Detection and attribution of global change effects on river nutrient dynamics in a large Mediterranean basin

Abstract

Attributing changes in river water quality to specific factors is challenging because multiple factors act at different temporal and spatial scales, and it often requires examining long-term series of continuous data. Data consistency is sometimes hindered by the lack of observations of relevant water quality variables and the low and uneven sampling frequency that characterizes many water quality monitoring schemes. Nitrate and dissolved phosphate concentration time series from 50 sampling stations across a large Mediterranean river basin were analyzed to disentangle the role of hydrology, land-use practices, and global climatic phenomena on the observed nutrient patterns, with the final aim of understanding how the different aspects of global change affected nutrient dynamics in the basin. Dynamic factor analysis (DFA) provided the methodological framework to extract underlying common patterns in nutrient time series with missing observations. Using complementary methods such as frequency and trend analyses, we sought to further characterize the common patterns and identify the drivers behind their variability across time and space. Seasonal and other cyclic patterns were identified as well as trends of increase or decrease of nutrient concentration in particular areas of the basin. Overall, the impact of global change, which includes both climate change and anthropogenic impacts, on the dynamics of nitrate concentration across the study basin was found to be a multifaceted process including regional and global factors, such as climatic oscillations and agricultural irrigation practices, whereas impacts on phosphate concentration seemed to depend more on local impacts, such as urban and industrial activities, and less on large-scale factors.Published by Copernicus Publications on behalf of the European Geosciences Union.

Disclosing the effects of climate, land use, and water demand as drivers of hydrological trends in a Mediterranean river basin

“…Similar shifts in long-term trends regarding nutrient concentrations have been reported in European rivers (Vigiak et al, 2023). For example, we observed that PO 4 -3 concentration shows a slight decreasing trend, possibly related to the wastewater treatments focused on PO 4 -3 reduction (Aguilera et al, 2015). Moreover, NO 3 and NH 4 + showed increasing trends, likely because of the increase in the use of N fertilizers and the expanded number of irrigated lands, crop productivity, and livestock production (Einarsson et al, 2021;Lassaletta et al, 2021).…”

“…Finally, the low phosphate concentrations observed in the alluvial aquifer, typically below 0.04 mg/l (Menció & Boix 2018), are one-tenth of the values found in surface waters. Such a significant difference suggest that phosphorus inputs mainly originate from other local sources (i.e., industrial activity and WWTP) and could be associated with flood events and sediment transport (Aguilera et al, 2015).…”

Trends and seasonality of river nutrients in agricultural catchments: 18 years of weekly citizen science in France

“…, asynchronous fluctuations appear to be the rule in disturbed ecosystems, likely associated with dilution of point sources during high flows and enhanced release of reactive phosphorus during warm periods (Aguilera et al, 2015;Bowes et al, 2009;Duan et al, 2012;Minaudo et al, 2015). DSi seasonality also appears to be consistently asynchronous with discharge, due to dilution and seasonal differences in uptake by diatoms (Bowes et al, 2009;House et al, 2001;Moatar et al, 2017;Neal et al, 2000).…”

Future trends of dissolved inorganic nitrogen concentrations in Northwestern Mediterranean coastal waters under climate change

“…The Ebro river delta, the most important delta in the Iberian peninsula, has a mean surface elevation of 0.87 m over the average sea water level, which makes it very sensitive to potential sea level rise, critically threatening nutrient removal dynamics (Genua-Olmedo et al, 2016). Both climate change and agricultural practices have significant impacts on nitrate concentrations in the Ebro basin, while phosphate concentrations are mainly driven by agricultural and industrial practices (Aguilera et al, 2015). In the case of the Jucar River Basin District (Southeast of Spain), temperatures are expected to increase up to 4.86°C in summer by 2040 (Chirivella et al, 2016) and consequently alter nitrogen transformation processes (Temino-Boes et al, 2019).…”