Influence of the phreatic aquifer in the nutrient dynamics (nitrogen and phosphorus) in lakes of different hydrodynamic characteristics / Influência do aqüífero freático na dinâmica de nutrientes (nitrogênio e fósforo) em lagoas com diferentes características hidrodinâmicas

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The discharge zone of Paranapanema river at Jurumirim reservoir is an area of decreased current velocity associated to a great number of aquatic environments with different hydrodynamic characteristics. To evaluate the influence of the superficial phreatic aquifer in the nutrient dynamics (nitrogen and phosphorus and main cations), three floodplain lakes with different degrees of connection to the main channel were studied: 1) Coqueiral Lake (LCQ), with high connection to Paranapanema river; 2) Camargo Lake (LCM), with permanent connection to the main channel but low "information" interchange and 3) Cavalos Lake (LCV), isolated from the main channel. In October 2002 (end of the regional dry period) piezometers were installed at drilled wells to evaluate the piezometric surface and the hydraulic gradient between the main channel and floodplain lakes. During drilling, samples of soil strata were collected to proceed granulometric analysis, cation interchange capacity, organic matter, sum of exchangeable bases, percent base saturation, macro and micro-nutrients. Sampling was undertaken from April 2003 to April 2005. Groundwater samples were collected with 1,0 L bailers, specific for piezometers sampling. At the main channel and floodplain lakes, sampling was undertaken at the subsurface at stations located near the transitions zone between the aquatic and terrestrial systems. The hydraulic conductivity was determined by slug tests. Values of pH, conductivity, total nitrogen and phosphorus, calcium, magnesium, sodium, aluminum, manganese, barium, zinc and cobalt were obtained for the water samples. Hydraulic gradient and pluviometric data showed that the lotic environment exerts influence during the raining period; during the dry one, this role is played by the lakes. Most variables showed temporal variation when submitted to generalized linear models and the test of Tukey. An increased relationship with time was observed for nitrogen, phosphorus and aluminum concentrations. Values of pH, conductivity, calcium, magnesium, manganese, zinc and cobalt showed a decreasing temporal relationship. Concerning the conductivity, pH and sodium data of the environment, differences among the three lakes were evaluated. Most variables showed significative differences between ground and surface waters (river and lakes). The aquifer and river waters showed differences concerning the concentrations of phosphorus. Mean estimates of the total nitrogen and phosphorus groundwater contribution to the total content fluctuated, in the connected system, between 6%, for the Coqueiral Lake system, to 16%, for Camargo Lake system respectively. For the isolated system Cavalos Lake, the groundwater contribution estimates related to the total content of the lake were higher for total phosphorus (average = 11%) when compared to the total nitrogen estimates (average = 7%).

ASSUNTO(S)

nitrogênio Água subterrânea phosphorus carga de nutrientes fósforo nutrient load groundwater nitrogen

ACESSO AO ARTIGO

Documentos Relacionados