Modelling nitrogen and phosphorus loads in a Mediterranean river catchment (La Tordera, NE Spain)

Abstract

Abstract. Human activities have resulted in increased nutrient levels in many rivers all over Europe. Sustainable management of river basins demands an assessment of the causes and consequences of human alteration of nutrient flows, together with an evaluation of management options. In the context of an integrated and interdisciplinary environmental assessment (IEA) of nutrient flows, we present and discuss the application of the nutrient emission model MONERIS (MOdelling Nutrient Emissions into River Systems) to the Catalan river basin, La Tordera (north-east Spain), for the period 1996-2002. After a successful calibration and verification process (Nash-Sutcliffe efficiencies E = 0.85 for phosphorus and E = 0.86 for nitrogen), the application of the model MONERIS proved to be useful in estimating nutrient loads. Crucial for model calibration, in-stream retention was estimated to be about 50 % of nutrient emissions on an annual basis. Through this process, we identified the importance of point sources for phosphorus emissions (about 94 % for 1996-2002), and diffuse sources, especially inputs via groundwater, for nitrogen emissions (about 31 % for 1996-2002). Despite hurdles related to model structure, observed loads, and input data encountered during the modelling process, MONERIS provided a good representation of the major interannual and spatial patterns in nutrient emissions. An analysis of the model uncertainty and sensitivity to input data indicates that the model MONERIS, even in datastarved Mediterranean catchments, may be profitably used by water managers for evaluating quantitative nutrient emission scenarios for the purpose of managing river basins. As an example of scenario modelling, an analysis of the changes in nutrient emissions through two different future scenarios allowed the identification of a set of relevant measures to reduce nutrient loads.

Nitrogen Stable Isotopes in Primary Uptake Compartments Across Streams Differing in Nutrient Availability

“…Our data indicated that point source inputs in the watershed (i.e., WWTP particularly concentrated at mainstem locations), usually characterized by increasing NH 4 + and SRP concentrations, are the main factor responsible for the high variability in nutrient concentrations. This is in agreement with results from a nutrient emission model for La Tordera and previous studies that show the large influence of WWTP effluents on the stream chemistry of this catchment. , WWTP effluents can also influence the δ 15 N value of the DIN species in streamwater, especially for ammonium, which may explain the high values observed at some of the mainstem sites and the positive relationships with nutrient concentrations. Moreover, the effects of point sources on receiving streams are amplified in streams from the Mediterranean region, such as La Tordera, because of their reduced dilution capacity, especially during summer low flow, when this study was conducted.…”

“…It covers a remarkable altitudinal gradient from the sea level up to 1700 m within a distance of 35 km. Although most of the catchment (77%) is covered by natural vegetation (mostly forest), agricultural (16%, mostly on the northeastern plains) and urban and industrial uses (7%, mostly along the main valley) are also present, resulting in a heterogeneous land use mosaic that translates into a large variability in the amount and apportionment of nitrogen emissions across the catchment . Within this catchment, we selected 25 sampling sites along the stream network (Table S1), 15 of which were located at the headwaters and were influenced by a broad variety of human impacts, spanning a wide range of stream nutrient conditions. , The other 10 sampling sites were located along the mainstem of La Tordera river, and were largely influenced by emissions from urban wastewater treatment plants (WWTP).…”

“…21 Within this catchment, we selected 25 sampling sites along the stream network (Table S1), 15 of which were located at the headwaters and were influenced by a broad variety of human impacts, spanning a wide range of stream nutrient conditions. 21,22 The other 10 sampling sites were located along the mainstem of La Tordera river, and were largely influenced by emissions from urban wastewater treatment plants (WWTP). During the sampling period, discharge was low−medium at headwaters (0.3 to 211.0 L/s).…”

Impact of forecasted changes in Polish economy (2015 and 2020) on nutrient emission into the river basins

“…The chosen model has a long track record in the analysis of large catchments in Northern and Central Europe (Danube, Daugava, Elbe, Oder, Vistula), Southern Europe (Po, Axios, Tordera), and rivers worldwide, e.g. in Canada, Brazil or China (Caille et al, 2012;Nikolaidis et al, 2009;Kronvang et al, 2007). Recently, Hirt et al (2012) proposed an interesting approach based on a network of different models (MONERIS model combined with regionalized agricultural economic model RAUMIS and other hydrological model GROWA/WEKU) in order to develop more appropriate tools for sustainable river basin Calibration of the model was based on the comparison between calculated with MONERIS and the monitored TN and TP loads (Water Resources in Poland, 1990Monthly Bulletins…, 2003) for all consecutive years of investigation.…”

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

“…In Spain, for instance, the construction rate of large dams peaked during the 1960s and 1970s, whereas human population density and urban area in the Mediterranean region increased during the 1990s (Cooper et al, 2013). Furthermore, nutrient pollution in Mediterranean rivers contributes to eutrophication because of the coexistence of naturally occurring low flows and high water demand (Caille et al, 2012). However, it is challenging to attribute changes in nutrient concentration dynamics to specific factors, because factors of change exist and act at different temporal and spatial scales (Kundzewicz and Krysanova, 2010).…”