While it is understood that reservoirs as a group are more highly connected to natural lakes, are located in warmer areas with increased precipitation, and experience more effects from land-use intensification and agricultural activities, it is unknown how water quality and biotic populations compare between these lake types. In chapter one, we studied 3,286 natural lakes and reservoirs (n = 1,514 and 1,772, respectively) over a 20-state extent in the midwestern and northeastern US. The limnological data was from the LAGOS research framework (LAke multi-scaled GeOSpatial and temporal). We built six generalized linear models (GLMs) to understand patterns and drivers of lake water quality. Compared to natural lakes, we found that reservoirs had significantly higher total phosphorus and chlorophyll-a concentrations, and significantly lower water clarity. We also found that the key driver lake maximum depth, as well as surface water connectivity, watershed cultivated cropland, watershed urbanization, and temperature were often significant predictor variables. In chapter two, we combined LAGOS data with that of ten species of in the Atlantic Flyway Breeding Waterfowl Survey from the United States Fish and Wildlife Service (spanning 21 years and 11 states). We compared population densities of the ten waterfowl species and built presence/absence models (n = 336) to understand which species were more likely to be found in natural lakes or reservoirs. For the subset of lakes with driver variables (n = 135, 91 reservoirs), we also built quasi-Poisson generalized linear models (GLMs) to understand patterns and drivers of waterfowl population densities. We found that seven waterfowl species did not differ by lake type. However, wood duck and mallard population densities were larger in reservoirs. We also found that mallards and wood ducks were more likely to be present in reservoirs as compared to natural lakes but that common mergansers were less likely to be present in reservoirs as compared to natural lakes. We also examined population densities of wood ducks, mallards, and common mergansers over time and found that mallard populations decreased and wood ducks increased in both RSVRs and NLs from 2000-2021, whereas common mergansers increased in NLs and decreased in RSVRs. Finally, our models revealed that chlorophyll-a, region, climate, morphometry, connectivity, and land use/cover were predictive of waterfowl population densities, although all of these predictors were species-dependent. This study improves understanding of which lake type has better water quality and larger waterfowl populations, and which predictor variables may be driving these results. This study demonstrates that a combination of drivers working at multiple scales may lead to significantly poorer water quality in reservoirs. We also found two species that may prefer reservoirs and one that may prefer natural lakes, as well as species-dependent change over time. Therefore, this research can inform future decisions regarding management and conservation of reservoirs for water quality and waterfowl populations.
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