An Assessment of the Benthic Community Structure: Implications on the Water Quality of Lake Palacpaquen, San Pablo City,

PhilippinesPerez, Terresita., Caasi, Hazel . de la Torre, Benjamin.Department of Environmental Science, Ateneo de Manila University, Loyola Heights, Quezon City, Philippines

73.05 hectares (25.22%) covered with fish cages and fish pens -(City Government of San Pablo, 2000)

RA 8550 limit: 10-12% of the total lake area

To investigate the macroinvertebrates diversity and relate this to the water quality and physical features of Lake Palacpaquen.

General Objective

Preliminary Field Work

Initial Survey of Sampling Site

Identification of Sampling Points

Sampling Points: Inlet, Pool, Periphery, Outlet

Benthic macroinvertebrates samplingPhysical characterization

In-situ water quality check

Water depth

Sediment/Substrate

Other site features

Substrate type

% particle sizeweight

Grain/particle size

Statistical Analysis

Application of BBI, FBI, and other indices and metrics

Sorting

Measurement of taxa richness and diversity

Laboratory processing

Invertebrate identification

Methodology

Abstract

Water Quality

pH levels are within the standard for Class C waters, which is 6.5-8.5 (DAO No. 34, 1990).

Mean pH in sampling sites, Lake Palacpaquen

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

INLET POOL PERIPHERY OUTLET

Sites

pH

Nov

Dec

Jan

Minimum DO conc. is 5.0 mg/L for Class C (DAO No. 34, 1990).

Mean DO concentration in sampling sites, Lake Palacpquen

0.001.002.003.004.00

5.006.007.008.009.00

INLET POOL PERIPHERY OUTLET

Sites

Dis

solv

ed O

xyge

n (m

g/L)

Nov

Dec

Jan

Turbidity levels were highest in January for all sites.

Mean Turbidity in sampling sites, Lake Palacpaquen

0.00

5.00

10.00

15.00

20.00

INLET POOL PERIPHERY OUTLET

Sites

Tuirb

idity

(NTU

)

Nov

Dec

Jan

Conductivity was lowest in December and highest in January across all sites.

Mean Conductivity of sampling sites, Lake Palacpaquen

0.000

0.050

0.100

0.1500.200

0.250

0.300

0.350

INLET POOL PERIPHERY OUTLET

Sites

Cond

uctiv

ity (m

S/cm

^3)

Nov

Dec

Jan

Substrate Characterization

0%

20%

40%

60%

80%

100%

%composition of substrate

Sampling Sites

<0.5mm

0.5mm-1mm

1mm-2mm

>2mm

November

January

Macroinvertebrate Diversity

Angulyagra Bellamya Pomacea Physella Gyraulus

Tarebia Physastra Thiara Melanoides Corbicula

Chironomidae (midge larvae) Tipulidae (cranefly)

Ceratopogonidae (biting midge)Stratiomyidae

Culicidae (mosquito)

Dixidae (dixid midge)

Adephaga (water beetle)

Caenis (mayfly)

Cloeon (mayfly)

Sericostomatidae (caddisfly)

Helicopsychidae (caddisfly)

Lumbricidae (worm)

Octogomphus (dragonfly)

Glossiphoniidae (leech)

Macroinvertebrate Diversity

•Lake is possibly affected by organic pollution.

•In situ water quality parameters had low correlations with biotic indices but they contribute to physical characteristics of habitat together with the substrata.

Conclusion

•Substrate composition at different points in the lake varied in type and sizes, from large organic debris to finer particles.

•BBI: Lake is moderately polluted to lightly polluted.

•FBI: substantial pollution is likely; water quality is fairly poor.

Evenness is negatively correlated with % dominance (r = -0.751).

Taxa richness is positively correlated with H’ (r = 0.791).

Indices and Metrics November December January

Shannon-Wiener Diversity Index (H') 0.539 0.720 0.834

Taxa Richness (Family) 11 14 18

Evenness Index (E) 0.484 0.574 0.622

% Dominant 64 54.8 40.7

H’, TR and E were lowest in November and highest in January.

Lake Palacpaquen is the shallowest and second largest lake in the Seven Lakes of San Pablo City, Laguna, Philippines. The lake is threatened by water quality deterioration caused by anthropogenic activities. The benthic macroinvertebrate community of the lake was investigated. The impact of water quality deterioration on the benthic community was evaluated using the Belgian Biotic Index (BBI) and the Family-Level Biotic Index (FBI). Samples were obtained from four stations in the lake: inlet, pool, periphery and outlet and in-situ water quality parameters were measured. Substrate varied from organic litter (leaves, twigs, roots) to gravel and fine sediments. DO concentrations and turbidity were generally lower in November while pH level, temperature and conductivity were lower in December, following a series of heavy rainfall.

Dominance of mollusca genera Melanoides, Tarebia, Bellamya and Angulyagra were observed to dominate. Six other genera of mollusks were found, including the bivalve Corbicula and the foreign species, Pomacea canaliculata. Larvae of the Family Chironomidae were abundant in the pool.

Taxa diversity was highest in the periphery and the lake outlet in December and January. Diversity of the entire lake obtained from composite samples was highest in January (H’= 0.834). BBI scores were lowest in November and highest in January for all sites. Based on the BBI, Lake Palacpaquen was moderately polluted in November and December, and was lightly polluted to unpolluted in January. FBI scores were lowest in January (6 = fairly poor), but this rating is still indicative of the possibility of substantial pollution.