Primary productivity and related parameters in three different types of inland waters in Sri Lanka

Abstract

Gross and net primary production together with chlorophyll-a biomass were investigated with respect to depth and diurnal changes in three categories of inland waters (reservoirs, temporary ponds, brackish water lagoons) in Sri Lanka. Ten field sites, in both the dry and wet zones of the island, were investigated. Bimodal productivity profiles were recorded in two of the three reservoirs studied. The die1 pattern of net photosynthetic rate varied between sites although peak photosynthetic efficiency occurred at solar noon. Surface photoinhibition was characteristic of the reservoirs and brackish water lagoons but not of the temporary ponds. Mean gross primary production was 3.02 g C m-2 d-' but was higher in the temporary ponds than in the reservoirs. The gross primary production in the brackish water Koggala Lagoon at 0.08 g C m-2 d-I is a record low for tropical lagoons and was 2.5 times less than the two other lagoons investigated. Variability in net primary production between sites was similar to the variation in gross production with a relatively low mean value for tropical inland waters of 0.495 C m-2 d-'. Mean maximum photosynthetic rate was 0.30 mg C m-3 h-I but was lower in the reservoirs than in the temporary ponds and lagoons.

The seasonality of monsoonal primary productivity in Sri Lanka

“…1) fed by two different tributaries (Silva & Davies, 1986a, 1986b. The calculated lake areas (Table 1) are substantially different from those previously published (De Silva, 1985;Maitipe & De Silva, 1985) which has resulted in De Silva (1985) mis-estimating the areal basis fish production.…”

“…The five reservoirs (Parakrama Samudra, Minneriya, Giritale, Kaudulla, and Pimburettewa ( Fig. 1)) are described by Silva & Davies (1986a, 1986b.…”

“…The SNK test showed that the conductivities of Parakrama Samudra, Kaudulla and Pimburettewa were significantly different from those of Giritale and Minneriya (Table 4). Since in Sri Lanka the conductivity of fresh water is mainly determined by the bicarbonate ions (Gunatilaka & Senaratne, 1981;Silva & Davies, 1986a) variability in conductivity can be attributed to the differential heterotrophic potentials of the bottom sediments. Pimburettewa with the highest allochthonous input produces more C02 in the water column, but the maximum recorded conductivity of 554 pSO is well below those recorded by Maitipe & De Silva (1985) for the same reservoirs but is within the range recorded by Gunatilaka & Senaratne (1981) and Silva & Davies (1986a).…”

“…Recent studies on phytoplankton primary production in Sri Lanka have emphasized the trophic status and optic properties of dry zone man-made lakes (Dokulil et al, 1983) and Silva & Davies (1986a) have shown the trophic similarities between three different types of inland waters. This study examines the relationships between phytoplankton primary production and seasonality in five man-made lakes in the dry zone of Sri Lanka.…”

Primary productivity and particulate organic matter flow in an estuarine mangrove-wetland in Hong Kong

“…Boynton et al (1982) documented reports of phytoplankton production in estuarine areas and mean production rates varying from 0.58 in river-dominated estuaries to 0.49 gC m-2 d-1 in lagoons. The present value of only 0.10 g m -2 d-1 (light and dark bottles) is outside the annual range of most studies (Wium-Andersen 1979, Mountford 1980, Pomeroy et al 1981, Boyneton et al 1982, 1983, Kennish 1986, Pennock and Sharp 1986, and is comparable only to the low readings obtained from a brackish lagoon in Sri Lanka (Silva and Davies 1986).…”