INTRODUCTION Changes in land use in basin areas, including conversion of previously forested areas into agricultural pastureland, can often have negative effects on water quality in nearby lakes and streams. Though much work has been done on the effect of agricultural land use on natural watersheds, little is known about the effects of changing land use patterns on man-made reservoir systems. Such reservoirs often provide drinking water for large numbers of people dispersed over wide areas, and as such, it is especially important to ensure high water quality in these areas.

The Influence of Land Use Patterns on Reservoir Water and Soil Quality Leigh Johnson SEE-U 2001

The purpose of the study was to determine the impact of various land use regimes on the water and soil quality of the reservoir. The study attempted to determine if eucalyptus silviculture was a sound alternative to forested shoreline for the purpose of maintaining water quality. A second aim was to analyze the effects of grazed shoreline on water quality and compare the results to those obtained at the eucalyptus silviculture site, with the overall goal of making a substantive report concerning the viability of silviculture and grazing land use practices and using this report to recommend land use policies and regulations.

HYPOTHESIS Alternative hypotheses were developed for four areas of data collection: pH, soil profile richness, sediment load, and microorganism abundance. The pH hypothesis predicted a pH measurement closer to neutral at the forested site as well as increasingly acidic measure-ments at the eucalyptus and pasture sites. The soil profile richness hypothesis predicted a more diverse profile in the secondary and eucalyptus forests than in the pasture. The sediment load hypothesis predicted a greater load at the pasture shoreline than at either of the other two sites. The microorganism abundance hypo-thesis predicted a greater number of microorganisms at the forested site than at the eucalyptus site, with the least abundance expected to occur at the pasture site.

METHODS AREA OF STUDY: Sites representing grazed, eucalyptus silviculture, and forested shorelines were selected on the Atibainha Reservoir, Bairro do Moinho, mun. Nazaré Paulista, São Paulo, Brasil (23°10’48” S, 46°23’53” W). The reservoir is one of four in the Cantareira system constructed in order to provide the cities of São Paulo and Campinas with water for domestic and industrial use. DATA COLLECTION:Every 5 meters along the shoreline, pH measurements were taken 5 meters offshore. Every 10 meters along the shore, soil core samples were taken 5 meters inland. Every 10 meters along the shoreline, microorganism water samples were taken 5 meters offshore. At 0, 25, and 50 meters, sediment load water samples were taken at the shoreline.

RESULTS Significant differences were found in soil profiles and microorganism abundances among sites. There were no statistically significant differences in sediment load and pH measurements among sites.

CONCLUSIONS A livestock-grazing land use regime appears to negatively influence shoreline water quality and soil richness, while eucalyptus silviculture land use appears to foster water quality and soil richness similar to that found on forested shoreline. The consistantly small differences in pH and sediment load measurements between silviculture and forested sites suggest that eucalyptus forest and secondary forest shorelines were at least superficially quite similar in water quality. However, microorganism surveys found a statistically significant difference in the number of individual organisms at the two sites.

Surveys of aquatic microbiotic integrity proved to be a more reliable method for predicting shoreline land use regimes than did measurements of water chemistry or aquatic sediment load. While pH and sediment load analysis did not indicate statistically significant differences in physical habitat quality, biotic surveying indicated statistically significant disturbances in the microbiotic populations offshore of the grazed survey site, which was impovrished in terms of individual abundance and species. This is most likely a result of biotic communities’ ability to integrate a large number of environmental factors not always apparent on a small scale. Because measures of biota incorporate longer time periods than do measures of point-specific physical habitats, biotic sampling may reveal critical environmental impacts that chemical or physical surveys unintentionally neglect.

Recommendations Based on the results obtained in this study, we recommend a policy of encouraging eucalyptus silviculture as a viable alternative to more damaging practices of livestock grazing. Such an alternative would require a reforestation policy to replace pasturelands with eucalyptus trees, coupled with a sustained effort to conserve remaining fragments of secondary forest. This dual strategy of silviculture and conservation would certainly do more to protect water quality and remaining forests than either strategy alone. Furthermore, officials and ecologists must embrace a more community-friendly strategy of education and compromise if such a reforestation-conservation policy is to ever enjoy widespread compliance and acceptance.