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

Sixteen Argentinean shallow lakes from the Pampa plains and the Patagonian steppe were characterized using optical properties and water-quality parameters. In this set of lakes a wide range in water transparency descriptors was observed [broadband vertical attenuation coefficient (kd PAR) varied from 0.40 to 47 m(-1), Secchi disk depth (Sd) from 0.07 to 12.00 m, and nephelometric turbidity (t(n)) from 0.50 to 103.70 NTU (+/- 10.00)]. Among Pampean lakes, highly turbid lakes presented significant higher kd PAR values (>13 m(-1)) than clear-vegetated ones (<10 m(-1)), though all Patagonian lakes showed significant lower light attenuation (kd PAR<2.5 m(-1)). Our estimations of light scattering were supported by the significant relationship found between t(n) and Effler and Auer's scattering coefficient estimate (b(est)). Allowing for lakes with t(n)<80 NTU, we obtained a significant linear regression with a slope close to the unity. However, when values of t(n) were higher than 80 NTU, no clear relationship was observed between t(n) and b(est). Although we found significant relationships between kd, Sd and t(n) over the whole range of underwater light scenarios, we noticed some disparities between Sd, t(n) and light attenuation in lakes with certain optical characteristics. Considering the whole data set, including clear and turbid lakes, as much as 92% of the variation observed in kd PAR could be explained by a regression model including absorption of chromophoric dissolved organic matter (CDOM) and t(n). Our results showed that a Suitable and practical method to estimate light attenuation could be the use of empirical models based on absorption coefficients and t(n), measured with bench top instruments. The direct measurement of paired values of Sd and t(n), in addition with main absorbing components are a useful and precise way of describing underwater light availability and optical regimes. The latter, combined with occasional in situ measurements of kd Would permit the development of highly accurate lake-specific models of light attenuation. (C) 2008 Elsevier GmbH. All rights reserved.