 |
| Titel |
Spatio-temporal dynamics of surface water quality in a Portuguese peri-urban
catchment |
| VerfasserIn |
Carla Ferreira, Rory Walsh, Celeste Coelho, Antonio Ferreira |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250122180
|
| Publikation (Nr.) |
 EGU/EGU2016-1142.pdf |
|
|
|
|
|
| Zusammenfassung |
| Urban development poses great pressure on water resources, but the impact of different
land-uses on streamwater quality in partly urbanized catchments is not well understood.
Focussing on a Portuguese peri-urban catchment, this paper explores the impact of a mosaic
of different urban and non-urban land-uses on streamwater quality, and the influence of a
seasonal Mediterranean climate on pollutant dynamics. The catchment has a 40% urban
cover, dispersed amongst patches of woodland (56%) and agricultural fields (4%). Apart from
the catchment outlet, streamwater quality was assessed at three sub-catchment sites: (i) Porto
Bordalo, encompassing a 39% urban area with a new major road; (ii) Espírito Santo,
draining a sub-catchment with 49% urban cover, mostly comprising detached houses
surrounded by gardens; and (iii) Quinta, with a 25% urban cover. The Porto Bordalo
sub-catchment is underlain by limestone, whereas the Espírito Santo and Quinta
sub-catchments overlie sandstone. Water quality variables (notably nutrients, heavy
metals and COD) were assessed for samples collected at different stages in the storm
hydrograph responses to ten rainfall events occurring between October 2011 and March
2013.
Urban areas had great impacts on COD, with highest median concentrations in Espírito
Santo (18.0 mg L−1) and lowest in Quinta (9.5 mgL−1). In Espírito Santo, the management
of gardens triggered greatest median concentrations of N-NO3 (1.46 mgL−1, p<0.05).
Porto Bordalo exhibited the highest median concentrations of Zn (0.14 mgL−1),
possibly derived from the major road, and dissolved phosphorus (0.07 mgL−1).
The latter may be linked to human activities, such as terrace and car washing, as
overland flow from impervious surfaces was observed to discharge directly into the
stream, whereas in other sub-catchments it mostly disperses into pervious soils.
Pastoral activities in agricultural fields adjacent to the stream led to highest median
concentrations of N-Nk and N-NH4 recorded at ESAC (1.34 mgL−1and 0.41 mgL−1,
respectively).
Hydrological regime exerted a major influence on water quality dynamics. COD and
nutrient variables (N-Nk, N-NH4, N-NO3 and P) attained highest concentrations after the
summer. Low discharges led to high pollutant concentrations at baseflow of N-NH4 in
ESAC and Porto Bordalo (up to 1.63 mgL−1 and 1.04 mgL−1, respectively). The
first storm events after the summer led to flushing of accumulated pollutants to
produce serious concentrations of N-Nk in Porto Bordalo (2.05 mgL−1) and Zn
at ESAC and Porto Bordalo (up to 0.55 mgL−1 and 0.59 mgL−1, respectively),
all recorded at peak flows. In wettest periods, greater flow connectivity over the
hillslopes led to pollutant concentrations of N-Nk at ESAC, Espírito Santo and
Quinta (up to 2.07 mgL−1, 2.54 mgL−1 and 2.83 mgL−1, respectively). Also high
levels of Cu and Zn occurred at ESAC (1.74 mgL−1and 0.77 mgL−1) during the
falling limb. Baseflow chemistry was influenced by bedrock, with highest median
concentrations of Ca and Mg, lowest values of Na, and higher pH recorded in limestone
(p<0.05).
Information about the spatio-temporal dynamics of pollutants, linked to urban patterns
and storm drainage system, should help enable urban planners to minimize adverse impacts
of urbanization on water quality. |
|
|
|
|
|
|