Table 1.
Nitrogen and carbon isotopic signatures (δ15N and δ13C, ‰, mean ± s.d.) at colony and control sites, and estimated contribution of marine-derived nitrogen (MDN) to the biomass of primary producers and consumers at colony sites. Calculations of the contribution of MDN to biomass were performed with mass balance models using as marine nitrogen source δ15N of peat at colony sites, adding 2‰ enrichment in the case of aquatic resources and consumers. This 2‰ enrichment represents the hydrolysable proportion of nitrogen reaching aquatic ecosystems. This estimate is tentative as the variability in δ15N reaching freshwaters is high due to diverse microbial processes affecting guano and soil δ15N, implying that values more than 100% may occur. Significant differences in isotopic fingerprints are marked in bold and marginal p-values are given in italics.
| no. samples analysed |
δ13C (mean ± s.d.) |
δ15N (mean ± s.d.) |
GLS test parameters (t; d.f.res; p-value) |
mass balance model. mean contribution of MDN to biomass (%) | ||||
|---|---|---|---|---|---|---|---|---|
| colony, control | colony | control | colony | control | test for δ13C | test for δ15N | colony | |
| PERMANOVA (all isotopic signatures) | 4; 9 | δ13C and δ15N: F = 9.9; d.f.res = 11; p < 0.01 | ||||||
| freshwater environment | ||||||||
| terrestrial debris | 3; 6 | −27.2 ± 2.9 | −29.8 ± 1.0 | 8.4 ± 6.5 | −1.3 ± 2.7 | 2.0; 7; p = 0.08 | 2.8; 7; p < 0.05 | nt |
| profundal lake sediment | 2; 5 | −24.2 ± 0.3 | −22.4 ± 5.2 | 20.7 ± 2.4 | 1.9 ± 0.4 | nt | nt | nt |
| aquatic moss | 15; 14 | −23.9 ± 1.7 | −28.7 ± 4.9 | 17.3 ± 5.8 | 1.8 ± 2.5 | 3.4; 26; p < 0.01 | 8.7; 26; p < 0.0001 | 116.5 |
| benthic algae | 39; 25 | −19.9 ± 4.4 | −21.7 ± 6.6 | 17.9 ± 8.8 | 1.1 ± 2.4 | 0.87; 33; p > 0.1 | 4.8; 33; p < 0.0001 | 127 |
| chironomids | 33; 42 | −17.5 ± 3.3 | −23.9 ± 4.7 | 16.2 ± 7.1 | 4.4 ± 3.2 | 4.5; 31; p < 0.0001 | 3.9; 31; p < 0.001 | 87.9 |
| other invertebrates | 4; 31 | −21.5 ± 1.8 | −21.3 ± 3.8 | 15.9 ± 5.0 | 4.6 ± 1.9 | −0.11; 12; p > 0.1 | 4.3; 12; p < 0.0001 | 86.1 |
| seston | 1; 3 | −19 | −24.6 ± 2.6 | 20.8 | 3.5 ± 0.7 | nt | nt | 128.7 |
| zooplankton | 1; 9 | −16.8 | −25.3 ± 3.4 | 34.2 | 4.2 ± 2.3 | nt | nt | 229.5 |
| terrestrial environment | ||||||||
| peat soil | 5; 6 | −26.1 ± 1.9 | −25.3 ± 0.9 | 11.1 ± 3.5 | 0.4 ± 1.5 | −0.9; 9; p > 0.1 | 6.8; 9; p < 0.001 | nt |
| terrestrial vegetation | 9; 9 | −28.7 ± 1.1 | −28.5 ± 1.4 | 16.5 ± 6.7 | 5.3 ± 6.6 | −1.0; 16; p > 0.1 | 5.5; 16; p < 0.001 | 97.8 |
| Arctic hare | 1; 2 | −25.2 | −25.7 ± 0.5 | 14.5 | 5.2 ± 2.9 | nt | nt | nt |
| Arctic fox | 1 | −16.7 | 13.5 | nt | nt | nt | ||