Abstract:The temporal variability in nitrogen (N) transport in the Corbeira agroforestry catchment (NW Spain) was analysed from October 2004 to September 2008. Nitrate (NO 3 -N) and total Kjeldahl nitrogen (TKN) loads and concentrations were determined at various timescales (annual, seasonal and event). The results revealed a strong intra-annual and inter-annual variability in N transport influenced by weather patterns and consequently by the hydrological regime. Mean annual export of total N in the catchment was 5.5 kg ha À1 year À1 , with NO 3 -N being the dominant form. Runoff events comprised 10% of the study period but contributed 40 and 61% of the total NO 3 -N and TKN loads, respectively. The NO 3 -N and TKN concentrations were higher during runoff events than under baseflow conditions, pointing to diffuse sources of N. The mobilization of TKN during runoff events was attributed to surface runoff, while NO 3 -N might be related to subsurface and groundwater flow. Runoff events were characterized by high variability in N loads and concentrations. Higher variability was observed in N loads than in N concentrations, indicating that event magnitude plays an important role in N transport in this catchment; event magnitude explained approximately 96% of the NO 3 -N load. However, a combination of variables related to runoff event intensity (rainfall, discharge increase and kinetic energy) explained only 66% of the TKN load.

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The use of tannery sludge in arid soils could be promising due to the high content of organic carbon and nitrogen. However, tannery waste also contains high amounts of Cr and salts that could leach into drainage water in response to rainfall. In order to study the effects of two tannery wastes as organic fertilizers on two types of semi-arid soils, simulated rainfall experiments were carried out. Soils collected from under and outside a mesquite tree canopy were amended with fleshing waste and/or tannery sludge and incubated 0 to 6 months prior to being subjected to simulated rainfall. The parameters measured were: infiltration, runoff, soil and Cr losses, and NH 4 + -N and NO 3 − -N released after a rainfall event. Results showed that fleshing waste added to soils from outside the canopy tree was the most effective treatment for decreasing runoff, soil losses, and Cr, NH 4 + -N and NO 3 − -N loss in runoff and infiltration, in general. However, the same treatment had the opposite results for soil under the canopy. These results indicate that the types of waste and soil must be taken into consideration when attempting to improve physical and chemical characteristics of semi-arid soils. Thus, the use of tannery waste represents a potential hazard, not only causing soil erosion but also Cr contamination in adjacent sites and aquifers.

El acuífero Cuautitlán-Pachuca ocupa la porción norte de la cuenca del Valle de México, justificando su nombre por la presencia de Cuautitlán en el Estado de México y Pachuca en el estado de Hidalgo. Dicho acuífero en la actualidad esta sobreexplotado. Por tal motivo en este trabajo se estimó la sustentabilidad del acuífero, utilizando el marco para la evaluación de sistemas de manejo de recursos naturales incorporando indicadores de sustentabilidad (MESMIS). Se realizó un estudio longitudinal comparando dos sistemas, el primero se analizó para el periodo 1970-1990 (sistema de referencia) y el segundo para el periodo 1991-2010 (sistema alternativo). Se analizaron 14 indicadores ambientales, económicos y sociales, para los dos periodos de tiempo. Encontrándose que los aspectos ambientales y económicos presentan los mayores rezagos con el paso de los años, en el caso de los indicadores sociales mostraron avances hacia la equidad. También se encontró que 9 de los indicadores presentaron mayor cercanía al valor óptimo propuesto en el sistema de referencia y solo cinco mostraron un acercamiento hacia el óptimo en el sistema alternativo. Los resultados muestran que el acuífero es menos sustentable en la actualidad.

Patterns of phosphorus (P; dissolved and particulate) and nitrate (NO 3 ) delivery were compared between times of base flow and events in a stream draining a small agroforestry catchment in Galicia, northwest Spain. Nutrient concentrations were low during base flow, and only nitrate shows a clear seasonal pattern. In general, particulate phosphorus (PP) was the dominant fraction of the total P. Particulate P concentrations increased significantly during storms, with maximum concentrations occurring on the rising limb of the hydrograph (clockwise hysteresis). The rapid response of PP suggests a near-stream source of PP during events. The surface runoff is the mainly route to transport PP to the stream, whereas for the dissolved phosphorus (DP) and NO 3 the subsurface path is also important.