Showing papers on "Secchi disk published in 1988"
TL;DR: The black disk is expected to be of particular value for assessing the clarity of river waters that are too shallow for deployment of the Secchi disk.
Abstract: Black targets have a major theoretical advantage over reflective targets such as the Secchi disk for assessing the visual clarity of water because their sighting ranges depend only on two optical properties of the water: the beam attenuation coefficient and the diffuse attenuation coefficient. The theory of visibility of black objects applies to observations made with a black disk in 11 rivers and eight lakes ranging 60-fold in water clarity. The horizontal sighting range of the black disk is similar to visual ranges of practical importance in water, for aquatic animals as well as man, and yields an immediate estimate of the beam attenuation coefficient. The black disk is expected to be of particular value for assessing the clarity of river waters that are too shallow for deployment of the Secchi disk.
164 citations
TL;DR: The relatively close relationships between Secchi depth and chlorophyll in Lake Constance are due to (1) high influence ofchlorophyll concentration on water transparency, (2) co-variation of phytoplankton and other suspended particles, and (3) limited variation of cellular chlorophyLL contents.
Abstract: In meseutrophic Lake Constance mean euphotic phytoplankton chlorophyll concentrations vary about 100-fold over the year. Concomitant fluctuations in euphotic depth (Zeu) and Secchi depth (Zs) are related to each other in a non-linear fashion that as a rough approximation can be expressed by Zeu ∼ 5 √Zs.
95 citations
TL;DR: A convection turbulence model was used to examine the vertical mixing process and showed that light wind and surface cooling after sunset can substantially influence the depth of mixing.
67 citations
TL;DR: In this paper, a cross-sectional data set of 80 lakes and reservoirs in nine southeastern states was examined to specify and parameterize trophic state relationships, and the relationships fitted are based on measurements of several limnological variables taken over the course of a growing season or year in each of the lakes.
Abstract: A cross-sectional data set of 80 lakes and reservoirs in nine southeastern states was examined to specify and parameterize trophic state relationships. The relationships fitted are based on measurements of several limnological variables taken over the course of a growing season or year in each of the lakes. The trophic state models relate phosphorus and nitrogen loading to inlake phosphorus and nitrogen concentrations, which in turn are related to maximum chlorophyll level, Secchi disk depth, dominant algal species, and hypolimnetic dissolved oxygen status. Due to the empirical nature of the study, causal conclusions are limited; rather, the models are most useful for prediction of average growing season conditions related to trophic state.
62 citations
TL;DR: In this paper, the authors show that the product of Secchi depth and the diffuse attenuation coefficient is markedly dependent on the reflectance coefficient (brightness) of the water.
Abstract: Optical information on a water body is often required when only Secchi disk depths are available. Many limnologists and water managers have attempted to estimate diffuse light attenuation in water from Secchi depth data assuming a simple inverse relationship. However, we show theoretically that the product of Secchi depth and the diffuse attenuation coefficient is markedly dependent on the reflectance coefficient (“brightness”) of water. Data from 28 New Zealand lakes of diverse optical character demonstrated this dependence over a wide range of reflectance (1.1 to 35.9 percent). Uncritical estimation of attenuation coefficients for diffuse light from Secchi depths, using the currently available simple inverse expressions, is discouraged because of the possibility of bias.
62 citations
TL;DR: In this article, an analysis of the data collected during summers between 1911 and 1982 demonstrates that, on the average, the Secchi disk depth has decreased in time and that a decrease in light penetration has reduced the benthic primary production and thus has increased the probability of an occurrence of anoxic events near the bottom.
35 citations
TL;DR: In this paper, the authors used optical data collected between 1973 and 1979 to discuss the relationship among the directly observed Secchi disk depths and the directly measured total attenuation coefficients and irradiance attenuation coefficient in Lakes Erie, Ontario, Superior, and Huron, as well as Georgian Bay.
28 citations