Identifying the Source of Nutrient Contamination in a Lagoon System

Abstract

Nutrient concentrations within watercourses are often associated with the input of sewage or the runoff of fertilizers. Due to population increases, there has been a dramatic rise in the amount of fertilizer applied to land, as well as in the further development of sewage treatment plants (STPs), both of which can lead to significant discharges with associated eutrophication risks in coastal waters. The implementation of the European Union Water Framework Directive (EU-WFD) should improve the management and quality of European water bodies. The Ria Formosa Lagoon, Portugal, is one such water body monitored under the WFD where two inter-calibration sites have been developed, that of the Ancão Basin, which has a status of "high/good," and that of the Ramalhete Channel, with a status of "good/moderate." Spatial nutrient concentrations (NH + 4 , NO -2 , NO -3 , PO 3-4 ) and lipids were measured in two areas that were thought to contribute nutrients into the Ancão Basin; a river that flows through several golf courses and the Ramalhete Channel, which receives discharge from both Faro Airport and a STP.Nutrient analyses showed that waters from the Ramalhete Channel had substantial concentrations, the highest of which was ammonium, which exceeded 180 µM near the sewage discharge site; however, concentrations diminished towards the sea, reaching 2.7 µM suggesting the utilization of NH + 4 by seagrasses (Zostera noltii).The Atlantic Ocean was also a source of nitrate, contributing 1.8 µM, whereas sources of phosphate originated in the Ancão Basin catchment and included a commercial horticulture site, several golf courses, and the STP. Principal component analysis (PCA) and cross plots of the 5β-coprostanol/cholesterol and 5β-coprostanol/(5β-coprostanol + 5α-cholestanol) ratios identified areas of fecal contamination, highlighting several sites previously unknown to contain sewage matter. In general, nitrogen sources were associated with agriculture and phosphate originated from the golf complex and sewage discharges. These effects were partly mitigated, however, by eutrophic ponds between the river and the lagoon.

Determining the footprint of sewage discharges in a coastal lagoon in South-Western Europe

“…Current water quality studies include sites in western Ria Formosa with restricted water exchange such as Ponte Praia de Faro in Ancão Basin and Ramalhete Channel (e.g. Loureiro et al, 2006;Pereira et al, 2007;Wayland et al, 2008;Goela et al, 2009;Meyers et al, 2010;Brito et al, 2010Brito et al, , 2012). Yet, these cannot be considered directly affected by sewage effluents and consequently do not allow a direct comparison with our data.…”

“…In addition, most agricultural fertilizers contain water soluble nitrogen compounds (e.g. nitrate, ammonium, urea) that can be easily washed out from the soil by rainfall (Addiscott, 1996;Wayland et al, 2008). For ammonium, it is worthy to remark that concentrations were much higher than nitrate, showing that the efficiency of the nitrification process was compromised during water treatment at the STP.…”

Revisiting two sympatric European seahorse species: apparent decline in the absence of exploitation

“…Clustering of the remaining populations of seahorses around the main channels and inlets could be explained by a difference in water quality throughout the lagoon (Wayland et al , ), or an apparent shift in the dominant seagrass species (Curtis and Vincent, ; Cunha et al , ). Although the lagoon has a large tidal exchange, the water in the smaller channels does not circulate as much as in the main channels (Newton and Mudge, ), and increased coastal development in the Ria Formosa has led to higher amounts of ammonium and phosphate at greatest concentrations within the inner channels (Wayland et al , ). Poor water quality in the inner channels could explain why seahorses have largely disappeared from those areas while they are still found in the main channels and inlets.…”

Sediment and waternutrients and microalgae in a coastal shallow lagoon, Ria Formosa (Portugal): Implications for the Water Framework Directive

“…These results have been widely reported in the literature for coastal systems in general, but also for Ria Formosa. 16,18,19,35,43,44 The larger nitrogen concentrations observed in the sediments suggest that the production is faster than the release to the water column, which can happen by molecular diffusion, tide influence or bioturbation, for example.…”

“…However, the WFD does not consider the interactions between sediments and the water column in shallow enclosed coastal waters, such as Ria Formosa lagoon. These interactions are considered very important in these systems and are discussed by Falcão, 16 Falcão and Vale, 17 Murray et al 18 and Wayland et al 19 Note that the WFD considers four water body types: rivers, lakes, transitional and coastal waters (until a distance of one nautical mile from land). Shallow enclosed coastal systems are a good example of how important the physical and biogeochemical processes are.…”