The influence of human activities on Pampean streams catchment: a biogeochemical approach

Pampean streams constitute a drainage network which discharges continental freshwater into the associated marine coastal zone. The present study concerned a set of streams within General Pueyrredón district, Southeastern province of Buenos Aires, Pampa’s region, Argentina, which deserves particular attention, since they flow in the area of influence of Mar del Plata, one of the most important tourist destination in the country. Different physical–chemical (i.e., temperature, conductivity, pH, dissolved oxygen), hydrographical and eco-physiological parameters were studied within five streams along an annual cycle, searching for seasonal variations and possible relations with land use. The behavior of physical–chemical parameters was consistent with previous reports on similar environments; inorganic nutrients presented high levels along the whole period, and have never been completely depleted. Within N nutrients, nitrate demonstrated to be the dominant along the whole period, with global mean values of ~ 18 µM and reaching values up to ~ 50 µM (total discharge of N ~ 1.23 Ton DIN y −1 ). A very high load of organic matter (from ~ 2000 mg Cm −3 in the fall up to ~ 4000 mg Cm −3 during summer) is discharged from these streams into the marine coastal zone (which represents ~ 214 Ton POC y −1 ) and, even until now, response effects have not been recorded there. The obtained results allowed us to sustain that anthropic activities (i.e., agriculture, cattle raising), continental runoff and climate conditions seem to be the main drivers of the hydrographical/biogeochemical behavior of the studied streams. Therefore, changes concerning them should also be included in future monitoring programs.