Response of Mary River phytoplankton to nitrogen and phosphorus enrichment

  • Edward James Webber

    Student thesis: Other thesis - CDU

    Abstract

    This work describes a laboratory nutrient enrichment study of four small oligotrophic floodplain billabongs in the wet-dry tropics of northern Australia, to establish whether the phytoplankton of the billabongs were nitrogen-limited, phosphorus-limited , or co-limited. The waters were collected during the transition from dry to wet season (September to November), and brought back to NTU where nitrogen where nitrogen (30 ug N L-1, 100 ug N L-1, 200 ug N L-1), phosphorus (10 ug P L-1, 30 ug P L -1, 50 ug P L-1) and combinations of N and P (30 ug N L-1 + 10 ug P L -1, 100 ug N L-1 + 30 ug P L-1, 200 ug N L-1 + 50 ug P L -1) were added. Phytoplankton growth was monitored by estimations of chlorophyll a. Standard methods were used for biological and chemical analyses. It was found that phytoplankton of the billabongs were nutrient limited, but showed variation in their limitation status, with those of Corroboree Billabong being phosphorus limited, B ridge Arm Billabong and Hardies Lagoon nitrogen limited, and Shady Camp Billabong co-limited before the rains, and nitrogen limited after the rains. This pattern of variation in nutrient limitation status, with a trend toward nitrogen limitation, is consistent with the majority of tropical water bodies, and contrasts to the general phosphorus limitation of natural temperate water bodies.

    The results will contribute to the know ledge of phytoplankton response to possible nutrient enrichment of natural water bodies in the Top End of Australia, and contribute to the general theory of nutrient limitations of tropical phytoplankton. A rising from this work it is proposed that Corroboree Billabong should be the site selected for the monitoring of nutrient inputs, as it was the only billabong studied that was phosphorus limited, and anthropogenic nutrient inputs generally have a low N:P ratio compared to natural water bodies. Consequently, Corroboree Billabong is the billabong likely to respond the quickest to unnatural nutrient inputs.

    Date of Award2000
    Original languageEnglish
    SupervisorJim Luong-Van (Supervisor) & Simon Townsend (Supervisor)

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