The assessment of water quality in the Lower Luja
´
n River (Buenos
Aires, Argentina): phytoplankton andalgal bioassays
Ine
´
s O’Farrell*, Ruben J. Lombardo, Paula de Tezanos Pinto, Carolina Loez
Lab. Limnologı
´
a, Dpto. Biologı
´
a, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria,
C1428EHA Buenos Aires, Argentina
Received7 September 2001; accepted25 January 2002
‘‘Capsule’’: An integrated study of water chemistry, phytoplankton, and algal bioassays indicated distinct regions of a
large river ecosystem.
Abstract
The monitoring of river phytoplankton andseveral hydrological, physical andchemical variables, in combination with bioassays
using Selenastrum capricornutum Printz, allowedthe characterisation of three distinct reaches of the Lower River Luja
´
n. The
upstream stretch, characterised by the lowest depth and discharge, registered the highest nutrient, dissolved heavy metal and
chlorophyll a concentrations in accordance with low phytoplankton diversity and the occurrence of several species typical of
organically polluted lowland rivers. A downstream improvement, concomitant to increasing river discharge, is revealed by a pro-
gressive decrease of organic pollution parameters even though algal toxicity is registered through bioassays. The water input from
the Parana
´
River through the G. Arias Channel plays an important role in the regulation of the limnology of the Lower Luja
´
n
River. As a result of marked increasing discharge, depth and width, there is a decrease in nutrient concentration and phytoplankton
density and an increase in dissolved oxygen concentration. Likewise, algal growth rates in the bioassays showed less toxic effect.
# 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Water quality; Lowlandriver; Phytoplankton; Algal bioassays; South America
1. Introduction
The studies using phytoplankton algae for water
quality monitoring have shown that changes in compo-
sition reflect not only variations in water quality, but
also changes in physical variables andbiotic interac-
tions. Wehr andDescy (1998) assert that variations in
water chemistry may alter relative proportions of a few
dominant taxa but often have little effect on the overall
assemblage. This complexity, added to uncertainties
about taxonomy andnutrient requirements andgrowth
rates of several algal taxa, limit the comprehension of
the main factors regulating algal assemblage and
obscure the possible relationship between water quality
andcomposition of riverine phytoplankton. Never-
theless, during the final session of the ‘‘Third Sympo-
sium of algae for monitoring rivers’’ (Prygiel et al.,
1999) phytoplankton was pointedout as a useful tool
for assessing long-term changes in rivers such as those
associatedwith eutrophication, river management,
changes in landuse at the scale of watershed, andcli-
mate changes. In this sense, Ibelings et al. (1998) asser-
tedthat phytoplankton seems a useful biological
indicator because it responds quickly to changes in
environmental conditions thus enabling a quick assess-
ment of water quality.
Regular andintegral water quality monitoring is lim-
itedin Argentina, as analytical programs are relatively
simple with measurements made for only the main che-
mical andbacteriological variables includedin the
establishedwater quality indices (Loez andTopalia
´
n,
1999). The use of biota for monitoring the aquatic
environments is uncommon. The most important pollu-
tion studies in which phytoplankton assemblages were
usedhave been conductedin rivers locatedin the Bue-
nos Aires Province. The Reconquista River has been
subject of a long-term systematic study of the water
quality by means of two monthly monitoring programs
andfour laboratory multispecific algal bioassays (Loez
0269-7491/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0269-7491(02)00136-7
Environmental Pollution 120 (2002) 207–218
www.elsevier.com/locate/envpol
* Corresponding author. Fax: +54-11-4576-3384.
E-mail address: ines@bg.fcen.uba.ar (I. O’Farrell).