The world’s population is concentrated in urban areas. This change in demography has brought landscape transformations that have a number of documented effects on stream ecosystems. The most consistent and pervasive effect is an increase in impervious surface cover within urban catchments, which alters the hydrology and geomorphology of streams. This results in predictable changes in stream habitat. In addition to imperviousness, runoff from urbanized surfaces as well as municipal and industrial discharges result in increased loading of nutrients, metals, pesticides, and other contaminants to streams. These changes result in consistent declines in the richness of algal, invertebrate, and fish communities in urban streams. Although understudied in urban streams, ecosystem processes are also affected by urbanization. Urban streams represent opportunities for ecologists interested in studying disturbance and contributing to more effective landscape management.

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Streams in the Urban Landscape

SUMMARY 1. The effects of catchment urbanisation on water quality were examined for 30 streams (stratified into 15, 50 and 100 km2 ± 25% catchments) in the Etowah River basin, Georgia, U.S.A. We examined relationships between land cover (implying cover and use) in these catchments (e.g. urban, forest and agriculture) and macroinvertebrate assemblage attributes using several previously published indices to summarise macroinvertebrate response. Based on a priori predictions as to mechanisms of biotic impairment under changing land cover, additional measurements were made to assess geomorphology, hydrology and chemistry in each stream.

2. We found strong relationships between catchment land cover and stream biota. Taxon richness and other biotic indices that reflected good water quality were negatively related to urban land cover and positively related to forest land cover. Urban land cover alone explained 29–38% of the variation in some macroinvertebrate indices. Reduced water quality was detectable at c. >15% urban land cover.

3. Urban land cover correlated with a number of geomorphic variables such as stream bed sediment size (–) and total suspended solids (+) as well as a number of water chemistry variables including nitrogen and phosphorus concentrations (+), specific conductance (+) and turbidity (+). Biotic indices were better predicted by these reach scale variables than single, catchment scale land cover variables. Multiple regression models explained 69% of variation in total taxon richness and 78% of the variation in the Invertebrate Community Index (ICI) using phi variability, specific conductance and depth, and riffle phi, specific conductance and phi variability, respectively.

4. Indirect ordination analysis was used to describe assemblage and functional group changes among sites and corroborate which environmental variables were most important in driving differences in macroinvertebrate assemblages. The first axis in a non-metric multidimensional scaling ordination was highly related to environmental variables (slope, specific conductance, phi variability; adj. R2=0.83) that were also important in our multiple regression models.

5. Catchment urbanisation resulted in less diverse and more tolerant stream macroinvertebrate assemblages via increased sediment transport, reduced stream bed sediment size and increased solutes. The biotic indices that were most sensitive to environmental variation were taxon richness, EPT richness and the ICI. Our results were largely consistent over the range in basin size we tested.

Stream macroinvertebrate response to catchment urbanisation (Georgia, U.S.A.)

Several geopolitical factors, aggravated by worries of global warming, have been fueling the search for and production of renewable energy worldwide for the past few years. Such demand for renewable energy is likely to benefit the sugarcane ethanol industry in Brazil, not only because sugarcane ethanol has a positive energetic balance and relatively low production costs, but also because Brazilian ethanol has been successfully produced and used as biofuel in the country since the 1970s. However, environmental and social impacts associated with ethanol production in Brazil can become important obstacles to sustainable biofuel production worldwide. Atmospheric pollution from burning of sugarcane for harvesting, degradation of soils and aquatic systems, and the exploitation of cane cutters are among the issues that deserve immediate attention from the Brazilian government and international societies. The expansion of sugarcane crops to the areas presently cultivated for soybeans also represent an environmental threat, because it may increase deforestation pressure from soybean crops in the Amazon region. In this paper, we discuss environmental and social issues linked to the expansion of sugarcane in Brazil for ethanol production, and we provide recommendations to help policy makers and the Brazilian government establish new initiatives to produce a code for ethanol production that is environmentally sustainable and economically fair. Recommendations include proper planning and environmental risk assessments for the expansion of sugarcane to new regions such as Central Brazil, improvement of land use practices to reduce soil erosion and nitrogen pollution, proper protection of streams and riparian ecosystems, banning of sugarcane burning practices, and fair working conditions for sugarcane cutters. We also support the creation of a more constructive approach for international stakeholders and trade organizations to promote sustainable development for biofuel production in developing countries such as Brazil. Finally, we support the inclusion of environmental values in the price of biofuels in order to discourage excessive replacement of natural ecosystems such as forests, wetlands, and pasture by bioenergy crops.

Expansion of sugarcane ethanol production in Brazil: environmental and social challenges.

Network design for water quality monitoring of surface freshwaters: A review

Effective catchment management in the face of landuse alteration depends on our ability to quantify ecologically significant changes and to discriminate among varying levels of impact. We compared the efficiency of traditional structural indices of change (species composition) with functional measures based on species traits (including life-history, trophic, and morphological features) in an analysis of grassland streams along a gradient of agricultural development (ungrazed native tussock, grazed tussock, extensively grazed pasture, and intensive dairy and deer farming). Streams were categorized in relation to overall agricultural intensity, and separately in terms of increasing nutrient concentrations and fine sediments on the streambed. Only 5 of 60 individual species demonstrated a significant separation across the landuse gradient, whereas 14 of 53 trait categories did so. Traits associated with population resilience (short generation time, asexual reproduction) became more prevalent with more intense agricultural pressure, reflecting predicted increases in intensity and frequency of stream disturbance. We observed a shift away from a tendency to lay unattached eggs at the water surface of the stream, reflecting the increasing likelihood of smothering by sediment, as well as increases in highly flexible and streamlined body shapes. Principal components and correspondence analyses involving species or trait composition all were able to discriminate landuse practises, but more of the overall between-landuse variance was accounted for by trait composition than species composition. All biological measures (species or trait composition) were correlated with both nutrient concentrations and sedimentation. Nutrient concentrations were better related to species and trait-category densities, whereas sedimentation was related to trait- category relative abundances. Overall, species traits successfully complemented traditional structural measures by helping to differentiate the consequences of landuse intensification in grassland stream communities. Rather than simply recording a loss or reduction of species, our functional approach was able to identify sensitive life-history characteristics linked to the functioning of ecosystems, thereby facilitating the development of targeted management actions.

https://www.jstor.org/stable/10.1899/0887-3593%282006%2925%5B44%3ACOSAFA%5D2.0.CO%3B2

Comparison of structural and functional approaches to determining landuse effects on grassland stream invertebrate communities

SUMMARY 1. Several studies have shown that land use has a strong influence on river chemistry and its biotic components. Most of these studies focused on nitrogen in temperate American and European catchments. Much less is known about the relationship between stream conditions and land use in tropical areas of developing countries. 2. Besides climate, there are three important differences between attributes of temperate and tropical catchments: non-point sources are the dominant contributor of pollution in USA, whereas point source pollution is the most important in our study; use of fertilizer is much smaller in developing countries, and the type of agriculture and management practices are distinct. 3. We test whether the chemical composition of streams and their macroinvertebrate communities can be related to land use. Accordingly, we compared the variability of chemical composition and macroinvertebrate communities in the streams of two catchments (Pisca and Cabras) belonging to the same ecoregion, but having different types of land use. 4. The main land use in the Pisca catchment in 1993 was sugar cane (62%), followed by pasture (22%) and urban centres (10%). In contrast, the main land use in the Cabras catchment was pasture (60%), followed by annual crops (13%) and forest (10%); urban centres occupied only 2% of the catchment. 5. In the Cabras catchment, most of the parameters correlated with a land use index (LUI) (Fig. 2). However, only conductivity, major cations and major anions (with exception of sulfate) had a statistically significant correlation coefficient. More than 90% of the variance was explained for these parameters. DIC, NO3 and richness of invertebrates (RI) also strongly correlated with LUI (R 2 = 0.75), although these correlation coefficients were not significant. Total suspended solids (TSS) had a significant correlation with LUI (R 2 = 0.98), but, the correlation was inverse. In the Pisca catchment, conductivity, major cations (with exception of potassium), major anions, and DIC, DO, and DOC had a strong and statistically significant correlation with LUI. Correlation coefficients were also high for respiration rate, although the correlation was not statistically significant.

Alaídes Gessner

Papers

Effects of land use on water chemistry and macroinvertebrates in two streams of the Piracicaba river basin, south-east Brazil.