D-INSTREAM

Hazy skies, dirty cars and poor air quality are some of the most visible signs of dust transport episodes. Aerosols from Sahara are transported mainly across the Atlantic as far as the Amazon rainforest or the Caribbean Islands, but also to the Mediterranean region. The amount of Saharan dust exported to the atmosphere has increased exponentially in recent decades as a consequence of droughts in North Africa, human-induced desertification4, and the development of commercial agriculture in the Sahel region.
Dust-derived inputs of limiting nutrients actually represents one of the major agents of fertilization of the biosphere through the atmosphere. Escaping the influence of such atmospheric nutrient subsidy via dust events is very unlikely for any ecosystem on the planet. However, the mechanisms and extent by which atmospheric nutrient inputs alter the functioning of receiving ecosystems cannot be extrapolated from one region to the other one.
High-mountain areas are a focus of special interest in the context of environmental change. They are areas of limited industrial or agricultural activity but, at the same time, they are regions where nutrients (e.g., N and P) are normally limited and heterogeneously stored in poorly developed soils, snow and ice. High-mountain lakes are actually considered sentinels (or sensors) of environmental change as they are highly oligotrophic (i.e., limited in nutrients), and thus very sensitive to the climate changes that act on a regional or global scale. Nevertheless, while a significant number of studies have addressed the influence of dust deposition on the biogeochemistry of lakes, the number of studies addressing this question in high-mountain running waters is still scarce.

Objectives

The general objective of D-INSTREAM is to assess whether dust-induced changes in the quantity and stoichiometry of elemental resources transferred to high-mountain streams influence their capacity to transform versus transport nutrients during hydrologic events.

Actions

Two main tasks we will carry out to achieve the proposed objective are:

1. Synoptic sampling: Similarly to other high-mountain areas of the Pyrenees massif, The APNP hosts a high density of small headwaters streams. During the first part of the project we will perform a synoptic sampling aimed to drown a first extensive picture of the spatial variability in stream dissolved nutrients (C, N and P) concentrations within the Park. Nutrient analysis will be used to determine which landscape features (distal drivers) and/or stream physicochemical properties (proximal drivers) are the most important factors in determining the nutrients concentrations (and stoichiometry) found in the streams. This analysis should help us to understand which streams are more (or less) influenced by the nutrient chemistry associated with the Saharan dust deposition

2. Quantification of nutrient uptake rates: The central methodological approach we propose for D-INSTREAM relies on the use of short-term constant rate additions to determine in-stream DOC, DIN and SRP uptake rates under experimental conditions. The amount (and composition) of nutrients added to the streams will manipulate the C:N:P stoichiometry of the stream water to simulate different scenarios by which dust is delivered to streams upon hydrological events (i.e., low, intermediate and high transport of dust to streams).

Project funded by Observatori de Recerca del Parc Natural de l'Alt Pirineu's 'SALVADOR GRAU I TORT' grant