**5. Sampling procedure and data collection**

Most of that data used for analyses in the study were primary data obtained from sampling and laboratory analyses. Data of benthic macroinvertebrate assemblage and water quality assessment were obtained from *in situ* analyses and further analyses in the laboratory. River habitat and morphology data were measured on‐site in field surveys. On the other hand, secondary data such as land use, rainfall data, and stream catchment maps were obtained from several agencies such as the Department of Environment, Department of Drainage and Irrigation, Department of Survey and Mapping and local authorities.

### **5.1. Benthic macroinvertebrate**

The multihabitat approach of USEPA's Rapid Bioassessment Protocol (RBP) was adopted for this study as it was suitable for sampling a wide variety of stream types [22]. In this study, a rectangular dipnet with 500‐µm mesh attached to a 0.5 m × 0.3 m frame and a long pole were used for this purpose. For multiple habitats, the habitat types were sampled in proportion to their relative surface area within the sampling reach. A total of 20 sample units were collected from all major habitat types by kicking the substrates or jabbing with a dipnet within a sampling station to obtain a composite of 60 sample units in total. The samples were washed and any detritus present was removed on‐site as it would be impractical to wash large samples in the laboratory. Following this, benthic materials were sieved and rinsed before preservation in 70% ethanol. The sample containers were labeled to show all the essential information, including date and sampling location. Preprinted labels were preferably used using marker pens as ethanol would remove writing. Moreover, labeling on container lids was avoided in case they were interchanged. In laboratory, benthic macroinvertebrates were rinsed thoroughly in 500 µm‐mesh sieves to remove preservative and sediment, while remaining debris was visually inspected and discarded. During the separation process, the samples were soaked for about 15 min in tap water to hydrate the preserved organisms and prevent them from floating on the water surface during sorting. The samples were then spread over an enamel tray and sorted out into major taxa. All organisms were identified to the lowest practical level using a dissecting microscope and taxonomic Key from Yule and Yong [23].

### **5.2. Water quality**

However, there is active logging in the area planted with *Acacia mangium*, a tree species of the pea family, Fabaceae. *Acacia mangium* is suitable as raw material for sawn timber, and wood‐ chips in the pulp and paper industry, and reconstituted wood for the furniture industry. In the Asia–Pacific region, Japan is among the larger importers of wood chips, while the pulp and paper industry finds markets in Taiwan and South Korea. Based on the macro‐EIA for forest management units (FMU) in Johor, Sg Berasau supports a variety of fish species such as Terbul,

Sg Mengkibol is a second‐order river located within the Endau watershed. This river receives flows from Sg Melantai before joining Sg Semberong. This river basin is approximately 185

Most of that data used for analyses in the study were primary data obtained from sampling and laboratory analyses. Data of benthic macroinvertebrate assemblage and water quality assessment were obtained from *in situ* analyses and further analyses in the laboratory. River habitat and morphology data were measured on‐site in field surveys. On the other hand, secondary data such as land use, rainfall data, and stream catchment maps were obtained from several agencies such as the Department of Environment, Department of Drainage and

The multihabitat approach of USEPA's Rapid Bioassessment Protocol (RBP) was adopted for this study as it was suitable for sampling a wide variety of stream types [22]. In this study, a rectangular dipnet with 500‐µm mesh attached to a 0.5 m × 0.3 m frame and a long pole were used for this purpose. For multiple habitats, the habitat types were sampled in proportion to their relative surface area within the sampling reach. A total of 20 sample units were collected from all major habitat types by kicking the substrates or jabbing with a dipnet within a sampling station to obtain a composite of 60 sample units in total. The samples were washed and any detritus present was removed on‐site as it would be impractical to wash large samples in the laboratory. Following this, benthic materials were sieved and rinsed before preservation

 width and 20 km long. The study area is located in the middle section of Sg Mengkibol, starting from the Sg Mengkibol Riverine Park until the wet market. From December 2006 until January 2007, Malaysia experienced large‐scale flood events that affected most of the state of Johor. This phenomenon was caused by extremely high rainfall attributed to Typhoon Utor that made landfall in the Philippines and Vietnam. A series of massive floods hit the states of Malacca, Pahang, and Negeri Sembilan, with Johor as the worst hit state. Among the major towns affected by the floods were Batu Pahat, Johor Bahru, Kluang, Kota Tinggi, Mersing, Muar, Pontian, and Segamat. Consequently, the Department of Irrigation and Drainage (JPS) allocated RM2 million to deepen Sg Mengkibol at its banks for flood mitigation in low‐lying

Sebarau, Baung, Seluang, and Tapah.

**4.3. Sg Mengkibol**

residential areas [21].

**5.1. Benthic macroinvertebrate**

**5. Sampling procedure and data collection**

Irrigation, Department of Survey and Mapping and local authorities.

km2

320 Water Quality

Water quality assessment data were obtained by two methods, namely *in situ* and laboratory analyses. *In situ* measurements were made on temperature, pH, conductivity, and dissolved oxygen (DO) by using a YSI Professional Plus handheld multiparameter instrument. Meanwhile, other parameters such as biochemical oxygen demand (BOD5), total suspended solid (TSS), ammoniacal nitrogen (NH3N), and chemical oxygen demand (COD) were measured in the laboratory based on the Standard Methods for the Examination of Water and Wastewater [24]. Both *in situ* readings and water samples were collected from the same location. Water samples were collected in 1‐L polyethylene bottles and chilled in a cold box filled with ice cubes (4°C) to minimize the metabolism of organisms contained in the water. The water samples were labeled in a manner similar to that used for the benthic samples.

The water quality index (WQI) was calculated to indicate the level of pollution and the corresponding suitability for use according to the National Water Quality Standards for Malaysia (NWQS). Water quality class was determined based on the water quality index (WQI), ascertained by the six parameters, *viz*. pH, DO, BOD5, COD, TSS, and NH3N, according to the DOE formula (1):

$$\begin{aligned} \text{WQI} &= (0.22 \text{\*SIDO}) + (0.19 \text{\*SIDO}) + (0.16 \text{\*SICO}) + (0.15 \text{\*SINN})\\ &+ (0.16 \text{\*SISS}) + (0.12 \text{\*SlpH}) \end{aligned} \tag{1}$$

where SI is the subindex of the respective water quality parameters which is used to calculate the WQI (**Table 1**). The WQI classification based on water use is shown in **Table 2**.



**Table 1.** Best fit equations for the estimation of various subindex values.


**Table 2.** Water classes and uses.

### **5.3. Characterization of river habitat**

A visual‐based habitat assessment based on the USEPA habitat assessment survey was carried out simultaneously with the biological sampling. Several features in habitat assessment include a general description of the site, a physical characterization and water quality assess‐ ment, and also a visual assessment of instream and riparian habitat quality. Physical charac‐ terization comprised documentation of general land use, description of the stream origin and type, and a summary of the riparian vegetation features that included measurements of instream parameters such as width, depth, flow, and substrates. The observed channel dimensions were carried out in the survey stretch, located either in the presence of riffle or at a suitable shallow section of the river. Channel dimension measurements were taken according to the river habitat survey (RHS) method.

### **5.4. Streamflow gauging**

**Subindex for DO (in % saturation)**

*Subindex for COD*

322 Water Quality

*Subindex for NH3-N*

*Subindex for SS*

*Subindex for pH*

**Class Uses**

Class IV Irrigation

Class V None of the above

**Table 2.** Water classes and uses.

SIBOD = 108 × exp(−0.055x) − 0.1x for x > 5

SICOD = −1.33x + 99.1 for x ≤ 20 SICOD = 103 × exp(−0.0157x) − 0.04x for x > 20

SIAN = 100.5 − 105x for x ≤ 0.3 SIAN = 94 × exp(−0.573x) − 5 × |x − 2| for 0.3 < x < 4 SIAN = 0 for x ≥ 4

SISS = 97.5 × exp(−0.00676x) + 0.05x for x ≤ 100 SISS = 71 × exp(−0.0061x) − 0.015x for 100 < x < 1000 SISS = 0 for x ≥ 1000

SIpH = 17.2 − 17.2x + 5.02 × 2 for x < 5.5 SIpH = −242 + 95.5x − 6.67 × 2 for 5.5 ≤ x < 7 SIpH = −181 + 82.4x − 6.05 × 2 for 7 ≤ x < 8.75 SIpH = 536 − 77.0x + 2.76 × 2 for x ≥ 8.75

Fishery III—common, of economic value and tolerant species; livestock drinking

A visual‐based habitat assessment based on the USEPA habitat assessment survey was carried out simultaneously with the biological sampling. Several features in habitat assessment include a general description of the site, a physical characterization and water quality assess‐ ment, and also a visual assessment of instream and riparian habitat quality. Physical charac‐ terization comprised documentation of general land use, description of the stream origin and

**Table 1.** Best fit equations for the estimation of various subindex values.

Water supply I—practically no treatment necessary

Fishery I—very sensitive aquatic species Class IIA Water supply II—conventional treatment required Fishery II—sensitive aquatic species

Class III Water supply III—extensive treatment required

Class I Conservation of natural environment

Class IIB Recreational use with body contact

**5.3. Characterization of river habitat**

Streamflow gauging was conducted to measure the flow rate of the study area. The equipments used in this study were flow meter, measuring tape, staff level, hammer, and ropes/cables. The Cole Parmer Model BS 11000 flow meter used in this study was equipped with a propeller to allow it to rotate according to the velocity of the water. The mean section method was used to measure the river discharge using the flow meter and other tools, whereby cross‐sectional area of the river was divided into several subsections. Stream velocity was measured at depths of 0.6d, 0.2d, and 0.8d depending on the need, where d represents the variable of depth from the water surface. This method was used to obtain the average velocity of the represented river. The general hydraulic formula for river discharge is as follows (2)

$$\mathbf{Q} = \mathbf{A}\mathbf{V} \tag{2}$$

where Q is discharge (volume/unit time‐e.g. m3 /s, also called cumecs), A is the cross‐sectional area of the stream (e.g. m2 ), and V is the average velocity (e.g. m/s).
