Dissolved organic matter regulates nutrient limitation and growth of benthic algae in northern lakes through interacting effects on nutrient and light availability

Megan L Fork,Jan Karlsson,Ryan A Sponseller

doi:10.1002/lol2.10166

Abstract

AbstractWidespread increases in dissolved organic matter (DOM) concentration across northern lakes can alter rates of primary production by increasing nutrient availability and decreasing light availability. These dual effects of DOM generate a unimodal relationship in pelagic primary production and primary producer biomass among lakes over a gradient of DOM concentration. However, the responses of benthic algae to variation in DOM loading are less clear because of their potential to access sediment nutrients. We tested algal production and nutrient limitation along a DOM gradient in northern Sweden. Without added nutrients, benthic algal production showed a unimodal relationship with DOM, similar to reported pelagic responses. Nutrient addition revealed widespread nitrogen limitation, with decreasing severity in lakes with higher DOM. Because the majority of northern Swedish lakes currently fall below the inflection point in this unimodal relationship, moderate increases in DOM have the potential to increase benthic primary production, particularly for epilithic algae.

Highlights

Widespread increases in dissolved organic matter (DOM) concentration across northern lakes can alter rates of primary production by increasing nutrient availability and decreasing light availability
We demonstrate a unimodal relationship between benthic algal growth and dissolved organic carbon (DOC) concentration across Arctic and Boreal lakes in northern Sweden, as reported elsewhere for pelagic and whole-lake primary production and primary producer biomass (Hanson et al 2003; Seekell et al 2015a; Kelly et al 2018; Bergström and Karlsson 2019)
Because DOM regulates the light environment and correlates with terrestrial nutrient supply, we observe similar unimodal relationships for benthic algal growth vs. light and TDN (Fig. 1). This pattern suggests that when DOM is low, light is abundant but nutrients are limiting to benthic algae; when DOM is high, nutrients are replete and primary production is increasingly light-limited

Summary

Introduction

Widespread increases in dissolved organic matter (DOM) concentration across northern lakes can alter rates of primary production by increasing nutrient availability and decreasing light availability. These dual effects of DOM generate a unimodal relationship in pelagic primary production and primary producer biomass among lakes over a gradient of DOM concentration. Because the majority of northern Swedish lakes currently fall below the inflection point in this unimodal relationship, moderate increases in DOM have the potential to increase benthic primary production, for epilithic algae. Author Contribution Statement: MLF, JK, and RAS designed the study and wrote the paper. All authors contributed to and approved the submitted version of the manuscript

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