Optical characteristics of shallow lakes from the Pampa and Patagonia regions of Argentina

G. L. PÉREZ, A. TORREMORELL, J. BUSTINGORRY, R. ESCARAY, P. PÉREZ, M. DIÉGUEZ AND H. ZAGARESE.

LIMNOLOGICA

Elsevier

Lugar: Alemania; Año: 2010 vol. 40 p. 30 - 39

0075-9511

A set of sixteen Argentinean shallow lakes of two different hydrological regions (Pampean and Patagonian), were characterized using apparent an inherent optical properties along with water-quality parameters. In Pampean lakes, values of vertical PAR diffuse attenuation coefficients varied from 3.4 to 47 m-1. Pampean clear-vegetated lakes presented significant lower values of kd (PAR) (< 10 m-1) than turbid Pampean lakes (> 13 m-1) (t-test, p < 0.001). In these lakes a significant positive linear relationship was observed between water transparency estimated as 1/Sd and kd (PAR) (r2 = 0.91, p < 0.001, n = 10). Conversely, Patagonian lakes presented significantly lower kd (PAR) values than Pampean lakes (t-test, p < 0.001), with values ranging from 0.4 to 2.5 m-1.  As regards of absorption properties obtained for Pampean lakes, turbid lakes presented higher at (440) (10.5 to 26.2 m-1) than clear-vegetated ones (2.6 to 7.1 m-1). In turbid inorganic lakes unpigmented particulate presented an important contribution to light absorption at surface level (> 37.4 %), thought in turbid organic lakes phytoplankton was the most important fraction (41.4 to 61.9 %). In clear Pampean lakes CDOM (45.9 to 80.2 %) and phytoplankton (39.9 to 41.7 %) presented the highest contribution to surface light absorption. On the other hand, values of at (440) obtained for Patagonian lakes were lower than those of Pampean lakes (0.35 to 5.09 m-1), presenting pure water (from 41.7 to 63.3 %) and CDOM (59.2 to 77.4 %) as fractions with largest contribution to absorbed quanta. Estimations of the scattering coefficients, using nephelometric turbidity, ranged from 4.0 to 114.7 NTU in Pampean lakes and showed significant differences between turbid and clear states (t-test, p < 0.001). Using CDOM absorption and nephelometric turbidity, we were able to explain the 98 % of the observed variation in kd (PAR) for Pampean lakes, thought in Patagonian lakes only CDOM absorption significant explain ( 89%) among lakes differences in  light attenuation.  Although we found significant relationships between kd, Sd and tn over the whole range of optical conditions, we noticed important disparities between Sd and tn and actual light attenuation (i.e., kd) for some surveyed lakes. Our results showed that the direct measurement of (PAR) attenuation, in addition with the determination of the main absorbing components,  are much more precise way of describing underwater light availability than more common estimation based either on Sd or tn . These measurements could therefore improve our ability to understand, the conditions that regulate macrophyte vs. phytoplankton dominance, as well as other important management issues in shallow lakes.