Graduation Year

2017

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Thomas L. Crisman, Ph.D.

Co-Major Professor

Mark C. Rains, Ph.D.

Committee Member

David B. Lewis, Ph.D.

Keywords

Costa Rica, Macroinvertebrates, Tropical Streams, Water Quality

Abstract

There is a paucity of data on dry forests, the most threatened biome in the tropics. The Nandamojo is a tropical dry forest watershed in Western Costa Rica that has been impacted by varying degrees of human induced modifications. This research was conducted to examine the influence of land use and channel characteristics on invertebrate communities within a sub basin of the Nandamojo watershed. This study addressed three hypotheses: (1) sites with low tree cover and small riparian buffer zones will have high erosion, (2) macroinvertebrate abundance will be lower at sites with low channel stability values, and (3) benthic macroinvertebrate abundance will be higher in years of high rainfall and flow regimes. Sites were established along three tributaries, which were surveyed in 2013 and 2015. Data were compared (1) along the length of respective tributaries and their elevation gradients, and (2) between survey years. Although Nandamojo is a mixed land use watershed, two of the four land uses were dominant; pasture and forest. Macroinvertebrate counts were statistically different across survey years and seasons. The abundance of macroinvertebrates was greatest on Tributary 3, where the dominant land use was forest. Regional interannual rainfall is suggested as a driving factor for interannual differences in macroinvertebrate abundance. Although results suggest that this sub basin is in good health, taking preventative action by developing a subbasin management plan is needed. As tropical dry forest is the most threatened forest biome, educating local residents not only about the numerous risks of human induced modifications such as forest to pasture land conversion, but also the corresponding importance of maintaining riverbank vegetation in headwater streams should be a foremost priority.

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