Modeling the Effects of Tripton on Water Clarity: Lake Champlain

Abstract

The development, testing, and application of a probabilistic modeling framework for Secchi disc (SD) transparency that resolves the effects of several light-attenuating constituents, including phytoplankton biomass [as chlorophyll concentration (Chl)] and nonphytoplankton particles (tripton) are documented. The model is consistent with optical theory, and accommodates sources of variations in the character and levels of attenuating constituents and ambient conditions during measurement of SD. Model validation is demonstrated for a broad range of SD values (0.75–5.0 m) measured at various locations on Lake Champlain. The major spatial differences in SD documented in long-term monitoring (1990–1998) of this lake are found to be primarily the result of spatial differences in levels of tripton. Tripton is found to be important in regulating SD throughout the lake. Management applications of the model demonstrate that there would be little benefit for clarity in the southern portion of the lake by reducing phytoplankton concentrations because of the high tripton levels. Erosion control is to be preferred over nutrient control as a management approach to improve clarity in that portion of the lake. A generalized version of the model is presented that has diagnostic value for managers for many lakes to support a first approximation of the contribution of tripton from paired measurements of SD and Chl.