie. Geographically, it is located at Latitude-N 5 o 29.3623', Longitude-E 7 o 1.4622' and area is filled with grassland Figure 1a and 1b.

Atmospheric CO 2 measurement
AZ 77535 CO 2 gas analyzer (AZ Technologies, Taiwan) was the instrument used to determine the CO 2 on the surface/air above the water. The instrument is designed with NDIR (Non-Dispersive Infrared) waveguide technology sensor. The instrument carried out automatic analysis of the sample of ambient air with the use of the physical properties that gives continuous output signal to the analyzer which returns the values of the CO 2 , temperature and relative humidity, which were read from the screen. The instrument which was held at arm length and about 10 cm above the water was used to obtain the concentration of CO 2 in the air. Sampling was carried at the hours of morning, afternoon and evening at six different points and the control point for seven weeks with mean reported for each week. These hours were chosen based on the fact that they are meteorological hours recommended for weather observation by world meteorological organization.
The data were collected in year 2016 dry season from November to December.    CO 2 ranged from 550 ppm to 572 ppm in week one, from 547 ppm to 572 ppm in week two, from 544 ppm to 563 ppm in week three, from 536 ppm to 575 in week four, from 568 ppm to 579 ppm in week six while week seven showed ranges of 509 ppm to 574 ppm respectively. Higher concentrations were recorded in the present study when compared with concentration of 402 ppm recorded in early 2016 for average global concentration of CO 2 . The obtained concentrations at river Nworie was generally higher than the control with range of 480 ppm (week one) to 490 ppm (week seven) and mean of 470.71 ± 15.43 ppm. The present study also showed higher concentrations when compared to annual average atmospheric CO 2 concentrations observed in Ahmedabad in western India (413.0 ± 13.7 ppm) in 2015 [24]. The high CO 2 is due mainly to anthropogenic activities carried out along the river such as the use of potable water, generation of wastewater, the generation of solid waste and vehicle exhaust [25,26]. The cycles of CO 2 is mostly governed by the strength of emission sources, sinks and transport patterns. NASA [27] reported that human-made carbon dioxide (CO 2 ) continues to increase above levels not seen before and is not absorbed by vegetation and the oceans. The increase in atmospheric concentration of CO 2 , and thus in the CO 2 induced greenhouse effect, is the reason for the rise in average global temperature causing global warming [8,27].

Weeks PARAMETERS
The variability of CO 2 along the river show little variations as all coefficients of variations are less than 20% (Table 1). However, the highest variability was recorded in the seventh week of the study (4.5%) while in week six the lowest was recorded (0.5). The reason for the little variations could be due to the sampling points falling in the same geographical location.
The trends of temperature from week one to seven is introduced in Figure 4. In week one temperature ranged from 31.9 o C at point C to 33.8 at point F. During week two, the temperatures at the sampling point dropped (as low as 30.5 o C) except for point B and F with slight and heavy increase in temperature respectively. From week three, there was temperature rise and drop from the week four to five. In the sixth, the highest temperature was recorded at point F while B and D recorded lowest. There was a significant increase at point B and D, temperature rising from 30.7 o C to 39.9 o C respectively. There were also temperature rise at points C, E, and F while reducing temperature was observed at point A. Throughout the study, all points showed higher temperature when compared to control where we recorded a range of 28 to 30 o C and mean of 29 ± 0.82 o C.
Though temperatures were high, it showed little variability like all other parameters revealed little variability (<20%, Table 1). High temperature in urban areas such as Lagos (33 o C), Warri (32.  [28]. This rise in temperature implies that there is rise in CO 2 . Soon [29] using climate modeling asserted that increase in atmospheric CO 2 increases with increasing atmospheric temperature. This is evident in the current study where high temperatures along river Nworie showed high CO 2 concentrations as opposed to the observation at the control where low temperature followed low CO 2 concentrations.
Generally, from week one to week seven low humidity was recorded in all points, except for week two where a maximum RH of 71.8% was recorded Figure 4. However, the control showed high humidity when compared with observations made at river Nworie except in week one. The range of RH was 60 to 73.9% with mean of 66.70 ± 6.37%. The low humidity could be due to the season of study. There is generally high temperature during dry season and thus little amount water vapors in the environment. Relative humidity gives amount of water vapour in the environment and depends on the temperature. Therefore, the high humidity recorded at the control points is due to the low temperature observed in that area.

Relationship between climatic parameters and CO 2 concentration during the study
In order to establish a relationship between ambient CO 2 concentrations and climatic parameters measured, we conducted a linear, exponential and power regression analysis. Table 2 shows the summary of the relationships showing equations and regression coefficients. A good correlation equation between temperature and CO 2 as well as RH and CO 2 was shown in Table 2. Regression analysis revealed that increasing temperatures could lead to increasing CO 2 concentration while CO 2 concentrations increased for decreasing    All relationships showed positive slope during the study except in week 5 for temperature-CO 2 relationship. Meanwhile, negative slope were obtained in week 2, 5, 6 and 7 for relative humidity-CO 2 relationship. The relationship equations showed that the plots didn't follow the origin (0) and thus having high intercept. This observation follows the regression coefficient obtained suggesting that the relationship isn't perfect (<1). Positive relationship was also reported for CO 2 emissions from the lower Red River in Vietnam [30].
To determine which relationship is more pronounced with CO 2 concentration, we created a trend plot which compared the different relationships. The trend results are presented in Figure 5. Looking at Figure 5a critically, it could be observed that the relationship between CO 2 and temperature is better described by an exponential equation especially in the fourth week. Although a power and linear relationships followed closely. However, with relative humidity the trend follows similar pattern (Figure 5b). There was high relationship was recorded in week 1 and 2 of the study which drops with weeks.

Anthropogenicity (Human Impact Estimation)
We estimated the impact of human activities on the high concentration of carbon dioxide along river Nworie using anthropogenic model as described in equation 2. When discussing climate change,    it is often used to refer to emissions produced as a result of human activities. We estimate the impact based on data obtained from the control point. The computed anthropogenicity is presented in Table 3.
Generally, high anthropogenic impact estimate were obtained throughout the study period which ranged from 103.88% to 127.25%. The high estimate obtained suggested that the many activities experienced along the river is causing high temperature and thus high CO 2 concentrations. Activities experienced along this area include waste dumpsite which contains organic matter and in the presence of warmer temperature and moisture decomposes and oxidizes, releasing CO 2 in the atmosphere. Other activities include emission for automobile exhaust, automobile workshop, building constructions, road construction, destroyed vegetation mostly grasses and polluted water, sand mining and dredging on both sides of the Nworie River. The drainage and destruction can result in substantial carbon emission [31-33].
The week-wise trend for anthropogneicity is introduced in Figure  6. Week-wise impact showed that the highest human impact on CO 2 concentration was observed in the fifth week (126.04%) while the least in week one (100.26%). The week-wise impact follows the trend; week 5>week 6>week 4>week 2>week 7>week 1 respectively. Meanwhile, site-wise trend is introduced in Figure 7. The highest estimated value was obtained at point F (121.08%) and least recorded at point C (117.92%). The site-wise impact follows the trend; point F>point E>point B>point A>point D>point C respectively.

Conclusion
With the rising global warming, awareness results from this work confirm elevated CO 2 concentrations over 44% above early 2016 average global CO 2 concentration. The concentrations according to sampling points varied with low % variability but it was observed that temperature had more linear and exponential relationships with CO 2 concentrations. Relative humidity exhibited similar trend for linear, exponential and power relationships with CO 2 concentrations. The various human activities have contributed to rising CO 2 concentrations along river Nworie which is confirmed by the high annthropohenicity (103.88% to 127.25%) recorded with respect to the control point. However, a bigger study with more study sites is required over multiple years to elucidate more accurate distributions of emissions and their source regions for tracking the changes associated with anthropogenic activities and emission mitigation policies.