Progressive changes in the structure and dynamics of the phytoplankton community along a pollution gradient in a lowland river — a multivariate approach

Abstract

The phytoplankton of the River Lujan (Buenos Aires, Argentina) was studied for a period of 18 months, together with physical and chemical variables, in relation to a pollution gradient. 167 taxa were recorded within a seasonal succession characterized by dominance of diatoms with a brief summer green algae facies. A combination of several biotic indices and multivariate analysis was employed to assess the impact of pollution on the phytoplankton community. The biotic indices used were species diversity and richness, algal quotients (green algae/diatom ratio, Centrales/Pennales ratio) and the SD succession rate index. Multivariate procedures included cluster analysis and ordination by PCA of both species and samples, stepwise discriminant analysis and multiple discriminant analysis of variance (MANOVA). Results indicate that community dynamism is attenuated at the more polluted sites, concomitant with an increased predominance of a broad-tolerance algal assemblage, co-dominated by Cyclotella meneghiniana and Nitzschia stagnorum. The changes in the community structure and dynamics described herein involved alterations in the distribution and relative proportions of the algae, rather than modifications in the basic species composition. These changes may not be readily detectable by methods which over-simplify the ecological information, such as systems of indicator species and biotic indices, designed to assess the degree of pollution. The suitability of multivariate analysis and biotic indices in river phytoplankton studies is further discussed.

Temporal and spatial dynamics in large rivers : example of a long-term monitoring of the middle Rhone River

“…In contrast, the periphyton seemed more typi cal of each sampling station. Most of the taxa were ty pical of eutrophic waters in the wider sense (meso-eutrophic to eutrophic), and consisted of ubiquitous op portunistic species (Fruget et al 1999) as is often the case in nutrient-rich lowland rivers (Descy 1992, Del Giorgio et al 1991.…”

Cyanobacteria abundance and its relationship to water quality in the Mid-Cross River floodplain, Nigeria

“…The lentic stations (Stations Iv and v) are located close to agricultural lands and frequently received organic fertilizer runoffs. The decomposition of these and litters from riparian vegetations could be responsible for the low pH and oxygen content of the lakes as suggested by del Giorgio et al (1991). Seasonal variations in rainfall could be responsible for the wide variation in water depth and velocity, as these variables are strongly linked to meteorological conditions in tropical waters (Aoyagui and Bonecker 2004).…”

“…High phosphate, nitrate and trace metals and low N:P have been widely reported as major factors limiting cyanobacteria bacteria abundance (Elser et al 1990, del Giorgio 1991, Akin-Oriola 2003. However, CCA analysis showed no significant correlation between these parameters and cyanobacteria of Cross River floodplain.…”

A 10 year study at four sites of the middle course of the River Loire I - Patterns of change in hydrological, physical and chemical variables in relation to algal biomass

“…Nutrients, whose quantities have been measured since the seventies (Oudin, 1990), were never depleted in these sites on the Loire, as in other temperate (Lack, 1971;Jones & Barrington, 1985;Descy et al, 1987) or tropical rivers (del Giorgio et al, 1991). This pattern might be general in the course of the middle and lower part of rivers, by reason of the different kinds of nutrient inputs which occured from the headwaters and tributaries, of rainfall associated with agricultural runoff, urban or industrial wastewaters and sewage effluents, and of the unceasing mixing of water and sediments, rapid flushing tending to reduce nutrient sedimentation and thus increase nutrient concentrations in the water (Vollenweider, 1976).…”