Fluvial nutrient dynamics in a humanized landscape. Insights from a hierarchical perspective

Enviem correu als editors per informar-nos sobre la política de drets d'autorGlobal change driven by human activity is overimposed on the hierarchical structure of fluvial ecosystems, causing a myriad of effects on their physical template and hydrology as well as on the quantity and quality of the resources for stream biota. Global change operates at all scales within this hierarchy, but its effects on the ecology of fluvial ecosystems at any particular scale may be exacerbated or overridden by concomitant effects occurring at other scales. The resulting effects can have major ecological implications on both ecosystem services (namely, biogeochemical processes associated to energy and matter flow) and biodiversity (namely, community structure), which currently are issues of central concern in environmental management. In this paper we focus on a particular ecological attribute of fluvial ecosystems, the capacity to process and retain nutrients, and examine how physical and chemical alterations caused by human activities, occurring at different scales, may interact to affect this capacity. We illustrate these effects based on existing knowledge and highlight the key changes at different scales which can be susceptible of major effects.El cambio global derivado de la actividad humana se sobrepone a la estructura jerárquica de los ecosistemas fluviales, causando múltiples efectos sobre la estructura física, la hidrología, y la cantidad y calidad de los recursos para los organismos de los ríos. El cambio global opera sobre todos los niveles de esta jerarquía estructural, pero sus efectos sobre la ecología de los ecosistemas fluviales en cada nivel pueden ser exacerbados o anulados por efectos que ocurren a otros niveles. Los efectos resultantes tienen implicaciones ecológicas tanto en relación con los servicios de los ecosistemas (por ejemplo, los procesos biogeoquímicos asociados al flujo de energía y materia) y la biodiversidad (por ejemplo, la estructura biótica de las comunidades). Actualmente, estos temas son una preocupación central en la gestión ambiental. En este artículo nos centramos en un atributo ecológico concreto de los ecosistemas fluviales, la capacidad de procesar y retener nutrientes, y examinamos cómo alteraciones físicas y químicas causadas por la actividad humana, que tienen lugar a diferentes niveles espaciales, pueden incidir en esta capacidad biogeoquímica. Estos efectos son ilustrados en base al conocimiento existente y enfatizan los cambios clave a diferentes niveles que pueden ser susceptibles de estos efectos

Nutrient dynamics and metabolism in Mediterranean streams affected by nutrient inputs from human activities

A full understanding of nutrient cycling in lotic ecosystems is crucial given the increasing influence of human activities on the eutrophication of streams and rivers. However, existing knowledge about nutrient cycling in human-altered streams (i.e., receiving point and diffuse sources) is still limited. The general objective of this dissertation was to examine point source effects on stream functional attributes, such as nutrient retention, denitrification and metabolism rates. We also quantified how the studied biogeochemical processes contribute to remove dissolved inorganic nitrogen (DIN) from point and diffuse sources, and examined relationships between N uptake measured based on experimental nutrient additions and N demand estimated from metabolism measurements. We selected two reaches located upstream and downstream of a point source in two streams draining a forest- and an agriculturaldominated catchments. Hence, the point source represented the main human influence in the forested stream, whereas the agricultural stream also received diffuse sources. The point source increased concentrations of ammonium (NH4 +-N), nitrate (NO3--N), soluble reactive phosphorus (SRP) and dissolved organic carbon in the forested stream, while only increased SRP concentration in the agricultural stream. The point source effect on water chemistry was likely to be overwhelmed by diffuse sources in this latter stream. Accordingly, point source inputs decreased nutrient retention efficiency, and increased denitrification and metabolism rates in the forested stream, whereas these effects were less clear in the agricultural stream. Retention of NH4 +-N was similar to potential nitrification rates in the two reaches of the two study streams, suggesting the importance of this process in NH4 +-N removal from the water column. Retention of NO3--N was similar to potential denitrification rates in the forested stream, suggesting the importance of this process as a net sink of NO3 --N. In contrast, high NO3--N fluxes in the agricultural stream resulted in low efficiency of denitrifiers to remove N from the water column. Hence, in-stream processes controlled DIN export in the forested stream, despite point source inputs, whereas much of the NO3--N reaching the channel via diffuse sources was lost downstream in the agricultural stream. Finally, estimated N demand was not correlated with measured N demand in any of the study reaches. Nevertheless, decoupling between measured and estimated N demand was clearly lower for the upstream reach of the forested stream (i.e., site with lowest human influence) than for the downstream reach and the two reaches of the agricultural stream (i.e., sites receiving nutrient inputs from human activities). Hence, coupling between carbon metabolism and N uptake in stream ecosystems is likely to become weaker with increasing anthropogenic nutrient inputs

Fluvial nutrient dynamics in a humanized landscape. Insights from a hierarchical perspective

Enviem correu als editors per informar-nos sobre la política de drets d'autorGlobal change driven by human activity is overimposed on the hierarchical structure of fluvial ecosystems, causing a myriad of effects on their physical template and hydrology as well as on the quantity and quality of the resources for stream biota. Global change operates at all scales within this hierarchy, but its effects on the ecology of fluvial ecosystems at any particular scale may be exacerbated or overridden by concomitant effects occurring at other scales. The resulting effects can have major ecological implications on both ecosystem services (namely, biogeochemical processes associated to energy and matter flow) and biodiversity (namely, community structure), which currently are issues of central concern in environmental management. In this paper we focus on a particular ecological attribute of fluvial ecosystems, the capacity to process and retain nutrients, and examine how physical and chemical alterations caused by human activities, occurring at different scales, may interact to affect this capacity. We illustrate these effects based on existing knowledge and highlight the key changes at different scales which can be susceptible of major effects.El cambio global derivado de la actividad humana se sobrepone a la estructura jerárquica de los ecosistemas fluviales, causando múltiples efectos sobre la estructura física, la hidrología, y la cantidad y calidad de los recursos para los organismos de los ríos. El cambio global opera sobre todos los niveles de esta jerarquía estructural, pero sus efectos sobre la ecología de los ecosistemas fluviales en cada nivel pueden ser exacerbados o anulados por efectos que ocurren a otros niveles. Los efectos resultantes tienen implicaciones ecológicas tanto en relación con los servicios de los ecosistemas (por ejemplo, los procesos biogeoquímicos asociados al flujo de energía y materia) y la biodiversidad (por ejemplo, la estructura biótica de las comunidades). Actualmente, estos temas son una preocupación central en la gestión ambiental. En este artículo nos centramos en un atributo ecológico concreto de los ecosistemas fluviales, la capacidad de procesar y retener nutrientes, y examinamos cómo alteraciones físicas y químicas causadas por la actividad humana, que tienen lugar a diferentes niveles espaciales, pueden incidir en esta capacidad biogeoquímica. Estos efectos son ilustrados en base al conocimiento existente y enfatizan los cambios clave a diferentes niveles que pueden ser susceptibles de estos efectos