**2. Data base**

The data from Itapeva Lake were gathered over more than one year (August 1998 – August 1999), at three fixed sampling stations (North, Center and South). Lake Mangueira has been sampled for several years, although for the modeling exercise reported here we used data also collected at three fixed sampling stations (North, Center and South) from 2000 to 2001.

The sampling protocol as well as some results were published previously by Cardoso & Motta Marques (2003, 2004a, 2004b, 2004c, 2009) for Itapeva Lake, and by Crossetti et al. (2007) and Fragoso Jr. et al. (2008) for Lake Mangueira.

Environmental data (air temperature, precipitation, wind velocity and wind direction) from the meteorological station (DAVIS, Weather Wizard III, Weather Link) installed at the Center point were recorded every 30 min (beginning 24 h before each sampling event) throughout the period. Based on the prevailing wind direction in each season, the effective fetch (Lf km) was calculated (Håkanson, 1981) for each sampling point using the map of the region on a 1:250 000 scale. An estimate was also made of the height of waves produced and the bottom dynamics, from wind velocity, depth and fetch (Håkanson, 1981).

Four sections were chosen to study seiches in the lake, one section for each region (North, Center and South), and one section running in the longest and most central direction. It was considered that the seiches occur at time intervals of over 120 min; to obtain this value, the length of the lake (fetch) in the direction of the seiche, the mean wind speed, and the time needed by the wind to cover this distance were considered. This time is the minimum time for seiche occurrence, i.e., it is the time needed by the wind to cover the fetch. In addition to evaluating the existence of seiches, the period was also studied using simulated values and an empirical equation. The period calculated empirically is based on the formula for a rectangular shape (Lopardo, 2002 as cited in Cardoso & Motta Marques, 2003).

Data for turbidity, temperature, dissolved oxygen, pH, and electrical conductivity from the YSI (Yellow Springs Instruments 6000 upg3) multiprobe installed at the three sampling points were recorded every 5 minutes during each seasonal campaign. Water level, direction and velocity were recorded every 15 minutes at the same locations.

Samples were collected during five seasonal campaigns: winter/98 (August 24–25/1998), spring (December 15–20/1998), summer (March 2–7 /1999), autumn (May 21–26/1999) and winter (August 14–19/1999). The water samples for plankton analyses were collected at three depths (surface, middle and bottom) during four shifts throughout the day (06:00, 10:00, 14:00 and 18:00 h), at 24-h intervals during the three days of each seasonal sampling. The water samples for analyses of solids, nitrogen and phosphorus (APHA, 1992) were collected and integrated into the water-column data during the same periods as the plankton sampling.

#### **2.1 Modeling in Itapeva Lake**

Modeling in Itapeva Lake was divided into two parts: watershed and lake modeling. First, we used two different hydrological models: a) to estimate the input from the Três Forquilhas basin, and b) to estimate the output from Itapeva Lake to the river downstream.

for rice production, and many of the local waterbodies are used for irrigation, with a total water withdrawal of approximately 2 L s-1 ha-1 on 100 individual days within a 5-month period, and a high input of nutrients from the watershed during the rice-production period.

The data from Itapeva Lake were gathered over more than one year (August 1998 – August 1999), at three fixed sampling stations (North, Center and South). Lake Mangueira has been sampled for several years, although for the modeling exercise reported here we used data also collected at three fixed sampling stations (North, Center and South) from

The sampling protocol as well as some results were published previously by Cardoso & Motta Marques (2003, 2004a, 2004b, 2004c, 2009) for Itapeva Lake, and by Crossetti et al.

Environmental data (air temperature, precipitation, wind velocity and wind direction) from the meteorological station (DAVIS, Weather Wizard III, Weather Link) installed at the Center point were recorded every 30 min (beginning 24 h before each sampling event) throughout the period. Based on the prevailing wind direction in each season, the effective fetch (Lf km) was calculated (Håkanson, 1981) for each sampling point using the map of the region on a 1:250 000 scale. An estimate was also made of the height of waves produced and

Four sections were chosen to study seiches in the lake, one section for each region (North, Center and South), and one section running in the longest and most central direction. It was considered that the seiches occur at time intervals of over 120 min; to obtain this value, the length of the lake (fetch) in the direction of the seiche, the mean wind speed, and the time needed by the wind to cover this distance were considered. This time is the minimum time for seiche occurrence, i.e., it is the time needed by the wind to cover the fetch. In addition to evaluating the existence of seiches, the period was also studied using simulated values and an empirical equation. The period calculated empirically is based on the formula for a

Data for turbidity, temperature, dissolved oxygen, pH, and electrical conductivity from the YSI (Yellow Springs Instruments 6000 upg3) multiprobe installed at the three sampling points were recorded every 5 minutes during each seasonal campaign. Water level, direction

Samples were collected during five seasonal campaigns: winter/98 (August 24–25/1998), spring (December 15–20/1998), summer (March 2–7 /1999), autumn (May 21–26/1999) and winter (August 14–19/1999). The water samples for plankton analyses were collected at three depths (surface, middle and bottom) during four shifts throughout the day (06:00, 10:00, 14:00 and 18:00 h), at 24-h intervals during the three days of each seasonal sampling. The water samples for analyses of solids, nitrogen and phosphorus (APHA, 1992) were collected and integrated into the water-column data during the same periods as the

Modeling in Itapeva Lake was divided into two parts: watershed and lake modeling. First, we used two different hydrological models: a) to estimate the input from the Três Forquilhas basin, and b) to estimate the output from Itapeva Lake to the river downstream.

the bottom dynamics, from wind velocity, depth and fetch (Håkanson, 1981).

rectangular shape (Lopardo, 2002 as cited in Cardoso & Motta Marques, 2003).

and velocity were recorded every 15 minutes at the same locations.

(2007) and Fragoso Jr. et al. (2008) for Lake Mangueira.

**2. Data base** 

2000 to 2001.

plankton sampling.

**2.1 Modeling in Itapeva Lake** 

Subsequently, we used a 2-D hydrodynamic model to evaluate the roles of the Três Forquilhas inflow and wind effects on the hydrodynamics and mixture processes of the lake. For the watershed analysis we used the IPH2 model, a rainfall, runoff-lumped model developed at the Instituto de Pesquisas Hidráulicas (IPH). Its mathematical basis is the continuity equation composed of the following algorithms: (a) losses by evapotranspiration and interception by leaves or stems of plants; (b) evaluation of infiltration and percolation by Horton; and (c) evaluation of surface and groundwater flows (Tucci, 1998). The model works by regarding a drainage basin as series of storage tanks, with rainfall entering at the top, and being split between what is returned to the atmosphere as evaporation, and what emerges from the basin as runoff (stream flow). Depending on the number of tanks and the number of parameters controlling the passage of water between them, it can be made more or less complex.

For the output analysis we used the MOLABI model (Ecoplan, 1997), a water-budget model based on the Puls method, which represents the continuity equation applied to the whole lake. The input data is rainfall over the lake, inflows from the watershed, and groundwater flux estimated by the Darcy equation. Evaporation was estimated using the Penman method.

The hydrodynamic patterns in Itapeva Lake were modeled using the model IPH-A (2D; Borche, 1996). The main inputs of the model were: water inflow, wind, rainfall and evaporation, spatial maps (including waterbody, bathymetry, bottom and surface stress coefficient). This model was applied because Itapeva Lake is a polymictic environment with no significant difference among depths (surface, middle and bottom), neither for the physical and chemical data nor for the plankton communities. The model was run from January to December 1999.
