Abstract:
Zooplankton are the heterotrophic aquatic organism that being drift by water currents and itact as
a strong linkage between primary producers and secondary consumers. Zooplankton community
structure (diversity and abundance) has been identified them as simple, accurate and important
ecological indicator to assess eutrophication, acidification and pollution. Thandikulam reservoir is
a seasonal reservoir with minimal disturbances of pollution and used for agriculture purpose in
Vavuniya District. Therefore, this study was carried out to detect the effect of nutrient loading on
zooplankton community structure. plankton sampling was done by using zooplankton net (80 um) in randomly selected four locations of this reservoir for couple of times per month from July, 2018
to February, 2019. Simultaneously, water samples were collected at each location to determine
nutrient concentrations (NO3
- and PO4
3-), dissolved oxygen and water temperature. Hydro-climatic
data (monthly total rainfall, air temperature, water level) were obtained from meteorology
department. Species identification was done based on standard zooplankton identification guides
under high power of microscope. Abundance of zooplankton community was performed using the
Sedgwick-Rafter cell under microscope. Zooplankton diversity was determined according to
Shannon- tion coefficient (r) was obtained to identify
the correlations between zooplankton community structure and nutrient concentrations. Total of
19 genera with 12 Rotifer species, 2 Cladocera species and 5 Copepod species were observed.
During this study period, high nutrient concentrations were recorded in dry season (July-August,
2018). Increase in PO4
3- concentration, significantly (p = 0.042) decrease the zooplankton diversity
and resulted strong negative correlation (r = - 0.805). Although, increasing NO3
- concentration
seems to be reducing the zooplankton diversity (r = - 0.686), no significant (p = 0.115) relationship
was observed. A negative correlation was recorded in overall zooplankton abundance with PO4
3-(r
= - 0.595, p = 0.145) and NO3
-
(r = - 0.608, p = 0.138) except Cladocera. Conclusively, this study
revealed that nutrient concentration is greatly influenced diversity rather than overall abundance
of zooplankton. These findings can be used in monitoring the health and water quality of reservoirs
using zooplankton community structure as the principal constituent.
