An Assessment of the Physicochemical Parameters of Mananga River, Cebu, Philippines

IAMURE International Journal of Ecology and Conservation

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An Assessment of the Physicochemical Parameters of Mananga River, Cebu, Philippines

MARY JOYCE L. FLORESORCID No. 0000-0003-1287-0882

[email protected] of the Philippines Cebu

Macrina T. ZafarallaORCID No. 0000-0002-9316-9766

[email protected] of the Philippines Los Baños

Abstract - The Mananga River today is a source of potable water to meet the demands of a fast growing Cebu metropolis. The physico-chemical parameters of Mananga River were studied to assess its water quality status. Six sample collections were done from February to De-cember 2006 in 3 monitoring stations covering the upstream (S1), mid-stream (S2) and downstream (S3) of Mananga River. Results showed significant spatial variation (p<0.05) in the studied physicochemical parameters except for alkalinity, total phosphates and nitrate-nitrogen (NO3-N). Significant temporal variation (p<0.05) was also observed for the factors except for stream width, biological oxygen demand (BOD5) and total suspended solids (TSS). Flow velocity showed significant positive correlation with discharge, pH, DO and NO3-N, and negative correlation with water temperature and TSS. Water temperature cor-related negatively with DO and pH, and positively with TSS, with the latter showing a positive correlation with BOD5. The results implied

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that water currents play a major role in the distribution of dissolved substances and the suspension of sediments. Water quality of the stud-ied segments of Mananga River progressively decreased downstream and was more pronounced during the dry periods. Results also indi-cated that the river was receiving loads of organic matter from natural and anthropogenic sources.

Keywords - ecology, Mananga River, water quality, flow velocity, Cebu City, Philippines

INTRODUCTION

Metropolitan Cebu is the second largest urban center in the coun-try. It includes the cities of Cebu, Mandaue, Lapu-Lapu, and Talisay; the municipalities of Cordova, Consolacion, Liloan, Compostela, Min-glanilla, and Naga. The strategic location of the province has attracted migrants to the newly established growth centers outside the met-ropolitan core, thus increasing the population of Metro Cebu (Cebu City Land Use Committee Technical Working Group, 1998). Cebu has an average annual growth rate of 3.07%, one of the fastest in the re-gion, with an estimated 1.69 million residents in Metro Cebu alone (NSO, 2000). As the population grew demand for potable water also increased. Metro Cebu’s water demand as of 1998 was estimated at 234,000 cubic meters per day (m3/day), and estimated to increase rap-idly to 375,000 m3/day by year 2010 (Villafañe, 2001). The water supply of Metro Cebu depends mainly (98%) on groundwater, wherein major-ity is supplied by the Metropolitan Cebu Water District (MCWD). The limited groundwater resources relative to water demand prompted the government of Cebu, with MCWD as the main water utility firm, to tap surface waters as sources of potable water. In 1986, a 2-phase development plan recommending the development of the Mananga River was prepared (Asian Development Bank [ADB], 2002). The first phase involved the construction of an infiltration facility to increase the recharge rate in Jaclupan Valley, Talisay City. Phase II sees the con-struction of a 90-m dam upstream of Mananga Phase I project. Manan-ga Phase I project has been in operation since 1997.

According to Bagarinao et al. (2003), the Mananga watershed from


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which the Mananga River drains, has already lost its original forest cover (i.e. molave and dipterocarp) since 1956. This predominantly ag-ricultural and brushland landscapes (29.8% and 56.7%, respectively) have threatened the ecological integrity of the watershed and the river that drains from this land. Corn and vegetables are usually planted on the steep slopes of the Mananga watershed where most of the time the soils are not good for agriculture (University of San Carlos-Water Re-source Center [USC-WRC], 2000), hence chemical fertilizers (e.g., Urea and N-P-K) are applied to increase soil fertility. A survey conducted by the Cebu City water resource committee in the upland communities of Cebu City (mostly located at the upper portion of the Mananga wa-tershed) revealed that about 83% of the upland community residents did not have sanitary toilets. Shrubs and open space were the common areas for human waste disposal (Magno, 2006). Similar problems can be encountered in the middle and lower portions of the Mananga wa-tershed (Talisay City area), where more than 40% of the total number of households have no toilets. Livestock is also raised in these areas either on backyard scale or in large farms (Talisay City Planning and Development Office [CPDO], 2001). During heavy rains, these human and animal wastes could be carried with runoff water into the river.

This study was carried out to determine the spatial and temporal changes in the Mananga River’s water quality based on the results of new monitoring of selected physicochemical parameters and extant data or information.

FRAMEWORK

Anthropogenic Impacts on Streams and Rivers

Water is vital for life, including human life. Unfortunately, only about 1% of the Earth’s water is freshwater; the rest is saltwater in seas and oceans. Major ecosystems (i.e. seas, oceans and forests) depend on freshwater inputs for growth and maintenance of quality (i.e. salinity, temperature, organic and inorganic material content, etc.). The impor-tance of freshwater sources, especially rivers and streams, to humans has been well documented throughout human history. In fact, the first civilizations arose in the Nile, Tigris, and Euphrates river basins (In-


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ternational Union for Conservation of Nature & Population Reference Bureau [IUCN & PRB], 1996).

According to Malmqvisti and Rundle (2002), running waters are perhaps the most exploited ecosystem on the planet as they have been the focus of humans for water supplies, irrigation, electricity genera-tion, and waste disposal. The major factors affecting changes in run-ning waters (i.e. physical habitat and water chemistry alteration) come from human activities, such as urbanization, industry, land use change and waterways alterations. Studies in Asian countries have shown a di-rect relationship between human population density, lack of sanitary infrastructure, and river water quality. In Ho Chi Minh City, Vietnam for instance, the increase in population and rapid economic growth after the Doi Moi (Renovation) Policy have resulted to the degradation of surface and underground water sources due to pollution (Duc and Truong, 2003). In the Philippines, the presence of effluents from the industries as well as domestic sewage have significantly contributed to the deterioration of the water quality of the rivers passing through highly populated areas, as in the case of the San Juan and San Cristobal Rivers in Calamba, Laguna (Madamba et al., 1992).

Physicochemical Monitoring in Rivers and Streams

For years, chemical examination has been the predominant moni-toring approach in aquatic bodies. It measures temperature, dissolved oxygen, pH, etc. This kind of monitoring gives a general assessment of how healthy or unhealthy a water body is. For most studies of aquatic systems, it is impossible to measure all variables. Analysis is usually limited to just a few selected parameters. The time required for collect-ing and analyzing a water sample has to be considered since this is the factor that most often limit the number of variables.

Temperature plays a vital part in chemical and biochemical reac-tions (Koycheva and Karney, 2009) and is one of the most important physical factors that influence species distribution on earth (Krohne, 2000). Water temperature affects the rate of many of the river’s biologi-cal and chemical processes (i.e. self-purification). It affects the oxygen content of the water (cold water holds more oxygen), the rate of plant growth, and the metabolic rate of aquatic organisms. It varies with


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geographical location and anthropogenic effects (Jurgelėnaitė et al., 2012).

The pH of water influences both physicochemical and biologi-cal processes, such as the availability and toxicity of nutrients, met-als, and other important compounds. A study by Vila-Gispert et al. (2002) shows the effect of riparian cover and nutrient runoff on river water pH. It was highest in areas with poorly developed riparian cover and abundant algae due to nutrient runoff, raising the pH through photosynthesis. In contrast, pH was lowest in the area where there is shading from well-developed riparian cover resulting to low nutrient input. Algae abundance was reduced, and the breakdown of organic detritus (mainly leaves) also lowered the pH.

Dissolved oxygen (DO) levels indicate the capacity of a natural body of water for maintaining aquatic life (Singh et al., 2010; Ugwu and Wakawa, 2012). Flowing water can dissolve more oxygen than still water. It fluctuates seasonally, and within a 24-hour period. The amount of DO varies with water temperature and with altitude. An adequate supply of DO is essential for the maintenance of self-purifi-cation processes in natural water systems and waste treatment plants Zeb et al. (2011). Decomposing organic material in the water lowers the amount of oxygen available to aquatic organisms.

Stream flow or discharge affects the dilution properties of a river, an important measurement for the quantitative analysis of pollution problems. Discharge of many rivers is often related to seasonality (Dettinger and Diaz, 2000).

Alkalinity levels measure the buffering ability of the stream—its ability to maintain constant pH levels inspite influx of acidic chemicals such as those from a hazardous materials spill or long-term exposure to acid rain (Oram, 2008).

Total suspended solids (TSS) affects water clarity and light pene-tration (due to increased turbidity), temperature, the dissolved constit-uents of surface water, the adsorption of toxic substances and the com-


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position, distribution and rate of sedimentation of matter. Suspended particles may inhibit light penetration (Adakole et al., 2003; Ugwu and Wakawa, 2012) thus greater absorption of solar energy occurs near the surface, increasing surface temperature. High TSS in a water body can often mean higher concentrations of bacteria, nutrients, pesticides, and metals in the water because suspended particles provide attachment places for these other pollutants (Health Canada, 2012).

Phosphorus is considered to be an essential macro nutrient. Ele-vated concentrations of this nutrient in some water bodies contribute to accelerated eutrophication (Sharpley et al., 2003). Sources include domestic wastewater, industrial effluents, agricultural drainage from fertilized land, and changes in land use in areas where phosphorous is naturally abundant in the soil (Ugwu and Wakawa, 2012).

Nitrogen in surface water and wastewater may come in the form of organic nitrogen, ammonia, nitrate and nitrite. Upon decay, vegetable and animal debris and animal excrement can also be significant natu-ral sources of nitrates in water (Adeyeye and Abulude, 2004). Anthro-pogenic sources of nitrates include municipal waters, industrial waste waters and septic tanks (Health Canada, 2012; Ugwu and Wakawa, 2012).

The aerobic decomposition of organic matter by bacteria requires oxygen. Biological oxygen demand (BOD5) is an important measure-ment of the impact that sewage discharge may have upon a water body because a certain amount of oxygen will be used in the breakdown of the wastewater (Glutting, 2001). Oxygen depletion is faster when the BOD is greater so that oxygen available to aquatic life becomes lesser (Ugwu and Wakawa, 2012). Since the effects of high BOD are the same as those for low DO, aquatic organisms become stressed. Less tolerant species could suffocate and die. BOD determination therefore, is one of the most useful and sensitive test for the detection and measure-ment of organic pollution.

Figure 1 shows the processes and interactions affecting Mananga River water quality. Changes in the physical and chemical aspects of Mananga River going downstream could be attributed to two poten-


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tial factors, namely: (a) the natural physical aspect of the stream such as gradient, channel depth and width, and (b) external factors such as season, riparian cover, watershed characteristics which included natu-ral geology and land use (used as proxy to reflect anthropogenic ac-tivities). Variability in Mananga River’s form and function showed the longitudinal connectivity and spatial complexity of the whole river, as well as the processes and interactions with the watershed from which it drains. The river as a sub-system integrates all the inputs coming from the watershed landscape (Fausch et al., 2002; Ward et al., 2002; Allan, 2004).

The physical gradient from source to mouth modify the chemical system. Precipitation falling on land flows to bodies of water carry-ing dissolved substances and particles along the way (Muniyan and Ambedkar, 2011). Volumes of water may run-off to rivers due to denuded riparian zones and watersheds, changing a stream chan-nel’s morphology, shape and even its hydrology. The environmental state of the river is therefore, reflective of the environmental state of the watershed from which it drains, hence the importance of stream and river monitoring.

OBJECTIVES OF THE STUDY

The general objective of this study was to assess the temporal and spatial changes in environmental quality of Mananga River based on selected physicochemical parameters. Specifically, this piece of research aimed to: (1) to measure the dissolved oxygen (DO), pH, temperature, stream flow, stream width, levels of alkalinity, nitrate-nitrogen (NO3-N), total phosphates, total suspended solids (TSS), and biological oxygen demand (BOD5); (2) to determine the relationship of the different parameters studied; and (3) to determine the interplay of factors impinging on the physicochemical state of the river.

Hypothesis of the Study

The Mananga River system has its own form and function that are subject to the influences of natural and anthropogenic factors in its watershed. Progressive changes in its physical and chemical attributes


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may occur owing to these factors. The changes can be detected along the length of the river using selected physicochemical parameters.

Figure 1. The conceptual framework.


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MATERIALS AND METHODS

The Study Site

The Mananga watershed is accessible through the Manipis Road via Barangay Tabunok in Talisay City or through the Transcentral High-way in Barangay Busay, Lahug, Cebu City. It has several sub-catch-ments that drain into the Mananga River, which starts in the middle of Cebu Island and goes to the south as it traverses the high mountain range at the eastern part. It drains into the southwestern part of the Mananga-Kotkot-Lusaran watershed through a narrow gorge in Ba-rangay Jaclupan, and finally traverses through Talisay City.

Based on a recent topographic map of the area (Fig. 2), 3 monitor-ing stations, Station 1 (S1, upstream), Station 2 (S2, midstream) and Station 3 (S3, downstream), were selected and marked using a Global Positioning System (GPS).

S1 of the Mananga River was located in barangay Bonbon (10°22’24.2”N, 123°49’53.3”E), where the headwaters of the watershed converge and had relatively minimal anthropogenic impact. How-ever, because of the presence of a spring, people were seen washing and bathing at this site. Vegetation near the banks was generally of the grass and shrub types with few coconut trees while in the river were few macrophytes. It is about 38 km from the Cebu City proper. S2 was located at Camp IV (10°19’06.1”N, 123°49’06.3”E) is about 6.3 km downstream of S1. There were agricultural, residential, and sand quarrying activities in the area. Riparian vegetation cover and macro-phytes were similar to that of S1. S3, about 8.4 km from S2, was near a closed dumpsite in barangay Dumlog, Talisay City (10°14’38.2”N, 123°50’05.5”E). It was a site with more agricultural, industrial and do-mestic activities than the other stations. Riparian cover was poor, and no vegetation was observed in the river. Description of the study sites can also be sourced from Flores and Zafaralla (2012).

Data Collection

There were 6 sample collections in each station between 0700 and 1100 hrs in the year 2006 (February 18, April 5, May 3, May 16, Sep-tember 23 and December 2) to establish data trends reflective of rain-


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fall variation. Direct on site measurements were done in replicates for dissolved oxygen (DO), pH, water temperature, stream flow, stream width, and water depth using pre-calibrated portable field instru-ments such as a DO meter (YSI brand); a field thermometer for tem-perature measurement; and an electronic hand-held pH pen (Mil-waukee brand). The protocols used were generally adapted from the USEPA Volunteer Stream Monitoring Methods Manual (1997). For the analyses of alkalinity, nitrate-nitrogen (NO3-N), total phosphates, total suspended solids (TSS), and biological oxygen demand (BOD5), water samples were brought to A Kaschel Laboratory Company (Technolab), which used methods adapted from American Public Health Associa-tion (1998). Rainfall data were gathered from the nearest MCWD sta-tion in barangay Bonbon. Secondary data (i.e. digitized maps) were used in the analyses of land use.

Figure 2. The study site and its sampling stations


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Statistical Analysis

The physicochemical variables were subjected to the Statistical Package for Social Sciences (SPSS) Version 17 software (trial version). To determine the significance of the temporal and spatial variability, the one-way Analysis of Variance (ANOVA) was used. Pearson corre-lation analysis was used to determine the magnitude and nature of the relationship between variables.

RESULTS AND DISCUSSION

Table 1 shows that all factors, with the exception of alkalinity, total phosphates and nitrate-nitrogen (NO3-N), varied significantly with lo-cation (p<0.05). There was also significant seasonal variability (p<0.05) for almost all physicochemical parameters, except for stream width, biological oxygen demand (BOD5) and total suspended solids (TSS).

Table 1. Summary of results of the one-way analysis of variance (ANOVA)

F-value

Parameter Station Sampling Period

Water temperature (°C) 11.95* 2.76*pH 9.49* 20.72*Dissolved oxygen (mg L-1) 7.19* 14.04*Flow velocity (m s-1) 3.77* 8.15*Water depth (m) 9.58* 2.83*Stream width (m) 7.49* 0.95Discharge rate (m3 s-1) 14.58* 7.99*BOD5 (mg L-1) 4.40* 0.27Alkalinity (mg L-1) 1.48 7.28*Total phosphates (mg L-1) 0.09 109.40*Nitrate-nitrogen (mg L-1) 0.15 186.22*Total suspended solids (mg L-1) 9.72* 1.09

* The mean difference is significant at p<0.05 level (One-Way ANOVA)


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Flow velocity was faster in the upper stations, S1 and S2, especially in September (Tables 2 and 3), a period of high rainfall (Fig. 3). Aside from the inherent change in slope gradient from upstream to down-stream, many rivers show an annual mean pattern of flow related to seasonality (Dettinger and Diaz, 2000) with high water causing in-creased velocity (Smith and Smith, 2000). Table 4 shows that in Manan-ga River, flow velocity significantly varied directly with discharge rate (r = 0.6), pH (r = 0.5), DO (r = 0.6) and NO3-N (r = 0.4), but inversely with temperature (r = -0.5) and TSS (r = -0.5). These correlations imply that flow velocity plays a major role in influencing river or stream vari-ables such as the distribution of dissolved substance (i.e. gases, nutri-ents) and the suspension of sediment (Muniyan and Ambedkar, 2011).

Discharge rate or stream flow was generally high in S2 and S3, com-pared with S1 (Table 2), especially during periods of high rainfall (Fig. 3 and Table 3). This did not coincide with the flow velocity results. This could be because stream flow is not only a function of velocity; it is also a function of volume which is obtainable from the product of the stream width and stream depth (Poole and Berman, 2001). Table 2 shows that the stream width and depth of S2 and S3 were higher than that of S1.

Table 2. Summary of the physicochemical variables per sampling station. Values are Mean ± SE (minimum

and maximum values in parentheses)

Parameter Station 1 (S1)a Station 2 (S2)b Station 3 (S3)c

Water temperature (°C) 26.00 ± 0.59 (22.00-31.00)

26.64 ± 0.19 (25.00-28.00)

28.94 ± 0.47 (27.00-32.00)

pH 8.76 ± 0.10 (8.20-9.60)

8.55 ± 0.12 (8.00-9.50)

8.03 ± 0.14 (7.30-9.20)

Dissolved oxygen (mg L-1)

6.52 ± 0.24 (5.30-8.40)

6.87 ± 0.35 (4.80-8.60)

5.45 ± 0.22 (3.60-6.60)

Flow velocity (m s-1) 0.34 ± 0.03 (0.11-0.59)

0.35 ± 0.03 (0.13-0.58)

0.23 ± 0.04(0.05-0.51)


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Water depth (m) 0.12 ± 0.02 (0.03-0.24)

0.21 ± 0.01 (0.15-0.27)

0.20 ± 0.02 (0.13-0.28)

Stream width (m) 8.27 ± 1.10 (3.10-13.10)

15.65 ± 1.32 (9.16-21.70)

16.26 ± 2.23 (7.30-27.62)

Discharge rate (m3 s-1) 0.24 ± 0.04 (0.08-0.53)

1.00 ± 0.15 (0.22-1.84)

0.54 ± 0.091 (0.08-1.19)

BOD5 (mg L-1) 1.98 ± 0.49 (0.80-3.20)

1.900 ± 0.431 (0.80-3.30)

4.60 ± 1.09 (2.00-9.00)

Alkalinity (mg L-1) 180.78 ± 11.48 (87-234)

211.28 ± 25.93 (80-436)

224.2 ± 14.19 (160-339)

Total phosphate (mg L-1)

1.97 ± 0.58 (0.01-7.01)

2.19 ± 0.67 (0.01-9.63)

2.30 ± 0.46 (0.01-5.25)

Nitrate-nitrogen (mg L-1)

2.28 ± 1.06 (0.01-12.00)

2.90 ± 1.43 (0.03-18.20)

3.15 ± 0.98 (0.01-12.00)

Total suspended solids (mg L-1)

15.33 ± 2.79 (4.00-38.00)

15.17 ± 2.93 (4.00-34.00)

56.17 ± 12.48 (20.00-160.00)

aUpstream station; bMidstream station; cDownstream stationSource: Macroinvertebrate Composition, Diversity and Richness in Relation to the Water Quality Status of Mananga River, Cebu, Philippines (Flores and Zafaralla, 2012).


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Table 3. Summary of the physicochemical variables per sampling period. Values are Mean ± SE (minimum

and maximum values in parentheses)

Parameter Feb 18 Apr 5 May 3 May 16 Sep 23 Dec 2

Water temperature (°C)

25.67 ± 0.88 (22.00-29.00)

28.33 ± 0.93(26.00-32.00)

28.78 ± 0.40 (28.00-31.00)

26.83 ± 0.08 (26.50-27.00)

26.56 ± 0.18 (26.00-27.00)

27.00 ± 1.04 (24.00-31.00)

pH 8.38 ± 0.10 (8.00-8.70)

8.27 ± 0.12 (7.80-8.70)

7.99 ± 0.18 (7.30-8.60)

7.93 ± 0.11 (7.50-8.20)

9.33 ± 0.07 (8.90-9.60)

8.79 ± 0.10 (8.40-9.00)

Dissolved oxygen (mg L-1)

6.32 ± 0.08 (5.90-6.70)

5.17 ± 0.06 (4.80-5.40)

4.80 ± 0.28 (3.60-5.70)

7.56 ± 0.36 (6.00-8.40)

7.03 ± 0.19 (6.20-7.70)

6.80 ± 0.49 (5.10-8.60)

Flow velocity (m s-1) 0.37 ± 0.06

(0.11-0.59)0.20 ± 0.04 (0.05-0.38)

0.16 ± 0.03 (0.09-0.29)

0.37 ± 0.03 (0.28-0.48)

0.46 ± 0.04 (0.28-0.58)

0.26 ± 0.04 (0.11-0.42)

Water depth (m) 0.23 ± 0.01

(0.17-0.27)0.19 ± 0.03 (0.06-0.28)

0.13 ± 0.03 (0.03-0.20)

0.20 ± 0.02 (0.14-0.27)

0.17 ± 0.03 (0.09-0.27)

0.12 ± 0.02 (0.07-0.17)

Stream width (m) 17.48 ± 4.05

(4.30-27.30)12.88 ± 4.12 (3.10-27.62)

9.63 ± 0.62 (7.30-11.30)

12.61 ± 2.44 (4.75-19.00)

14.98 ± 1.33 (11.00-19.20)

12.78 ± 1.52 (7.85-16.97)

Discharge rate (m3 s-1)

0.92 ± 0.16 (0.46-1.52)

0.25 ± 0.04 (0.08-0.46)

0.14 ± 0.02 (0.08-0.23)

0.77 ± 0.15 (0.32-1.43)

1.08 ± 0.23 (0.25-1.84)

0.38 ± 0.10 (0.08-0.84)

BOD5 (mg L-1) 1.70 ± 0.67 (0.80-3.00)

2.77 ± 1.92(0.80-6.60)

3.67 ± 2.67 (1.00-9.00)

2.33 ± 0.33 (2.00-3.00)

3.17 ± 0.09 (3.00-3.30)

3.33 ± 0.33 (3.00-4.00)

Alkalinity (mg L-1)

196.89 ± 8.14 (166.00-222.00)

109.33 ± 12.96

(80.00-163.00)

258.56 ± 42.30 (171.00-436.00)

181.67 ± 8.83 (170.00-

205.00)

237.00 ± 2.53 (231.00-247.00)

249.11 ± 22.55

(193.00-339.00)

Total phosphates (mg L-1)

6.71 ± 0.46 (5.25-9.63)

2.54 ± 0.23 (2.03-3.51)

2.49 ± 0.20 (1.85-3.25)

1.07 ± 0.19 (0.71-2.15)

0.10 ± 0.02 (0.07-0.25)

0.01 ± 0.00 (0.008-0.01)

Nitrate-nitrogen (mg L-1)

0.64 ± 0.06 (0.4-0.9)

0.80 ± 0.36 (0.07-2.37)

0.75 ± 0.36 (0.006-2.30)

1.04 ± 0.14 (0.70-1.60)

13.33 ± 0.76 (12.00-18.20)

0.103 ± 0.03 (0.008-0.20)

Total suspended solids (mg L-1)

22.33 ± 8.24 (4.00-50.00)

56 ± 27.09 (12.00-160.00)

27.33 ± 7.74 (4.00-48.00)

26.67 ± 11.90 (4.00-68.00)

21.33 ± 3.89 (10.00-34.00)

19.67 ± 0.61 (18.00-22.00)


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Figure 3. Rainfall pattern: February, April, May, September and December 2006

Table 4. Correlation coefficients of the selected physicochemical pa-rameters of Mananga River from February to December 2006.

Parameter pH DO FV DR AL-KALI

TSS NO3-N TP BOD5

TEMP -0.399** -0.409** -0.496** -- -- 0.604** -- -- --

pH -- 0.484** 0.532** -- -- -0.412* 0.587** -0.354** --

DO -- 0.620** 0.539** -- -- -- -0.299* --

FV -- 0.628** -- -0.454** 0.431** -- --

DR -- -- -- 0.472** -- --

ALKALI -- -- -- -- --

TSS -- -- -- 0.550*

NO3-N -- -0.349** --

TP -- --

BOD5 --

* Correlation is significant at the 0.05 level (2-tailed).


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** Correlation is significant at the 0.01 level (2-tailed).

TEMP – water temperature TSS – total suspended solidsDO – dissolved oxygen NO3-N – nitrate-nitrogenFV – flow velocity TP – total phosphatesDR – discharge rate BOD5 – biological oxygen demandALKALI – alkalinity FC – fecal coliform

Water temperature readings significantly increased in the down-stream direction (p<0.05). It is suspected that time of sampling may have caused the spatial variation since S1 was sampled the earliest during each sampling date. Increased solar radiation with the time of the day can significantly raise the temperature of surface waters in the river. Water temperature was lowest in the cooler month of February at 22.7°C in S1, and highest in the warm month of April at 32.0°C in S3 (Tables 2 and 3).

Degree of exposure to solar radiation of the river water could lead to differences in temperature (Madamba et al., 1992). Station 1 had a fuller canopy of foliage than the downstream. The geographical loca-tion, flow, depth, etc., and anthropogenic effects (i.e., agricultural land uses, discharge of industrial coolants, sewage, and other effluents) are factors that also influence temperature readings (Jurgelėnaitė et al., 2012).

Mananga River generally had a basic pH. Upstream waters were strongly basic with a maximum of pH 9.6 (Table 2) registering on the rainy month of September (Fig. 3). Except for the September 23, 2006 reading (Table 3), most of the pH values observed were within the per-missible range of pH for Classes AA to D waters which is 6.5 to 9.0 (Table 5).


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Table 5. Water quality criteria for fresh waters

Parameter

Water Body ClassificationClassAA

ClassA

ClassB

ClassC

ClassD

pH (range) 6.5-8.5 6.5-8.5 6.5-8.5 6.5-8.5 6.0-9.0DO (mg/li) 5 5 5 5 3BOD5, (mg/li) 1 5 5 7(10) 10(15)TSS (mg/li) 25 50 (f) (g) (h)Nitrate as Nitrogen (mg/li) 1.0 10.0 NR 10(j) --Phosphate as Phosphorus (mg/li) nil 0.1 0.2 0.4 --

Fecal coliform (MPN/100 mL) 20 100 200 -- --

Source: Department of Environment and Natural Resources-Philippines (DENR, 1990).

(f) = not more than 30% increase, (g) = not more than 30 mg/L increase, (h) = not more than 60 mg/L increase, (j) = applicable only to lakes, reservoirs, and similarly impounded water, NR =no recommendations made

A high pH implies richness in carbonates, bicarbonates, and associ-ated salts (Smith and Smith, 2000). Since Cebu is made up mostly of tertiary and quaternary limestone of coralline origin (Talisay CPDO, 2001), the positive correlation between pH and flow velocity (r = 0.5) in Table 4 suggests that the high amount of rainfall in September could have led to increased flow velocity that caused dissolution of sedimen-tary rocks (i.e. limestone) rich in carbonates and bicarbonates. Another possible influential factor was the state of the riparian cover. Poor ri-parian cover could result to more nutrient runoff, favoring growth of algae and raising water pH through photosynthetic activity (Vila-Gispert et al., 2002). The strong positive relationship of pH with NO3-N (r = 0.6) also implies an increased leaching of nitrates into the stream as the flow velocity increased.

Dissolved oxygen (DO) generally decreased towards the down-stream. The highest reading of 8.6 mg/L was observed in S2 on De-cember 2 (Tables 2 and 3). The values noted in the downstream were generally lower, the lowest value of 3.7 mg/L observed on May 3 (Ta-bles 2 and 3). The strong negative relationship of DO with water tem-perature (r = -0.4) is consistent with the general observation that warm


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water holds less oxygen (Jurgelėnaitė et al., 2012). Studies of rivers in the Philippines that reported higher DO levels upstream compared with downstream stations, have attributed the pattern to rapid land use changes in the watershed that increased organic loads associated with urbanization (Madamba et al., 1992; Asuncion, 1996, unpubl.; Nazareno, 2000). The DO content of river water may be affected by water temperature, dissolved or suspended solids, and organic load (Murphy, 2007).

Although TSS significantly varied with location, no significant vari-ation was observed with season (p<0.05). What was evident was that TSS and flow velocity showed strong negative correlation (r = -0.5); TSS values were low at S1 and S2 where flow velocity was stronger. This could be the result of suspended solids being carried away by strong flow from higher areas and eventually deposited in areas with low flow. TSS was positively correlated with water temperature (r = 0.6); and both parameters were higher in S3 than in S1 and S2 (Table 2). Suspended particles that inhibit light penetration have greater absorp-tion of solar energy especially near the surface, hence an increase in surface water temperature (Green Bay Metropolitan Sewerage District, 2013).

NO3-N levels were generally high in S2 and S3 than in S1 (Fig. 4), however, the difference in values was not significant. NO3-N concen-trations though showed significant temporal variation (p<0.05) but they were below the water quality standard (WQS) for Class A wa-ters (Table 5), except for the September sampling where the amount of rainfall was highest. A study by Madamba et al. (1992) of the San Cris-tobal River in Laguna, Philippines showed nitrate levels at the mouth of the river to be always high (more than 2.0 mg/L) in September. Ni-trate levels of more than 10 mg/L in natural waters indicate man made pollution (Ugwu and Wakawa, 2012). If the amount of nitrate inputs into the river will remain the same or increase, the chances of eutrophi-cation of the water body will also increase.

The strong positive correlation of NO3-N with flow velocity (r = 0.4) and stream flow (r = 0.5) in Mananga River is consistent with the ob-servation of Singh et al. (2010) on the nitrate concentration of Thoubal River. It was at maximum during rainy season where nitrate-rich fer-tilizer runoff from croplands, animal manure storage areas, and failing


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on-site septic systems could be carried into rivers. About 29.8% of the Mananga watershed area is planted to crops (like corn, vegetables and paddy rice), coconut and/or mango (Table 6).

Chemical fertilizers (e.g., Urea and N-P-K) are applied to crops planted on the steep slopes of the watershed, where the soils are of-ten not suitable for agriculture, to increase soil fertility (USC-WRC, 2000). During heavy rains, fertilizer runoff from these agricultural ar-eas could have been washed into the Mananga River. Drainage and septic tank waters from built-up areas within the Mananga watershed could be other sources of nitrate.

Total phosphates in Table 1 showed significant temporal variability (p<0.05). Almost all values exceeded the WQS for Classes A to C wa-ters (Fig. 5). Like NO3-N, phosphate is essential to plant growth, but in excessive amounts could lead to hastened eutrophication of the wa-ter body. The excessive levels of phosphates in Mananga River could be due to runoff from the agricultural areas and/or sewage pollution from the built-up areas. Highest levels are often associated with sew-age pollution and agricultural areas where the sources are fertilized farm fields and feedlots (Ugwu and Wakawa, 2012).

Figure 4. Mean nitrate-nitrogen levels of the Mananga River from February to December 2006


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Table 6. Land use and vegetation profile of the Mananga watershed

Land use Area Subtotal % %Shrub 4460 4460 56.7 56.7Forest 712 712 9.1 9.1Coconut/mango 916 11.6Coconut 298 1519 3.8Mango 305 3.9Corn 95 1.2 29.8Corn/Vegetable 481 6.1Vegetable/Cutflower 109 823 1.4Vegetable 29 0.4Paddy rice 109 1.4Built-up area 352 352 4.5 4.5Total 7866 7866 100.0 100.0

Source: USC-WRC, 2000

Figure 5. Mean total phosphate level of the Mananga Riverfrom February to December 2006


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The BOD5 levels were generally within the 5.0 mg/L WQS standard set for Classes A and B waters. Significant spatial variations were evi-dent (p<0.05); lower concentrations were noted at S1 and S2 except on April 5 and May 3 when the WQS for Classes A and B waters (Fig. 6) were exceeded. The downstream had relatively higher values com-pared with the upstream and midstream (Table 2). A significant BOD5 correlation with TSS (r = 0.5) was evident, where the levels of the latter were lower at S1 and S2 compared with that at S3.

A high BOD5 may be the result of high TSS in the water column (Al-Ali et al., 2011). High TSS in a water body can often mean higher concentrations of bacteria, nutrients, pesticides, and metals in the wa-ter (Murphy, 2007) because suspended particles provide attachment places for these other pollutants (Health Canada, 2012). A higher BOD5 in the downstream of Mananga River could be indicative of a higher amount of anthropogenic oxidizable matter in that region. Levels of BOD5 tend to be raised by sewage, animal wastes, or any kind of or-ganic refuse (Al-Ali et al., 2011). The downstream part of the Mananga River is the destination of effluents from sewers and of leachates from solid and liquid waste dumps, and agricultural run-off.

Figure 6. BOD5 level of the Mananga River from February to December 2006


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CONCLUSIONS

Natural change in slope gradient, channel depth, and width re-sulted in diminishing velocity but increasing discharge downstream. These characteristics led to increased TSS, water temperature, and BOD5 but decreased flow velocity and DO levels downstream. The in-herent physical properties along the longitudinal gradient were not the sole determinants of the change in water quality of Mananga River. There were significant external inputs as well. For instance, stream ve-locity and flow were observed to increase with increasing precipita-tion, which could have also been exacerbated by the poor vegetation cover in the river’s riparian zone and in the watershed. Seasonal varia-tion had significant effects on flow velocity, discharge rate, tempera-ture, DO, pH, alkalinity, NO3-N, and total phosphates. Also observed were strong correlational relationships among variables. Flow veloc-ity which was higher in S1 and S2, was correlated at p<0.01 with dis-charge, pH, DO, NO3-N, temperature, and TSS.

The water quality of the studied segments of the Mananga River generally failed to meet water quality standards for a Class A water resource. Water quality deterioration increased from the upstream to downstream, and was more pronounced during periods of low rain-fall as indicated by the low DO level, high amounts of TSS, and high levels of BOD5. Deterioration could be attributed to the river receiving high loads of organic matter from natural and anthropogenic sources as indicated by sudden increments in NO3-N level and the consistently high amounts of total phosphate. If organic pollution from sewage ef-fluents, dumped garbage and refuse, and from agricultural materials is not stopped, the river is bound for further deterioration.

The river and its tributaries are vital for providing water to peo-ple, crops and aquatic life. Water quality determines the suitability of water for these uses. Mananga River’s water quality was seemingly affected by natural factors such as gradient, geology, climate; and hu-man-caused factors, such as sewage effluent, and runoff from agricul-tural and built-up areas. The relative effects of these factors could have changed over time and are expected to continue because of changing land use that go with urbanization and economic development.


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RECOMMENDATIONS

Water quality must be regularly monitored to gauge the impacts of these so that the necessary mitigating measures can be applied. Infor-mation from this study could serve as a baseline for evaluating future water-quality changes. Future researches could address the state of the river’s production and biodiversity, and the exploration of ways by which the river can be protected from further deterioration and its bio-diversity resources conserved.

ACKNOWLEDGMENT

The funding of this research, which was part of a Ph.D. disserta-tion, was provided by the University of the Philippines Visayas and the Philippine Council for Aquatic and Marine Research and Develop-ment (PCAMRD).

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An Assessment of the Physicochemical Parameters of Mananga River, Cebu, Philippines

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