Dataset of flows and nutrient inputs to the Albufera Coastal Lagoon (Valencia, Spain) during hydrological year 2023-2024

Anthropogenic eutrophication, caused by human inputs of nitrogen (N) and phosphorus (P), is a global problem that leads to excessive organic production in aquatic ecosystems. Despite concerted efforts to address specific sources of pollution, diffuse pollution remains an issue. The Albufera of Valencia, a Mediterranean coastal lagoon, has been hypertrophic since the 1970s due to the impact of agricultural, urban and industrial activities. This study provides updated data (October 2023 to September 2024) through monthly sampling of 18 primary irrigation channels (representing 75% of the inflow) and the lagoon, as well as supplementary sampling of Wastewater Treatment Plants (WWTPs) and supply channels. A quantitative analysis of hydrology and water quality was conducted, with nutrient loads and contributions by hydrological sector from WWTPs and rice fields being estimated. The total inflow (265.27 hm³) was deemed acceptable; however, human management had a significant impact on the volume. Overa channel constituted the primary source of flow (29.98%) and was a significant contributor of Total Phosphorus (TP) (15.09 t) and Total Nitrogen (TN) (681.36 t). The southern agricultural sector contributed the majority of the TN (49.17%) and 26.07% of the TP, while the north, influenced by WWTPs, supplied 33.96% of the TP. Poyo stream exhibited an abnormally high TN load (28.62 t) from a contaminated aquifer. The rice fields located in the north and west have been observed to assimilate nutrients during irrigation. In the Albufera lagoon, a strong correlation was observed between phycocyanin (PC) and the total TP load (R² = 0.84). With the exception of "red water" periods, total TN exhibited a significant correlation with chlorophyll-a and carotenoids (Car), thereby suggesting co-limitation. The study corroborates the hypothesis that the Albufera's "poor" trophic status is the result of ongoing diffuse pressure from agriculture, urbanisation and industry. The findings emphasise the necessity for transparent water governance and integrated water quantity/quality management for ecosystem recovery