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  1. Estuaries function as important transporters, transformers, and producers of organic matter (OM). Along the freshwater to saltwater gradient, the composition of OM is influenced by physical and biogeochemical processes that change spatially and temporally, making it difficult to constrain OM in these ecosystems. In addition, many of the environmental parameters (temperature, precipitation, riverine discharge) controlling OM are expected to change due to climate change. To better understand the environmental drivers of OM quantity (concentration) and quality (absorbance, fluorescence), we assessed both dissolved OM (DOM) and particulate OM (POM) spatially, along the freshwater to saltwater gradient and temporally, for a full year. We found seasonal differences in salinity throughout the estuary due to elevated riverine discharge during the late fall to early spring, with corresponding changes to OM quantity and quality. Using redundancy analysis, we found DOM covaried with salinity (adjusted r2 = 0.35, 0.41 for surface and bottom), indicating terrestrial sources of DOM in riverine discharge were the dominant DOM sources throughout the estuary, while POM covaried with environmental indictors of terrestrial sources (turbidity, adjusted r2 = 0.16, 0.23 for surface and bottom) as well as phytoplankton biomass (chlorophyll-a, adjusted r2 = 0.25, 0.14 for surface and bottom). Responses inmore »OM quantity and quality observed during the period of elevated discharge were similar to studies assessing OM quality following extreme storm events suggesting that regional changes in precipitation, as predicted by climate change, will be as important in changing the estuarine OM pool as episodic storm events in the future.« less
  2. Abstract. The net ecosystem productivity (NEP) of two seagrassmeadows within one of the largest seagrass ecosystems in the world, FloridaBay, was assessed using direct measurements over consecutive diel cyclesduring a short study in the fall of 2018. We report significant differencesbetween NEP determined by dissolved inorganic carbon (NEPDIC) and bydissolved oxygen (NEPDO), likely driven by differences in air–water gasexchange and contrasting responses to variations in light intensity. We alsoacknowledge the impact of advective exchange on metabolic calculations ofNEP and net ecosystem calcification (NEC) using the “open-water” approachand attempt to quantify this effect. In this first direct determination ofNEPDIC in seagrass, we found that both seagrass ecosystems were netheterotrophic, on average, despite large differences in seagrass netabove-ground primary productivity. NEC was also negative, indicating thatboth sites were net dissolving carbonate minerals. We suggest that acombination of carbonate dissolution and respiration in sediments exceededseagrass primary production and calcification, supporting our negative NEPand NEC measurements. However, given the limited spatial (two sites) andtemporal (8 d) extent of this study, our results may not berepresentative of Florida Bay as a whole and may be season-specific. Theresults of this study highlight the need for better temporal resolution,accurate carbonate chemistry accounting, and an improved understanding ofphysical mixingmore »processes in future seagrass metabolism studies.« less
  3. Abstract

    Prediction of high latitude response to climate change is hampered by poor understanding of the role of nonlinear changes in ecosystem forcing and response. While the effects of nonlinear climate change are often delayed or dampened by internal ecosystem dynamics, recent warming events in the Arctic have driven rapid environmental response, raising questions of how terrestrial and freshwater systems in this region may shift in response to abrupt climate change. We quantified environmental responses to recent abrupt climate change in West Greenland using long-term monitoring and paleoecological reconstructions. Using >40 years of weather data, we found that after 1994, mean June air temperatures shifted 2.2 °C higher and mean winter precipitation doubled from 21 to 40 mm; since 2006, mean July air temperatures shifted 1.1 °C higher. Nonlinear environmental responses occurred with or shortly after these abrupt climate shifts, including increasing ice sheet discharge, increasing dust, advancing plant phenology, and in lakes, earlier ice out and greater diversity of algal functional traits. Our analyses reveal rapid environmental responses to nonlinear climate shifts, underscoring the highly responsive nature of Arctic ecosystems to abrupt transitions.