Influence of littoral periphyton on whole‐lake metabolism relates to littoral vegetation in humic lakes

Abstract

. Influence of littoral periphyton on whole-lake metabolism relates to littoral vegetation in humic lakes. Ecology, 98 (12), 3074-3085. doi:10.1002 Abstract. The role of littoral habitats in lake metabolism has been underrated, especially in humic lakes, based on an assumption of low benthic primary production (PP) due to low light penetration into water. This assumption has been challenged by recent recognition of littoral epiphyton dominance of whole-lake PP in a small highly humic lake and of epiphyton as an important basal food source for humic lake biota. However, as these studies have mostly concerned single lakes, there is a need to test their wider generality. We studied the whole-lake PP and community respiration (CR) in eight small humic lakes in southern Finland during July 2015 using 14 C incorporation to measure pelagic PP and the changes in dissolved inorganic carbon in light and dark in situ incubations to measure CR and littoral PP by epiphyton. Changes in O 2 concentration in both pelagic and littoral surface water were measured periodically from each lake and, additionally, continuously with a data logger from one lake during the study period. The results revealed that the littoral dominated whole-lake net primary production (NPP) in five of the eight lakes, which was supported by observed O 2 supersaturation in the littoral surface water in most of the lakes. Calculated pelagic:littoral ratios by area correlated negatively with both littoral NPP and littoral contribution to whole-lake NPP. Moreover, there was a significant positive relationship between littoral proportion of whole-lake NPP and the fraction of lake surface area covered by littoral aquatic vegetation. This demonstrates that increased aquatic littoral vegetation cover increases the overall importance of the littoral to whole-lake PP in highly humic lakes. Littoral NPP also correlated strongly with littoral O 2 saturation, and the continuously measured O 2 revealed substantial temporal variation in O 2 saturation, particularly in the littoral zone. Whole-lake gross primary production:community respiration (GPP:CR) ratios revealed that accounting for littoral metabolism produced a marked shift towards lake metabolic balance, although all the eight lakes remained net heterotrophic. This study emphasizes that littoral metabolism needs to be accounted for when estimating whole-lake C fluxes in all lakes, even in highly colored humic waters.

Pelagic food webs of humic lakes show low short‐term response to forest harvesting

“…, Vesterinen et al. ). Supporting this hypothesis that neither littoral nor benthic processes were, to a large extent, buffering forest harvest effects on the lakes, we could not find any changes in zoobenthos resource use of primary production or terrestrial organic carbon after tree removal (A. Deininger, unpublished data ).…”

“…), littoral zones can still be important for whole‐lake metabolism even in highly humic lakes (Vesterinen et al. ). However, the low estimated relative area covered by the littoral zone (10% ± 4% [mean ± SD]; A. Deininger, unpublished data ), as well as the comparably high energy mobilized by pelagic vs. benthic producers (83% ± 11%; A. Deininger, unpublished data ) indicate that pelagic metabolism was the major contributor to whole‐lake energy mobilization in our set of lakes (Ask et al.…”

“…Additionally, we cannot exclude that benthic and, especially, littoral zones might have acted as additional buffers for allochthonous material as well as nutrients entering the lakes after forest harvest. Although benthic metabolism is typically of decreasing importance for whole-lake metabolism with increasing terrestrial organic matter content and increasing light attenuation in lakes (Vadeboncoeur et al 2008, Ask et al 2009), littoral zones can still be important for whole-lake metabolism even in highly humic lakes (Vesterinen et al 2017). However, the low estimated relative area covered by the littoral zone (10% AE 4% [mean AE SD]; A. Deininger, unpublished data), as well as the comparably high energy mobilized by pelagic vs. benthic producers (83% AE 11%; A. Deininger, unpublished data) indicate that pelagic metabolism was the major contributor to whole-lake energy mobilization in our set of lakes (Ask et al 2009, Vesterinen et al 2017.…”

“…Although benthic metabolism is typically of decreasing importance for whole-lake metabolism with increasing terrestrial organic matter content and increasing light attenuation in lakes (Vadeboncoeur et al 2008, Ask et al 2009), littoral zones can still be important for whole-lake metabolism even in highly humic lakes (Vesterinen et al 2017). However, the low estimated relative area covered by the littoral zone (10% AE 4% [mean AE SD]; A. Deininger, unpublished data), as well as the comparably high energy mobilized by pelagic vs. benthic producers (83% AE 11%; A. Deininger, unpublished data) indicate that pelagic metabolism was the major contributor to whole-lake energy mobilization in our set of lakes (Ask et al 2009, Vesterinen et al 2017. Supporting this hypothesis that neither littoral nor benthic processes were, to a large extent, buffering forest harvest effects on the lakes, we could not find any changes in zoobenthos resource use of primary production or terrestrial organic carbon after tree removal (A.…”

Differentiation in Aquatic Metabolism between Littoral Habitats with Floating-Leaved and Submerged Macrophyte Growth Forms in a Shallow Eutrophic Lake

“…Nevertheless, most studies on aquatic metabolism have been limited in north-temperate systems and concern the pelagic habitats without taking into consideration the metabolic processes that occur in the littoral [17]. Only a few studies have covered both pelagic and littoral habitats [18][19][20] and even fewer have taken into account the role of the littoral aquatic vegetation and periphytic communities [21]. In addition, there is a profound lack of studies that have dealt with the dynamics of ecosystem metabolism in shallow warm lakes.…”