| Abstrakt: |
Abstract The easiest way to evaluate water transparency is from the Secchi disk depth (SD). The behavior of radiation passing through water can also be quantified by the light attenuation coefficient (k) of photosynthetically active radiation (PAR), measured using quanta meters. Due to the high costs of quanta meters, k is usually predicted from SD. This prediction can be made using the index SD × k or using nonlinear models that correlate these variables. The aims of this study were to generate models predicting k through SD in two large Neotropical ecosystems (a reservoir and a floodplain) and to test whether 1.7, the index used worldwide, is adequate for predicting k in these ecosystems. The current paper also tested the effects of time (between seasons and among years) and space (between ecosystems and inside each ecosystem) upon such predictions. A standard 30-cm Secchi disk was used to measure SD. Simultaneously, PAR was measured at two depths to estimate k. A total data set of 2,136 measurements taken from 2001 to 2005 was used. The index generated, 2.26, was significantly different from 1.7 (t test, p k = 2.00 × SD−0.76, N = 2,136) was more reliable for predictions. [ABSTRACT FROM AUTHOR] |
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