Human impacts on the coupling of terrestrial and marine ecosystems.

摘要

Human impacts in coastal zones are rapidly increasing, but seldom considered in marine ecology or management in part because we lack quantitative data addressing the effects of common land uses on marine ecosystems. Studying 14 watersheds in the Pacific Northwest Coast ecoregion (USA), I found at least an order of magnitude higher river concentrations of dissolved organic carbon (DOC), phosphate (PO42-) and nitrate (NO3 -) associated with commercial logging. There was also a strong threshold response; at relatively low logging intensity, watersheds became nitrogen saturated and rivers switched abruptly from exporting organic nitrogen to NO3-. Following a subset of these rivers into the ocean, I found that rivers draining logged watersheds locally increased NO 3- and DOC concentrations in the coastal zone. Stable carbon and nitrogen isotope analyses showed that kelp and rivers subsidize rocky intertidal filter feeders (Balanus glandula, Semibalanus cariosus, Pollicipes polymerus, Mytilus californianus), and that natural or logging-related increases in riverine inputs were related to higher trophic position for all species. This trophic shift indicates that riverine carbon likely enters the rocky intertidal food web through the microbial loop and changes rocky intertidal trophic structure. I provide the first evidence that logging has a chemical footprint in the coastal ocean with biological implications, lending quantitative evidence to the argument that conservation planning and socio-ecological decision making need to consider links between natural systems. I developed a method that allows the inclusion of cross-system links, specifically those that act as threats, in terrestrial and marine planning efforts. I evaluated the importance of this advance by comparing two MARXAN scenarios; a "standard" scenario, with only system-specific threats and an "integrated" scenario, with cross-system threats for the coastal Pacific Northwest. Comparing scenarios showed that the standard planning approach would lead to the establishment of many marine protected areas (161,500 ha) that are at risk from land-based threats. This relatively simple method identified areas that avoid this risk. Management decisions are often made at a scale much larger than that considered in conservation planning, and I make several realistic suggestions to enhance the utility of global socio-ecological models in decision-making.