
%0 Journal Article
%A Townsend, Simon A. 
%T Seasonal pattern and inferred phosphorus limitation of phytoplankton biomass in two tropical reservoirs in northern Australia
%J Marine and Freshwater Research
%D 2000/02/04
%V 51
%N 1
%P 91-96
%K 
%R https://doi.org/10.1071/MF99004
%U https://www.publish.csiro.au/paper/MF99004 
%X Manton River Reservoir (MRR) and Darwin River Reservoir (DRR) are two small impoundments in the Australian wet/dry tropics. Over an eight-year period, chlorophyll a concentrations in the mixed layer averaged 3.6 &#181;g L&#8722;1 in DRR, and 7.1 &#181;g L&#8722;1 in MRR. The seasonal pattern of chlorophyll a at MRR was influenced by wet season wash-out (February average 4.8 &#181;g L&#8722;1 ), and dry season destratification and nutrient enrichment of the surface waters (July average 8.4 mg L&#8722;1 ). In contrast, DRR exhibited near uniform chlorophyll a concentrations over the year. The seasonal patterns of DRR and MRR chlorophyll a are typical of tropical water bodies which tend to have a smaller annual range than temperate lakes, though this can be modified by significant wash-out. Empirical evidence suggests that the phytoplankton biomass of each reservoir is phosphorus limited, relative to the potential provided by other nutrients and light energy. This conclusion is based on a regression of total phosphorus and chlorophyll a concentrations of pooled DRR and MRR data (P &#60; 0.001; r2 = 0.90), and the high total-nitrogen to total-phosphorus concentration ratios (by weight) of 50 and 37 in DRR and MRR, respectively. Annual chlorophyll a and total phosphorus concentrations for both reservoirs are in accord with the OECD regression for temperate lakes and reservoirs. 
