Evaluation of a Modified Monod Model for Predicting Algal Dynamics in Lake Tai

Abstract

Several modified versions of the Monod model have been proposed to simulate algal dynamics in lakes by keeping the parent model's advantages of simplicity and low data requirement. This study evaluated the performance of a widely-used modified Monod model in predicting algal dynamics at various time scales in Lake Tai, a typical shallow lake in east China, using multiple time series. Chlorophyll-a (Chl-a) concentration was used as a surrogate for algal (CyanoHABs: cyanobacterial harmful algal blooms) growth and the independent variables were total nitrogen (TN), total phosphorus (TP), and either water temperature or air temperature. The evaluation indicated that the model parameters could have distinctly different values, depending on whether or not constraints are imposed, time scales, and types of nutrients. The model performance varied in terms of time scales as well as magnitudes and fluctuations of Chl-a and TN or TP concentrations, achieving a relative OPEN ACCESSWater 2015, 7 3627 better performance for the monthly rather than three-day time scale and for the central part rather than bays of the study lake. The model with TP as the independent variable had a better performance than the model with TN as the independent variable, regardless of the time scale used. The temperature-nutrient interactions were important for algal growth when the temporal fluctuations of these two factors were large but the interactions could become minimal otherwise.

Spatiotemporal Distribution of Eutrophication in Lake Tai as Affected by Wind

“…This is because a number of other factors also affect water quality [34]. For instance, depending on the timing, amount, location and constituents of wastewater discharge, the TN and TP concentrations could be elevated almost instantaneously, in particular in the bays and lake areas along the shorelines.…”

“…Such a high dynamic ratio indicates that the lakebed sediments of Lake Tai are particularly susceptible to resuspension by wind-induced shear stress [36]. Most other lakes in China have a much smaller dynamic ratio than Lake Tai [34].…”

“…Although most of the wastewater was discharged into the lake through the drainage system (e.g., channels and pipelines) located in the northwestern part, a considerable amount of wastewater was discharged into the lake from numerous locations along the lake shore. The water quality in Lake Tai is spatially heterogeneous [34]: Meiliang Bay and Zhushan Bay, both in the northern part of the lake, have the worst water quality, while the water quality in the eastern part (labeled as East Lake in Figure 1) is much better than that in other parts of the lake. In terms of the spatial heterogeneity of water quality, the lake can be subdivided into five zones (Figure 1), namely Meiliang Bay, Zhushan Bay, Gonghu Bay, Central Lake and East Lake.…”

“…As mentioned above, the ratio of wind speed to water depth can be used as a surrogate for the vertical distribution of wind-induced shear stresses [34]. For Meiliang Bay, the shear stress was found to be beneficial to the water quality.…”

“…Moreover, the data on wind speed and water depth at Site 1 of Meiliang Bay ( Figure 1) were used to compute the ratios of wind speed to water depth, which can be used as a surrogate for the vertical distribution of wind-induced shear stresses [34]. Such ratios were computed for 56 days because the data were just available for some days in four months (July to October) of 2010 and four months (May and July to September) of 2011.…”