Impact of Intensive Agricultural Production on the Ecotoxicologic Quality of Associated Medium-Order Streams: Cereal and Oilseed versus Horticultural Production.

Streams associated with agroecosystems receive inputs of chemicals used within a basin that negatively impact its environmental quality. In this work, we aimed at comparing, through a battery of ecotoxicological tests, the relative impact of the cereal and/or oilseed and vegetable and/or flower agricultural-production models on the ecotoxicologic quality of both the water column and the bottom sediments of medium-order streams. The study, performed over 4 years, involved two major agroproductive areas of Argentina, one predominating in cereal and/or oilseed crops (Area 1), the other in vegetable and/or flower agriculture (Area 2). Both productive systems impacted the associated surface water bodies negatively, with the intensive production of vegetables and flowers producing greater ecotoxicologic effects on diagnostic organisms. The intensive-agriculture systems associated with Area 2 caused greater negative impacts on the water column than those of Area 1, with this pattern occurring in reverse for the bottom sediments. Furthermore, the samples from the sites associated with horticulture were more frequently toxic than those from Area 1. Of the organisms used to assess sample toxicity-Lactuca sativa, Daphnia magna, and Hyallela curvispina-L. sativa was the most sensitive to the type of contaminants associated with the form of agricultural land use; whereas no differences in sensitivity were observed between the two crustaceans. We found that the sublethal effects were significantly more sensitive than the lethal. The findings from this work would strongly advocate more sustainable agricultural-management plans that employed phytosanitary products whose action were more environmentally sustainable.

Stemflow generation as influenced by sugarcane canopy development.

Rainfall is generally partitioned into throughfall, stemflow, and interception in ecosystems. Stemflow variability can affect the hydrology, ecology, and soil chemistry patterns. However, the influence of canopy structure and rainfall characteristics on stemflow production in sugarcane plantations which are important for renewable energy production remain poorly understood. By using funnels attached to the sugarcane stems, the present study determined the stemflow amount during the period of sugarcane growth and its relationship with plant development. Approximately, 14% of gross rainfall reached the soil as stemflow, and the funneling ratios was 60. In general, it was observed a positive relationship between stemflow rates with both leaf area index and plant height. This was attributed to an increasing number of acute branching angles of the sugarcane leaves as well as high stem tillering and density. However, at the end of growth cycle, stemflow rate was lower than in previous periods which can be attributed to changes in sugarcane canopy such as stems inclination and lodging, reducing the effectiveness of water conveyance along the stem. Our study showed the need to include stemflow to better understand the hydrology of sugarcane plantations.