Chemical composition and the nitrogen-regulated throphic state of Patagonian lakes

DIAZ, M; PEDROZO, F; REYNOLDS, C; TEMPORETTI, P

LIMNOLOGICA

Elsevier

Lugar: Neuglobsow, Alemania; Año: 2006

0075-9511

Chemical composition and nutrient concentrations of 39 relatively poorly known Patagonian lakes (38ºS to 50ºS and from 70°W to 68°W) are described and analysed using Principal Component Analysis (PCA). The general relationships between nutrients (total phosphorus, bioavailable phosphorus and dissolved inorganic nitrogen) are examined. We seek to demonstrate that the extreme oligotrophy characterising many lakes and reservoirs of the Argentine Patagonian region of South America owes more to nitrogen deficiency than to a shortage of available phosphorus. The data show a range of trophic conditions with variable water chemistry characteristics. The first two axes of the PCA ordination explain most of the variance (63 %). The first imponent of the variance in the environmental data is a trophic gradient, with positive correlations with the concentrations of nutrients (TP, SRP, DIN) and electrical conductivity and a negative correlation with transparency. For all the reservoirs considered, the calculated annual, summer and winter chlorophyll-a carrying capacities of the available phosphorus were consistently and significantly (P < 0.05) in excess of observations but maximum chlorophyll a values correlate with DIN availability. Indeed the capacity of the available nitrogen gives a better predictive yield relationship than does P. Our findings are remarkable in so far as the general expectation that nitrogen-fixing phytoplankton should thrive, at least to the supportive limits of the available phosphorus, is unfulfilled.