In situ nutrient assays of periphyton growth in a lowland Costa Rican stream.
Abstract: Nutrient limitation of
primary production was experimentally assessed using an in situ
bioassay technique in the Quebrada Salto, a third-order tropical stream
draining the northern foothills of the Cordillera Central in Costa Rica.
Bioassays employed artificial substrata enriched with nutrients that slowly
diffuse through an agar-sand matrix (Pringle & Bowers, 1984).
Multiple comparisons of regression coefficients, describing chlorophyll-a
accrual through time for different nutrient treatments, revealed positive
micronutrient effect(s). Micronutrient treatment combinations (Fe,
B, Mn, Zn, Co, Mo EDTA), supplemented with and without nitrate and phosphate,
exhibited significantly greater chlorophyll-a accrual over all other treatments
(P < 0.05), supporting over three times that of the control after 14-d
of substratum colonization. Neither the major nutrients (N or P)
produced a significant stimulation, although the N treatment displayed
~50% more chlorophyll-a than the control after 14-d. Similarly, Si,
EDTA, and Si + N + P treatments did not exhibit chlorophyll-a response
curves that were significantly different than the control. During
the experiment, mean NH4-N and (NO2 + NO3)-N
concentrations in the Salto were 2.0 uM (28.6 ug·1-1)
and 7.2 uM (100.2 ug·1-1), respectively.
High concentrations of PO4-P (Mean = 2.0 uM; 60.9 ug·1-1)
and TP (Mean = 3.0 uM; 94.0 ug·1-1) were
also found, and consequently low molar N:P ratios (Mean = 4.7). Despite
the potential for N limitation in the system, both N and P appear to be
at growth saturating levels. This may be due to micronutrient limitation
and/or light limitation of periphyton growth in densely shaded upstream
portions of the stream.
Pringle, C.M., P. Paaby-Hansen, P.D. Vaux, and C.R. Goldman. 1986. In situ nutrient assays of periphyton growth in a lowland Costa Rican stream. Hydrobiologia 134: 207-213.
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