PRIMARY RESEARCH PAPER Epipelic and pelagic primary production in Alaskan Arctic lakes of varying depth Stephen C. Whalen Æ Brian A. Chalfant Æ Eric N. Fischer Received: 11 March 2008 / Revised: 9 June 2008 / Accepted: 16 June 2008 / Published online: 11 July 2008 Ó Springer Science+Business Media B.V. 2008 Abstract We compared on eight dates during the ice- free period physicochemical properties and rates of phytoplankton and epipelic primary production in six arctic lakes dominated by soft bottom substrate. Lakes were classified as shallow ( z \ 2.5 m), intermediate in depth (2.5 m \ z \ 4.5 m), and deep ( z [ 4.5 m), with each depth category represented by two lakes. Although shallow lakes circulated freely and interme- diate and deep lakes stratified thermally for the entire summer, dissolved oxygen concentrations were always [ 70% of saturation values. Soluble reactive phospho- rus and dissolved inorganic nitrogen (DIN = NO 3 - – N + NH 4 + –N) were consistently below the detection limit (0.05 lmol l -1 ) in five lakes. However, one lake shallow lake (GTH 99) periodically showed elevated values of DIN (17 lmol l -1 ), total-P (0.29 lmol l -1 ), and total-N (33 lmol l -1 ), suggesting wind-generated sediment resuspension. Due to increased nutrient availability or entrainment of microphytobenthos, GTH 99 showed the highest average volume-based values of phytoplankton chlorophyll a (chl a) and primary production, which for the six lakes ranged from 1.0 to 2.9 lgl -1 and 0.7–3.8 lmol C l -1 day -1 . Overall, however, increased z resulted in increased area-based values of phytoplankton chl a and primary production, with mean values for the three lake classes ranging from 3.6 to 6.1 mg chl a m -2 and 3.2–5.8 mmol C m -2 day -1 . Average values of epip- elic chl a ranged from 131 to 549 mg m -2 for the three depth classes, but levels were not significantly different due to high spatial variability. However, average epipelic primary production was significantly higher in shallow lakes (12.2 mmol C m -2 day -1 ) than in intermediate and deep lakes (3.4 and 2.4 mmol C m -2 day -1 ). Total primary production (6.7–15.4 mmol C m -2 day -1 ) and percent contribu- tion of the epipelon (31–66%) were inversely related to mean depth, such that values for both variables were significantly higher in shallow lakes than in interme- diate or deep lakes. Keywords Primary production Á Phytoplankton Á Epipelic Á Arctic Introduction A pelagic-based paradigm has historically dominated lacustrine research (Vadeboncoeur et al., 2003). Due to spatial segregation, benthic habitats have often been considered functionally independent from pelagic environments (Carpenter et al., 1996) with Handling editor: L. Naselli-Flores S. C. Whalen (&) Á B. A. Chalfant Á E. N. Fischer Department of Environmental Sciences and Engineering, CB #7431, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA e-mail: steve_whalen@unc.edu 123 Hydrobiologia (2008) 614:243–257 DOI 10.1007/s10750-008-9510-1