Aquatic Ecosystem Function Under Climate Stress: Linking Hydroclimate Volatility to Biogeochemical Responses in Streams and Lakes
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Authors
Loria, Kelly A
Issue Date
2025
Type
Dissertation
Language
en_US
Keywords
Aquatic Ecosystem Metabolism , Biogeochemical Cycling , Hydroclimatic Change , Nearshore Productivity , Stream Ecology
Alternative Title
Abstract
Freshwater ecosystems are undergoing rapid and widespread transformations in response to accelerating and volatile global hydroclimatic change. Hydroclimate refers to the climate-driven dynamics of water availability and movement, shaped by both global and regional atmospheric processes (e.g., evaporation, precipitation) and hydrologic storage (e.g., snowpack, groundwater, surface waters, and vegetation). Climate-driven shifts in hydroclimatic regimes, land-use intensification, and biogeochemical disturbance are altering the structure and function of rivers, lakes, and wetlands across the globe—disrupting their ability to cycle nutrients, carbon, and support biodiversity. In aquatic environments, metabolism (e.g., gross primary production [GPP], ecosystem respiration [ER], and net ecosystem productivity [NEP]) represents a tractable, integrative measure of ecosystem function. Because metabolic rates reflect the balance of autotrophic and heterotrophic processes, they are sensitive to both chronic pressures and episodic disturbances, offering insight into how ecosystems respond to variability in light, temperature, hydrology, and nutrient availability. As hydroclimate volatility increases the frequency and intensity of wet-dry transitions, it becomes increasingly urgent to understand how aquatic metabolism responds across spatial and temporal scales to anticipate shifts in ecosystem resilience and biogeochemical cycling.The three chapters presented here offer novel empirical and theoretical contributions to aquatic ecosystem ecology, focusing on the metabolic consequences of changing hydroclimatic conditions. Chapter one demonstrates how shifts in the timing and magnitude of streamflow in mountain headwater catchments decouple hydrologic and biological processes, whereas wet years reduce GPP and alter nitrogen dynamics—even between neighboring streams with similar morphology. Chapter two expands this case study perspective to the downstream oligotrophic lake, by evaluating how stream inflows influence nearshore metabolic regimes across four different shores in Tahoe, Sierra Nevada, USA. Here we show how GPP or ER differ from drought to wet years depending on hydrologic connectivity across the different nearshore locations. In chapter three we quantified the spatial synchrony in both GPP and ER for 48 unique streams spanning, geographic, land cover, and morphometric gradients to find that local factors such as flow and light mediate spatial synchrony in GPP and ER more strongly than regional climatic drivers. Collectively, these studies highlight that while aquatic ecosystem function is influenced by broad-scale environmental forcing, it can be more strongly mediated by local conditions. By examining aquatic ecosystem metabolism across gradients of connectivity, flow, and climatic variability, this work advances both applied understanding of freshwater vulnerability and theoretical frameworks for scaling carbon fluxes in a changing world.