Browning affects pelagic productivity in northern lakes by surface water warming and carbon fertilization

Abstract

Global change impacts important environmental drivers for pelagic gross primary production (GPP) in northern lakes, such as temperature, light, nutrient, and inorganic carbon availability. Separate and/or synergistic impacts of these environmental drivers on pelagic GPP remain largely unresolved. Here, we assess key drivers of pelagic GPP by combining detailed depth profiles of summer pelagic GPP with environmental and climatic data across 45 small and shallow lakes across northern Sweden (20 bo-

Declining calcium concentration drives shifts toward smaller and less nutritious zooplankton in northern lakes

“…The large‐scale impacts of global change [e.g., warming, hydrological intensification, acidification recovery, extension of vegetation cover, and forest harvesting (Creed et al., 2018; Finstad et al., 2016; Moldan et al., 2017; Watmough et al., 2003)], are likely to promote continued declines in catchment delivery and lake concentrations of Ca that might hamper plankton and consumer development in northern lakes. Yet, other lake environmental variables, and changes in these, such as pH (Futter et al., 2014), TP (Isles et al., 2023), TOC (de Wit et al., 2023) and warming (Puts et al., 2023), may modify the responses in zooplankton to declining Ca. While Ca‐poor lakes are prevalent globally (Weyhenmeyer et al., 2019), and the decrease in Ca poses challenges to the fauna in these lakes, lake at low latitudes—typically more buffered and nutrient rich—show little tendency of Ca decline, even when previously exposed to acid deposition (cf., Weyhenmeyer et al., 2019).…”

“…Increased TOC concentrations may also favor unselective filtering feeding cladocerans capable of feeding directly on detritus and bacteria over copepods that selectively feed primarily on phytoplankton (Berggren et al., 2015; Bergström et al., 2021; Hessen, 1985), although both bacteria and detritus are low quality food that do not sustain rapid growth or reproduction of Daphnia (Wenzel et al., 2021). Increased TOC further induces additional warming of the epilimnion (Puts et al., 2023), where higher water temperatures combined with reduced phytoplankton biomass may enhance the susceptibility of Daphnia to low Ca (Ashforth & Yan, 2008). Thus, the impact of temporal changes in water quality on zooplankton community composition is also related to climate (Ashforth & Yan, 2008; Couture et al., 2021).…”