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

摘要

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 47m1, Secchi disk depth (Sd) from 0.07 to 12.00m, and nephelometric turbidity (tn) from 0.50 to 103.70 NTU (710.00)]. Among Pampean lakes, highly turbid lakes presented significant higher kd PAR values (413m1) than clear-vegetated ones (<10m1), though all Patagonian lakes showed significant lower light attenuation (kd PAR<2.5m1). Our estimations of light scattering were supported by the significant relationship found between tn and Effler and Auer’s scattering coefficient estimate (best). Allowing for lakes with tno80 NTU, we obtained a significant linear regression with a slope close to the unity. However, when values of tn were higher than 80 NTU, no clear relationship was observed between tn and best. Although we found significant relationships between kd, Sd and tn over the whole range of underwater light scenarios, we noticed some disparities between Sd, tn 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 tn. 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 tn measured with bench top instruments. The direct measurement of paired values of Sd and tn, 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.