G. Goyenola, Departamento de Ecología Teórica y Aplicada, CURE-Facultad de Ciencias, Universidad de la República, Maldonado, Uruguay goyenola@gmail.com
,
M. Meerhoff, Departamento de Ecología Teórica y Aplicada, CURE-Facultad de Ciencias, Universidad de la República, Maldonado, Uruguay
,
F. Teixeira-de Mello, Departamento de Ecología Teórica y Aplicada, CURE-Facultad de Ciencias, Universidad de la República, Maldonado, Uruguay
,
I. González-Bergonzoni, Departamento de Ecología Teórica y Aplicada, CURE-Facultad de Ciencias, Universidad de la República, Maldonado, Uruguay, Sino-Danish Centre for Education and Research Beijing China
,
D. Graeber
,
C. Fosalba, Departamento de Ecología Teórica y Aplicada, CURE-Facultad de Ciencias, Universidad de la República, Maldonado, Uruguay
,
N. Vidal, Departamento de Ecología Teórica y Aplicada, CURE-Facultad de Ciencias, Universidad de la República, Maldonado, Uruguay, Sino-Danish Centre for Education and Research Beijing China
,
N. Mazzeo, Departamento de Ecología Teórica y Aplicada, CURE-Facultad de Ciencias, Universidad de la República, Maldonado, Uruguay
Climate and hydrology are relevant control factors for determining the
timing and amount of nutrient losses from agricultural fields to
freshwaters. In this study, we evaluated the effect of agricultural
intensification on the concentrations, dynamics and export of phosphorus
(P) in streams in two contrasting climate and hydrological regimes
(temperate Denmark and subtropical Uruguay). We applied two alternative
nutrient sampling programmes (high frequency composite sampling and low
frequency instantaneous-grab sampling) and three alternative methods to
estimate exported P from the catchments. A source apportionment model
was applied to evaluate the contribution derived from point and diffuse
sources in all four catchments studied. Climatic and hydrological
characteristics of catchments expressed as flow responsiveness
(flashiness), exerted control on catchment and stream TP dynamics,
having consequences that were more significant than the outcome of
different TP monitoring and export estimation strategies. The impact of
intensification of agriculture differed between the two contrasting
climate zones. Intensification had a significant impact on subtropical
climate with much higher total (as high as 4436 μg P L-1),
particulate, dissolved and reactive soluble P concentrations and higher
P export (as high as 5.20 kg P ha-1 year-1).
However, we did not find an increased contribution of particulate P to
total P as consequence of higher stream flashiness and intensification
of agriculture. The high P concentrations at low flow and predominance
of dissolved P in subtropical streams actually exacerbate the
environmental and sanitary risks associated with eutrophication. In the
other hand, temperate intensively farmed stream had lower TP than
extensively farmed stream. Our results suggest that the lack of
environmental regulations of agricultural production has more severe
consequences on water quality, than climatic and hydrological
differences between the analysed catchments.