Stream water chemistry in three meso-scale hydrologic basins in Eastern Amazonian Ricardo de O. Figueiredo 1, Daniel Markewitz 2, Eric A. Davidson 3, Ewerton S. da Cunha 4, Marysol A.E. Schuler 4, and Patrício de S. Silva 5 1. Embrapa Amazônia Oriental; 2. The University of Georgia; 3. The Woods Hole Research Center; 4. Instituto de Pesquisa Ambiental da Amazônia; 4. Instituto de Pesquisa Ambiental da Amazônia; 5. Universidade do Estado do Pará / CNPq-CTHidro

Main Objective and Previous Studies  This work addresses the effects of land use change on stream water chemistry  In previous studies, we showed:  significantly lower soil nitrate concentration in pasture soils compared to forest soils  significant leaching of cations from pasture soils to the stream (larger concentrations at high flows)

Streams (Igarapés): Cq = Igarapé Cinquenta e quatro St = Igarapé do Sete Pj = Igarapé Pajeú Three watersheds near Paragominas (Eastern Amazonia) * Landsat 1999 scenes Cq (130 km 2 ) - 18% forest St (150 km 2 ) - 34% forest Pj (45 km 2 ) - 45% of forest Field campaigns from April/2003 to July/2004, from headwaters in remnant mature forests, through pastures, secondary forests, and agricultural fields.

headwaters in remnant mature forests headwaters in an extremely explored forest

Crops Pasture IGARAPÉ DO SETE IGARAPÉ PAJEÚ A view of a farm area between two of the studied streams

Stream dammed up flow completely interrupted controled flow A very typical streamwater use: water supply and electricity for the farms

Two distinct downstream patterns Let’s see the first results …

 Decrease in turbidity, temperature and pH related to decreasing in percentual watersheds forested areas.  In this graph we also present values of an entire forested microbasin (FL) situated about 80 km from Paragominas.

Sete - 34% forest Cinquenta e Quatro - 18% forest Pajeú - 45% of forest downstream  In the watershed where the remmant forest has been extremely explored, pH is high at headwaters decreasing downstream.  It is the opposite downstream pattern of the other two watersheds that have remnant mature forests and larger percentual forested areas.

 Dissolved oxygen (mg L -1 ) decreases due to the low flow caused by dams in the Igarapé do Sete.

 Temporal variation of Nitrate month means (  M L -1 ) in the 3 streams from April to July/ y = x x x aprmayjunjul NO3 (uM/L) * nitrate month averages in the 3 streams increase with rainy season and decreases sharply when stop raining.This fact may be related to the importance of superficial and subsuperficial flows as main sources of nitrate. equation of the polynomial trendline

 Nitrate means and range (  M L -1 ) for the first 4 months (April to July/2003) in each station of the Igarapé Pajeú. y = Ln(x) Pj1Pj2Pj3 NO3 (uM/L) equation of logarithimic trendline Pj1 - forested headwaters (flowing slowly) Pj2 - pasture/capoeira (flowing just after dam) Pj3 - capoeira/pasture/crops (flowing) * trend of nitrate decreasing from forested headwaters * denitrification in the lake formed by dam at Pj2 may be an important factor for nitrate decreasing * secondary vegetation may function nitrate source at Pj3

 Nitrate means (  M L -1 ) for the first 4 months (April to July/2003) in each station of the Igarapé Pajeú aprmayjunjul NO3 (uM/L) Pj1 Pj2 Pj3 forested headwaters (flowing slowly) pastures/capoeiras (flowing just after dam) capoeira/pastures/crops (flowing) * Nitrate decreases when stop raining in July * forests as nitrate sources are clear at these more preserved headwaters areas among studied catchments

 Nitrate means and range (  M L -1 ) for the first 4 months (April to July/2003) in each station of the Igarapé Cinquenta e Quatro.

 Nitrate means (  M L -1 ) for the first 4 months (April to July/2003) in each station of the Igarapé Cinquenta e Quatro.

 Nitrate means and range (  M L -1 ) for the first 4 months (April to July/2003) in each station of the Igarapé do Sete. Dams also promoting nitrate decreasing in the Igarapé do Sete.

 Temporal variation of Calcium month means (  M L -1 ) in the 3 streams from April to July/2003.

 Calcium means (  M L -1 ) for the first 4 months (April to July/2003) in the Igarapé do Pajeú aprmayjunjul Ca (uM/L) Pj1 Pj2 Pj3 forested headwaters (flowing slowly) pastures/capoeiras (flowing just after dam) capoeira/pastures/crops (flowing) * As observed in early studies calcium concentrations are larger during rainy season. * Perhaps there is a signal of agriculture at Pj3. This must be investigated along a larger period of time.

 Calcium means (  M L -1 ) for the first 4 months (April to July/2003) in each station of the Igarapé Cinquenta e Quatro.

An ongoing research work… We are measuring: temperature, pH, conductivity, turbidity, alkalinity, O 2, Ca 2+, Mg 2+, K +, Na +, NH 4 +, NO 3 -, PO 4 3-, Cl -, DOC, DIC, pCO 2, stream discharge, and rainfall. Since March 2004 we are also sampling runoff, soil solution and groundwater at these watersheds (transects across riparian zones). In addition, storm events will be sampled four times on each stream during 2005 rainy season to evaluate hydrologic flow paths during storm events. Because soils are relatively similar within the study area, we suspect land use conversion is an important factor affecting the observed trends in stream chemistry.