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

Abstract

Forest harvest in the boreal zone can increase the input of terrestrial materials such as dissolved organic carbon (DOC) and nitrate (NO3−) into nearby aquatic ecosystems, with potential effects on phytoplankton growth through enhanced nutrient (i.e., positive) or reduced light availability (i.e., negative), which may affect ecosystem productivity and consumer resource use. Here, we conducted forest clear‐cutting experiments in the catchments of four small, humic, and nitrogen‐limited unproductive boreal lakes (two controls and two clear‐cut, 18% and 44% of area cut) with one reference and two impact years. Our aim was to assess the effects of forest clear‐cutting on pelagic biomass production and consumer resource use. We found that pelagic biomass production did not change after two years of forest clear‐cutting: Pelagic primary and bacterial production (PP, BP), PP:BP ratio, chl a, and seston carbon (seston C) were unaffected by clear‐cutting; neither did tree harvest affect seston stoichiometry (i.e., N:phosphorus [P], C:P) nor induce changes in zooplankton resource use, biomass, or community composition. In conclusion, our findings suggest that pelagic food webs of humic lakes (DOC > 15 mg/L) might be resilient to a moderate form of forest clear‐cutting, at least two years after tree removal, before mechanical site preparation (e.g., mounding, plowing) and when leaving buffer strips along lakes and incoming streams. Thus, pelagic food web responses to forest clear‐cutting might not be universal, but could depend on factors such as the time scale, share of catchment logged, and the forest practices involved, including the application of buffer strips and site preparation.

Terrestrial diet influences mercury bioaccumulation in zooplankton and macroinvertebrates in lakes with differing dissolved organic carbon concentrations

“…Light attenuation in brown water lakes (DOC concentrations > 15 mg L -1 ) could have overridden the effects of phytoplankton production and biomass increase after nitrogen addition (Deininger et al, 2017a). A similar situation occurred in forest clear-cut lakes as the phytoplankton community changed little while lake nutrient and DOC remained stable (Deininger et al, 2019). The elevation of zooplankton Hg bioaccumulation was likely a consequence of decreased or stable phytoplankton biomass as lake DOC increased and led to increased zooplankton utilization of terrestrial OM-Hg complexes.…”

“…Table S3 and S4 are PLS model scores for both predictor variables and response variables. (Deininger et al, 2019).…”

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

“…All lakes were sampled between 21 June and 5 August, in variable years (years 1999–2019; see Figure S1 ). Data and sampling methods of pelagic GPP and water chemistry for 35 of the lakes are described in detail in earlier publications (Ask et al, 2009 ; Deininger et al, 2017 , 2019 ; Karlsson et al, 2001 ), and the remaining 10 lakes (four in the boreal and six lakes in the subarctic biome, original to this study) are sampled using similar techniques. The data can be found at https://doi.org/10.5061/dryad.t1g1jwt5k .…”

“…see Deininger et al, 2019) from the dataset including GPP. GPP z,max rates and GPP lake-averages were log-transformed to meet conditions for performing parametric tests.…”

The influence of stream tributaries to lakes and upstream forest harvest on benthic, lake delta communities

“…While streams have received much attention in the Pacific Northwest, especially in relation to forest harvesting (Richardson et al 2012), forestry impacts on lakes in this area have been understudied (but see Laird et al 2001;Bredesen et al 2002;Nordin et al 2007). Understanding of the effects of riparian forest harvest on lakes within this region is limited, particularly with respect to cascading effects transported through the riverscape, including to littoral LD habitats (but see Tanentzap et al 2014;Klaus et al 2018;Deininger et al 2019). Downstream effects may accumulate in LDs as littoral areas are the first lake habitat to receive watershed inputs (Vander Zanden and Vadeboncoeur 2020), making these suitable locations in which to detect disturbance.…”