Terrestrial organic matter (TOM) constitutes an important source of energy in many aquatic environments (streams, lakes, wetlands). This is the first study to examine the role of TOM in food webs of the rocky intertidal zone. We compared the consumption of red alder leaves (Alnus rubra) to common marine sources of drifting detritus along the southern Oregon coast (Nereocystis luetkeana, Phyllospadix spp., and Fucus gardneri). We used short term (hours to days) and long term (months) feeding experiments to compare the rate of consumption among each plant species during the Spring and Fall of 2014 and 2015. In addition, we quantified the amount of TOM in beach wrack and in the drift of two streams that flowed directly to the rocky intertidal zone. We also measured the food quality of each plant species (C:N and polyphenolic concentrations). On average, the two small streams in this study transported 1,113.6 kg AFDM/m3 of TOM per day during Fall leaf abscission to the rocky intertidal zone. Also, the biomass of terrestrial leaves in beach wrack varied from negligible (2.1 g AFDM) to the dominant source of detritus (60.7 g AFDM) depending on if it was the dominant riparian plant growing along the edges of the shore. Consistent with previous research, N. luetkeana was a high quality food (C:N = 15:1; polyphenolics = 418 mg/ml), whereas F. gardneri (C:N = 22:1; polyphenolics = 8098 mg/ml) was more recalcitrant. Phyllospadix spp. was puzzling because it had low concentrations of polyphenolics (800 mg/ml) but was not consumed. Alnus rubra had a high concentration of structural compounds (C:N = 33:1) and intermediate levels of polyphenolics (3,415 mg/ml after leaching). Both short term and long term experiments showed that the rates of consumption of Spring-shed, green leaves and freshly fallen brown leaves of A. rubra were intermediate between N. luetkeana and the less palatable marine species (F. gardneri and Phyllospadix spp.). Thus, A. rubra was eaten by common intertidal consumers and may constitute an important source of energy between brief inputs of more nutritious marine resources (e.g. N. luetkeana).

Fjords contain a significant quantity of sediments deposited in coastal zones over the last ~100,000 years. Studies of Northern Hemisphere fjords have shown that a large part of the high concentration of sedimentary organic matter (OMsed) is terrestrial in origin (OMterr), composed of a modern detrital fraction and an old mineral-associated fraction (OMfossil). These results suggest that fjords are disproportionately responsible, on a per area basis, for the burial of organic matter in coastal zones. This study, after a rigorous examination of CuO and GDGT biomarker methods used to quantify terrestrial organic matter in coastal environments, demonstrated this hypothesis in a Southern Hemisphere fjord system, Fiordland, New Zealand. CuO analysis of Doubtful Sound surface sediments indicated a large contribution of vascular plant material to fjord sediments. The BIT Index correlated strongly with both delta13C and C/N values in Doubtful Sound surface sediments, indicated that it may accurately trace the relative proportions of marine and soil organic matter (OMsoil) in Fiordland. However, a detailed analysis of the conversion of the BIT Index to quantitative estimates of terrestrial (soil) organic matter revealed that these values are overestimates. Reconstructions of the BIT Index and tetraethers in cores from two locations on the Louisiana continental shelf demonstrated the influence of the crenarchaeol term on BIT Index-based terrestrial organic matter estimates. The differences in the applicability of the BIT Index to these two coastal environments was most likely due to large seasonal changes in productivity on the Louisiana Continental Shelf as well as higher marine relative to terrestrial inputs. Six cores were reconstructed for contributions from marine OM (OMmar), OMfossil, and OMterrestrial representing the last ~500 years of sedimentation. Spatial variations were larger than temporal variations, owing to negligible development and deforestation in the region. OMterr was the dominant fraction in all but one core, and OMfossil inputs were significant. Additionally, source reconstructions from a variety of biomarkers indicated that Landslides deliver large volumes of detrital organic matter to fjord sediments. These results confirm that fjords bury quantitatively significant volumes of organic carbon on a global scale.