## 3 Results
### Effects on Primary Production  
A total of 14 rock measurements at the FAB site (of 30 total) and five measurements at the non-FAB site (of 12 total) resulted in negative GPP values, meaning that, in these cases, DO concentrations declined more rapidly under light vs. dark conditions. These were excluded from further analyses. Regarding CR, three measurements from the FAB site and one from the non-FAB site produced positive values and were therefore also not included in the associated analyses. All but one water-only incubation provided negative GPP values, and phytoplankton GPP (used to correct for lake water GPP in rock incubations) was therefore estimated from the water chl \(a\) concentrations.  
The periphton biomass on rocks that was sampled at the FAB site was significantly greater than that at the non-FAB site (Mann-Whitney U test, \(p<0.05\), Figure 4A). Despite much higher periphton biomasses present at the FAB site, the measured total GPP rates from rocks on the non-FAB site were significantly greater than the rates that were measured at the FAB site (\(t\)-test, \(p=0.005\), Figure 4B). This difference remains significant if one high GPP outlier is removed from the non-FAB site, as well as if only the two months during which both sites were sampled are compared. This difference also remains significant if zero-values are applied to the negative GPP rates that were removed from the analyses (as discussed in Methods). Calculated per mg chl \(a\) (i.e., considering the productive efficiency of periphton on rocks), this difference between sites is substantially greater (\(t\)-test, \(p=0.0001\), Figure 5). The non-FAB sites had significantly lower values of CR (\(t\)-test \(p=0.048\), Figure 4C), while there were no significant differences between the FAB and non-FAB site NEP (\(t\)-test, \(p=0.08\), Figure 4D) measured rates. The statistical significance of the differences that were observed between the sites was not affected by the inclusion or exclusion of the June sampling campaign (for which only the data from the FAB site was available).  
Figure 3: \(\delta^{15}\)N signature and N content (**A**) and \(\delta^{13}\)C signature and C content ((**B**), n = 4) of filamentous algae blooms (FAB) at the western shore and non-FAB at the eastern shore of Bear Lake in October 2019 and June 2021 (+standard error). Different letters indicate significant differences among FAB 2019, FAB 2021 and non-FAB 2021 values (one way ANOVA, \(p<0.05\), [PERSON]’s post hoc test).  
Although the lake water chl \(a\) concentrations were higher in the FAB site (\(30\pm 7\)\(\mu\)g L\({}^{-1}\), n = 5) compared to the non-FAB site (\(7\pm 10\)\(\mu\)g L\({}^{-1}\), n = 3), the resulting planktonic GPP rates in both sites were minor compared to the overall measured rates (FAB mean = 25 \(\pm\) 7 mg C m\({}^{-3}\) h\({}^{-1}\); non-FAB mean = 4 \(\pm\) 10 mg C m\({}^{-3}\) h\({}^{-1}\)). All measurements are means \(\pm\) standard error).  
Figure 4: (**A**) Periphyton biomass, (**B**) gross primary production (GPP), (**C**) community respiration (CR), and (**D**) net ecosystem production (NEP) at FAB (filamentous algae blooms) and non-FAB sites in Bear Lake (June, July, October for FAB, n = 16; just July/October for non-FAB, n = 7, +standard error). Asterisks indicate significant differences between FAB and non-FAB values (_t_-tests, \(p\) < 0.05).  
Figure 5: Periphyton gross primary production (GPP) efficiency at FAB (filamentous algae blooms) and non-FAB sites in Bear Lake (June, July, October for FAB, n = 16; just July/October for non-FAB, n = 7. +standard error). * significant difference between FAB and non-FAB values (_t_-test, \(p\) < 0.05).