EFFECTS OF PHOSPHORUS AND ALLOCHTHONOUS HUMIC MATTER ENRICHMENT ON THE METABOLIC PROCESSES AND COMMUNITY STRUCTURE OF PLANKTON IN A BOREAL LAKE (LAKE-PAAJARVI)
L. Arvola et al., EFFECTS OF PHOSPHORUS AND ALLOCHTHONOUS HUMIC MATTER ENRICHMENT ON THE METABOLIC PROCESSES AND COMMUNITY STRUCTURE OF PLANKTON IN A BOREAL LAKE (LAKE-PAAJARVI), Canadian journal of fisheries and aquatic sciences, 53(7), 1996, pp. 1646-1662
During the ice-free period, three experiments each of 16-17 days were
performed in four enclosures to evaluate the effects of moderate pulse
s of allochthonous humic matter (5-29% of the ambient dissolved organi
c carbon concentration) and phosphorus (PO4-P was increased from 1-2 t
o 15-20 mu g . L(-1)) on the plankton. The addition of phosphorus, alo
ne or with humic matter, clearly raised the primary production in summ
er (54-56%), and to a lesser extent in spring (17-23%) and in autumn (
17-58%). A significant correlation existed between primary production
and bacterial production indicating that bacterial production was cont
rolled primarily by organic substrates released by algae rather than b
y phosphorus or humic matter. In the control enclosure, bacterial prod
uction constituted 23-32% of primary production while with extra phosp
horus and humic matter the proportion rose to 59%, indicating that hum
ic matter was used by bacteria as an additional energy and carbon sour
ce besides algal exudates. Simultaneous enrichment with phosphorus and
humic matter resulted in substantially higher bacterial production th
an with humic matter alone. In autumn, the addition of humic matter al
one increased bacterial production, indicating that humic matter conta
ined more easily utilizable organic material at that point than it did
earlier. Some algal taxa responded positively to phosphorus and (or)
humic matter enrichment, but the effects on proto- and meta-zooplankto
n communities were less obvious.