An ecological and methodological assessment of benthic gross primary production in northern lakes

Abstract

Benthic gross primary production (GPP) is often the most important part of aquatic food webs in northern lakes, which are gradually warming and receiving increased terrestrial colored dissolved organic carbon loadings due to global change. Yet, measurements of benthic GPP are fairly uncommon, and methods and unit dimensions of benthic GPP are unstandardized and rarely compared. In this study, we measured benthic GPP in 27 headwater lakes from three regions in northern Sweden and analyzed potential constraining drivers of benthic GPP z rates at discrete depths and estimates of benthic GPP averages across the whole lake, as well as across the littoral zone. We also compared in situ measurements of benthic GPP averages across the whole lake with modeled values using the "autotrophic structuring model." We found that benthic GPP z rates were best explained by, and positively related to, available light (i.e., a function of depth and water color) and temperature. Benthic GPP averages across the whole lake, on the contrary, were best explained by the relative size of the littoral area, which is a measure that combines lake bathymetry and water color. The comparison between in situ measured and modeled estimates of benthic GPP averages across the whole lake revealed that (1) the autotrophic structuring model underestimates GPP at low values and overestimates GPP at high values compared with measured data, and that (2) measured values were related to temperature, which is not included as a variable in the autotrophic structuring model. Considering future predicted changes impacting northern latitude lakes, our results suggest that increased lake water temperatures can to some extent mitigate the negative impacts of reduced light availability from lake browning on benthic GPP z rates. The combined impact of these changes on benthic GPP averages across the whole lake will depend on, and be moderated by, lake bathymetry determining the relative size of the littoral area.

Landscape determinants of pelagic and benthic primary production in northern lakes

“…The DIC concentration was calculated from the headspace CO 2 concentration in closed vials containing acidified lake water according to Åberg et al ( 2007 ), and were analyzed as soon as possible. More details and specific laboratory operating procedures afterwards can be found in Ask et al ( 2009a , 2009b ) and Puts et al ( 2022 ) and Appendix S1 . Detailed lake bathymetry was acquired through integrated GPS and echo‐sounding depth measurements, from which we calculated lake average depth ( z avg ), lake volumes and areas (as a whole, or in different sections), as well as the relative areal size of the littoral benthic habitat (% A littoral ; see Appendix S2 : Table S1 for overview parameters).…”

“…Such lakes can, through complex feedback loops, abruptly shift into clear‐watered states in the presence of macrophytes (Althouse et al, 2014 ; Kosten et al, 2009 ; Scheffer, 2004 ; Schindler & Scheuerell, 2002 ). However, in northern oligotrophic lakes, shading by colored DOM concentrations, and not by phytoplankton, is the most important inhibiting factor for pelagic and especially benthic algal growth (Ask et al, 2009a ; Bergström & Karlsson, 2019 ; Hansson, 1992 ; Jones, 1992 ; Puts et al, 2022 ; Thrane et al, 2014 ). Also for such systems, complex feedback loops and sudden changes are expected to occur in response to browning (Spears et al, 2017 ).…”

“…GPP was measured between 21 June and 28 July in variable years between 2005 and 2017 in situ in the benthic and pelagic on the same date. Benthic GPP was measured using the Dome method (subarctic) or the DIC method (Arctic and boreal; see Appendix S1 andPuts et al, 2022 for detailed descriptions and comparison).…”

Carbon dioxide limitation of benthic primary production in a boreal lake

“…This study shows that soft‐bottom benthic GPP can be stimulated by DIC, either directly (DIC addition) or indirectly following mineralisation of DOC. Since benthic GPP can be substantial in high‐light areas of lakes (Puts et al, 2022), and important at the whole‐lake scale (Ask et al, 2009; Karlsson et al, 2009), DIC stimulation might be a general, but understudied, feature of northern (including boreal) lakes at low to moderate DOC concentrations.…”

Filamentous Algae Blooms in a Large, Clear-Water Lake: Potential Drivers and Reduced Benthic Primary Production

“…All methods for measuring aquatic metabolism rates are associated with some errors [31,32], and research focusing on benthic metabolism in particular has generally been more recent than research on planktonic dynamics [33]. Nevertheless, in situ measurements of changes in oxygen concentrations in sealed transparent benthic chambers or domes are a common method for assessing periphyton metabolism rates both in marine [34] and freshwater [35,36] environments. We thus measured oxygen dynamics in sealed clear and dark chambers containing rocks with attached FAB (Cladophora) or non-FAB periphyton assemblages and exposed in the lake (in situ), as this general approach has also been applied to determine periphyton metabolism rates in other large lakes [37,38].…”