Linking land use -- land cover change and ecosystem function in tropical lowland watersheds of Belize, Central America

Ecosystems in tropical regions are expected to experience substantial impacts related to human land use and land cover change in the coming decades. Freshwater ecosystems will likely experience a disproportionate impact relative to other tropical ecosystems. My dissertation research takes an interdisciplinary approach to examine interactions between humans and their environment in lowland tropical watersheds of Belize, Central America.;I present results from a rapid assessment technique (Chapter 2) designed to estimate the intensity of impacts on freshwater ecosystems stemming from riparian zone land use practices. The technique provides an accessible, low-tech method for identifying river reaches experiencing high degrees of impact. Chapter 3 also examines riparian zone land use practices and focuses on the use of agrochemicals by small-scale Q’eqchi’ Maya farmers. A high percentage of farmers in the Temash River watershed of Belize are cultivating corn within riparian zones and are using herbicides without adequate training. The continued use of herbicides in these riparian zone farms represents an emerging threat to both human and ecosystem health in the Temash River.;Chapters 4 and 5 look at slash-and-burn agriculture (locally referred to as milpa) in the Temash River watershed and its impact on soil nutrient dynamics (Chapter 4) and the loss of nutrients from terrestrial landscapes to streams (Chapter 5). In general, soil nutrients in the upper 10 cm are not significantly impacted by milpa. Plant-available nitrogen (as NO3--N) declines significantly in milpa fields and recovery to re-disturbance concentrations requires approximately 15 years, suggesting that 15 years is an ideal fallow period for milpa farmers in the Temash. In-stream nutrients in watersheds dominated by milpa are generally P-limited, as reflected in TN:TP concentrations. A seasonal flux of nutrients is exported from catchments at the onset of the rainy season but estimates for annual export of nutrients are similar to or less than other tropical watersheds.